Hayes Maurice G, Oliveira Jorge C, Mcsweeney Paul L H, Kelly Alan L
Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland.
J Dairy Res. 2002 May;69(2):269-79. doi: 10.1017/s0022029902005472.
The aspartic proteinase, chymosin (EC 3.4.23.4) is the principal milk clotting enzyme used in cheese production and is one of the principal proteolytic agents involved in cheese ripening. Varietal differences in chymosin activity, due to factors such as cheese cooking temperature, fundamentally influence cheese characteristics. Furthermore, much chymosin is lost in whey, and further processing of this by-product may require efficient inactivation of this enzyme, with minimal effects on whey proteins. In the first part of this study, the thermal inactivation kinetics of Maxiren 15 (a recombinant chymosin preparation) were studied in skim milk ultrafiltration permeate, whole milk whey and skim milk whey. Inactivation of chymosin in these systems (at pH 6.64) followed first order kinetics with a D45.5 value of 100 +/- 21 min and a z-value of 5.9 +/- 0.3 degrees C. D-Values increased linearly with decreasing pH from 6.64 to 6.2, while z-values decreased as pH decreased from 6.64 to 6.4, but were similar at pH 6.4 and 6.2. Subsequent determination of chymosin activity during manufacture of Cheddar and Swiss-type cheese showed good correlations between predicted and experimental values for thermal inactivation of chymosin in whey. However, both types of cheese curd exhibited relatively constant residual chymosin activity throughout manufacture, despite the higher cooking temperature applied in the manufacture of Swiss cheese. Electrophoretic analysis of slurries made from Cheddar and Swiss cheese indicated decreased proteolysis due to chymosin activity during storage of the Swiss cheese slurry, but hydrolysis of sodium caseinate by coagulant extracted from both cheese types indicated similar levels of residual chymosin activity. This may suggest that some form of conformational change other than irreversible thermal denaturation of chymisin takes place in cheese curd during cooking, or that some other physico-chemical difference between Swiss and Cheddar cheese controls the activity of chymosin during ripening.
天冬氨酸蛋白酶凝乳酶（EC 3.4.23.4）是奶酪生产中使用的主要凝乳酶，也是奶酪成熟过程中涉及的主要蛋白水解剂之一。由于奶酪烹饪温度等因素导致的凝乳酶活性品种差异，从根本上影响着奶酪的特性。此外，大量凝乳酶会流失在乳清中，对这种副产品进行进一步加工可能需要有效灭活这种酶，同时对乳清蛋白的影响要最小。在本研究的第一部分，研究了Maxiren 15（一种重组凝乳酶制剂）在脱脂牛奶超滤透过液、全脂牛奶乳清和脱脂牛奶乳清中的热失活动力学。在这些体系中（pH值为6.64），凝乳酶的失活遵循一级动力学，D45.5值为100±21分钟，z值为5.9±0.3℃。D值随着pH值从6.64降至6.2呈线性增加，而z值随着pH值从6.64降至6.4而降低，但在pH值为6.4和6.2时相似。随后在切达干酪和瑞士型奶酪生产过程中对凝乳酶活性的测定表明，乳清中凝乳酶热失活的预测值与实验值之间具有良好的相关性。然而，尽管瑞士奶酪生产中应用的烹饪温度较高，但两种类型的奶酪凝块在整个生产过程中都表现出相对恒定的残余凝乳酶活性。对切达干酪和瑞士奶酪制成的浆液进行电泳分析表明，在瑞士奶酪浆液储存期间，由于凝乳酶活性导致的蛋白水解减少，但从两种奶酪类型中提取的凝结剂对酪蛋白酸钠的水解表明残余凝乳酶活性水平相似。这可能表明，在烹饪过程中，奶酪凝块中发生了除凝乳酶不可逆热变性之外的某种形式的构象变化，或者瑞士奶酪和切达干酪之间的其他一些物理化学差异控制了成熟过程中凝乳酶的活性。
