Lactococcus lactis enhances the flavor of fermented milk by producing 4-hydroxy-2-butanone

The fermentation of dairy products is a complex biotransformation process, with flavor characteristics linked to the metabolic activities of specific strains, highlighting the necessity of identifying unique strains to enhance product quality. Here, 50 Lactococcus lactis ( L. lactis ) strains were isolated from traditional dairy products collected from four major pastoral regions in China, namely Xinjiang, Yunnan, Inner Mongolia, and Tibet. Based on the physiological characteristic indices of the strains, combined with the TOPSIS-entropy weight method, NZZ1 and RB12 with excellent fermentation performance were screened out. Among these, strain NZZ1 was identified as a significant producer of 4-hydroxy-2-butanone, the key volatile compound with the highest variable importance in projection, due to its complete coding genes for acetolactate synthase and acetolactate decarboxylase, enabling the biosynthesis of this compound. Comparative analysis with commercial starter cultures demonstrated that NZZ1 exhibits a shorter milk coagulation time (6 h), a faster fermentation rate (8 h), strong water holding capacity, and no excessive post-acidification (90.16 °T), along with outstanding sensory preference scores. Furthermore, co-fermentation with commercial starters significantly increased the yield of 4-hydroxy-2-butanone by more than threefold. These findings highlight the potential of NZZ1 as a distinctive starter culture, offering innovative strategies for enhancing dairy product quality.