Structural and Compositional Changes During Processing of Dry Beans

Chapter 10

Structural and Compositional Changes During Processing of Dry Beans (Phaseolus vulgaris)

Downloaded by MONASH UNIV on November 27, 2015 | http://pubs.acs.org Publication Date: September 7, 1989 | doi: 10.1021/bk-1989-0405.ch010

Mark A. Uebersax and Songyos Ruengsakulrach Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824

Improved utilization of dry beans can be maximized through an understanding of how p h y s i c a l and chemical components f u n c t i o n and react under given process conditions. Variability i n the physico-chemical composition of dry beans occurs among c u l t i v a r s , geographic l o c a t i o n s , crop seasons, and growing & harvesting conditions (1 and 2). Undesirable chemical changes a l s o occur during adverse storage c o n d i t i o n r e s u l t i n g i n poor q u a l i t y such as bin burn, h a r d - s h e l l and hard-to-cook d e f e c t s . In general, dry beans are cooked, f r i e d , or baked to be used i n soups, eaten as a vegetable, or combined with other protein foods to make a main d i s h . Commercially, they are t y p i c a l l y processed i n cans to y i e l d a number of bean-based foods. Research and q u a l i t y c o n t r o l programs are d i r e c t e d to provide a consistent product possessing c h a r a c t e r i s t i c s of good flavor, bright color, attractive appearance, firm texture and high n u t r i t i o n a l quality. The p h y s i c a l and chemical properties of dry beans are primary f a c t o r s i n determining subsequent f i n a l product q u a l i t y . Dry bean seed structure i s comprised of a seed coat and an embryonic cotyledon. S t r u c t u r a l l y , seed coat, c e l l walls, middle lamella and other c e l l u l a r membranes g r e a t l y influence performance. Further, chemical components (carbohydrates, p r o t e i n s , phytate, polyphenols and lignin) d i r e c t l y influence q u a l i t y . The seed coat i s the outermost t i s s u e layer which p r o t e c t s the embryonic s t r u c t u r e and c o n s i s t s of approximately 7-8 % of the t o t a l dry weight i n the mature bean with a protein content of 5% (db) (3 and 4). Two e x t e r n a l anatomical features include the hilum and micropyle which each have a r o l e i n water absorption. The major components in the seed coat structure include a waxy c u t i c l e layer, palisade c e l l layer, hourglass c e l l s and t h i c k c e l l - w a l l e d parenchyma cells. The c u t i c l e i s the outermost p o r t i o n of the seed coat and its 0097-6156/89/0405-0111$06.00/0 o 1989 American Chemical Society

In Quality Factors of Fruits and Vegetables; Jen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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QUALITY FACTORS OF FRUITS AND VEGETABLES

hydrophobic p r o p e r t y r e t a r d s water p e n e t r a t i o n though does allow permeation o f some p o l a r and n o n - p o l a r compounds. S e f a - D e d e h a n d S t a n l e y ( 5 ) , d e m o n s t r a t e d s e e d c o a t t h i c k n e s s , s e e d volume, a n d h i l u m s i z e a l o n g w i t h p r o t e i n c o n t e n t were a l l f a c t o r s i n r e g u l a t i n g water uptake. The c o t y l e d o n ( a p p r o x . 92 % w/w) contributes a valuable component t o the functional (appearance, t e x t u r e , f l a v o r , e t c . ) and n u t r i t i v e v a l u e o f t h e bean. Parenchyma cells make up t h e m a j o r p o r t i o n of the c o t y l e d o n which a r e bound by a d i s t i n c t c e l l w a l l and m i d d l e l a m e l l a w i t h few v a s c u l a r b u n d l e s ( F i g u r e 1 a) . The c e l l w a l l s a r e c o m p r i s e d o f an o r g a n i z e d p h a s e o f c e l l u l o s e m i c r o f i b r i l s surrounded by a continuous m a t r i x of h e m i c e l l u l o s e , p e c t i c p o l y s a c c h a r i d e s , h y d r o x y p r o l i n e r i c h g l y c o p r o t e i n , and l i g n i n . These c e l l w a l l s f u n c t i o n to g i v e r i g i d i t y t o t h e c o t y l e d o n t i s s u e . The m i d d l e l a m e l l a i s composed p r i m a r i l y o f p e c t i c s u b s t a n c e s w h i c h provide adhesion t o adjacent c e l l s resulting i n the i n t e g r i t y o f t o t a l t i s s u e . In a d d i t i o n , p e c t i c substances also allow divalent cation cross-linking and thus, forming intercellular polyelectrolyte gels which s i g n i f i c a n t l y c o n t r i b u t e t o t h e t e x t u r a l q u a l i t y (6,7 and 8 ) . The c e l l w a l l p o l y s a c c h a r i d e s c o n t r i b u t e an i m p o r t a n t source of crude fiber (3.4-7.2%); however, the s i g n i f i c a n t p r o p o r t i o n o f the crude f i b e r (80-93%) i s l o c a l i z e d i n t h e s e e d c o a t (9 a n d 1 0 ) .

