Physiological, Toxicological, and Nutritional ... - ACS Publications

23 Physiological, Toxicological, and Nutritional Aspects of Various Maillard Browned Proteins TUNG-CHING LEE and CLINTON O. CHICHESTER

Downloaded by TUFTS UNIV on November 27, 2015 | http://pubs.acs.org Publication Date: October 25, 1983 | doi: 10.1021/bk-1983-0234.ch023

Department of Food Science and Technology, Nutrition and Dietetics, University of Rhode Island, Kingston, RI 02881 The Maillard, or nonenzymatic browning reaction between reducing sugars and proteins is known to cause serious deterioration of the nutritional quality of foods during processing and storage. Recently, considerable attention has focused on the physiological effects of the ingestion of Maillard browned compounds beyond those that can be attributed to nutritionally related causes. In addition, the food and feed industry often encourages the reaction to produce desirable aromas, colors, and flavors. Thus, if there is indeed a food safety risk associated with Maillard browning, priorities in the food and feed industry may have to be redirected to minimize and control the reaction, rather than encourage it. The present paper will discuss the physiological, toxicological and nutritional aspects of Maillard browning reaction of proteins in foods using many experimental data as illustration. Some of the experiments were done by eliminating variables that may lead to nutritional problems secondary to the effects of feeding Maillard proteins. In addition to using model system approach, some of the experiments were using representative, commercial food products which may undergo some degree of browning due to the processing or storage. In general, thermal processing of foods i s extremely benef i c i a l , r e s u l t i n g i n increases i n d i g e s t i b i l i t y , d e s t r u c t i o n of antagonists of vitamins and enzymes, and i n many instances i n d e s t r u c t i o n of toxins that occur normally i n foods. However, when p r o t e i n s or amino a c i d s a r e heated i n the presence o f c a r bohydrates, a r e a c t i o n takes place between these two components. This r e a c t i o n i s c a l l e d the M a i l l a r d nonenzymatic browning reaction (1) , Hence foods that undergo browning range from toasted bread through such things as d r i e d f r u i t s , gravy mixes, and

0097-6156/83/0234-0379$08.50/0 © 1983 A m e r i c a n C h e m i c a l S o c i e t y

In Xenobiotics in Foods and Feeds; Finley, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


380

XENOBIOTICS IN FOODS AND FEEDS

syrups, to thermally processed meat mixtures such as beef stew, f r a n k f u r t e r s and beans, e t c . In almost a l l cases, the browning r e a c t i o n r e s u l t s i n the production of compounds that are respons i b l e f o r the c h a r a c t e r i s t i c cooked f l a v o r s and c o l o r s of foods. The chemistry of the browning r e a c t i o n has been reviewed p e r i o d i c a l l y (1-7). The carbohydrate-amino a c i d browning r e a c t i o n produces l i t e r a l l y hundreds of r e a c t i o n products. Despite the f a c t that the M a i l l a r d r e a c t i o n has been i n v e s t i g a t e d f o r many years, we cannot as yet i d e n t i f y a l l the reactant compounds. The f i r s t steps a r e , however, c l e a r l y e s t a b l i s h e d . The aldose or ketose r e a c t s with amine to produce N-substituted g l y c o s y l amine ( F i g . 1 ) . This rearranges, as i l l u s t r a t e d , to produce a 1-aminodesoxy-2-ketosyl amine. I f i t i s blocked, the o v e r a l l r e a c t i o n i s blocked. This key compound or compounds can then continue to r e a c t ( F i g . 2 ) . The desoxy-ketose or amadori rearrangement product can dehydrate to produce f u r f u r a l - l i k e compounds o r , through the l o s s of water, produce reductones. A l l of these compounds can r e a c t with one another or with other amine compounds to produce a wide v a r i e t y of r e a c t i o n products. Two aspects of the r e a c t i o n are p a r t i c u l a r l y i n t e r e s t i n g . F i r s t , the c o l o r or the brown product i s a long chain of r a t h e r unsaturated n i t r o g e n - c o n t a i n i n g products sometimes c a l l e d mélan i n e s . I t s composition i s not constant, but i s dependent upon the extent of the r e a c t i o n , and the mix of r e a c t a n t . I t appears to be a moderately good c h e l a t i n g compound and thus may have some i n t e r e s t i n g c h a r a c t e r i s t i c s from a n u t r i t i o n a l standpoint. Another part of the r e a c t i o n which i s of i n t e r e s t i s shown on the r i g h t , the Strecker degradation of the amino a c i d s which produces carbon d i o x i d e (sometimes causing container f a i l u r e ) , and an aldehyde which may then f u r t h e r condense with other compounds. These aldehydic condensation products, together w i t h the amino acid-carbohydrate r e s i d u e , are r e s p o n s i b l e f o r many f l a v o r s . By d e l i b e r a t e l y r e a c t i n g mixtures of d i f f e r e n t amino a c i d s , f l a vors of chicken, beef and pork can be reproduced. The browning r e a c t i o n i s f a i r l y r a p i d and occurs a t comparatively low temperatures . Evidence i s accumulating i n our research group at the Univers i t y of Rhode I s l a n d and elsewhere, that under v a r i o u s processing and storage c o n d i t i o n s there i s a s i g n i f i c a n t and r a p i d decrease i n the n u t r i t i v e value of foods which undergo the M a i l l a r d r e a c t i o n (8-14). The reduced value of the brown products does not seem to be l i m i t e d to the l o s s of amino a c i d s , s i n c e supplementat i o n of the d i e t with those amino a c i d s could not completely r e s t o r e i t s b i o l o g i c a l value (15,16,17). This suggests the p o s s i b l e formation of some i n h i b i t o r y or a n t i - n u t r i t i o n a l compounds during the M a i l l a r d r e a c t i o n . Recently, considerable a t t e n t i o n has focused on the p h y s i o l o g i c a l and t o x i c o l o g i c a l e f f e c t s of the i n g e s t i o n of M a i l l a r d browned compounds beyond those that can be a t t r i b u t e d to n u t r i t i o n a l l y r e l a t e d causes i n c l u d i n g short-term and long-term animal t e s t s . In a d d i t i o n , the mutagenicity of


