1 Plant Proteins: The ABCs Robert L. Ory
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Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, LA 70179
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 s t i l l 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
In Plant Proteins: Applications, Biological Effects, and Chemistry; Ory, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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PLANT PROTEINS
For example, peanut p r o t e i n m e a l , low i n l y s i n e and m e t h i o n i n e , can be blended w i t h such t h i n g s as high methionine c i t r u s seed meal (J>) or r i c e bran f l o u r (6) to improve the chemical s c o r e . Use of l e s s e x p e n s i v e p l a n t p r o t e i n s blended w i t h complementary proteins i s the l o g i c a l and economical way to improve protein n u t r i t i o n f o r those not consuming any animal p r o t e i n , but t h i s has raised questions concerning nutritional quality, presence of antinutrients, and p h y s i o l o g i c a l s i g n i f i c a n c e of such foods on human h e a l t h . Major changes i n l i f e styles i n the past two decades have a l s o had an impact on e a t i n g h a b i t s ; i . e . : more women work out today, life i s l i v e d a t a more r a p i d pace, attitudes about meals prepared at home, meals eaten away from home, and members of f a m i l i e s t h a t e a t t o g e t h e r have changed. These changes have s t i m u l a t e d the i n t r o d u c t i o n of many convenience foods, snack i t e m s , and i n t e r e s t i n n u t r i t i o n a l c o m p o s i t i o n and l a b e l l i n g of processed f o o d s . In addition, consumption of fresh fruits and vegetables, m i l k , m i l k p r o d u c t s , and red meats decreased d u r i n g t h i s p e r i o d w h i l e consumption of snack items and f a s t food s e r v i c e p r o d u c t s increased. Though f a s t food s e r v i c e s are still the largest segment of the f o o d - s e r v i c e i n d u s t r y , w i t h a 3.5% i n c r e a s e i n r e a l growth between 1983 and 1984 ( 7 ) , a growing awareness of n u t r i t i o n by consumers i s showing a s i i g u t t r e n d back to f r e s h foods v e r s u s p r o c e s s e d foods by some g r o u p s . Growth of snacks and convenience foods h a s , n e v e r t h e l e s s , s t i m u l a t e d r e s e a r c h on improving q u a l i t y , f l a v o r , c o l o r , t e x t u r e , n u t r i t i o n a l value and s a f e t y of these new food i t e m s . Research on p l a n t and seed p r o t e i n s has moved f a s t as technology improved and the literature reporting these achievements has a l s o grown. In a d d i t i o n to hundreds of papers p u b l i s h e d i n t e c h n i c a l j o u r n a l s , t h e r e have been s e v e r a l r e c e n t books devoted to seed and p l a n t p r o t e i n s f o r human c o n s u m p t i o n . These were devoted to world p r o t e i n supplies, functional and n u t r i t i o n a l p r o p e r t i e s [8); c h e m i s t r y , b i o c h e m i s t r y and g e n e t i c s of plant proteins (j), 10); or to structure, localization, e v o l u t i o n , b i o s y n t h e s i s , d e g r a d a t i o n , and improvement by b r e e d i n g of seed p r o t e i n s (11). Each of these p r o v i d e s e x c e l l e n t coverage of t h e i r s u b j e c t matter but none focus on a p p l i c a t i o n s of p l a n t p r o t e i n s i n t r a d i t i o n a l and new foods and on b i o l o g i c a l e f f e c t s of p l a n t p r o t e i n s i n the human d i e t . P l a n t foods are b i o l o g i c a l l y more complex than animal food and, as noted earlier, plant p r o t e i n s are n u t r i t i o n a l l y not as complete as animal proteins. P l a