Bean

Preparation

and Process

Conditions

P r e p a r a t i o n o f d r y beans i n v o l v e s preliminary h y d r a t i o n f o l l o w e d by v a r i o u s h e a t t r e a t m e n t s t o o b t a i n a tender, palatable product. Water and h e a t p l a y an important r o l e i n c h e m i c a l r e a c t i o n s , heat t r a n s f e r and c h e m i c a l t r a n s f o r m a t i o n s , such as p r o t e i n d e n a t u r a t i o n a n d s t a r c h g e l a t i n i z a t i o n . I n a d e q u a t e w a t e r u p t a k e may result in insufficient heat t r a n s f e r to inactivate antinutritional factors and result in reduced c o o k a b i l i t y . I n g e n e r a l , b e a n s w i t h an i n i t i a l m o i s t u r e c o n t e n t b e t w e e n 12 a n d 18%, a r e s o a k e d t o h y d r a t e t h e s e e d t o a m o i s t u r e c o n t e n t o f 53 t o 57% a n d s u b s e q u e n t l y b l a n c h e d , c o o k e d o r c a n n e d . T h i s c o o k i n g s t e p , i f done f o r an o p t i m a l t i m e , r e n d e r s t h e s e e d n o n t o x i c , i m p r o v e s d i g e s t i b i l i t y , d e v e l o p s a c c e p t a b l e f l a v o r and s o f t e n s t h e seed coat and c o t y l e d o n . Processing environmental factors, such as t e m p e r a t u r e , pH, i o n i c s t r e n g t h , a n d t h e p r e s e n c e o f s e l e c t e d f o o d c o n s t i t u e n t s (product sauce f o r m u l a t i o n s ) i n f l u e n c e t h e predominate r e a c t i o n s which a f f e c t bean quality and performance. P r o c e s s m e d i a pH p l a y s a n important r o l e i n determining i o n i c c h a r g e on m a j o r c o n s t i t u e n t s , p a r t i c u l a r l y s t a r c h and p r o t e i n . Changing pH w i l l r e s u l t i n c h a n g i n g i o n i c p r o p e r t i e s o f t h e s e constituents and ultimately influence their f u n c t i o n a l i t i e s . S t a r c h g r a n u l e h y d r a t i o n and g e l a t i o n


UEBERSAX & RUENGSAKULRACH

Processing ofDry Beans


10.

F i g u r e 1. S t r u c t u r a l c h a n g e s o f n a v y b e a n s a t v a r i o u s stages o f p r o c e s s i n g : l a , d r y bean; l b , s o a k e d / b l a n c h e d bean; l c , canned bean (scanning electron photographs: S = starch granule; Ρ = protein bodies; M = middle lamella)


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properties a r e pH dependent due to changes in i n t r a g r a n u l a r bonding f o r c e s and t h e v a r i a b l e degree o f hydrolysis of the native starch molecule. S i m i l a r l y , f u n c t i o n a l p r o p e r t i e s o f p r o t e i n s v a r y w i t h changes i n pH due to the d i f f e r e n t i a l i o n i z a t i o n . Thus, t h e water absorption and t h e water h o l d i n g p r o p e r t i e s o f cooked b e a n s a r e v e r y much i n f l u e n c e d by pH o f t h e s o a k i n g a n d f i n a l c a n n i n g o r c o o k i n g media. S e l e c t e d r e s u l t s o f an e x p e r i m e n t u s i n g citrate b u f f e r a s a soak a n d p r o c e s s media r a n g i n g f r o m pH 3 t o 7 a r e p r e s e n t e d i n F i g u r e 2. The f i n a l e q u i l i b r a t e d pH o f t h e c a n n e d beans d e m o n s t r a t e a n a t i v e b u f f e r i n g c a p a c i t y effect o f t h e bean. Soaking and b l a n c h i n g weights i n c r e a s e d w i t h i n c r e a s e pH; however, t h e f i n a l drained w e i g h t d e c r e a s e d w i t h i n c r e a s e d pH. T h e s e r e s u l t s were a t t r i b u t e d t o i n c r e a s e d bean clumping and s p l i t t i n g r e s u l t i n g a greater s o l i d l o s s t o the canning brine with i n c r e a s e d pH. W i t h i n t h i s r a n g e o f t h e pH, b e a n t e x t u r e ( c o m p r e s s i o n and s h e a r ) was s o f t e s t a t pH r a n g e 4-5. T h i s curvilinear t e x t u r a l r e l a t i o n s h i p i s c o m p l e x due t o competitive i n t e r a c t i o n s and i o n i z a t i o n s t a t e s o f bean macromolecular constituents (starch, protein and s t r u c t u r a l p o l y s a c c h a r i d e s ) under t h e t e s t e d c o n d i t i o n s . Further, i n c r e a s e d pH p r o d u c e d a d a r k e r c o l o r p r o d u c t (decreased Hunter L, a L a n d b L v a l u e s ) and though untested, t h e s e d a t a a r e g e n e r a l l y c o n s i s t e n t w i t h pH influence a t t r i b u t e d t o M a i l l a r d Browning reaction p r o d u c t s (Uebersax, M.A. a n d R u e n g s a k u l r a c h , S., M i c h i g a n State U n i v e r s i t y , unpublished data).

