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Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
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Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
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Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
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Page 20
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
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Page 21
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 22
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 23
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 24
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 25
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 26
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 27
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 28
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 29
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 30
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 31
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 32
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 33
Suggested Citation:"Nutritionally Improved Maize." National Research Council. 1988. Quality-Protein Maize: Report of an Ad Hoc Panel of the Advisory Committee on Technology Innovation Board on Science and Technology for International Development National Research Council, in Cooperation With the Board on Agriculture National Research Co. Washington, DC: The National Academies Press. doi: 10.17226/18563.
×
Page 34

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

3 Nutritionally Improved Maize OPAQUE-2 MAIZE Not until 1963 was there much hope of boosting maize's levels of lysine, tryptophan, and available niacin. That year, three Purdue University scientists—Edwin T. Mertz, Oliver E. Nelson, Jr., and Lynn S. Bates—were searching for maize kernels (actually endosperms) high in lysine. Using the recently developed automatic amino acid analyzer, they found one mutant maize that had about twice the normal levels of lysine and tryptophan. This "new" maize produced soft, opaque kernels instead of the hard, transparent ones typical of most maize grown in the world (figure 3.1), but its composition would make it extraordinarily nutritious by comparison with normal maize. The new maize, called opaque-2,1 had the same amount of protein as conventional maize,2 but its protein contained not only twice the normal levels of lysine but elevated levels of tryptophan as well. News of this discovery came at a time when protein malnutrition and "the protein gap" were among the most discussed world problems. It energized nutritionists, plant breeders, and decision makers. In opaque-2 maize they saw, for the first time, a way to raise the nutritional quality of a vital cereal food. All around the world, maize breeders began transferring opaque-2 genes into local maize varieties, and they enthusiastically rushed the 1 It was named opaque because, when placed over a light box, its kernels appear dark; normal, vitreous maize kernels are transparent enough to allow light to pass through. It was designated "2" because it was the second mutant that researchers had discovered in the opaque group. It was sometimes known as "high-lysine" maize, a partial misnomer because it is also high in tryptophan and its nutritional benefits far exceed those provided by lysine alone. 2 Throughout this report, the protein referred to is that of the endosperm rather than that of the germ or whole kernel. The nutritional quality of the germ is roughly the same in both common maize and nutritionally improved maize. The opaque-2 gene influences only the protein of the endosperm, the major source of protein in the kernel. Early forms of opaque-2 maize had an unusually high proportion of germ because their endosperm was shriveled; current versions have plump endosperm and a proportion of germ like that in normal maize. 18

NUTRITIONALLY IMPROVED MAIZE 19 FIGURE 3.1 Opaque-2 maize (center) differed from normal maize (left) in having soft, chalky kernels rather than hard kernels. QPM (right), on the other hand, has the "normal" hardness. (J. Kinney) new crop into production. Soon, opaque-2 varieties were being mar- keted in Brazil and Colombia; vigorous research programs were under way in Eastern Europe and the Soviet Union; and opaque-2 production in the United States rose from essentially nothing in 1970 to an estimated 240,000 tons in 1975. From the beginning, feeding trials indicated that the new maize could significantly improve protein-deficiency malnutrition as well as prevent pellagra. For instance, a Colombian pediatrician, Alberto G. Pradilla, fed the new maize (under controlled metabolic observation) to seven children who were in advanced stages of malnutrition and near death. One six-year-old weighed no more than a normal two- year-old, and had skin lesions, a swollen body, no appetite, and severe diarrhea. One five-year-old was in the same state; his hair, reddened and brittle, could be plucked out by handfuls. After merely two weeks of eating opaque-2 maize, both children were improving; body swelling had subsided, diarrhea had ceased, and weight had started to increase. Within 100 days they had recovered and looked normal.3 However, as is common in plant breeding, the desirable character- istics of the new crop turned out to be closely associated with undesirable ones. The opaque-2 grain was chalky, not shiny, as is preferred in most regions. Moreover, its ears were small; its yields were 8-15 percent lower than those of traditional maize varieties; it was more susceptible to fungi and insects, both in the field and in storage; and it dried more slowly. In addition, the opaque-2 kernel Pradilla et al., 1975; Harpstead, 1971.

