The objective of this study was to investigate the effect of adding different levels of a thermoresistant protease produced by a Pseudomonas fluorescens strain to milk on the manufacture and quality of Cheddar cheese. Fresh raw milk was collected, standardized, and pasteurized at 72°C for 15 s, and the enzyme was added to give a protease activity of 0.15 or 0.60 U/L (treatments P1 and P4, respectively), while one sample had no enzyme added (control). Milk was stored at 4°C for 48 h and Cheddar cheese was manufactured after 0 and 48 h of storage. Results indicated that the protease was active in milk during 48 h of storage; however, its effect on milk composition was minimal. The protein that was preferentially hydrolyzed by the protease over storage was β-casein, followed by κ-casein. The mean cheese yield and recovery of fat and protein obtained for all cheeses were not affected by protease activity. The protease showed low activity during cheese manufacture, possibly because of unfavorable conditions, including low pH. One of the factors that might have influenced protease activity was the pH of the curd (approximately 6.55 after acidification and 5.35 at milling), which was lower than that at which the enzyme would have optimum activity (pH 7 to 9). Consequently, the composition, pH, patterns of proteolysis, and hardness of all cheeses produced were similar and in accordance with values expected for that type of cheese, independently of the protease activity level. However, slight increases in proteolysis were observed in P4 cheeses and produced using milk stored for 48 h. Both the P1 and P4 cheeses had higher concentrations of free amino acids (FAA) compared with the control, whereas urea-PAGE electrophoretograms indicated a greater breakdown of caseins in the P4 cheese samples, which may be related to possible increases in numbers of proteolytic bacteria in milk during storage. Therefore, the thermoresistant psychrotrophic bacterial protease(s) tested in this study may affect the manufacture or quality of Cheddar cheese during ripening to a relatively limited extent. However, controlling initial levels of proteolytic bacteria in raw milk remains essential, because proteolysis affects the development of flavor and texture in cheese.

这项研究的目的是研究添加不同水平的荧光假单胞菌产生的耐热蛋白酶的影响切达干酪的生产和品质对牛奶造成压力。收集新鲜的生乳，标准化，并在72°C进行巴氏消毒15 s，然后添加酶以提供0.15或0.60 U / L的蛋白酶活性（分别处理P1和P4），而一个样品没有酶添加（控制）。牛奶在4°C下储存48小时，切达干酪在储存0和48小时后制成。结果表明，蛋白酶在牛奶中储存48小时具有活性。但是，它对牛奶成分的影响很小。被蛋白酶优先水解而不是储存水解的蛋白质是β-酪蛋白，其次是κ-酪蛋白。所有奶酪的平均奶酪产量以及获得的脂肪和蛋白质的回收率均不受蛋白酶活性的影响。蛋白酶在奶酪制造过程中显示低活性，可能是因为条件不利，包括pH值低。可能影响蛋白酶活性的因素之一是凝乳的pH值（酸化后约为6.55，研磨时约为5.35），低于酶具有最佳活性的pH（pH 7至9）。因此，所产生的所有干酪的组成，pH，蛋白水解模式和硬度是相似的，并且与那种干酪的预期值一致，而与蛋白酶活性水平无关。但是，在P4奶酪中观察到蛋白水解略有增加，并且使用储存48小时的牛奶即可生产。与对照相比，P1和P4干酪均具有较高的游离氨基酸（FAA）浓度，而尿素-PAGE电泳图则表明P4干酪样品中酪蛋白的分解程度更高，这可能与储存过程中牛奶中蛋白水解细菌数量的增加有关。因此，本研究中测试的耐热精神营养细菌蛋白酶可能会在相对有限的程度上影响切达干酪的生产或品质。但是，控制原奶中蛋白水解细菌的初始水平仍然很重要，因为蛋白水解会影响奶酪的风味和质地。