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Processing- Options for Improving the Nutritional Value of Animal Products ROBERT E. RUST The issue of altering meat products to fit residual. It has been my experience that dietary requirements must address these 125 ppmnitriteincurecibaconwillproduce points: 1. Elect on product safety; 2. Effect on economics of manufacture; 3. Effect on storage life; 4. Effect on sensory characteristics such as flavor, texture, and color; ant] 5. Product identity for example, a mor tadelIa without dices of fat is no longer a mortadelIa. NITRATES AND NITRITES Let us examine some of the areas where dietary concerns have been expressed. Ni trates and nitrites are one. About a decade ago we agonized over the potential hazard presented by these processing ingredients. Nitrates largely passed out of the picture once their mechanism of action was under stood. Nitrites, in most products, have been voluntarily reduced by processors. The cur rent use level is 156 ppm, except for pumped bacon, where it is 120 ppm. In most cured meats, sausages, and lunch eon meats, the addition of 156 ppm nitrite will generally yield around 30 to 50 ppm 278 125 ppm - - -I -- 1- - - - - residuals of less than 15 ppm, and probably more like 10 to 12 ppm. Are these significant from a dietary standpoint? Most likely not, since most reliable estimates indicate that nitrite intake from processed meats equals only 3 to 5 percent of total dietary nitrite intake. Current U. S. Department of Agriculture (USDA)-Food Safety Inspection Service (FSIS) regulations (318.7) permit nitrite to be used at the levels given in Table 1. It might be wise for the USDA to bring these regulations further into line with current good manufacturing practice. SALT Salt (sodium chioricle) is a processing adjunct about which I feel no definite con- clusion can be reached that would justify a recommendation to impose limits. To a certain extent, the use of salt is self-limiting, depending on consumer tastes. The general trend toward lower salt levels in food has forced the meat industry to reduce its in- going levels. Although no general survey
PROCESSING OPTIONS TABLE 1 Levels of Curing Agents for Products Other Than Bacon 279 Curing Agent Dry Cure/ 100 lb of Meat (oz) Sausage/ 100 lb of Meat (oz) Curing Pickle/ 100 gal, 10 percent Pump (lb) Sodium nitrate Potassium nitrate Sodium nitrite Potassium nitrite 3.5 3.5 .0 .0 2.75 2.75 0.25 0.25 2 2 NOTE: In all cases, residuals shall not exceed 200 ppm calculated as sodium nitrite. data are available, it has been my experience that sodium levels in cooked sausage have declined by perhaps 20 percent over the past 10 years. Sodium chloride performs three major functions in a meat product: It helps pre- serve it, it adds flavor, and it develops the binding properties of the proteins. From a preservation standpoint, the role of salt is still critical in ciry cured meats such as hams as well as in dry sausage. Salt also plays a small role in shelf-life extension of cooked sausages. Levels in these products are com- monly 2 to 2.75 percent of the meat block* used in formulation. In Europe, a 2 percent salt addition is customary, but distribution chains are much shorter and shelf-life expectations much less than in the Uniter] States. Through goof! manufacturing practices, the United States can, I believe, achieve adequate shelf-life. However, there are those who would argue that this is the low end of the safety limit. It must be kept in mind that there are certain interactions between salt and nitrite * The notion of meat block is illustrated in the following example. Say that in producing a batch of frankfurters, you start with 100 pounds of meat. All the adjuncts are calculated based on a percentage of this 100 pounds. Thus, if you add 2.5 percent salt, 3.5 percent extender, 0.5 percent sugar, and 10 percent water, you will end up with 116.5 pounds of finished product. The actual salt level in the finished product would therefore be 2.15 percent. (The curing ingre- dients were deliberately omitted from this example.) . , ~ in the inhibition of Clostridium botuZinum that are significant from a public health standpoint. Some research indicates an in- creased clanger of toxin formation as salt levels decrease; however, no clear-cut rec- ommendations for minimum salt levels have been proposed to date. Most other patho- gens of major public health concern, such as Staphylococcus species, are salt-tolerant in the ranges being (liscussed, so salt re- duction probably would have no significant impact on their prevalence (still, the evi- dence here is less than conclusive). In terms of flavor, the preference for sodium is an acquired taste that can be mollified by total (lietary intake. As con- sumers have reclucec! their sodium intake, the meat industry has been obligates] to follow suit. Proposals to substitute other chiori~les (it is the chloride ion that is significant) have encountered flavor prob- lems. Potassium chloride, for instance, could] perhaps partially substitute for sodium chIo- ride but the bitter flavor is undesirable. Furthermore, there is still the question of whether adde(1 dietary potassium would have any significant impact on health. The effect of reclucec] sodium on flavor can be somewhat compensated for by other flavor- ings such as spices and spice extracts. There are no hard-and-fast recommendations that can be made here, since flavorings are a highly variable consideration. The role of salt in developing the binding properties of proteins is critical. Actually, this is twofold. First, sodium chloride ex
280 tracts the salt-soluble myofibrillar proteins, which, in turn, encapsulate the fat particles as: to form a stable "emulsion" or meat batter. Second, it promotes the swelling of these proteins to allow for exposure of more bond ing sites for water binding. This is crucial for the production of a stable sausage. In practical terms, salt levels of much less than 1.5 percent of the meat block are not functional. Even then, optimum technology must be exercised to make this level oper ational. There are some significant interac tions between sodium chloride and the alkaline phosphates that improve the func tioning of low sodium chloride. For the most part, however, these alkaline phos phates are mostly the sodium salts; hence, actual sodium reduction is minimal. The alkaline potassium phosphates currently al lowed under USDA-FSIS regulations are dipotassium phosphate, monopotassium phosphate, potassium tripolyphosphate, and potassium pyrophosphate. These are not commonly used, though, because of solu bility problems, flavor problems, and the fact that they function somewhat less effec tively than JO their sodium counterparts. In dry cured products, particularly dry and semi-dry sausage, the salt levels needed for preservation become much more signif icant. It appears that a level of 3 Dercent ingoing, which translates to 4.25 to 5 percent salt in the finished product, is optimum. Only recently did the USDA recognize levels less than 3.3 percent ingoing for trichina inactivation. This recognition pro vides a sliding scale of extended drying times in proportion to ingoing salt levels. However, it would be far better to exercise trichina control through an identification program or raw material control rather than through processing treatment. In addition to controlling trichina, it is necessary to achieve a sufficiently high brine concentration to inhibit microbial growth, including the more salt-tolerant molds and yeasts. A brine concentration of 12 percent is generally considered necessary for shelf APPENDIX stability. Percent concentration is calculated Percent salt x 100. Percent salt + Percent water FAT Reduction of caloric intake from fats, particularly the saturatect tatty acids, is an- other major area of concern. This discussion does not focus on mollification of animal fat depots by dietary or other means. Never- theless, such modification must be looked at in light of its effect on the manufacturing characteristics of the meat raw materials, such as flavor, texture, color, and suscep- tibility to oxidation. Reduction of fat in a processed meat product is not as simple as it sounds. A notable success in this area is the commer- cial production of"95 percent fat free', hams. This probably represents the ultimate in fat reduction, since a muscle with all the visible intermuscular fat removed still contains at least 5 percent fat in the form of intramus- cular fat and extractable intra- and inter- cellular lipids. In cooked sausage, such as a frankfurter, the common accepted fat levels of 25 to 30 percent defy significant reduction without sacrificing textural and other sensory prop- erties. A few commercial attempts at straightforward fat reduction have, in gen- eral, resulted in a product with a distinct rubbery texture ant! reduced consumer cle- mand. If the reduction in textural charac- teristics is to be overcome, other compo- nents will have to be mo(lifiecl. For example, the addition of water will offset the fat reduction by softening the texture of the product. Here, however, we encounter USDA regulations that restrict water levels in a product. Right now, the USDA does not permit substitution of water for fat. These interacting regulations need careful examination. I would suggest regulating product composition based on minimum
PROCESSING OPTIONS protein rather than the current fat/water maximums. Another textural modification involves the substitution of a nonbinding protein gen- erally originating from a by-product source for some of the fat. There has been success in substituting 10 percent cooked pork skins for 10 percent pork fat in dry sausage. However, this has run afoul of regulatory restrictions in labeling requirements. The inclusion of mechanically separated meat (MSM) has generally been shown to reduce textural firmness, but, again, its labeling is in fact restrictive to the point that most processors assume that consumers will be driven away from products containing MSM. In its quest for truth in labeling, the USDA may have erected barriers to intelligent dietary modification of meat products. Clearly, the whole area needs examination. Regulatory tradition should not be allowed to interfere with efforts at dietary modifi- cation of meat products when such modifi- cation is based on sound scientific data. One promising area in the modification of fat in processes] meat products is the substitution of fats and oils of vegetable origin for the animal fat. Through a tech- nique common in Europe, that of pree- mulsifying the fat with milk proteins such as sodium caseinate or its calcium counter- part, two-thirds of the animal fat has been replaced with preemulsified vegetable oil in a slicing bologna without any practical reduction in sensory properties. Preemul- sions are usually made up of eight parts oil, eight parts water, and one part milk protein, which in effect gives a finished emulsion with approximately 48 percent fat. It is likely that somewhat similar results can be obtained with soy or blood plasma proteins. Once again, though, USDA reg- ulations restrict the inclusion of vegetable fats and oils in meat products. Also, calcium caseinate, despite its widespread use in nonmeat products, is not on the Generally Recognized As Safe list (as is sodium cas- einate), and the USDA is reluctant to extend 281 approval for use until there is greater clar- ification from the Food and Drug Admin- istration. Inclusion of stabilized preemulsions that can effectively reduce fat content of the "show fat" appears to be another area worth pursuing. Again, the question of labeling must be considered. A fat/water/protein emulsion diced and incorporated as show fat in a meat product would trigger labeling problems under current regulations. Ob- viously, labeling requirements are a signif- icant stumbling block. What is needed, above all, is a thorough scientific review of labeling regulations and policies totally di- vorced from emotion, tradition, and the like. LABELING A few more words should be said on the subject of labeling. I view the policies (or lack thereof regarding such fanciful labels as Lean and Lite as a regulatory quagmire that is totally out of hand. There needs to be a firm, definitive policy established that would clarify these promotional labels, which currently are being exploited to the confu- sion of the consumer, despite the USDA's recent attempts to clarify them. Another labeling issue that comes to mind is the USDA grades for beef and lamb. These still place an unwarranted emphasis on fat. Even though most responsible sci- entists agree that only about 10 to 15 percent of the palatability differences are explained by the factors considered in USDA grades for beef, this system is still in use. Clearly, it is an emotionally charged issue that has been debated extensively, but can't it be resolved rationally? Personally, I wonder if USDA grades of beef serve any useful pur- pose, and I challenge this committee to reach a consensus on this system, particu- larly insofar as it hinders the consumer in making wise decisions on selecting meat and meat products. The application of pres- ent USDA grade standards, particularly yield
282 grades, may be the major limitation to processing developments such as immediate postslaughter fat removal. There appears to be very little that can be done under current regulatory con- straints to achieve mollification of meat products through the inclusion of various nutrients (that is, vitamins, minerals, and the like). If I react current regulations cor- rectly, the clirect inclusion of, say, thiamine to a sausage product would not be approved. At the very least it would trigger nutritional labeling, an activity that is cumbersome and often beyond the capabilities of the small processor, since present USDA policy re- quires a Partial Quality Control program as a minimum. Even calcium, one of the nu- trients whose inclusion appears to be a "plus," is in fact restricted when it appears as a component in mechanically separated meat. Does this make sense, if, indeed, additional calcium is an asset to our diets? The United States is the only major de- veloped country to restrict the incorporation of blood in meat products. I can find no sound scientific reason for this restriction. Incleed, it makes little sense considering that blood provides an excellent source of such nutrients as iron and protein. Are we, because of purely esthetic considerations, ignoring some potential good sources of nutrients? It woulc! seem so. CONCLUSIONS Our regulatory bodies too often base their decisions on unsupported opinion an(1 es- thetic considerations rather than scientific fact. Are regulations in elect hampering positive dietary mortification of meat and meat products, especially insofar as proc- essing adjuncts are concerned? This is a APPENDIX question that must be addressed. Following is a list of specific considerations that must be examined, as well as areas important for research. Considerations 1. Regulate composition of meat products on the basis of a minimum protein standard, thus allowing interchange of water/fat for textural purposes. 2. Remove esthetic considerations from labeling requirements (that is, flagging of "variety meats," mechanically separates] meats, and so on). 3. Change fat labeling to allow separation and recombination of fats in manufactured products. 4. Develop simplified procedures for nu- tritional labeling to enable small processors to apply nutritional labeling. 5. Set definitive standar(ls for such fan- ciful labels as Lean and Lite or recommenc! their elimination. 6. Define the roles of beef and lamb grades. Are they a marketing too} or a label for consumer information? 7. Should consideration be given to con- trol of pathogenic microorganisms such as Staphylococcus and SalmoneZZa species as part of dietary considerations? Areas for Research 1. Salt/nitrite/phosphate interactions and their elect on pathogens; 2. Nutritional contributions of meat by- products and processing adjuncts after in- clusion in a processes! meat product; and 3. Mollification of current beef ant] lamb gracles to a system similar to that used for pork (quantitative and age).
Integrated Nutrition, Genetics, and Growth Management Programs for Lean Beef Production F. M. BYERS, H. R. CROSS, and G. T. SCHELLING We have evolved into a"lean-conscious society," where fats has become a four- letter word and a high priority is placed on getting and staying trim. In no area is this more evident than in our selection of and desire for leaner beef products. Efficient production of palatable lean beef must be a primary objective of the beef cattle industry if it is to compete in the long term. Current yearly production of the 5 billion pouncis of waste ant] trim fat must be reducer! as rapidly as possible. Although beef fat is trimmed extensively at slaughter and by the consumer, which results in a reasonably lean beef product, only the pre- vention of this excessive fat deposition where it occurs will correct the image of beef as a fat, high-calorie product. A diversity of beef products are needed, all of which must be separated from the current image of fat cattle and fat beef. Industry must focus on producing and ef- fectively marketing lean beef and work to associate beef with active life-styles and healthful living. Products must be engi- neered to coincide with consumer needs and to acIdress consumer fears, both per- ceived and real. Since it is easier to create 283 new attitudes than to change olc] ones, the industry must use innovative marketing strategies to reposition beef products with a new identity. Unique challenges face the beef industry to clesign and clevelop new technologies that will allow production of lean beef rather than beef that must be extensively trimmed to make it lean. This will require greater lean tissue deposition throughout the life cycle ant] extensive redirection of feed en- ergy from fat to protein deposition through all phases of growth. This can only be accomplished if all segments of the industry target on the same goal and integrate avail- able technology to effectively manage growth. INDUSTRY PERSPECTIVE The beef cattle industry has evolved from production of extremely lean beef, based largely on Longhorn-type cattle in extensive grazing systems in the nineteenth century, to production of very fat beef from small- size English breeds in the mid-twentieth century. During the second half of the twentieth century, the trend has shifted back toward leaner beef, with selection of
284 large-framecI, later-maturing, large mature size exotic types of cattle. Recent consumer pressure for leaner beef has accelerated this change and encouraged consideration of many new cattle breeds not formerly part of the U.S. beef cattle industry. The current beef cattle population in- cludes cattle of all types and sizes. They are fed a wide variety of feedstuffs, both grazed and harvested, ranging from poor-quality mature range grasses to high-energy feedIot rations, with most combinations in between. They are managed in systems including wintering, backgrounding, summer grazing, growing, forage finishing, and high-grain feediot programs. The traditional end prod- uct of these diverse cattle-resource combi- nations is Choice grade beef with 30 to 35 percent carcass fat. Consumer preference for a leaner beef product indicates the need to devise systems to economically produce this kind of beef. MECHANISMS TO PRODUCE LEAN BEEF The traditional method user! to increase the production of lean beef is to feed larger mature size cattle. However, an increase in mature size means a larger cow that has greater requirements per unit of weight and greatly increaser! levels of maintenance en- ergy committed to beef production. For example, Chianina cattle produce large, lean carcasses, but because of their size they require more maintenance feed energy. Therefore, a more effective approach for producing lean beef is to modify the patterns of growth in cattle to produce more lean beef from all cattle. While this is the even- tual target of genetic engineering initiatives, systems using these concepts are not likely to surface any time soon. An understanding of growth and its regulation is required to effectively use growth management strate- gies to produce leaner beef products. An outline of options ant! factors involved in APPENDIX regulation through genetics, nutrition, and growth follows: Genetics Establishes upper limit of growth Determines base patterns of growth Sets priorities for growth of tissues At any rate of growth During intervals of growth Targets composition at any weight Sets physiological maturity at points of growth Nutrition: Energy Schedule versus phase of growth Growing versus later stages Current versus earlier nutritional his- tory Deferred versus advanced systems Level and source Forage versus grain Quantity/day versus limits for lean tis- sue growth Rate and composition of growth Substrates for tissue growth Nutrition and function Optimize lean tissue growth Feedback on lean tissue priorities Storage an :1 retrieval of tissues Nutrition en cl physiological limits Growth management: Synchronizing nu trients and needs Endogenous regulation Bulls, steers, heifers Patterns during growth Exogenous regulation Repartitioning agents Estrogens Zerano} Growth hormone Beta-aclrenergic agonists Mechanisms of regulation Priorities for protein versus fat Redirection of nutrients Tissue mobilization Limits for daily deposition Other effects