20 QUALITY-PROTEIN MAIZE weighed less than normal because air spaces surrounded its loosely packed starch granules. Soon came disillusionment; opaque-2 maize began losing its appeal. Hardly anybody seemed to like it. Farmers refused to grow it because of its poor field performance—even where governments provided subsidies to encourage its cultivation. Millers resisted handling it because of its poor storage characteristics—regardless of the premium price they could charge. And consumers would not buy it because of its soft, floury texture and unconventional appearance—despite its nutritional benefits. By the late 1970s, opaque-2 maize had been discredited. QUALITY-PROTEIN MAIZE Despite almost universal abandonment, research to improve opaque- 2 maize continued at the Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT), near Mexico City.4 For more than a decade, maize breeders and chemists at this international research center, which was established to improve the performance of the world's maize and wheat, tried one approach after another. Eventually, they settled on the process of combining the opaque-2 gene with genetic modifiers—genes that themselves do not express a trait, but that influence the way a major gene expresses itself. The main thrust was to use genetic modifiers to harden kernels, to make the endosperm transparent, to raise yields, and to make the grain dry faster. Over the last decade, this approach has brought about a slow but continuous improvement in the qualities that should raise its consumer acceptance, as well as in the traits that should raise its farmer acceptance. All of this had to be done without losing the nutritional value.5 The key was the development, by Evangelina Villegas, of analytical methods so sensitive that tissue could be sampled from a single kernel without damaging its ability to germinate. With this, individual kernels that showed desirable nutritional and agronomic traits could be both identified and propagated. The research has produced a new class of maize that combines the nutritional excellence of opaque-2 maize with the kernel structure of 4 A few researchers at other institutions also maintained their faith and continued opaque-2 studies (see sidebar). 5 This demanded close coordination between the plant breeders making the selections and the biochemists making the nutritional analyses and is one of the best examples of cross-disciplinary research cooperation that can be found.

NUTRITIONALLY IMPROVED MAIZE 21 FIGURE 3.2 Ears of QPM (right) are now indistinguishable from those of normal maize (left). (ICTA) conventional maize varieties (figure 3.2). CIMMYT labeled the new type "quality-protein maize" (QPM).6 The basic QPM germplasm now at CIMMYT comprises about 30 experimental populations with widely different adaptabilities, maturi- ties, and grain types. It includes both white and yellow grain types. This germplasm resource is now beginning to generate interest among researchers and industry. In 1987, for example, agronomists in 40 countries requested seed for 127 experimental trials. As a result, QPMs are in formal international trials in most parts of the world. In addition, four QPM varieties have been commercially released in the developing world: Nutricta in Guatemala, Nutri-Guarani-V241 in Par- aguay, Tuxpeno 102 in China, and Population 63 in Vietnam. Other varieties have been released in Eastern Europe. This rising enthusiasm for QPM is reminiscent of that for its predecessor, opaque-2 maize, some 20 years ago. Thus, it is important to assess carefully how QPM measures up in the qualities that led to the previous failure. 6 Despite the emphasis on hardening the endosperm, some work still continues with opaque-2 (now called soft-endosperm QPM or QPM-SE). This is because in a few regions, notably the high Andes, soft, floury maize is preferred over the hard type that is popular elsewhere.

22 QUALITY-PROTEIN MAIZE The first demonstration of the nutritional quality of opaque-2 maize came from rat-feeding studies conducted by Edwin Mertz, Oliver Nelson, and graduate student Olivia Veron in 1964. The following is Mertz's description. The first feeding test was made with about 3 kg of opaque-2 popcorn. The popcorn was ground and incorporated into a diet containing 90 percent popcorn, 5 percent corn oil, 4 percent mineral mixture, and 1 percent vitamin fortification mixture. This ration was compared with one containing the same amount of one of our best hybrids, Indiana 257. Six weanling albino rats were placed on each diet. At the end of 28 days, the average individual gain of the rats on the opaque-2 popcorn was 86 g, that of the animals on Indiana 257, 23 g, a 3.7-fold difference. In the photograph, the animals on opaque-2 popcorn are shown on the right, the control animals on the left. They are arranged in descending order according to weight. The smallest rat fed opaque-2 popcorn (bottom right) gained more than twice the amount gained by the largest rat receiving Indiana 257 (top left). The results with opaque-2 popcorn were very exciting, and we immedi- ately repeated the tests using our small supply (about 3 kg) of opaque-2 maize harvested in the fall of 1964. The diets were identical with those used with the popcorn, except that another high-quality hybrid, Indiana 453, replaced Indiana 257. The graph shows the growth curves obtained in this feeding test. In 28 days, the individual average gains on opaque-2 maize were 97 g, and on Indiana 453, 27 g, a 3.6-fold difference. 100 14 21 28 DAYS