Structural

Changes

Thermal p r o c e s s i n g induces t h e l a r g e s t a l t e r a t i o n i n structure and t h e i n i t i a t i o n of diverse chemical r e a c t i o n s among b e a n c o n s t i t u e n t s . The s c a n n i n g e l e c t r o n microscope (SEM) p h o t o g r a p h o f s o a k e d / b l a n c h e d b e a n s (Figure lb) i l l u s t r a t e s the increase i n s o l u b i l i t y o f p r o t e i n ( l o s s o f i n d i g e n o u s s p h e r i c a l s t r u c t u r e ) and t h e relatively unchanged starch granules. During the s o a k / b l a n c h t r e a t m e n t , n a t i v e p r o t o p e c t i n may a l s o f o r m p e c t i n which w i l l r a p i d l y p o l y m e r i z e . S o l u b l e p r o t e i n and p e c t i n may l e a c h c a u s i n g increased viscosity of the c o o k i n g media. I t has been p r o p o s e d t h a t t h e d i f f e r e n c e s i n p e c t i n c o m p o s i t i o n c o u l d be a m a j o r f a c t o r d e t e r m i n i n g c o o k a b i l i t y o f d r y b e a n s (11) . S o a k e d / b l a n c h e d b e a n s a r e s u b j e c t e d t o f u r t h e r h e a t i n g under p r e s s u r e d u r i n g r e t o r t processing (Figure 1 c ) . The a b s o r b e d w a t e r a n d h e a t i n g i n i t i a t e t h e r m a l d e g r a d a t i o n o r i n t e r / i n t r a - c e l l u l a r and c o h e s i v e m a t e r i a l s (middle l a m e l l a ) and t h u s a l l o w s c e l l s t o s e p a r a t e a n d s o f t e n (12 a n d 1 3 ) . R e s u l t s d e m o n s t r a t e d t h a t i n d r y a n d s o a k e d / b l a n c h e d (30 m i n u t e s a t 2 1 ° C + 30 m i n u t e s a t 88°C) b e a n s , f r a c t u r e o c c u r s a c r o s s t h e c e l l w a l l ; however, i n t h e c a n n e d b e a n f r a c t u r e o c c u r s i n t h e m i d d l e l a m e l l a , l e a v i n g t h e c e l l i n t a c t ( F i g u r e 1 a, b



10. UEBERSAX & RUENGSAKULRACH


115

and c ) . T h i s c e l l s e p a r a t i o n may a c c o u n t f o r t h e notable texture differences exhibited. Various significant chemical changes have been i n d u c e d w i t h i n the cell inclusions during heating. Protein bodies lose their normal spherical structure due t o s w e l l i n g a n d denaturation (14) . S t a r c h granules demonstrate t h e deformation, expansion and l o s s of birefringence a s s o c i a t e d with g e l a t i n i z a t i o n , although the presence o f i n t a c t c e l l w a l l s impede c o n f o r m a t i o n a l changes (15) . Hahn e t a l . (15) r e p o r t e d t h a t t h e r a n g e o f i n t r a c e l l u l a r s t a r c h g e l a t i n i z a t i o n i n s o a k e d b e a n s t o be f r o m 7 6°C t o over 95°C. Intracellular starch g e l a t i n i z a t i o n and protein denaturation occurs during moist heating which d e v e l o p s a u n i f o r m smooth t e x t u r e . C h a r a c t e r i s t i c c o o k e d bean flavor develops through the degradation or i n t e r a c t i o n o f n a t i v e t i s s u e c o n s t i t u e n t s mediated by Maillard reaction.

Compositional

Changes

Carbohydrates Starch functional properties i n f l u e n c i n g process y i e l d and product t e x t u r e include swelling, solubility, g e l a t i n i z a t i o n temperature and p a s t i n g c h a r a c t e r i s t i c s . I n - v i t r o , s e v e r a l changes o c c u r upon h e a t i n g a s t a r c h - w a t e r s y s t e m , i n c l u d i n g e x t e n s i v e swelling, increase i n viscosity, translucency, s o l u b i l i t y , and l o s s o f b i r e f r i n g e n c e . Reddy e t a l . ( 1 6 ) s u g g e s t e d t h a t t h e s w e l l i n g a b i l i t y a n d s o l u b i l i t y depend on starch source, temperature a n d pH. Most legume s t a r c h e s e x h i b i t a r e s t r i c t e d s w e l l i n g and b e a n s t a r c h e s have a h i g h i n i t i a l g e l a t i n i z a t i o n t e m p e r a t u r e . B r a b e n d e r viscosity patterns show restricted swelling c h a r a c t e r i s t i c s s i m i l a r t o t h o s e shown b y c h e m i c a l l y cross-linked starches (17 a n d 18) . A c c o r d i n g t o S c h o c h and M a y w a l d ( 1 9 ) , t h e s e r e s t r i c t e d s w e l l i n g p a s t e s a r e c l a s s i f i e d a s Type C s t a r c h e s w h i c h show no p a s t i n g peak, w i t h h i g h v i s c o s i t y which remains constant o r i n c r e a s e s during cooking. E l b e r t and W i t t (20) s t u d i e d t h e c o u r s e o f s t a r c h g e l a t i n i z a t i o n f r o m Phaseolus vulgaris before and a f t e r c o o k i n g i n w a t e r . T h e y f o u n d t h a t a n i n i t i a l l o w e r m o i s t u r e c o n t e n t was f o u n d t o b e a s s o c i a t e d w i t h a lower tendency f o r t h e s t a r c h t o g e l a t i n i z e i n s i t u . F a c t o r s w h i c h i n f l u e n c e t h i s p r o p e r t y may i n c l u d e t h e s i z e and shape o f the s t a r c h g r a n u l e s , t h e i o n i c c h a r g e on t h e s t a r c h , t h e k i n d a n d d e g r e e o f c r y s t a l l i n i t y w i t h i n the granules, the presence o r absence o f f a t and p r o t e i n , and perhaps, t h e molecular s i z e and degree o f b r a n c h i n g o f the s t a r c h f r a c t i o n s (19). V a r r i a n o - M a r s t o n a n d de Omana (21) o b s e r v e d t h a t many g r a n u l e s i n b l a c k b e a n s t a r c h e x h i b i t some b i r e f r i n g e n c e , even after prolonged cooking, i n d i c a t i n g incomplete g e l a t i n i z a t i o n . Such i n c o m p l e t e g e l a t i n i z a t i o n o f s t a r c h g r a n u l e s i n s e e d l e g u m e s may b e d u e t o t h e b a r r i e r i m p o s e d b y c e l l u l a r s t r u c t u r e s such as c e l l w a l l s and p r o t e i n and/or t h e