GROWTH MANAGEMENT PROGRAMS Role of Genetics in the Production of Leaner Beef Mature size ant] genetics establish the limits (both dally and cumulative), base patterns, priorities, and type of growth predominating through phases of growth. In addition, the genetic directives provide general targets for body ant] carcass com- position and degree of physiological matu- rity over time and weight intervals through growth. However, other factors really de- termine the extent to which these theoret- ical limits will actually be reached, or how patterns and priorities for growth will be followed or translated into and realized as growth. Some general principles that are usually associated with genetic regulation may be useful as a reference point. In general, cattle of larger mature size have greater limits for daily protein growth and have accumulated more protein than smaller cattle at any point during growth and when mature size is reached (Byers and Rompala, 1980; Byers et al., 1986~. Large mature size cattle are typically physiologically younger at any point during growth than smaller mature size cattle. They also place a higher priority on protein growth and deposit a greater fraction of protein at any rate of growth, but espe- cially at lower rates. However, many cattle types violate these notions. For instance, all smalI-size cattle are not early maturing; Longhorn or Scottish HighIanclers, for ex- ample, are small and late maturing. Also, limits for daily protein growth do not au- tomatically follow potential cumulative stor- age. While both Simmental and Limousin accumulate large quantities of protein, rates of protein growth in Limousin may be no greater than in Red or Black Angus, while Simmental have the potential to deposit protein more rapidly. However, both Sim- mental and Limousin are leaner at most weights through growth than Angus. In Simmental this occurs because of rapid 285 protein growth, while in Limousin it is primarily a reflection of Tower energy intake and lower rates of fat deposition. It becomes immediately evident that rate and compo- sition of growth are directly related and not independent of each other. Available energy translates genetic directives through tissue regulation into patterns of growth. Role of Nutrition in Growth Nutrition is directly linked to rate and composition of growth in several ways (Byers, 1982~. Available energy is used to meet the needs for maintenance, protein growth, and fat deposition, primarily in that order. Thus, composition of growth reflects levels of available substrates prowled relative to maintenance and limits for protein growth, with additional energy usually deposited as fat. In general, rates of protein deposition increase at decreasing rates and rates of fat deposition increase at increasing rates with rate of growth. Consequently, percentage protein in growth decreases while percent- age fat in growth increases with rate of growth. Empty body and carcass composi- tion reflects these patterns of tissue growth, and cattle growing rapidly through higher levels of nutrition are fatter at subsequent points in growth and at slaughter. The magnitude of nutritionally regulated changes in body composition at a given weight reflect animal priorities, rates of growth, and length of time that animals are growing at respec- tive rates. Slower (deferred) growth for extended periods of time invariably results in leaner carcasses at any selected weight. However, most cattle deposit some fat, even at slow rates of growth, and the priorities for protein versus fat deposition at any rate of growth are established through genetic directives that are implemented through physiological mechanisms. Physiological mechanisms exist to allow retrieval of fat to provide energy for protein growth if suffi- cient stored fat is available from a previous
286 phase of growth. Important components of nutrition include the stage of growth versus nutritional schedule, level and source that is, forage versus grain and level relative to growth process priorities. Nutrition is normally considered relative to phase of growth such as preweaning, stocker, or finishing, ant] ranges of nutri- tional levels are implied in each phase. However, the general relationship of rate to composition of Growth applies to all ~O phases of growth; only the relative priorities for protein versus fat deposition change with stage of growth. Commonly used beef cattle feeding and management systems include a range of nutritional programs where periods of rapid and deferred growth are included. All periods of deferrer! growth where pro- tein growth is allowed result in restriction of fat deposition such that the animal is older and has hack more time to deposit protein and thus has accumulated more lean tissue. Animals that have been managed in (referred feeding programs wait be leaner at any slaughter weight and will be heavier when typical slaughter end points are reached. Common systems of deferred feeding in- clucle growing feeder calves after weaning in winter grazing or backgrounding pro- grams to yearling weight before placement on high-energy feecIlot finishing rations that maximize rate of growth. Cattle managed in this system will be more than 150 pounds heavier at slaughter when similar in com- position to cattle placed on feedlot rations at weaning (Byers, 1980~. It follows that they will be leaner at any slaughter weight than cattle fed to grow rapidly immediately after weaning. While this deferrer] system allows smaller mature size cattle to produce larger and more acceptable carcasses when slaughter end points are reached, large mature size cattle will yield unacceptably large carcasses weighing in excess of 1,000 pouncis. This provides the basis for genotype by nutrition interactions, indicating the util- ity of deferred feeding programs for smaller APPENDIX mature size cattle and high-energy feecilot programs for large mature size cattle as soon as feasible after weaning. Some of the great- est real opportunities for growth manage- ment exist within cattle types ant! involve mollifying an animal's inherent priorities for growth. Integrated Growth Management The objective of growth management is to regulate growth and synchronize nutrient sunDlies with nutrient needs to support the desired type of growth. This can be accom- plishe(1 through both endogenous mecha- nisms inherent to an animal (that is, castra- tion) or through exogenous mechanisms such as estrogenic repartitioning agents (Byers, 1982; Lemieux et al., 1983b). The mecha- nisms involvecl in redirection of growth include modification of (1) priorities for nutrient use for protein versus fat cleposi- tion, (2) tissue turnover (Roeder et al., 1984), (3) daily tissue (1eposition limits, ant! (4) nutrient supply. Eventually, growth hor- mone, releasing factors for growth hormone, beta-adrenergic agonists, or immunization strategies to remove negative feedback on growth (that is, somatostatin) may provide additional ways to regulate growth. They may work with or in place of current growth regulation technology. These alternatives are in the early stages of development and probably will not be available any time soon. In the interim, elective systems of growth regulation must be implemented to allow more lean tissue ant] less fat deposition in production of carcass beef. Anabolic estro- genic implants are elective repartitioning agents that modify growth by shifting nu- trients from fat to protein accretion, result- ing in priorities for growth more analogous to those for bulls (Byers et al., 1985a, 1985c; Lemieux et al., 1985a). In a(lclition, they usually enhance rate of growth, serving to further increase lean tissue production (Byers et al., 1985b). Rate and efficiency of lean tissue growth are critical to enhancing lean
GROWTH MANAGEMENT PROGRAMS beef production through conventional cattle feeding and management systems. In ad- dition to more efficient production, anabolic implants provide the opportunity to regulate growth so as to tailor beef production to meet consumer demand for leaner beef products. While implants have been used for several decacles, the basis for their growth regulator functions have only recently be- gun to be understood (Lawrence et al., 1985~. This is important for the development of growth regulation systems that allow programmer! growth of cattle. Rationale for Anabolic Implant Response Recent research has provided new in- sights into mechanisms by which growth- promoting implants modify growth in beef cattle. Protein growth is a daily function, and cellular mechanisms establish the max- imum rates for daily protein synthesis. Cel- lular limits for protein growth are not often reached because of physiological factors, such as hormonal en c] nutritional mecha- nisms, that set priorities for and limits to protein deposition. Cattle of cli~erent types have different priorities for protein depo- sition at different rates of growth, ant] larger mature size cattle direct more energy to- ward protein growth at any rate of growth. Priorities for protein growth are enhancer! by anabolic implants, which redirect nu- trients from fat to protein in a"daily double play"-increasing lean growth at the ex- pense of fat, especially at rapid rates of gain. The effectiveness of repartitioning im- plants increases with rate of growth (Byers, 1982), with maximal redirection of nutrients from fat to protein at the most rapid! rates of gain (Lemieux et al., 1983b). The effec- tiveness of anabolic regulators is predicated on inherent rates of fat deposition providing the opportunity for repartitioning of nu- trients from fat to protein accretion. Estra- diol-17-beta and zeranol are currently avail- able compounds that occur naturally and 287 are very effective repartitioning agents, en- hancing rates of protein ant! lean tissue production whenever present at effective levels in cattle depositing fat. In recent studies, implants consistently increaser] overall rates of carcass and total protein accretion and yield! of lean retail product. Just as we are what we eat, cattle are what they accrete, with carcass beef reflect- ing cumulative growth from birth to slaugh- ter. Consequently, use of anabolic implants from birth to slaughter provides lifetime growth regulation and provides the maximal redirection of nutrients from fat to protein and lean tissue production. The longer an- abolic agents are proviclec! in efficacious closes, the greater is the increase in total beef lean with a simultaneous reduction in fat. PRODUCING MARKETABLE LEANER BEEF The leaner beef product must be accept- able and, hopefully, even desirable in the marketplace. Thus, the impact of strategies to produce leaner beef on product accept- ability must be included in an assessment of production options. Effects of Breed Type on Acceptability The following general observations can be made after evaluating 29 separate re- search studies: 1. Carcasses from English-type cattle ranked first in the U. S. Department of Agriculture (USDA) quality grade and mar- bling ratings. Continental breeds were in- termediate, while Zebu and dairy purebreds ranked last. 2. Flavor and juiciness appeared not to be affected by breed or breed type. 3. Meat from Zebu and their crosses were rated less tender than the English, dairy, or continental breeds or crosses. These low ratings were supported by significantly higher Warner-Bratzler shear force values.
288 APPENDIX In conclusion, with the exception of the In summary, forage-fed animals produce Zebu influence, breed appears to have little carcasses that are borderline in acceptability practical influence on muscle quality (Cross et al., 1984; McKeith et al., 1985~. Forage- Versus Grain-Fed Beef A consiclerable amount of data has been published on the effect of forage versus grain feeding on carcass traits (Byers, 1980; Lemieux et al., 1983a, 1985b) and muscle quality (Bidner et al., 1986; Crouse et al., 19841. Animals from forage-fed systems pro duce carcasses that have less marbling, darker lean color, softer lean, coarser-tex tured lean, and lower USDA quality grades than grain-fed animals. Grain-fed animals averaged two-thirds of a quality grade ad vantage over forage-fed animals. The quality grade difference was significant in 12 of 29 comparisons. When the difference was not significant, the trend was almost always in favor of the grain-fed animals. Forage-fed beef, because of its darker and softer lean, will not have the retail shelf-life of grain fed beef. This presents a serious problem from the consumer acceptance standpoint. Grain-fed animals produced carcasses that were significantly more tender than forage fed animals in more than 41 percent of the comparisons. Perhaps even more important, 62 percent of the flavor desirability ratings favored grain-fed beef. The flavor-intensity ratings were almost always higher in meat from forage-fed animals. These intensity ratings were likely related to "oh' flavors rather than to desirable flavors. Limited data are available on taste ac ceptance of forage-fed versus grain-fed beef as evaluated by consumer panels. Gener ally, the differences were either very small or in favor of the grain-fee] beef. Obviously, differences in the literature with regard to quality traits of forage- versus grain-fed beef vary considerably, partly because of the variability in quality of forage, age of the animal, and amount of grain supplemented to the diet. in terms of color, firmness, and retail shelf- life. Meat from these carcasses is borderline in taste acceptability. To date, the U. S. beef industry has not been willing to risk losing its "taste" image by moving to a total forage production system. Such a system would be impractical for other reasons, too, such as retained ownership because of the time required to reach acceptable market weights and the inability to supply the marketplace on a consistent basis. Bulls Versus Steers Castration of meat-producing animals has long been practicer] in the United States. It is intended to produce an animal more acceptable to current management systems and to provide a more desirable carcass for marketing. During the past four decades, a number of research studies have been con- ductec! to assess the performance and meat characteristics of castrates versus noncas- trates (Griffin et al., 1985; Sei(leman et al., 1982~. In general, the results have indicated that bulls grow more rapidly, utilize feed more efficiently, and produce leaner car- casses. Increased production efficiency ob- taine(1 through the use of intact males has often been offset by management problems, particularly with animal behavior. Meat pro- duction from young bulls has met with strong resistance from meat packers, in part because of carcass size variability, difficulty of hide removal, and inability to obtain an acceptable USDA quality grade. Retailers have resisted using meat from young bulls because their meat has been labeled as less tender and less clesirable in color and tex- ture. The obvious advantages of using the young bull for meat production are efficiency of growth, leanness, and muscling. The dis- advantages are in the area of carcass traits and tenderness. Some of the problems as- sociated with tenderness can be corrected
GROWTH MANAGEMENT PROGRAMS with adequate postmortem handling of the carcass, such as postmortem aging and elec- trical stimulation. Electrical stimulation can also improve muscle color and retail ap pearance. Variability in size and quality has been associated with young bulls. The North Central Regional Research Group (NRC- 132) prepares] guidelines for the production of young bulls of slivering frame sizes to meet certain compositional end points. Un- der varying market conditions, it is possible that end points for young bulls in each frame size could shift, but it is very unlikely that large-framed bulls should ever be fed to reach the Choice grade. Small- and me- dium-sized bulls are better suited to reach a particular compositional end point without obtaining excessively heavy market weights. When properly managed, young bulls provide a good option for efficiently pro- ducing lean beef that is acceptable in qual- ity. Considerable effort should be made to develop markets for meat from these ani- mals. This will involve the education of some segments of the meat industry to correct misconceptions about young bulls. Impact of Growth Regulators on Beef Quality Growth regulators and repartitioning agents function by reducing fat deposition. Since a relationship between fatness and marbling exists, a reduction in marbling and resulting quality grade can be expected when fatness is reduced. However, in most instances, acceptability, shear force, palat- ability, and tenderness are altered to a lesser extent than expected from the reduction in fat. Also, electrical stimulation of carcasses yields taste values equivalent to those for carcasses from nonimplanted cattle without electrical stimulation. While the need to produce a leaner beef product has become clear, the segmentation of industry and the resulting divergent goals, objectives, and profit centers result in mixer! 289 signals at best, and incentives to produce fatter beef often prevail. Incentives for pro- ducing leaner beef must be established in all segments of the industry to ensure co- orclination of growth toward optimal market end points. Currently, profit incentives favor maximal weaning weight in the cow/calf phase, max- imal rate of gain in stocker and growing programs, maximal rates of gain in feedlot phases, and extended feeding in finishing phases to increase dressing percent and quality gracle. For any specific animal type or breed, these goals enhance fat deposition while reducing the perio(l of time allowed for protein and lean tissue growth, thereby limiting progress toward producing a leaner beef product (Figure 1). Faster growth through nutrition invaria- bly increases the percentage of fat producer! in each phase of growth. This is true whether the energy comes from milk or creep in cow/calf operations; supplementation, bet- ter forage, or higher energy growing diets in stocker systems; or the combination of rapid rates of gain, packer/buyer requests to "feet! them another 3 weeks," and feedlot priorities to move more grain in the feecIlot phase. Shelf-Life in the Feedlot One of the major problems the industry faces is the short shelf-life of cattle nearing slaughter end points. The concept of shelf- life (Perry et al., 1986) was developed to define the time and/or weight interval over which an animal maintains its current qual- ity or yield grade. For some cattle types, shelf-life in the feedlot may not be appre- ciably longer than postharvest shelf-life in the retail tracle. Extending this interval would provide more flexibility in marketing, ant! cattle would increase in fatness at a slower rate such that overfeeding wouIc! be less deleterious to lean beef production. The use of larger mature size cattle and implants as repartitioning agents provides
290 Prac~c" That Increase Fat Cowls High milk production Croop feed Small mature size Incroa~ weaning weight Trough nutrition % FAT 35 n Stocker Fast gain Energy supplement -307~o ~ ~-~ ~--~--t20-~-~ n Practices That Increase Lean Or Reduce Fat Lower milk product/on No supplement Implant hormones Bulls APPENDIX F - dlot Packer Merchandize grain More time on feed Fast gain Higher dressing Longer fading percentage period More choice C~trlmming Retaller Consumer No trim Prepare and eat enUre product ~ _ _: ___ o Deferred growth Shorter feeding Implant hormones period Continuous Implant of hormon" Trim hit Trim rail cuts Trim products (such as 114~) to 1/4" Dlecard plate waste YAW grade Bonel~ trimmed Discard fat dripping spociticadons products FIGURE 1 Practices that alter fat content in beef products. Options for increasing the shelf-life of cattle. Shelf-life is shortest for small mature size cattle growing rapidly without growth reg ulators and longest for large mature size cattle receiving implants and growing at slower rates. CONCLUSIONS Synchronization of nutritional levels with needs for protein growth, continuous deliv ery of repartitioning agents in all phases of growth from birth to slaughter, and use of intact males where possible will allow in dustry to reduce fat deposition across the board; produce, rather than trim to produce, lean beef; maintain desirable beef quality, flavor, and taste; and reposition beefs image as a lean product in the market. To be successful, industry must system atically develop programs to produce the priority lean beef products that integrate breecis, feecls, and growth management re gimes to optimize growth en c] development from conception to consumption. Diet/health concerns, beef image prob lems, and animal efficiency in producing quality lean beef all require immediate attention to increasing lean tissue ant! re- of tissue deposition in small or large mature size ducing fat deposition in beef cattle. beef cattle. Pp. 141-146 in Proceedings of the 8th Research programs must provide infor- mation on consumer preferences, imple- mentation of currently available technology to provide leaner beef, and development of long-term technology to allow more precise regulation of growth through an animal's lifetime. The focus must be on protein production, rather than live weight en cl fat, and on systems that optimize energetic and economic efficiencies in protein and lean beef production. Rate of gain and feed efficiency criteria will not allow us to make progress toward this goal. REFERENCES Bidner, T. D., A. R. Schupp, A. B. Mohamad, N. C. Rumore, R. E. Montgomery, C. P. Bagley, and K. W. McMillin. 1986. Acceptability of beef from An- gus-Hereford or Angus-Hereford Brahman steers finished on all-forage or a high-energy diet. J. Anim. Sci. 62:381. Byers, F. M. 1980. Systems of beef cattle feeding and management to regulate composition of growth to produce beef carcasses of desired composition. Ohio Agric. Res. Dev. Cent. Res. Circ. 258:1-18. Byers, F. M. 1982. Nutritional factors affecting growth of muscle and adipose tissue in ruminants. Fed. Proc. 14:2562. Byers, F. M., and R. E. Rompala. 1980. Level of energy effects on patterns and energetic efficiency
GROWTH MANAGEMENT PROGRAMS International Symposium on Energy Metabolism. Cambridge, England: Butterworth. Byers, F. M., G. T. Schelling, H. R. Cross, and L. W. Greene. 1985a. Anabolic agent modification of protein and fat deposition in steers of two sizes. Proc. W. Sec. ASAS 36:440. Byers, F. M., G. T. Schelling, H. R. Cross, and L. W. Greene. 1985b. Efficacy of anabolic implants in enhancing protein synthesis and carcass lean tissue in large and small frame steers. J. Anim. Sci. 61(Suppl. 1~:93. Byers, F. M., G. T. Schelling, H. R. Cross, and L. W. Greene. 1985c. Homeorhetic repartitioning to enhance protein growth in steers with anabolic effecters. Fed. Proc. 44:547. Byers, F. M., G. T. Schelling, H. R. Cross, and L. W. Greene. 1986. Growth regulation in steers with respect to mature size and carcass endpoints. J. Anim. Sci. 63(Suppl. 1~:144. Cross, H. R., J. D. Crouse, and M. D. MacNeil. 1984. Influence of breed, sex, age and electrical stimulation on carcass and palatability traits of three bovine muscles. J. Anim. Sci. 58:1358. Crouse, J. D., H. R. Cross, and S. C. Seideman. 1984. Effects of a grass or grain diet on the quality of three beef muscles. J. Anim. Sci. 58:619. Griffin, C. L., D. M. Stiffler, G. C. Smith, and J. W. Savell. 1985. Palatability characteristics of loin steaks from Charolais crossbred bulls and steers. Meat Sci. 15:235. Lawrence, M. E., R. A. Roeder, G. T. Schelling, F. M. Byers, and L. W. Greene. 1985. Influence of zeranol implants on serum growth hormone levels in growing steers. Fed. Proc. 44:760. Lemieux, P. G., F. M. Byers, G. T. Schelling, L. M. 291 Schake, and G. C. Smith. 1983a. Anabolic effects on protein and fat deposition in cattle fed forage and grain diets. Fed. Proc. 42:533. Lemieux, P. G., F. M. Byers, G. T. Schelling, G. C. Smith, L. M. Schake, and T. R. Dutson. 1983b. Anabolic effects on rate of protein and fat deposition and energy retention in cattle fed forage and grain diets. Proc. W. Sec. ASAS 34:240. Lemieux, P. G., F. M. Byers, G. T. Schelling, and L. W. Greene. 1985a. Redirection in priorities of protein and fat deposition in cattle with anabolic regulators in growing versus finishing phases. J. Anim. Sci. 61(Suppl. 1):267. Lemieux, P. G., F. M. Byers, G. T. Schelling, G. C. Smith, and T. R. Dutson. 1985b. Carcass merit of steers receiving anabolic implants and fed forage and grain diets. J. Anim. Sci. 61(Suppl. 1):93. McKeith, F. K., J. W. Savell, G. C. Smith, T. R. Dutson, and Z. L. Carpenter. 1985. Tenderness of major muscles from three breed types of cattle at different times-on-feed. Meat Sci. 13:151. Perry, R. J., F. M. Byers, G. T. Schelling, D. Hale, H. R. Cross, and L. W. Greene. 1986. A microcom- puter model for estimating body composition, yield grade and quality grade of feedlot cattle. J. Anim. Sci. 63(Suppl. 1~:144. Roeder, R. A., S. D. Thorpe, J. M. Gunn, G. T. Schelling, and F. M. Byers. 1984. Influence of anabolic agents on protein synthesis and degra- dation in muscle cells grown in culture. Fed. Proc. 43:790. Seideman, S. C., H. R. Cross, R. R. Oltjen, and B. D. Schanbacher. 1982. Utilization of the intact male for red meat production: A review. J. Anim. Sci. 55:826.
