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4 Enhancing the Food Supply It should be a goat of our country to provide a sufficient variety of foocis throughout the year to meet the energy and nutrient needs of its citizens, promote health, and export value-added food products that im- prove our international competitiveness and trade balance and create jobs. Our food supply should be safe and properly preserved to maintain high quality, yet should be low enough in cost for all to have access to a nutri- tionally adequate diet, irrespective of income. Because of the numerous technological advances in food preservation, some of which are noted in this chapter, and the productive system of agriculture in the United States, we enjoy a relatively abundant, safe, and nutritious food supply. Furthermore, the amount we spend on food at home about 12 percent of disposable personal income is the lowest in the world among countries for which comparable data are available. Micronutrient-deficiency diseases and foodborne illnesses that plagued our nation earlier this century have largely disappeared as a result of the improved supply, preservation, and enrichment and fortification of foods. In addition, technologies developed by foot! scientists since the 1940s are helping to reduce nutrient deficiencies throughout the world, although the challenges are still great. Current dietary needs in the United States go beyond providing suffi- cient food and nutrients. They involve modifying and enhancing the food supply to help combat coronary heart disease, cancer, and other chronic diseases. The safety of the food supply continues to be of concern as we 98

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ENHANCING THE FOOD SUPPLY 99 learn more about microbial contamination and the toxic effects of some components of food. Food technologists are producing modified foods to help people meet dietary recommendations (for example, to consume foods with fewer calo- ries or less total fat, saturated fat, and cholesterol). Many of these prod- ucts incorporate newly developed fat and sugar substitutes. More "func- tional foods," as these products are called, will be developed through collaborative efforts among plant geneticists, biotechnologists, and food technologists to enrich or reduce the amounts of biologically active com- ponents in these foods. Functional foods are the wave of the future: for example, a cancer-preventing compound may be increased in a food through addition or by biotechnology. Exciting opportunities and challenges lie ahead as we enhance the food supply for optimal health. Nutritional recommendations per se will not be effective unless people can meet them by eating generally available food products. Technological responses to consumers' concerns and nutri- tional recommendations have already changed the food-product landscape. Low-calorie, low-fat, low-salt, higher-fiber, and fortified foods, as well as decaffeinated coffee, cholesterol-free egg products, and fat and sugar sub- stitutes are all familiar examples. As the driving forces for a healthier, safer, more convenient, competi- tively superior, seasonally invariant, and environmentally friendly food supply have accelerated in recent years, new technical needs have begun to emerge, with actions and contributions in one area affecting the others. The next generation of novel materials, new and hybrid technologies, and unique applications will emerge from the progressively specialized frontiers of scientific research. Their synergistic linkages with the scale and range of existing food-manufacturing practices will offer new opportunities and fresh challenges worthy of special efforts. The impetus for safe foods also re- quires new technologies and associated biological, physical, and engineer- ing concepts. Success will indeed vitalize the science and engineering basis for enhancing the quality, safety, and sustainability of the U.S. food system and for long-term amelioration of increasingly serious global com- petition. In the following examples, applications of biological, physical, and engineering principles form the basis of theoretical and experimental understanding of foods and food systems. ENGINEERING FOODS FOR DIETARY COMPLIANCE Dietary recommendations may be perceived by much of the public as promoting a shift to less food and perhaps to less aesthetically pleasing foods, often resulting in noncompliance. Technology can play a key role in this scenario by creating new formulated foods and modifying whole foods

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100 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES THE FOOD-PROCESSING INDUSTRY Based on the value of its shipments, the food-processing industry is the largest manufacturing industry in the United States, employing 1.6 million people. The U.S. food system stretching from farms to grocery stores plays a distinctly vital role in the national economy. As a total system, it employs 14 million people directly and another 4 million in related industries. It contributes nearly 20 percent of the gross national product (GNP). The overall contribution of the food-processing industry to this country is far greater than the mere dollar value of its shipments, the number of its employees, or its position in worldwide competition would indicate. The recent evolution of a scientifically based, integrated, effi- cient system of food engineering, processing, and packaging allows Amer- icans the unique luxury of acting as if food were a constant around which other activities can be planned. This has considerably enhanced the quali- ty of life that we enjoy today. Its total contribution is considerably great- er than its cost to U.S. consumers on average, about 12 percent of disposable income in 1991 (15 percent including beverages). This is much lower than food costs in any other country in the world. The importance of food engineering, processing, and packaging in this area cannot be overestimated. Adding value not only captures the benefit of economic output, but also provides employment and generates government revenues. In today's global economy, value-added processing of consumer-oriented foods has assumed new dimensions. In 1990, inter- national trade in consumer-oriented foods grew at a 4 percent annual rate, while growth in bulk and intermediate commodities was up by only I percent. In the same year, 53.8 percent of U.S. agricultural exports were exported in bulk form, 22.7 percent in intermediate form, and 23.5 percent in consumer-oriented form. However, the United States accounts for only 8 percent of the $140 billion world market for consumer-orient- ed foods. It is reasonable to assume that as disposable income increases across the globe, there will be new demands for consumer-oriented food products. A 15 percent U.S. share of the high-value product market would generate a I to 2 percent increase in GNP ($52 to $104 billion in 1991) and create about 1.5 million new jobs. A critical question is how to tailor a vigorous and dynamic research program to meet the demands and dimensions of the international food trade and take advantage of growing markets. It has been recognized for some time that competition from abroad is favored by lower labor costs and that competing on the basis of cost alone is less successful than competing on the basis of new products and product quality. Improve- ments in cost and quality can be achieved effectively through developing new technologies and by applying recent engineering and manufacturing advances.