116


inherent structural characteristics of the starch g r a n u l e s . M o s t b e a n s t a r c h e s show some t e n d e n c y to r e t r o g r a d e d u r i n g c o o l i n g a n d have r e l a t i v e l y c o n s t a n t c o l d - p a s t e v i s c o s i t y d u r i n g a h o l d i n g p e r i o d a t 50°C. R e t r o g r a d e d s t a r c h p r e s e n t i n f i n a l canned bean p r o d u c t s may c o n t r i b u t e t o t h e i r r e l a t i v e l y low d i g e s t i b i l i t y . Although, total sugars (monosaccharides and oligosaccharides) represent only a small percentage of the total carbohydrate, these reducing sugars can participate i n non-enzymatic browning r e a c t i o n s and c o n t r i b u t e t o f l a v o r f o r m a t i o n ( 2 2 ) . Among t h e s u g a r s , oligosaccharides of the raffinose family (raffinose, s t a c h y o s e , v e r b a s c o s e , a n d a j u g o s e ) p r e d o m i n a t e i n most legumes and account f o r 31,1% t o 76.0% o f t h e t o t a l sugars ( 2 3 - 2 9 ) . The s u g a r c o n t e n t o f s o a k e d b e a n s i s a f u n c t i o n o f soaking time (30), but not t h e bean-to-water ratio. The s u c r o s e , r a f f i n o s e , a n d s t a c h y o s e c o n t e n t o f d r y beans d e c r e a s e d a p p r o x i m a t e l y 20%, 35%, a n d 45%, r e s p e c t i v e l y a f t e r soaking. Sugar l o s s e s d u r i n g s o a k i n g are not p r o p o r t i o n a l t o the s o l u b i l i t y o f the r e s p e c t i v e sugars, however, heat treatments increase sugar s o l u b i l i t y a n d e n h a n c e s l e a c h i n g f r o m t h e t i s s u e . The p h y s i c a l and c h e m i c a l changes o c c u r r i n g d u r i n g s o a k i n g and b l a n c h i n g t r e a t m e n t s were s t u d i e d b y T i t t i r a n o n d a ( 3 1 ) . Two s o a k i n g m e t h o d s (1:4, b e a n : w a t e r ratio) i n c l u d e d room t e m p e r a t u r e s o a k i n g (21°C) a n d h o t s o a k i n g (88°C, 30 m i n s ) . A f t e r e a c h s o a k i n g t r e a t m e n t , soaked b e a n s were c o o k e d (88°C) f o r 30, 60 and 90 m i n u t e s . The content o f a v a i l a b l e carbohydrates, t o t a l s o l u b l e sugars, reducing sugars, and n o n - r e d u c i n g sugars i n legumes d e c r e a s e s d u r i n g s o a k i n g and c o o k i n g a r e p r e s e n t e d i n T a b l e 1. S u b s t a n t i a l amounts o f f l a t u s - p r o d u c i n g components i n b e a n s c a n be r e d u c e d b y v a r i o u s common processes (soaking, cooking and d i s c a r d i n g t h e cook water, germination, or fermentation). Since the sugars of r a f f i n o s e f a m i l y a r e w a t e r - s o l u b l e , d i s c a r d i n g t h e soak and cook waters w i l l remove most o f t h e s e sugars; however, s u b s t a n t i a l l o s s e s i n t o t a l s o l i d s , v i t a m i n s and minerals are also sustained. Proteins Generally, proteins react non-covalently w i t h substances i n t h e i r environment p r i m a r i l y through h y d r o p h o b i c f o r c e s a n d i o n i c b o n d i n g . The m a c r o m o l e c u l a r s t r u c t u r e o f p r o t e i n s and t h e l a r g e d i f f e r e n c e s i n t h e i n t r i n s i c r e a c t i v i t i e s of t h e i r side chains dramatically i n f l u e n c e water i n t e r a c t i o n and f u n c t i o n a l p r o p e r t i e s . E l i a s e t a l . (32) have s t u d i e d t h e e f f e c t s o f p r o c e s s i n g on t h e p r o t e i n c o n t e n t o f f i v e c u l t i v a r s o f d r y b e a n s . On a d r y w e i g h t b a s i s , t h e c o o k e d b e a n s h a d a p r o t e i n c o n t e n t w h i c h was 70 t o 8 6% o f t h e raw b e a n s . Four t o t e n p e r c e n t o f t h e p r o t e i n o f t h e raw b e a n s was l e a c h e d into t h e c o o k i n g b r i n e . These r e s u l t s a r e i n good agreement w i t h those of Koehler and Burke (33) a n d



