Effect of normal and strict anaerobic fermentation on physicochemical quality and metabolomics of yogurt

Generally, yogurts on the market are usually anaerobic fermentation, but oxygen can be still dissolved in the production process, which is actually not strict anaerobic. This study explored the multiple quality indicators and the metabolomic analysis of yogurts fermented by Lactobacillus bulgaricus and Streptococcus thermophilus using two fermentation methods, namely, strict anaerobic and normal fermentation. The changes in flavor substances in yogurts, including 17 free amino acids, 17 fatty acids, and 7 response value, were detected using principal component and multi factor analyses. Based on the results of the comparisons between basic physical and chemical indicators, strict anaerobic fermentation increased the growth and acidification of the two bacteria, the response value of sourness, umami and richness. Strict anaerobic fermentation increased the free amino acid (Fold change = 1.53) and short chain fatty acid levels (Fold change = 1.73), and reduced the polyunsaturated fatty acid (Fold change = 0.51) levels. Furthermore, metabolomic analysis based on UPLC-Triple TOF-MS/MS showed that 92 differential metabolites were screened; 45 differential metabolites were increased and 47 were decreased. The results revealed that strict anaerobic fermentation was beneficial to metabolic changes and nutritional indicators of yogurt, which may be as indicators of valuable reference to improve dairy fermentation process.