n t s c o n s i s t of many d i f f e r e n t t i s s u e s and s t r u c t u r a l elements t h a t i n c l u d e f r u i t s , seeds and seed h u l l s , n u t s , r o o t s and t u b e r s , f l o w e r s , l e a v e s , and stems. Some of these t i s s u e s a r e c o n s i d e r e d u n s u i t a b l e f o r humans because of wide v a r i a t i o n s i n n u t r i t i o n a l value and/or i n a b i l i t y to d i g e s t i n the g a s t r o i n t e s t i n a l t r a c t and they s e r v e as feed f o r a n i m a l s . In c o n t r a s t , animal foods are d e r i v e d p r i m a r i l y from one t i s s u e - m u s c l e ( p l u s e g g s , m i l k and some organ m e a t s ) , but f a r fewer s p e c i e s of a n i m a l s s e r v e as food sources f o r humans than do p l a n t s p e c i e s . The chapters in this book were carefully selected to complement the e x i s t i n g i n f o r m a t i o n on p l a n t p r o t e i n s by f o c u s i n g on the A, B, C ' s : a p p l i c a t i o n s i n new and t r a d i t i o n a l foods, b i o l o g i c a l e f f e c t s of a l l - v e g e t a b l e p r o t e i n d i e t s on humans, and c o m p o s i t i o n and c h e m i s t r y of some l e s s e r - k n o w n sources of p r o t e i n
In Plant Proteins: Applications, Biological Effects, and Chemistry; Ory, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Downloaded by COLUMBIA UNIV on February 15, 2015 | http://pubs.acs.org Publication Date: June 18, 1986 | doi: 10.1021/bk-1986-0312.ch001
1.
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Plant Proteins: The ABCs
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t h a t c o u l d p l a y an i m p o r t a n t r o l e i n areas where the major seed proteins ( e . g . : s o y , c o t t o n s e e d , peanut, s u n f l o w e r , rapeseed) may not be a v a i l a b l e . D e s p i t e the w e a l t h of i n f o r m a t i o n a v a i l a b l e on the b i o c h e m i s t r y , g e n e t i c s , and n u t r i t i o n a l v a l u e s of p l a n t p r o t e i n s , people eat foods that look, smell, and t a s t e good; not because of nutritional importance. Thus, new blended plant foods or p r o t e i n - s u p p l e m e n t e d snacks or food p r o d u c t s w i l l have to look and t a s t e l i k e the t r a d i t i o n a l items i f they are t o gain s u f f i c i e n t acceptance to become commercially feasible. Absolute food d e f i c i t s are not the s o l e cause of hunger i n the w o r l d s i n c e , theoretically, the 1.088 billion metric tons of food grains produced worldwide c o n t a i n more than enough c a l o r i e s to p r o v i d e the minimal requirement of 2 , 5 0 0 c a l o r i e s / d a y f o r i t s 3 . 5 b i l l i o n people. The b i g problem i s the uneven d i s t r i b u t i o n of these resources. Not j u s t i n poor c o u n t r i e s but even i n small r e g i o n s of the r i c h c o u n t r i e s pockets of m a l n u t r i t i o n s t i l l e x i s t . Some reasons for the poor distribution, besides transportation p r o b l e m s , are the use o f 27-30% of the g r a i n f o r animal feed and almost a f o u r t h of the s u p p l y i s l o s t to insects, rodents, pathogens and w a s t e . S i n c e most snack foods are based on c e r e a l s (wheat, c o r n , r i c e ) , a g r e a t deal of a t t e n t i o n has focused on f o r t i f i c a t i o n / s u p plementation of traditional cereal-based foods. Worldwide, c e r e a l s r e p r e s e n t the major source of c a l o r i e s and p r o t e i n s f o r humans; i . e . : 52% and 47% of the w o r l d ' s average per c a p i t a i n t a k e of c a l o r i e s and p r o t e i n , r e s p e c t i v e l y ( 1 2 ) . Cereal g r a i n s account f o r about 20% of the c a l o r i c i n t a k e ~ T n the