a

SOAKING

(88°C/30

min) 1 . .42 a 0.. 63 c 0..52 b 0..40 a

ND ND ND

1 . .03 b 0..76 a 0.. 62 a

ND ND ND

0..22 a

0..27 a 0..23 a ND

0.. 44 a 0..42 a

0 .27 a

2 .50 c

2,.05 b 1..44 a

Raffinose

Sucrose

ND

ND ND ND

10 a ND

12 a

Glucose

a a

0..76 b 0 .60 . a 0..53 a

1.,38 a

0..88 b 0..87 b 0..73 a

1,.35 1 . .15

2 .32 b

Stachyose

Means w i t h i n e a c h column a n d t r e a t m e n t f o l l o w e d b y l i k e l e t t e r s a r e n o t s i g n i f i c a n t l y d i f f e r e n t (p,0.05). A l l values a r e expressed i n percent d r y b a s i s .

Hot-soaked beans Cook t i m e (88°C) 30 m i n u t e s 60 m i n u t e s 90 m i n u t e s

HOT

Condition

(21°C)

(88°C)

SOAKING

beans

Soak t i m e 8 hours 16 h o u r s Cook t i m e 30 m i n u t e s 60 m i n u t e s 90 m i n u t e s

COLD

Raw

S o a k i n g and C o o k i n g

Table 1. Changes of Sugar Content During Preparation of Navy Beans


η χ

ι

I

Ο

M

§

I

es


118

QUALITY FACTORS OF FRUITS AND

VEGETABLES

H a y t o w i t z a n d Matthews (34) who r e p o r t e d 93% t o 100% r e t e n t i o n o f p r o t e i n a f t e r cooking. However, t h e y d i d n o t a g r e e w i t h t h o s e o f M e i n e r s e t a l . (35) who r e p o r t e d 50% t o 60% l o s s o f p r o t e i n a f t e r c o o k i n g . The l o s s i n protein i s attributed t o the extraction of soluble p r o t e i n s , h y d r o l y s i s o f p r o t e i n t o f r e e amino a c i d s , a n d non-enzymatic browning r e a c t i o n s . Phytohaemagglutenin (PHA) i s a t e t r a m e r i c h e a t l a b i l e g l y c o p r o t e i n ( s u b u n i t , c a . MW 30,000) e x h i b i t i n g a n t i n u t r i t i o n a l r e s p o n s e s due to disruption of intestinal microvilli. Proper and thorough heating i s e s s e n t i a l f o r i n a c t i v a t i o n o f t h i s factor (36) . A l m a s a n d B e n d e r (37) attributedthe r e d u c t i o n i n the a v a i l a b l e l y s i n e content and p r o t e i n quality o f legumes d u r i n g heating t o non-enzymatic browning r e a c t i o n s . The o b s e r v e d l o s s e s were r e l a t e d t o t h e l e n g t h and s e v e r i t y o f t h e h e a t t r e a t m e n t and l o s s e s i n the r e d u c i n g sugar content. M i n o r Con s t. i f c u e n t. s Losses o f t o t a l bean s o l i d s , Ν compounds, t o t a l s u g a r s , o l i g o s a c c h a r i d e s , Ca, Mg, a n d three water-soluble vitamins (thiamin, r i b o f l a v i n and n i a c i n ) were m e a s u r e d a n d f o u n d t o b e v e r y s m a l l a t s o a k i n g t e m p e r a t u r e s up t o 50°C; however, a t h r e e t o f o u r f o l d i n c r e a s e was f o u n d when t h e s o a k i n g t e m p e r a t u r e was r a i s e d a b o v e 60°C (38). T h e r e h a v e b e e n f e w p u b l i s h e d r e p o r t s on t h e e f f e c t s o f processing on t h e l i p i d c o m p o s i t i o n o f legumes. A l t h o u g h l i p i d s c o n s t i t u t e o n l y a s m a l l p e r c e n t a g e o f t h e d r y b e a n (2-3%), t h e f a t t y a c i d s are h i g h l y unsaturated (39). L i p i d o x i d a t i o n , c a t a l y z e d by h e a t , enzymes, l i g h t o r m e t a l s , l e a d s t o t h e f o r m a t i o n o f h y d r o p e r o x i d e s w h i c h f u r t h e r decompose t o p r o d u c e o f f flavors (40) . T h e s e d e c o m p o s i t i o n p r o d u c t s (carbonyl compounds) c a n c h e m i c a l l y i n t e r a c t w i t h p e p t i d e s t o y i e l d c r o s s l i n k e d e n d p r o d u c t s . Thus, t h e s t o r a g e o f l e g u m e s c a n r e s u l t i n a l o s s o f q u a l i t y ( o f f f l a v o r s and o d o r s ) , n u t r i t i o n a l v a l u e a n d f u n c t i o n a l i t y . Dry beans c o n t a i n 3.9% t o 4.8% t o t a l a s h (33,35,41) and c o n s i d e r a b l e l o s s e s of these mineral constituents leach during both soaking and c o o k i n g p r o c e d u r e s . G r e a t e s t l o s s e s o c c u r a s a r e s u l t of increased solubility a n d t i s s u e breakdown as p r e p a r a t i o n temperature i n c r e a s e s . P h e n o l i c a c i d s have i n c r e a s i n g l y b e e n r e c o g n i z e d t o influence q u a l i t y o f d r y bean during storage and subsequent thermal processing due p a r t i c u l a r l y t o r e a c t i o n and c r o s s l i n k i n g w i t h p r o t e i n s . The p r e d o m i n a n t p h e n o l i c a c i d s found i n d r y navy bean a r e p-coumaric, f e r u l i c a n d s i n a p i c a c i d s ( F i g u r e 3) . S t o r a g e o f d r y b e a n s a t h i g h t e m p e r a t u r e and h u m i d i t y c o n d i t i o n s w i l l r e s u l t i n " h a r d - t o - c o o k " (HTC) phenomenon. This defect, c h a r a c t e r i z e d by extended cooking time r e q u i r e d f o r adequate c o t y l e d o n s o f t e n i n g , i s d i s t i n g u i s h e d from a d e f e c t termed "Hard S h e l l " . HTC b e a n s p r e s e n t : 1) a n energy problem during preparation, 2) inferior nutritional qualities, a n d 3) poor acceptance by