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ENHANCING THE FOOD S UPPLY The food system comprises the biggest complex of businesses in the United States, involving the production, processing, manufacturing, wholesaling, retailing, and importing or exporting of food. Infrastructures to produce and supply people with their food and drink are enormous and tightly linked. They are dependent on, and use, natural resources as fundamental as air, water, soil, energy sources (e.g., solar, coal, and oil) and elements necessary for materials (e.g., glass, steel, and aluminum). There are an estimated 3 million farmers and an additional 11 million employees in the food industry. Approximately 53 percent of those em- ployed in the food industry work in eating and drinking places, 27 percent in food stores, and 20 percent in food manufacturing and wholesaling. The 380,000 firms that process, wholesale, and retail the nation's food supply have become more international in character, deeper in debt (pri- marily due to mergers and leveraged buyouts), and more concentrated, productive, and profitable. 7 ~ ~ or ingredients to be used in whole foods and enhancing both their health benefits and acceptability. Fortification and Enrichment As knowledge of nutrient needs evolved earlier this century, it be- came apparent that nutrient deficiency diseases were a critical problem in the United States and the rest of the world, and various approaches to solving them were considered. In the end, these public health problems were solved in large part by enriching and fortifying foocls. Enrichment of cereal-grain products with iron, thiamin, riboflavin, and niacin has been a remarkably effective and efficient means of enhancing the nutrient quality of the food supply and is a classic example of an effective, well-designed public health approach to providing needed nutrients. Cereal grains were selected for enrichment because they are eaten frequently by virtually all populations groups. Subsequently, breakfast cereals were fortified. The result has been a significant increase in the amount of these enrichment nutrients available for consumption (Figure 4.1~. Other nutrient-deficiency problems were addressed by fortifying various foods with specific nutri- ents (e.g., iodized salt and vitamin D-fortified milk). Recently, the Food and Drug Administration (FDA) began examining the feasibility of fortify- ing flours and other foods with folio acid to reduce the occurrence of neural tube defects in infants.

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102 140 US ~ 100 of to - o en 8 OPPORTUNITIES IN TTIE NUTRITION AND FOOD SCIENCES o - . . . ~:~111111~1 Calories Protein Thiamin Riboflavin Niacin Pyridoxine Nutrients C1 ~ 909-1 913 ~ ~ 925-1 929 ~ ~ 935-1 939 1~1 ~ 947-1 949 957-1 959 ~ ~ 965-1 969 1111111 ~ 975-1 979 1~ ~ 985-1 988 FIGURE 4.1 Nutrients available for consumption, 1909-1988. From U.S. Bu- reau of the Census, Statistical Abstract of the United States: 1992 (112th edition), Washington, D.C. Research Opportunities Provicle nutrients that are bioovailable yet stable in food Iron, zinc, cal- cium, and folio acid fortification of adult and infant foods wouIc! benefit from increased knowledge of the bioavailability of micronutrients. Iron deficiency is the most common nutritional deficiency in the United States, affecting young children, women of childbearing age, pregnant women, and poor people. The typical U.S. diet is estimated to provide only 6 to 7 milligrams (mg) of iron per 1,000 kilocalories (kcal) of food, and women of childbearing age have difficulty achieving their recom- mended dietary allowance (RDA) of 15 mg per day because they generally eat fewer calories. Premenopausal women risk developing a negative iron balance because of menstrual blood loss. Iron deficiency may also be exacerbated by the relatively low amount of iron available from grains, legumes, fruits, and vegetables. Such problems exist in many parts of the developing Florid where there is little meat consumed and in this country among those choosing diets low in red meat. Iron deficiency may increase because all the major dietary guidelines recommend increasing the con- sumption of grains, fruits, and vegetables. Readily bioavailable forms of iron are often the most chemically and biologically reactive, thereby creating color and flavor problems in forti

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ENHANCING THE FOOD SUPPLY 103 fled food. Stabilized forms of iron and other fortificants would allow for more effective fortification. identify and understand the mechanisms by which meat and ascorbic acid enhance iron absorption Both ascorbic acid (vitamin C) and meat en- hance the bioavailability of non-heme iron in foods. However, ascorbic acid, an unstable nutrient, is often not a good candidate for processed food or food that might be stored in warm, humid climates. Therefore, we need to discover how meat enhances iron absorption. Several investigators have offered data to support the notion that meat's action is attributable, in part, to amino acids or a peptide. If meat's potent enhancing factor is a peptide (at least in part) and that peptide can be isolated. it would c rove a tremendous boon to the 500 million cases or so of nutritional anemias worldwide. Such a peptide could be added to food; even more important, the major grain crops might be genetically engineered to produce it. Such a development would not only provide relief to the developing world but would allow a greater shift to plant foods in the United States without creating concerns about iron deficiency. Define and resolve potential dietary inadequacies of other nutrients such cars folic acid, vitamin B6, copper, zinc, and calcium These problems could be addressed by adding nutrient mixtures to traditionally fortified foods such as flour. Issues of bioavailability and reactivity of these nutrients with foods have only been partially addressed by food scientists. Consider- ation should be given to fortifying traditionally unfortified foods such as beverages and snacks. Low-Fat and Low-Calorie Foods Compliance with dietary recommendations to reduce fat and calorie intake will not be easily achieved by the general population. Gains in this area require changing behavior as well as modifying and reformulating traditional foods. Because of the energy density of macronutrients (protein, fat, and carbohydrate), one goal is to lower consumption of all of them, but par- ticularly fat. Now the problems begin how do we achieve this laudable modification and still have enough foods with desirable sensory character- istics? This offers some great technological challenges, including, in some cases, the development of low-calorie substitutes for sugars, starches, and fat. However, substitutes cannot directly replace macronutrients unless they have equivalent properties for their intended use. Indeed, eliminat- ing certain macronutrients from food, whether replaced or not, can create serious sensory problems related to flavor and texture. The safety and

