Plant Proteins: The ABCs

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1 1 Plant Proteins: The ABCs Robert L. Ory Downloaded via on September 27, 2018 at 17:13:28 (UTC). See for options on how to legitimately share published articles. Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, LA What has been is what will be and there is nothing new under the sun. [Ecclesiates 1:9] Interest in seed and vegetable proteins has been growing steadily over the past two decades because of the major role plant proteins play in both human and animal diets. Animal proteins are still acknowledged to have higher nutritional value than those from plant sources but for economic, health, or religious reasons, some populations derive all of their protein from plants. In addition to this interest in new sources of protein, we have also seen a growing concern over antinutrients present in some plant foods and their effect on human health (1-3). Yet none of the plant, seed, or animal proteins we eat today are "new". They have been eaten for centuries - but in different forms. The "new" aspects include more modern ways of food preparation, better technology for measuring chemical composition, nutrients and antinutrients in foods, and a greater awareness of the health implications of food constituents. Proteins are a vital part of living muscle tissue and are one of our most important nutrients. They have been called the building blocks of nutrition because they are broken down by digestive enzymes to provide amino acids for the building and repair of tissues. Animal proteins and those from most legumes and nuts contain all of the essential amino acids but the quantities of some (e.g.: lysine, methionine) in plants are lower. To envision the worldwide consumption of proteins in a different perspective, consider the major sources eaten by humans. Of the average 69 g. protein/day consumed worldwide in 1974, 63% was derived from plants (48% from cereals, roots and tubers, and 15% from fruits, vegetables, nuts, oilseeds and pulses), 36% from animal sources (meats, fish, eggs and dairy products), and 1% from other sources (4). To achieve sufficient essential amino acids or a better amino acid balance (chemical score), plant proteins must be consumed in larger quantities or be blended with other complimentary proteins. This chapter not subject to U.S. copyright. Published 1986, American Chemical Society

2 2 PLANT PROTEINS For example, peanut protein meal, low in lysine and methionine, can be blended with such things as high methionine citrus seed meal (J>) or rice bran flour (6) to improve the chemical score. Use of less expensive plant proteins blended with complementary proteins is the logical and economical way to improve protein nutrition for those not consuming any animal protein, but this has raised questions concerning nutritional quality, presence of antinutrients, and physiological significance of such foods on human health. Major changes in life styles in the past two decades have also had an impact on eating habits; i.e.: more women work out today, life is lived at a more rapid pace, attitudes about meals prepared at home, meals eaten away from home, and members of families that eat together have changed. These changes have stimulated the introduction of many convenience foods, snack items, and interest in nutritional composition and labelling of processed foods. In addition, consumption of fresh fruits and vegetables, milk, milk products, and red meats decreased during this period while consumption of snack items and fast food service products increased. Though fast food services are still the largest segment of the food-service industry, with a 3.5% increase in real growth between 1983 and 1984 (7), a growing awareness of nutrition by consumers is showing a siigut trend back to fresh foods versus processed foods by some groups. Growth of snacks and convenience foods has, nevertheless, stimulated research on improving quality, flavor, color, texture, nutritional value and safety of these new food items. Research on plant and seed proteins has moved fast as technology improved and the literature reporting these achievements has also grown. In addition to hundreds of papers published in technical journals, there have been several recent books devoted to seed and plant proteins for human consumption. These were devoted to world protein supplies, functional and nutritional properties [8); chemistry, biochemistry and genetics of plant proteins (j), 10); or to structure, localization, evolution, biosynthesis, degradation, and improvement by breeding of seed proteins (11). Each of these provides excellent coverage of their subject matter but none focus on applications of plant proteins in traditional and new foods and on biological effects of plant proteins in the human diet. Plant foods are biologically more complex than animal food and, as noted earlier, plant proteins are nutritionally not as complete as animal proteins. Plants consist of many different tissues and structural elements that include fruits, seeds and seed hulls, nuts, roots and tubers, flowers, leaves, and stems. Some of these tissues are considered unsuitable for humans because of wide variations in nutritional value and/or inability to digest in the gastrointestinal tract and they serve as feed for animals. In contrast, animal foods are derived primarily from one tissue-muscle (plus eggs, milk and some organ meats), but far fewer species of animals serve as food sources for humans than do plant species. The chapters in this book were carefully selected to complement the existing information on plant proteins by focusing on the A, B, C's: applications in new and traditional foods, biological effects of all-vegetable protein diets on humans, and composition and chemistry of some lesser-known sources of protein

