The Maillard Reaction in Foods and Nutrition - American Chemical

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18 Nutritional Value of Foods and Feeds of Plant Origin: Relationship to Composition and Processing J. E. KNIPFEL, J. G. McLEOD, and T. N. McCAIG Agriculture Canada, Research Station, Research Branch, Swift Current, Saskatchewan, S9H 3X2 Canada

Historically, alterations in amino acid availability and p r o tein digestibility have been considered as the primary effects of processing reactions leading to reduced nutritional values of food and feeds. Predominant among these reactions are Maillard and crosslinking types. In plant materials used as foods and feeds, including both grains and roughages, reactions among nitrogenous compounds and complex polysaccharides such as hemicellulose appear to be of considerable importance in determining nutritive value responses to processing. Heating of alfalfa increased the content of Neutral Detergent Fibre (NDF) and the nitrogen contents of both NDF and Acid Detergent Fibre (ADF). Associated with increased NDF and increased Ν content of the fibre fractions was a reduction in organic matter digestibility by rumen bacteria, and in Ν d i g e s t i b i l i t y by both rumen bacteria and pepsin digestion in v i t r o . In lower quality roughages, a large proportion of total Ν was associated with NDF and ADF. Ammonia treatment resulted in decreases in NDF and increases in d i g e s t i b i l i t y and intake of wheat straw by sheep. Following ammoniation, increased levels of Ν in both NDF and ADF occurred. Investigations with rye grain suggested that the pentosan frac tion is of prime importance in the adverse effects observed when rye is fed to animals. Increased chick performance observed f o l lowing supplementation of rye with amino acids or high-quality protein suggests that pentosans adversely affected digestibility of rye protein through unknown mechanisms. Arabinose was easily released from rye hemicellulose by acid hydrolysis; following

0097-6156/83/0215-0361$06.00/0 © 1983 American Chemical Society

In The Maillard Reaction in Foods and Nutrition; Waller, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

362

M A I L L A R D REACTIONS


heating of arabinose and xylose at 40°C with l y s i n e for 1 hr, browning reactions were observed, r a i s i n g the p o s s i b i l i t y that Mai H a r d - t y p e reactions occur at r e l a t i v e l y low temperatures in plant m a t e r i a l s . The hemicellulose f r a c t i o n of plant food and feed m a t e r i a l s appears to be of considerably greater importance i n determining n u t r i t i o n a l value of such foods and feeds than has been g e n e r a l l y recognized. Processing of foods and feeds by man has been c a r r i e d out from p r e h i s t o r i c times, as a method of preservation or for the purpose of i n c r e a s i n g e i t h e r p a l a t a b i l i t y or n u t r i t i v e value of many f o o d s t u f f s . During the past quarter-century, however, there has been a tremendous and e v e r - i n c r e a s i n g use of foods and feeds which have been subjected to various types of processing. This dramatic increase i n processing of foods and feeds occurred as a r e s u l t of f a c t o r s such as increased populations and has r e s u l t e d in considerable pressure to develop new processing technologies and new sources of food and feed. In conjunction with t h i s increase i n processing of foods and feeds there has been increased research into the e f f e c t s of processing on the n u t r i t i v e value of these m a t e r i a l s , and a number of symposia have been held to discuss these e f f e c t s during the past decade. From these d i s c u s s i o n s i t has become apparent that there have been s i g n i f i c a n t advances i n knowledge of c e r t a i n aspects of n u t r i t i o n a l consequences of processing of foods and feeds. In many instances there i s l i t t l e known of the i n t e r actions among food or feed c o n s t i t u e n t s that occur n a t u r a l l y or f o l l o w i n g p r o c e s s i n g . This i s of p a r t i c u l a r concern when dealing with the wide v a r i e t y of p o t e n t i a l feed- and foodstocks which may be derived from nonconventional sources such as forages. In t h i s p r e s e n t a t i o n the i n t e r r e l a t i o n s h i p s of carbohydrates and p r o t e i n s i n c e r e a l grains and fibrous feeds w i l l be discussed and r e l a t e d to selected aspects of processing of these materials. I n v e s t i g a t i o n s o f N u t r i t i v e Value of Rye N u t r i t i v e value of foods and f e e d s t u f f s depends to a large degree on p r o t e i n l e v e l and q u a l i t y , i . e . , the r e l a t i v e amounts of the component amino acids compared to the requirements of the animal f o r various metabolic f u n c t i o n s . The c e r e a l grains are n o t o r i o u s l y low i n c e r t a i n e s s e n t i a l amino a c i d s . U s u a l l y l y s i n e i s the f i r s t or second l i m i t i n g amino a c i d . The grain of rye (Secale céréale L.) e x h i b i t s an amino acid p r o f i l e superior to that of other c e r e a l g r a i n s , e s p e c i a l l y wheat (1,2,3,4,5). Despite this f a c t , l y s i n e i s s t i l l the f i r s t l i m i t i n g amino acid in rye i n most instances (6,7). In recent years f a c t o r s such as a l k y l r e s o r c i n a l s ( 8 ) , t r y p s i n i n h i b i t o r s , (9,10) and water-soluble polysaccharides have been implicated in the poor feeding q u a l i t y of rye. I n v e s t i g a -



18.

KNiPFEL E T AL.