Processing Technologies for Improving the Nutritional Value of Dairy Products DAVID H. HETTINGA Milk is a liquid food designed to provide nourishment for rapidly growing young mammals. Bovine milk is an excellent source of nutrients for humans; it contains 3.5 to 3.7 percent fat, 3.5 percent protein, 4.9 percent lactose, and 0.7 percent ash on an "as is" basis. In addition, milk contains nearly all the vitamins required for human nutrition ant] has a high calcium bioavaila- bility (Kansal en c] Chauc~hary, 19821. Milk is widely considered nature's most perfect food because of its balances] availa- bility of protein, fat, carbohydrates, vita- mins, and minerals, and its high content of essential nutrients such as calcium, essential amino acids, ant] essential fatty acids. Con- centrating these nutrients through process- ing further enhances the nutritional value of milk and its by-products. For instance, the cheese-making process concentrates the protein and fat, reduces the water, and eliminates the carbohydrate component. The whey derived from cheese making can be further processed through a technique called ultrafiltration to concentrate the alpha-lac- talbumin and beta-lactogiobulin, proteins of high nutritional value. 292 ULTRAFILTRATION Ultrafiltration is a high-pressure microfil- tration process that selectively segregates components of various molecular weights. For milk processing, membranes with vary- ing pore sizes are used to retain the fat and protein while allowing the lactose, water, and salts to pass through. Ultrafiltration has multiple applications in the dairy industry. Examples include the concentration of whey proteins, the manufacture of cheese base for processing, and the concentration of total milk proteins anal fat for the manufacture of all cheese varieties. The application of heat cluring milk or product processing can be helpful or harm- ful. On one hand, heating reduces microbial loacis and eliminates pathogens; it also de- natures milk proteins to create specific prop- erties, such as the melting of components in cheese processing to create a homoge- neous mass. On the other hand, heating destroys, through protein clenaturation, val- uable components such as immunoglobu- lins, enzymes such as lactoperoxiciase, and vitamin activity.
IMPROVING NUTRITIONAL VALUE OF DAIRY PRODUCTS Multiple processing techniques can be applied to prevent or reduce the destructive ejects of heat. For instance, in clearing with a heat-sensitive element for which preser- vation is necessary, such techniques can be user! as freeze-<lrying (versus spray-drying in a heated atmosphere); freeze concentra- tion, ultrafiltration, or reverse osmosis (ver- sus heated evaporator concentration); or microfiItration or irradiation (versus heat pasteurization or sterilization). Simply re- clucing heat to recluce bacterial loads can also be effective; of course, the heat level must be high enough to eliminate pathogens but not so high as to affect the desired elements. ALTERING THE CARBOHYDRATE IN DAIRY PRODUCTS Lactose is the primary carbohydrate in milk. A segment of the population is lactose intolerant (that is, these individuals cannot metabolize lactose). Many dairy products (for example, yogurt and sour cream) are manufactured via fermentative processes that eliminate or reduce lactose and can therefore be consumer! even by those who cannot tolerate lactose. In these cases, the fermentative process converts the lactose to lactic acid, an element cligestible by almost everyone. In abolition, yogurt has been shown to contain an inactive form of lactase (the enzyme which breaks down lactose), which is activated in the neutral pH envi- ronment of the small intestine (Kolars et al., 1984~. Conventional milk, rich in lactose, can be enzymatically treated with the enzyme lactase to hydrolyze about 80 percent of the lactose. This process, which substantially reduces the intolerance, creates a milk prod- uct that is nutritionally unaffected. The product is available under the trade name Lactaid@. Also available are packets of the enzyme lactase, which the consumer can add to conventional milk. 293 ALTERING THE FAT IN DAIRY PRODUCTS Considerable effort has undoubtedly been expended in finding new uses for milk fat. However, because milk fat is the second most expensive edible fat, the economic equation works against its increased use as a food ingredient in its native form. Nevertheless, if the desirable and undesirable characteristics of milk fat, relevant to its utilization, are evaluated, some viable pathways begin to emerge. On the positive side, milk fat is a rich source of essential fatty acids and pos- sesses a uniquely pleasing flavor found in no other fat. It contains a higher proportion of short-chain fatty acids than other fats, which contributes to its ease of digestibility. On the negative side, its high melting range (30 to 41°C) makes butter chilled to below 15°C hard to spread and unsuitable for use in a number of important areas of utilization such as the production of flaky bakery products. Walker (1972) reported that the concentra- tions of lactose and methyl ketone precursors in fractions with low melting points were slightly higher than those in the anhydrous milk fats. Furthermore, fractions with high melting points contain only 50 to 60 percent of the lactose potential and 60 to 70 percent of the methyl ketone potential of fractions with low melting points. If the dairy industry is to achieve any success in utilizing its abundant milk fat, technological mollifications will have to be undertaken to improve milk fat's utility as a food ingredient of choice. In terms of surplus butter fat, it would be both practical and profitable to extract butter flavor and concen- trate it. This product could then be used in pastries, cooking oils, breads, edible creams, and imitation dairy products (Kinsella, 1975~. ALTERING THE CIIOLESTEROL IN DAIRY PRODUCTS The concentration of cholesterol in bovine milk ranges from 10 to 15 mg/100 ml
294 LaCroix et al. (1973) reporter! that 95 per- cent of the cholesterol in milk was unester- ifiecI; the remainder was esterified to long- chain, usually saturated, fatty acids. Ac- cording to lenness (1974), about 75 percent of the cholesterol present in whole milk is dissolved in the milk fat, 10 percent resides in the fat globule membrane, ant! the rest is present in the skim milk. The effects of commercial processing on the concentra- tions and distribution of milk cholesterol are poorly defined, but such information is necessary for proper interpretation of data and application of methods for decreasing the cholesterol concentration of milk. A hypothesis exists that the cholesterol reductase from Eubacterium species can be user] to convert the cholesterol in fluid milk to products (primarily coprostano} and cho- lestanol) that are either poorly absorber] or completely unabsorbed in the human intes- tine and that will therefore be excreted. MacDonald et al. (1983) report that the major end product of cholesterol reduction (coprostanol) by Eubacterium species is in- deecI poorly absorber] by humans. Further- more, a lesser amount of cholesterol would be available in the intestine for oxidation to compounds that are potentially carcino- genic. Products from the chemical reduction of cholesterol are not carcinogenic. Con- version of cholesterol to chemically reduced and poorly absorbed compounds should therefore decrease the concerns of choles- terol-conscious people about consuming milk and other dairy products. Supercritical fluid extraction (SFE) is a state-of-the-art unit operation that exploits the dissolving power of supercritical fluids at temperatures and pressures above their critical values. It involves the use of a gas elevated above its critical pressure and tem- perature as a solvent for selected compo- nents of a solic] or liquid mixture. Under supercritical conditions, the solvent displays an increase in density, approaching that of a liquid, but retains the diffusivity associated with a gas. These properties allow a super APPENDIX critical fluid to penetrate the structure of a material to be separated, dissolve soluble components, and carry them out of the extraction vessel. The extract can be easily recovered from the solvent by manipulation of pressure and/or temperature conditions such that they become insoluble and pre- cipitate out of solution. The solvent can be vented off or recirculated through the ex- traction vessel. A number of advantages have been cited for SEE compared with conventional ex- traction techniques currently used in the food industry. These include reducer! en- ergy costs, higher yielcls, better quality products owing to lower operating temper- atures, and elimination of explosive or toxic solvents. It is anticipated that the use of supercritical fluid extraction and its range of applications will continue to grow cluring the coming years. Supercritical carbon dioxide is receiving increased attention from the food industry as a solvent to replace hydrocarbons and chlorinated hydrocarbons currently used in vegetable oil extraction, cleca~einating cof- fee, and spice extraction. It has one obvious advantage in food in that it is nontoxic in any concentration. Its low critical temper- ature (31°C) combined with its pressure- clepenclent dissolving power make it attrac- tive for separating particularly heat-labile flavor and aroma constituents at near-am- bient temperatures. Supercritical carbon dioxide has been used for the supercritical fluid extraction of oils from soybeans (Friedrich et al., 1982) and corn and cottonseed (List et al., 1984~. The oil from these three oilseeds obtained by SEE, compares] to hexane-extracted oil, was reported to be much less pigmented, require less refining, and have greater re- sistance to oxidative rancidity (Friedrich ant! Pryde, 1984). The last trait was attributed to the lower levels of free fatty acids and free iron and phosphorus (phospholipids) and the higher levels of tocopherols (Frie(l- rich and Pryde, 1984) in the oil after SEE.
IMPROVING NUTRITIONAL VALUE OF DAIRY PRODUCTS This indicates that supercritical carbon diox- ide is able to remove a specific lipic! fraction while leaving the other fractions intact. The main structural units of milk are fat globules, casein micelles, globular proteins, and lipoprotein particles (Walstra and len- ness, 19841. Fat globules are the primary source of lipids in milk. Their structure ant] composition are exceeclingly complex. A typical fat globule is probably 2 to 3 Em in diameter. Its core is composed of triacyl- glycerols (99 percent), with the remaining 1 percent composed of cholesterol ant] trace amounts of other lipid components. To effectively remove the cholesterol Tom the milk lipid system, the fat globule must be penetrated, since it contains the largest deposit of cholesterol in milk. However, the cholesterol must be removed from the fat globule without destroying any of the globule's ability to function. Therefore, a crucial factor affecting the ability of the supercritical fluid to extract the lipids from the fat globule is the status of the fat globular membrane. ALTERING TlIE TRACE ELEMENTS IN DAIRY PRODUCTS The addition of trace elements to the diet of a lactating human or other animal can, under certain conditions, increase to a lim- itecl extent the concentration of metals in the milk. In lactating humans, iron status seems to have little influence on milk iron concentration, and neither overt iron defi- ciency nor iron supplementation apprecia- bly alters milk iron (Vuori et al., 1980~. A similar observation has been made for cows (Archibalcl, 1985~. In mice, however, iron supplementation of the lactating dams sig- nificantly increases milk iron (Carmichael et al., 1977~. In humans, addition of copper to the diet causes little change in the milk copper concentration (Vuori et al., 1980~. Unfortified milks and formulas are poor sources of iron. However, the percentage of iron absorbed by infants varies widely 295 with the source. About 50 percent of the iron in breast milk is absorbed compared to 10 to 12 percent for cow's milk or formula (Dallman et al., 1980~. Fortification of cow's milk with iron sulfate or iron gluconate increases the total iron assimilated. Pro- longed breast-feeding protects against iron deficiency; fortified cow's milk or infant formulas are also effective. The total amount of iron absorbed from fortified cow's milk can be four times that absorbed from breast milk. Fortification must use chelated forms of the metals to ensure initial transfer to the phosphoserine groups of casein; this ligand- exchange reaction removes the metals from the reactive environment of milk lipids and ensures more effective utilization. Milk is an important foot! of high nutri- tional value, wale distribution, and reason- able price. The opportunity to fort)* it with several essential trace element gives us the chance to make it even more nourishing, particularly for infants, children, adoles- cents, and pregnant women who are at risk of iron and other trace metal deficiencies. REFERENCES Archibald, J. 1985. Trace elements in milk: A review. Dairy Sci. Abstr. 20:71~725, 80~812. Carmichael, D., J. Hegenauer, M. Lem, L. Ripley, P. Saltman, and L. Hatlen. 1977. Iron supplemen- tation of the lactating mouse and suckling neonates. J. Nutri. 107:1377-1384. Dallman, P. R., M. A. Slimes, and A. Stekel. 1980. Iron deficiency in infancy and childhood. Nutrition Foundation. Am. J. Clin. Nutr. 33(1~:8~118. Friedrich, J. P., and E. H. Pryde. 1984. Supercritical CO2 extraction of lipid-bearing materials and char- acterization of the products. J. Am. Oil Chem. Soc. 61:22~228. Friedrich, J. P., G. R. List, and A. J. Heakin. 1982. Petroleum-free extraction of oil from soybeans with supercritical CO2. J. Am. Oils Soc. 59:288-292. Jenness, R. 1974. The composition of milk. In Lactation III, Nutrition and Biochemistry of Milk, B. L. Larson and V. R. Smith, eds. New York: Academic Press. Kansal, V. K., and S. Chaudhary. 1982. Biological availability of calcium, phosphorus and magnesium from dairy products. Milchwissenschaft 37:261-263.
296 Kinsella, J. E. 1975. Butter flavor. Food Technol. 29(5):8~98. Kolars, J. C., M. D. Levitt, M. Avugi, and D. A. Savaiana. 1984. Yogurt: An autodigesting source of lactose. N. Engl. J. Med. 310:1. LaCroix, D. E., W. A. Mattingly, N. P. Wong, and J. A. Alford. 1973. Cholesterol, fat and protein in dairy products. J. Am. Diet. Assoc. 62:275-279. List, G. R., J. P. Friedrich, and D. D. Christianson. 1984. Properties and processing of corn oils obtained by the extraction with supercritical carbon dioxide. J. Am. Oil Chem. Soc. 61:1849-1851. MacDonald, I. A., V. D. Bokkenheuser, J. Winter, APPENDIX A. M. McLernon, and E. H. Mosbach. 1983. Deg- radation of steroids in the human gut. J. Lipid Res. 24:675-700. Vuori, E., S. M. Makinen, R. Kara, and P. Kuitunen. 1980. Iron supplementation in infancy and child- hood. Am. J. Clin. Nutr. 33:227-231. Walker, N. J. 1972. Distribution of flavour precursors in fractionated milkfat. N.Z. J. Dairy Sci. Technol. 7(4~: 135-139. Walstra, P., and R. Jenness. 1984. Pp. 58, 229, and 254 in Dairy Chemistry and Physics. New York: John Wiley & Sons. ~,
Technological Options for Improving the Nutritional Value of Poultry Products ROY GYLES People in the United States are becoming more concerned with the nutritional value of the food they consume. But nutritional improvement per se is ineffective if the product is not consumed by the population at large. For example, there were high expectations for foot! yeast as a source of protein for developing countries after World War II. The production of large quantities of food yeast was realized and the protein quality was unexcelled. However, tropical workers found no appeal in a light flaky material with no gustatory attributes, and thus the project failed. Therefore, the nu- tritional status of a product is a function of its nutritional value and the extent of its consumption. To be of nutritional benefit to a population, there are two prerequisites for any food product: The cost must not be prohibitive, ant] the product must be pal- atable. Poultry meat and eggs excel in both respects. Mass production of poultry meat and eggs became established through a combination of individual initiatives by pri- vate enterprise and research at land-grant colleges. Hybrid corn research at the Uni- versity of Connecticut in 1911, the devel- opment of coccidiostats, the eradication of 297 Salmonella pullorum and Mycoplasmas, the application of genetic selection through pop- ulation genetics, and the introduction of high-energy feeds have all contributed to the elevation of chicken meat from its former status as a Sunday luncheon luxury meal to its current status as an everyday meal for the general public. Eggs for the breakfasts of people accustomed to hard manual labor were supplied from numerous small flocks owner! by independent egg producers. Mass production by large centralized farms came about when research en cl development pro- vided the technological means for ensuring feet! supplies, poultry health, and the im- proved genetic strains that were required. Ongoing research, keen competition, and integration of the poultry industry have hel(l clown the cost of production of poultry meat and eggs. This has given poultry a compet- itive edge against other animal proclucts. Relative costs ant] consumption of animal products have been reporte(l by the U.S. Department of Agriculture (USDA) and show the following trends.* The cost per pound * U.S. Department of Agriculture, Economic Re- search Service, Poultry and Egg Situation Report No. 249, and Economics Statistics and Cooperatives Ser- vice, Poultry and Egg Situation Report No. 300.