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04 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES health aspects of these macronutrient manipulations must also be consid- ered while provicling the consumer with acceptable sensory characteris- tics. Some reduction in the fat content of foods of animal origin has been achieved through applier] genetics and altered livestock feeding practices. However, technologies exist to further reduce fat in foods. The most com- mon approach to date is to replace a portion of the fat with an aqueous dispersion of a hydrocoTIoicI such as starch, dextrins, or gums. The objec- tive is to structure carbohydrates or proteins, or both, in such a way that they feel in the mouth like the high-fat food. Interestingly, certain cellulose ethers can be used in a different con- text to reduce fat. These polymers have unique thermal "elation proper- ties that, when put in fried-food batters, act as a barrier to of} absorption. Another fat-reduction technology involves the use of microparticulated proteins processed into spheroidal particles so small that they fee! to the tongue like a fatty, creamy liquid. In this case, 4 kcaT can replace 27 kcal of fat in an ice-cream-like product, since the fat substitute is a hydrated protein at 1.33 kcaT per gram (g), which replaces l g (9 kcal) of fat. The practical applications are almost exclusively in nonheated foods such as frozen desserts, yogurt, and margarine because these proteins are dis- persed en c! denatured if heated and lose their fat-like mouthfeel. Macronutrient replacement has had a significant impact on (lietary patterns. Two-thircds of aclults in the United States consume "light" prod- ucts an average of nearly four times each week. Approximately 10 percent of the new food products introduced in 1990 claimed to be Tow-fat or nonfat products. Among the new (fairy products, 41 percent were low- or nonfat. And 31 percent of new products in the category of processed and fresh meat, poultry, seafood, and eggs were low- or nonfat products. Lower- fat products are not confined to supermarket shelves. Restaurants, fast- food establishments, and school cafeterias are also increasingly offering low-fat fare, although none of these has taken full advantage of this tech- nology, particularly school cafeterias (see box). EATING LESS FAT The Institute for Science in Society has developed a report card on fat-reduction activities, using the goals set by the Healthy People 2000 report of the U.S. Department of Health and Human Services (DHHS): Development of Low-Fat Products- A The food industry has surpassed the year 2000 goal calling for more than 5,000 products to be developed, with the Food and Drug

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ENHANCING THE FOOD SUPPLY Administration reporting more than 5,600 new and improved lower-fat products on the market since the publication of The Surgeon General's Report on Nutrition and Health in 1988. As new ingredients are introduced, such as those designed to replace fat, the numbers can be expected to rise. Restaff rants BE Industry-wide surveys of table service and fast-food restaurants show steady progress in adding lower-fat items to menus. According to the National Restaurant Association, 78 percent of restaurants offer at least one lower-fat menu option, such as salads or skinless chicken breasts. Even fast-food restaurants are beginning to provide healthful options. Some restaurants, including a number of hotel chains, are completely revamping their menus. Good progress toward the year 2000 goal is evident among at least 90 percent of restaurants offering low-fat choices. Nutrition Labeling BE Spurred by the Nutrition Labeling and Education Act of 1990, the marketplace will see a complete overhaul of labeling within the next two years. The year 2000 goal is nutrition labeling on all processed foods and at least 40 percent of fresh foods. Under the comprehensive regulations proposed by the DHHS and U.S. Department of Agriculture (USDA), nutrition labeling will be on all processed foods by 1993, as mandated by Congress. Labels will include vital information on fat content. They should be clearer, with less opportunity for misleading health claims and vague descriptors. Important labeling format issues are still to be resolved. The National School Lunch Program C USDA has steadfastly refused to mandate that school lunches meet the recommendations on fat in its joint publication with DHHS, Dietary Guidelines for Americans, 3rd edition, and it has no plans to do so. The year 2000 goal calls for at least 90 percent of schools to meet the guidelines. USDA has promised comprehensive data on the amount of fat in school lunches nationwide when its survey is completed at the end of 1992. But sporadic evidence consistently points out that 35 to 45 percent of calo- ries in school lunches are derived from fat. While supporting the dietary guidelines in school nutrition education programs, USDA's failure to re- quire the fat limits in school meals suggests that schoolchildren must eat much less fat during the rest of the day to keep within the fat recommen- dations of the dietary guidelines. SOURCE: Institute for Science in Society (ISIS), 1992. Eating Less Fat: A Progress Report on Improving America's Diet. ISIS, Washington, D.C. 105 -