23.

L E E AND CHICHESTER

H :N-R H


o* H-Ç H-C-OH HO-C-H H-Ç-OH H-C-OH C'H O H

Various

Maillard

Browned

(OH )? -

(H + )?

2

Proteins

O-H H-6 H-C-OH ΗΟ-φ- Η Η -Ç-OH H-C-OH C'H OH 2

ALDOSE OR KETOSE

N-SUBSTITUTED GLYCOSYLAMINE

+ AMINE AMADORI REARRANGEMENT

-H 0 2

V H-C-NHR Ç-0 HO-C-H H-C-OH H-C-OH CH-OH 2

H-Ç-NHR C-OH HO-Ç-H H-Ç-OH H-C-OH CH-OH 2

1-DEOXY-2-KETOSYLAMINE Figure

1. Initiation

1,2-ENEAMINOL

of the Maillard reaction. If the keto (Amadori) not formed, there is no Maillard browning.

compound


382

XENOBIOTICS IN FOODS AND FEEDS

aldose sugars

amino compounds

1-amino-1-deoxy-2-ketose -3H 0


2

HMFor furfural

J

-2H 0 2

fission products (carbonyl products)

reductones

Strecker degradation CO* +

aldehyde + amino compounds

+ amino compounds with or without amino compounds

aldimines aldose and N-free polymers

+ amino compounds

I aldimines + ketimines

aldimines

1 CONDENSATION REACTION water soluble water insoluble Figure

2. The Hodge

scheme

M E L A N O I D I N S (brown pigments)

of the browning

reaction.



23.

L E E A N D CHICHESTER

Various

Maillard

Browned

Proteins

383

browning products has been i n t e n s i v e l y s t u d i e d (19-23). The formation of mutagenic substances i n cooked foods which may be p a r t i a l l y a t t r i b u t e d to M a i l l a r d browning r e a c t i o n have been r e ported by many researchers (24,25,26,27,29). Given the f a c t that many processed foods, e.g., dry mixes, canned soups, e t c . , c o n t a i n p r o t e i n and carbohydrates that undergo browning during processing and continue to brown upon storage, and that processed foods are widely d i s t r i b u t e d and consumed, i t i s l i k e l y that the average person d a i l y i n g e s t s low l e v e l s of various "brown" substances, the long-term e f f e c t s of which are as yet completely unknown. Thus i t i s extremely important to i n v e s t i g a t e f u r t h e r the n u t r i t i o n a l , p h y s i o l o g i c , and s a f e t y a s pects of the M a i l l a r d r e a c t i o n products and to study the p o s s i b i l i t y of modifying processing and storage procedures to minimize the undesirable e f f e c t s of browning. TABLE I . Brown c o l o r development of p r o t e i n and p r o t e i n - g l u c o s e mixtures during cooking