Nutritional Value: Relationship to Processing

363

t i o n s have shown that l e v e l s of 15 to 20% rye grain in the diet depress the appetite and growth of chicks (8, 11, 12, 13). Higher l e v e l s of rye in the diet decrease u t i l i z a t i o n . Although t h e l i t e r a t u r e contains many reports on feeding rye to swine and p o u l t r y , there are r e l a t i v e l y few on the e f f e c t s of rye on ruminants. The i m p l i c a t i o n of âlkylresorcinals in the low feeding q u a l i t y of rye (8) has been l a r g e l y disproved (14,15). Protein supplementation studies (16) revealed that rye d i e t s supplemented with low l e v e l s of low-quality p r o t e i n accentuated the detriment a l e f f e c t s of feeding rye while supplementation with high l e v e l s of h i g h - q u a l i t y p r o t e i n g r e a t l y reduced the e f f e c t s of feeding rye g r a i n . A d d i t i o n of various m i l l i n g f r a c t i o n s of rye to chick d i e t s showed that the growth-depressing f a c t o r was d i s t r i b u t e d throughout a l l such f r a c t i o n s of the grain (14). In a d d i t i o n , the growth depression could be a l l e v i a t e d by water e x t r a c t i o n of the rye (17). Water e x t r a c t i o n of the grain also eliminated the wet-feces problem associated with feeding rye to c h i c k s . Reduced nitrogen r e t e n t i o n was reported when chicks were fed rye d i e t s (18). Supplementation of those d i e t s with amino acids increased the r e t e n t i o n of only the supplemented amino acids and not those contributed by the rye. These observations are compatible with the t r y p s i n i n h i b i t o r hypothesis of other researchers (9,10). On the other hand, examination of the d i f ferences between endosperm and embryo and t r y p s i n i n h i b i t o r s of b a r l e y , wheat, and rye has revealed that, in contrast to c e r t a i n t r y p s i n i n h i b i t o r s from leguminous seeds, those from the c e r e a l grains appeared to be r e l a t i v e l y weak, nonstoichiometric inhibit o r s of t r y p s i n (19). Although p r o t e i n e f f i c i e n c y i n d i c e s (PEI) c a l c u l a t e d from animal feeding t r i a l s (20) do give an estimate of the b i o a v a i l a b i l i t y of p r o t e i n s , they represent an i n t e g r a t i o n of many f a c t o r s working i n d i v i d u a l l y or in combination. It is possible that other f a c t o r s such as c r o s s l i n k i n g of p r o t e i n s , amino acid b a l ance or protein-carbohydrate i n t e r a c t i o n s are much more important i n producing the adverse e f f e c t s of rye g r a i n than is t r y p s i n inhibitor. Rye-type growth depression in chicks fed p e c t i n has been reported (21). S i g n i f i c a n t l e v e l s of p e c t i n were reported to be present i n rye g r a i n (22) (as high as 8%). In our laboratory no p e c t i n (as p o l y g a l a c t u r o n i c acid) could be detected in rye g r a i n . A n t i b i o t i c s have been shown to a l l e v i a t e the e f f e c t s of feeding rye to some extent (11,12,17,18,23). These observations led to the p o s t u l a t i o n that rye i n the d i e t stimulated the prol i f e r a t i o n of an adverse m i c r o f l o r a i n the gut. This is further substantiated by an adaptive response in chicks fed rye (24). Rye does contain a s i g n i f i c a n t amount of a polysaccharide (Table I) composed mostly of two pentose sugars, arabinose and xylose. This polysaccharide c o n s t i t u t e s about 6 to 9% of the g r a i n by weight and can be separated into a water-soluble and a



364


water-insoluble f r a c t i o n . These polysaccharide l e v e l s are of the same order as those p r e v i o u s l y determined as p e c t i n (22). Both f r a c t i o n s have been i s o l a t e d and s u b s t i t u t e d into diets of a wheat base (25). The detrimental e f f e c t s of feeding rye were observed when e i t h e r of the s o l u b i l i t y f r a c t i o n s were fed. Both f r a c t i o n s of rye polysaccharide were more powerful i n h i b i t o r s of c h i c k growth than were a l t e r n a t i v e polysaccharides used by other researchers (26). The polysaccharides of rye, often r e f e r r e d to as pentosans, were s i m i l a r to those of wheat f l o u r i n composition and have been studied mainly with respect to e f f e c t s i n the breadmaking process. The polysaccharides of rye are h i g h l y hygroscopic (27), produce viscous s o l u t i o n s , and should be studied further to determine t h e i r mode of a c t i o n , composition, and nutrient-binding properties. Table I.

1

Pentosan" " l e v e l s of rye, wheat, and

% Pent

Crop

Cultivar

Pent

Rye

6.0 6.4 6.6 9.6 5.7 6.9

Wheat

Neepawa Leader Norstar Lemhi Pitic Glenlea NB 320 Norquay Mean

5.9 5.9 4.8 4.8 5.9 5.3 5.7 5.5 5.5

+

%

%

Crop C u l t i v a r Frontier Cougar Puma Kodiak Musketeer Mean

triticale

Crop Triticale

Pentosan was determined by the method of Dische (28) on grains grown at Swift Current, 1981

Cultivar Welsh Carman Mapache Mean

and

Pent 6.5 5.8 5.6 6.0

Borenfreund

Generally, there are higher l e v e l s of pentosans in rye than i n wheat as shown i n Table I I . T r i t i c a l e , a hybrid of wheat and rye, has pentosan l e v e l s intermediate to the parental species. The arabino-xylan f r a c t i o n s of the water-soluble polysaccharides of wheat and rye have been examined (27). In general, the molecu l a r weight of rye pentosans was considerably higher than that of wheat pentosans but component sugar r a t i o s were s i m i l a r . The component sugars of the pentosans were determined (27) by the formation of a l d i t o l acetates and gas chromatography (29). The sample was f i r s t hydrolyzed i n IN H2SO4 for 4 hr at 100°C, which i s r e l a t i v e l y strong acid h y d r o l y s i s . In forage, i t has been shown that h y d r o l y s i s with d i l u t e acid can release arabinose from the h e m i c e l l u l o s e f r a c t i o n while leaving xylose polymerized. An experiment was set up to determine i f arabinose could be released from rye pentosans by gentle h y d r o l y s i s and to test the p o s s i b i l i t y of nonenzymatic browning at p h y s i o l o g i c temperatures using sugar-lysine s o l u t i o n s . Rye pentosans were extracted by the method of Medcalf _ejt



18.