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106 OPPORTUNITIES IN TTIE NUTRITION AND FOOD SCIENCES Clearly, technology ret ~. _~ has improved the nutritional value and conve- nience of these foods. There is as yet no unequivocal evidence that low-fat or low-calorie foods are lowering fat or energy intake in the total diet, since all the compensation mechanisms have not yet been fully studied. However, foods with lower fat content are available in a convenient, at- tractive, and, for the most part, acceptable form for consumers. Research Opportunities Develop new tow- or no-fat and low-calorie substitutes Critical to the success of low-fat and low-calorie food products is presentation of the sensory attributes (taste, aroma, and mouthfeel) of such foods. Altered lipids and structural fats with modified fatty acid profiles are providing challenging opportunities for research. Consumers are not yet satisfied with the mouthfeel and taste of some low-fat products. Compensation mechanisms in humans should be clearly established If low-fat technology is to succeed in providing clear health benefits to con- sumers, we must understand if and how humans compensate for lowered macronutrient intake. Develop con understanding of how macronutrient replacement might affect the overcall diet Micronutrient intake might be affected in individuals who significantly alter their diet to consume better-tasting, lower-fat, or low-calorie products. As the total fat content of their diets decreases, the ratio of saturated to unsaturated fat might actually increase. Develop barriers to reduce fat uptake in fried foods Since fried foods form a high percentage of appealing fast foods, the development of com- pounds to inhibit fat absorption by the food will provide interesting op- portunities. Sensory Needs of the Elderly One of the most crucial problems facing the elderly is their volun- tary reduction of food and beverage intake, with a consequent reduction in fluids, calories, essential nutrients, and fiber. The anorexia of aging is multifactorial, having both physiological and pathological causes. Obvi- ously, food technology cannot address all the causes of this reduced food intake, but it certainly can make some major contributions. One of the reasons for decreased caloric intake may be impaired den- tition. One study of older subjects with teeth or dentures showed that, compared to subjects with teeth, the denture wearers had a drop of al

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ENHANCING THE FOOD SUPPLY 107 most 20 percent in the nutritional quality of their diets (including calories and most of the 19 nutrients studied). Such a drop could accelerate nutri- tional deficiencies or poor health. Decreases in caloric intake have also been seen in people with full dentition. Nonetheless, it must be assumed that, at the least, difficulties in chewing certain foods might affect variety in the diet and certainly would affect enjoyment of foods and quality of life. Taste and smell perceptions are reduced markedly in the elderly, with losses occurring at both threshold and suprathreshold concentrations for taste and especially smell. Flavor, odor, color, and perception also play an important role in food acceptance in the elderly. Designing foods to over- ride these challenges would provide a valuable service to this increasing population. Research Opportunities Enhance our understanding of the sensory physiological processes The operation of individual receptors and the physiology and biomechanics of the sensation process are age-dependent. Therefore it will be necessary to correlate objective measures of sensation such as flavor, taste, texture, and color, with physiological mechanisms in various age groups in order to better understand how to optimize food acceptability at every age. Fur- ther, it has been observed that sensory stimulation is linked to physiologi- cal changes in immune response in humans and gene expression in ani- mals. Therefore, providing good tasting, high-quality food will not only increase the quality of life but may also increase the length of life. Develop products for the elderly and other people with special needs It is possible, for example, to increase fragility and maintain crunchiness of foods or to make chewy foods that require less chewing in order to mini- mize fatigue. Texture, although most directly involved with dentition, is not the only sensory attribute important to the enjoyment of food and food intake. Design foods and beverages with enhanced flavor to increase fluid and food intake Foods for the elderly population should have enhanced fla- vor and aroma to compensate for the reduced perception of these sensory characteristics. Experiments suggest that the thresholds for many odors are often as much as 12 times higher in the elderly than in young persons. As a result, it is not surprising that the elderly have been found to prefer flavor enhancement in a wide variety of foods. Technology can provide almost any flavor, but it can also provide high-intensity flavors. Enzymatic and other biotechnological techniques are available to produce these fla

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108 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES vors, and their use in this nontraditional approach might prove beneficial to an elderly population. Such high-intensity flavors could be manufac- tured independently or, through genetic engineering, be produced within the food by the plant or animal itself. Extract objectionable compounds in food Technology could also be used to remove food constituents that are objectionable from a sensory or physi- ological viewpoint. For instance, compounds in the Brassica genus of plants (e.g., cabbage and broccoli) that cause stomach upset might be removed by supercritical fluid extraction (a process now used to decaffeinate cof- fee) with little effect on the food itself. Oligosaccharides like stachyose and raffinose, found in soybeans and other legumes and responsible for the flatulence experienced by people who consume them, could be re- moved by selective extraction or genetic manipulation of the plants. Develop visual cues to replace losses in flavor and taste Studies have shown that color influences the perception of sweetness in flavored and unflavored foods. Color interferes with judgments of flavor intensity and identification and in so doing dramatically influences the pleasantness and acceptability of foods. Functional Foods for Health Traditionally, food scientists and nutritionists have focused their re- search and development efforts upon providing a food supply that is both safe and acceptable from sensory, economic, and nutritional standpoints. The guiding light for nutritional content of foods and diets has been the RDAs. The RDAs were first established in 1943 to provide "standards to serve as a goal for good nutrition." Over the years, good nutrition has typically meant avoiding nutrient-deficiency diseases and maintaining ideal weight. Thus, the traditional view has been that the food supply should provide sufficient energy, macronutrients, and micronutrients to meet the needs of consumers. With the recent surge of research into the role of nutrients in promoting optimal health and the recognition that nonnutrient components of foods may increase or alleviate the incidence of various diseases has come increased interest in designing foods and diets for opti- mal health, not just to prevent classic nutrient-deficiency diseases. Modern genetic engineering techniques make it possible to enhance, suppress, or even transfer genes from one species to another to attain health benefits. Food-processing techniques may achieve the same goal by selectively removing or concentrating components of interest or by devel- oping more acceptable products with a high concentration of health-pro- moting constituents in whole foods.

