Udabage P, McKinnon I R, Augustin M A
Chemistry Department, Monash University, Clayton, Victoria, Australia.
J Dairy Sci. 2001 Jul;84(7):1569-75. doi: 10.3168/jds.S0022-0302(01)74589-4.
The effects of adding CaCl2, orthophosphate, citrate, EDTA, or a mixture of these, to reconstituted skim milk (90 g of solids/kg solution) on the gelation of renneted milk were mediated by changes in Ca2+ activity and the casein micelle. At pH 6.65, the addition of citrate or EDTA, which removed more than 33% of the original colloidal calcium phosphate with the accompanying release of 20% casein from the micelle, completely inhibited gelation. Reformation of the depleted colloidal calcium phosphate and casein in the micelle, by the addition of CaCl2, removed this inhibition. When the minimum requirements for colloidal calcium phosphate and casein in the micelle were met, the coagulation time decreased with increasing Ca2+ activity, leveling off at high Ca2+ activity. The storage modulus of renneted gels, measured at 3 h, increased with increasing colloidal calcium phosphate content of micelles up to a level at which it was approximately 130% of the original colloidal calcium phosphate in the micelles. Further increases in colloidal calcium phosphate by the addition of CaCl2, orthophosphate, or mixtures of these, which did not change the proportion of casein in the micelle, decreased the storage modulus. The gelation of the renneted milk was influenced by Ca2+ activity, the amounts of colloidal calcium phosphate, and casein within the micelle, with the effects of colloidal calcium phosphate and casein within the micelle clearly dominating the storage modulus. These results are consistent with the model of Horne (Int. Dairy J. 8:171-177, 1998) which postulates that, following cleavage of the stabilizing K-casein hairs by rennet, the properties of the rennet gel are determined by the balance between the electrostatic and hydrophobic forces between casein micelles.
向复原脱脂乳（90 g 固形物/kg 溶液）中添加氯化钙、正磷酸盐、柠檬酸盐、乙二胺四乙酸（EDTA）或它们的混合物，对凝乳酶凝乳凝胶化的影响是由钙离子活性和酪蛋白胶粒的变化介导的。在pH 6.65时，添加柠檬酸盐或EDTA会去除超过33%的原始胶态磷酸钙，并伴随从胶粒中释放出20%的酪蛋白，从而完全抑制凝胶化。通过添加氯化钙使胶粒中耗尽的胶态磷酸钙和酪蛋白重新形成，可消除这种抑制作用。当胶粒中胶态磷酸钙和酪蛋白的最低要求得到满足时，凝固时间随钙离子活性的增加而缩短，在高钙离子活性时趋于平稳。在3小时时测量的凝乳酶凝胶的储能模量随着胶粒中胶态磷酸钙含量的增加而增加，直至达到约为胶粒中原始胶态磷酸钙130%的水平。通过添加氯化钙、正磷酸盐或它们的混合物进一步增加胶态磷酸钙，而不改变胶粒中酪蛋白的比例，则会降低储能模量。凝乳酶凝乳的凝胶化受钙离子活性、胶粒内胶态磷酸钙的量以及酪蛋白的影响，其中胶粒内胶态磷酸钙和酪蛋白的影响明显主导着储能模量。这些结果与霍恩（Horne）的模型（《国际乳品杂志》8:171 - 177，1998）一致，该模型假设，在凝乳酶切割稳定的κ-酪蛋白链后，凝乳酶凝胶的性质由酪蛋白胶粒之间的静电力和疏水力之间的平衡决定。
