N-Lactoyl amino acids in fermented foods: occurrence, biosynthesis, and flavor enhancement mechanisms.

N-Lactoyl amino acids (Lac-AAs) are common metabolites in fermented foods, contributing to their distinctive flavors. This review examines the natural occurrence of Lac-AAs in fermented dairy products, meats, vegetables, alcoholic beverages, and traditional fermented foods. It discusses the microorganisms involved in Lac-AA synthesis - particularly lactic acid bacteria and specific yeasts - together with the enzymatic mechanisms underlying their formation. The taste characteristics of different Lac-AAs are highlighted, together with their roles in enhancing umami, modulating the kokumi effect, and masking bitterness at various threshold concentrations. Molecular docking studies provide insight into interactions between Lac-AAs and taste receptors, including T1R1/T1R3 for umami perception and CaSR for kokumi perception, explaining their sensory properties at the molecular level. Structure-activity relationships of Lac-AAs are also analyzed, providing a basis for the development of targeted flavor enhancers. These results emphasize the importance of Lac-AAs as natural flavor modulators in fermented foods and suggest potential applications in food flavor improvement and formula optimization.