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32 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES flavor enhancers, pigments, stabilizers, thickeners, surfactants, sweeten- ers, antioxidants, and preservatives. Genetic engineering techniques offer more precise tools for improv- ing food-grade microorganisms. Although significant research has been conducted on genetic engineering of food-grade microorganisms, no ge- netically engineered organisms have yet been approved by the FDA for use in foods. Several enzymes derived from genetically engineered organ- isms, including rennet (used in cheese making) and alpha-amylase (used for the production of high-fructose corn syrup), have been approved for use in the United States. Research Opportunities Develop basic toolsfor the genetic manipulation of microorganisms The regulatory elements and signal sequences involved in control of gene ex- pression in microbial systems need to be identified and isolated. This will make possible the construction of strains that excrete valuable secondary metabolites into the culture medium, from which they can be readily extracted and purified. Construction of multifunctional integrative cloning vectors will allow the transfer and stable integration into the chromosome of single genes as well as coding for entire metabolic pathways. Efficient and reliable gene transfer systems applicable to bacteria, yeast, and molds need to be cleveloped. Construct microorganisms with unique metabolic properties Identification of microorganisms for metabolic screening will greatly expand the num- bers and types of microorganisms that can be user] in food fermentation ant! in the production of food ingredients. Genetic improvements will be targeted to a specific organism anc! fermentation system and may involve improved processing characteristics (e.g., more consistent and improved leavening of bread and accelerated ripening of cheese), decreased waste (e.g., bacteriophage-resistant organisms that eliminate economic Tosses caused by destruction of cultures by bacteriophage>, enhanced food safety (e.g., microbial production of bacteriocin, which inhibits foodborne pathogens), improved nutritional quality (e.g., microbial production of amino acids or vitamins and engineered yeast for production of low-calorie beer), or en- hanced bioavailability of nutrients (e.g., engineering of the meat factor influencing iron absorption into starter cultures and engineered starter cultures as delivery systems for digestive enzymes). Understand the role of microorganisms as probiotics Microorganisms have been reported to play key roles in maintaining the health of humans anct animals by colonizing the gastrointestinal tract and controlling intestinal

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ENHANCING THE FOOD SUPPLY 133 microorganisms capable of producing toxic effects in the host. Lactobacilli assist in the digestion of lactose, provide important digestive enzymes, inactivate toxins, bind cancer-causing chemicals, modulate the gut flora, deconjugate bile acids, and supply B vitamins. Further research is war- ranted, since the exact mechanisms for these effects are not well under- stood. Probiotic effects have been studied extensively in animals, and it is not uncommon to add certain organisms directly to animal feed to en- hance digestibility of the feed and to protect the gastrointestinal tract from microbial invasion. The efficacy of this approach in human diets needs to be tested. Enzymes and Protein Engineering Enzymes are catalysts, generally proteins, that enhance the rate of the synthetic and clegradative reactions of living organisms. The food- processing industry is the largest single user of enzymes, accounting for, on average, more than 50 percent of enzyme sales. Proteases, lipases, pectinases, cellulases, amylases, and isomerases are used extensively to control the texture, appearance, flavor, and nutritive value of processed foods. Although enzymes are produced by animals and plants as well as microorganisms, the enzymes from microbial sources are generally most suitable for commercial applications. Microbial products produced without such limitations as season of the year or geographic location, which might be imposed by plant-derivec3 enzymes. In addition, microorganisms grow quickly, and production costs are relatively Tow. In view of the metabolic diversity of microorganisms, nature has provident a vast reservoir of enzymes that act on all major biological molecules. Unfortunately, enzymes frequently do not function optimally under the conditions of temperature and pH used in food processing. Chemical modification has been used successfully to improve enzymes; however, the general lack of specificity in the reagents and the requirement for difficult and tedious purification and characterization to insure homoge- neity severely limits the power of the method for routine improvement of enzymes. Site-s~ecific mutagenesis, a specializecl form of genetic engi _ . . 1 can be mass J 1 peering, has been used to introduce In tne structure or enzymes minor changes that have dramatic effects on substrate specificity, pH and ther- mal stability, and resistance of the enzyme to proteolytic degradation. For example, substitution of amino acids at specific key locations within the active site of the enzyme subtilisin demonstrated that properties of the enzyme could be altered dramatically, both positively and negatively, when compared to the native enzyme. Site-specific mutagenesis could improve the versatility of enzymes in food systems and decrease the cost of pro- cessing food. This technology could also be used to modify other proteins

