Key Laboratory of Dairy Science, Ministry of Education, College of Food Science, Northeast Agricultural University, Harbin, China.
Key Laboratory of Dairy Science, Ministry of Education, College of Food Science, Northeast Agricultural University, Harbin, China.
Food Chem. 2025 Jan 15;463(Pt 3):141367. doi: 10.1016/j.foodchem.2024.141367. Epub 2024 Sep 19.
Due to the scarcity of yak milk in Tibetan areas, local herders primarily use traditional freezing methods for preservation. However, the extent of microbial contamination in raw yak milk during frozen storage and its impact on milk quality remains largely unexplored. This study analyzed the changes in bacterial populations and quality of raw yak milk stored at -18 °C for 6 months. The results indicated that, compared to fresh milk, the freshness of yak milk showed no significant change after 2 months of frozen storage (P > 0.05). After 4 months, the bacterial diversity of flora in yak milk increased significantly, with Pseudomonas and Acinetobacter emerging as the dominant psychrophilic bacteria. Correspondingly, the expression of metabolic pathways related to quality deterioration increased, with a significant increase in physicochemical indicators such as acidity, proteolysis degree, acid value and fat oxidation degree (P < 0.05). Extending the frozen storage to 6 months resulted in a slight but no significant decrease in bacterial diversity, with no significant difference in quality deterioration compared to the 4-month group (P > 0.05). Correlation analysis further revealed that Acinetobacter and Psychrobacter were significantly positively correlated with quality deterioration of frozen milk (P < 0.05). In summary, when frozen for more than 4 months, raw yak milk exhibited the highest bacterial diversity and predicted the most abundant metabolic pathways, with dominant psychrophilic bacteria massive proliferation leading to a decline in quality and safety.
由于藏区牦牛奶资源稀缺，当地牧民主要采用传统的冷冻方法进行保存。然而，生牦牛奶在冷冻储存过程中微生物污染的程度及其对牛奶质量的影响在很大程度上仍未得到探索。本研究分析了在-18°C下储存 6 个月的生牦牛奶的细菌种群变化和质量。结果表明，与新鲜牛奶相比，冷冻储存 2 个月后牦牛奶的新鲜度没有明显变化（P>0.05）。4 个月后，牦牛奶中菌群的细菌多样性显著增加，假单胞菌和不动杆菌成为优势嗜冷菌。相应地，与质量恶化相关的代谢途径的表达增加，酸度、蛋白水解度、酸值和脂肪氧化度等理化指标显著升高（P<0.05）。将冷冻储存延长至 6 个月，细菌多样性略有下降但无统计学意义，与 4 个月组相比，质量恶化无显著差异（P>0.05）。相关性分析进一步表明，不动杆菌和嗜冷杆菌与冷冻奶的质量恶化呈显著正相关（P<0.05）。综上所述，当冷冻超过 4 个月时，生牦牛奶表现出最高的细菌多样性和预测到最丰富的代谢途径，大量增殖的优势嗜冷菌导致质量和安全性下降。
