Transglycosylation reactions, a main mechanism of phenolics incorporation in coffee melanoidins: Inhibition by Maillard reaction

•Non-enzymatic transglycosylation reactions (TGRs) are induced by roasting.•One third of the phenolics present in coffee melanoidins are incorporated via TGRs.•Proteins play a regulatory role in TGRs extension, modulating melanoidins composition.•TGRs are inhibited by amino groups through Maillard reaction.

Under roasting conditions, polysaccharides depolymerize and also are able to polymerize, forming new polymers through non-enzymatic transglycosylation reactions (TGRs). TGRs can also occur between carbohydrates and aglycones, such as the phenolic compounds present in daily consumed foods like coffee. In this study, glycosidically-linked phenolic compounds were quantified in coffee melanoidins, the polymeric nitrogenous brown-colored compounds formed during roasting, defined as end-products of Maillard reaction. One third of the phenolics present were in glycosidically-linked form. In addition, the roasting of solid-state mixtures mimicking coffee beans composition allowed the conclusion that proteins play a regulatory role in TGRs extension and, consequently, modulate melanoidins composition. Overall, the results obtained showed that TGRs are a main mechanism of phenolics incorporation in melanoidins and are inhibited by amino groups through Maillard reaction.

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