Meng Lu, Zhang Yangdong, Liu Huimin, Zhao Shengguo, Wang Jiaqi, Zheng Nan
Ministry of Agriculture Laboratory of Quality and Safety Risk Assessment for Dairy Products, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, China.
Ministry of Agriculture Milk and Dairy Product Inspection Center, Beijing, China.
Front Microbiol. 2017 Nov 8;8:2158. doi: 10.3389/fmicb.2017.02158. eCollection 2017.
Milk spoilage is caused by the presence of proteolytic enzymes produced by spp. during storage at low temperatures. The aim of this study was to identify spp. in raw milk and investigate their associated proteolytic properties at low temperatures. Raw milk samples ( = 87) were collected from 87 bulk tanks in Shaanxi Province in China. spp. were identified using specific 16S, universal sequencing, and B gene sequencing. The proteolytic properties of spp. were examined using milk agar, quantitative trinitrobenzenesulfonic acid assay, and by the presence of alkaline metallopeptidase gene (X). A total 143 isolates from all 87 samples were confirmed as , and were identified as belonging to 14 species. Of these, 40 (28.0%) isolates revealed proteolysis on milk agar at 2°C, 74 (51.8%) at 4°C, 104 (72.7%) at 7°C, and 102 (71.3%) at 10°C. However, proteolytic activity of 45 (31.5%) isolates exceeded 2 μmol of glycine equivalents per mL at 7°C, followed by 43 (30.1%) at 10°C, 18 (12.6%) at 4°C, and 7 (4.9%) at 2°C. The results reveal proteolytic activity of spp. present in milk and their spoilage potential at different temperatures.
牛奶变质是由低温储存期间某些菌种产生的蛋白水解酶导致的。本研究的目的是鉴定生牛奶中的某些菌种，并研究它们在低温下的相关蛋白水解特性。从中国陕西省的87个储奶罐中采集了87份生牛奶样本。使用特定的16S、通用测序和B基因测序来鉴定某些菌种。通过牛奶琼脂、定量三硝基苯磺酸测定以及碱性金属肽酶基因（X）的存在来检测某些菌种的蛋白水解特性。所有87个样本中共143株分离株被确认为某些菌种，并被鉴定为属于14个物种。其中，40株（28.0%）分离株在2°C时在牛奶琼脂上显示蛋白水解，74株（51.8%）在4°C时显示，104株（72.7%）在7°C时显示，102株（71.3%）在10°C时显示。然而，45株（31.5%）分离株在7°C时的蛋白水解活性超过每毫升2微摩尔甘氨酸当量，其次是43株（30.1%）在10°C时，18株（12.6%）在4°C时，7株（4.9%）在2°C时。结果揭示了牛奶中某些菌种的蛋白水解活性及其在不同温度下的变质潜力。
