Li Nan, Yang Zhigang, Yuan Zhiyu, Zhen Zizhu, Xie Xinna, Zhu Danqing, Lu Gang, Zhao Feng, Qu Bo, Qi Bingli, Jiang Yujun, Zhao Qianyu, Man Chaoxin
Key Laboratory of Dairy Science, Ministry of Education, Department of Food Science, Northeast Agricultural University, Harbin 150030, China.
Key Laboratory of Infant Formula Food, State Administration for Market Regulation, Harbin 150030, China.
Foods. 2024 Dec 24;14(1):3. doi: 10.3390/foods14010003.
This study investigated the variations and alterations in the concentrations of plasmin system components in raw and UHT (ultra-high-temperature) milk under cold stress (WCT ≤ -25 °C), heat stress (THI ≥ 80), and normal (THI < 70 and WCT ≥ -10 °C) circumstances. The findings indicated elevated amounts of plasmin system components in cold-stressed raw milk. While storing UHT milk at 25 °C, the concentrations and activity of plasmin in the milk exhibited an initial increase followed by a decrease, peaking around the 30th day. The maximum plasmin level and activity in cold-stressed milk were 607.86 μg/L and 15.99 U/L, respectively, with the beginning of gelation occurring around day 60. The higher activity of plasmin in cold-stressed milk led to the poorer stability and sensory assessment of the milk. However, heat-stressed milk is not such a problem for UHT milk as cold-stressed milk. The findings indicate shortcomings in the quality of cold-stressed milk and its adverse effects on the stability of UHT milk, underscoring the necessity of preventing cold stress in the herd and refraining from utilizing cold-stressed milk as a raw material for UHT production.
本研究调查了在冷应激（WCT≤-25°C）、热应激（THI≥80）和正常（THI<70且WCT≥-10°C）条件下，原料奶和超高温（UHT）奶中纤溶酶系统成分浓度的变化。研究结果表明，冷应激原料奶中纤溶酶系统成分含量升高。将UHT奶储存在25°C时，奶中纤溶酶的浓度和活性最初升高，随后下降，在第30天左右达到峰值。冷应激奶中纤溶酶的最高水平和活性分别为607.86μg/L和15.99U/L，大约在第60天开始出现凝胶化。冷应激奶中纤溶酶活性较高导致奶的稳定性较差和感官评价较低。然而，对于UHT奶来说，热应激奶不像冷应激奶那样存在问题。研究结果表明冷应激奶的质量存在缺陷及其对UHT奶稳定性的不利影响，强调了防止牛群冷应激以及避免使用冷应激奶作为UHT生产原料的必要性。