NUTRITIONALLY IMPROVED MAIZE 23

24 QUALITY-PROTEIN MAIZE c_ CO An early demonstration of the nutritional quality of opaque-2 maize for humans came from trials in which it was fed to malnourished children in Colombia. The photographs show one child before and after the trial. The following description was reported by Francis C. Byrnes of the Rockefeller Foundation, the project's sponsor. Nine-year-old Ana Ruth did not know why her aunt had left her in the hospital. But her younger brother had died at home just two weeks before, and her aunt, already overburdened with caring for her own five children, decided to let the University of Valle's hospital worry about the little orphan girl's final care and burial. Her condition was critical. She was suffering not only from serious protein deficiency, but also from pneu- monia, which frequently occurs in victims of malnutrition. In the Metabolic

NUTRITIONALLY IMPROVED MAIZE 25 Unit, Dr. Alberto G. Pradilla and his staff took over. As they treated Ana Ruth for pneumonia, they also placed her on a minimum-level protein diet, watching carefully the sodium-potassium balance in her system so as to avoid the risk of sudden death from additional strain on the heart. Ana Ruth responded rapidly. She lost almost one kilogram of water a day for three consecutive days, and the bloating and swelling abated. Once she was on a recovery diet, her abnormal hair fell out, and her head began to sprout a fuzz promising a luxuriant growth of silky black hair. Ana Ruth is one of seven critically malnourished children restored to health at the university's hospital. She and the other six children quickly achieved a normal nutritional balance on a diet using maize as the protein source—not ordinary maize, but the newly developed quality-protein maize called "opaque-2."

26 QUALITY-PROTEIN MAIZE ce o z u E 111 110 100 - 90 - 70 — 60- " 1971 I 72 I 73 I 74 76 77 YEARS I 71 79 I 81 82 FIGURE 3.3 Grain yields of nutritionally improved maize have been rising steadily for more than a decade and are now essentially equal those of normal maize. The figure is based on international trials expressed as a percentage of normal-maize check in different years across more than 10 test locations in various parts of the world. Both types of maize were treated identically, and the normal check was usually the top- yielding commercial variety of the test location. (C1MMYT) Yield Of all the features that held back opaque-2 maize, low grain yield was the most crippling. CIMMYT's most significant advance in its 16 years of work on QPM has been to overcome this. Today, within the range of experimental error, certain QPM genotypes can equal the yields of the conventional maize varieties now under cultivation in developing countries (figure 3.3). Indeed, during the growing seasons of 1983, 1984, and 1985, several experimental QPM varieties performed better than the normal-maize checks in several regions of the world. In some cases they equal the yields of the latest experimental releases of normal maize. Some examples follow: Mexico. In Mexican experiment stations, QPM yields have been as high as 6,900 kg per hectare. Indeed, three open-pollinated QPM