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34 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES of interest to the food-processing industry, possibly altering functional properties or nutritive value. Enzymes are frequently used in batch food-processing systems; how- ever, they can be immobilized and used in continuous processing systems where applicable. For example, the enzymes used to convert starch in corn to high-fructose corn syrup and the enzyme rennet used in cheese manufacture have been immobilized and used continuously for weeks and sometimes months or years without substantial loss of activity. Cost sav- ings in excess of 40 percent have been achieved by conversion from batch to immobilized enzyme systems. Research Opportunities Develop analytical tools to improve understanding of enzyme structure ancifunction Improved computer modeling systems are needed to pre- dict the structural and functional impact of base pair or amino acid substi- tutions in DNA and protein, respectively. We need to develop models for evaluating the impact that structural changes in enzymes or proteins exert on their behavior in food systems (i.e., interactions with proteins, other macromolecules, and water) and chemical and physical tests for measur- ing properties directly associated with the? desired chnn~ec in native slants and processed foods. Design improved enzymes Enzyme and protein engineering will make it possible to create tailor-made enzymes that function optimally under food- processing conditions. In addition to modifying reaction rate, pH and thermal stability, and resistance of the enzyme to proteolytic degradation, it may be desirable under certain circumstances to modify substrate speci- ficity of enzymes. Theoretically, it will be possible to construct enzymes that modify fat, protein, or carbohydrates in ways not possible with en- zymes that now exist in nature creating the potential for new biological _ 1 , 1 ~1 . ~ ~1 1 ~1 1 . ~ molecules In food systems. Enzymes could also be engineered to {unction in unusual environments, such as in organic solvents, or under extremes of pressure or temperature for unique food-processing applications. Pro- tein engineering could be used to make noncatalytic proteins catalytic by attaching an active site to an existing protein. It may be possible to engi- neer antibodies that possess catalytic activity; their binding and recogni- tion sites could be used to immobilize the enzyme for food-processing applications. Improve enzymes in intact plants Enzyme- and protein-engineering tech- niques, coupled with plant genetic engineering, could be used to modify

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ENHANCING THE FOOD SUPPLY 135 enzymes and proteins in intact plants. For example, methods now exist to construct genes coding for synthetic proteins enriched in essential amino acids. Since cereal grains are deficient in one or more of the essential amino acids isoleucine, lysine, methionine, threonine, or tryptophan, transfer of these genes to plants deficient in these amino acids could improve their nutritive value. Many plant components used in food processing are chemi- cally modified following extraction from the plant (e.g., hydrogenation of oils and cross-linking of starch). Engineering of plants with enzymes ca- pable of chemically modifying starch or oils could eliminate the need for chemical modification after extraction. MOLECULAR BASIS OF FOOD QUALITY Clearly, these are exciting times for researchers involved in the study of the chemistry, physics, and biochemistry of foods. Quality and stability of food products are determined by the molecular properties of their constituents. However, the molecular properties often express themselves in unique, supramolecular structures that have an overriding influence. Techniques for measuring chemical structure, reactivity, and physical properties have become available at an unprecedented rate, and there is every indication that developments will continue. Some, such as nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) imaging, are nondestructive, thus allowing for continuous monitoring of changes. Theoretical interpretation of data has been greatly improved by computer-assisted data processing. All of this promises to aid our under- standing of the complex interactions of molecules that make up tissue or reformulated foods. Improved understanding of the relationship between the molecular structure of food biopolymers and the functional properties of biopoly- mers in food products will be one important application of these new techniques. This will enable us to substitute more readily available, less expensive, or nutritionally or functionally superior ingredients in our food supply. A food biopolymer of particular interest is the class of cyclodextrins, which are six- to eight-membered donut-shaped rings of glucose mol- ecules produced enzymatically from starch (Figure 4.3~. They have the ability to bind noncovalently with many different types of molecules in their "core." In doing so, they alter the physical and chemical properties of the molecularly encapsulated "guest" molecules. Cyclodextrins have many potential applications in food products. For example, they can be used to carry flavors, enhance the solubility of otherwise water-insoluble compounds, and remove such undesirable compounds as cholesterol from food.

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136 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES a_ _ FIGURE 4.3 This molecular model illustrates the beta-cyclodextrin molecule and its ability to entrap materials in its hollow "core." Through available molecular modeling systems, it is possible to identify the uses of beta-cyclodextrins in specif- ic applications. Determination of the important properties of biopolymers such as proteins will make it possible to improve structure by biotechnological techniques, both genetic and enzymatic. For example, the use of magnetic resonance techniques in determining the types of interactions and mo- lecular conformations of proteins in gels could allow for both higher qual- ity and more economical production of these products. Research Opportunities Study the role of water in foods One of the most important functional properties of food biopolymers is the ability to bind water. The amount, association with structural elements, distribution, and structure of water are without cloubt critical to the quality of foods. It is perhaps not an exaggeration to suggest that in many ways water is the most important determinant of food quality. Water determines the structure of biopoly- mers and is both the medium of and a participant in most of the reactions that occur in foodstuffs. One of the difficulties in dealing with the prob- lem of water structure in foods is that there is considerable uncertainty about the structure of water itself. Not only does water modify the struc

