Dairy Science and Technology, Food Quality and Design Group, Wageningen University and Research, P.O. Box 17, 6700 AA Wageningen, The Netherlands.
Food Chem. 2018 Oct 15;263:127-134. doi: 10.1016/j.foodchem.2018.04.128. Epub 2018 Apr 30.
Destabilization of UHT milk during its shelf life is mainly promoted by the residual proteolytic activity attributed to the psychrotrophic bacterial proteases and native milk proteases. In this study, we built skim UHT milk-based model systems to which either the major bacterial protease (AprX from Pseudomonas fluorescens), or the major native milk protease (plasmin) was added, to allow a direct comparison between the destabilization of skim UHT milk by both categories of enzymes. The physical and chemical properties were studied during 6 weeks. Our results showed AprX induced compact gels when almost all the κ-casein was hydrolyzed and the degree of hydrolysis (DH) exceeded 1.3%. Plasmin induced soft gels when around 60% of both β- and α-casein were hydrolyzed and the DH reached 2.1%. The knowledge gained from this study may be used for developing diagnostic tests for determining the protease responsible for UHT milk destabilisation.
在保质期内，UHT 奶的不稳定性主要是由嗜冷菌蛋白酶和天然乳蛋白酶的残留蛋白水解活性所促进的。在这项研究中，我们构建了基于脱脂 UHT 奶的模型体系，向其中添加主要的细菌蛋白酶（荧光假单胞菌来源的 AprX）或主要的天然乳蛋白酶（纤溶酶），以直接比较这两类酶对脱脂 UHT 奶的不稳定性。在 6 周的时间里研究了其物理和化学性质。结果表明，当几乎所有κ-酪蛋白被水解且水解度（DH）超过 1.3%时，AprX 会诱导形成紧凑的凝胶。当大约 60%的β-和α-酪蛋白被水解且 DH 达到 2.1%时，纤溶酶会诱导形成软凝胶。从这项研究中获得的知识可用于开发用于确定导致 UHT 奶不稳定的蛋白酶的诊断测试。
