Microbial diversity analysis and isolation of thermoresistant lactic acid bacteria in pasteurized milk

Pasteurization is a common method for dairy products, typically heating at 72 °C for 15 s or 63 °C for 30 min. The 17 samples of commercial pasteurized milk were divided into three groups according to the shelf life: group A (1-5 days), group B (6-10 days) and group C (11-15 days), and the diversity composition of microbial communities in the samples was analyzed. Among all groups, Proteobacteria, Firmicutes, and Bacteroidetes were the dominant bacterial phyla. The lactic acid bacteria (LAB) were mostly Streptococcus, Weissella and Lactobacillus, and there were high proportions of Streptococcus thermophilus in group A, Weissella paramesenteroides in group B, and Lactobacillus plantarum in group C. Furthermore, a strain of Enterococcus faecium SFM2 was isolated from the A2 sample, which showed better temperature tolerance compared to the E. faecium SFM1 of oral origin. After treatment at 50 °C for 2 h, the survival rates of E. faecium SFM1 and SFM2 were 28.20 ± 0.04% and 82.58 ± 0.01%, respectively. This study investigated the diversity of microorganisms in pasteurized milk, providing effective information for analyzing the potential microbiota of commercial pasteurized milk. Meanwhile, it provided new ideas for expanding the resource pool of thermoresistant LAB.