Cucurbit Seed Protein and Oil - ACS Symposium Series (ACS

20 Cucurbit Seed Protein and Oil T. J. Jacks

Downloaded by TUFTS UNIV on December 6, 2015 | http://pubs.acs.org Publication Date: June 18, 1986 | doi: 10.1021/bk-1986-0312.ch020

Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, LA 70179

Research concerning the structure, composition, and usefulness of cucurbit seeds (gourds, melons, squash, etc.) is reviewed. Cytological features are typical of those for oilseeds. Compositionally, decorticated seeds contain by weight 50% oil and 35% protein. The oil is unsaturated and edible; however, certain species contain conjuated trienoic fatty acids (drying oils). Globulins account for 70 to 90% of the protein and consist of two, four or six subunits of 54,000 daltons. Disulfide reduction of the subunit yields polypeptides of 19,000 to 37,000 daltons. Globulins are rich in arginine, aspartic and glutamic acids, and are deficient in lysine and sulfur-containing amino acids. Nutritional values of the globulin are similar to those of other oilseed globulins; supplementation with the limiting amino acids increases the values. The f i r s t general r e v i e w of the c o m p o s i t i o n and c h a r a c t e r i s t i c s of o i l and p r o t e i n from s e v e r a l s p e c i e s of c u c u r b i t seeds was p u b l i s h e d i n 1972 ( 1 ) . S i n c e t h e n , a resurgence of i n t e r e s t has developed i n the e x p l o T t a t i o n of seeds from w i l d , x e r o p h y t i c c u c u r b i t s , e s p e c i a l l y B u f f a l o gourd ( C u c u r b i t a f o e t i d i s s i m a ) , as u s e f u l , n u t r i t i o u s f o o d s t u f f components ( 2 - 4 ) . ' Reviews c o n c e r n i n g r e s u l t s of f i e l d s t u d i e s o f B u f f a l o gourd p r o d u c t i o n and a d e s c r i p t i o n of the U n i v e r s i t y of A r i z o n a ' s program to domesticate i t have a l s o appeared ( 5 , 6 ) . In a d d i t i o n , seeds of o t h e r c u c u r b i t s seem j u s t as economicFlTy and n u t r i t i o n a l l y promising. In t h i s c h a p t e r , p e r t i n e n t r e s u l t s o f r e s e a r c h on c u c u r b i t seeds w i t h regard to y i e l d , c y t o l o g i c a l s t r u c t u r e , c o m p o s i t i o n , and c h a r a c t e r i z a t i o n s and n u t r i t i o n a l a s p e c t s of o i l and p r o t e i n are summarized.

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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Yield Seed y i e l d in c u c u r b i t s is seldom i n v e s t i g a t e d because commercial p r o d u c t i o n o f the c a r b o h y d r a t e - r i c h f r u i t is the major c o n c e r n . Wide v a r i a t i o n s in s i z e s and weights o f seeds, numbers o f seeds per f r u i t and even numbers o f f r u i t s per p l a n t seems the r u l e , p a r t i c u l a r l y in w i l d p l a n t s and even w i t h i n one s p e c i e s (7). E s t i m a t i o n s from l i m i t e d o b s e r v a t i o n s o f C. f o e t i d i s s i m a , Z. d i g i t a t a and C. pal ma t a growing w i l d in d e s e r t areas i n d i c a t e t h e o r e t i c a l y i e l d s Trom 500 t o 3,000 l b o f seeds per a c r e Ç. f o e t i d i s s i m a c u l t i v a t e d in n o r t h w e s t e r n Texas y i e l d s a p p r o x i m a t e l y 700 t o 2,000 l b o f seeds per a c r e (10). C. pepo (pumpkin) produces up t o 1,200 l b per acre and an improved s e e d - c o a t l e s s l i n e y i e l d s from 1,200 t o 1,400 l b o f seed per a c r e ( £ , 11). These y i e l d s are comparable to y i e l d s o f o i l s e e d s of commerce. Cytological