U. S. but p r o v i d e 55% i n M e x i c o , 63% i n I n d i a , and 67% i n E a s t A f r i c a . C e r e a l s p r o v i d e 44% of the p r o t e i n requirement i n M e x i c o , 58% i n T h a i l a n d , and 83% i n the M i d d l e E a s t . The p r i n c i p a l c e r e a l of L a t i n America i s maize ( c o r n ) , i n A s i a i t i s r i c e , i n the M i d d l e E a s t i t i s wheat, and i n A f r i c a , o t h e r g r a i n s such as sorghum. Applications and uses of high p r o t e i n legume f l o u r s in f o r t i f i c a t i o n of f r i e d and baked goods and o t h e r food p r o d u c t s f o r both Western and t r a d i t i o n a l d i e t s of d e v e l o p i n g c o u n t r i e s are covered i n g r e a t e r d e t a i l i n Chapters 2 - 6 . To a c h i e v e t h e b a l a n c e needed i n a t r e a t i s e on food p r o t e i n s and to i n c l u d e i n f o r m a t i o n on another growing use of vegetable proteins, t h a t of "meat extenders" i n Western diets, Chapters 7 and 8 d e s c r i b e the a d d i t i o n of p l a n t p r o t e i n s to processed meat p r o d u c t s and whole muscle meats. The incorporation of plant protein (primarily soybean h i g h p r o t e i n meals and i s o l a t e s ) met w i t h l i t t l e success i n the l a t e 1 9 6 0 ' s / e a r l y 1970's because of f l a v o r problems i n defatted f l o u r s or m e a l s . As t e c h n o l o g y i m p r o v e d , off-flavors were removed by p r o d u c t i o n of c o n c e n t r a t e s and i s o l a t e s , so t h a t soy p r o t e i n - e x t e n d e d ground beef p r o d u c t s a r e used e x t e n s i v e l y today i n school lunch programs, i n m i l i t a r y i n s t a l l a t i o n s , and i n s e v e r a l commercial ground beef p r o d u c t s , hamburger, c h i c k e n and tuna h e l p e r s . B i o l o g i c a l e f f e c t s of p l a n t p r o t e i n s on human h e a l t h have a t t r a c t e d wide a t t e n t i o n i n the r e c e n t past because of the p r e sence of various antinutrients such as trypsin inhibitors, h e m a g g l u t i n i n s , and t o x i c p r i n c i p l e s (1). Adequate cooking and/or p r o c e s s i n g i n a c t i v a t e s these m a t e r i a l s and can improve the q u a l i t y
In Plant Proteins: Applications, Biological Effects, and Chemistry; Ory, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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of p l a n t f o o d s , but the problem of s u f f i c i e n t e s s e n t i a l amino acids i n the p r o t e i n i s not r e s o l v e d s o l e l y by c o o k i n g or processing. B l e n d i n g of two or more p r o t e i n s i s s t i l l n e c e s s a r y t o improve the chemical s c o r e and t h e r e are some b i o l o g i c a l e f f e c t s caused by the p r o t e i n q u a l i t y and q u a n t i t y . The e f f e c t s of p r o t e i n on s k e l e t a l i n t e g r i t y i n e a r l y l i f e and t r a c e m i n e r a l s u t i l i z a t i o n by r a t s and humans are d i s c u s s e d i n Chapters 9 and 10. A d d i t i o n a l c h a p t e r s d e s c r i b i n g the e f f e c t s of p r o t e i n - p r o c y a n i d i n interactions on nutritional quality (Chapter 11), the a c c e p t a b i l i t y of cottonseed protein foods by H a i t i a n children (Chapter 1 2 ) , e f f e c t s of p r o t e i n on experimental atherosclerosis (Chapter 1 3 ) , and on i n t a k e and r e l a t i o n to cancer i n c i d e n c e i n Seventh Day A d v e n t i s t s (Chapter 14) p r o v i d e a d d i t i o n a l information on b i o l o g i c a l e f f e c t s r e l a t e d t o p l a n t p r o t e i n i n t a k e . Chapters 15 and 16 d e s c r i b e t h e e f f e c t s of wet and d r y p r o c e s s i n g on p r o p e r t i e s of legumes f o r