298 of ready-to-cook broilers was 54.8 cents in 1940 and 81.4 cents in 1984. Choice grade beef was 75.4 cents per pouncT in 1940 and 239.6 cents in 1984. Pork was 54.4 cents in 1940 ant] 162.0 cents in 1984. Broiler meat rose 49 percent versus 218 percent for beef and 198 percent for pork. In the United States, the per capita consumption of broil- ers rose from 2.0 pounds in 1940 to 53.0 pounds in 1984. The per capita consumption of turkey meat rose from 2.9 pouncis in 1940 to 11.4 pounds in 1984. However, the per capita consumption of eggs dropped from 391 in 1940 to 261 in 1984. This decline may be attributer] to several factors, includ- ing a greater awareness of the possible link between heart disease and cholesterol. BROILERS Fat, protein, minerals, and water are the basic components of poultry meat. The composition of the fat-free tissue in poultry is relatively constant over a wide range of body weights and ages and is not affected by the degree of fatness (Leenstra, 1984; Lin, 1981~. However, the most variable component of dressecI ready-to-cook broil- ers is fat (Lohman, 1973~. As the percentage of fat increases, the percentages of protein, minerals, and vitamins decrease. Thus, the fat content of poultry meat affects the var- iation in its nutritional value more than any other ingredient. The fat in broiler meat can be categorizes! as either physiologically necessary fat or extraneous wasteful fat. Cell membranes, which are primarily lipid, control the permeability of cells. In addition, some intracellular and intramuscular fat appears to be necessary for normal growth and reproduction (Brody et al., 1984; Gyles et al., 1982~. Extraneous wasteful fat may be found subcutaneously, at the crop; inter- muscularly, attacher] to mesentery and giz- zard; and as leaf fat in the abdomen. The most frequently used measure of fatness in broilers is abdominal fat, which APPENDIX is the combined weight of the leaf fat and the fat attacher] to the gizzard. Because abdominal fat is highly correlates] with total body fat ant] fat in the various depots, it is used as the main measure of fatness in chickens and tissues (Cahaner et al., 1986; Chambers and Fortin, 1984; LeClercq and Simon, 1982; LeClercq et al., 1980; White- head and Griffin, 1984~. Abdominal fat is the most variable fat deposit (Becker et al., 1979; Leenstra, 1984~. It represents the greatest inefficiency in feed usage and is the largest source of loss when discarder] at cooking. Hood (1984) suggests that from an evolutionary standpoint, the purpose of ex- traneous fat was to provide a reserve of energy when food supplies became low. Today, domestication and mass production of poultry meat ensures a constant food supply. Therefore, excessive deposition of abdominal fat and extraneous fat at other depots is no longer required and represents unnecessary wastage of feed. Ricar(1 et al. (1983) and Becker et al. (1984) point out that large changes in reduction of abdominal fat are possible without affecting the lipids requires! for optimum growth and repro- duction. Broilers currently contain about 2 to 3 percent of the live borly weight as abdominal fat; total body fat ranges between 15 and 20 percent of the live body weight (Griffin et al., 1982~. The coefficient of variation for abdominal fat may be as high as 53 percent in broilers (GyTes et al., 1984~. The coeffi- cients of variation for protein, minerals, and water in poultry meat are about 3, 8, and 2 percent, respectively (Leenstra, 1984~. During the second half of the 1970s, the broiler industry became aware of a problem with excessive fatness of reacly-to-cook broiler carcasses. Consumers complained about throwing away large quantities of leaf fat at cooking and about too much subcutaneous fat and intermuscular fat in cooked broiler meat. Poultry processors complained about losing abdominal fat when the carcasses were cut up to sell by parts, as well as at
IMPROVING NUTRITIONAL VALUE OF POULTRY PRODUCTS evisceration. In response to current con- sumer demand, some processors are now trimming fat from broilers and deboned meat. The onset of the problem has been de- veloping over several generations of selec- tion. Poultry breeders produced broilers in 1950 that were marketed at 4.0 pounds live body weight at 12 weeks of age using 3.0 pounds of feed per 1-pound gain in weight. Intense genetic selection by poultry breed- ers for increased body weight at younger ages resulted in broilers being marketed in 1986 at 4.0 pounds live body weight at 6 weeks and 5 days of age using 1.98 pounds of feed per pound of gain. Genetic selection for body weight caused chickens with above- average appetites to be chosen as breeders. As a result, broilers were produced that ate more feed at a given age and became unable to synthesize protein and lean meat fast enough to keep pace with increased intake of food energy. The excess food energy was deposited as lipids, and broilers became fatter. Age and sex have a distinct influence on the relative amount offal in young chickens. Older broilers have higher quantities of fat than younger broilers (Edwards et al., 1973; Leenstra, 1984; Lin, 1981~. Pfaff and Austic (1976) and March and Hansen (1977) found that fatness in broilers up to 14 weeks of age increased through a proliferation in the number of fat cells. After 14 weeks of age, the numbers of fat cells were fairly constant, but the sizes of the cells increased. Management Options Numerous management options are avail- able that may improve the nutritional status of the dressed broiler carcass. A discussion of these follows. Marketing Broilers at Younger Ages Marketing broilers at younger ages with smaller body size and weight than is cur 1 299 rently practiced may be useful for certain marketing requirements to reduce fatness. However, the current thrust in broiler mar- keting is toward cleboned meat for further processed items. (A detailed description of "further processing" is given by Mast and Clouser in this volume.) Processing larger broilers at older ages has an economic ad- vantage for these requirements because older broilers yield more meat. Growing Males and Females Separately Growing the sexes separately for broiler production offers opportunities for reducing carcass fatness. Males may be processed at standard ages or older to provide more deboned meat for further processing, whereas females may be marketed at younger ages before they become undesirably fat. And because females require less protein in their feed than males, formulation of two separate feeds for males and females has potential for economic gain. Furthermore, increased uniformity of carcass size is obtained by processing sexes separately. This increases the efficiency of processing with associated . . economic gains. To grow sexes separately requires that the sex of each broiler chicken be deter- mined on the day of birth. Sexing by the vent method is too costly to be feasible for this purpose; therefore, autosexing by ge- netics is required. Two options are available. Feather sexing based on rate of feathering at day of age is easily accomplished by mating fast-feathering males to slow-feath- ering females. However, there is a cost for manual evaluation of the feather status in the wing of each day-old broiler to deter- mine sex. Also the producer sometimes experiences difficulties in growth and car- cass quality from slow-feathering male broil- ers. Autosexing by down color is possible and highly attractive because there are no extra expenses for this type of procedure and no production problems. The poultry industry would benefit from the availability
300 of genetic strains that produce autosexing broiler offspring by down color. These strains are available, but because their growth and feed conversion performance are substand- ard, they are uneconomical at this time. Cage Versus Floor Rearing Almost all broilers in the United States are reared on the floor. However, there are aspects of rearing broilers in cages that are appealing. Cages require less floor space of housing per broiler and negate the laborious task of catching chickens on the floor at marketing. However, Deaton et al. (1974) found that broilers reared in cages had more abdominal fat than those grown on the floor. This suggests that the current industry prac- tice of raising broilers on the floor contrib- utes less to fatness than does cage rearing. Texture of Feed For high-density diets, the texture of the feed has no influence on abdominal fat. However, for low-density diets, more time is taken to consume the feed in mash form as compared with crumbles or pellets. Pesti et al. (1983) found that feeding crumbles increased abdominal fat by 23 percent. Genetic and Other Options The following genetic and other options to reduce fatness in broilers have been considered, and some are currently being used by poultry breeders. Family Selection Against Abdominal Fat Genetic selection against abdominal fat cannot be accomplished by a direct measure of indiviclual performance, because this re- quires killing the chicken to obtain the weight of abdominal fat. However, family average performance of abdominal fat may be obtained by killing full siblings or half siblings. This procedure requires the de APPENDIX struction of some outstanding candidate breeders and involves time and expense at the processing plant. Becker et al. (1982) determined that a selection index of carcass weight and abdominal fat weight (0.1108 carcass weight - abdominal fat weight) reduces abdominal fat weight in a population and at the same time allows body weight to increase. Cahaner (1986) reporter! that di- vergent selection for abdominal fat based on measurement of abdominal fat among full siblings gave a heritability of 0.77 for reduction of abdominal fat and a realized heritability of 0.73 for separation of the lines. Cahaner further reported that for every gram of reduction in abdominal fat there was a general reduction of 0.8 gram in other body fat. This method of genetic selection is probably being used to some extent by poultry breeders. Specific Gravity of Broiler Carcasses Fortin and Chambers (1981) found that using the specific gravity of the chilled dressed broiler carcass or the individual carcass parts was an unreliable, indirect indicator of fatness, apparently because of entrapment of air in the abdominal cavity and the existence of air sac extensions in the parts. Abdominal Fat in Spent (Killed) Parents The determination of the weight of ab- dominal fat in spent parents is a destructive procedure, but the chickens are sent to the processing plant at the end of their procluc- tive year as normal practice. Therefore, killing the chickens does not incur the loss of a potential breeder. Gyles et al. (1982, 1984) reported that there was a significant (F < 0.05) relationship between the abdom- inal fat in spent females and their broiler offspring when the female parents were fell ad libitum, but not when they were on feed restriction as practiced commercially. Spent females that are switched from restricted to
IMPROVING NUTRITIONAL VALUE OF POULTRY PRODUCTS ad libitum feeding for a few weeks before killing for fat determination may show a positive relationship between fatness of par- ents and offspring at broiler ages. Selection of young candidate breeders based on the abdominal fat content of spent dams is a possible option for reducing abdominal fat but is probably not currently practiced by poultry breeders. Selection for Improved Feed Efficiency Selection for feed efficiency is an effective way to maintain or reduce abdominal fat while improving growth rate and carcass yield. Brody (1935) pointed out that in- creased weight per age should change the lean/fat ratio in favor of lean tissue deposi- tion. Thomas et al. (1958) fount] that broilers with higher feed efficiencies tended to have less body fat. Shook et al. (1966) pointer] out variations in feed conversion among turkey toms of similar belly weights and suggested a way for turkey breeders to use genetic selection to improve feed efficiency of turkeys. Gyles (1968) proposed a new concept in poultry breeding termed] "con- version breeding," which was applied to a commercial male parent line for broiler production. Subsequent work by Washburn et al. (1975), Pym and Solvyns (1979), and Chambers et al. (1983) reported that selec- tion for increased feed efficiency reduced the fat content of broiler carcasses. Cham- bers et al. (1983) found that a correlation of -0.48 between carcass fat and feed effi- ciency was-0. 62 after adjusting for cliffer- ences in weight gain. Selection for improved feed efficiency of both male and female parent lines of broilers in order to reduce abdominal fat is widely practiced in the poultry industry. Selection Against Very-Low-Density Lipoproteins (VLDL) in Sera Gruncler et al. (1984) fount] that the percentage of abdominal fat and plasma 301 \7LDL increased while abdominal fat lipase decreased as broilers advancer! in age. The decrease in lipase activity may be associates! with an increase in lipogenesis and serve as an indirect measure of fatness. The Cloaca Probe Pym and Thompson (1980) developer] a set of calipers to measure indirectly the amount of abdominal fat in live chickens. Chickens were placed on their backs and a probe was inserter! into the cloaca. The distance was then measurer! between the probe and the ventral abdominal skin. The authors reporter] a significant (P < 0.05) correlation of 0.80 between caliper meas- urement and weight of abdominal fat pact. Other researchers, however, have been un- successful in duplicating these results. Mi- rosh and Becker (1982) reported a correla- lion of 0.30 between caliper measures at the midline of the abdomen and abdominal fat weight. Gyles et al. (1982) obtained correlations below 0. 20. This method is probably not being used by poultry breed- ers. Skin Pinches Mirosh et al. (1981) removed feathers from the left wing-web of broilers and used calipers to measure the skin thickness at the center of the wing-web. The broilers were subsequently killed and dressed. A pinch (double skin thickness) at the center of the humeral feather tract on the left and right shoulder region of each carcass was measured with calipers. Correlation coeffi- cients between wing-web thickness and ab- dominal fat weight were 0.14 for males and 0.05 for females. Correlations for humeral tract pinch with abdominal fat weight were 0.12 and 0.17 for males and 0.18 and 0.13 for females. These small associations suggest that both these measures are unsuitable for estimating abdominal fat.
302 Lipids of Pectoral Feathers Becker et al. (1981) found a genetic cor- relation of 0.90 between percent lipids of pectoral feathers and percent abdominal fat, but this procedure requires further inves- tigation. Ultrasonics Ultrasonic techniques for determining fat- ness in poultry have been disappointing. Gillis et al. (1973) found that ultrasonics gave unreliable predictions of the percent- age of fatness in turkeys. The correlations between two methods of ultrasonic meas- urement and breast fat and back fat were 0.06 ant] -0.06, respectively. Miller and Moreng (1963) used a somascope (ultrasonic flow detector) to measure fat thickness on ciressed turkey carcasses. Highly significant (P < 0.01) correlations of 0.85 and 0.84 were found between somascope readings ant] fat thickness in the breast feather tract and back feather tract, respectively. Selection Against Sartorial Fat Burgener et al. (1981) suggested that the sartorial (Musculus sartorius) fat depot was a useful indirect measure of broiler fatness. They found highly significant (P < 0.01) correlations of 0.78 ant! 0.79 between the total weight of left and right sartorial fat and abdominal fat in 42- ant] 56-day-old broilers, respectively. They infer that since the sar- torial fat is outside the body cavity, it may be readily biopsied. However, the practi- cality of using this procedure on large flocks is questionable. Heritability Estimates of Abdominal Fat The genetic options are well established and supported by moderate to large esti- mates of the heritability of abdominal fat based on the sire component of variance and reported by several researchers: Leen APPENDIX stra (1984), 0.38; Friars et al. (1983), 0.42; Becker et al. (1984),0.38; Gyles et al. (1984), 0.72 and 0. 23; and Cahaner (1986),0.77 and 0.73. Nutrition Options Several nutrition options have been re- portec3 in the literature that reduce the amount of fat in broilers. However, nutrition options are short term and palliative com- pared with genetic solutions. Furthermore, the consequences of nutrition options must be carefully evaluated as to whether the reduction in fat is accompanied by some loss in performance that adversely affects net profits. Each option must be evaluated in accordance with the particular goals and circumstances of individual production or- ganizations. The following options may be considered. Manipulation of the EnergylProtein Ratio The energy/protein ratio of the diet has a central role in fat deposition in broilers. Fraps (1943) was among the first to describe this effect. Since then many other investi- ~ators have reported on its ramifications (Bartov et al., 1974; Donaldson et al., 1956; Farrell, 1974; Jackson et al., 1982~. Energy levels fed in excess of mainte- nance requirements result in fat deposition. The energy/protein ratio affects the amount of feed consumed by chickens because the chicken tends to regulate consumption to meet its protein requirements. Decreasing dietary energy while maintaining the same protein level causes a reduction in feed consumption and fat deposition. Maintain- ing the energy level and increasing the amount of protein has the same effect (Ya- mashita et al., 1975~. Therefore, the amount of fat in broilers can be influenced by changing the energy/protein ratio in accord- ance with desired product quality and net economic gain. The goal must be to for
IMPROVING NUTRITIONAL VALUE OF POULTRY PRODUCTS mutate a well-balanced diet to maximize growth rate without increasing fat (Marion and Woodroof, 1966~. When the diet is not balanced and chickens are fed insufficient protein, they consume more energy than is required and fat deposition increases. This may occur when there is only a slight protein deficiency (Waldroup et al., 1976~. Restriction of Feed During Early Life of Broilers Changing diets during the course of rear- ing broilers may produce rapid changes in fatness. Khalil et al. (1968) showed that groups of chickens fed low-protein diets for 8 days developed obese (24.1 percent body fat) carcasses. Chickens fed high-protein diets developed lean (1.8 percent belly fat) carcasses. When both groups were switched to a balances! diet for 9 clays, their carcass fat differences were narrowed (13.6 and 10.3 percent). The determination that proliferation of fat in broilers is primarily due to an increase in the number of adipose cells has lead to the concept that restriction of feed during the early life of a broiler, followed by normal feeding, may result in reduced fatness. Results reported by March and Hansen (1977) tended to support fat reduction by this feeding regimen, but Griffiths et al. (1977) found that restricting the energy intake of chicks from hatching to 3 weeks of age had no significant (P < 0.05) eject on the fat pad size at 8 weeks of age. Restriction of Energy in Feed Shortly Before Marketing Arafa et al. (1983) restricted feeding of broilers for 10 days before marketing and reduced abdominal fat by 79 percent com- pared with broilers fed ad libitum. The energy intake was 80 percent of the ad libitum intake. The live body weight at marketing and the dressed carcass weight of the restricted groups were slightly less 303 than those of the chickens fed ad libitum, but the average weights of the cooked broil- ers were the same for both groups. Com- mercial organizations that have a high per- centage of their business in further processing should examine this option. Recent work by Cabel et al. (1986) showed that the addition of feather meal from 2 to 6 percent of the diet fed for the 14 days before marketing at 49 days of age signifi- cantly (P < 0.05) reduced the abdominal fat in the carcasses. Formulation of Separate Feeds for Mates and Females Formulation of separate feeds for male and female chickens requires growing the sexes separately. (This was also discusser! in the section on genetic options.) Female broilers require less protein in feed than males (Siegel and Wisman, 1962; Wells, 1963~. Lowering the protein below 20 per- cent with an energy/protein ratio of 160 was found to increase the carcass fat in males but had no effect on females until the protein level was reduced below 16 percent with an energy/protein ratio of 200 (Lipstein et al., 1975~. Formulation of separate feeds to meet more exactly the nutritional require- ments of the sexes and produce less fat and more uniform size of carcasses at the proc- essing plant should increase the overall efficiency of broiler production. Protein Quality of Feed Fisher and Shapiro (1961) observer! that a proper balance of amino acids was essential for optimum growth of broilers. Chickens on a diet deficient in some amino acids tended to compensate for the deficiency by overeating, consuming more energy, and depositing more fat. Carew and Hill (1961) found that a slight methionine deficiency did not reduce the growth rate of chickens significantly (P < 0.05) but did increase fat deposition. On the other hand, when there
304 was more than the optimum amount of protein in a diet, fatness was reduced. Leveille et al. (1975) observed that addition of excess protein or amino acids to an already balanced diet reduced abdominal fat, prob- ably clue to utilization of energy to synthe- size uric acid, which is the main end product of nitrogen metabolism in the chicken. Feeding Fat as a Form of Energy Edwards et al. (1973) reported that chick- ens on a diet supplemented with fats of animal or vegetable sources had slightly more carcass fat than controls. However, the difference was not significant (P < 0.054. Fuller ant! Rendon (1977) confirmed] that the addition of fat in place of carbohydrate, without altering the energy/protein ratio, clid not affect the amount of carcass fat. Therefore, the form in which energy is supplied in the diet does not seem to influence significantly the degree offatness. Type of Fat in Diet Affects Chemical Composition of Carcass Fat Marion and Woociroof (1966) pointed out that because carcass fat is deposited in two ways directly from diet fat and through liver lipogenesis-the dietary constituents significantly influence the chemical com- position of the carcass fat. The feeding of unsaturated fatty acids increaser! unsatu- ratec] fatty acids in the carcass, thereby reducing the carcass's shelf life. Edwards et al. (1973) reported that the type of fatty acids in the diet affected the composition of carcass fat. Chickens fed beef tallow had much firmer carcasses than those fed fats of vegetable origin. Beef tallow increased the stearic and oleic acid levels in place of the linolenic acid of vegetable fats. TURKEYS Genetic selection for increased body weight at younger ages has not been as intense for APPENDIX turkeys as for chickens. Rather, selection has been directed primarily toward body conformation to increase yield of breast meat, ant! also to increase body weight at a standard age. Therefore, while the modern turkey has shown significant gains in body weight and breast meat, excessive fatness has not occurred (Nestor and Bacon, 1985~. Bacon et al. (1985) reported that three large- boclied lines were selectee! from a ranclom- bred control population over 17 generations. The three heavy lines of turkeys, selected in different ways from a common random- brec! control, were similar in percentages ofprotein, ash, ctry master, end fat ofUressed carcasses. The abdominal fat as a percent of body weight in the three selected lines was similar at 0.94 to 0.95, as compared with 0.49 for the random-bred control popula- tion. Females had larger quantities of leaf fat than males. Turkey breeders have recently instituted changes in their selection criteria to prevent or delay any development of excessive fat- ness in turkeys. They are currently testing all the candidate male breeders of their commercial lines for individual feed-con- verting ability. The young toms are placed in individual floor pens, and their feed- converting abilities over several weeks are determined. Final selection of male breed- ers is made on more than one trait, but feed-converting ability is strongly empha- sized. EGGS The hen's egg is regarded as the near- perfect food. However, egg consumption has declined during the past 40 years, pri- marily because of changing life-styles (fewer individuals eating"hearty" breakfasts), in- creased awareness of the importance of food quality to health, and the evidence that cholesterol is linked to cardiovascular dis- ease. Gilbert (1971) describes the yolk of the egg, on which the germinal disc floats, as an orange-yellow viscid fluid of oil-water
IMPROVING NUTRITIONAL VALUE OF POULTRY PRODUCTS emulsion with the continuous phase as aqueous protein. Chemically, it contains proteins, lipids, cholesterol, pigments, and a variety of minor organic and inorganic substances. In contrast, the albumin, or egg white, is describer! as almost pure aqueous protein, consisting of about 40 proteins. The obvious single nutritional improve- ment in eggs in terms of human consump- tion is the reduction of cholesterol. Turk and Barnett (1971) found that the concen- tration of cholesterol in eggs clid not differ significantly (P c 0.05) with age of hen, cage versus floor management, strain of commercial hen, or geographic location of feet] source. Eggs from meat-type hens contained higher levels of cholesterol than eggs from commercial layers. Turkey, duck, and Coturnix quail eggs contained greater concentrations of cholesterol than chicken eggs. These differences are of little concern to the U.S. consumer, however, because chicken eggs from commercial layers are consumed almost exclusively. However, in some Oriental countries, cluck eggs are widely consumed. Differences in egg size that occur along with disproportionate cli~erences between yolk and albumin result in changes in the percentage of yolk ant] albumin. Marion et al. (1964) found that differences in egg size are highly associates] with egg components and that variation in any component is primarily because of covariation with egg size. The percentage yolk of egg tended to increase with a decrease in egg size. Cor- respondingly, the percentage albumin in- creased in larger eggs. Therefore, there are genetic ant] nutritional reasons for improv- ing the nutritional value of eggs. Genetic Options Cholesterol Reducing the amount of cholesterol in eggs by genetic selection is the most desir- able way to improve their nutritional value. 305 Cunningham et al. (1974) reported a realized heritability of 0.21 for (1ivergent selection on cholesterol concentration in yolks for one generation of selection. Washburn and Nix (1974) found sufficient genetic variation of cholesterol concentration that resulted in heritability estimates ranging from 0.14 to 0.22. These early reports implied that cho- lesterol concentration was responsive to selection. Marks and Washburn (1977) prac- ticed divergent selection in one population for four generations and in another for three generations ant] obtained realized herita- bility estimates of 0. 11 to 0.25 for separation of cholesterol concentration. However, in both populations the (livergent separations of cholesterol concentration were due en- tirely to an increase in cholesterol in the high-cholesterol lines. There were no re- ductions in cholesterol in the low lines. Interestingly, numbers of eggs produced were reduced in the high-cholesterol lines, ant! consequently, when the high-choles- terol lines were compared with the low- cholesterol lines for total daily mass output of cholesterol, there were no differences between them. Becker et al. (1977) got similar results in that they were unable to obtain a response to selection for lower cholesterol in the yolk, but they did get a positive response to increased cholesterol. In this divergent selection study, realizer] heritabilities ranged from 0.04 to 0.13. The measurements of cholesterol in the above experiments were based on the amount of cholesterol in the total wet yolk. Con- ceivably, cholesterol measured in milli- grams per gram of wet yolk could have been reducecl in the low-cholesterol lines without being detected by total cholesterol per wet yolk if yolk size increased. Accordingly, Washburn ant! Marks (1985) con(lucted an- other (livergent selection experiment in which cholesterol was measured in milligrams per gram of wet yolk. When total cholesterol was expressed as total amount in yolk or grams of dry matter, the separation between the lines was similar to that when calculated
306 as milligrams of cholesterol per gram of wet yolk. Therefore, it appears that regardless of the mode of expression of cholesterol concentration in eggs, genetic selection thus far has not been successful in significantly (P < 0.05) reducing cholesterol in eggs. There are no breecis or strains of chickens that lay eggs of superior nutritional value with significantly (P < 0.05) lower choles- terol than other chickens. In the past an advertisement in the press states! that the blue eggs laid by the Araucana breed were lower in cholesterol than eggs from other breeds. Cunningham (1976) ant] Somes et al. (1977) refuted this allegation and found that eggs of the Araucana breed were equal to or higher in cholesterol than eggs of other breeds. Proteins, Fatty Acids, and Vitamins There are several reports that ascribe genetic influences to the polymorphic pro- teins in egg white (for example, see Wash- burn, 1979~. Strain differences for fatty acids in yolks have been shown to be small or negligible (Chen et al., 1965; Sell et al., 1968~. Differences between breeds for vi- tamin A (Arroyave et al., 1957), thiamine (Howes and Hutt, 1956), and riboflavin (Mayfield et al., 1955) have been reported. Considering the excellent nutritional value of eggs (except for high cholesterol), there is no need to use genetic selection to influ- ence the status of these nutrients. Nutrition Options Cholesterol Naber (1979) stated that the nutrient composition of the egg hack not changed greatly in response to modern industry practices. Naber (1976) pointed out that there appeared to be little variation in cholesterol content of eggs from hens fed the usual commercial diets. Given this ob APPENDIX servation, it is important to note that de- viations from a normal diet may significantly increase or decrease cholesterol. However, these deviations may negatively affect the nutritional value of the egg or the perform- ance of the hen. Weiss et al. (1964) showed that diets containing 30 percent fats or 1 percent cholesterol causer! a significant in- crease in the cholesterol content of eggs. Addition of certain drugs to the hens' diet namely, triparano! (Burgess et al., 1962), certain azasterols (Singh et al., 1972), and probucol (Naber et al., 1974) have caused significant reductions of cholesterol in the eggs. Use of these drugs was experimental, and harmful side effects have made them undesirable. Vitamins Hill et al. (1961) found that the vitamin A content of egg yolks increased when levels in the diet were increased. However, the levels of increase in the egg were much less in proportion to those in the feed, because significant amounts were stored in the liver. In the case of vitamin D, there was negli- gible storage in the liver, and the quantities of the vitamin increased in the egg yolk in proportion to increases in the feed. Denton et al. (1954) pointed out that among the water-soluble vitamins, only the vitamin BE content of the egg may be significantly (P < 0.05) enhancer] by feeding quantities of the vitamin above the normal dietary re- quirements. Minerals Wilder et al. (1933) showed that the iodine content of the egg varies according to the quantities in the diet. Latshaw and Osman (1975) were able to significantly (P ~ 0.05) increase the levels of selenium in the egg white by feeding increased levels of either natural sources of the mineral or inorganic selenite.
