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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