Decolorization and Degradation Products of the Melanoidins by Hydrogen Peroxide

Abstract

Nondialyzable melanoidins prepared from a glucose-glycine system were incubated with glucose oxidase under optimal conditions and then the melanoidins were decolorized to 65%. The decolorization of melanoidins by glucose oxidase may be mainly caused by hydrogen peroxide produced from the enzyme-substrate reaction. Therefore, oxidative decomposition and decolorization of melanoidins were tried using hydrogen peroxide. Melanoidins were treated with hydrogen peroxide (final cone. 6.72%) under neutral (pH 7.0) and alkaline (pH 10.0) conditions at 37°C for 28 hr. Melanoidins were decolorized to 64% and 97%, respectively the under above optimum conditions. The mean molecular weight of melanoidins decreased from 5,300 to 3,500 after hydrogen peroxide treatment. The major components in the ether-soluble fraction obtained from melanoidins by oxidative degradation of alkaline hydrogen peroxide were identified as 2-methyl-2,4-pentanediol, N,N-dimethylacetamide, phenol, acetic acid, oxalic acid, methylpropane-dioic acid, propanedioic acid, 2-furancarboxylic acid, butanedioic acid, 2-hydroxypropanoic acid, 2,5-furandicarboxylic aicd and 5-(hydroxymethyl)-2-furancarboxylic acid. On the other hand, the major degradation product in aqueous fraction was identified as glycine, and glycine was produced in 1.73% yield per nondialyzable melanoidin. © 1984, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.