Structure

C u c u r b i t seeds are exalbuminous o r l a c k i n g endosperm in the mature state. In such seeds the embryo is l a r g e in r e l a t i o n to the seed a s a w h o l e . I t f i l l s the seed a l m o s t c o m p l e t e l y and i t s body p a r t s , p a r t i c u l a r l y the c o t y l e d o n s , s t o r e the food r e s e r v e s f o r g e r m i n a t i o n . S i n c e the predominant t i s s u e o f the seed is c o t y l e d o n o u s , and s i n c e c o t y l e d o n s are l e a v e s , anatomy and h i s t o l o g y o f t y p i c a l l e a f t i s s u e s u f f i c e t o d e s c r i b e the preponderant p a r t o f the seed. Epidermal c e l l s cover the c o t y l e d o n a r y s u r f a c e f o l l o w e d by p a l i s a d e and abundant parenchyma c e l l s t h a t c o n t a i n the food r e s e r v e s . Vascular t i s s u e s are a l s o present. A c r o s s - s e c t i o n a l view o f a C. d i g i t a t a seed is shown in a scanning e l e c t r o n m i c r o g r a p h (SENfT in F i g u r e 1. The s e c t i o n was t r e a t e d w i t h hexane b e f o r e being s p u t t e r - c o a t e d (12) and is m o r p h o l o g i c a l l y i d e n t i c a l to a s i m i l a r view o f C. pepo (12). The seed c o a t comprises the somewhat t h i n o u t e r boundary o f TRe s e c t i o n and the remainder is composed o f two c o t y l e d o n s separated by the f i r s t " t r u e " l e a v e s o f the embryo. To show the i n t r a c e l l u l a r s t r u c t u r e o f a c u c u r b i t s e e d , t h i s time C. f o e t i d i s s i m a , an SEM a t higher m a g n i f i c a t i o n is given in F i g u r e 2~ W i t h i n the c e l l w a l l a r e l a r g e p a r t i c l e s o f p r o t e i n ( p r o t e i n b o d i e s ) and a c y t o p l a s m i c r e t i c u l u m in which oil-rich spherosomes were embedded. T h i s emptied spherosoma complex, a p p e a r i n g as a net-work, is p r e s e r v e d U 2 , 13) when the sample is prepared by the aqueous method o f A r n o t t ancTWebb U 2 ) . When the method g i v e n f o r F i g u r e 1 was used, the i n t r a c e l l u l a r s t r u c t u r e ( p r o t e i n bodies but no c y t o p l a s m i c r e t i c u l u m ) was s i m i l a r to t h a t o f C. f o e t i d i s s i m a shown by Tu e t a l (13). C y t o l o g i c a l f e a t u r e s o f the c o t y l e d o n s a r e shown in F i g u r e 3, which is a composite e l e c t r o n micrograph p o r t r a y i n g t y p i c a l p a r e n chyma c e l l s t h a t comprise the c o t y l e d o n a r y storage t i s s u e s of £ . f o e t i d i s s i m a , C. pepo, C. p a l ma t a , C. d i g i t a t a , and Apodanthera u n d u l a t a Π Τ ) . The bul7 o f the c y t o p l a s m c o n s i s t s o f two o r g a n e l l e s : spherosomes ( l i p i d b o d i e s ) and p r o t e i n b o d i e s ( a l e u r o n e grains). S t a r c h g r a i n s a r e a b s e n t U ) . Spherosomes a r e about 1 micron in d i a m e t e r , a r e surrounded by h a l f - u n i t membranes (15), and c o n t a i n the r e s e r v e oil o f o i l s e e d s (16). P r o t e i n bodies a r e from 5 t o 20 microns in d i a m e t e r , a r e e n c l o s e d in u n i t membranes, c o n t a i n s t o r a g e p r o t e i n (17, 18), and harbour two i n c l u s i o n s : c r y s t a l l o i d s and globoids. C r y s t a l l o i d s are c r y s t a l l i n e deposits of storage 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.


