Revealing the Microbial Origins of <i>N</i>‑Lactoyl\nAmino Acids in Soy Sauce: Synthesis Conditions, Potential\nEnzymes, and Utilization Preference

The flavor contribution of <i>N</i>-lactoyl amino acids\n(Lac-AAs) to soy sauce is gradually gaining attention. However, research\non their formation mechanism is limited. In this study, the production\nof Lac-AAs of 12 species of yeasts commonly detected in soy sauce\nwas investigated, and Candida orthopsilosis, Candida parapsilosis, and Millerozyma farinosa were identified as key yeasts\nbecause of their productivity and high correlation coefficients with\npeak areas of Lac-AAs (<i>r</i> > 0.8). According to\nsynthesis\nexperiments, the formation of Lac-AAs was catalyzed by endoenzymes,\nwith an optimal pH of 5–7 and a temperature of 50–60\n°C. After BLAST comparison, cytosolic nonspecific dipeptidase\n2 (CNDP2) or other similar metallodipeptidases may be potential enzymes\nfor Lac-AAs synthesis. According to preference experiments, 13 amino\nacids were exploitable to form the corresponding Lac-AAs by selected\nyeasts, except Gly, Ala, Ser, Pro, and Asp, presumably related to\nthe structure of side chains. Among them, nonpolar amino acids were\npreferred by yeasts. These findings enrich knowledge on taste substances\nand microorganisms and can help to regulate the microbial community\nfor flavor improvement of soy sauce.