NUTRITIONALLY IMPROVED MAIZE 27 OTHER PIONEERS In this report we have concentrated on CIMMYT's conversion of the soft opaque-2 maize to hard endosperm QPM. This has led to the form of nutritionally improved maize that is most likely to be released into Third World production for food use. However, a few other researchers continued studying the original opaque-2 maize. In the United States, these were notably at U.S. Agricultural Experiment Stations (at Purdue University as well as at the universities of Illinois, Kansas, and Missouri). In addition, Crow's Hybrid Corn Company of Milford, Illinois, has been working on opaque-2 maize for more than 15 years and now sells a number of hybrid varieties. Trials with them at the University of Nebraska have yielded promising results in pig rations (appendix A). Elsewhere, opaque-2 programs continued in Germany (University of Hohenheim, Stuttgart), Italy (Istituto Sperimentale Cerealicoltura, Bergamo), and Yugoslavia (Maize Research Institute, Belgrade). South Africa has conducted a particularly noteworthy effort at the Department of Agriculture in Pietermaritzburg and in 1987 released a hybrid for commercial use (chapter 8). varieties (La Posta QPM, Obregon 7740 QPM, and Tuxpeno-1 QPM) gave yields close to those of two hybrids and one open-pollinated variety, all of which are widely used commercially. In trials at more than 20 locations around the world, Mexican QPM varieties have shown yields fully comparable to those of common maize—the actual performance of seven samples were 98, 110, 107, 105, 100, 97, and 95 percent of the control (see figure 7.2). Guatemala. In Guatemala, where tests have been extensive, QPM yields have equaled or exceeded those of open-pollinated varieties of common maize in virtually every recent trial. In one, the newly released QPM (Nutricta) and the most popular normal-maize variety in Guatemala (ICTA B-l) were compared. Nutricta yielded 4,211 kg per hectare; the normal maize yielded 4,217 kg per hectare. In another, Nutricta equaled the yield of Guatemala's best experimental varieties of (open-pollinated) common maize as well as of some leading com- mercial hybrids (see figure 8.2). China. In China, the yields of one QPM variety (Tuxpeno-H.E.o2) have been as high as those of its normal-maize counterpart (Tuxpeno-1). These encouraging observations suggest that the yield limitations of opaque-2 maize have been overcome in at least some genetic back- grounds. Indeed, even if QPM may not ever be fully equal to normal maize on all sites, the overall differences already seem too small to preclude it from being commercially competitive in many locations.

28 QUALITY-PROTEIN MAIZE TJ O O O I u. 1 O S a. 50 H 40 - 30 - 20 - 10 - Soft- -Hard FIGURE 3.4 As maize breeders at CIMMYT took opaque-2 maize through nine generations they changed the preponderance of soft endosperm (clear bars) to a preponderance of hard endosperm (stippled bars). The figure shows the percent frequency of modified kernels. The ratings are based on a scale of I (completely soft) to 5 (completely hard). (Based on data in Vasal et al., 1984a) 3 a. tn S a. O u. O EC 01 m 25 -j Opaque-2 Maize 20 - 15 - 10 - 5 - 1.12 1.20-1.24 1.25-1.29 1.30-1.34 DENSITY g per cm3 FIGURE 3.5 QPM kernels now mostly have the density of normal maize (1.29), and differ greatly from the density of opaque-2 maize (1.12). The denser packing of the starch granules now makes the endosperm hard. The graph shows the frequency distribution of grain density in 31 QPM populations. (Protein Quality Laboratory, CIMMYT)

NUTRITIONALLY IMPROVED MAIZE 29 Kernel Type The conversion of opaque-2 maize into QPM has drastically changed the kernel structure. Overall, it can be said that the trait for soft, opaque, floury endosperm has, for all practical purposes, disappeared. In contrast to opaque-2 maize's chalky and dull appearance, QPM kernels are shiny and transparent like those of traditional (flint or dent) maize varieties (figures 3.1, 3.2). The density has increased as well. QPM kernels are just as hard as those of maize traditionally grown throughout most of the world. Their endosperm cells are tightly packed, there are few air spaces around the starch granules, and in any given batch there are virtually no soft kernels (figures 3.4, 3.5). As a result, kernel texture and density no longer seem to be factors restricting acceptance by farmers, millers, or consumers. Moreover, with the improved hardness, QPM can be harvested and handled by conventional machinery without the kernels being crushed or cracked. La Posta Pool 25 Pool 24 Amarillo Dentado Tuxpenb-1 Blanco Cristalino Amarillo Cristalino Tuxperfo Caribe Pool 23 Normal Version QPM Counterpart 25 30 PERCENT MOISTURE FIGURE 3.6 The moisture content of normal and QPM versions in the same genetic backgrounds is now essentially identical. These moisture levels were recorded at Poza Rica in 1977. (CIMMYT)