IMPROVING NUTRITIONAL VALUE OF POULTRY PRODUCTS BIOTECHNOLOGY Meat Production Work is being done on identifying a single gene in the poultry population that reduces abdominal fat to an acceptably low level and that can then be isolated, cloned, and in- serted into the germ plasm of commercial broiler lines. Identification, cloning, and transfer of a single gene from an avian species other than poultry may provide a similar genetic scenario. Identification, cloning, and transfer of a single gene from a species other than avian may provide a third similar genetic situation. In each in- stance, population geneticists will have to determine whether insertion of a specific gene allows the broiler lines to be signifi- cantly (P < 0.05) superior in net bioeco- nomic performance to lines under conven- tional genetic selection. Egg Production ~.' . 307 SUMMARY AND RECOMMENDATIONS Poultry products are widely consume( ant! contribute greatly to the nutrition of people in the United States. The commer- cial poultry industry and land-grant colleges must continue their traditional cooperation through research ant! teaching to maintain the relatively low cost of production and high overall palatability of poultry products. The nutritional value of poultry products can be improved by reducing the amount of fat in broiler carcasses, preventing the occurrence of excessive fatness in turkeys, and producing eggs with a greatly re(luce cholesterol content. Several technological options have been discussed for improving the nutritional value of poultry products. The following are recommender] for their effectiveness ancl practicality. Broilers Genetic Options family selection against abdominal fat Since genetic selection has so far failed ' ~~ to reduce the cholesterol level of eggs, biotechnology should be investigated as a way to improve the nutritional value of eggs. Identification, cloning, and insertion into the germ plasm of commercial egg layers of a single gene that reduces choles terol in eggs should be attempted, and the search for this gene should be ma(le within ant] without the avian species. Determination of Sex Biotechnology may make a significant contribution to the poultry industry by de- veloping a way to determine the sex of fertilized eggs, embryos, or chicks at hatch- ing. Such a procedure would] allow broilers to be grown separately by sex, with the advantages mentioned previously for reduc- ing abdominal fat en c] increasing production efficiency. and very-low-density lipoproteins in blood sera and selection for improved feed efE- ciency have been shown to be effective in reducing fatness. A poultry breeding orga- nization should pursue whichever of these or other avenues are consiclerec] suitable for the particular breeding program. Nutrition Options Manipulation of the energy/protein ratio in the diet should] be clone to suit the marketing needs of each integrated poultry organization an(1 with the knowledge that this ratio is the main option available to nutritionists to reduce fatness in broilers. Restriction of energy in feed shortly before marketing may be effective. In this regard, the recent report (Cabel et al., 1986) on addition of feather meal to the diet for the 14-day period before marketing should be considered.
308 Turkeys Turkey producers should gain from the experience of broiler producers and prevent excessive fatness in turkeys. Breeders are well advised to test and select their candi date male breeders on the basis of individual feed-converting ability. Eggs Researchers in biotechnology should] be encouraged to cooperate with population geneticists in reducing the cholesterol in eggs. REFERENCES Arafa, A. S., M. A. Boone, D. M. Janky, M. R. Wilson, R. D. Miles, and R. H. Harms. 1983. Energy restriction as a means of reducing fat pads in broilers. Poultry Sci. 62:314-320. Arroyave, G. N., S. Schrimshaw, and O. B. Tandon. 1957. The nutrient content of the eggs of five breeds of hens. Poultry Sci. 36:469 173. Bacon, W. L., K. E. Nester, and P. A. Renner. 1985. The influence of genetic increases in body weight and shank width on the abdominal fat pad and carcass composition of turkeys. Poultry Sci. 64(Suppl. 1):60. Bartov, I., S. Bornstein, and B. Lipstein. 1974. Effect of calorie to protein ratio on the degree of fatness in broilers fed on practical diets. Br. Poultry Sci. 15:107-117. Becker, W. A., J. V. Spencer, J. A. Verstrate, and L. W. Mirosh. 1977. Genetic analysis of chicken egg yolk cholesterol. Poultry Sci. 56:895-901. Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate. 1979. Prediction of fat and fat free live weight in broiler chickens using back-skin fat, ab- dominal fat and live weight. Poultry Sci. 58:835- 842. Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate. 1981. Genetic correlation between pectoral feather tract lipids and abdominal fat in female broilers. Poultry Sci. 60:1621-1622 (Abstr.). Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate. 1982. Selection of broilers for large carcass weight and low abdominal fat. Poultry Sci. 61:1415 (Abstr.). Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate. 1984. Genetic variation of abdominal fat, body weight and carcass weight in a female broiler line. Poultry Sci. 63:607~11. Brody, S. 1935. Nutrition. Annul Rev. Biochem. 4:383- 412. APPENDIX Brody, T. B., P. B. Siegel, and J. A. Cherry. 1984. Age, body weight, and body composition require- ments for the onset of sexual maturity of dwarf and normal chickens. Br. Poultry Sci. 25:245-252. Burgener, J. A., J. A. Cherry, and P. B. Siegel. 1981. The association between sartorial fat and fat depo- sition in meat-type chickens. Poultry Sci. 60:54~2. Burgess, T. L., C. L. Burgess, and J. D. Wilson. 1962. Effect of MER-29 on egg production in the chicken. Proc. Soc. Exp. Biol. Med. 109:21~221. Cabel, M. C., T. L. Goodwin, and P. W. Waldroup. 1986. Reduction in abdominal fat content of broilers by addition of feather meal during the finisher period. Poultry Sci. 65(Suppl. 1~: 157. Cahaner, A. 1986. Direct and correlated responses to divergent selection on abdominal fat. Pp. 71~8 in Proceedings of the 35th Annual National Breeders Roundtable, St. Louis, Mo., May 1-2, 1986. De- catur, Gal: Poultry Breeders of America and South- eastern Poultry and Egg Association. Cahaner, A., Z. Nitsan, and I. Nir. 1986. Weight and fat content of adipose and non-adipose tissues in broilers selected for or against abdominal adipose tissue. Poultry Sci. 65:215-222. Carew, L. B., and F. W. Hill. 1961. Effect of methi- onine deficiency on the utilization of energy by chicks. J. Nutr. 74:185. Chambers, J. R., and A. Fortin. 1984. Live body and carcass measurements as predictors of chemical com- position of carcasses of male broiler chickens. Poultry Sci. 63:2187-2196. Chambers, J. R., A. Fortin, and A. A. Grunder. 1983. Relationships between carcass fatness and feed ef- ficiency and its component traits in broiler chickens. Poultry Sci. 62:2201-2207. Chen, P. H., R. H. Common, N. Nikolaiczuk, and H. F. MacRae. 1965. Some effects of added dietary fat on the lipid composition of hen's egg yolk. J. Food Sci. 30:83~845. Cunningham, D. L., W. F. Krueger, R. C. Fanguy, and J. W. Bradley. 1974. Preliminary results of bidirectional selection for yolk cholesterol level in laying hens. Poultry Sci. 53:38~391. Cunningham, F. E. 1976. Composition of Araucana eggs. Poultry Sci. 55:2024. Deaton, T. W., L. F. Kubena, T. C. Chen, and F. N. Reece. 1974. Factors influencing the quantity of abdominal fat in broilers. 2. Cage versus floor rearing. Poultry Sci. 53:574-576. Denton, C. A., W. L. Kellogg, J. R. Sizemore, and R. J. Lillie. 1954. Effect of injection and feeding vitamin B12 to hens on content of the vitamin in the egg and blood. J. Nutr. 54:571-577. Donaldson, W. E., G. F. Combs, and G. L. Romoser. 1956. Studies on energy levels in poultry rations. 1. The effect of calorie protein ratio of the ration on growth nutrient utilization and body composition of chicks. Poultry Sci. 35:1100.
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Simon. 1982. Selecting broilers for low or high abdominal fat: Observations on the hens during the breeding period. Ann. Zootechnol. 31:161-170. Leenstra, F. R. 1984. Influence of diet and genotype on carcass quality in poultry and their consequences for selection. Pp. 3-16 in Recent Advances in Animal Nutrition, W. Haresign and D. J. A. Cole, eds. London: Butterworth. Leveille, G. A., D. R. Romsos, Y. Y. Yeh, and E. K. O'Hea. 1975. Lipid biosynthesis in the chick. A consideration of site of synthesis, influence of diet and possible regulatory mechanisms. Poultry Sci. 54:1075. Lin, C. Y. 1981. Relationship between increased body weight and fat deposition in broilers. World Poultry Sci. 37:106-110. Lipstein, B., S. Bornstein, and I. Bartov. 1975. The replacement of some of the soya bean meal by the first limiting amino-acids in practical broiler diets. Br. Poultry Sci. 16:627. Lohman, T. G. 1973. Biological variation in body composition. J. Anim. Sci. 32:647-653. March, B. E., and G. Hansen. 1977. Lipid accumu- lation and cell multiplication in adipose bodies in White Leghorn and broiler-type chickens. Poultry Sci. 56:886-894. Marion, J. E., and J. G. Woodroof. 1966. Composition and stability of broiler carcasses as affected by dietary protein and fat. Poultry Sci. 45:241. Marion, W. W., A. W. Nordskog, H. S. Tolman, and Et. H. Forsythe. 1964. Egg composition as influenced by breeding, egg size, age and season. Poultry Sci. 43:255-264.
310 Marks, H. L., and K. W. Washburn. 1977. Divergent selection for yolk cholesterol in laying hens. Br. Poultry Sci. 18: 179-188. Mayfield, H. L., R. R. Roehm, and A. F. Beeckler. 1955. Riboflavin and thiamine content of eggs from New Hampshire and White Leghorn hens fed diets containing condensed fish or dried whale solubles. Poultry Sci. 34:1106-1111. Miller, B. F., and R. E. Moreng. 1963. Studies on turkey body composition. 2. Measuring carcass fat of turkeys by ultrasonic detection. Poultry Sci. 42:26~273. Mirosh, L. W., and W. A. Becker. 1982. Components which form the thickness of the abdomen region in broiler chickens. Poultry Sci. 61:1515. Mirosh, L. W., W. A. Becker, J. V. Spencer, and J. A. Verstrate. 1981. Prediction of abdominal fat in broiler chickens using wing web and humeral feather tract measurements. Poultry Sci. 60:509-512. Naber, E. C. 1976. The cholesterol problem, the egg and lipid metabolism in the laying hen. Poultry Sci. 55:1~30. Naber, E. C. 1979. The effect of nutrition on the composition of eggs. Poultry Sci. 58:51~528. Naber, E. C., J. F. Elliot, and T. L. Smith. 1974. Effect of Probucol on reproductive performance and liver lipid metabolism in the laying hen. Poultry Sci. 53:1960. Nestor, K. E., and W. L. Bacon. 1985. Turkey fat problem? Canada Poultryman 72410):54. Pesti, G. M., T. S. Whiting, and L. S. Jensen. 1983. The effect of crumbling on the relationship between dietary density and chick growth, feed efficiency and abdominal fat pad weights. Poultry Sci. 62:490- 494. Pfaff, F. E., and R. E. Austic. 1976. Influence of diet on development of the abdominal fat pad in the pullet. J. Nutr. 106:443~50. Pym, R. A. E., and A. J. Solvyns. 1979. Selection for food conversion in broilers. Body composition of birds selected for increased body weight gain, food consumption and food conversion ratio. Br. Poultry Sci. 20:87-97. Pym, R. A. E., and J. M. Thompson. 1980. A simple caliper technique for the estimation of abdominal fat in live broiler chickens. Br. Poultry Sci. 21:281. Ricard, F. H., B. LeClercq, and C. Touraille. 1983. Selecting broilers for low or high abdominal fat: Distribution of carcass fat and quality of meat. Br. Poultry Sci. 24:511-516. Sell, J. L., S. H. Choo, and P. A. Kondra. 1968. Fatty acid composition of egg yolk and adipose tissue as influenced by dietary fat and strain of hen. Poultry Sci. 47:1296-1302. Shook, J. G., J. E. Valentine, L. D. Andrews, and N. APPENDIX R. Gyles. 1966. How turkey breeders may select for feed conversion. Ark. Agric. Exp. Stn. Bull. 710. Siegel, P. B., and E. L. Wisman. 1962. Protein and energy requirements of chicks selected for high and low body weight. Poultry Sci. 41:1225. Singh, R. A., J. F. Weiss, and E. C. Naber. 1972. Effect of azasterols on sterol metabolism in the laying hen. Poultry Sci. 51:449~57. Somes, R. G., Jr., P. V. Francis, and J. J. Tlustohowicz. 1977. Protein and cholesterol content of Araucana chicken eggs. Poultry Sci. 56:1636-1640. Thomas, C. H., E. W. Glazener, and W. L. Blow. 1958. The relationship between feed conversion and ether extract of broilers. Poultry Sci. 37:1177-1179. Turk, D. E., and B. D. Barnett. 1971. Cholesterol content of market eggs. Poultry Sci. 50:130~1306. Waldroup, P. W., R. J. Mitchell, J. R. Payne, and Z. B. Johnson. 1976. Characterization of the response of broiler chickens to diets varying in nutrient density content. Poultry Sci. 55:130. Washburn, K. W. 1979. Genetic variation in the chemical composition ofthe egg. Poultry Sci. 58:529- 535. Washburn, K. W., and H. L. Marks. 1985. Changes in egg composition of lines selected for divergence in yolk cholesterol concentration. Poultry Sci. 64:205- 211. Washburn, K. W., and D. F. Nix. 1974. Genetic basis of yolk cholesterol content. Poultry Sci. 53: 109-115. Washburn, K. W., R. A. Guill, and H. M. Edwards, Jr. 1975. Influence of genetic differences in feed efficiency on carcass composition of young chickens. J. Nutr. 105:1311-1317. Weiss, J. F., E. C. Naber, and R. M. Johnson. 1964. Effect of dietary fat and other factors on egg yolk cholesterol. 1. The "cholesterol" content of egg yolk as influenced by dietary unsaturated fat and the method of determination. Arch. Biochem. Biophys. 105:521-526. Wells, R. G. 1963. The relationship between dietary energy level, food consumption and growth in broiler chicken. Br. Poultry Sci. 4:161. Whitehead, C. C., and H. D. Griffin. 1984. Devel- opment of divergent fat lines of lean and fat broilers using plasma very low density lipoprotein concen- tration as selection criterion: The first three gener- ations. Br. Poultry Sci. 25:573-582. Wilder, O. H. M., R. M. Bethke, and P. R. Record. 1933. The iodine content of hen's eggs as affected by the ration. J. Nutr. 6:407~12. Yamashita, C., Y. Ishimoto, T. Yamada, H. S. Medada, and S. Ebisawa. 1975. Studies on the meat quality of broilers. 1. Effect of dietary protein and energy levels on abdominal fat content and meat taste. Jpn. Poultry Sci. 12:78.