KNIPFEL

ET AL.


365

a l . (27). Samples of the pentosans were hydrolyzed i n 2 ml of .05 Ν H2SO4 for 1 hr at 99°C. A f t e r h y d r o l y s i s the s o l u t i o n was n e u t r a l i z e d with Na2HP04 and prepared for gas chromatography. Chromatography i n d i c a t e d that arabinose had been released from the polysaccharide but almost no xylose was detected. This i s s i m i l a r to r e s u l t s reported by Burdick and S u l l i v a n (30), that arabinofuranoside linkages are much more e a s i l y cleaved than the pyranoside linkage of the main xylan chain. Many studies of nonenzymatic browning have been c a r r i e d out using model systems o f monosaccharides and amino a c i d s . Given the ease of release of arabinose from the pentosan, there i s the p o s s i b i l i t y that M a i l l a r d reactions could take place i f the tem perature i s appropriate. Four sugar-lysine s o l u t i o n s were prepared and heated i n a water bath. In a d d i t i o n , a pentosan-lysine s o l u t i o n and the pen tosan, l y s i n e , and sugars alone were heated (Table I I ) . Table

Temp. C O

92 78 60 40

I I . Rating of c o l o r i n t e n s i t y (browning) when sugar- l y s i n e s o l u t i o n s were heated for 1 hr

Lysine mixed with Glu Ara Xyl Gal Pent ++++ ++++ ++++ ++++

+

+++

+

+

++++ ++++ +++ ++ ++ + + +

+

Glu

_ -

Single compounds Ara X y l GalPent

_ -

-

_ -

+ + +

-

Lys

-

The pentose sugars gave more intense browning and e x h i b i t e d browning r e a c t i o n s with l y s i n e at lower temperatures than did the hexoses (Table I I ) . M a i l l a r d (31) observed browning r e a c t i o n between g l y c i n e and xylose at temperatures of 40 and 34°C when the aqueous mixtures were incubated f o r 20 h r , while g l y c i n e glucose s o l u t i o n s required more extended periods of time to give browning. In the present study, we were able to detect browning when e i t h e r xylose or arabinose were incubated at 40°C f o r 1 hr while higher temperatures were necessary to cause n o t i c e a b l e browning with glucose- or g a l a c t o s e - l y s i n e s o l u t i o n s heated for 1 hr. The pentosan c o l o r development occurred i n the presence or absence of l y s i n e (Table I I ) only at 60°C or above and may be r e f l e c t i v e of reactions other than those of the M a i l l a r d type. On the other hand, i t i s conceivable that there may have been some p r o t e i n or other nitrogenous compounds present i n the pento san which d i d undergo M a i l l a r d r e a c t i o n s . The demonstrations of M a i l l a r d (31) that browning reactions could occur at p h y s i o l o g i c a l temperatures, and the r e s u l t s reported i n t h i s presentation, suggest that n u t r i t i o n a l a l t e r a t i o n s due t o Mai Hard-type reac t i o n s may be much more prevalent than i s g e n e r a l l y considered, for food- and f e e d s t u f f s not subjected to extensive processing.


366



N u t r i t i v e Value of Fibrous Feed M a t e r i a l s i n R e l a t i o n to ing

Process

In the 1 9 4 0 ' s P i r i e (32) suggested that p r o t e i n extracted from a l f a l f a could represent a p o t e n t i a l p r o t e i n source for monog a s t r i c animals, i n c l u d i n g humans. Further development of this concept into a commercial process was undertaken in several coun t r i e s and i t i s expected that further development in this area w i l l occur. It i s , however, beyond the scope of t h i s presenta t i o n to cover t h i s subject; the reader i s r e f e r r e d to B i c k o f f , e_t al_. (33) and P i r i e (34) for more d e t a i l e d treatment. Feedstuffs containing r e l a t i v e l y high l e v e l s of f i b r e , such as forages and c e r e a l crop residues, have t r a d i t i o n a l l y been con sidered as feeds for ruminant species. It was usually assumed under accepted production schemes that the rumen m i c r o b i a l a c t i v i t y would supply s u f f i c i e n t q u a n t i t i e s of m i c r o b i a l amino acids to the lower d i g e s t i v e t r a c t i f an adequate quantity of nitrogen was supplied. As production systems i n t e n s i f i e d and the product i v i t y of the ruminant, p a r t i c u l a r l y the d a i r y cow, increased, i t was r e a l i z e d that a l i m i t i n g f a c t o r i n production was the supply of amino acids reaching the lower d i g e s t i v e t r a c t ( 3 5 , 3 6 ) . This supply of amino a c i d s , however, represents a combination of both m i c r o b i a l p r o t e i n and feed p r o t e i n . Since the rumen m i c r o b i a l p r o t e i n has a b i o l o g i c a l value of about 55 to 70%, the feeding of a p r o t e i n with a higher b i o l o g i c a l value than that of the micro b i a l p r o t e i n w i l l be of value only i f the feed p r o t e i n is not ex t e n s i v e l y degraded i n the rumen and used to resynthesize micro b i a l p r o t e i n of lower b i o l o g i c a l value. Several processing methods have been employed to reduce the d e g r a d a b i l i t y of high b i o l o g i c a l value proteins in the rumen. D e s c r i p t i o n s of these processes and the a l t e r a t i o n s i n n u t r i t i v e value accompanying the treatments have been reviewed in d e t a i l e a r l i e r ( 3 7 , 3 8 , 3 9 , 4 0 ) . E f f e c t s of Heat Treatment on

