Unveiling of the key pathway in flavor formation in fermented milk of Lactococcus lactis subsp. lactis via genomics and metabolomics

Lactococcus lactis subsp. lactis is a common starter culture in the dairy industry. In this study, the key pathway of five strains of Lactococcus lactis subsp. Lactis regarding their fermentation characteristics in milk systems were studied by metabolomic approach, fermentation characterization and sensory evaluation. Strains DSCAB11M15 and DYNDL21-2, which express the cell wall proteinase PrtM/P, exhibited rapid proliferation and acidification, with significant differences in volatile and non-volatile metabolites including upregulation of flavor compounds such as ethyl butyrate and 2,3-butanedione. Additionally, DYNDL21-2, which carries the α-ketoacid decarboxylase gene, significantly increased the content of 3-methyl-butyric aldehyde, a compound that imparts a caramel-like flavor, in fermented milk. This study offers guidance for the comprehensive investigation of starter cultures with multiple approaches.