Intermediary and/or advanced Maillard products exhibit prooxidant activity on Trp: In vitro study on α-lactalbumin

Complex glycoxidation reactions take place during heat treatment of proteic foods leading to protein oxidative damage and nutritional loss. This study investigates the oxidative effect of Maillard products on Trp in α-lactalbumin incubated at 90 °C, and compares it with that of radical generating model systems. Trp oxidation rates were measured, on the one hand during the Maillard reaction—by incubation in the presence of lactose or preformed intermediary and advanced Maillard products—and on the other hand, in the presence of H2O2/FeII and ascorbate/FeIlI mixtures. After 2 h at 90 °C, similar Trp degradations were observed in the different systems, but exclusively in the undenatured proteins soluble at pH 4.6. Initial degradation rates were, however, much higher in the radical-generating systems, and in the presence of pre-formed Maillard products, than in the samples where the Maillard reaction developed. These results suggest that Maillard products are responsible for Trp degradation, probably as a consequence of production of oxygen radical species during the intermediary and advanced Maillard reaction.