Teagasc Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, P61 C996 County Cork, Ireland; School of Food and Nutritional Sciences, University College Cork, T12 K8AF County Cork, Ireland.
Teagasc Food Research Centre, Moorepark, Fermoy, P61 C996 County Cork, Ireland.
J Dairy Sci. 2020 Sep;103(9):7865-7878. doi: 10.3168/jds.2019-18043. Epub 2020 Jun 26.
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.
本研究旨在探讨在牛奶中添加不同水平的荧光假单胞菌产生的耐热蛋白酶对切达干酪制造和质量的影响。收集新鲜原料奶，标准化后在 72°C 下巴氏杀菌 15 秒，并添加酶，使蛋白酶活性分别达到 0.15 或 0.60 U/L（处理 P1 和 P4），而一个样品未添加酶（对照）。牛奶在 4°C 下储存 48 小时，在储存 0 和 48 小时后制造切达干酪。结果表明，蛋白酶在牛奶储存的 48 小时内保持活性；然而，其对牛奶成分的影响很小。在储存过程中，蛋白酶优先水解的蛋白质是β-酪蛋白，其次是κ-酪蛋白。所有奶酪的平均奶酪产率和脂肪及蛋白质回收率不受蛋白酶活性的影响。蛋白酶在奶酪制造过程中的活性较低，可能是由于不利的条件，包括低 pH 值。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，研磨后为 5.35），低于酶的最适活性 pH 值（7 至 9）。因此，所有奶酪的组成、pH 值、蛋白质水解模式和硬度都相似，且符合该类型奶酪的预期值，与蛋白酶活性水平无关。然而，在使用储存 48 小时的牛奶生产的 P4 奶酪中，观察到轻微增加的蛋白质水解。与对照相比，P1 和 P4 奶酪的游离氨基酸（FAA）浓度都更高，而尿素-PAGE 电泳图谱表明 P4 奶酪样品中乳清蛋白的分解程度更大，这可能与储存过程中牛奶中蛋白酶细菌数量的增加有关。因此，本研究中测试的耐热嗜冷细菌蛋白酶可能在成熟过程中对切达干酪的制造或质量产生相对有限的影响。然而，控制原料奶中初始蛋白酶细菌的数量仍然至关重要，因为蛋白质水解会影响奶酪的风味和质地的发展。
