Model studies on the oxidation of benzoyl methionine in a carbohydrate degradation system

The stability of benzoyl methionine was analyzed during incubation with carbohydrate compounds such as reducing sugars, dicarbonyl compounds, reductones, and Amadori rearrangement products (ARPs). The reaction products were identified and quantified by HPLC-UV and HPLC-MS. In the presence of ARPs, >40% of benzoyl methionine was oxidized to benzoyl methionine sulfoxide after 48 h at 80 °C in acetate-buffered solution (pH 6.0), whereas <10% was oxidized in the presence of mono- and disaccharides. As an important side reaction, peptide bond cleavage through α-amidation was verified. The influence of benzoyl methionine on carbohydrate degradation reactions was assessed through analysis of vicinal dicarbonyl compounds by HPLC-UV. Glyoxal, methylglyoxal, diacetyl, and 3-deoxyglucosone were quantified as the most important derivatives. The thioether group of methionine strongly influenced carbohydrate degradation pathways: Less glyoxal was formed from reducing carbohydrates, showing that benzoyl methionine can act as a radical scavenger. However, more diacetyl was formed from ARPs and reductones, indicating that also radical-dependent pathways could be influenced by benzoyl methionine. The degradation of reducing carbohydrates should thus be an important contributor to protein oxidation in food items with low fat content.