30 QUALITY-PROTEIN MAIZE Moisture Content Excessive moisture at the time of harvest plagued opaque-2 maize. Its kernels were generally 2-4 percent higher in moisture than were those of traditional maize. This meant that it required additional drying after harvest, and that it was more likely to become moldy. Early on, CIMMYT researchers noticed that different opaque-2 strains dried at different rates. By tagging plants that flowered (silked) at the same time and by measuring the relative rates at which these dried down at harvest time, they could select ears that dried faster than average. As a result, QPM varieties now have little of the slow-drying characteristic that limited opaque-2. Today's QPM dries at a rate comparable to that of normal maize (figure 3.6). The dry-down time no longer seems to be a barrier. 10.3 10.0 - 9 - o 8 - tr tr 7 - UJ 6 - UJ O 5.0 - DC 111 4 - Q. 3 - 2 - 1 - 8.6 9.4 Trial 1 (ELVT 19) Normal Maize • Pl\ Trial 2 (EVT15A) Trial 3 (EVT 15 B) FIGURE 3.7 The ear-rot resistance of QPM materials has been improving gradually. This results from improvement in kernel phenotype, better drying following physiological maturity, and reduced frequency of genes responsible for pericarp splitting. It also derives from population improvement involving selection for resistance under natural and artificially induced disease conditions. The figure shows ear-rot incidence of QPM compared with the best normal-check maize entries in three different trials under severe forcing conditions. On average, the QPM materials still show higher incidence of ear rots but not disastrously so, even under these worst-case conditions. (Vasal et al., 1984b)

NUTRITIONALLY IMPROVED MAIZE 31 Disease Resistance As noted, the soft, nutritious, higher moisture kernels of opaque-2 maize fostered fungal growth. In particular, the crop was more susceptible to "ear rots" than normal maize. To speed up the incorporation of mold-resistance, CIMMYT scientists created artificial infections. They cultured ear-rot fungi in the laboratory, and then injected the spores into developing maize ears. Also, they grew QPM at humid tropical locations where ear rots are naturally prevalent, even on normal maize. Under these forcing conditions particularly good progress has been made. Although ear rots still affect QPM materials more than their normal counterparts, susceptibility is decreasing generation by gen- eration (figure 3.7). In most locations, fungal infections are now usually no worse than in common maize varieties. Only in humid regions where ear rots are exceptionally severe are the differences still noticeable. Resistance to fungal disease has increased partly because QPM kernels are harder and dry more quickly than those of opaque-2. It has increased also because the influences that cause the endosperm to shrink and the seed coats to split—which opens the kernels to infections—have been reduced or eliminated. Apart from ear-rotting organisms, other maize diseases seem to attack both QPM and normal maize with comparable severity. Storage Stability The difficulty of storing opaque-2 was due mainly to insects pene- trating the soft kernels. However, the cracking and splitting of the seed coat also fostered decay, and it was particularly bad in mechan- ically harvested samples because machinery tended to damage the soft kernels. With QPM, storage damage is no worse than in common maize because the endosperm hardness is virtually the same; the excessive incidence of broken kernels and the resulting storage damage has essentially been eliminated. Nutritional Value Over the years of development, the genetic modifications have been accompanied by constant chemical monitoring. Thus, the advances have been made without losing nutritional benefits. The QPM of today retains in essence all of the the high-quality nutritional components that were in the opaque-2 maize of the 1970s (figure 3.8). As a demonstration of its nutritional quality, more than 20 mal- nourished children have been "treated" with QPM in a Guatemalan

32 QUALITY-PROTEIN MAIZE 19 - 18 - 17 - 16- 15 - 14 - z 13 - 1 12 - EC a 11 - U- O 10- ill 9 - 0 DC 8 - Ul a. 7- 6- 5 - 4- 3- 2 - 1- n LYSINE TRYPTO- PHAN LEUCINE ISOLEUCINE FIGURE 3.8 QPM has about twice the lysine and tryptophan of normal maize. It also has less of an imbalance between leucine and isoleucine. This is possibly beneficial because leucine is thought to interfere with the biosynthesis of niacin. The graph shows the average amino acid content in normal maize and QPM endosperms measured in g per 100 g of protein. (E.I. Ortega and E. Villegas, Protein Quality Laboratory, CIMMYT) hospital. In the series of tests, the physicians found it to be a flexible "cure," thanks to its acceptability and its superior biological value.7 Research in Lima, Peru, has shown that babies in their second year of life grow normally when QPM is fed as the only source of protein in the diet (see box).8 QPM's benefits result mainly from its lysine and tryptophan, but they go far beyond that. Although QPM has about the same amount of protein as common maize, it has twice the usable protein because the quality and biological value of its protein is so much higher. For example, the biological value of common-maize protein is equal to about 40 percent of the biological value of milk protein, whereas the 7 Information from A. Fuentes. 8 Information from G. Graham.