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ENHANCING THE FOOD SUPPLY 137 ture of cellular components, the structure of water is in turn modified by the components of the cell. The large surface area of cellular structures makes the effects at inter- faces of particular importance. The more highly developed structure of water at these interfaces affects its function as a solvent and most likely reduces its ability to disassociate into hydrogen and hydroxyl ions. This latter is of critical importance in determining plI and chemical reactions. Methods for determining water structure are based primarily on relax- ation techniques, measuring either the properties of water directly by proton magnetic resonance or the properties of molecules in water, such as the use of electron spin resonance (ESR) and NMR to study the trans- lational or rotational movements of free radicals and other food constitu- ents. The rate of formation and growth of ice crystals is an important factor in the quality of frozen foods. Much attention has been paid recently to the extremely high viscosity of the glassy state of water in frozen foods. This phenomenon illustrates the importance of water in chemical reac- tions in foods en cl offers a potential for improved quality during frozen food storage. Techniques such as differential scanning calorimetry can distinguish between temperature-inclucecl changes in the glassy state and phase changes brought on by melting of ice crystals. In the 1980s, food scientists realized that they could better under- stand the relationships of food structure, food function, and water in food materials, products, and processes by applying polymer science, with its study of glassy states, glass transitions, and plasticization by water. Food polymer science, emphasizing the basic similarities between synthetic poly- mers and food molecules, provides a practical experimental framework to study real-world food systems that are not at equilibrium. It is being widely applied to explain and predict the functional properties of food materials cluring processing and storage of the final products. Quantify the specific structural changes in the various levels offooc! mac- romolecular organization In spite of the potential promised by polymer science approaches to the study of water in foods, other lines of investiga- tion should not be neglected. In particular, it should also be recognized that, in many cases, the relevant properties of fooc3 molecules result not from their generalized polymer behavior but rather from their specific molecular structure, as should be expected for biological macromolecules, with their well-known ability to assume diverse functions by varying their basic structure (in the case of polymers, their primary sequence). Such aspects are particularly important in foods containing components that retain significant aspects of biologically imposed structure: cells, mem- branes, fat globules, globular proteins, and so on. The specific details of -

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13S OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES the interaction of macromolecular functional groups with water are known to be crucial in biological self-or~anization and in maintaining viability, such as the role of hydrophobicity in protein conformation and membrane structure, the role of water structuring in ionic salvation, and specific hydration effects such as hydrogen bonding. Altering the hydration envi- ronment of food molecules, as in processing, often leads to irreversible and undesirable changes in food quality. In many cases, these changes cannot be understood in terms of general polymer theory but must be considered in terms of the specific structural details of the system under consideration. As a result, we need much more study of the molecular details of food polymer hydration particularly under conditions of low water content or low temperatures. Learn more about- the beEc~vior.s of food components in solution A re- lated requirement is the need for greater basic work in simple model systems containing one or only a few components and variables. Until the behaviors of individual food components in solution are understood, and then the interactions of simple combinations of such polymers in solution, there is little hope of significant progress in understanding much more complicated systems. Much more needs to be learned about hydration forces, their role in colloidal stabilization, and whether these forces over- ride more traditional models of colloidal interactions in food systems. Explore mechanical-p1?ysical properties offoods related to bond energies Often the properties of a food are more related to the unique supramolecular architecture of the major food polymers than to their specific molecular properties. Many food polymers like proteins and starches are extensive structures of interacting components joined by noncovalent bonds. Col- lagen and the contractile proteins of muscle are examples of this, as are the cellulose and hemicelluloses of plant cell walls. Many techniques, some rather elegant, have been developed to measure mechanical forces in processed foods. In addition, there has been good progress in under- standing some of the chemical and physical changes occurring in indi- vidual molecules and supramolecular structures during processing. What is lacking is a theory to relate the changes at the molecular or supramolecular level to the overall physical or mechanical properties of the food tissues. For example, how do the noncovalent bonds formed by protein denaturation and aggregation influence a physical measurement such as tensile strength? An understanding of these phenomena would make it possible to modify processing techniques and food formulations to produce foods with any desired physical attribute. In a similar manner, it will be important to establish the contribution to these physical properties of covalent bonds in food biopolymers. Split

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ENHANCING THE FOOD SUPPLY 139 tiny of covalent bonds by hydrolysis of polymers is a technique that has been used for centuries to modify physical properties and produce prod- ucts of desirable quality. Examples of this would be tenderization of meat by protein hydrolysis and increased yield and quality of fruit juices by hydrolysis of pectins. However, in most cases results have been achieved by trial and error, without a firm understanding of the number of bonds necessary to be broken to achieve optimal results. Understand free-radical reactions in foods Biopolymers play a critical role in determining the physical-mechanical properties of food tissues. Both covalent and noncovalent bonds between biopolymers govern these properties. An area of great importance in food processing is the effect that mechanical actions such as grinding and cutting have on these pro- cesses. It has been reported that this type of mechanical action can break covalent bonds and form free radicals, which have been associated with food deterioration. Little attention has been given to this phenomenon in food research, although the principle is well established with man-made polymers. Since many of our food products are subjected to these kinds of mechanical stresses, understanding the extent of the changes they cause is critical. Not only would the physical properties of various food polymers such as proteins be affected, but the formation of free radicals could set off chain reactions leading to degradation of lipids and other components in foods. ESR spectroscopy is a powerful tool for measuring the production of radicals in situ and in real time. It measures free radicals directly, rather than just the decomposition products of the radicals. This type of kinetic information makes it possible to understand free-radical reactions occur- ring in food tissues without having to macerate and extract foods, pro- cesses that can themselves create free radicals. These in situ techniques should improve our understanding of other free-radical reactions as well. These other reactions would include those initiated by various forms of reactive oxygen species, thus allowing for improved strategies to counter- act the effects of these free-radical oxidation processes. Enhance understanding of biomembrc~ne changes Understanding of membrane structure and function has increased greatly in recent years, but much remains to be done. Good progress has been made in understanding the interactions of membrane proteins and lipids; however, interaction of membrane components with the proteins of the cell cytoskeleton is just beginning to be understood. These interactions will undoubtedly play a great role in the quality of foods. To give some idea of the significance of membranes in food tissues, it can be calculated that 1 kilogram of lean beef has approximately 8,000