Alfalfa

P r e v i o u s l y i t was reported (41) that dry heating of a l f a l f a at 105°C for up to 1440 min r e s u l t e d i n a reduction of rn v i t r o organic matter d i g e s t i b i l i t y (IVOMD) by rumen microbes. Increas es i n Acid Detergent Insoluble Ν (ADIN) and Neutral Detergent F i b r e (NDF) were also observed. For the convenience of the reader these data have been included with more recent observa t i o n s in this study. As shown i n Table I I I , NDF, suggested to represent the h e m i c e l l u l o s e - c e l l u l o s e - l i g n i n f r a c t i o n of the plant c e l l (45), increased at 480 and 1440 min of heating, while ADF, representing c e l l u l o s e + l i g n i n ( 4 5 ) , d i d not. This r e s u l t e d in an increase in the hemicellulose f r a c t i o n of a l f a l f a from 7.1% to 12.2%. No s i g n i f i c a n t changes in e i t h e r c e l l u l o s e or l i g n i n occurred. The e f f e c t of heat treatment therefore appeared to be p r i m a r i l y an increase in the hemicellulose component of NDF, although i t must be r e a l i z e d that the term "hemicellulose represents a f r a c t i o n obtained by d i f f e r e n c e which may contain compounds other than hemicellulose. 11


18.

KNiPFEL E T A L . Table

III.

F r a c t i o n (%) 1

NDF ADF Hemicellulose^ Cellulose^ Lignin^


2


367

A l t e r a t i o n s i n a l f a l f a f r a c t i o n following heating

0 35.3 28.2 7.1 27.0 1.0

Time of heating (min) 10 60 120 30 35.3 28.7 6.6 27.1 1.6

35.1 28.3 6.8 27.4 0.9

35.5 28.5 7.0 27.9 0.6

35.8 29.1 6.7 27.7 1.4

at 105°C 240 480

1440

35.1 28.5 6.6 27.6 0.9

40.6 28.4 12.2 27.4 1.0

37.5 29.2 8.3 27.6 1.6

Neutral Detergent F i b r e (42) •Acid Detergent F i b r e (43) NDF minus ADF By methods of Crampton and Maynard (44) 'ADF minus c e l l u l o s e l

Examination of the p a r t i t i o n o f Ν i n the f i b r e f r a c t i o n s (Table IV) shows a s l i g h t decrease i n t o t a l Ν at the two longest heating times. ADIN showed a gradual increase as the duration o f heating increased, as was shown (46,47,48,49) with i n c r e a s i n g heat damage to a l f a l f a . This i s more obvious when the r a t i o s of ADIN to t o t a l Ν are c a l c u l a t e d and shows about a 50% increase i n ADIN at the longest duration of heating. NDIN increased more r a p i d l y than did ADIN f o l l o w i n g heating and also to a much great er extent, p a r t i c u l a r l y at the longest duration (Table IV) o f heating. The r a t i o of ADIN to NDIN (Table IV) a l s o i n d i c a t e d that before heating almost a l l of the f i b r e Ν (94.1%) was a s s o c i ated with ADF ( l i g n o - c e l l u l o s e ) while a f t e r 1440 min of heating, 58.3% of the f i b r e Ν was associated with h e m i c e l l u l o s e . The amount of i n s o l u b l e p r o t e i n increase i n the hemicellulose f r a c t i o n from t = 0 to t = 1440 can be c a l c u l a t e d as: NDINi44Q - NDINQ = Increased NDIN ( K j e l d a h l conversion factor) = % Insoluble P r o t e i n Increase, or 1.20 - 0.34 = 0.86 X 6.25 = 5.38% From Table I I I the NDF f r a c t i o n increased from 35.3% to 40.6%, i . e . , by 5.3%, which i s v i r t u a l l y i d e n t i c a l to the c a l c u l a t e d increase i n i n s o l u b l e p r o t e i n . These data suggest that the increase i n NDF caused by heating was a r e s u l t of p r o t e i n a s s o c i a t i o n with the hemicellulose f r a c t i o n . Several authors (35,45) suggested that M a i l l a r d reactions might cause binding of the pro t e i n to i n d i g e s t i b l e carbohydrate f r a c t i o n s of the c e l l w a l l while the proposal that a f r a c t i o n of hemicellulose i s associated with p r o t e i n (47) i s also consistent with the observations o f Tables I I I and IV. In v i t r o rumen fermentation of the heated a l f a l f a s showed (Table V) a decrease i n organic matter d i g e s t i b i l i t y (OMD) which was of the same order o f magnitude as the increase i n NDIN, sug g e s t i n g that the NDIN f r a c t i o n was r e s i s t a n t to m i c r o b i a l attack at rumen pH (6.9). The a d d i t i o n o f HCl-pepsin to give a pH of


368

MAILLARD REACTIONS

Table

0

(%) Total Ν ADIN ADIN/N NDIN NDIN/N ADIN/NDIN 1

tQt

Z

tot


IV.

