Plant Proteins - ACS Publications - American Chemical Society

18 Tropical Seeds, Legumes, Fruits, and Leaves as Sources of Protein

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Robert E. Berry U.S. Citrus and Subtropical Products Laboratory, South Atlantic Area, Agricultural Research Service, U.S. Department of Agriculture, Winter Haven, F L 33883-1909

Many tropical plants are surprisingly high potential sources of protein with some leafy plants comprising as much as 40% dry-matter as protein, some fruits ranging as high as 40% protein and some aquatic weeds containing up to 5% protein. The amino acid compositions of many of these are well balanced, while others, particularly proteins from fruits, often need amino acid supplements or combinations with other protein sources. In extraction and use of leaf proteins, certain types of lipids provide interference and must be removed prior to or during the protein extraction process. In fruits and some tubers, caloric density becomes an important factor. Often, in order to obtain the recommended dietary allowance of protein from a specific fruit source, a higher than recommended amount of calories would need to be consumed. Thus, in order to be useful dietary sources of protein, some sources must be reduced in caloric content and/or supplemented with protein concentrates. While protein and amino acid composition of some water weeds are low compared with other leaves, they are easy and very low cost to produce. In many tropical areas they grow wild and would only need to be harvested. Natural production would be sufficient for supplying very large quantities.

Mention of identification the p r o d u c t by p r o d u c t s which

a trademark o r p r o p r i e t a r y product is f o r o n l y and does not imply a warranty o r guarantee the U. S. Department of A g r i c u l t u r e o v e r o t h e r may a l s o be s u i t a b l e .

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.

of


18.

BERRY

Tropical Plants as Sources of Protein

221

H i s t o r i c a l l y , a major form o f m a l n u t r i t i o n in most p a r t s of the world has been p r o t e i n d e f i c i e n c y and t h i s has been e s p e c i a l l y p r e v a l e n t in s u b t r o p i c a l and t r o p i c a l a r e a s where 80% of the world p o p u l a t i o n w i l l r e s i d e by the end o f the next decade ( 1 ) . While legumes and l e a v e s have been c o n s i d e r e d as p o t e n t i a l p r o t e i n s o u r c e s f o r many y e a r s , o n l y r e c e n t l y have the p r o t e i n p o t e n t i a l s of l e s s o b v i o u s s o u r c e s such as t r o p i c a l f r u i t s , some unique t r o p i c a l seeds and a q u a t i c water weeds been c o n s i d e r e d . As the p r o t e i n d e f i c i e n c i e s in world d i e t s become more c r i t i c a l , i n c r e a s i n g a t t e n t i o n w i l l be g i v e n to new s o u r c e s of p r o t e i n which can be grown in t r o p i c a l and s u b t r o p i c a l a r e a s and which have not been g i v e n s i g n i f i c a n t a t t e n t i o n in the past (2^). While, in g e n e r a l , f r u i t and v e g e t a b l e s p r o v i d e o n l y about 3-4% of the d i e t a r y p r o t e i n in most c o u n t r i e s , t h i s is more than doubled in a few such as S p a i n , Peru and the P h i l i p p i n e s ( 3 ) . A r e v i e w of the o v e r a l l p r o t e i n c o n t e n t s of some t r o p i c a l p l a n t s , the crude p r o t e i n and e x t r a c t a b l e amounts in comparison w i t h average s i z e s and e d i b l e amounts o f some f r u i t s and the p o t e n t i a l p r o d u c t i o n y i e l d s o f some seeds and l e a v e s , i n d i c a t e s t h e r e is s i g n i f i c a n t p o t e n t i a l f o r a d d i t i o n a l p r o t e i n as d i e t a r y supplements in t r o p i c a l a r e a s . P a s t work on p r o t e i n e x t r a c t a b i l i t y from l e a v e s and g r a s s e s has i n d i c a t e d , w h i l e they a r e good p o t e n t i a l s o u r c e s of l e a f p r o t e i n c o n c e n t r a t e s ( L P C ) , some l i p i d components i n t e r f e r e w i t h p r o t e i n e x t r a c t a b i l i t y (h). The concept of c a l o r i c d e n s i t y of foods is of importance when c o n s i d e r i n g c e r t a i n p r o t e i n s . The U.S. Senate S e l e c t Committee on N u t r i t i o n and Human Needs recommended consumption of f r u i t s and v e g e t a b l e s s h o u l d be i n c r e a s e d , meats, f a t s and r e f i n e d s u g a r s d e c r e a s e d , and about 12-14% of the t o t a l c a l o r i c i n t a k e s h o u l d be d e r i v e d from p r o t e i n (_5). In many s t a r c h y c r o p s ( r o o t s and t u b e r s ) and f r u i t s , the sugars and s t a r c h e s so d i l u t e the p r o t e i n c o n t e n t t h a t in o r d e r to be a s i g n i f i c a n t p r o t e i n s o u r c e , too many c a l o r i e s would have t o be consumed. Thus, many foods of these k i n d s must be consumed as complements t o o t h e r d i e t a r y components h i g h e r in p r o t e i n c o n t e n t , o r the p r o t e i n from t h e s e foods must be e x t r a c t e d and c o n c e n t r a t e d . Many waterways of t r o p i c a l a r e a s a r e plagued w i t h water weeds which must c o n t i n u a l l y be removed t o keep l a k e s and streams n a v i g a b l e and they g e n e r a l l y cause a n u i s a n c e . These a q u a t i c weeds can a l s o s e r v e as p o t e n t i a l p r o t e i n s o u r c e s . Though they have the d i s a d v a n t a g e of b e i n g r e l a t i v e l y low in p r o t e i n c o n t e n t , they have the advantage of b e i n g w i d e l y a v a i l a b l e , e a s i l y grown and p r a c t i c a l l y no c o s t to produce. P r o t e i n in t r o p i c a l p l a n t s The p r o t e i n c o n t e n t o f many t r o p i c a l and s u b t r o p i c a l p l a n t s is s u r p r i s i n g l y h i g h . A study by M a r t i n and Ruberte in 1975 (6) i n c l u d e d l e a v e s of many p l a n t s which c o u l d be e a s i l y grown in t r o p i c a l a r e a s and which c o n t a i n e d about 20% o r h i g h e r p r o t e i n on a dry-weight b a s i s . In 1975, H a l l e t a l . (7) determined amino a c i d c o m p o s i t i o n s o f many of t h e s e p l a n t s by s e m i - q u a n t i t a t i v e t h i n - l a y e r chromatography. T h e i r r e s u l t s , i n d i c a t e d in T a b l e I , showed many types of t r o p i c a l p l a n t s have p r o t e i n c o n t e n t s above 20%, w i t h the h i g h e s t b e i n g the c a s t o r bean and the balsam p e a r .