Absorbance ( A ) * Microwave oven time (min) Samples Egg albumin Egg albumin-glucose Soybean-protein Soybean-protein-glucose Casein-glucose Lactalbumin-glucose Zein-glucose

Conventional oven time (min)

1

3

5

0.010 0.001 0.002 0.050 0.007 0.002 0.046

0.015 0.135 0.008 0.170 0.102 0.259 0.057

0.059 0.506 0.043 0.135 ND 0.994 0.107

30 0.00 0.246 0.015 0.140 ND 0.894 0.088

45 0.045 0.788 0.050 0.290 1.744 1.084 0.092

From T.H. Chen, T . C Lee and C O . Chichester, unpublished data. ND =not determined. *The absorbance (A) of T C A - ( t r i c h l o r o a c e t i c acid) s o l u b l e p o r t i o n at 420 nm as measured against the uncooked sample. The purpose of t h i s paper i s to d i s c u s s the p h y s i o l o g i c a l , t o x i c o l o g i c a l and n u t r i t i o n a l aspects of M a i l l a r d browning r e a c t i o n of p r o t e i n s i n foods. N u t r i t i o n a l and P h y s i o l o g i c E f f e c t s of M a i l l a r d Browning The d i f f e r e n c e between heating a p r o t e i n and a p r o t e i n with an aldose sugar i s shown i n Table I . There i s a 10-fold i n c r e a s e i n l i g h t absorption of the egg albumin-glucose mixture above egg albumin when heated f o r 5 min i n a microwave oven. An even l a r g e r d i f f e r e n c e i s shown between soybean p r o t e i n with added glucose.


384

X E N O B I O T I C S IN F O O D S A N D F E E D S

The l o s s of n u t r i t i v e value when p r o t e i n or p r o t e i n - r i c h foods are heated or stored i n the presence of carbohydrates has been studied by a l a r g e number of groups (8,10,12,18,29,30). A decrease i n the d i g e s t i b i l i t y of p r o t e i n s and i n the a v a i l a b i l i t y of amino acids and carbohydrates a f t e r the M a i l l a r d r e a c t i o n i s shown i n Table I I . I t can be concluded from t h i s that the b i o l o g i c value of p r o t e i n s has a l s o decreased. For example, i n Table III one can see s i g n i f i c a n t decreases i n amino a c i d s of egg albu-n


TABLE I I . Loss of n u t r i t i v e value when p r o t e i n s or p r o t e i n - r i c h foods are heated i n the presence of carbohydrates. N u t r i t i v e Value

Change

D i g e s t i b i l i t y of p r o t e i n s A v a i l a b i l i t y of amino acids A v a i l a b i l i t y of carbohydrates B i o l o g i c value of p r o t e i n s

Ψ Ψ Ψ Ψ

TABLE I I I . Amino a c i d composition (g/16 g Ν) of browned egg a l b u min hydrolyzed by 6 Ν h y d r o c h l o r i c a c i d Percentage loss i n protein Amino a c i d s

0 days

10 days

20 days

30 days

Aspartic acid Threonine Serine Glutamic a c i d Proline Glycine Alanine Valine 1/2-Cystine Methionine Isoleucine Leucine Tyrosine Phenylalanine Lysine Histidine Arginine Tryptophan*

10. 12 3. 50 7. 26 11. 01 2. 39 3. 99 7. 52 6. 53 3. 44 3. 34 5. 97 8. 97 3. 33 5. 26 7. 68 2. 76 3. 68 1. 61

10. 15 3. 39 6. 40 9. 78 2. 82 3. 42 5. 51 6. 24 2. 46 3. 47 5. 71 9. 13 2. 97 5. 92 5. 92 2. 53 3. 26 1. 47