2.85 0.32 11.2 0.34 11.9 94.1

Partition

10

of Ν in a l f a l f a

Time o f heating 30 60

2.89 0.29 10.0 0.48 16.6 60.2

2.85 0.32 11.2 0.64 22.5 49.8

2.85 0.37 13.0 0.64 22.5 57.8

subjected

to

(min) at 105°C 120 240 2.85 0.37 13.0 0.70 24.6 52.8

2.85 0.39 13.7 0.74 26.0 52.7

heating

480

1440

2.75 0.44 16.0 0.82 29.8 53.7

2.75 0.50 18.2 1.20 43.6 41.7

•'•Acid Detergent Insoluble Ν ^Neutral Detergent Insoluble Ν 1.3 r e s u l t e d i n an increase i n organic matter d i g e s t i b i l i t y (OMDP) over that caused by m i c r o b i a l degradation (Table V ) . The organic matter s o l u b i l i z e d by pepsin-HCl increased as the dura t i o n of heating of the a l f a l f a increased; t h i s suggested that a large proportion of the increase i n the NDIN f r a c t i o n observed e a r l i e r (Table IV) c o n s t i t u t e d m a t e r i a l s o l u b i l i z e d by the a c i d pepsin s o l u t i o n . In v i t r o Nitrogen D i g e s t i b i l i t y (ND) decreased with i n creased heating of the a l f a l f a (Table V) when the m i c r o b i a l degradation was considered. This observation i s consistent with those of previous workers (46,48,49), who observed decreases i n ruminant d i g e s t i o n of a l f a l f a f o l l o w i n g heat treatment. PepsinHCl d i g e s t i o n removed 62.9% of the Ν l e f t i n the residue f o l l o w ing m i c r o b i a l d i g e s t i o n , for unheated a l f a l f a , and this propor t i o n decreased when the a l f a l f a was heated f o r 30 minutes or more (Table V ) . T o t a l i n v i t r o Ν d i g e s t i b i l i t y therefore decreased as the duration of heating increased, even though the OMDP d i d not i n d i c a t e t h i s to be the case. E a r l i e r studies (43,47) demon s t r a t e d that the s o l u b i l i t y o f hemicellulose increased markedly f o l l o w i n g treatment of plant t i s s u e with p r o t e o l y t i c enzymes. The present data i n d i c a t e that t h i s s o l u b i l i t y i n HCl-pepsin may be a f a c t o r which masked d i f f e r e n c e s i n n u t r i t i v e value caused by excessive heating when the i n v i t r o OMDP was used f o r assessment. Table V. Component (%)

In v i t r o rumen fermentation

0

of heated

alfalfa

Time of heating (min) at 105°C 10 30 60 120 240 480 1440

OMD OMDP OMSP

58.7 58.5 56.6 58.2 57.2 56.2 56.5 54.9 65.6 66.8 65.9 67.2 65.8 66.5 66.2 65.8 6.9 8.3 9.3 9.0 8.6 10.3 9.7 10.9

ND (% t o t a l N) NDP (% r e s . N) T o t a l ND

71.2 71.6 68.4 69.8 68.4 67.7 66.5 62.2 62.9 62.4 51.1 53.5 51.1 53.9 52.8 49.4 89.3 89.3 84.6 86.0 84.6 85.1 84.2 80.9



18.

KNIPFEL E T A L .


369

At the present time the actual mechanisms by which the d i g e s t i b i l i t y of the p r o t e i n was reduced have not been e l u c i d a t ed. As already noted, a number of workers have suggested that M a i l l a r d r e a c t i o n s may cause binding of the p r o t e i n to i n d i g e s t i b l e carbohydrates i n the c e l l w a l l (35,45), while a v a i l a b l e Ν may also be reduced s u b s t a n t i a l l y through several c r o s s l i n k i n g r e a c t i o n s (37,38) or through i n t e r a c t i o n s with other plant com ponents (40). In e a r l i e r studies (41,50) c e l l u l o s e d i d not appear to react with casein, egg, or soy proteins to cause de creases i n n u t r i t i v e value upon heating, which i s consistent with the r e s u l t s of the present study showing no changes i n c e l l u l o s e content with heating (Table I I I ) . The increase i n ADIN, however, suggests that there was b i n d i n g of Ν by components of t h i s f i b r e f r a c t i o n , perhaps to a v a r i e t y of carbohydrate and/or noncarbohydrate compounds. As w e l l , the increase i n NDIN i n d i c a t e d that p r o t e i n i n t e r a c t i o n with the h e m i c e l l u l o s e f r a c t i o n of the f i b r e occurred r a p i d l y and to a s i g n i f i c a n t extent. Chemical Treatment

E f f e c t s on Fibrous Feeds

Processing of h i g h l y fibrous feeds to improve the n u t r i t i o n a l value of these m a t e r i a l s for ruminants has been p r a c t i c e d since the beginning of the 20th century. The Beckmann (51) pro cedure has been used i n Europe u n t i l very r e c e n t l y ; t h i s process involved soaking straw with NaOH to improve c e l l u l o s e d i g e s t i b i l ity. A number of other procedures to improve the d i g e s t i b i l i t y of the f i b r e f r a c t i o n of roughages have been developed more recently. These include ammoniation, r e f i n e d NaOH procedures, steaming, and other treatments, which have been reviewed by sev e r a l authors (52,53). Several of these treatments have been developed into commercial processes i n Europe and North America. The primary e f f e c t of treatment of roughages to improve d i g e s t i b i l i t y for ruminants i s to provide a more r e a d i l y a v a i l a b l e source of energy f o r some phase of production. With roughages, a strong p o s i t i v e c o r r e l a t i o n e x i s t s between d i g e s t i b i l i t y and intake, however, so that by i n c r e a s i n g d i g e s t i b i l i t y of rough ages an increase i n intake w i l l also occur and the a v a i l a b l e energy to the animal (and thus production) i s l i k e l y to be g r e a t er than would be expected from the increase i n d i g e s t i b i l i t y . In order to achieve acceptable l e v e l s of production, however, other n u t r i e n t d e f i c i e n c i e s , e s p e c i a l l y that o f N, must be corrected. Ammoniation has been chosen as a method of choice for treatment of crop residues and other low-quality roughage i n Western Cana da, since i t does not r e s u l t i n any increase i n c a t i o n return to the land i n manure, i s r e a d i l y a v a i l a b l e commercially for on-farm use, and also may supply a large part of the Ν d e f i c i t i n lowq u a l i t y roughages (54). Very l i m i t e d information e x i s t s on the actual mechanism(s) by which ammonia or NaOH exert t h e i r e f f e c t s on low-quality f o r ages, although the mechanisms are thought to be s i m i l a r to those proposed by Tarkow and F e i s t (55) f o r hardwoods, i n v o l v i n g both



