Lipid Oxidation in Food - ACS Publications - American Chemical Society

Chapter 8

Maillard Reaction Products and Lipid Oxidation Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 1, 2016 | http://pubs.acs.org Publication Date: August 5, 1992 | doi: 10.1021/bk-1992-0500.ch008

Milton E. Bailey and Ki Won Um Department of Food Science and Human Nutrition, 21 Agriculture Building, University of Missouri, Columbia, MO 65211

An important aspect of food processing involving Maillard reaction products (MRP) is their reactivity as antioxidants in food systems, particularly meat. A brief review is given of the general pathways of the Maillard reaction and the components of MRP as antioxidants and some possible mechanisms of antioxidants in the various reaction fractions. More specific results are given concerning the use of MRP to reduce oxidation of lipids in cooked meats. Both the water-soluble low molecular weight and polymeric fractions of MRP have antioxidant potential. The intermediate constituents such as maltol, dihydroxyacetone, glyceraldehyde and reductones behave as antioxidants or anti oxidant precursors in these reaction systems. Low molecular weight diffusate components, as well as MRP from glucosehistidine and other precursors for meat flavor, improve and preserve the acceptance of cooked meat during storage. A most difficult aspect of food preservation is the control of oxidation that most natural and processed foods undergo, which results in formation of characteristic undesirable odors and flavors. The most general approach for improving flavors of oxidizable foods is through the use of additives. Antioxidants most frequently used include synthetic additives such as B H A and B H T , which are constantly under safety surveillance and investigation. These and related additives are becoming less acceptable to the consuming public and food legislators. One solution used by manufacturers for decreasing risk to consumers and increasing food acceptability is the use of natural products as additives. One such group of antioxidants that have utility in a number of food products is that produced by the Maillard reaction. The precursor chemical constituents for these reactions can be considered natural because the reactions occur normally

0097-6156/92/0500-0122$06.00/0 © 1992 American Chemical Society St. Angelo; Lipid Oxidation in Food ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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Maillard Reaction Products and Lipid Oxidation

123

in the processing of many foods. The use of M R P for retarding lipid oxidation in foods has been revisited and discussed by several authors (1-4).

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 1, 2016 | http://pubs.acs.org Publication Date: August 5, 1992 | doi: 10.1021/bk-1992-0500.ch008

The Maillard Reaction The Maillard reaction has been discussed by numerous authors in the past and is under constant review. Some early important reviews of the Maillard reaction were those of Hodge (5, 6), Anet (7), Reynolds (8-10) and Baltes (11). More than 20 reviews have been published on the chemistry of the Maillard reaction since 1975 (4, 12-27), and there have been four symposia on this important subject during the same time (28-31). The Maillard reaction (nonenzymatic browning) is the interaction of carbonyl compounds and amines (amino-carbonyl reaction) to produce, through a series of complex reactions, a number of flavor precursors, flavorants and antioxidants, as well as polymerized brown pigments (melanoidins). One series of reactions involves the condensation of the carbonyl and amine through the C - l of aldoses and the C-2 of ketoses with subsequent rearrangement to the keto or aldo sugars (Amadori or Heynes intermediates) involving reactions that are reasonably well understood. A n important step in these reactions is the Amadori rearrangement of the sugar moiety to irreversibly produce ketosyl compounds that enolyze and degrade by complex reactions to produce intermediate products (4). The most widely accepted mechanisms for degradation pathways of Amadori compounds by dehydration and fission were suggested by the brilliant work of Hodge in early publications (5, 6) and there have been few improved ideas since that time, although some new supportive data have been published (32-35). As diagrammed in Figure 1, three major pathways leading to the formation of intermediate compounds in flavor, antioxidant and pigment formation arise from Amadori compounds. These are the 1-deoxyosone, the 1-deoxyreductone and the 3-deoxyosone. A fourth major leg of degradation involving intermediates is the Strecker degradation. Compounds such as maltol, isomaltol, cyclotene, 5-hydroxy-5,6-dihydromaltol, 4-hydroxy-3(2H)-furanone and similar components arise from the 1- deoxyosone pathway by dehydration. A n enol form of the 1-deoxyosone (1-deoxyreductone) is degraded by fission to produce pyruvaldehyde, diacetyl, acetaldehyde, acetic acid and reductones. These compounds have tremendous potential as precursors for antioxidants and flavor compounds, particularly when heated with amines. The third pathway begins with a 1-2-enediol form of the Amadori compound by eliminating a hydroxyl group at C-3. Deamination yields a 3-deoxy component that becomes a reductone by eliminating another molecule of water. Further dehydration under acidic conditions occurs to yield 2- furaldehydes (16, 32). This type of dehydration of sugars under acetic conditions without the interactions of the amines is of extreme importance in the analytical chemistry of carbohydrates and the caramelization reactions have been studied in detail by Feather and coworkers (33, 36-38).

St. Angelo; Lipid Oxidation in Food ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

LIPID OXIDATION IN FOOD

124

H C—7.0

I

H-C-OH

O

2 u H

C—OH

|

X CH

aC

N

Diacetyl 7

3

O

x

H-C-OH

HaC^^CHgOH

Hydroxyacetone

,, _ „ Reductone pH < 5.0 -2H 0 -RNH 2

>

2

H-C=0 I

c=o

I C—H

-H 0 2

R

~"^s

s

^ ^ C H O

(

-Furfural H) R

II

C—H

I

H-C—OH 3-Deoxyosone Amadori Compounds

Carbonyl Intermediates

Flavour Compounds

Figure 1. Deamination-dehydration of Amadori compounds to reductones and "flavor compounds" which serve as intermediates for meat flavor volatiles.