JACKS

Cucurbit Seed Protein and Oil

F i g u r e 1. Scanning e l e c t r o n micrograph of a c r o s s s e c t i o n of a dormant, h e x a n e - t r e a t e d seed of C u c u r b i t a d i g i t a t a . Note o u t e r seed c o a t s , two c o t y l e d o n s ( C ) , and c e n t r a l c l e f t t h a t c o n t a i n s f i r s t " t r u e " l e a v e s between the c o t y l e d o n s . Bar r e p r e s e n t s 1 mm.

F i g u r e 2. Scanning e l e c t r o n micrograph of a mesophyll c e l l of a dormant c o t y l e d o n of B u f f a l o gourd ( C u c u r b i t a f o e t i d i s s i m a ) . T i s s u e was f i x e d in aqueous g l u t a r a l d e h y d e , dehydrated w i t h e t h a n o l and c r i t i c a l l y p o i n t d r i e d . Note c e l l w a l l (W) and i n t r a c e l l u l a r components i n c l u d i n g p r o t e i n bodies (P) and emptied spherosomes t h a t appear as a c y t o p l a s m i c r e t i c u l u m . Bar r e p r e s e n t s 10 ym.


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F i g u r e 3. T r a n s m i s s i o n e l e c t r o n micrographs of mesophyll c e l l s of dormant c o t y l e d o n s o f : A, C u c u r b i t a f o e t i d i s s i m a ; B, C u c u r b i t a pepo; C., C u c u r b i t a pa] ma t a ; D, C u c u r b i t a d i g i t a t a ; E, Apodanthera u n d u l a t j T Note c e l l w a l l (W), p r o t e i n body ( P ) , spherosome ( S ) , g l o b o i d ( G ) , and c r y s t a l l o i d ( X ) . In each m i c r o g r a p h , the bar r e p r e s e n t s f i v e m i c r o n s . Reproduced from r e f e r e n c e 14.


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( c u c u r b i t i n ) and are g e n e r a l l y abundant and l a r g e in c u c u r b i t s (17, 18). G l o b o i d s are composed mostly of m e t a l l i c s a l t s of p h y t i c a c i d ΤΓ9, 2 0 ) . Energy d i s p e r s i v e x - r a y a n a l y s i s of C. maxima (squash) g l o b o i d s have shown t h a t , in a d d i t i o n to phosphorus due to p h y t i c a c i d , p o t a s s i u m , magnesium, and sometimes c a l c i u m are l o c a t e d in globoids (17). These c a t i o n s comprise the m e t a l l i c s a l t s of p h y t i n in the g l o b o i d ; they are a b s e n t in the p r o t e i n a c e o u s m a t r i x of the p r o t e i n body in which g l o b o i d s are embedded (17, 1 9 ) . Other i n t r a c e l l u l a r o r g a n e l l e s , such as mitocïïondria, p l a s t i d s , and endoplasmic r e t i c u l a , a l l of which are r a r e l y observed in the c y t o p l a s m of q u i e s c e n t seed c e l l s , are not apparent in q u i e s c e n t c u c u r b i t seed c o t y l e d o n s . N u c l e i , however, are p r e s e n t .