PLANT PROTEINS

222


T a b l e I . P r o t e i n and F r e e Amino A c i d C o m p o s i t i o n s o f Leaves from T r o p i c a l and S u b t r o p i c a l P l a n t s [Adapted from H a l l e t a l . ( 7 ) ]

Common Name C a s t o r bean Balsam pear Cowpea Cassava Purslane Chayote Mulberry Ceylon spinach P i g e o n pea Cup panax Peperomia Banana Dwarf C o r a l tree Coffee Hibiscus Beach morning glory Poor man's orchid Indian mulberry Tamarind Bignay Baobab Mango Indian rubber

Type and Growth P r o t e i n Content (Mean %) Hii b i t P" herb 41.3 A vine 32.5 31.8 Ρ vine Ρ shrub 31.6 A herb 27.5 24.4 Ρ vine Ρ tree 23.9 Ρ vine 23.3 23.3 Ρ shrub 22.4 Ρ shrub Α herb 21.6 Ρ herbaceous tree 20.9

Free Amino Acids .165 .107 .182 .107 .243 .162 .128 .152 .081 .091 .109 .133

Ρ tree

20.4

.124

Ρ shrub Ρ shrub

19.5 17.5

.076 N.D.

Ρ herb

16.3

N.D.

Ρ tree

15.5

N.D.

Ρ tree

14.5

N.D.

Ρ Ρ Ρ Ρ

herb tree tree tree

13.0 11.4 10.8 7.5

N.D. N.D. N.D. N.D.

Ρ tree

5.9

N.D.

M i l l i e q u i v a l e n t s o f f r e e amino a c i d p e r gm o f d r y cleaves. Ρ = Perennial. ^A = A n n u a l . N.D. = Not d e t e r m i n e d .



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Cow peas, c a s s a v a and p i g e o n peas a l s o ranked h i g h and t h e s e p l a n t s a r e c u r r e n t l y used as p a r t of the s t a p l e d i e t in many tropical countries. T h e i r s t u d i e s c o n c l u d e d t h a t any l e a f c r o p w i t h h i g h p r o t e i n c o n t e n t and s i g n i f i c a n t e s s e n t i a l amino a c i d s s h o u l d be s t r o n g l y c o n s i d e r e d as a p o t e n t i a l s o u r c e f o r l e a f p r o t e i n c o n c e n t r a t e ( L P C ) . They a l s o i n d i c a t e d such c r o p s i f not a l r e a d y consumed, s h o u l d be promoted f o r consumption as supplementary f o o d s . T h e i r s t u d i e s v e r i f i e d t h a t leguminous p l a n t s such as cowpea and pigeonpea c o u l d s e r v e as good s o u r c e s o f supplementary amino a c i d s because o f the h i g h l y s i n e c o n t e n t which is commonly l i m i t i n g in many d i e t s based on c e r e a l s such as r i c e , c o r n , and wheat ( 8 ) . They a l s o recommended t h a t the n u t r i t i o n a l q u a l i t y of c a s s a v a l e a v e s ( h i g h in l y s i n e and m e t h i o n i n e ) would g r e a t l y enhance a d i e t of c a s s a v a r o o t , a s t a p l e food in the tropics. The c a s t o r bean has not been used as a p r o t e i n s o u r c e p r i m a r i l y because of a poisonous a l k a l o i d which combines w i t h the p r o t e i n r i c i n in the mature l e a v e s . They recommended s t u d i e s t o s o l v e t h i s problem through improved p r o c e s s i n g t e c h n i q u e s o r p l a n t h y b r i d i z a t i o n methods. P r o t e i n in t r o p i c a l

fruits

While f r u i t s a r e not n o r m a l l y c o n s i d e r e d p o t e n t i a l s o u r c e s of p r o t e i n , some have been found r e c e n t l y t o be s u r p r i s i n g l y h i g h in crude p r o t e i n in the e d i b l e p o r t i o n (9^, 1£, 11). As i n d i c a t e d in T a b l e I I some o f the more common f r u i t such as banana, persimmon and mango have crude p r o t e i n in the range o f 1 g o r l e s s / 1 0 0 g o f fruit flesh. However, some l e s s w i d e l y known f r u i t s such as Mamey s a p o t e , tucuma, and decne have crude p r o t e i n c o n t e n t s above 2 g/100 g and baobab-seeds c o n t a i n e d o v e r 12 g/100 g.