Processing Options for Improving the Nutritional Value of Poultry Meat and Egg Products M. G. MAST and C. S. CLOUSER American consumers are becoming more aware of the nutritional value of the foods they eat. This knowledge, together with the current emphasis on being physically fit and trim, has led to an increase in the emphasis on "diet" foocis ant] labels such as Light, Lean, low-fat, reducecT-fat, ant] reduced calories. Poultry and egg products are natural candidates to meet this emerging demand because of their high nutrient content and relatively low caloric value. They are a good source of high-quality, easily digested pro- teins; egg proteins have traditionally been a standarc! by which other proteins are evaluated. In spite of these attributes, there are still . . . nagging Issues-some real, some exagger- atecl, some imagines] facing the poultry industry. For eggs, cholesterol continues to be a concern; the steady decline in shell egg consumption undoubtedly reflects this. For poultry meat, the current focus is on reducing the fat content of the final product. This emphasis on fat comes partly from the consumer ancl, more recently, from the industry itself, as indiviclual companies com- pete to capture the market that desires the "leaner" product. 311 This paper reviews the impact of proc- essing steps on the nutritional value of poultry products and explores some proc- essing options for improving nutritional value. THE INFLUENCE OF PRIMARY PROCESSING OF POULTRY MEAT ON NUTRITIONAL VALUE Processing and its ejects on the nutri- tional value of poultry have become more of a concern cluring the past few years (Demby and Cunningham, 1980; Mast ant! Clouser, 1985; Post, 19841. Processing can be divided into primary processing (stun- ning, scalding, plucking, chilling, postmor- tem aging, ant! cold storage) and further processing (heating, storage, freeze-drying, irradiation, and creation of restructurer! or ready-to-eat products). Primary processing, with the possible exception of wet chilling, does very little to alter the nutritional value of poultry. Stun- ning has no effect. Although semiscalding (S~54°C) and subscalding (57-58°C) can cause loss of the pigmented epidermal layer (Demby and Cunningham, 1980), Harris and von Loesecke (1960) reported no evi
312 dence of significant nutritional losses at these temperatures. Scholtyssek et al. (1970) found that semiscalding produced less drip, a lower pH, and better tenderness than subscalding. In the United States, most poultry chilling is accomplished by immersing the carcasses in ice water for 30 to 60 minutes. An alternative method is air chilling; carcasses are not immersed but instead are chilled by refrigerated air. Air chilling is used by the European Economic Community for broil- ers that are sold fresh (that is, nonfrozen) to consumers. Several authors have indicated that im- mersion chilling may affect the water-solu- ble nutrients in poultry meat. Hurley et al. (1958) reported increases in calcium, so- dium, phosphorus, potassium, chlorine, and nitrogen in chill water during immersion chilling; they recorded losses of solids from the poultry (4.8 mg/gram of meat) after 24 hours of immersion in water. Pippen and Klose (1955) also indicated losses of sodium and phosphorus to the chill water from broiler carcasses; they reported that about 4 g of dry solids/kg of meat leached out of the tissue during wet chilling. If chicken is 70 percent water, this would mean that 4 grams/300 grams of solids, or 1.3 percent, leached into chill water during 18 hours of immersion. Harris and von Loesecke (1960) also stated that wet chilling may leach as much as 1 percent of the total solids. Ang and Hamm (1983) compared the nutrients of breast meat from broilers that were immersion chilled or hot-deboned (no chilling). Hot-clebonec] birds had signifi- cantly less moisture (0.9 percent), more ash (12 percent), more phosphorus (5.2 per- cent), more potassium (5.8 percent), and less sodium (10 percent) than water-chilled broilers. The authors suggested that the higher sodium content in the water-chilled meat may be attributed to absorption from the skin during the 24-hour chilling period in crushed ice. Wet chilling also causes water uptake, APPENDIX leading to a dilution effect on other com- ponents and yielding an increase in drip loss and a further leaching of solids (Froning et al., 1960; Pippen and Klose, 1955~. Hale and Stadelman (1973) determined that initial weight gains from wet chilling were negated upon cooking and that net losses of 20 grams after cooking (as compared with air-chilled birds) were recorded. Therefore, it does appear that water chill- ing may lead to a slight loss in some water- soluble nutrients, primarily minerals. How- ever, no significant losses occur for proteins or lipids. Although kosher processing of poultry is accomplished in a similar manner to the conventional processing discussed above, three practices differentiate the two proc- essing methods. In kosher processing, no hot-water scalding is permitted, additional mechanical pickers are required, ant! evis- cerated carcasses are liberally salted inside and out and held for 1 hour to draw out residual blood (Powers and Mast, 1980~. This salting process significantly increased the ash and sodium content of the meat an(l skin. Mast and MacNeil (1983) reported that the sodium content of raw breast meat was 291 mg/100 grams for kosher processing and 66 mg/100 grams for conventional process- ing; corresponding values for thigh meat were 243 versus 64 mg/100 grams and for skin, 357 versus 55 mg/100 grams. Dukes and lanky (1985) also reported an increase in sodium chloride of broiler breast meat that hack been subjected to chilling solutions containing varying amounts of sodium chlo- ride. In deference to consumers who wish to restrict sodium intake, labeling of the sodium content of kosher processed poultry is desirable. After chilling, the next primary process- ing step is postmortem aging. Khan and Lentz (1965) found that time of aging may make a difference in the nutritional content of poultry meat. Three periods of time were defined in their experiments: prerigor, or within 15 minutes of slaughter; rigor, or 4
IMPROVING NUTRITIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS 313 hours postslaughter; and postrigor, 24 hours or more postslaughter. Freezing during ri- gor caused the most drip loss during thaw- ing, the lowest protein solubility, and the greatest cooking loss. Larger losses of nitro- gen constituents and ribose also occurred in birds frozen during rigor. Khan and van den Berg (1964) reported maximum extract- ability of nitrogen from broiler meat after 24 hours (postrigor). Hay et al. (1973) also reported lipid changes in postmortem chicken muscle with an in- crease in free fatty acids and decreases in phosphaticlyl choline and phosphatidyl eth- anolamine. Long-chain polyunsaturated fatty acids were procluced in aged muscle, but not in unaged muscle. THE EFFECT OF STORAGE ON PRIMARY PROCESSED POULTRY Storage time and storage conditions can affect the vitamin, mineral, and fat content of foods. Losses clepend on the type of processing preceding storage, the length of storage time, and the temperature at which the food is helcI. Chilling Fresh poultry, if chilled ant] storer] uncler ideal conditions, can have a shelf-life of 2 to 3 weeks. Ang et al. (1982) used four treatments (control, iced whole, iced breast, deep-chilled breast) to determine nutri- tional losses in fresh poultry. Thiamine and riboflavin losses were negligible over the entire 14 days of the study. Magnesium, potassium, ant] phosphorus decreased sig- nificantly (P < 0. 01) in the iced breast treatment, while significant losses of potas- sium and magnesium were reported in the iced whole treatment. Only potassium de- creased significantly in the deep-chillec! breast treatment. Calcium levels in all treatments significantly increased; the authors hypoth- esized a leaching of calcium from the bone over time. Proximate analysis indicated no statistically significant differences, although moisture content was higher in the two iced treatments. Conclusions indicate that deep chilling is the best method tested for r etaining mineral content of the meat. Vitamin and protein retention were the same for all methods. Freezing Vitamin retention is excellent in frozen foods if proper temperature ~-20°C) is maintained (Somers et al., 1974~. The In- stitute of Food Technologists Expert Panel and Committee on Public Information (1974) stated that storage temperatures of -18°C or below result in excellent retention of the vitamin content of frozen foods. Nutrient levels can actually be higher in frozen foods than in fresh, depending on how old the fresh product is and how soon the frozen product was processed. The rate of freezing can also influence drip losses resulting in losses of B vitamins during thawing and subsequent cooking (Bender, 1978~. Studies conducted by Kahn and Livingstone (1970) and Singh and Essary (1971) report B vita- min losses of 10 percent because of drip loss. In most cases, the freezing process itself was shown to have little effect on nutritional values. Details on methods of freezing were not given in most cases, and differences in values may have arisen from differences in standing time and rate of freezing. Losses during frozen storage do occur, particularly with thiamine. Freezing does not affect the nutritional value of protein. Bowers and Fryer (1972) showed that no significant loss of riboflavin or thiamine occurs in a cooked product after 5 weeks of storage at - 17. 5°C. Singh and Essary (1971) user] four different methods of thawing birds stored for 10 months (running cold water 21-22°C, run- ning warm water 4~46°C, room tempera- ture, and refrigerated SYNC). All birds were in sealed plastic bags. Niacin, thiamine, and riboflavin were measured before freezing
314 and after thawing. The only significant loss (P < 0.05) occurred! in niacin from the birds thawed] at room temperature. The authors stated that "the lower value of niacin ob- served in birds thawed at room temperature was apparently clue to some reason not understoocI." West et al. (1959) fount] that after 2 and 4 months of frozen storage (-29°C), pre- cooked, frozen chicken breasts had the same thiamine content as those frozen raw, thawed, and then cooked. Samples frozen for 2 months were found to have thiamine values of 0.18 to 0.19 ,ug/100 grams, while 4-month samples with similar moisture content had levels of thiamine ranging from 0.13 to 0.14 ~g/100 grams. Although statistical differ- ences were not mentioned, a decreasing trend in thiamine retention can be seen. Thiamine was well retained (96 percent) in a freshly preparer] chicken a la king frozen at -10°C (Kahn and Livingstone, 1970~. Morgan et al. (1949) found that riboflavin and niacin were fairly stable in three groups of chickens for up to 8 months. Thiamine was significantly lower after 4 months in one of the groups but appeared to be stable in the others. Cook et al. (1948) found similar results, reporting no significant losses in thiamine, riboflavin, or niacin after 3 to 9 months of storage at - 23°C. In a study conclucted by Lee and Dawson (1973), precooked and raw chickens that were subsequently frozen were tested for retention of linoleic acid. The raw chicken had linoleic acid levels of 20 percent of the total lipid, which increased to 34 percent upon cooking (fried). Slow losses occurred over the storage period. Linoleic acid levels in the raw and frozen chicken dropped to 20 percent after 3 months and 16 percent after 6 months. INFLUENCE OF FURTHER PROCESSING OF POULTRY MEATS ON NUTRITIONAL VALUE The term "further processed" is used in the poultry industry in a similar manner as APPENDIX the term "processed meats" is user] in the red meat industry. U.S. Department of Agriculture (USDA) economists compile data for further processing under the cat- egory of"beyonc3 cut-up." Examples of methods used in preparing further-proc- essed poultry products are size reduction, deboning, restructuring, emulsifying, bat- ter/breading, heating, and freezing. Many of the products are "ready to eat" at the time they leave the processing plant, in contrast to the "ready to cook" status of non-further-processed whole birds. Fur- ther processing reduces the preparation efforts of the consumer, hence, the term "convenience foods," which is frequently used for such products. Critics of further processing have implied that the a(lditional steps involved in pre- paring these products reduce their nutri- tional value. A review of some of the incli- vidual processes ant] their impact on nutritional value of poultry meat follows. Heat Processing Heat is by far the most destructive of all processing methods. Most affected of the amino acids are lysine and threonine. Of the B vitamins, thiamine is the most heat labile ant! large losses can occur depending on the amount of time heated and the degree of heat. Oven Mulley et al. (1975) demonstratecl the time/temperature relationship of thiamine destruction. Hall and Lin (1981) found sig- nificant differences in thiamine content of broiler breast muscle ant! thigh muscle roasted to an internal temperature of 82°C at both 204°C (46 minutes) and 121°C (131 minutes). Retention of thiamine was signif- icantly higher (P < 0.01) for the higher temperature, shorter cooking time. A sig- nificantly higher percent of thiamine (P < 0. 01) was also retained in breast meat versus
IMPROVING NUTRITIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS 315 dark meat; the authors felt this was due to a lower end temperature of the breast meat (82°C) compared to the thigh meat. Since the breast muscle is thicker ant! larger, it would heat more slowly. The latter part of this study concurred with one concluctec] by Cook et al. (1948), which showed a twofold increase in thiamine loss in turkey leg meat (62 to 87 percent) compared to turkey breast meat (38 to 43 percent). An end point temperature was not reported. These meat samples were cooked for 2 to 3 hours at 168°C. Again, breast and thigh were cooked together. Percent losses of riboflavin and niacin are always less than percent losses of thiamine; riboflavin is stable up to 130°C and niacin is also stable at even higher temperatures. Niacin is also stable to air and light at all pH levels, while riboflavin can be destroyer] under alkaline conditions (Bender, 1978~. No significant loss of riboflavin in chicken after 45 minutes of roasting was reported by Hodson (1941~. Similarly, Rowe et al. (1963) found no decrease of riboflavin in chicken cooked 15 minutes in a pressure saucepan. Losses of only 20 to 30 percent in turkey and chicken muscle were reported by Cook et al. (1948) and Morgan et al. (1949) for both riboflavin and niacin. It shouIcT be noted that cooking times for the studies by Hocison (1941) and Cook et al. (1948) were very different. Additionally, two different methods were used (fluorometric and microbiological, respectively) to cleter- mine losses. The effects of heating on protein appear to be minimal. The following studies all used acid hydrolysis to calculate amounts of amino acids present. Sheldon et al. (1980) found no significant differences in the pro- tein efficiency ratios of rats fed rations containing turkey meat roaster! to end points of 74, 79, 85, or 91°C; however, the rats fed the ration containing the turkey with the highest end point temperature gained the least amount of weight. Millares ant] Fellers (1949) showed small losses of all amino acids except tryptophan, leading to the conclusion that "destruction of amino acids is probably not a principal factor in the alteration of the nutritive values of proteins as a result of heating." Finally, Thomas and Calloway (1961) found no loss in essential or semiessential amino acids subjected to heat processing. However, they did find losses in availability of many of the amino acids upon pepsin digestion of the treated samples, indicating that acid hy- cirolysis does indeed camouflage the biolog- ical availability of the amino acids. Studies by Warner et al. (1962), Myers and Harris (1975), and Chang and Watts (1952) indicate that no significant losses of fatty acids occur in poultry or meat products. Frying Both Cheldelin et al. (1943) and Hodson (1941) found no significant losses in ribofla- vin upon frying. Cheldelin et al. (1943) also reported no significant loss of thiamine. In both studies, chicken parts were fried for 15 minutes in an open pan. Warner et al. (1962) found no change in the biological value of the fats in skillet-frie(1 chicken. Nakai and Chen (1984) point out that al- though total amounts of fat in chicken meat do not change after frying, there is an alteration of fatty acid composition. Using four different coatings for treatments (bat- terecI, battered and breaded, breadecl, anc! no coating), chicken parts were deep fat fried and evaluated for changes in fatty acid content. Decreases in palmitic (Cue), pal- mitoleic (Cat If, and linoleic (Cal 2) acids and an increase in oleic acid indicated that the shortening was being absorber] into the meat. These changes were not as great in chicken that was battered and flour crusted or batterer] ant! breaded as in chicken that was just breaded or noncoated, suggesting that batter and breading may help "seal" the meat. Chang and Watts (1952) also verified that there was some increase in unsaturated fats because of the vegetable oil.