UEBERSAX & RUENGSAKULRACH


F i g u r e 2. Q u a l i t y c h a r a c t e r i s t i c s o f n a v y b e a n s ( v a r . S e a f a r e r ) c a n n e d i n d i f f e r e n t pH p r o c e s s m e d i a

F i g u r e 3. S t r u c t u r e s i n d r ynavy beans

o f predominant phenolic

acids



120

QUALITY FACTORS OF FRUITS AND

VEGETABLES

consumers ( 4 2 ) . HTC c o n t r i b u t e s t o l o w e r n u t r i t i v e v a l u e through longer cooking times r e s u l t i n g i n the l o s s of l a b i l e amino a c i d s and i m p a i r e d p r o t e i n d i g e s t i b i l i t y (43) . The e x t e n t o f t h e n u t r i t i o n a l damage p r o d u c e d i s d e t e r m i n e d by t h e t i m e , t e m p e r a t u r e and r e l a t i v e h u m i d i t y of s t o r a g e . S e v e r a l h y p o t h e s e s have b e e n p r o p o s e d t o explain HTC i n c l u d i n g : 1) lipid oxidation and/or p o l y m e r i z a t i o n (39,44 and 4 5 ) ; 2) p h y t i n c a t a b o l i s m , and pectin demethylation with subsequent formation of insoluble pectate ( 4 6 - 4 8 ) ; 3) a u t o l y s i s o f cytoplasmic organelles, weakening plasmalemma integrity and l i g n i f i c a t i o n o f m i d d l e l a m e l l a (14); and 4) i n t e r a c t i o n s of proteins and polyphenols and polymerization of p o l y p h e n o l i c compounds (4 9 ) . E x p o s u r e t o h i g h t e m p e r a t u r e and humidity storage may potentiate phytase which h y d r o l y z e s phytate, thus reducing c h e l a t i o n of C a and Mg i o n s w i t h i n t h e m i d d l e l a m e l l a . R e c e n t l y , H i n c k s and Stanley (50) p r o p o s e d a m u l t i p l e mechanism o f bean hardening which included phytate loss as a minor c o n t r i b u t o r d u r i n g i n i t i a l s t o r a g e and p h e n o l m e t a b o l i s m as a m a j o r c o n t r i b u t o r d u r i n g e x t e n d e d s t o r a g e . P h e n o l i c a c i d s and t h e i r d e r i v a t i v e s a r e w i d e l y d i s t r i b u t e d i n plants (51) and can be p r e s e n t i n e i t h e r f r e e and/or bound forms. A n a l y s i s of changes in total phenolic c o n t e n t o f p l a n t t i s s u e s must i n v o l v e d e t e r m i n i n g the content o f a l l p h e n o l i c forms. Changes i n p h e n o l i c a c i d c o n t e n t related to HTC defect were s t u d i e d by S r i s u m a e t a l . ( 5 2 ) . Navy b e a n s were s t o r e d f o r 9 months u n d e r t h r e e c o n d i t i o n s (5°C/40% RH, 2 0 o c / 3 7 % RH, and 35oc/80% RH) t o produce d i f f e r e n t d e g r e e s o f HTC. Canned p r o d u c t q u a l i t y c h a r a c t e r i s t i c s d e m o n s t r a t e u n d e s i r a b l e d a r k e r c o l o r ( d e c r e a s e d H u n t e r L, a and b v a l u e s ) and increased firmness with adverse storage ( T a b l e 2) . S e v e r a l r e s e a r c h e r s a t t r i b u t e d t h i s d a r k e r c o l o r t o p o l y m e r i z a t i o n o f p h e n o l i c compounds (5354) . C h a n g e s i n free hydroxycinnamic acids, hexane s o l u b l e and m e t h a n o l s o l u b l e h y d r o x y c i n n a m i c a c i d s , c e l l w a l l bound h y d r o x y c i n n a m i c a c i d s , and l i g n i n c o n t e n t were d e t e r m i n e d . S t o r a g e i n d u c e d HTC b e a n s c o n t a i n e d higher l e v e l s of hydroxycinnamic acids ( e s p e c i a l l y f e r u l i c acid) t h a n the c o n t r o l beans i n a l l f r a c t i o n s p r e p a r e d from s e e d c o a t s and c o t y l e d o n s e x c e p t f o r t h e m e t h a n o l s o l u b l e and cell wall bound phenolic acid fractions from cotyledons. No s i g n i f i c a n t c h a n g e s i n l i g n i n content were d e t e c t e d among t h e t r e a t m e n t s . Large i n c r e a s e s i n f r e e h y d r o x y c i n n a m i c a c i d c o n t e n t were a s s o c i a t e d w i t h the degree of hardening (e.g. f e r u l i c a c i d l e v e l s , ITIg/g i n seed c o a t : c o n t r o l , not d e t e c t a b l e ; moderately hard, 23.1; hard, 86.3; and in cotyledon: control, 8.4; m o d e r a t e l y h a r d , 46.6; h a r d , 64.8) , thus suggesting a r e l a t i o n s h i p between t h e two phenomena. + +