Composition As w i t h y i e l d s of seeds given above, the amount of seed c o a t per seed v a r i e s c o n s i d e r a b l y , anywhere from 18% (C. pepo) t o 60% ( L a g e n a r i a v u l g a r i s , b o t t l e gourd) (21, 2 2 ) . IndeecT, s e e d - c o a t l e s s l i n e s of C. pepo have l i t t l e or no c o a t (TT, 2 3 ) . The amounts of oil and p r o t e i n in d e c o r t i c a t e d seeds a r e somewhat l e s s v a r i e d . C a l c u l a t i o n s of e a r l i e r data from t h i r t e e n s p e c i e s show t h a t d e c o r t i c a t e d seeds c o n t a i n , by w e i g h t , 49.5 + 2.3% oil and 35.0 +^ 2.4% p r o t e i n a t 95% c o n f i d e n c e i n t e r v a l s in the~2 t e s t (U. More r e c e n t r e p o r t s ( 7 , 24-32) a r e in s u b s t a n t i a l agreement wTth these v a l u e s . Some s t u d i e s r e p o r t oil and p r o t e i n c o n t e n t s o f u n d e c o r t i c a t e d seed (whole seed) or p r o t e i n c o n t e n t of oil-free m e a l . R e c a l c u l a t i o n s to d e c o r t i c a t e d f u l l - f a t seeds f i t these r a n g e s . Oil Unsaturated f a t t y a c i d s are the preponderant f a t t y a c i d s of c u c u r b i t o i l s , and in some seeds conjugated t r i e n e comprises o n e - t h i r d of t h i s u n s a t u r a t i o n . Table I shows the f a t t y a c i d d i s t r i b u t i o n in o i l s of c u c u r b i t seeds ( ] ) . More r e c e n t d e t e r m i n a t i o n s ( 7 , £ 7 , _31» 33) a r e in c l o s e agreement w i t h these r e s u l t s . O c c a s i o n a l l y a s p e c i e s Table I.

Content of F a t t y A c i d s in C u c u r b i t O i l s *

Palmitic Edible Drying

Oils Oils

Stearic

Oleic

Linoleic

Conjugated Trienes

14.2 + 3.18.4 + 2.5 28.5 + 4.147.3 + 4.5 7.8 + 2.9 8.4 + 5.9 22.4 + 5.7 31.0 + 8.4 29.2

+ 6.7

95% c o n f i d e n c e i n t e r v a l s c a l c u l a t e d from the Ζ t e s t . Data from more than one d e t e r m i n a t i o n on a g i v e n s p e c i e s were averaged b e f o r e the means of data from a l l s p e c i e s were c a l c u l a t e d so t h a t each s p e c i e s was e v a l u a t e d , or w e i g h t e d , e q u a l l y . Reproduced from r e f e r e n c e 1.

c o n t a i n s an unusual amount of a given f a t t y a c i d , such as 49% o l e i c a c i d in s e e d - c o a t l e s s C. pepo (26) o r 78% l i n o l e i c a c i d L a g e n a r i a masacarena ( 3 4 ) . C l e a r l y , the "data show t h a t c u c u r b i t seeds are i m p o r t a n t sources of e d i b l e oil, and d i g e s t i b i l i t y s t u d i e s w i t h


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c h i c k s and r a t s s u p p o r t s t h i s ( 2 7 , 33, 3 5 ) , unless conjugated t r i e n e s are p r e s e n t . In t h a t c a s e , the oil is v a l u a b l e as a d r y i n g oil and s t u d i e s of £ . d i g i t a t a and C. palmata seed o i l s i l l u s t r a t e t h e i r u s e f u l n e s s as p r o t e c t i v e c o a t i n g s ( 8 ) . I t is of i n t e r e s t t h a t c a r o t e n o i d pigments ( x a n t h o p h y l l s ) , s t e r o l s ( s p i n a s t e r o l and c h o n d r i l l a s t e r o l ) and a t r i t e r p e n e a l c o h o l have been i d e n t i f i e d in c u c u r b i t seed oil (31 , 36, 3 7 ) . However, c u c u r b i t o i l s such as t h a t from B u f f a l o gourcT are amenable to r e f i n i n g , b l e a c h i n g and d e o d o r i z i n g ( 3 8 ) .


