Nelson L S, Jacobs F A, Brushmiller J G, Ames R W
J Inorg Biochem. 1986 Mar;26(3):153-68. doi: 10.1016/0162-0134(86)80038-1.
Computer models estimated the ligand speciation and solubility of calcium, magnesium, zinc, and copper over a pH range for low molecular weight fractions characteristic of either human or bovine milks. Above pH 4 calcium is the only metal predicted to precipitate. Most of the remaining soluble calcium, magnesium, and zinc should be complexed with citrate. The solubility of calcium, magnesium, and zinc in human and bovine milks was measured experimentally from pH 2 to 7. The solubility of all three metals decreased as the pH increased. Calcium and zinc were soluble over a narrower pH range in bovine milk than in human milk. Increasing the levels of either calcium or inorganic phosphate alone in decaseinated human milk did not affect the solubility of zinc, but when both calcium and inorganic phosphate were added at levels comparable to bovine milk the solubility of zinc decreased at the higher pH's. The decreased solubility of zinc in skimmed milks in pH's characteristic of the small intestine is likely due to coprecipitation of zinc with calcium phosphate--a reaction not predicted for milk systems from known chemical solubility product data.
计算机模型估计了在人乳或牛乳低分子量部分所特有的pH范围内钙、镁、锌和铜的配体形态及溶解度。pH高于4时，预计只有钙会沉淀。其余大部分可溶性钙、镁和锌应与柠檬酸盐络合。通过实验测定了人乳和牛乳中钙、镁和锌在pH 2至7范围内的溶解度。随着pH升高，这三种金属的溶解度均降低。与母乳相比，牛乳中钙和锌在更窄的pH范围内可溶。单独增加脱酪人乳中钙或无机磷酸盐的含量不会影响锌的溶解度，但当钙和无机磷酸盐的添加量与牛乳相当时，在较高pH值下锌的溶解度会降低。在小肠特有的pH值下，脱脂乳中锌溶解度降低可能是由于锌与磷酸钙共沉淀所致——根据已知的化学溶解度积数据，该反应在乳体系中无法预测。
