Putative Transformation Mechanism of γ-l-Glutamyl-S-Allyl-l-Cysteine during the Processing of Black Garlic.

γ-l-Glutamyl-S-allyl-l-cysteine (GSAC) is renowned for its flavor-modifying effects and beneficial biological activities. However, the level of GSAC decreases significantly during the processing of black garlic, and the pathways and degradation products resulting from this decline remain unclear. To investigate the potential transformation mechanisms of GSAC in black garlic, simulation systems for thermal decomposition, Maillard reactions, and enzymatic hydrolysis were established. In addition to GSAC and fructose, a total of 6 products were identified and confirmed. Findings indicate that thermal decomposition and enzymatic hydrolysis are the two primary pathways through which GSAC is transformed, whereas the Maillard reaction between fructose and GSAC is unlikely to occur. GSAC can be converted into S-allylcysteine and glutamic acid through thermal processing and the action of γ-glutamyl transpeptidase. Notably, the majority of Glu transformed into pyroglutamic acid via intramolecular dehydration at 75 °C, whereas in enzymatic hydrolysis simulation systems, it is converted into glutamine. Additionally, alliin, S-allylcysteine, and S-allylmercaptocysteine were detected, suggesting new pathways for the production of these compounds during the processing of black garlic.