This research communication describes enzymatic and physico-chemical changes during storage of UHT milk. The UHT milk sample was stored at 5 and 30°C for 4 months and analyzed regularly at intervals of one month. During storage of UHT milk, there was a significant (P < 0.001) increase in non-protein nitrogen, non-casein nitrogen, soluble calcium, soluble magnesium and proteolysis, while a significant (P < 0.001) decrease in pH was observed. There was a slight change in the particle size and zeta potential of casein micelles. Changes were more pronounced in milk samples stored at 30°C than in those stored at 5°C. During storage, there occurred changes in pH, viscosity, salt balance and nitrogenous components which adversely affected quality. It was concluded that the proteolysis led to the acidification which had a destabilizing effect on the milk.

中文翻译：

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UHT牛奶在不同温度储存过程中的物理化学变化评估

该研究通讯描述了 UHT 牛奶储存过程中的酶促和物理化学变化。UHT 牛奶样品在 5°C 和 30°C 下储存 4 个月，并每隔一个月定期分析。在 UHT 牛奶的储存过程中，有一个显着的 (磷 <0.001) 增加非蛋白氮、非酪蛋白氮、可溶性钙、可溶性镁和蛋白水解，而显着的 (磷 <0.001) 观察到 pH 值降低。酪蛋白胶束的粒径和 zeta 电位略有变化。储存在 30°C 的牛奶样品的变化比储存在 5°C 的牛奶样品的变化更明显。在储存过程中，pH、粘度、盐平衡和含氮成分发生变化，对质量产生不利影响。得出的结论是，蛋白水解导致酸化，这对牛奶有不稳定的影响。