Table I I .

P o t e n t i a l P r o t e i n in Some T r o p i c a l

Average Fruit Weight Baobab-seedsj -pulp Decne Tucuma Mamey sapote Avocado Longan , Breadfruit Banana Persimmon Mango

(g) 114 56 714 20 800 85 6 2018 257 20 550

fFrom H a l l e t a l . ( 9 ) . °100% - % moi s t u r e . N χ 6.25.

0

b

%

%

Edible 35 68 90 19 82 57 52 80 68 60 69

Solids 90 90 30 45 34 21 19 32 24 24 15

^From O l i v e r i a From Adams

Crude Protein g/100 g of F r u i t 12.56 3.31 4.58 2.67 2.12 1.61 1.31 1.36 1.00 O.62 O.42

Fruits

3

Total Required Amino A c i d s rag/100 g Fresh F r u i t

1181 535 666 301

234 428

(10).

C



224

PLANT PROTEINS

However, O l i v e r i a (10) i n d i c a t e d the decne f r u i t c o n t a i n e d a v e r y h i g h m o i s t u r e c o n t e n t and the baobab-seeds had a v e r y h i g h f i b e r content. Thus, i t would not be p r a c t i c a l t o expect one t o consume r e l a t i v e l y l a r g e q u a n t i t i e s o f these f r u i t s in t h e f r e s h form. However, t h e r e a r e p o t e n t i a l t r e a t m e n t s by which the f i b e r c o n t e n t c o u l d be l e s s e n e d o r the moibture c o n t e n t c o u l d be reduced. On a per f r u i t b a s i s , b r e a d f r u i t , Mamey sapote and decne appeared t o be good p r o t e i n s o u r c e s because o f the r e l a t i v e l y h i g h f r u i t w e i g h t , as w e l l as the s i g n i f i c a n t crude p r o t e i n c o n t e n t . According to H a l l e t a l . ( 9 ) the tucuma was one o f the b e s t apparent s o u r c e s o f crude p r o t e i n among the t r o p i c a l f r u i t s they s t u d i e d . Because these f r u i t a r e q u i t e u n u s u a l , a b r i e f d e s c r i p t i o n seems appropriate. These a r e f r u i t from a type o f palm grown around the Amazon b a s i n in South America and s o l d in t h a t r e g i o n . They a r e u s u a l l y h a r v e s t e d from w i l d stands and the f r u i t has a heavy, s t a r c h y , semi-moist c o n s i s t e n c y and b l a n d f l a v o r . I t has been used in soups, stews, and cooked w i t h o t h e r f o o d s . While the Mamey sapote and the avocado a l s o c o n t a i n s i g n i f i c a n t crude p r o t e i n in the e d i b l e p o r t i o n s , they both c o n t a i n v e r y h i g h s t a r c h , f a t , and c a r b o h y d r a t e and t h e r e f o r e a r e h i g h in d i e t a r y calories. Thus, they would be i m p r a c t i c a l t o s e r v e as p r i m a r y protein sources. When q u a l i t y o f f r u i t p r o t e i n s , ( i n d i c a t e d by the c o n t e n t o f amino a c i d s r e q u i r e d in the human d i e t ) is c o n s i d e r e d s e v e r a l a r e s i g n i f i c a n t , as i n d i c a t e d in T a b l e I I I . T h i s l i s t s , from l e f t t o r i g h t in d e s c e n d i n g o r d e r , the amounts o f r e q u i r e d amino a c i d s in several f r u i t s , recently reported. Among the f r u i t s r e p o r t e d h e r e , the tucuma and avocado p r o v i d e a good b a l a n c e and a h i g h q u a n t i t y o f the r e q u i r e d amino a c i d s . Almost a l l f r u i t s r e p o r t e d here were r e l a t i v e l y low in the s u l f u r c o n t a i n i n g amino a c i d s , p a r t i c u l a r l y c y s t e i n e and c y s t i n e . However, d r i e d d a t e , tucuma, and Mamey s a p o t a were r e l a t i v e l y h i g h in amounts o f these amino a c i d s as w e l l . Most o f the more common f r u i t s such as peach, orange and mango were r e l a t i v e l y low in s u l f u r c o n t a i n i n g amino a c i d s , as w e l l as o t h e r r e q u i r e d amino a c i d s . As i n d i c a t e d by these s t u d i e s many f r u i t s would make e x c e l l e n t d i e t a r y supplements to improve c o n t e n t o f c e r t a i n amino a c i d s . P r o t e i n source vs p r o d u c t i o n

potential

Where a r a b l e l a n d is h i g h c o s t , h i g h v a l u e , o r in s c a r c e s u p p l y the p r o d u c t i o n p o t e n t i a l o f p r o t e i n becomes an e s p e c i a l l y important f a c t o r . F r u i t s and l e a v e s from w i l d , undomesticated p l a n t s p r o v i d e a t t r a c t i v e s o u r c e s o f p r o t e i n in the d i e t because of t h e i r n a t u r a l a c c e p t a b i l i t y by l o c a l i n h a b i t a n t s and t h e i r wide-spread a c c e s s i b i l i t y due t o n a t i v e growth. However, f o r d o m e s t i c a t e d and c o m m e r c i a l i z e d s i t u a t i o n s the p r o d u c t i o n o f p r o t e i n per u n i t a r e a o f a r a b l e l a n d is an important f a c t o r . Seeds, l e a f c r o p s , and g r a s s e s a r e v e r y e f f i c i e n t p r o t e i n p r o d u c e r s from the s t a n d p o i n t o f amount p e r u n i t a r e a . As i n d i c a t e d in T a b l e IV, the more commonly used seeds and legumes, soybeans and wheat have r e l a t i v e l y h i g h p r o t e i n p r o d u c t i o n p o t e n t i a l s (around 400 t o 800 kg/ h e c t a r e ) .



a

From FAO (20).