+ +



Hard

35/80

34.0a

51.8b

52.4c

L

0.1b

-4.8a

-4.9a

aL

bL

13.4a

15.1b

15.2b

Hunter Color

Means w i t h i n e a c h c o l u m n f o l l o w e d b y l i k e l e t t e r s significantly different (p,0.05). k e x p r e s s e d as g/100 g o f i n i t i a l d r y b e a n s o l i d s

a

Partially Hard

Normal

Subjective Classification

20/73

5/40

Storage Condition (°C/% RH)

a

are not

234.2a

285.4b

301.0c

b

Drained Weight (g)

Table 2. Canned Bean Quality Attributes of Navy Beans Stored Under Selected Conditions f o r 9 Months


237.9c

58.5b

51.0a

Shear Force (kg/100g)

122

QUALITY FACTORS OF FRUITS AND VEGETABLES Summary


Numerous c h e m i c a l a n d p h y s i c a l c h a n g e s o c c u r d u r i n g p r o d u c t i o n , h a n d l i n g and p r o c e s s i n g o f d r y e d i b l e beans. Many o f t h e c h e m i c a l c h a n g e s a r e a s s o c i a t e d w i t h t h e m a c r o - c o n s t i t u e n t s o f t h e seed. I n t e r a c t i o n o f water, h e a t a n d pH d i r e c t l y i n f l u e n c e t h e f u n c t i o n a l p r o p e r t i e s of s t a r c h and p r o t e i n s and s i g n i f i c a n t l y alter the c e l l u l a r s t r u c t u r e and i t s d i s r u p t i o n . In order t o adequately c o n t r o l o r modify p r o c e s s e d bean q u a l i t y , a greater understanding of the chemical interaction o c c u r r i n g d u r i n g p r o c e s s i n g must be a c h i e v e d .

Literature

Cited

1. Hosfield, G . L . and Uebersax, M.A, J. Am. Soc. Hort. Sci. 1980, 105, 246. 2. Hosfield, G . L . , Ghaderi, A. and Uebersax, M.A. Can. J. Plant S c i . 1984, 64, 285. 3. Powrie, W.D., Adams, M.W. and Pflug, I . J . Agron. J. 1960, 52, 163. 4. O t t , A . C . and B a l l , C.D. Arch. Biochem. 1943, 3, 189. 5. Sefa-Dedeh, S. and Stanley, D.W. Cereal Chem. 1979, 56, 367. 6. Ginzburg, B , Z . J. E x p t l . Bot. 1961, 12, 85-107. 7. Sterling, C. in Postharvest Biology and Handling of F r u i t s and Vegetables. 1975 pp 43-54. AVI Publishing Co., Westport, Conn. 8. Uebersax, M.A. and Bedford, C . L . Research Report 410, Michigan State University A g r i c u l t u r a l Experiment Station, East Lansing, MI. 1980 9. Reddy, N.R., Pierson, M.D., Sathe, S.K. and Salunkhe, D.K. Food Chem. 1984, 13: 25. 10. Salunkhe, D . K . , Kadam, S.S., and Chavan, J.K. in Postharvest Biotechnology of Food Legumes. 1985 pp 29. CRC Press, Inc., Boca Raton, FL. 11. Loh, J. and Breene, W.M. J. Text. Studies. 1982, 13, 381-396. 12. Bourne, M.C. in Rheology and Texture in Food Quality 1976. pp 275 AVI Publishing Co. Inc. Westport, CT. 13. Loh, J., Breene, W.M. and Davis, Ε.A. J. Text. Studies. 1982, 13, 325-347. 14. Varriano-Marston, E . and Jackson, G. M. J. Food Sci. 1981, 46, 1379. 15. Hahn, D.M., Jones, F.T., Akhavan, I . , and Rockland, L . B . J. Food S c i . 1977, 42, 1208-1212. 16. Reddy, N.R. Pierson, M.D., Sathe, S.K. and Salunkhe, D.K. Food Chem. 1984, 13, 25. 17. Naivikul, O. and D'Appolonia, B . L . Cereal Chem. 1978, 55, 913. 18. Lii, C.Y. and Chang, S.M. J. Food S c i . 1981, 46, 78.