Protein D e c o r t i c a t e d c u c u r b i t seeds c o n t a i n by w e i g h t about 35% p r o t e i n . T r a d i t i o n a l l y , seed p r o t e i n s are c l a s s i f i e d as g l o b u l i n s and albumins a c c o r d i n g to t h e i r s o l u b i l i t y in c e r t a i n aqueous s o l v e n t s . B i o c h e m i c a l l y , o i l s e e d g l o b u l i n s are g e n e r a l l y c o n s i d e r e d s t o r a g e p r o t e i n s w h i l e albumins are b e l i e v e d to be m e t a b o l i c ( c a t a l y t i c ) proteins. Albumins have not been as thoroughly i n v e s t i g a t e d as have globulins. Albumins i s o l a t e d from C i t r u l l us v u l g a r i s (watermelon) and C. maxima are composed of 9-12 major components t h a t d i f f e r in e l e c t r o p h o r e t i c m i g r a t i o n (39-41 ) and 6-9 components in gel f i l t r a t i o n (40). Many e l e c t r o p h o r e t i c a l l y d i s t i n g u i s h a b l e p r o t e i n s comprise t h e T l b u m i n f r a c t i o n of Cucumis s a t i v u s (cucumber), which is dominated by albumins of m o l e c u l a r w e i g h t of 7000 to 9000 d a l t o n s (42). A thorough study of Cucumis s a t i v u s albumin (43) showed t h a t aïïôut o n e - f o u r t h of i t s p r o t e i n is water s o l u b l e . TRTs low m o l e c u l a r w e i g h t albumin has a s e d i m e n t a t i o n c o n s t a n t o f 2 S (Svedberg u n i t s ) in the a n a l y t i c a l u l t r a c e n t r i f u g e . I t was concluded t h a t , b e s i d e s c u c u r b i t g l o b u l i n s , a l a r g e p o r t i o n of the albumins a l s o a c t s b i o c h e m i c a l l y as storage p r o t e i n , b u t f o r s u l f u r in a d d i t i o n to n i t r o g e n s i n c e t h e i r amino a c i d c o m p o s i t i o n is s i m i l a r to t h a t o f n i t r o g e n - r i c h g l o b u l i n , y e t they c o n t a i n an e x c e p t i o n a l l y high c o n t e n t of c y s t e i n e (8.9% of the t o t a l amino a c i d s ) . C u c u r b i t seed g l o b u l i n s , which a c c o u n t f o r about 70 to 90% o f the t o t a l p r o t e i n c o n t e n t , c o n t a i n about 18% n i t r o g e n , are s o l u b l e in 10% s a l t s o l u t i o n s from which they r e a d i l y c r y s t a l l i z e upon d i l u t i o n , and are a l s o s o l u b l e in both a c i d i c and b a s i c s o l u t i o n s of low i o n i c s t r e n g t h . S i n c e the c l a s s i c a l i s o l a t i o n of c r y s t a l l i n e c u c u r b i t i n in 1892 ( 4 4 ) , many chemical and p h y s i c o c h e m i c a l s t u d i e s of c u c u r b i t i n have been c o n d u c t e d . V a r i e d r e s u l t s from d e t e r m i n a t i o n s of the m o l e c u l a r weight of the n a t i v e o l i g o m e r i c g l o b u l i n s and the number and m o l e c u l a r weights of i t s s u b u n i t s have been o b t a i n e d . In a d d i t i o n to s l i g h t n a t u r a l v a r i a t i o n s among s p e c i e s , the v a r i a b i l i t y appears due to p r e p a r a t i v e procedures as w e l l as to c o n d i t i o n s and modes of a n a l y s e s . E a r l i e r s t u d i e s of the m o l e c u l a r weight of the o l i g o m e r i c g l o b u l i n , the number of s u b u n i t s and t h e i r e l e c t r o p h o r e t i c h e t e r o g e n e i t y have been reviewed U ) . R e s u l t s p r i o r to 1972 i n d i c a t e d t h a t c u c u r b i t i n is a hexamer of about 340,000 m o l e c u l a r w e i g h t and s e d i m e n t a t i o n c o n s t a n t s in three s t a t e s of a s s o c i a t i o n d i s a s s o c i a t i o n are 3 S (monomeric s u b u n i t ) , 7 S and 12 S. At a c i d i c pH v a l u e s or high i o n i c s t r e n g t h s , c u c u r b i t i n appears homogeneous d u r i n g e l e c t r o p h o r e s i s or u l t r a c e n t r i f u g a t i o n ; however, a t n e u t r a l pH v a l u e s and low i o n i c s t r e n g t h s , the p r o t e i n c o n t a i n s up to four major components.