Amino acid Isoleucine Leucine Lysine Methionine Cysteine + Cystine Phenylalanine Tyrosine Threonine Valine Histidine Total

Table I I I .

Tucuma 125 201 135 33 28 107 145 130 153 125 1181

Avocado 72 126 106 28 4 74 50 75 109 21 666

Dried a Date 66 114 81 22 52 74 21 76 93 33 632

Mamey Sapota 46 84 84 18 18 53 55 58 77 42 535 Longan 26 54 46 13 3 30 25 34 58 12 301

Peach 13 29 30 31 9 18 21 27 40 17 235

Orange 23 22 43 12 10 30 17 12 31 12 212

Mango 20 32 28 7 4 19 11 20 29 13 182

Dietary Required Amino Acids (mg/100 g Fresh F r u i t ) in Some F r u i t s [Adapted from H a l l et a l . (9)]


226

PLANT PROTEINS T a b l e IV. P r o d u c t i o n P o t e n t i a l of P r o t e i n From Some Seeds and L e a f y V e g e t a b l e s [from B e r r y ( 2 ) ] kg P r o t e i n /ha


Seeds Soybean ( o i l s e e d ) Wheat ( c e r e a l seed) Cowpea (legume seed) Urd bean (legume seed)

510* 392

D

3 3 0

d 254

Leaves A l f a l f a (Medicago s a t i v a ) Sorghum χ sudan g r a s s h y b r i d (Sorghum s u d a n e s i s ) Transvala digitgrass ( D i g i t a r e a decumbenc) Tetrakalai (Phasedus a u r e u s ) *From From °From From

785

d

300CT, 2690 2320 f 2179

1

1760

s

Food Ind. S. A f t . ( 1 ) . ^Frorn Singh ( 2 2 ) . Stahmann ( 1 9 ) . From Sotomayor-Rios e t a l . ( 2 3 ) . FAO ( 2 0 ) . From Kohler et a l . (24). Jeswani ( 2 1 ) . g

Cow pea and urd bean, two common legumes a r e o n l y s l i g h t l y l o w e r . An e x c e l l e n t review by H. D. T i n d a l l of the leguminosae p l a n t s i n d i c a t e s most of t h e i r seeds have h i g h p r o t e i n c o n t e n t s , a r e d i r e c t l y consumable, and they a r e e a s i l y grown in t r o p i c a l and s u b t r o p i c a l climates (30). However, n e i t h e r seeds nor f r u i t can approach the e x t r e m e l y e f f i c i e n t p r o d u c t i o n of l e a f y p l a n t s and most f o r a g e g r a s s e s . A l f a l f a , one of the most commonly grown s o u r c e s , produces around 3,000 k g / h e c t a r e . C e r t a i n g r a s s e s such as the sorghum χ sudan g r a s s h y b r i d and the t r a n s v a l a d i g i t g r a s s i n d i c a t e d in T a b l e IV have r e l a t i v e l y h i g h p r o t e i n but not as h i g h as a l f a l f a . These g r a s s e s a r e some of the b e t t e r p r o s p e c t s among those surveyed a t the USDA T r o p i c a l H o r t i c u l t u r a l L a b o r a t o r y in R i o P i a d r e s , P u e r t o R i c o where many g r a s s e s , l e a f c r o p s and h y b r i d s a r e b e i n g studied. I t is n o t a b l e t h a t l e a v e s produced more crude p r o t e i n than seeds by f a c t o r s of 6 to 8 times and l e a f y v e g e t a b l e s y i e l d the h i g h e s t p r o t e i n / u n i t a r e a . As r e p o r t e d by Abbott in 1966 ( 3 ) , one a c r e of l a n d can produce in t h r e e t o f o u r months about e i g h t tons of f r e s h l e a f y v e g e t a b l e s ( g r a s s e s e s p e c i a l l y ) c o n t a i n i n g up to 350 pounds (160 kg) o f p r o t e i n . Legumes have a much lower y i e l d and in f a c t , peas and beans rank below some s t a r c h y c r o p s l i k e p o t a t o e s and c o r n in q u a n t i t i e s of p r o t e i n produced per u n i t of l a n d a r e a ( 1 2 ) . Another p o i n t to be c o n s i d e r e d is the form in which the p r o t e i n - c o n t a i n i n g food is consumed and the e f f i c i e n c y of e x t r a c t i o n o r use of the p r o t e i n in human d i e t . When t h i s is c o n s i d e r e d , most of the seed-type f o o d s , beans and legumes, have e f f i c i e n c i e s which overcome t h e i r lowered p r o d u c t i o n p o t e n t i a l . Thus, these foods can be d i r e c t l y consumed and t h i s r e s u l t s in a v e r y e f f i c i e n t use in the human body. Many g r a s s e s and


18.

