Early Maillard reactions

The extent of heat-induced changes in protein-rich foods can be measured by determining some early Maillard reaction products (O Brien and Morrissey, 1989). Acid treatment of protein-bound or free A -fructoselysine liberates lysine, with a yield of 50%, and two other amino acids, furosine (20%) and pyridosine (10%) (Figure 13.1). The three products that result from hydrolysis of A -lactuloselysine are formed in the proportions of approximately 5 3 to 4 1 to 2, however the yield of different derivatives is variable. Therefore, in order to use these unique amino acids as indicators of changes in lysine content, the hydrolysis should be carried out in strictly-defined conditions. Furosine is present in various food products in a very wide range of concentrations (Table 13.2). 

Although the early Maillard reaction products are reported to have antioxidant properties and, in fact, can be utilized by processors to inhibit lipid oxidation in animal protein foods such as fish products, there is an accompanying lysine loss (4 5). 

T. Henle, H. Walter, and H. Klostermeyer, Evaluation of the extent of the early Maillard-reaction in milk products by direct measurement of the Amadori-product lactuloselysine, Z. Lebensm. Unters. Forsch., 1991, 193, 119-122. 

T. Matsuda, Y. Kato, K. Watanabe, and R. Nakamura, Direct evaluation of P-lactoglobulin lactosylation in early Maillard reaction using an antibody specific to protein-bound lactose, J. Agric. Food Chem., 33 (1985) 1193-1196. 

B. PignatelU, C. Malaveille, M. Friesen, A. Hautefeuille, H.Baitsch, D. Piskorska, and G. Descotes, Syndiesis, analysis and mutagenic activity of A-nitroso derivatives of glycosylamines and Amadoii compounds Nitrosated model substances for the early Maillard reaction products, lARC Sci. Publ, 84 (1987) 277-283. 

U. Schwietzke, U. Schwarzenbolz, and T. Henle, Influence of cheese type and maturation time on the early Maillard reaction in cheese, Czech J. Food Sci., 27 (2009) S140-S142. 

A. Rerat, R. Calmes, R Vaissade, and R-A. Finot, Nutritional and metabolic consequences of the early Maillard reaction of heat treated milk in the pig. Significance for man, Eur. J. Nutr., 41 (2002) 1-11. 

Radical reaction mechanisms during the early Maillard reaction were first detected by Namiki et al. (7, 2). He identified iV.A -dialkylpyrazine-cation radicals that originated from the primary Schiff base formed by reaction between glucose and amino acids. The glycolaldehyde alkylimine formed by a reverse aldol reaction of the Schiff base leads to a dialkylpyrazinium radical cation after self-condensation. The formation of dialkylpyrazinium radical cations, which could be detected by EPR spectrometry, represents an alternative pathway of the Maillard reaction it starts at the very beginning of die reaction, well before the formation of Amadori rearrangement products and depends on the pH value it starts around pH 7 and increases up to pH 11. 

Low temperatures (70 C) favor the formation of early products (1 and 7) and slow down their degradation to more stable compounds (Figure 11). On the other hand higher temperatures lead to more rapid production of early Maillard reaction products. At 130 C for exanple, p-pyranone, cyclopentenone and 3-furanone are barely detectable, whereas late products such as glucosyl isomaltol, acetylpyrrol and pyrraline become predominant. 

In heat treated or stored food products several amino acids are not fully available because of derivatization or crosslinking reactions. Since 30 years furosine is known as a useful indicator of early Maillard reaction which is applied in food science, nutrition and medical biochemistry. Recently more sensitive analytical methods for furosine determination are available which have again increased the attractivity of this important indicator. Lately, N -carboxymethyllysine (CML) became available as another marker of special interest, because CML is a more useful indicator of the advanced heat damage by Maillard reaction than furosine. In addition, CML has the advantage to indicate reactions of lysine with ascorbic acid or ketoses such as fructose. Indicators for protein oxidation of sulfur amino acids are methionine sulfoxide and cysteic acid. An established marker for cross-linking reactions is lysinoalanine, which also indicates protein damages due to processing under alkaline conditions. Other markers formed as a consequence of alkaline treatment are D-amino acids. 

Several methods have been developed for assaying non-enzymatic glycosylation. As far as biological systems are concerned, these have been extensively reviewed by A. J. Furth in 1988 (5). They include both assays on intact proteins after chemical degradation and selective detection of e.g. 5-hydroxymethylfurfural (HMF) and formaldehyde using the thiobarbituric assay (TEA), and assays on protein hydrolysates with or without previous reduction of the protein-bound Amadori compound. In this last case, the analysis is based on the determination of furosine which is specifically formed from lysine Amadori compounds with a yield of approximately 30% (6). The furosine method, originally developed for milk (7), has been the subject of several analytical improvements both for food products (8) and biological materials (9). More recently, another method has been proposed to evaluate the extent of early Maillard reaction in milk products. This method is based on direct measurement of the Amadori product lactuloselysine which is released after complete enzymatic hydrolysis (10). 

ANTITUMOR EFFECTS OF THE EARLY MAILLARD REACTION PRODUCTS... 

Antitumor Effects of the Early Maillard Reaction Products Table 1. 

Maillard reactions are complex and as yet not fully understood but they do appear to follow common pathways which can be divided conveniently into early Maillard reactions and advanced Maillard reactions. The preliminary steps are shown in Fig. 2. The first step... 

Reduction with borohydride (Lys J), This method, developed by Hurrell and Carpenter first stabilises the bond between the e-amino group and the sugar derivative by hydrogenation and then applies the usual acid hydrolysis. Blocked lysine from an early Maillard reaction, stabilised in this way, does not regenerate lysine upon acid hydrolysis. 

The determination oj furosine (LySfu )- This method is based on the fact that lysine blocked in an early Maillard reaction in the form of e-N-deoxyketosyl-lysine yields upon acid hydrolysis a constant proportion of furosine (Fig. 2) (e-N-2-furoylmethyl-L-lysine). The blocked lysine corresponds, then, to 3-1 times furosine. The available lysine value can then be calculated by subtracting the blocked lysine value from the theoretical lysine value (ThL = lysine present in the unheated milk sample). 

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