Abstract：
To investigate the prevalence of Pseudomonas in the pasteurized milk production process and its effect on milk quality, 106 strains of Pseudomonas were isolated from the pasteurized milk production process of a milk production plant in Shaanxi Province, China. The protease, lipase and biofilm-producing capacities of the 106 Pseudomonas strains were evaluated, and the spoilage enzyme activities of their metabolites were assessed by simulating temperature incubation in the refrigerated (7 °C) and transport environment (25 °C) segments and thermal treatments of pasteurization (75 °C, 5 min) and ultra-high temperature sterilization (121 °C, 15 s). A phylogenetic tree was drawn based on 16S rDNA gene sequencing and the top 5 strains were selected as representative strains to identify their in situ spoilage potential by examining their growth potential and ability to hydrolyze proteins and lipids in milk using growth curves, pH, whiteness, Zeta-potential, lipid oxidation, SDS-PAGE and volatile flavor compounds. The results showed that half and more of the isolated Pseudomonas had spoilage enzyme production and biofilm capacity, and the spoilage enzyme activity of metabolites was affected by the culture temperature and sterilization method, but ultra-high temperature sterilization could not completely eliminate the enzyme activity. The growth of Pseudomonas lundensis and Pseudomonas qingdaonensis was less affected by temperature and time, and the hydrolytic capacity of extracellular protease and lipase secreted by Pseudomonas lurida was the strongest, which had the greatest effect on milk quality. Therefore, it is crucial to identify the key contamination links of Pseudomonas, the main bacteria responsible for milk spoilage, and the influence of environmental factors on its deterioration.
摘要：
调查巴氏杀菌奶生产过程中假单胞菌的流行情况及其对牛奶品质的影响,从陕西省某奶厂的巴氏杀菌奶生产过程中分离出106株假单胞菌,中国。蛋白酶，评估了106株假单胞菌菌株的脂肪酶和生物膜生产能力，并通过在冷藏（7°C）和运输环境（25°C）段中模拟温度孵育以及巴氏灭菌的热处理（75°C，5分钟）和超高温灭菌（121°C，15s).根据16SrDNA基因测序绘制系统发育树，并选择前5个菌株作为代表菌株，通过生长曲线检查其生长潜力和水解牛奶中蛋白质和脂质的能力，鉴定其原位腐败潜力，pH值,白度,Zeta电位,脂质氧化，SDS-PAGE和挥发性风味化合物。结果表明，一半以上的假单胞菌具有腐败酶的产生和生物膜能力，培养温度和灭菌方法对代谢产物腐败酶活性的影响,但超高温灭菌不能完全消除酶活性。阴阳假单胞菌和青道假单胞菌的生长受温度和时间的影响较小，蓝藻假单胞菌分泌的细胞外蛋白酶和脂肪酶的水解能力最强，这对牛奶质量影响最大。因此,确定假单胞菌的关键污染环节至关重要，导致牛奶腐败的主要细菌，以及环境因素对其恶化的影响。
