Microbial diversity of consumption milk during processing and storage. Microbial diversity of consumption milk

Bovine milk contains a complex microbial community that affects the quality and safety of the product. Detailed knowledge of this microbiota is, therefore, of importance for the dairy industry. In this study, the bacterial composition of consumption milk was assessed during different stages in the production line and throughout the storage in cartons by using culturing techniques and 16S rRNA marker gene sequencing. Monthly samples from two dairies were analyzed to capture the seasonal variations in the milk microbiota. Although there was a core microbiota present in milk samples from both dairies, the composition of the bacterial communities were significantly influenced by sampling month, processing stage and storage temperature. Overall, a higher abundance of operational taxonomic units (OTUs) within the order Bacillales was detected in samples of raw and pasteurized milk from the spring and summer months, while Pseudomonadales and Lactobacillales OTUs were predominant in the winter months. OTUs belonging to the order Lactobacillales, Pseudomonadales, Clostridiales and Bacillales were significantly more abundant in milk samples taken immediately after pasteurization compared to raw milk samples. During storage of milk in cartons at 4 °C, the bacterial composition remained stable throughout the product shelf life, while storage at 8 °C significantly increased the abundance of OTUs belonging to the genus Bacillus and the plate count levels of presumptive Bacillus cereus. The knowledge obtained in this work will be useful to the dairy industry during their quality assurance work and risk assessment practices.

牛乳中存在复杂的微生物群落，其会对产品的品质与安全产生影响。因此，全面解析该牛乳微生物组的详细信息对乳品工业具有重要意义。本研究采用培养技术与16S rRNA标记基因测序法，对生产线不同加工阶段及盒装存储全程的饮用牛乳的细菌组成进行了分析。研究采集两家乳品厂的月度样本，以捕捉牛乳微生物组的季节变化规律。尽管两家乳品厂的牛乳样本均存在核心微生物组，但细菌群落组成显著受到采样月份、加工阶段与存储温度的影响。总体而言，春夏季采集的生鲜乳与巴氏杀菌乳样本中，芽孢杆菌目（Bacillales）的操作分类单元（operational taxonomic units，OTU）丰度更高；而冬季样本则以假单胞菌目（Pseudomonadales）与乳杆菌目（Lactobacillales）的OTU占主导。与生鲜乳样本相比，巴氏杀菌后即刻采集的牛乳样本中，乳杆菌目、假单胞菌目、梭菌目（Clostridiales）与芽孢杆菌目的OTU丰度显著更高。在4℃条件下进行盒装牛乳存储时，全程货架期内细菌组成均保持稳定；而8℃存储则会显著提升芽孢杆菌属（Bacillus）OTU的丰度，以及疑似蜡样芽孢杆菌（Bacillus cereus）的平板菌落计数水平。本研究所得成果可为乳品工业的质量保障与风险评估工作提供重要支撑。