3 1. ORY Plant Proteins: The ABCs 3 that could play an important role in areas where the major seed proteins (e.g.: soy, cottonseed, peanut, sunflower, rapeseed) may not be available. Despite the wealth of information available on the biochemistry, genetics, and nutritional values of plant proteins, people eat foods that look, smell, and taste good; not because of nutritional importance. Thus, new blended plant foods or protein-supplemented snacks or food products will have to look and taste like the traditional items if they are to gain sufficient acceptance to become commercially feasible. Absolute food deficits are not the sole cause of hunger in the world since, theoretically, the billion metric tons of food grains produced worldwide contain more than enough calories to provide the minimal requirement of 2,500 calories/day for its 3.5 billion people. The big problem is the uneven distribution of these resources. Not just in poor countries but even in small regions of the rich countries pockets of malnutrition still exist. Some reasons for the poor distribution, besides transportation problems, are the use of 27-30% of the grain for animal feed and almost a fourth of the supply is lost to insects, rodents, pathogens and waste. Since most snack foods are based on cereals (wheat, corn, rice), a great deal of attention has focused on fortification/supplementation of traditional cereal-based foods. Worldwide, cereals represent the major source of calories and proteins for humans; i.e.: 52% and 47% of the world's average per capita intake of calories and protein, respectively (12). Cereal grains account for about 20% of the caloric intake~tn the U. S. but provide 55% in Mexico, 63% in India, and 67% in East Africa. Cereals provide 44% of the protein requirement in Mexico, 58% in Thailand, and 83% in the Middle East. The principal cereal of Latin America is maize (corn), in Asia it is rice, in the Middle East it is wheat, and in Africa, other grains such as sorghum. Applications and uses of high protein legume flours in fortification of fried and baked goods and other food products for both Western and traditional diets of developing countries are covered in greater detail in Chapters 2-6. To achieve the balance needed in a treatise on food proteins and to include information on another growing use of vegetable proteins, that of "meat extenders" in Western diets, Chapters 7 and 8 describe the addition of plant proteins to processed meat products and whole muscle meats. The incorporation of plant protein (primarily soybean high protein meals and isolates) met with little success in the late 1960's/early 1970's because of flavor problems in defatted flours or meals. As technology improved, off-flavors were removed by production of concentrates and isolates, so that soy protein-extended ground beef products are used extensively today in school lunch programs, in military installations, and in several commercial ground beef products, hamburger, chicken and tuna helpers. Biological effects of plant proteins on human health have attracted wide attention in the recent past because of the presence of various antinutrients such as trypsin inhibitors, hemagglutinins, and toxic principles (1). Adequate cooking and/or processing inactivates these materials and can improve the quality

4 4 PLANT PROTEINS of plant foods, but the problem of sufficient essential amino acids in the protein is not resolved solely by cooking or processing. Blending of two or more proteins is still necessary to improve the chemical score and there are some biological effects caused by the protein quality and quantity. The effects of protein on skeletal integrity in early life and trace minerals utilization by rats and humans are discussed in Chapters 9 and 10. Additional chapters describing the effects of protein-procyanidin interactions on nutritional quality (Chapter 11), the acceptability of cottonseed protein foods by Haitian children (Chapter 12), effects of protein on experimental atherosclerosis (Chapter 13), and on intake and relation to cancer incidence in Seventh Day Adventists (Chapter 14) provide additional information on biological effects related to plant protein intake. Chapters 15 and 16 describe the effects of wet and dry processing on properties of legumes for food applications. Because composition and nutritional properties of the major food legumes and oilseeds have been reported in numerous technical journals and books (listed above), the section devoted to composition and chemistry highlights lesser-known but potentially important sources of plant protein that have not received the same attention. Some of these food crops have been cultivated for many years so that they are not "new" sources. Such crops as winged bean, sweet potato, tropical seeds, fruits and leaves, yams and cucurbits are potential sources of protein in areas where they are grown. These are discussed in greater detail in the remaining five chapters. The problem of protein malnutrition is too complex to be resolved with one single approach or single food. Nontechnical factors such as supply, availability, distribution, seasonal variations, age and health status of the consumer also play a role. However, with the technological advances made in the food industry today, we can now produce food products that are more nutritious and often cheaper than the traditional foods. Cereal grains, the world's principal source of food calories, can be fortified or supplemented with various plant proteins to produce very nutritious foods that look, taste, smell, and feel like traditional foods. The purpose here is certainly not to imply that animal products are bad for us but to show that there are also good proteins in plants that should not be overlooked in this search for edible proteins. It seems ironic that man has successfully conquered space by putting men on the moon and circling the earth in space stations but still has not eradicated hunger and malnutrition on earth. Literature Cited 1. Ory, R. L. "Antinutrients and Natural Toxicants in Foods". Food and Nutrition Press, Inc., Westport, Conn., Finley, J. W.; Schwass, D. E. "Xenobiotics in Foods and Feeds". American Chemical Society, Washington, D.C., Ames, Β. N. Science 1983, 221, Dunne, C. P. J. Chem. Educ. 1984, 61, Ory, R. L.; Conkerton, E. J.; Sekul, A. A. Peanut Sci. 1978, 5, 31.

5 1. ORY Plant Proteins: The ABCs 5 6. Conkerton, Ε J.; Ory, R. L. Peanut Sci. 1983, 10, Ellis, R. F. Food Process. 1984, 45 (9), Bodwell, C. E.; Petit, L. "Plant Proteins for Human Food". Martinus Nijhoff/Dr. W. Junk Publishers, The Netherlands, Harborne, J. B.; Van Sumere, C. F. "The Chemistry and Biochemistry of Plant Proteins". Academic Press, Inc., London, Gottschalk, W.; Muller, H. P. "Seed Proteins: Biochemistry, Genetics, Nutritial Value". Martinus Nihhoff/Dr. W. Junk Publishers, The Netherlands, Daussant, J.; Mosse J.; Yaughan, J. "Seed Proteins". Academic Press, Inc., London, Austin, J. E. Cereal Foods World 1978, 23(5), 229. RECEIVED February 10, 1986