BERRY

227


l e a f y - t y p e v e g e t a b l e s must be e i t h e r e x t r a c t e d and c o n c e n t r a t e d o r f e d t o a n i m a l s and p r o t e i n consumed by e a t i n g the a n i m a l . Protein can u s u a l l y be more e a s i l y e x t r a c t e d from beans and seeds than from l e a v e s . However, in an e x t e n s i v e s t u d y , M a r t i n and Ruberte (6) i n d i c a t e d t h e r e a r e many t r o p i c a l l e a v e s t h a t can be consumed d i r e c t l y and s e r v e as e x c e l l e n t s o u r c e s of e f f i c i e n t p r o t e i n in the human d i e t .


P r o t e i n in l e a f y

vegetables

As p o i n t e d out by M a r t i n and Ruberte (6) of many v e g e t a b l e s n o r m a l l y consumed such as beans, seeds, peas, and t u b e r s , the l e a v e s c o n t a i n s i g n i f i c a n t l y more p r o t e i n than the p a r t commonly consumed. They r e p o r t e d t h a t the % crude p r o t e i n in many l e a v e s ranges as h i g h as 20% in bamboo, c u r r y , and l e t t u c e t o g r e a t e r than 30% in l e a v e s from c a s s a v a , cowpea, balsam pear and pumpkin. C a s s a v a , t a r o , o k r a , soybean and p i g e o n pea a r e good examples of p r o t e i n c o n t e n t of l e a v e s b e i n g h i g h e r than t h a t of seed, pod, o r tuber. Many s t u d i e s have been r e p o r t e d on e x t r a c t a b i l i t y and c o n c e n t r a t i o n of p r o t e i n from l e a f y p l a n t s (13, 14). While i t is more e f f i c i e n t t o consume the l e a f y v e g e t a b l e o r f r u i t d i r e c t l y , c o n s i d e r a b l e q u a n t i t i e s of l e s s a v a i l a b l e p r o t e i n can be made a v a i l a b l e through e x t r a c t i o n and c o n c e n t r a t i o n i n t o LPC. As p o i n t e d out by P i r i e (13) and K o h l e r & Knuckles ( 1 4 ) , an LPC p r o c e s s i n g p l a n t c o u l d be o r i e n t e d near packinghouses f o r l e a f y v e g e t a b l e s so t h a t l e a v e s , stems, and s t a l k s trimmed from these v e g e t a b l e s b e f o r e b e i n g sent t o market, c o u l d s u b s e q u e n t l y be e x t r a c t e d f o r p r o t e i n . L e a f p r o t e i n p r o c e s s e s a r e c o v e r e d in more d e t a i l in a n o t h e r c h a p t e r . The p r o t e i n in f o u r d i f f e r e n t t r o p i c a l l e a v e s and the y i e l d o f crude and f i n a l LPC were s t u d i e d by Nagy e t a l . in 1978 ( 1 5 ) . They found t h a t the crude p r o t e i n in c a s s a v a l e a v e s and sorghum χ sudan h y b r i d g r a s s were r e l a t i v e l y h i g h ( T a b l e V) but the d r i e d y i e l d o f t r u e l e a f c o n c e n t r a t e was much h i g h e r from sauropus.

T a b l e V.

Weights and P r o t e i n Contents o f Leaves from Four T r o p i c a l P l a n t s [from Nagy e t a l . ( 4 ) ] F r e s h Wt Dry Leaves Content

T r o p i c a l Leaves Chaya Sorghum χ sudan Cassava Sauropus

g 873 1230 561 1216

g 170 180 102 281°

Crude P r o . Dry Leaves, g 41.3 18.7 18.0 83.7

a

Crude LPC Prot., g 15.1 11.1 10.2 21.4

b True LPC Prot., g 7.2 4.7 5.7 10.5

*N χ 6.25. Dried weight. C o n t a i n s woody stems.


PLANT PROTEINS


228

A problem e n c o u n t e r e d e s p e c i a l l y in the LPC from g r a s s e s and some types of l e a v e s is the i n t e r f e r e n c e of l i p i d s e x t r a c t e d w i t h the p r o t e i n c o n c e n t r a t e which were d i f f i c u l t t o s e p a r a t e . As i n d i c a t e d in T a b l e V I , a l t h o u g h the p r o t e i n from g r a s s e s is c o n s i d e r e d h i g h e s t q u a l i t y from p l a n t s , based on r e q u i r e d amino a c i d s , t h a t from o t h e r t r o p i c a l l e a v e s such as c a s s a v a , Chinese cabbage and Tamu-TEX-sci (an e x p e r i m e n t a l g r a s s h y b r i d from the U n i v e r s i t y of T e x a s ) a l l compare f a v o r a b l y . These p l a n t s a l l show a good b a l a n c e of amino a c i d s r e q u i r e d f o r humans and e s p e c i a l l y some of those such as m e t h i o n i n e which a r e u s u a l l y low in p l a n t protein. However, they a l l have a r e l a t i v e l y low l e v e l of t h r e o n i n e and the e x p e r i m e n t a l g r a s s h y b r i d is low in phenylalanine. Three of these p l a n t s , C h i n e s e cabbage, the g r a s s h y b r i d and c a s s a v a l e a v e s can be consumed d i r e c t l y as human f o o d , as w e l l as used as a source of LPC. Regarding the i n t e r f e r e n c e of l i p i d s and f a t t y a c i d s in p r e p a r a t i o n of LPC, Nagy e t a l . (15) made an e x t e n s i v e study of t h i s problem and d e t e r m i n e d , as i n d i c a t e d in T a b l e V I I , t h a t the l i p i d c o n t e n t and t o t a l l i p i d d i s t r i b u t i o n in some g r e e n p r o t e i n f r a c t i o n s is i n d e e d s i g n i f i c a n t and can p r e s e n t a problem w i t h p r o t e i n e x t r a c t a b i l i t y and p u r i f i c a t i o n . They i n d i c a t e d however, most of the l i p i d appeared t o come from e x t r a c t i o n of c e l l w a l l s and r u p t u r e d c e l l u l a r c o n t e n t s d u r i n g the m a c e r a t i o n p r o c e s s . They a l s o suggested the l i p i d s were r e l e a s e d and became e x t r a c t a b l e p r i m a r i l y through enzymatic r e a c t i o n s a f t e r m a c e r a t i o n of the l e a v e s f o r e x t r a c t i o n . Thus, they p o s t u l a t e d t h a t the time i n t e r v a l between m a c e r a t i o n of the p l a n t t i s s u e and the a p p l i c a t i o n of heat to c o a g u l a t e p r o t e i n s was c r i t i c a l . They recommended heat i n a c t i v a t i o n of enzymes and p r e c i p i t a t i o n of p r o t e i n s as q u i c k l y as p o s s i b l e a f t e r m a c e r a t i o n to m i n i m i z e t h i s interference. Role of c a l o r i c