8. BAILEY & UM


US

The Strecker degradation is an oxidative decarboxylation of amino acids by reactions with dicarbonyls such as glyoxal, diacetyl and perhaps 3-deoxyosones. The new Schiff base formed has one less carbon atom than the original amino acid and is hydrolyzed to an aldehyde. The Strecker aldehydes are very reactive as flavor precursors and can condense with themselves by aldol condensation or with cyclic compounds to form melanoidins that have antioxidant properties. The evolution of C 0 during melanoidin formation has been demonstrated implicating Strecker degradation of amino acids as an important step (4). These reactions do not, however, explain all the activities of Maillard reaction products as antioxidants and the formation of reductones by specific pathways and free radical formation through mechanisms described by Namiki and Hayashi (59), who proposed a mechanism of free-radical formation in the early stage of carbonyl-amine reaction prior to Amadori rearrangement. Analysis of hyperfine structures of E S R spectra led to the identity of radicals such as N , N and pyrazine cation radicals. The radicals produced were assumed to be formed by condensation of 2 moles of 2-carbon alkylamine (enaminol) compounds produced by fragmentation of the sugar or sugar-amine with subsequent dimerization to form N , N'-disubstituted pyrazine radicals. Since the autoxidation of unsaturated fatty acids is believed to occur by freeradical mechanisms following hydroperoxide formation, there is justification for believing that components formulated by this mechanism contribute to antioxidant properties of these reactions.


2

+

M R P Antioxidants Antioxidants can be formed at several levels during heating of carbonyl-amine mixtures, including degradation of Amadori compounds to amino reductones, to reductones, or formation of polymers with antioxidants activity. Namiki (4) recently published an excellent review of the Maillard reaction which revealed superior knowledge and interest in the development of the types of antioxidants mentioned above. His discussions are most comprehensive regarding use of M R P as antioxidants in foods. Hodge and coworkers (40-42) were the first to demonstrate that M R P had antioxidant activity for preserving oils. Evans et al. (42) were able to demonstrate that reductones from M R P could retard oxidation of vegetable oils. Reductone is a trivial name for 3-hydroxy-2-ketopropane and consists of vicinal dicarbonyl compounds capable of enolization or enol forms forming keto groups following loss of hydrogen atoms. -2H R - C ( O H ) = C ( O H ) - C O - R ' - R - C O - C:0 - C O - R ' Where R and R ' can be alkyl aryl or ends of cyclizing biradicals. Prominent examples are triose reductone, dihydroxymaleic acid, reductic acid and dihydroxy pyrogallol. Reductones as organic reducing agents were


126

LIPID OXIDATION IN FOOD

discussed by Hodge and Osman (13), who described them as having functional groups derived from conjugated enedial and carbonyl forms as above. These authors also indicated that amino analogs where hydroxyl groups were replaced by N H or where carbonyl groups were replaced by - C = N R groups could behave as strong reducing agents. Triose reductone ( H - C ( O H ) = C ( O H ) - C : 0 - H ) is formed when reducing sugars are heated in alkaline solution. Reductic acid is easily formed from uronic acids such as pectin in acid solutions above 100 °C. The cyclic reductones such as reductic acid and ascorbic acid are generally more stable than their acyclic counterparts. Crystalline amino-reductones have been prepared from hexoses and secondary amines (42), which were shown to inhibit peroxide formation in a variety of animal fats and oils. Oxidation inhibition by some of these compounds is approximately a linear function of concentration when used between 0 and 0.02%. Some of these reductones were much more effective in reducing oxidation of soybean oil and cottonseed oil than treatments with propyl gallate of the same level. The structure of amine reductones was elucidated (43) using piperidino reductone as a model. This reductone was characterized as N-[l-methyl-1,2,3trihydroxy-cyclopenten(2)-ylidine(4)]piperidinium beatin (N-+2 or 3). The other amino-hexose reductones in all probability have analogous structures. Ledl et al. (44) recently expanded and confirmed some of these reactions where they identified several new heterocyclic and carbocyclic compounds from reactions between sugars and secondary amines. Among products identified were j8-oxypyridinium betainols, 0-pyranones, pyridones and cyclopentenones. Another important group of compounds formed by further dehydration of 2,3-enolization compounds (2,3-osones) following recondensation with amines are amino reductones, which have possible activities as antioxidants. Davidek et al. (45) summarized reactions from other workers (46) showing the degradation of D-fructoseamine in alkaline solution (Figure 2). The importance of this type of compound as an antioxidant in M R P reaction mixtures cannot be overemphasized since the presence of an amino group appears to be essential for the formation of antioxidants. Amino reductones are possibly more effective and stable than their enediol counterparts. The amino reductones of Evans et al. (42) were excellent antioxidants because the nitrogen moiety can contribute electrophilic groups which might form chelates with metal ions such as copper and iron, which are known for their oxidative catalytic activities. As reviewed by Bailey et al. (2), the melanoidin polymers formed from the interaction of carbonyl amines contribute to the antioxidant properties of M R P . A strong contributor to data regarding the effectiveness of melanoidins as antioxidants has been Yamaguchi et al. (47), who published information on the antioxidant activity of several melanoidin fractions using a model system of linoleic acid at p H 7.0 and peroxide values as a measure of oxidation. The melanoidins prepared by heating glycine and xylose were separated into three molecular weight fractions on Sephadex G-100 and thin layer chromatography. The highest molecular weight fraction (4,500 daltons) had the


2


8. BAILEY & UM


D-FRUCTOSAMINE


CH 1

2.3-ENIDIOL

CH

\ 3

I

3

c=o

c=o

I H-C-OH I

I

c=o H-

Lipid Oxidation in Food - ACS Publications - American Chemical Society

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