The interaction between Lactobacillus delbrueckii ssp. bulgaricus M-58 and Streptococcus thermophilus S10 can enhance the texture and flavor profile of fermented milk: Insights from metabolomics analysis

Lactobacillus delbrueckii ssp. bulgaricus M-58 (M58) and Streptococcus thermophilus S10 (S10) are both dairy starter strains known for their favorable fermentation characteristics. Therefore, this research aimed to study the effects of 1-d low-temperature ripening on the physicochemical properties and metabolomics of fermented milk. Initially, the performance of single (M58 or S10) and dual (M58+S10) strain fermentation was assessed, revealing that the M58+S10 combination resulted in a shortened fermentation time, a stable gel structure, and desirable viscosity, suggesting positive strain interactions. Subsequently, nontargeted metabolomics analyses using liquid chromatography-MS and GC-MS were performed to comparatively analyze M58+S10 fermented milk samples collected at the end of fermentation and after 1 d of low-temperature ripening. The results showed a significant increase in almost all small peptides and dodecanedioic acid in the samples after 1 d of ripening, although there was a substantial decrease in indole and amino acid metabolites. Moreover, notable increases were observed in high-quality flavor compounds, such as geraniol, delta-nonalactone, 1-hexanol,2-ethyl-, methyl jasmonate, and undecanal. This study provides valuable insights into the fermentation characteristics of the dual bacterial starter consisting of M58 and S10 strains and highlights the specific contribution of the low-temperature ripening step to the overall quality of fermented milk.