d e n s i t y in p r o t e i n

effectiveness

A s e r i o u s problem w i t h some v e g e t a b l e s and p a r t i c u l a r l y w i t h f r u i t as a s o u r c e of p r o t e i n is the d i l u t i o n of p r o t e i n w i t h c a r b o h y d r a t e s so t h a t an i n o r d i n a t e amount of c a l o r i e s must be consumed t o o b t a i n the needed amount of p r o t e i n and amino a c i d s f o r human growth. A s u r v e y of c a l o r i e s and p r o t e i n content/100 g f r e s h weight of s e v e r a l d i f f e r e n t l e a v e s , pods, seeds and t u b e r s is shown in T a b l e V I I I . T h i s i n d i c a t e s the d e s i r a b i l i t y of c e r t a i n l e a v e s , pods and seeds o v e r t u b e r s , f o r example, as a protein source. Foods t h a t y i e l d in the range of 5-10 c a l o r i e s / g p r o t e i n s h o u l d be e x c e l l e n t d i e t a r y s o u r c e s of p r o t e i n . However, those t h a t y i e l d 50-100 o r more c a l o r i e s / g p r o t e i n s h o u l d p r o b a b l y be used more where c a l o r i e s f o r energy a r e needed and supplemented with other protein sources. In many c o u n t r i e s man has supplemented h i s d i e t w i t h p r o t e i n by the consumption of a n i m a l p r o d u c t s and meat in o r d e r t o e l i m i n a t e t h i s problem and b a l a n c e the p r o t e i n - c a l o r i c v a l u e s .


BERRY

229


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230

PLANT PROTEINS

Table VIII.

P r o t e i n and C a l o r i c V a l u e of D i f f e r e n t Types o f V e g e t a b l e s ( P e r 100 g F r e s h wt)


Protein

Adapted

from T e r r a

Cal/ Prot.

(8)

53 44 17 22 18

7.0 4.0 3.0 2.4 1.5

7.6 11.0 5.6 9.2 12.0

33 18 48

2.2 2.0 3.4

15.0 9.0 14.1

Leaves Cassava T r o p i c a l spinach Kankong Green v e g e t a b l e s (avg) Y e l l o w v e g e t a b l e s (avg) Pods and seeds Beans (pods) Asparagus bean (pods) Peas ( s e e d s ) Tubers Cassava Sweet p o t a t o Cocoyam a

g.

Calories

131 121 88

O.7 2.0 2.0

187.0 61.0 44.0

(29).

A q u a t i c weeds as s o u r c e s o f p l a n t

protein

While many types o f p l a n t s o u r c e s a r e a t t r a c t i v e as s o u r c e s o f p r o t e i n , perhaps the most a t t r a c t i v e o f a l l would be those p l a n t s which a r e a n u i s a n c e , grow w i l d r a p i d l y and whose removal would be an advantage t o mankind. Roe and Bruemmer (16) s t u d i e d t h e e x t r a c t a b l e p r o t e i n as p e r c e n t o f d r y - m a t t e r from s e v e r a l a q u a t i c weeds which had become a n u i s a n c e in F l o r i d a and o t h e r t r o p i c a l and s u b t r o p i c a l a r e a s o f t h e U.S. These and s i m i l a r v a r i e t i e s a r e a l s o wide-spread among most t r o p i c a l a r e a s o f the w o r l d . As i n d i c a t e d in T a b l e IX they found p r o t e i n c o n t e n t s r a n g i n g from .3 to 5.4 % o f t h e d r y - m a t t e r . A f u r t h e r study i n d i c a t e d a higher y i e l d o f p r o t e i n c o u l d be o b t a i n e d when d i m e t h y l s u l f o x i d e (DMS0) was used f o r e x t r a c t i o n . T h e i r s t u d i e s a l s o i n d i c a t e d , ( T a b l e X) t h a t t h e p r o t e i n from these water-weeds had a r e l a t i v e l y good b a l a n c e o f amino a c i d s , b e i n g low m a i n l y in m e t h i o n i n e . I t was a l s o observed t h a t those e x t r a c t s made w i t h DMS0, a l t h o u g h y i e l d i n g g e n e r a l l y h i g h e r amounts o f p r o t e i n and i n d i v i d u a l amino a c i d s , y i e l d e d much lower amounts o f t h e s u l f u r - c o n t a i n i n g c y s t e i n e , c y s t i n e and m e t h i o n i n e . They s p e c u l a t e d t h a t t h e DMSO p r o b a b l y decomposed t h e s u l f u r - c o n t a i n i n g amino a c i d s due t o i t s chemical a f f i n i t y f o r s u l f u r groups. They a l s o noted a lower amount o f l y s i n e in those e x t r a c t s from DMSO and, a l t h o u g h they c o u l d n o t e x p l a i n t h i s c o m p l e t e l y , i t may a l s o be due t o r e a c t i o n between t h e b a s i c amino a c i d and DMSO.