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A l a t e r study (45) i n d i c a t e s t h a t c u c u r b i t i n from pumpkin has a m o l e c u l a r weight o f TT2,000 d a l t o n s t h a t can be e l e c t r o p h o r e t i c a l l y s e p a r a t e d i n t o s u b u n i t s of 63,000 and 56,000 d a l t o n s . Reduction of d i s u l f i d e s produces p o l y p e p t i d e s o f 36,000 and 22,000 d a l t o n s . G l o b u l i n s from s i x c u c u r b i t s examined c h r o m a t o g r a p h i c a l l y (46) have m o l e c u l a r weights o f 220,000 to 260,000 d a l t o n s t h a t e x h i b i t p r e d o m i n a n t l y 10.4 - 11.2 S v a l u e s (about 95% o f the t h r e e g l o b u l i n fractions). C u c u r b i t i n from Cucumis s a t i v u s appears a tetramer o f 240,000 d a l t o n s composed of f o u r s u b u n i t s of 54,000 d a l t o n s ( 4 2 ) . D i s u l f i d e r e d u c t i o n produces s i x p o l y p e p t i d e s u b u n i t s r a n g i n g T r o m 37,000 t o 19,000 d a l t o n s . A more r e c e n t study of c u c u r b i t i n i s o l a t e d from s e v e r a l s p e c i e s (47) i n d i c a t e s t h a t i t is composed of o n l y 12 S (90% o f the g l o b u l i n ) and 18 S v a l u e s . By e l e c t r o p h o r e t i c a n a l y s i s and chromatography combined w i t h u l t r a c e n t r i f u g a t i o n , n a t i v e c u c u r b i t i n appears a hexamer of about 325,000 d a l t o n s (12 S f o r m ) , composed of s i x monomeric s u b u n i t s of about 54,000 d a l t o n s e a c h , and forms a dimer of 630,000 d a l t o n s (18 S f o r m ) . The l a r g e and small p o l y p e p t i d e s u b u n i t s of the monomer, prepared by r e d u c t i o n w i t h 2 - m e r c a p t o e t h a n o l , range from 33,000 to 36,000 d a l t o n s and 22,000 to 25,000 d a l t o n s , r e s p e c t i v e l y . S t u d i e s o f the secondary s t r u c t u r e of c u c u r b i t i n have shown i t s c o n f o r m a t i o n a l modes c o n s i s t o f 5% a - h e l i c a l , 32% p l e a t e d s h e e t , and 62% unordered s t r u c t u r e s ( 4 8 ) . These v a l u e s are s i m i l a r in d i s t r i b u t i o n to those o f otiïer o i l s e e d g l o b u l i n s ( 4 8 ) . The amino a c i d c o m p o s i t i o n s of t o t a l c u c u r b i t seed p r o t e i n (meal) and p u r i f i e d g l o b u l i n a r e presented in Table I I . More r e c e n t c o m p o s i t i o n a l data ( 7 , 29, 32, 4 3 , 4 5 , 46, 49-51) s i n c e those summarized e a r l i e r (T) a r e TrT s u b s t a n t i a l agreement w i t h the mean d i s t r i b u t i o n shown in T a b l e I I , which i n d i c a t e s t h a t c u c u r b i t seeds, as o i l s e e d s in g e n e r a l , are r i c h in g l u t a m i c a c i d (and g l u t a m i n e ) , a r g i n i n e , and a s p a r t i c a