370

MAILLARD REACTIONS

chemical and p h y s i c a l changes, which w i l l be further discussed i n a later section. Following treatment of b a r l e y straw with 5% NaOH, I s r a e l sen, et^ a l . (56) observed a decrease i n NDF of 14.6 percentage u n i t s , while Braman and Abe (57) found the ADF f r a c t i o n of wheat straw decreased by 5.7 units following NaOH treatment. Rexen (58) showed a s u b s t a n t i a l decrease i n ADF o f barley straw follow ing NaOH treatment, but no e f f e c t o f NaOH on r i c e straw. Itoh, et a l . (59) observed s i g n i f i c a n t decreases i n NDF o f ammoniated r i c e straw, r i c e h u l l s , and orchard hay. Treatment with 3.5% ammonia (Table VI) considerably decreased NDF for both chaff and straw, while ADF showed l i t t l e change. C e l l u l o s e and l i g n i n con tents s i m i l a r l y changed only to a minor extent following ammonia t i o n , with the major change i n the f i b r e f r a c t i o n appearing to be a decrease i n h e m i c e l l u l o s e . A s u b s t a n t i a l increase i n both Ν content and in_ v i t r o OMD also occurred upon ammoniation. In an e a r l i e r study, Kernan ^ t j l . (60) showed that ammoniation doubled the ADIN content of wheat straw and increased that of sweet c l o v er hay by 25%, and these workers proposed that a Mai Hard-type r e a c t i o n between ammonia and some component of thec e l l wall earbohydrate f r a c t i o n would account for theincrease in ADIN. Table VI. %

E f f e c t s of 3.5% Straw

Ν NDF ADF Hemicellulose Cellulose Lignin In v i t r o OMD

0.54 78.8 47.9 30.9 41.1 6.8 38.8

anhydrous NH3 on crop residue

Straw + NH3 1.40 73.8 47.7 26.1 41.9 5.8 53.7

Chaff

Chaff + NH

0.62 70.7 37.9 32.8 34.3 3.6 47.8

3

1.96 65.6 38.3 27.3 35.5 2.8 60.0

Following ammoniation of wheat straw or c h a f f , or crested wheatgrass or A l t a i wild ryegrass hays (Table V I I ) , increases i n NDIN and ADIN were observed. In a l l of the untreated roughages the NDIN represented 30% or more of t o t a l N, which decreased as a percentage o f Ν following ammoniation even though the absolute amount of NDIN increased. Of the Ν absorbed by the feedstuff a f t e r ammoniation the major proportion was present i n the nonf i b r e f r a c t i o n of the c e l l . Except for untreated wheat straw, 50% or more of NDIN was present i n h e m i c e l l u l o s e (Table VII) as i n d i c a t e d by the r a t i o of ADIN to NDIN. A s i g n i f i c a n t decrease in h e m i c e l l u l o s e content of both straw and chaff occurred f o l l o w ing ammoniation, which suggests that the amount of Ν taken up by h e m i c e l l u l o s e was greater per unit of weight than i s apparent when the r e s u l t s are expressed as a proportion of t o t a l sample weight. It i s possible that Ν associated with both NDF and ADF may


18.

KNiPFEL ET A L . Table VII.

Ammoniation e f f e c t s on roughage Ν (%) d i s t r i b u t i o n

Ν

NDIN

ADIN

NDIN Ν

ADIN Ν

Wheat straw Untreated +NH

0.54 1.28

0.20 0.32

0.12 0.16

37.0 25.0

22.2 12.5

60.0 50.0

Wheat c h a f f Untreated +NH

0.68 1.64

0.24 0.34

0.10 0.16

35.3 20.7

14.7 9.8

41.7 47.1

Crested wheatgrass Untreated +NH

0.60 1.36

0.20 0.28

0.08 0.12

33.3 20.6

13.3 8.8

40.0 42.9

A l t a i wild ryegrass Untreated +NH

0.76 1.48

0.24 0.42

0.10 0.16

31.6 28.4

13.2 10.8

35.3 38.1

Roughage

3


371


3

3

3

ADIN NDIN

x

1

0

0

have been removed during the e x t r a c t i o n procedures f o r these fractions. In view o f the decrease i n hemicellulose content of both roughages a s u b s t a n t i a l proportion of the Ν determined as s o l u b l e Ν may have, i n f a c t , been associated with hemicellulose; t h i s should be i n v e s t i g a t e d f u r t h e r . In v i v o d i g e s t i b i l i t y data obtained with sheep using 75% straw and 25% oats (Table VIII) show that ammoniation increased the d i g e s t i b i l i t i e s of a l l r a t i o n components measured. In the f i b r e f r a c t i o n a l l components were increased i n approximately the same order of magnitude i n d i g e s t i b i l i t y . In a d d i t i o n , h e m i c e l l ulose was somewhat higher i n d i g e s t i b i l i t y than c e l l u l o s e both before and a f t e r ammoniation. Of considerable i n t e r e s t would be information regarding the forms and a v a i l a b i l i t y o f Ν to the animal from both untreated and treated straw. The apparent d i g e s t i b i l i t y o f Ν increased f o l l o w i n g ammoniation but t h i s increase was not as pronounced as would have been expected from the increase i n Ν content (Table V I I ) , which was presumably i n a r e a d i l y a v a i l a b l e form since i t was not associated with the f i b r e fraction. Abidin and Kempton ( 6 4 ) r e c e n t l y reported that 65% of the Ν i n ammoniated b a r l e y straw was p o t e n t i a l l y degradable i n the rumen, which i s of the same order o f magnitude as the r e s u l t s of Table V I I I . Intake of d i g e s t i b l e organic matter and d i g e s t i b l e energy increased about 50% f o l l o w i n g ammoniation, while d i g e s t i b l e Ν intake increased more than twofold (Table IX), showing that ammoniation increased the n u t r i t i v e value of straw markedly for the ruminant. The increase i n intake of ammoniated roughages, which has been c o n s i s t e n t l y observed i n our studies, has been considerably greater than increases i n d i g e s t i b i l i t y caused by


372

MAILLARD REACTIONS

Table V I I I .