316 Broiling Hodson (1941) found no significant losses in riboflavin after chicken thighs were broiled for 20 minutes. Boiling Boiling probably affects the B vitamin content more than any other treatment. Some of the thiamine, riboflavin, and niacin leaches into the water during boiling. The amount of each vitamin lost depends on the cooking time and the surface area involved. An extreme example was presented by Bender (1978) in the manufacture of meat extract. The meat was cut up into small pieces and boiled for 15 minutes; 80 percent of the water-soluble vitamins and muscle extractives were lost. Proteins, on the other hand, are dena- tured by boiling, but this does not affect nutritional value (Bender, 1978~. Canning Thomas and Calloway (1961) reported a loss in thiamine due to canning, but the amount and significance of the loss were not reported. Riboflavin and niacin did not decrease, and total amino acid levels were unaffected. However, in vitro pepsin diges- tion revealed that less than 50 percent of the available lysine, cystine, methionine, and tryptophan found in the raw state re- mained available after canning. Similar re- sults were indicated in a study by Millares and Fellers (1949), but losses in thiamine were reported as significant, with the insta- bility of thiamine at high temperatures with pH values close to neutrality given as a possible explanation. Microbiological assays indicate riboflavin retention as 100 percent or better (complex molecules released ri- boflavin upon heating) and no significant losses of niacin. Amino acid content was changed only slightly, with a 50 to 80 percent decrease in tryptophan. APPENDIX Ascorbic acid and thiamine, both present in only minimal quantities in poultry meat, are susceptible to loss during prolonged storage of conventionally canned foods. Hel- lendoorn et al. (1969) found most vitamins stable to processing and storage at 22°C in canned whole meals. Immediately after processing, a 50 percent loss was observed for thiamine and vitamin C. After 1.5 years, all the vitamin C was destroyed and losses of thiamine were 75 percent. Niacin loss was 10 percent owing to processing and an additional 10 percent because of storage. Riboflavin was not affected. Curing and Smoking Significant losses in thiamine and niacin of cured, smoked, and cured canned chicken versus canned chicken were observed by MilIares and Fellers (1949~. Greenwood et al. (1943) noted significant (12 to 69 percent) thiamine losses in the presence of 0.02 to 0.10 percent sodium nitrite in thiamine solutions. Higher pH (6.1 versus 5.6) and length of heating increased the losses. But when Greenwood et al. (1943) investigated the possibility of loss in the presence of sodium nitrite in pork, they found no sig- nificant loss when the pork was heated in the presence or absence of meat-curing ingredients or in meat cured 10 days and held 1 hour at 98°C. Microwave Cooking Microwave cooking can alleviate two ma- jor destructive components of conventional heating: external heat and time of heating. Goldblith et al. (1968) reported no loss of thiamine by microwaves when held at 0°C for 45 minutes or at 33°C for 30 minutes. However, continuous loss over time was observed when thiamine in solution was held at 102.8°C for 50 minutes. The loss was roughly equivalent to losses occurring at the same temperature in a conventional oven. Goldblith et al. (1968) used thiamine
IMPROVING NUTRITIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS 317 in solution for this experiment, which is more easily destroyed than thiamine found in muscle tissue. McMullen and Cassilly (1976), however, clemonstrated no cliffer- ence in thiamine or riboflavin losses be- tween microwaved or conventionally heated chicken. Similar results were obtained by Hall and Lin (1981), who looked at two cli~erent wastage s of microwaves versus two different cooking temperatures in a conventional oven. No significant differences in the retention of thiamine in pectoralis muscles cooked at 400°F (204°C) in an 800-watt microwave or a 1,600-watt microwave were found. How- ever, a significantly higher loss of thiamine was found in birds cooked at 250°F (121°C) for more than 2 hours. This study points out the obvious problem of the time/temperature relationship. The temperature of the oven and, consequently, the time of cooking significantly affect out- come. Wing and Alexander (1972) reported a 91 percent retention of vitamin B6 in chicken cooked by microwave and only an 83 percent retention for conventional cooking. The mi- crowavec! chicken was cooked for 1.5 min- utes, while the conventionally heated chicken was heated to an internal temperature of 88°C (45 minutes, no oven temperature given). Retention of vitamin B6 found in the drippings was then added to the retention in the meat, resulting in a total loss of 7.5 percent in the microwaves] chicken ant! 11.6 percent in the conventionally cooked chicken. Bender (1978) points out that finclings by Miller et al. (1973) indicate that the coeffi- cient of variation of analysis of B6 is 9 percent; therefore, a real difference be- tween the values reported by Wing ant] Alexander (1972) may not exist. No studies on the effects of microwaves on poultry protein were identified in the literature. Causey et al. (1950) reported no statistical differences in lysine retention be- tween beef patties cooked in a microwave (90 percent retention) and those cooked in a conventional oven. Campbell et al. (1958) found losses of five essential amino acids to be about 15 percent in both microwaved and conventionally cooked beef. Myers and Harris (1975) studied the ef- fects of microwave cooking on fatty acids and concluded that there were no significant differences between fatty acids of conven- tionally cooked chicken and microwaved chicken. Additionally, no differences were fount! between raw or cooked chicken. Microwave cooking apparently causes no more nutrient loss than does conventional cooking. Any benefit would come from cle- creased drip loss and shorter cooking time, but only when compared with prolonged conventional cooking. Riboflavin and niacin losses were minimal in both cases. Amino acid and fatty acid losses were also found to be insignificant. Irradiation Irradiation is still considered a food ad- ditive by the U. S. Food and Drug Admin- istration. Most researchers, however, treat it as a food process, and it is considered as such in this review. Irradiation of poultry is not approved in the United States. Although the World Health Organization has unTimitecl clear- ances on irradiation levels of 2 to 7 kGy, only The Netherlands ant] South Africa have set clearances (up to 3 kGy) for use on poultry. The USSR has approved test batches (radurization only) up to 6 kGy, and Canada is test marketing poultry irradiated up to levels of 7 kGy (Goresline, 19831. Irradiation of food is considered a "coicl" process because of only slight temperature rises. This minimizes nutritional losses (Thomas and Josephson, 19701. Two forms of radiation processing, radurization ant] radicidation, are used on chilled poultry in a few countries to prolong shelf life. Rad- urization, pasteurization designed to kill or inactivate food spoilage organisms, and rad- icidation, pasteurization designed to kill or
318 inactivate all disease-causing organisms, are accomplished at processing levels below 10 kGy. Foods are then stored refrigerated. Both processes show minimal, if any, losses in protein, fat, and vitamin levels. However, these processes only pasteurize, and shelf- life can be extended by 2 weeks at most (Froning, 1978~. A third] form of irradiation processing, radappertization, incorporates heating. Ra- dappertization is sterilization by irradiation. Precooked foods in vacuum-sealed con- tainers are exposed to ionizing radiation while frozen (-20 to -40°C) at absorbed doses high enough to achieve commercial sterility (25 to 70 kGy). Care must be taken that absorbed radiation floes not exceed 70 kGy, or palatability may be affected. Pack- aging is critical as exposure to light, oxygen, moisture, ant! microorganisms could quickly deteriorate food quality. Precooking must achieve an internal temperature of at least 70 to 80°C to inactivate enzymes that would cause food degradation upon storage. After irradiation, the product is thawed and stored at room temperature. Because of the proc- essing in sealed containers and storage at room temperature, radappertization has been equated to thermal canning. In early studies, radappertization done at room or chilled temperatures resulted in the formation of off flavors ant! odors. A study by Brasch and Huber (1948) indicated that irradiation at low temperatures (-20 to-40°C) could! reduce or eliminate these problems. Holding the foot! at these tem- peratures in an oxygen-free environment during the irradiation process also helps to retain nutrients. Palliation, at levels envisioned for food processing, has minimal effects on the nu- tritional value of protein, although other physical properties can be affected. Irradia- tion in meat causes intermolecular cross- linking reactions of proteins, leacling to decreases in molecular weight, solution weight, tensile strength, ant! solubility. Ir- racliation also causes a decrease in water APPENDIX holding capacity, while drip loss increases Josephson and Peterson, 1983~. Similarities exist between the effects of freeze-drying and irradiation in that solubility and water- hoicling capacity are climinished (Diehl, 19831. In a study by Ley et al. (1969), rats fed diets of radappertized (up to 70 kGy) meat and bone meal showed no significant differ- ences from rats fed nonirracliated diets in total digestibility, biological value, and net protein utilization or in amino acid com- position. Levels of cystine, methionine, and tryptophan were measured, since these are considered the most sensitive to ionizing radiation. DeGroot et al. (1972), in comparing ir- radiated versus nonirradiated chicken, found that lysine avaflability and protein efficiency ratios in both groups were unaffected by irradiation (6 kGy) after 6 days of refriger- ation followed by conventional cooking. The authors concluded that irradiation did not affect the nutritional value of the protein fraction. Sheffner et al. (1957) found no changes in content or enzymatic availability of amino acids in ground turkey meat at irradiation levels of 19.4 kGy and concluded that ir- radiation was superior to canning. The ob- servations of Calloway et al. (1957), which indicated that neither irradiation nor cook- ing altered the biological value of turkey protein, concurred with those of Sheffner et al. (19571. Thiamine is the most radiation-sensitive B vitamin. As absorbed radiation levels are decreased, thiamine levels in aqueous so- lution increase (Groninger and Tappet, 1957~. Thomas and Josephson (1970) also com- mented on studies showing increased vita- min retention as temperatures decreased, which indicated that vitamins are affected by the heat and not the irradiation process. Riboflavin and niacin were found to be stable to all forms of radiation processing in several studies, with maximum loss levels of 20 percent (Alexander et al., 1956; De- Groot et al., 1972; Proctor et al., 1956~.
IMPROVING NUTRITIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS 319 Radappertization causes oxidation, deg- radation, and decarboxylation of the lipid fraction (Thomas and Josephson, 1970~. Un- saturated fats are the most affected. Antiox- iclant factors form in the nonlipid constitu- ents of irradiates] meat that protect the lipid fraction. The antioxidant factors work best in ground products where lipid and nonlipid components are in intimate contact with one another. In whole-meat products, where fat and lean are separated, autooxiclation of the lipid fraction occurs rapidly in the pres- ence of oxygen. Chemical changes are mini- mized by packaging (to exclude light and oxygen) and freezing irradiation Josephson and Peterson, 1983~. Digestibility of fats seems unaffected. dehydrated chicken, pepsin digestibility of the cooked clehydratec] chicken was signif- icantly lower. Digestibility of the freeze-ciried chicken was good by both pepsin and humans. The overall conclusions were that freeze-drying least affected the nutrient content of poultry as compared with all other methods studied, with excellent vitamin stability during sub- sequent storage. This was confirmed by a later study done by Rowe et al. (1963) that demonstrated that freeze-crying was not destructive to thiamine, niacin, or riboflavin in chicken muscle, although losses of thia- mine occurred! if the meat was cooked before freeze-clrying or after freeze-drying and re- hydrating. Conclusions of most of the authors cited here are that losses of nutrients clo occur in irracliated foods but that they are compa rable to those observed in other processing methods ant! therefore are consiclerec] ac- Mott et al. (1982) showed differences ceptable. between levels of protein, fat, water, ash, iron, and fluoride in mechanically deboned meat from whole birds, frames with skin, an(l frames without skin. Whole birds had lower protein, higher fat, lower water, and lower iron contents than die] bird frames with or without skin. Fluoride content was higher in the frames without skin, as was ash (indicative of higher bone content). The kilocalories per 100 grams were significantly higher in the whole, deboned birds. Protein efficiency ratios were not significantly dif ferent. In vitro cligestibility of homogenates of mechanically or hancI-cleboned chicken (us ing hydrogen chloride, pepsin, and pan creatin) showed a 79 to 93 percent retention, with no differences between raw versus cooker! or hank] versus mechanically cle boned meat (Schoenhauser et al., 1980~. Marriot et al. (1982) showed that chicken hot dogs provided 104 mg of calcium in a 100-gram serving. This was attributed to limited amounts of pulverized bone and larger amounts of bone marrow. Higher values (than beefor pork hot dogs) for cobalt, Dehydration and Freeze-Drying Freeze-cirying and low-temperature cle- hydration produce few changes in the nu- tritional value of poultry since heat is not used. In a stucly by Thomas ancI Calloway (1961), five clifferent processes (clehycirated, raw state; cooked`, dehydrated; enzyme in- activated, then irradiated; precooked, irra- diatecI; and conventionally canned) were tested for their nutrient retention. Thiamine retention was most favored by freeze-drying raw poultry and least favored by irradiation. Riboflavin levels increased in the canning process, but changes were not statistically different in any other process. Niacin was well preserved in all processes, with no one method better than any other. Pyridoxine was completely stable after freeze-crying, as was pantothenic acid. A 20 percent loss in dienoic fatty acids occurred during freeze- drying. Although total levels of essential and semiessential amino acids remained unchanged for both the raw and cooked Size Reduction Mechanically Deboned Meat
320 iron, magnesium, and phosphorus were also attributed to the use of mechanically de- boned poultry in the hot dog formulation. THE EFFECTS OF PROCESSING, STORAGE, AND FURTHER PROCESSING ON THE NUTRITIONAL VALUE OF EGGS Shell eggs lose very few nutrients when stored properly. Everson and Souders (1957), in a comprehensive literature review on egg composition, cited several studies showing no significant losses of protein, fat, or min- erals in shell eggs. Changes in solids were attributed to the transfer of water from the white to yolk or evaporation through the shell. Riboflavin, thiamine, and vitamin A decreased slightly during cold-storage times of 3 to 4 months. The quality of eggs stored at room tem- perature deteriorates at a much faster rate than does the nutritional value. Imai (1981) demonstrated that although coating the eggs slowed the rate of deterioration at room temperature in a 4-week storage study, egg quality was much higher in both coated and noncoated eggs stored for up to 4 months at 3°C. Cooking of eggs (frying, scrambling, poaching, and hard boiling) results in very few compositional changes. The most not- able decreases are in thiamine and riboflavin (17 percent and up to 11 percent, respec- tively). Protein, iron, calcium, and fats re- main stable, although frying may increase saturated or unsaturated fats, depending on the type of butter or shortening used. Vi- tamin A increases in fried products if butter is used. Spray-drying is the most common form of drying. The drying process itself results in no nutritional loss. Sugar is removed from dried egg products to prolong shelf-life. Everson and Souders (1957) reported that vitamin A, niacin, riboflavin, and thiamine were stable at storage temperatures below 15°C but that higher storage temperatures APPENDIX resulted in losses of these nutrients. Pack- aging of eggs stored at room temperature in sealed tins increased vitamin A retention. Vitamin D was not significantly affected by drying or subsequent storage. Protein, fats, and minerals were also not affected. Cot- teril1 (1981) reported that dried whole egg and yolk products should be stored at 10°C or less. Egg white is stable at room tem- perature for several years. PROCESSING OPTIONS FOR INCREASING NUTRITIONAL VALUE Collection and Utilization of Blood According to Satterlee (1981), animal blood is not used in human foods in the United States because the consumer has an unfa- vorable image of blood as a food. Disadvan- tages of blood protein as a food ingredient are the strong taste and odor of dried plasma and hemoglobin and the red color of hemo- globin, which may be disagreeable to con- sumers (Calvi et al., 1984a). The off flavor, which is probably due to lipid breakdown, can be minimized with newer, low-temper- ature drying methods (Stevenson and Lloyd, 1979). Blood from larger animals is routinely collected, decolorized when desired, and used in foods such as blood sausage in other countries. In the United States, blood is currently used in nonfood products such as fertilizers and as a feed additive. However, like soy and milk proteins, blood protein could be used to enrich food (Calvi et al., 1984a). In a recent issue of Meat Industry (Anon- ymous, 1986a), the editors, commenting on a rumor that USDA is close to approving limited use of blood in U. S. -produced meat products, stated that "blood may turn out to be yet another of those things that's considered a delicacy in other parts of the world but doesn't excite the American ap- petite." Animal blood is a potential source of high
IMPROVING NUTRITIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS 321 quality protein. Beef blood, for example, contains 18 percent protein and is rich in lysine, valine, tryptophan, phenylalanine, ant] leucine. However, blood proteins are very low in isoleucine, which can result in an amino acid imbalance (Olson, 19704. The plasma component of blood contains about 70 percent protein and the cellular fraction (rec! ant! white celIs) about 94 percent pro- tein (Stevenson and Lloyd, 1979~. Young et al. (1973) demonstrates! that the protein efficiency ratio of a diet containing dried bovine plasma could be increaser] from -1.05 to 2.88 by adding 1.2 percent Dk- isoleucine to the diet. The composition of dried poultry blood is 80 percent protein, 8 percent moisture, 1 percent fat, and 11 percent fiber or ash (Mountney, 1976~. Broiler chickens contain about 7.5 per- cent of their body weight in blood, 45 percent of which is collectible during slaugh- ter operations (Kotula and Helbacka, 1966~. In 1985, more than 23 billion pounds of poultry were inspected! in the United States (U.S. Department of Agriculture, 1986~. Therefore, some 800 million pouncis of blood could have been collected. Efficient processes for hygienic blood col- lection from large animals using hollow knives and sodium citrate (to prevent co- agulation) have been reporter] by Stevenson and Lloyd (1979) and Wismer-Peclersen (1979~. Systems for collecting blood] have also been constructed and commercially tested in poultry-processing plants (Childs et al., 1976~. These systems were effective ant] reliable in handling the blood and also reduced the pollution entering the plant effluent. However, they were not designed for collecting blood for use in human food. Although a sanitary system for blood col- lection may be technologically possible, the economic aspects of protein recovery from blood remain a problem. Satterlee (1981) stated that the "problem is the cost of recovering protein from dilute solutions and resulting energy needler! to dry the whole solution, to concentrate and preserve the protein." New energy-efficient recovery processes are required to make such recov- ery feasible. Increased Use of Giblets Poultry giblets heart, gizzard, and liver are not fully used in the Uniter! States. In some processing plants, especially those slaughtering bircis for use in further proc- essing, it has become economically infeasi- ble to harvest, clean, and package giblets. These three foods are high in protein, iron, and niacin. In addition, liver is high in vitamins A and C. The undesirable texture of gizzard and heart tissue has been a factor in the underuse of these foods. In acldition, the functional properties of the proteins in these tissues are not as acceptable as those in the skeletal muscle of poultry. A number of studies have demonstrated that protein modification can improve the functional properties of various tissues: beef (DuBois et al., 1972~; fish (Spinelli et al., 1972~; beef heart (Smith and Brekke, 1984~; and mechanically deponed fowl (Smith and Brekke, 1985a,b). Accord- ing to Franzen (1977), mollification refers to the intentional alteration of the physio- chemical properties of proteins by chemical, enzymatic, or physical agents to improve functional properties. According to Brekke and Eisele (1981), acylation reactions, involving the direct ad- dition of chemical groups to functional groups of amino acid side chains via substitution, have the most potential for chemically mod- ifying food proteins. The anhydrides of acetic and succinic acids are usually the acylating agents, since they are easy to use, safe, ant] inexpensive and produce acylated deriva- tives that are functionally important. When a protein is reacted with acetic anhy(lride, the acylation reaction is termed acetylation; when succinic anhydride is used, the reac- tion is referred to as succinylation. Succinylation affects the physical char- acter of proteins by increasing the net neg
322 ative charge, changing conformation, and increasing the propensity of proteins to dissociate into subunits, breaking up protein aggregates, and increasing protein solubility (Franzen, 19771. For acylated proteins to be incorporated into foods, they will need to be safe, diges- tible, and probably approved by the Food and Drug Administration en c] USDA as food ingredients since the protein has been mod- ified. Groninger and Miller (1979) indicated that the influence of acylation on protein utilization and nutritional quality clepends on the type of protein, the amount of protein mollification, and the acylating agent used. Similar techniques may also be useful in improving the functional properties of poul- try giblets, thereby making these products, with good nutritional properties, more us- able by the poultry further-processing in- dustry. Hot-Deboning and Hot-Stripping Hot-cleboning is the removal of meat from the eviscerated carcass before the onset of rigor mortis. Hot-stripping is a modification of hot-cleboning in that the muscle is re- moved from a nonevisceratec3 bird. As much as 1 percent of the total solids in poultry meat may be lost cluring water chilling of the carcass. These losses, al- though minor, do occur with water-soluble components such as vitamins ant] minerals. Air chilling or hot cleboning alleviates this loss, since the carcass is not in contact with water for a prolonged period. Of probably greater importance than this 1 percent loss in solids content, however, is the potential economic advantage of hot eboning or hot-stripping. The economic savings that could be expected with these techniques include energy savings through a decrease in cooling costs, decreases! water consumption, lowered equipment expend- itures, recluced labor and time, and im- proved yields. APPENDIX For hot-stripping to be used, changes in USDA inspection regulations are necessary, since muscle tissue is remover! from car- casses prior to the inspection of the viscera. Removal of the Abdominal Fat Pad Consumers do not like to buy chicken containing the abdominal fat pad. Most remove it themselves before preparing the chicken. Several large poultry companies are currently removing this fat at the proc- essing plant in an effort to sell a product that is lower in total fat than their compet- itor's chicken. The average abclominal fat pad weighs about 40 grams, which consti- tutes 2.5 percent of the total weight of the carcass ant! 10 percent of the total body fat (F. E. Pfaff, personal communication, 19861. These values are basec] on whole carcass composition determinations and not on spe- cific cuts of boneless meat. Reduction in Sodium Content of Further-Processed Products In recent years, considerable attention has been focused on sodium and its potential impact on public health. Although the value of Tow-sodium diets is questioned by some scientists (Kolata, 1982), there is sufficient concern within the scientific community (Putnam and Reilly, 1981) ant! by many consumers to warrant production of food products containing less sodium. Poultry meat itself is not high in sodium content; cooke(l breast meat contains 63 mg of sodium/100 grams of meat, and cooker] thigh meat contains 75 mg/100 grams. How- ever, during the further processing of poul- try meat into products, the sodium content may increase dramatically as sodium chlo- ride and various sodium phosphates are added to the product. Sodium chloride is generally used in fur- ther-processed products such as frankfurters at levels of 1.5 to 2.5 percent. Salt influences the flavor, may affect the shelf-life, and
IMPROVING NUTRITIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS affects the functional properties of the my- ofibrilIar proteins. One option for lowering sodium content is to use substitutes for all or part of the sodium chloride, such as calcium chloride, magnesium chloride, and potassium chlo- ride (Hand et al., 1982; Maurer, 1983~. Hand et al. (1982) reported that replacing 100 percent of the sodium chloride with magnesium chloride or potassium chloride was detrimental to the flavor of the frank- furters prepared from mechanically de- boned turkey. The authors suggested that 35 percent of the sodium chloride could be successfully replaced with potassium chlo- ride; magnesium chloride caused offflavors, even at the 35 percent level. Smith and Brekke (1985b) varied the sodium chloride content of frankfurters pre- parec] from enzyme-moclified, mechanically clebonec! fowl. They found that 0.5 percent salt was the least amount that could be added and still produce a satisfactory frank- furter from which the casing could be easily removed. Brekke ant! Eisele (1981) had earlier reported that enzymatic modification also has potential as a partial substitute for salt in processed meat products. The low- salt (0.5 percent) frankfurters were rated as having less chicken frankfurter flavor than products prepared with 2 percent salt. The authors states] that if low-salt franldurters are to gain consumer acceptance, appropri- ate spice formulations will need to be de- veloped to compensate for the salty flavor. Barbut et al. (1986) reported that turkey frankfurters with 1.5 percent salt combined with phosphate were as acceptable as "ref- erence" frankfurters, which contained 2.5 percent salt. The sodium chloride in poultry frank- furters could be reduced to at least 1.5 percent (590 mg of sodium/100 grams of meat) without detracting from the flavor and to as low as 0.5 percent (197 mg of sodium/ 100 grams of meat) if additional spices can be found to improve the flavor. 323 Reduction of Fat Content in Poultry Frankfurters Chicken and/or turkey frankfurters tra- clitionally contain 18 to 22 percent fat, compared to pork and/or beef franks, which usually contain 25 to 30 percent fat. Some producers of poultry franks have lowered the fat content of their product to 13 to 16 percent by using mechanically debonec! meat from portions of the poultry such as the front quarter, breast cage, or skinless necks, which contain less fat than backs or legs. According to a study in Consumer Reports (Anonymous, 1986b), poultry frankfurters ranged in caloric content from 180 to 300 keal/100 grams of meat; the mean was 243 kcal/100 grams. From a sensory standpoint, fat is an important component in increasing the pal- atability in a food such as frankfurters. If the fat content is too low, the resulting product tends to be rubbery and tough. Therefore, although consumers may think they want a much leaner frankfurter, such a product may not be acceptable to them. Reduction in Fat Content of Fried Poultry Products Batter/brea(led, deep-frie(1 poultry pro(l- ucts have been a mainstay of the further- processed and fast-food industry for many years. The current emphasis is toward bone- less products, such as nuggets and patties. According to Przybyla (1985), the single fastest growing area within the processed chicken category is frozen, boneless, breaded chicken, partly because of increased sales of chicken-based finger foods in fast-food outlets. Retail sales of such items increased 71 percent from 1982 to 1984. There is also more interest in producing a product that is lower in fat and therefore lower in calories. Baker et al. (1986) recently evaluated four cooking methods for battered and breadecl broiler parts: FF (full frying in 177°C oil),
324 FSF (fry, steam, fry: brief fry, followed by longer steam cook plus additional short fry), WC (water cook: thoroughly cooked in hot water followed by 45 seconds of frying), and FOC (fry, oven cook: fries! for 2.5 minutes followed by thorough heating in a 218°C oven). The three most commonly used methods for commercial preparation of retail frozen, fully cooker! and browned, battered and breacled chicken are WC, FF, and FOC, respectively. Baker et al. (1986) found that the fat content was slightly higher in breasts cooked by FF and FSF compared with breasts cooker! by WC ant] FOC, but the differences were not significant; for thighs, there was very little difference in fat content due to cooking treatments. Gen- erally, there were no differences in the flavor or acceptability of parts heated by any ofthe four methods; yields were highest for pieces cooker] by FSF, followed by FOC. Staclelman (1985) illustrated that breaded chicken products can be producer] with reduced caloric content by using hot air cooking instead of deep-fat frying, which resulted in a 23 to 31 percent decrease in fat content of parts and a 13 to 15 percent decrease in calories, ant] by removing the skin before breading an(l hot air cooking, which resulted in a 42 to 65 percent decrease in calories (see Table 1~. According to Stadelman (1985), when TABLE 1 Analyses of Chicken Parts APPENDIX breaded, fried chicken contains 20 percent fat, as it frequently does with open kettle frying, 60 percent of the calories come from the fat. By removing the skin and cooking in hot air, a chicken breast or drumstick can be prepared with only 27 percent of the calories coming from the fat. Cooking systems such as the one men- tioned above and/or broiling will become more commonplace in the future as the demand for poultry products with less fat and fewer calories increases. Increased Utilization of Proteins Recovered from Bone Residue of Mechanically Deboned Poultry Bones from slaughtered animals, espe- cially larger animals such as beef and swine, are usually used for animal feed, gelatin, and glue. However, they could be used as ingredients in certain processed products; they are high in protein and provide a dietary source of minerals such as calcium. Bone products are used as food ingredients in some European countries. Some coun- tries consider bone-derived protein added to a meat product to be meat; others con- sicler it to be a nonmeat ingredient. In the Unitecl States, bone-(lerived protein is not currently permitted in food products (Calvi et al., 1984b). Breast Thigh Drumstick Percent Kcal/ Percent Kcal/ Percent Kcal/ Source Fat 100 g Fat 100 g Fat 100 g USDAa 13.2 260 16.2 275 15.8 268 Lab friedb 15.7 275 16.9 279 14.0 244 Lab modified 10.8 233 13.0 243 9.9 209 Lab ultimates 5.7 186 9.8 218 4.9 166 aData from U.S. Department of Agriculture. 1979. Composition of Foods Poultry Products. Agricultural Handbook No. 8-5. Washington, D.C.: U. S. Department of Agriculture. bPressure deep fat fried, commercial equipment. CPieces with skin; hot air, no frying. Pieces without skin; hot air, no frying. SOURCE: W. J. Stadelman. 1985. This chicken product breaks "grease barrier." Broiler Ind. 48:46.