c i d (and a s p a r a g i n e ) . The abundance of these n i t r o g e n - r i c h amino a c i d s accounts f o r the 18% n i t r o g e n c o n t e n t of c u c u r b i t p r o t e i n . Other n o n p r o t e i n amino a c i d s have been i d e n t i f i e d in c u c u r b i t seeds ( 5 2 ) , i n c l u d i n g 3 - a m i n o - 3 - c a r b o x y p y r o l i d i n e ( c u c u r b i t i n e ) , whicTPhas a n t h e l m i n t i c a c t i v i t y ( 5 3 ) . From amino a c i d c o m p o s i t i o n s , e v a l u a t i o n s oT~~the n u t r i t i o n a l p o t e n t i a l s of c u c u r b i t meals and g l o b u l i n s can be c a l c u l a t e d a c c o r d i n g to FA0/WH0 ( 5 4 ) . The A:E r a t i o s , which a r e the amounts o f each e s s e n t i a l amino a c i d r e l a t i v e to the t o t a l amount of e s s e n t i a l amino a c i d s , a r e shown in T a b l e I I . These data i n d i c a t e t h a t , l i k e most o t h e r o i l s e e d s , c u c u r b i t seeds a r e d e f i c i e n t in l y s i n e and s u l f u r - c o n t a i n i n g amino a c i d s . However, s u l f u r - c o n t a i n i n g amino a c i d s a r e c o n s i d e r a b l y high in C i t r u l l u s c o l o c y n t h i s ( e g u s i , a n c e s t r a l watermelon) seed p r o t e i n and exceed the suggested l e v e l in FA0/WH0 r e f e r e n c e p r o t e i n ( 5 5 ) . A p r o t e i n t h a t is unduTy r i c h in the ten e s s e n t i a l amino a c i d s would n o t p r o v i d e s u f f i c i e n t n i t r o g e n f o r o t h e r m e t a b o l i c processes w i t h o u t o b l i g a t o r y c a t a b o l i s m of the e s s e n t i a l amino a c i d s . Thus, the p r o p o r t i o n of the t o t a l n i t r o g e n i n t a k e t h a t e s s e n t i a l amino a c i d s form i n d i c a t e how a given p r o t e i n f u l f i l l s n u t r i t i o n a l requirements f o r p r o t e i n s . T h i s p r o p o r t i o n , the E/T r a t i o ( 5 4 ) , i n d i c a t i v e of the amount of p r o t e i n n i t r o g e n s u p p l i e d by e s s e n t i a l amino a c i d s , is ( i n g of e s s e n t i a l amino a c i d s per g of n i t r o g e n ) 2.18 f o r c u c u r b i t meal and 2.67 f o r c u c u r b i t g l o b u l i n . The value f o r meal is s i m i l a r in magnitude to those f o r o t h e r seeds and the v a l u e



1.0

+ O.3

τ τ τ τ

+ 1.3 1.9 2.4 1.3 O.5

+ O.5 Τ O.7 Τ 1.4 τ O.4 τ O.4 τ O.4 τ O.1 τ O.1 τ 1.3 124 187 124 52 126 78 46 86 149

A/E R a t i o 25

O.2 2.5 τ O.2 5.1 τ O.2 5.9 τ O.7

1.7

1.1

O.6

+ O.3 Τ O.1 Τ O.3 Τ O.2 τ O.2 τ O.5 τ O.3 τ O.2 τ O.3 τ O.3 τ O.3

16.6 τ 9.8 τ 20.0 τ 5.1 τ

3.8 5.9 5.2

2.1

1.5 4.8 8.3 3.0 3.0 7.3 3.2 112 194 70 66 171 75 49 89 138

Globulins

4.2 4.8 4.2 2.2

Cucurbit Seed Protein and Oil - ACS Symposium Series (ACS

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