Investigation of the influence of reaction conditions on the elementary composition of melanoidins

The elementary composition of melanoidins produced in solvent-free reaction mixtures differs, markedly, depending on whether pentoses (ribose) or hexoses (glucose, fructose) are used. In the case of ribose, more than 4 mol sugar are incorporated into the melanoidin per mol amino acid, whereas, under the same reaction conditions, only about half the number of moles for hexoses are involved. The fundamental composition of model melanoidins under constant reaction conditions is only negligibly influenced by the molar ratio of the reactants. Reaction conditions have a significant influence on the composition of the polymers. Depending on the reaction temperature in a solvent-free milieu, at least 2 mol glucose per mol amino acid are incorporated into the polymer. In aqueous solution this ratio decreases to less than 1:1. In agreement with results of the elementary composition of melanoidins, a new fundamental structure of the polymer which is formed by reaction of dicarbonyl compounds with one another or with amino components is proposed. The structure is supported by IR, UV and CP-MAS NMR studies.