Effects of yeast screened from traditional fermented milk on commercial fermented milk as adjunct flavor culture

Two yeast strains with better overall flavor quality were isolated and screened from traditional fermented milk in western Sichuan, identified as Kluyveromyces marxianus and Saccharomyces cerevisiae, and their role as adjunct cultures in fermented milk was studied. Fermented milk (LS, LSK, LSS and LSKS) were respectively inoculated with Lactobacillus bulgaricus + Streptococcus thermophiles (LS), LS + K. marxianus, LS + S. cerevisiae, and LS + K. marxianus + S. cerevisiae. The obtained LSKS has the best overall quality with moderate ethanol and ester aroma, rich in fermentation aroma, delicate taste, and the highest acidity (87.52 ± 0.44 °T), viscosity (418.18 ± 18.73 mPa·s), and organic acid content (449.736 mg/100 g), as well as the abundant ethyl esters (ethyl ocanoate, ethyl caprate, ethyl hexanoate). Non-targeted metabolomics revealed the metabolites differences for LSKS versus LS. Sixty-five metabolites upregulated and seventy-two metabolites downregulated, which were significantly enriched in arginine biosynthesis and glycerophospholipid metabolism pathway. A large number of short peptides were upregulated, and calenduloside G methyl ester has the potential to be used as a differential biomarker. This study provides a theoretical basis for the application potential of K. marxianus SY11 and S. cerevisiae SY32 to stimulate fermentation with LS as adjunct flavor cultures in commercial fermented milk.