BERRY


T a b l e IX. E x t r a c t a b i l i t y o f P r o t e i n from A q u a t i c Dry

Matter (DM)


% I l l i n o i s pondweed Water h y a c i n t h Water l e t t u c e Hydrilla Cattails

13.3 10.6 6.9 7.8 27.5

Adapted from Roe and Bruemmer

231

Weeds

a

Extractable Protein % o f DM 5.4 1.8 O.9 O.6 O.3

(16).

T a b l e X. Amino A c i d C o m p o s i t i o n s o f A c i d H y d r o l y z e d P r o t e i n F r a c t i o n s from DMSO and Aqueous E x t r a c t s o f Pondweed and Water S p i n a c h

Amino A c i d Lysine Histidine Arginine Aspartie Threonine Serine Glutamic Proline Glycine Alanine Cystine (1/2) Valine Methionine Isoleucine Leucine Tyrosine Phenylalanine

Amino A c i d C o n t e n t : g/100 g Recovered Water S p i n a c h Pondweed Aqueous DMSO Aqueous DMSO 2.89 6.63 3.40 7.03 2.43 5.06 3.17 2.59 5.88 2.43 2.67 5.33 10.12 10.27 10.08 10.29 6.44 5.38 5.99 5.33 4.99 5.42 6.22 5.50 11.77 12.33 10.77 11.11 5.12 4.70 5.09 4.61 6.44 5.24 5.45 7.35 5.77 7.22 7.33 5.87 3.64 O.30 3.54 O.29 7.21 6.32 6.25 7.36 00 O.22 2.10 2.05 5.00 6.34 5.18 6.16 10.97 8.56 8.71 11.25 4.86 4.60 2.53 2.63 5.78 7.07 5.40 7.28

Adapted from Roe and Bruemmer (16) and FAO ( 1 8 ) .

Bruemmer and Roe's f i n d i n g (17) t h a t h o t DMSO c o u l d e x t r a c t 8% of t h e d r y - m a t t e r o f water s p i n a c h as p r o t e i n s h o u l d encourage a g r i c u l t u r a l i s t s and s a n i t a t i o n e n g i n e e r s i n t e r e s t e d in t h e economic a s p e c t s o f a q u a t i c p l a n t s . These a r e o f t e n grown t o c o n t r o l t h e n u t r i e n t r u n - o f f in l a k e s from a g r i c u l t u r a l l a n d s and waste-treatment p l a n t s . Water s p i n a c h grows p r o l i f i c a l l y and a c t s as a l i v i n g sponge f o r removing the water s o l u b l e n u t r i e n t s from l a k e s and s t r e a m s . C a t t a i l s , water h y a c i n t h s , water s p i n a c h and h y d r i l l a d r a s t i c a l l y lower the n i t r i t e - n i t r o g e n c o n t e n t o f water streams passed t h r o u g h t h e i r beds, o r in which beds o f t h e s e p l a n t s a r e grown. They a r e c u r r e n t l y used in f i e l d t e s t s in


232

PLANT PROTEINS

s e v e r a l waste d i s p o s a l systems as methods t o remove n u t r i e n t s from d r a i n a g e water and waste treatment streams. The d i s c o v e r y of ways to i n c r e a s e the e x t r a c t a b l e p l a n t p r o t e i n w i t h a p o t e n t i a l food o r a n i m a l f e e d use f o r these p l a n t s s h o u l d g r e a t l y enhance the economic f e a s i b i l i t y of u s i n g them t o c o n t r o l waste and excess n u t r i e n t s in water streams. The c a p a b i l i t y of such p l a n t s to c o n c e n t r a t e p o t e n t i a l l y t o x i c metals would have to be c o n s i d e r e d and c a r e f u l l y c o n t r o l l e d .


Conclusions Seeds, legumes and l e a v e s a r e among the b e s t s o u r c e s of p o t e n t i a l l o w - c o s t p r o t e i n , c o n s i d e r i n g the e f f i c i e n c y w i t h which they can be used by the human body upon d i r e c t consumption, c o u p l e d w i t h t h e i r p r o t e i n p r o d u c t i o n p o t e n t i a l per u n i t a r e a of a r a b l e l a n d . While p r o t e i n s from these s o u r c e s a r e v e r y s i m i l a r in amino a c i d c o m p o s i t i o n , a few c u l t i v a r s showed n o t a b l e v a r i a t i o n s in m e t h i o n i n e c o n t e n t and a w e l l - b a l a n c e d d i e t s h o u l d c o n t a i n p o r t i o n s of s e v e r a l of those c u l t i v a r s , perhaps mixed w i t h c e r t a i n f r u i t s as w e l l . Some l e s s e r known t r o p i c a l f r u i t s c o n t a i n s i g n i f i c a n t amounts of p r o t e i n s and almost a l l f r u i t s c o n t a i n f a i r l y w e l l - b a l a n c e d p r o t e i n s c o n s i d e r e d from the c o n t e n t of e s s e n t i a l amino a c i d s . However, in c o n s i d e r i n g f r u i t s and t u b e r s as s o u r c e s of p r o t e i n the c a l o r i c d e n s i t y o f the food must be c a r e f u l l y c o n s i d e r e d so t h a t p r o t e i n / c a l o r i e s is not too low due t o h i g h c a l o r i e c a r b o h y d r a t e s and/or l i p i d s . A q u a t i c weeds and c e r t a i n n u i s a n c e p l a n t s , w h i l e not w i d e l y c o n s i d e r e d as p r o t e i n s o u r c e s , n e v e r t h e l e s s have s i g n i f i c a n t amounts of p r o t e i n which w i t h the use of s p e c i a l i z e d e x t r a c t i o n t e c h n i q u e s such as e x t r a c t a b i l i t y w i t h DMSO, y i e l d new s o u r c e s of p r o t e i n . Although c o n t e n t s o f these p l a n t s a r e not as h i g h as those grown s p e c i f i c a l l y f o r f o o d s , they o f f e r the a d d i t i o n a l a t t r a c t i o n s of b e i n g e a s i l y grown, low c o s t to grow, widespread in a v a i l a b i l i t y and a g r e a t advantage f o r c l e a n - u p of waste-waters and streams by h a r v e s t i n g and u s i n g them as a p r a c t i c a l s o u r c e f o r l e a f p r o t e i n concentrate.