IMPROVING NUTRZTIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS 325 Recent estimates indicate that 300 million pounds of mechanically deponed poultry are produced annually in the United States. This represents yields of about 60 to 70 percent mechanically cleboned poultry de- pencling on the type of machine used. On the basis of these estimates, 150 million pounces of bone residue (BR) are produced annually, most of which is used in fertilizer, pet food, or animal feeds. Bone residue is the material remaining when mechanically cleboned poultry is prepared. Bone residue has characteristics that make it a valuable potential source of human food. It contains 20 percent protein, which represents an additional 30 million pouncis of protein avail- able annually for human use, assuming all protein could be extracted. Bone residue contains approximately 18.9 percent protein, 7.7 percent fat, 11.7 per- cent ash, and 60.0 percent moisture (Mast and Opiacha, 1987; Opiacha et al., 1986~. The two methods that have been developed to extract protein from BR are use of sodium chloride solutions (Kijowski ant] Niewiarow- icz, 1985; Young, 1976) and use of mild alkali solutions Jelen et al., 1982; Opiacha et al., 1986~. Freeze-clriecl protein isolates from BR using sodium chloride, prepared by Young (1976), contained 60 to 65 percent lipid, 5 to 10 percent ash, and 4 to 6 percent moisture. The freeze-cTried protein extract obtained by Opiacha et al. (1986), using alkali, container] 45 percent protein, 47 percent fat, ant] 14 percent ash. Yields of dried extract represented! 7 percent of the original BR. Limiter] information is available on the nutritional quality of protein from BR. Law- rence and lelen (1982) state that severe alkali treatments of protein may cause ra- cemization or destruction of certain amino acids; in abolition, unusual new amino acids may be produced, such as lysinoalanine, lanthionine, and ornithinoalanine. These authors concluded that the alkali extraction methods, as usually conducted with BR, should not produce material such as lysi- noalanine that could pose health hazards for consumers. Protein extracts from BR have relatively good functional properties (water-holding capacity, emulsifying capacity, solubility) and could serve as ingredients in other poultry proteins. The poultry industry should be encouraged to explore the economic feasibility of using this protein source, which is currently underutilized or cliscarded. Reduction of Cholesterol Content of Much research has focused on reducing the cholesterol content of chicken eggs by altering the diet or through genetic selec- tion. These approaches have met with vary- ing degrees of success. Another alternative is to modify the egg yolk after the egg is laid. Since this disrupts the shell, albumin, and yolk, only processed eggs (currently about 15 percent of all eggs consumed) are available for this procedure. Approaches used to date include dilution of whole liquid egg with egg white, thereby reducing the cholesterol content of the final product; removal of portions of the yolk lipids and cholesterol with various "sol- vents," thereby producing a product lower in cholesterol; and complete removal of the yolk and formulation of a substitute "yolk" from vegetable oils and other ingredients, thereby producing a product that is choles- terol-free. Numerous U.S. patents have been ob- tained to accomplish the above goals. A few are discussed below. Metnick (1971g, U.S. Patent 3,563,765: Egg yolk solids were treated with nonpolar solvents (for example, hexane) at '160°F (71°C) to extract 50 to 90 percent of the fat and 70 to 98 percent of the cholesterol. The author indicated that n-hexane caused "lit- tle, if any, damage to the functional prop- erties of the remaining protein."
326 Melaick et al. (1971g, U. S. Patent 3,594,183: A specific objective of this patent was to provide an egg yolk product high in polyunsaturates, low in saturates, and low in cholesterol. Egg yolk solicis, from which most of the fat and cholesterol have been extracted with n-hexane, were mixed with vegetable oil, salt, emulsifiers, and coloring compounds. After emulsifying, pasteuriz- ing, and drying, "refatted egg yolk solids" were obtained. These can be used as a replacement for conventional egg yolk sol- ids. Seeley (1974), U.S. Patent3,843,811: A frozen egg product was prepared that con- tained 0 to 1.1 percent fat, 8 to 18 percent protein, and <0.05 percent cholesterol. The product contained-92 percent egg white and '8 percent egg yolk. Other ingredients added were 2 to 2.6 percent potato flour, 0.1 to 0.2 percent carboxymethy! cellulose, 1.4 to 1.8 percent nonfat milk solids, and citric acid. Glasser and Matos (1976), U.S. Patent 3,941,892: This patent differed from others in that a frozen "sunny-sicle up" egg product was cleveloped; the mold used to form the shape was also used as the package. The "yolk" portion was synthesized with 20 to 45 percent dried egg white, 5 to 35 percent oil (with a polyunsaturated/saturated tP/S] fatty acid ratio > 0.6), ciry milk protein, vegetable gum, colors, flavorings, and emul- sifiers. Seeley et al. (1976J and Seeley and Seeley (1980), U. S. Patents 3,987,212 and 4,200,663, respectively: A frozen egg product that con- tains no cholesterol or egg fats was producecl that was suitable for making scrambled eggs, omelets, and so on. The product was pre- pared by blending egg whites and small amounts of nonfat milk solids, vegetable gums, and flavor enhancers. Fioriti et al. (1978), U. S. Patent 4,103,040: The goal of these authors was to produce wet egg yolks and egg products that were low in cholesterol ant! had a P/S ratio > 1, while maintaining the functional properties APPENDIX of natural eggs. Wet egg yolks were pre- pared using a high-energy, higher shear mixer for a short time. During mixing, cholesterol was extracted from the yolk by the oil. At the same time, the P/S ratio increased. The wet yolk was then separated (centrifuged) from the oil. Egg yolk products were produced in which > 70 percent of the cholesterol was removed and the P/S ratio was > 1.3. BoZ(lt (1981), U. S. Patent 4,296,134: A 99 percent cholesterol-free egg blend was prepared that was low in fat (1. 25 percent) and calories (80 kcal/100 grams). The blend contained 60 to 96 percent liquid egg white, 0 to 18 percent water, 2 to 10.5 percent protein replacement (nonfat dried milk solids, powdered egg albumin, and soy protein), stabilizers, flavoring, and coloring. Tan et al. (1982), U. S. Patent 4,360,537: These authors developed a "lipoprotein emulsion system composed of protein, edi- ble oil, and other selected food ingredients" that could be used to replace egg yolk. Their primary objective was to improve the com- position ant! processes for preparing a pro(l- uct with good functional properties. The nutritional quality of one egg substi- tute has been compared to whole eggs by several investigators. Navidi and Kumme- row (1974) reporter! that raw egg substitute caused severe nutritional deficiencies in weanling rats ant! that all animals died within 4 weeks of weaning. Francis (1975) reported 100 percent mortality of chicks within 12 days when fed egg substitute as their only foocl. Since eggs are not usually the only food in a diet, Ryan and Kienholz (1979) prepared diets for chicks in which egg substitute or whole eggs constituted only 40 percent of the diet. These authors concluded that when cooked and fell in a palatable form, egg substitute is a satisfac- tory source of protein to support chick growth. Chicks fed whole-egg diets weighed 787 grams after 28 days, whereas chicks fed
IMPROVING NUTRITIONAL VALUE OF POULTRY MEAT AND EGG PRODUCTS 327 egg substitute averaged 687 grams (about 13 percent less). Baker and Darner (1977) ant] Baker ancI Bruce (1986) prepared egg blends by varying the yolk to white ratio from 1:1 to 1:10. Liquid egg with a 1:3 ratio of yolk to white pro~lucecl scrambler! eggs and omelets com- parable to those made with whole eggs but contained only 50 percent as much choles- tero! and 30 percent fewer calories. In the 1977 study, the authors found that egg blencis containing as little as one-fourth the normal amount of egg yolk, with protein and lipid raised to the content of normal egg by the addition of ciried albumin and corn oil, made egg products that were as acceptable as those made with whole eggs. The patents and research studies re- viewed have focused on cholesterol elimi- nation or reduction in egg yolk products. Larsen and Froning (1981) suggested that fractionating egg yolk into its lipid, protein, and aqueous components may also lead to entities with new properties that could then be used in food systems. After trying several solvent systems, they reported that either hexane-isopropyl alcohol or hexane-ethyl alcohol was the most efficient for separating the egg oil fraction. If a protein isolate is desirecl, ethyl alcohol or isopropyl alcohol is the appropriate solvent; the use of hexane altered the integrity of the protein so that it was no longer an effective emulsifier. Tokarska and Clandinin (1985) described a method for the preparation of egg yolk oil that did not cause decomposition of unstable polyunsaturated fatty acids. They obtained optimal extraction of lipid from egg yolk with ethanol/hexane/water. They reduced the cholesterol content of the egg yolk oil by 80 percent by washing with 90 percent ethanol; the cholesterol content of the prod- uct was 7 mg/gram of oil. Solvent extraction procedures do not se- lectively remove cholesterol and can impair the functional properties of certain compo- nents. An alternative to solvent extraction is supercritical fluid extraction (SFE); the lipid components need not be extracted and functional properties are not clestroyed. A supercritical fluid is produced when the temperature of a gas is raised above the critical point and is then subjected! to high pressure. As pressure is applied to a gas above critical temperature, the density of the gas will increase and may approach that of a liquid, while the viscosity of the gas is virtually unchanged. This combination of high density ant! low viscosity allows it to be an excellent extracting agent. The su- percritical fluid has the ability to readily diffuse in and out of the food, thereby increasing extraction efficiency. By varying the density of the fluid through pressure changes, the solubflity of the fluid] can be adjuster! to preferentially extract certain components. For egg products, the goal is to selectively extract cholesterol without removing the polar lipids responsible for functional and sensory properties of the resulting product (G. W. Froning, personal communication, 1986~. The food industry is currently using SFE to decaffeinate coffee; other applications may be extraction of spices; removal of oil Tom snack foods; extraction of of} from cottonseecl, corn, and soybeans; an(l extraction of flavors from foods. To ~late, no one has used SFE with eggs or egg products; however, scientists at the University of Nebraska have initiated research to extract egg yolk with supercritical carbon dioxicle at various pressures and tem- peratures to obtain extraction of cholesterol. SFE is further discussed by Hettinga in this volume. Incorporation of Eggs To Increase Nutritional Value of Foods The consumption of shell eggs is rapidly declining in the United States. One ap- proach to curbing an overall (that is, shell plus processed) decline in egg consumption is to increase efforts for developing new products made entirely or partly from yolk, albumin, or whole eggs.
328 SUMMARY From a nutritional point of view, poultry and egg products are good because they contain high-quality protein and provide many other essential nutrients. Even with their excellent nutritional quality, however, these products are not the "perfect" food- nor should they be. No one foot! can be expected to provide all the nutrients we require; a balanced diet of many different foods is essential for well-being. Nutrient loss during primary or further processing of poultry is minimal. Aspects of processing that may further enhance the nutritional value of poultry are increasing the utilization of blood, giblets, and bone residue protein; hot-cleboning; removal of the abdominal fat pad in ready-to-cook car- casses; and reduction of fat en c] sodium content in further-processec! products. The primary negative aspect of egg nu- trition is the high amount of cholesterol in the yolk. Numerous methods have been proposed to reduce or remove cholesterol from processed egg products. The industry needs to look at these approaches as it develops much-needed, new, egg-based products. REFERENCES Alexander, H. D., E. J. Day, H. E. Sauberlich, and W. D. Salmon. 1956. Radiation effects on water soluble vitamins in raw beef. Fed. Am. Soc. Exp. Biol. Fed. Proc. 15:921. Ang, C. Y. W., and D. Hamm. 1983. Comparison of commercial processing methods vs. hot deboning of fresh broilers on nutrient content of breast meat. J. Food Sci. 48: 1543, 1544, 1565. Ang, C. Y. W., D. Hamm, and G. K. Searcy. 1982. Changes in nutrient content during chill-holding of ice-packed and deep-chilled broilers. J. Food Sci. 47:1763. Anonymous. 1986a. Inside stuff. Meat Ind. 32(7~: 118. Anonymous. 1986b. Hot dogs. Consumer Reports June, 364. Baker, R. C., and C. Bruce. 1986. Development of a low cholesterol and low calorie egg blend. Poultry Sci. 65(Suppl. 1):8. Baker, R. C., and J. M. Darner. 1977. Functional and organoleptic evaluation of low cholesterol egg blends. Poultry Sci. 56:181. APPENDIX Baker, R. C., D. Scott-Kline, J. Jutchison, A. Good- man, and J. Charvat. 1986. A pilot plant study of the effect of four cooking methods on acceptability and yields of prebrowned battered and breaded broiler parts. Poultry Sci. 65:1322. Barbut, S., A. J. Maurer, and R. C. Lindsay. 1986. Effects of reduced sodium chloride and added phos- phates on sensory and physical properties of turkey frankfurters. Poultry Sci. 65(Suppl. 1):10. Bender, A. E. 1978. Food Processing and Nutrition. New York: Academic Press. Boldt, W. A. 1981 (October 20). Liquid egg blend. U. S. Patent 4,296,134. Bowers, J. A., and B. A. Fryer. 1972. Thiamine and riboflavin in cooked and frozen, reheated turkey. J. Am. Diet. Assoc. 60:399. Brasch, A., and W. Huber. 1948. Reduction of un- desirable by-effects in products treated by radiation. Science 108:536. Brekke, C. J., and T. A. Eisele. 1981. The role of modified proteins in the processing of muscle foods. Food Technol. 35(5):231. Calloway, D. H., E. R. Cole, and H. Spector. 1957. Nutritive value of irradiated turkey. J. Am. Diet. Assoc. 33:1027. Calvi, B., G. Kasaoka, A. Jarboe, and G. Kuester. 1984a. Animal blood protein as a food ingredient. Memorandum of Screening and Surveillance 3(1):5. Washington, D. C.: U. S. Department of Agriculture. Calvi, B., G. Kasaoka, A. Jarboe, G. Kuester, and C. Spenser. 1984b. Edible bone protein. Memorandum of Screening and Surveillance 3~3):25. Washington, D. C.: U. S. Department of Agriculture. Campbell, C. L., T. Y. Lin, and B. E. Proctor. 1958. Microwave vs. conventional chicken. J. Am. Diet. Assoc. 34:365. Causey, K., M. E. Hausrath, P. E. Ramstad, and I. Fenton. 1950. Effect ofthawing and cooking methods on the palatability and nutritive value of frozen ground meat. 2. Beef Food Res. 15:249. Chang, I. C., and B. M. Watts. 1952. The fatty acid content of meat and poultry before and after cooking. J. Am. Oil Chem. Soc. 29:334. Cheldelin, V. H., A. M. Woods, and R. J. Williams. 1943. Losses of B vitamins due to cooking of foods. J. Nutr. 26:477. Childs, R. E., W. K. Whitehead, and E. J. Lloyd. 1976. Automated Blood and Lung Collecting and Handling Systems for Poultry Processing Plants. Marketing Research Report No. 1062. Washington, D. C.: U. S. Department of Agriculture. Cook, B. B., A. F. Morgan, and M. B. Smith. 1948. Thiamine, riboflavin, and niacin content of turkey tissues as affected by storage and cooking. Food Res. 14:449. Cotterill, O. J. 1981. A Scientist Speaks about Egg Products. American Egg Board Report No. 1460. Park Ridge, Ill.: American Egg Board.
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