food a p p l i c a t i o n s . Because c o m p o s i t i o n and n u t r i t i o n a l p r o p e r t i e s of t h e major food legumes and o i l s e e d s have been r e p o r t e d i n numerous t e c h n i c a l journals and books (listed above), the section devoted to c o m p o s i t i o n and c h e m i s t r y h i g h l i g h t s l e s s e r - k n o w n but p o t e n t i a l l y i m p o r t a n t sources of p l a n t p r o t e i n t h a t have not r e c e i v e d t h e same attention. Some of these food c r o p s have been c u l t i v a t e d f o r many y e a r s so t h a t they a r e not "new" s o u r c e s . Such c r o p s as winged bean, sweet p o t a t o , t r o p i c a l s e e d s , f r u i t s and l e a v e s , yams and c u c u r b i t s are p o t e n t i a l sources of p r o t e i n i n areas where they a r e grown. These are d i s c u s s e d i n g r e a t e r d e t a i l i n the r e m a i n i n g five chapters. The problem of p r o t e i n m a l n u t r i t i o n i s too complex t o be r e s o l v e d w i t h one s i n g l e approach or s i n g l e f o o d . Nontechnical factors such as s u p p l y , availability, distribution, seasonal v a r i a t i o n s , age and h e a l t h s t a t u s o f the consumer a l s o p l a y a role. However, w i t h the t e c h n o l o g i c a l advances made i n the food i n d u s t r y t o d a y , we can now produce food products t h a t are more n u t r i t i o u s and o f t e n cheaper than the t r a d i t i o n a l f o o d s . Cereal grains, the w o r l d ' s p r i n c i p a l source o f food c a l o r i e s , can be f o r t i f i e d o r supplemented w i t h v a r i o u s p l a n t p r o t e i n s to produce very n u t r i t i o u s foods t h a t l o o k , taste, smell, and f e e l like traditional foods. The purpose here i s c e r t a i n l y not to i m p l y t h a t animal p r o d u c t s are bad f o r us but to show t h a t t h e r e are a l s o good p r o t e i n s i n p l a n t s t h a t should not be o v e r l o o k e d i n t h i s search for edible proteins. It seems i r o n i c t h a t man has s u c c e s s f u l l y conquered space by p u t t i n g men on t h e moon and c i r c l i n g the e a r t h i n space s t a t i o n s but s t i l l has not e r a d i c a t e d hunger and m a l n u t r i t i o n on e a r t h .
Literature Cited 1. Ory, R. L. "Antinutrients and Natural Toxicants in Foods". Food and Nutrition Press, Inc., Westport, Conn., 1967. 2. Finley, J. W.; Schwass, D. E. "Xenobiotics in Foods and Feeds". American Chemical Society, Washington, D.C.,1983. 3. Ames, Β. N. Science 1983, 221, 1256. 4. Dunne, C. P. J. Chem. Educ. 1984, 61, 271. 5. Ory, R. L.; Conkerton, E. J.; Sekul, A. A. Peanut Sci. 1978, 5, 31.
In Plant Proteins: Applications, Biological Effects, and Chemistry; Ory, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
1.
ORY
Plant Proteins: The ABCs
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6. 7. 8.
Conkerton, Ε J.; Ory, R. L. Peanut Sci. 1983, 10, 56. E l l i s , R. F. Food Process. 1984, 45 (9), 34. Bodwell, C. E.; Petit, L. "Plant Proteins for Human Food". Martinus Nijhoff/Dr. W. Junk Publishers, The Netherlands, 1983. 9. Harborne, J. B.; Van Sumere, C. F. "The Chemistry and Biochemistry of Plant Proteins". Academic Press, Inc., London, 1975. 10. Gottschalk, W.; Muller, H. P. "Seed Proteins: Biochemistry, Genetics, Nutritial Value". Martinus Nihhoff/Dr. W. Junk Publishers, The Netherlands, 1983. 11. Daussant, J.; Mosse J.; Yaughan, J. "Seed Proteins". Academic Press, Inc., London, 1983. 12. Austin, J. E. Cereal Foods World 1978, 23(5), 229. RECEIVED
February 10,
1986
In Plant Proteins: Applications, Biological Effects, and Chemistry; Ory, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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