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140 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES square meters of membrane surface. Thus, many of the reactions that go on in food result from the chemistry and enzymology of surfaces. Many of the functions of membranes in food tissues are an extension of their meta- bolic roles. These include energy production, the movements of ions and small and large organic molecules, receptor sites for hormones and there- fore for cellular control responses, and involvement in the control of ionic composition and phi of cellular compartments. Membranes are respon- sible for postharvest vectorial metabolism and osmochemistry. In addi- tion, the lipids of membranes are highly unsaturated and their extremely large surface area per unit of weight makes them particularly susceptible to oxidative reactions. These membrane processes are critical in the post- harvest metabolism of fruits and vegetables anc3 the postmortem control of calcium ion concentrations in the sarcoplasm of muscle tissue. Thus, quality control and maintenance are in large part a function of the mem- brane systems. ENVIRONMENTAL ISSUES Sustainability Each step in the food system production, transportation, processing, storage, and marketing has some effect on the environment. Therefore, the concept of sustainability in the food system is critical to a finite world with an expanding population. An important challenge in this age of envi 1 1 ----r--~ =~ no- ronmental and economic concerns is to identify, develop, and implement new systems for producing high-quality, economical, wholesome foods with reduced adverse effects on the environment and with better use of raw materials. Sustainable agriculture attempts to minimize environmental degrada- tion through a range of practices that includes integrated pest manage- ment; low-intensity animal production systems; crop rotations to reduce pest damage, improve crop health, decrease soil erosion, and (for legumes) fix nitrogen in the soil; and tillage and planting practices that reduce soil erosion and help control weeds. In the food-processing industry, proces- sors are beginning to recycle more by-products that were formerly dis- carded. These by-proclucts include the soluble materials in wastewater, such as sugar washed off peaches, tomato juice in flume water, starch removed from potatoes during washing and Fuming operations, and solid materials such as corn husks and crab shells. If suitable uses can be found for these by-products, they can be converted to raw materials or ingredi- ents in feed, food, or other products and removed from the waste stream. An excellent example of sustainability exists in the fishing industry. In 1987, fish processors in Massachusetts designated fish waste disposal as

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ENHANCING THE FOOD SUPPLY 141 one of their main future concerns. Regulations at that time prevented offshore disposal of the waste, and fees for landside disposal were steadily increasing, along with its potential for pollution. Scientists developed an economically viable liquid fertilizer from fish waste material for regional crops such as cranberries. Much of the fertilizer was liquefied using en- dogenous enzymes from the fish waste itself. They found that all plant material fertilized with the liquid fish fertilizer had equal or better growth than plants grown using commercial fertilizers. These and further studies have led to the addition of liquid fish fertilizer to the official list of ap- proved cranberry fertilizers. Research Opportunities Develop alternative energy sources and agricultural chemicals U.S. agri- culture depends heavily on fossil fuels to provide power for machinery, for the production and application of fertilizers and pest control chemi- cals, for crop drying, and for many other purposes. Improving our under- standing of plant and pest interactions and the biology and genetics of insects and weeds will enable us to design integrated pest management strategies that reduce the need for pesticides. Advances in biotechnology should lead to the development of plants that are more resistant to pests and less dependent on the application of manufactured fertilizers. There is a need for new, effective pesticides that do not pose long-term health ris as to consumers or to the environment. With additional research, we will learn how to collect and store solar, wind, and other sources of energy more reliably for applications on the farm, including the heating of live- stock buildings and the drying of harvested crops. Identify economically viable uses for by-products of the food industry and develop processes for separating them Information is needed on the iden- tities, composition, and quantities of the solid and liquid by-products gen- erated by the food industry. Research would help to identify the ways in which by-products can be incorporated into new foods, animal feed, or nonfood products. New technologies and devices such as membranes are needed to remove suspended and dissolved by-products from waste water and to separate by-proclucts that become mixed together in a solid or liquid state. Develop databases and water quality standards that will expand the use of water recycling and reuse technologies Food-processing operations are major users of water. Expanded use of water recycling and reuse tech- nologies could reduce the quantity of water used and decrease the dis- posal of by-products of food-processin~, operations. Before these tech

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49 OPPORTUNITIES IN THE NUTRITION AND FOOD SCIENCES nologies can be widely expanded, however, the federal government must establish regulatory criteria governing their use. Before the government can do this, however, it must construct a database on the current use of these technologies. Minimum chemical and microbiological standards need to be established for water recycling and reuse. Also needed are residue and quality standards for finished products that come into contact with recycled and reused water. CONCLUDING REMARKS Food science and technology have made remarkable strides in provid- ing people with high-quality, safe, and wholesome foods. Food chemists, food microbiologists, nutritionists, and food engineers have combined their skills and applied many of the basic science advances and new methods to produce today's food supply. It is hard to believe, walking the aisles of the average supermarket with more than 70,000 items, that the formalized field of food science is just over 50 years old. It evolved about the time that technologists were discovering how to fortify foods with iodine, vita- min D, iron, and B-complex vitamins. Food science is a young, dynamic field facing many challenges. Con- sumers have always demanded an array of foods pleasing to the senses. They want food to be convenient and of a composition that enables them to more easily meet dietary guidelines. Many technologies are in place to respond quickly to consumer desires or public health needs. However, scientists must seize the newer techniques developed by molecular biolo- gists to design functional foods for health needs. Food engineers and microbiologists must work together to optimize new processing techniques to ensure the safety of foods while reducing food and packaging waste. In addition, this field must apply its most creative minds to developing the equipment and technologies that will provide us with the value-added foods we need to compete successfully in world markets. Exciting ad- vances certainly await us in the years ahead. -