Straw component d i g e s t i b i l i t y response to ammoniation Treatment


D i g e s t i b i l i t y of:

Untreated 52.8 59.8 62.4 57.7 53.6 61.3 64.0

Ν Energy OM NDF ADF Cellulose Hemicellulose

+NH

3

57.8 64.2 67.2 66.0 62.2 68.9 72.9

ammoniation. This observation i n d i c a t e s that a major e f f e c t of ammoniation has been to increase s u s c e p t i b i l i t y of the f i b r e f r a c t i o n to m i c r o b i a l degradation and thus to increase the rate of d i g e s t i o n to a greater extent than the amount of d i g e s t i b i l ity. However, a number of fundamental questions remain regarding the b a s i c mechanisms of a c t i o n of ammonia (or other treatments) on the f i b r e f r a c t i o n , and the e f f e c t s upon the a v a i l a b i l i t i e s of the native p r o t e i n (N) and carbohydrate f r a c t i o n s . Table IX.

Intake of d i g e s t i b l e components of straw f o l l o w i n g ammoniation Treatment Untreated

1

Intake of: Digestible Ν D i g e s t i b l e energy D i g e s t i b l e organic matter x

g of Kcal/kg

Proposal

7

0.39 180 40.6

+NH

3

0.90 265 59.9

5

f o r Some

Nitrogen-Carbohydrate

Interactions i n

Cereal

In view o f the extreme complexity o f molecular species com p r i s i n g plant c e l l s , obviously any model or explanation f o r n i trogen ( p r o t e i n ) i n t e r a c t i o n s with carbohydrates must be extreme ly s i m p l i s t i c i n r e l a t i o n to t o t a l events o c c u r r i n g i n the plant c e l l , e i t h e r f o l l o w i n g any form of processing or i n r e l a t i o n to reactions o c c u r r i n g under " n a t u r a l " c o n d i t i o n s . For the purposes of attempting to derive a useful working hypothesis f o r studies of n u t r i t i v e value i n c e r e a l grains such as rye, f o r low-quality roughage e v a l u a t i o n , and f o r developing techniques f o r improve ment of n u t r i t i v e value, the diagrammatic s t r u c t u r e f o r the i n t e r a c t i o n of the h e m i c e l l u l o s e f r a c t i o n with nitrogenous mater i a l s such as p r o t e i n or ammonia has been adopted from the o r i g i n a l proposal of Tarkow and F e i s t ( 5 4 ) , and i s shown in Figure 1.


18.

KNIPFEL E T A L .


373

R

0 0 =C A (X) -X-(X) -X-(X) n

n

n


OH R— OH

+

NH

2

0=C

\

A

n

+ H 0 2

Figure 1.

.n

(X) -f-(X)-X-(X)' A ι

Λ simplified model for plant fiber interactions.

Hemicellulose may be considered as a polymer of pentosans although a number of hexoses and other m a t e r i a l s are u s u a l l y pre sent a l s o . The simple s t r u c t u r e can be represented by a xylan chain, with side chains of several sugars but with arabinose prominent. The arabinose u n i t s may be bonded to other compounds (R, e.g., l i g n i n ) by ester linkages with these bonds a c t i n g as c r o s s l i n k s to l i m i t s w e l l i n g or d i s p e r s i o n of the polymer seg ments i n water ( 5 4 ) . There may also be free carbonyl groups as shown i n Figure 1, which could react with p r o t e i n i n amide or Mai H a r d - t y p e r e a c t i o n s . In Figure 1, f o r s i m p l i c i t y , the c a r bonyls shown are carboxyl groups which would undergo r e a c t i o n to produce amide linkages with p r o t e i n . However, there are undoubt edly arabinose and other monosaccharide residues present as branches of the xylan chain which would have aldehyde or keto end groups a v a i l a b l e for c l a s s i c a l M a i l l a r d r e a c t i o n s . While we have not e s t a b l i s h e d that t h i s i s indeed the case, the evidence of increased Ν a s s o c i a t i o n with h e m i c e l l u l o s e f o l l o w i n g heat t r e a t ment i s s t r o n g l y suggestive. Other authors ( 4 6 , 4 8 , 4 9 ) have demonstrated the occurrence of the M a i l l a r d r e a c t i o n i n forages, although there i s considerable controversy over the exact molec ular species r e a c t i n g . From t h i s type of schematic r e p r e s e n t a t i o n i t would be expected that a more h i g h l y branched xylan chain would give more p o t e n t i a l f o r r e a c t i o n of the arabinose residues, e i t h e r through c r o s s l i n k formation or by Mai Hard-type r e a c t i o n s . Indirect evidence supporting t h i s concept can be derived from pentosan a n a l y s i s of the hemicellulose f r a c t i o n of grasses and legumes.