NUTRITIONALLY IMPROVED MAIZE 33 At the Instituto de Investigacion Nutricional in Lima, Peru, QPM has been fed to malnourished children with striking results. In a controlled in-patient situation, infants recovering from malnutrition were provided diets in which cow-milk "baby formula," QPM, or common maize supplied all of the protein. In one program, the diets of six infants were diluted to critical levels of intake so that protein-quality differences between QPM, common maize, and casein (the protein in milk) could be distinguished. At the low level of 6.4 percent calories as protein, apparent nitrogen absorption (the difference between the intake of nitrogen and the amount excreted in the feces) from QPM (70 ± 5 percent) and common maize (69 ± 7 percent) was much lower than from casein (82 ± 4 percent). This indicates that the amount of protein passing from the digestive tract into the bloodstream was much higher in casein than in either form of maize—a reflection of the better digestibility of the animal protein over these vegetable proteins. At the same time, however, the apparent retention of nitrogen (the difference between the amount absorbed and the amount excreted in the urine) from QPM (34 ± 4 percent) was much higher than from common maize (22 ± 10 percent). Nitrogen retention is a measure of the amount of protein retained by the body to build tissues such as muscle, liver, spleen, and brain. Therefore, these results suggest that QPM was almost 50 percent more effective than common maize at fostering growth in these malnourished children. Breath hydrogen excretions were much lower in children consuming QPM than in those consuming common maize. Because breath hydrogen conies from carbohydrate fermentation in the large intestine, the differ- ences reflect the amounts of carbohydrate passing undigested through the small intestine. The lower level of breath hydrogen from QPM diets indicates that its carbohydrate is far more digestible than is that of common maize. In a second program, the diets of eight similar infants were formulated at a level where 90 percent of the calories were provided by maize and were fed for three months. It was found that QPM could be the only source of protein and fat with just enough added sugar to make up the necessary remaining calories.1 This diet supported growth rates statistically indistinguishable from those provided by milk formula. In combination, these results confirm in real-life conditions that the level of utilization of both protein and carbohydrate is considerably greater in QPM than in common maize. George Graham Jorge Lembcke Enrique Lancho Enrique Morales 1 In these diets, protein provided 9 percent of calories; fat, 10 percent of calories; and carbohydrate (fiber, starch, and simple sugars), 81 percent of calories. Commercial infant formulas are similar to this, containing 9 percent calories as protein; human breast milk contains 6-7 percent calories as protein.

34 QUALITY-PROTEIN MAIZE biological value of QPM protein is about 90 percent of that of milk protein.9 Thus, QPM's nutritional benefits approach those of milk protein, a common standard of nutritional excellence. Whether QPM will benefit victims of pellagra is not certain, but it does seem likely because of its elevated levels of tryptophan, the biological precursor of niacin. Also, there are indications that the yellow-kernel types of QPM may prove unusually valuable in helping to overcome xerophthalmia, a vitamin A deficiency that is the primary cause of childhood blindness in many developing countries. Processed Foods CIMMYT and others have recently studied food products made with QPM. Tortillas, breads, biscuits, and cakes have been prepared with good results both in acceptance and nutritional value. Visiting scientists and trainees have prepared typical nshima and munkoyo products of Africa, with equally good results. And a large food company in Mexico City has tested quality snack foods using QPM maize. In all cases, the QPM had normal functional properties and yielded products with normal characteristics. In the United States, similar tests have been made. In trials at Texas A & M University, corn chips and tortillas made with QPM were found to be normal in physical and commercial characteristics. Their superior protein quality was clearly established by chemical analyses and bioassays (see chapter 6 and appendix A).10 9Bressaniet al., 1969a. 10 Sproule et al., 1988.

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