Literature Cited 1. U.N. Items 8 and 9 of the Provisional Agenda E/Conference, United Nations World Food Conference, Rome, 1974. 2. Berry, R. E. Food Technol. 1981, 35(11), 45-49. 3. Abbott, J. C. In "World Protein Resources": ADVANCES IN CHEMISTRY SERIES No. 57, American Chemical Society: Washington, D.C., 1966; p. 1-14. 4. Nagy, S.; Telek, L.; Hall, N.T.; Berry, R. E. J. Agric. Food Chem. 1978, 26(5), 1016. 5. Peterkin, Β. B. Food Technol. 1978, 32(2), 34. 6. Martin, F. W. and Ruberte, R. M. In "Edible Leaves of the Tropics"; Antillian College Press: Mayaguez, Puerto Rico, 1975. 7. Hall, N. T.; Nagy, S.; Berry, R. E. Proc. Fla. State Hortic. Soc.,1975, 88, p. 486. 8. Betscart, Α. Α.; Kinsella, J. E. J. Agric. Food Chem. 1974, 22, 116-122.



18.

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9. Hall, N. T.; Smoot, J. M.; Knight, R. J. Jr.; Nagy, S. J. Agric. Food Chem. 1980, 28, 1217. 10. Oliveria, J. F. Ecology of Food and Nutrition 1974, 3, 237. 11. Adams, C. F. "Nutritive Value of American Foods," Agricultural Handbook #456, U. S. Dept. of Agric., 1975. 12. Milner, M. J. Agric. Food Chem. 1974, 22(4), 458. 13. Pirie, N. W. Nutr. Clin. Nutr. 1975, 1, 341. 14. Kohler, G. O.; Knuckles, Β. E. "Edible proteins from leaves." Food Technology 1977, 31(5) 191. 15. Nagy, S.; Nordby, H. E.; Telek, L. J. Agric. Food Chem. 1978, 26(3) 701-706. 16. Roe, B.; Bruemmer, J. H. Proc. Fla. State Hort. Soc., 1980, 93, p. 338-340. 17. Bruemmer, J. H.; Roe, B. Proc. Fla. State Hort. Soc., 1979, 92, p. 140-143. 18. FAO, "Amino Acid Content of Foods and Biol. Data on Protein, "U.N. Food and Agriculture Organization, Rome, 1970. 19. Stahmann, M. A. Econ. Bot. 1968, 22, 73. 20. FAO, FAO Agricultural Studies, No. 55, U. N. Food and Agriculture Organization, Rome, 1961. 21. Jeswani, L. M. "Food Protein Sources"; Pirie, N. W., Ed.; Cambridge Univ. Press: Cambridge, 1975; p. 13. 22. Singh, Ν., Central Food Technological Research Institute Report, Mysore, India, 1967. 23. Sotomayor-Rios, Α.; Velez-Santiago, J.; Torres-Riveria, S.; Silva, S. J. Agric Univ. P.R.,1976, 60, 294. 24. Kohler, G. O.; Bickoff, E. M.; deFremery, D. Univ. Calif. Spec. Publ. 3058, 1976, p. 116. 25. Byers, M. "Leaf Protein: Its Agronomy, Preparation, Quality and Use"; Pirier, N. W., Ed.; Blackwell Scientific Publications: Oxford, 1971. 26. Brown, H. E.; Stein, E. R.; Saldana, G. J. Agric. Food Chem. 1975, 23, 545. 27. Otoul, E. Bull. Rech. Agron. Gembloux. 1974, 9(2), 159. 28. Bickoff, Ε. M.; Booth, A. N.; de Fremery, D.; Edwards, R. H.; Knuckles, Β. E.; Miller, R. E.; Saunders, R. M.; and Kohler, G. O. "Protein Nutritional Quality of Foods and Feeds"; Friedman, M., Ed.; Marcel Dekker; New York, 1975, p. 319. 29. Terra, G. J. A. Tropical Vegetables Comm. 54e, Ept. Agric. Res. Royal Tropical Inst., Amsterdam, Holland, 1966. 30. Tindall, H. D. In "Vegetables in the Tropics", The leguminosae; AVI Publishing Co.: Westport, Connecticut, 1983; pp. 250-321. RECEIVED December 26, 1985


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