374

MAILLARD REACTIONS

A l f a l f a hemicellulose has been observed (61) to contain an a r a b i nose :xylose r a t i o of about 1:5.5, i n d i c a t i n g that the hemicellu lose i s not h i g h l y branched. In grass species, the r a t i o has been observed to be i n the order of 1:2.6 (62) for g r a s s - a l f a l f a mixtures, but c l o s e r to unity for grasses (63). These data i n d i cate that the hemicelluloses of grasses are more h i g h l y branched, and perhaps c r o s s l i n k e d , than is that of a l f a l f a , which is con s i s t e n t with the observation (60) that ammoniation response i s much greater with grasses than with a l f a l f a . That l i g n i n i s i n t i m a t e l y involved in the s u s c e p t i b i l i t y of these s t r u c t u r a l carbohydrates to degradation i s well docu mented. Considerable a v a i l a b l e evidence (65,66,67) i n d i c a t e s that the ester linkages between l i g n i n and hemicellulose are major f a c t o r s i n t h i s process. The involvement of proteins i s less well defined, although e a r l i e r studies (46,47) demonstrated the close r e l a t i o n s h i p between l i g n i n and p r o t e i n i n heated f o r ages. In a number of studies i t is apparent that the determina t i o n of l i g n i n could have included a s u b s t a n t i a l amount of a r t i fact l i g n i n , which has been suggested (47) to r e s u l t from M a i l lard reactions and be unavailable as a source of amino acids to the animal. The evidence of increases i n NDIN and ADIN i n heated a l f a l fa suggests that Mai H a r d - t y p e phenomena and l i k e l y other r e a c tions are involved i n the decrease i n a v a i l a b i l i t y of Ν o c c u r r i n g f o l l o w i n g heat damage. The e f f e c t s of ammonia in breaking ester linkages and thus i n c r e a s i n g s u s c e p t i b i l i t y of fibrous f r a c t i o n s to b a c t e r i a l attack is well documented, but whether t h i s , i n turn, may render native proteins more a v a i l a b l e i s not known. Furthermore, evidence from studies of rye suggests that the hemi c e l l u l o s e (pentosan) f r a c t i o n of rye g r a i n is involved in e f f e c t s upon amino acid a v a i l a b i l i t y and in intake and d i g e s t i b i l i t y of the g r a i n by monogastric animals. While M a i l l a r d reactions may represent only a portion of the i n t e r a c t i o n s responsible for a l t e r a t i o n s i n n u t r i t i v e value of plant m a t e r i a l s , the r e c o g n i t i o n that such r e a c t i o n may occur at temperatures that can be considered as p h y s i o l o g i c a l in plants r a i s e s a considerably wider spectrum of p o s s i b i l i t i e s for a l t e r a tions i n n u t r i t i v e value of feed- and foodstuffs than has gener a l l y been assumed. As pressure for increased production effi ciency of animals and increased use of nonconventional n u t r i e n t sources increases, the e f f e c t s of processing upon n u t r i t i v e value of these materials w i l l be studied i n greater d e t a i l . Conclusions 1.

2.

The hemicellulose (pentosan) f r a c t i o n of rye grain appears to be i n t i m a t e l y involved i n poor feeding value of rye, perhaps as a r e s u l t of n a t u r a l l y o c c u r r i n g M a i l l a r d r e a c t i o n s . Heat treatment of a l f a l f a r e s u l t s i n increases in p r o t e i n content of the f i b r e f r a c t i o n of the feed. Associated with t h i s increase i s a decrease i n in v i t r o d i g e s t i b i l i t y of OM


18.

3.

4.

KNiPFEL ET A L .


375

by rumen microbes, and reductions i n both ruminai and HC1pepsin d i g e s t i o n of Ν i n v i t r o . Ammoniation of l o w - q u a l i t y roughages g e n e r a l l y reduces the NDF content of the roughage while having lesser e f f e c t s upon ADF or l i g n i n . These changes are associated with increased d i g e s t i b i l i t y and intakes of treated roughages by sheep. The hemicellulose fraction of diverse plant feedstuffs appears to be of considerable importance i n determining n u t r i t i o n a l value and response to processing.


Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

Jones, D.B.; Caldwell; Widness, K.D. J . Nutr. 1948, 35, 639-650. Stromnaes, A.-S.; Kennedy, Barbara M. Cereal Chem. 1957, 34, 96-200. Kihlberg, R.; Ericson, L . - E . J . Nutr. 1964, 82, 385-394. Knipfel, J.E. Cereal Chem. 1969, 46, 313-317. Riley, R.; Ewart, J.A.D. Genet. Res. (Camb.) 1970, 15, 209219. Kubiczek, R.; Rakowska, M. Acta Agrobot. 1974, 27, 105-113. Kubiczek, R.; Molski, B.; Rakowska, M. Hodowla Rosl. Aklimat Nascien. 1975, 19, 617-631. Wiringa, G.W., Wageningen, Holland. Publ. 156, 68 pp. Knoblauch, C . J . ; Elliott, F.C.; Penner, D. Crop Sci. 1967, 17, 269-272. Tanner, D.G.; Knoblauch, C . J . ; Reinbergs, E . ; Su-Wong, H. Cereal Res. Comm. 1980, 8, 461-467. Moran, E . T . , J r . ; Lall, S.P.; Summers, J.D. Poultry Sci. 1969, 48, 939-949. MacAuliffe, T.; McGinnis, J . Poultry Sci. 1971, 50, 11301134. Misir, R.; Marquardt, R.R. Can. J. Anim. Sci. 1979a, 58, 691-701. Misir, R.; Marquardt, R.R. Can. J. Anim. Sci. 1978c, 58, 717-730. Fernandez, R.; Lucas, E . ; McGinnis, J. Poultry Sci. 1973, 52, 2252-2259. Misir, R.; Marquardt, R.R. Can. J. Anim. Sci. 1978b, 58, 703-715. Misir, R.; Marquardt, R.R. Can. J. Anim. Sci. 1978d, 58, 731-742. Marquardt, R.R.; Ward, A.T.; Misir, R. Poultry Sci. 1979, 58, 631-640. Mikola, J.; Kirsi, M. Acta Chem. Scand. 1972, 26, 787-795. Knoblauch, C . J . ; Elliott, F.C. Crop Sci. 1977, 17, 267-269. Wagner, D.D.; Thomas, O.P. Poultry Sci. 1977, 56, 615-619. McNab, J.M.; Shannon, D.W.F. Br. Poultry Sci. 1975, 16, 9-15. Wagner, D.D.; Thomas, O.P. Poultry Sci. 1978, 57, 971-975.


376

24. 25. 26. 27. 28.


29. 30. 31. 32. 33.

34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58.

MAILLARD REACTIONS

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RECEIVED October 5,

1982


The Maillard Reaction in Foods and Nutrition - American Chemical

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