10. UEBERSAX & RUENGSAKULRACH


19. Schoch, T.J. and Maywald, E . C . Cereal Chem. 1968, 45, 564. 20. E l b e r t , E . M . , and Witt, R.L., J. Home Econ. 1968, 60, 186. 21. Varriano-Marston, E . and de Omana, E . J. Food S c i . 1979, 44, 531. 22. Maga, J.A. J. A g r i c . Food Chem. 1982, 30, 1. 23. Akpapunam, M.A. and Markakis, P. J. Food S c i . 1979, 44, 1317. 24. Kon, S . , Olson, A.C., F r e d e r i c k , D . P . , E g g l i n g , S . B . and Wagner, J.R. J. Food S c i . 1973, 38, 215. 25. Rockland, L.B., Zaragosa, E . M . and Oracca-Tetteh, R. J. Food S c i . 1979, 44, 1004. 26. Ekpenyong, T.E. and Borchers, R.L. J. Food S c i . 1980, 45, 1559. 27. Reddy, N.R. and Salunkhe, D . K . Cereal Chem. 1980, 57, 356. 28. Fleming, S . E . J. Food S c i . 1981, 46, 794. 29. Sathe, S . K . , Iyer, V. and Salunkhe, D . K . J. Food Sci. 1981, 47, 8. 30. S i l v a , H . C . and Braga, G . L . J. Food S c i . 1982, 47, 924. 31. T i t t i r a n o n d a , A. M.S. Thesis, Michigan State U n i v e r s i t y , 1984. 32. E l i a s , L.G., DeFernandez, D . G . and Bressani, R. J. Food Sci. 1979, 44, 524. 33. Koehler, H . H . and Burke, D.W. J. Amer. Soc. Hort. S c i . 1981, 106, 313. 34. Haytowitz, D . B . and Matthews, R.H. Cereal Foods World 1983, 28, 362. 35. Meiners, C.R., Derise, N.L., Ritchey, S . L . and Murphy, E.W. J. A g r i c . Food Chem. 1976, 24, 1122. 36. Coffey, D . G . , Uebersax, M . A . , H o s f i e l d , G . L . and Brunner, J.R. (1985) J. Food S c i . 5 0 ( 1 ) : 78-81 and 87. 37. Almas, K. and Bender, A.E. J. S c i . Food A g r i c . 1980, 31, 448. 38. K o n , S . , J. Food S c i . 1979, 44, 1329. 39. Takayama, K . K . , Muneta, P. and Wiese, A.C. J. Agr. Chem. 1965, 13, 269. 40. Sessa, D . J . and Rackis, J.J. J. Am. O i l Chem. Soc. 1977, 54, 468. 41. Watt, R.T. and Merrill, W. USDA Handbook Number 8, 1963. 42. Stanley,D.W. and A g u i l e r a , J.M. J. Food Biochem. 1985, 9, 277. 43. Rockland, L.B., and Radke, T.M. Food Technol. 1981, 35(3), 79-82. 44. M o r r i s , H . J . and Wood, E . R . Food Technol. 1956, 10, 225. 45. Muneta, Pl., Food Technol. 1964, 18, 130. 46. Mattson, S . , A c t a . Agr. Suecana II 1946, 2, 185.


123



124

47. Jones, P.M.B. and Boulter, D. J . Food S c i . , 1983, 48, 623. 48. Moscoso, W., Bourne, M.C., and Hood, L.F. J . Food S c i . 1984, 49, 1577. 49. Rozo, C. Ph.D. Thesis, C o r n e l l Univ., Ithaca, NY., 1982. 50. Hincks, M.J. and Stanley, D.W. J . Food Tech. 1986, 21, 734. 51. Krygier, K., S o s u l s k i , F., and Hogge, L. J . A g r i c . Food Chem. 1982, 30, 330. 52. Srisuma, N., Hammerschmidt, R., Uebersax, M.A., Ruengsakulrach, S., Bennink, M.R. and H o s f i e l d , G.L., J. Food S c i . 1989, 54, 311. 53. Burr, H.K., Kon, S., and Morris, H.J. J . Food S c i . & Tech. 1968, 22, 336. 54. G a r r u t i , R.D.S. and Bourne, M.C. J . Food S c i . 1985, 50, 1067. RECEIVED April 21, 1989


Structural and Compositional Changes During Processing of Dry Beans

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