Melanoidins oxidation

Oxidation—reduction reaction MELANOIDIN-TYPE POLYMERS... 

The pigments of soy sauce, first studied by Kurono and Katsume (100), are melanoidins, which were reported by Omata, et al. (101) to be produced from the reaction of sugars and amino acids. Kato, e a l. (102) found 3-deoxyglucosone as an intermediate in browning of soy sauce (cf. 103). Oxidative browning (104,105) was again reviewed (44) with emphasis on the browning of Amadori compounds and interaction between melanoidins and iron. 

Kato, H. Tsuchida, H. Estimation of melanoidin structure by hydrolysis and oxidation. Prog. Food Nutr. Sci. 1981, 5, 147-56. 

Motai, H. Nonenzymatic oxidative browning Polymerization of melanoidins. Kagaku To Seibutsu 1975, 13, 292-4. 

Lipid oxidation products react with proteins and other amino compounds to form brown substances, similar to melanoidins. The formation of such brown substances was reviewed already at the first Maillard Symposium.150 The pigments formed are partly soluble in chloroform-methanol and partly insoluble, whereas true melanoidins are largely water-soluble. As most brown pigments of fish muscle are soluble in benzene-methanol and only to a lesser extent in water, the implication is that here oxidised lipid-protein interactions are more important than Maillard browning due to ribose-amino acid interactions. 

Electron-spin resonance (ESR) indicated free radicals in a brown polymer (mean ca 1 kDa by field-desorption MS) from a glucose-4-chloroaniline model system.185 Such free radicals (see Chapter 2) could be a source of visible colour. Exposure of the melanoidin to nitric oxide, a radical-trapping agent, diminished the ESR signal by 48% and changed the colour to red-brown. 

Overall, there is no doubt that the Maillard reaction produces substances with an antioxidative effect, but it is by no means clear as yet how and to what extent that effect is exerted. Melanoidins not only have increased reducing power, but are able to complex metals and, in this way, lower their ability to act as catalysts in lipid and other oxidations. 

Superoxide radicals are another factor in oxidative damage. They can be determined with nitrobluetetrazolium (NBT), which then forms the colourless formazan. When melanoidins scavenge the superoxide radicals, the colour of the NBT persists.490,491 The activity of a glucose-glycine melanoidin on superoxide radicals is equivalent to the effect of 16 units of superoxide dismutase. The effect of the HMM and LMM fractions of this melanoidin is almost the same. The reaction rate constant of the melanoidin was markedly higher than that of ascorbic acid. If this were due to the reductone structures embedded in the melanodin, it is difficult to explain why the reducing power of the melanoidins is only 0.7 that of ascorbic acid.490... 

J. Gasic-Milenkovic, S. Dukic-Stefanovic, K. Nowick, W. Conrad, and G. Munch, Oxidative stress and re-entry of neurones into the cell cycle can advanced glycation end-products derived from food cause double trouble in the brain in Melanoidins in Food and Health, J. M. Ames (ed), European Communities, Luxembourg, 2001, 107-115. 

Calligaris et al. (2004) studied changes in antioxidant and pro-oxidant activity in milk subjected to different heat treatments. Their results indicated that short heat treatments can be potentially responsible for a depletion in the overall antioxidant properties of milk. Only the application of severe heat treatments, associated with the formation of brown melanoidins, allowed a recovery and even a possible increase in the antioxidant properties of milk. 

There have been a number of reports on the Maillard reaction. Oxidation of the melanoidins produced from D-glucose and glycine with potassium permanganate and peracetic acid yielded, among other products, furan-2,5-dicarboxylic acid, suggesting that 5-hydroxymethyl-2-furaldehyde is a precursor of the melanoidic pigments produced in the Maillard reaction. 2-(2-Formyl-5-hydroxymethyl-... 

Figure 10. The comparison of antioxidative activity of melanoidin with that of oxidized melanoidins. The concentration of melanoidin was 20 mg/100 ml of distilled water.

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