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At present, most liquid milk products use high-temperature short-time heat treatment (HTST). However, HTST treatment cannot completely inactivate the bacteria in milk, which seriously affects the quality, safety, and shelf life of the product. Therefore, exploring the combined use of HTST and other technologies is of great importance to the production of high-quality pasteurized milk. In this study, we compared thermosonication (TS), ε-Polylysine (ε-PL), ε- PL combined with TS (ε-PL-TS), and HTST to inactivate B. cereusin pasteurized milk. Based on this comparison, we further discussed the inactivation ability and potential mechanism of ε-PL-TS treatment on B. cereus. The experimental result indicated that ε-PL-TS treatment had an obvious inactivation impact on B. cereus. The cell architecture was damaged by ε-PL-TS treatment, causing the leakage of proteins and DNA from the cell. ε-PL-TS treatment caused metabolic disorders by reducing the activities of key enzymes such as succinate dehydrogenase (SDH) (72.5%), malate dehydrogenase (MDH) (70.5%), and ATPase (80.3%). Meanwhile, the activity of CAT and POD decreased by 42.5% and 48.7%, respectively, suggesting that oxidative stress may be involved in the bactericidal mechanism. In addition, the combined treatment effectively inhibits microbial proliferation of pasteurized milk during storage at 4 °C. Therefore, ε-PL-TS treatment can be used as a potential new inactivated microorganism technology that is helpful to obtain high-quality pasteurized milk with a long shelf life.

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 bulgaricusand Streptococcus thermophilususing 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.