Harzer G, Kauer H
Am J Clin Nutr. 1982 May;35(5):981-7. doi: 10.1093/ajcn/35.5.981.
An investigation of the binding of zinc to cow's milk proteins has shown that zinc binds avidly in a pH-dependent manner to casein, but has little affinity for the total whey protein fraction. At slightly alkaline pH 1 mg casein binds 8.4 micrograms zinc. No zinc binds to casein at pH 2 and to dephosphorylated casein at pH 7.4. Bound zinc is released only by casein precipitation at pH 4.6 but not by casein precipitation using Ca2+-ions or rennin. It could also be shown that zinc binds to phosphopeptides derived from tryptic or chymotryptic casein digestion and that metal complexing agents, such as citrate or picolinic acid compete for zinc binding with these phosphopeptides and casein. Binding of zinc to casein and its tryptic or chymotryptic phosphopeptides may explain in part the comparatively low zinc availability from cow's milk and some milk-based infant formulas.
一项关于锌与牛奶蛋白结合的研究表明，锌以pH依赖的方式与酪蛋白紧密结合，但对总乳清蛋白部分的亲和力很小。在略呈碱性的pH值下，1毫克酪蛋白结合8.4微克锌。在pH值为2时，没有锌与酪蛋白结合，在pH值为7.4时，没有锌与去磷酸化酪蛋白结合。结合的锌仅在pH值为4.6时通过酪蛋白沉淀释放，而不是通过使用钙离子或凝乳酶进行酪蛋白沉淀释放。还可以表明，锌与胰蛋白酶或胰凝乳蛋白酶消化酪蛋白产生的磷酸肽结合，并且金属络合剂，如柠檬酸盐或吡啶甲酸，与这些磷酸肽和酪蛋白竞争锌的结合。锌与酪蛋白及其胰蛋白酶或胰凝乳蛋白酶磷酸肽的结合可能部分解释了牛奶和一些基于牛奶的婴儿配方奶粉中锌的利用率相对较低的原因。