10. 42 9.58 4. 22 3.45 6. 57 6.88 10. 24 10.01 2. 50 2.41 3. 65 3.33 6. 50 5.84 6. 77 6.37 2. 62 2.71 3. 55 3.28 5. 36 5.37 8. 97 8.27 3. 02 3.04 5. 82 5.52 4. 19 4.04 2. 36 2.39 3. 01 2.22 1. 34 1.24

40 days 10. 58 3. 53 5. 72 9. 44 2. 40 3. 88 6. 82 6. 49 2. 86 3. 07 5. 25 7. 46 3. 04 4. 93 3. 29 2. 12 1. 78 1. 26

40 dayi

— — 21.2 14.3

— 2.8 9.3

— 16.9 9.1 12.1 16.8 9.7 6.3 57.2 23.3 51.6 21.7

From r e f . 32 *Tryptophan was determined a f t e r a l k a l i n e h y d r o l y s i s .



23.

L E E A N DCHICHESTER

Various

Maillard

Browned

Proteins

385

min s t o r e d at 37°C i n the presence of roughly the equivalent amount of glucose. The moisture content of the mix was 15%. A f t e r 10 days, there i s a very s i g n i f i c a n t decrease i n l y s i n e a v a i l a b i l i t y , which combines to decrease as the browning i s prolonged. At 40 days, roughly 57% of the l y s i n e i s l o s t (10). Other changes are shown i n Table IV (31) where a number of n u t r i t i o n a l i n d i c e s are compared f o r the egg albumin-glucose mixt u r e , which our group has used as a model mixture. Using the zero or nonreactive day as 100, there i s a steady decrease i n the p r o t e i n score, chemical s c o r e , e t c . P a r t i c u l a r l y i n t e r e s t i n g i s the o b s e r v a t i o n that p r o t e i n e f f i c i e n c y r a t i o (PER), a measurement of the a b i l i t y of the d i e t to maintain growth, decreased by one-third w i t h i n 10 days. T h i s i s a s i g n i f i c a n t l y higher decrease than any of the other measurements would suggest. Thus the b i o l o g i c n u t r i t i v e changes observed are more complicated than merely a l o s s i n the a v a i l a b i l i t y of amino a c i d s or p r o t e i n s . Our group and s e v e r a l others have shown that supplementing a d i e t that has undergone browning w i t h l o s t amino a c i d s cannot completely r e s t o r e i t s b i o l o g i c value (15,16,17). This suggests the p o s s i b l e formation of some i n h i b i t o r y or a n t i n u t r i t i o n a l compounds during the M a i l l a r d r e a c t i o n . Even a very short period of browning at 37 C i s measurable i n terms of PER. A f t e r 1 day of browning at 37 C there i s a 30% r e d u c t i o n i n the PER (Table V) (32). We have standardized most of our work i n u t i l i z i n g the 10-day sample. The PER of t h i s m a t e r i a l i s s u f f i c i e n t l y high that the animals can s u r v i v e and yet s u f f i c i e n t l y low that the maximum p h y s i o l o g i c e f f e c t on the animals i s observed. I f one observes animals on a d i e t with a high c o n c e n t r a t i o n of browned m a t e r i a l s , one immediately notes that almost a l l of the animals have severe d i a r r h e a . I t i s also obvious on f u r t h e r examination that animals on the d i e t develop enlarged cecums. Another observed e f f e c t upon the d i g e s t i v e system of animals i s the i n c r e a s e i n the e x c r e t i o n of e s s e n t i a l and n o n e s s e n t i a l amino a c i d s i n the form of short peptides, 4-6 r e s i d u e s l o n g , i n the f e c e s . Coupled with t h i s , the f e c a l n i t r o g e n content i s approximately 35% above the c o n t r o l , p o s s i b l y r e l a t i n g to the e x i s t e n c e of d i a r r h e a and the decrease i n the r a t e of stomach emptying (33). Although these changes were p r i m a r i l y noted when d i e t s such as egg albumin-glucose were f e d , s i m i l a r changes are observed when more conventional d i e t s are f e d . For i n s t a n c e Tsen et a l . (34) observed equivalent reductions i n PER when a number of breads were heated i n microwave ovens, i n steam, or were baked using conventional methods. Here, reductions i n PER were t h r e e f o l d or more.


386

X E N O B I O T I C S IN F O O D S A N D ο

Physiological, Toxicological, and Nutritional ... - ACS Publications

Recommend Documents