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Analysis of calcium phosphate cross-linkage in casein micelles by radioactive isotope Professor

用放射性同位素分析酪蛋白胶束中的磷酸钙交联教授

基本信息

批准号：
07660362
负责人：
AOKI Takayoshi
金额：
$ 1.34万
依托单位：
Kagoshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Although calcium and inorganic phosphate (Pi) in bovine casein micelles were at equilibrium with those in soluble form, their properties have not yet been elucidated sufficiently. In this study, the behavior of calcium and Pi in casein micelles was studied using ^<45>Ca and ^<32>P by ultrafiltration, equilibrium dialysis and gel permeation HPLC in the presence of 6M urea. Approximately 30-40% of the calcium and Pi in bovine casein micelles were estimated to be hard to exchanged with those in soluble phase. Then, artificial casein micelles were prepared at a casein concentration of 2.5% with 30-40 mM calcium, 22-27 mM Pi and 10mM citrate using ^<45>Ca and ^<32>P.About 75 and 65% of micellar calcium and Pi in artificial casein micelles were exchanged after dialysis of artificial casein micelles against a simulated milk ultrafiltrate at 4ﾟC for 72h.The percentage of ^<45>Ca and ^<32>P in the fraction of casein aggregates cross-linked by micellar calcium phosphate were 26.9 and 27.6%, which decreased to about 10% after equilibrium dialysis against a simulated milk ultrafiltrate at 4ﾟC for 72h. The proportion of exchanged calcium and Pi in artificial casein micelles during dialysis for 72h were higher at 25ﾟC than at 4ﾟC,suggesting that the exchange of calcium and Pi between diffusible and micellar phases depended on temperature. The effects of calcium and Pi on the formation and properties of casein micelles were also examined using response surface analyzes. The results suggest that the exchange of calcium and phosphate between diffusible and micellar phases proceeds slowly, and a proportion of calcium and Pi in casein micelles is difficult to exchage.

尽管牛酪蛋白胶束中的钙和无机磷酸盐（Pi）与可溶形式的钙和无机磷酸盐处于平衡状态，但它们的性质尚未得到充分阐明。本研究<45><32>采用超滤法、平衡透析法和凝胶渗透高效液相色谱法，在6 M尿素存在下，以钙和磷为底物，研究了酪蛋白胶束中钙和磷的行为。酪蛋白胶束中约有30-40%的钙和磷难以与可溶相的钙和磷进行交换。然后，在酪蛋白浓度为2.5%的条件下，加入30-40 mM Ca、22-27 mM Pi和10 mM柠檬酸盐，用磷酸钙和磷酸二钙制备了酪蛋白人工胶束<45><32>。在4 ℃下用模拟牛奶超滤液透析72 h后，人工酪蛋白胶束中约75%和65%的胶束Ca和Pi被交换<45><32>。用模拟牛乳超滤液在4 ℃下平衡透析72 h后，其降解率降至10%左右。透析72 h后，25 ℃时酪蛋白胶束中钙和磷的交换比例高于4 ℃时，表明钙和磷在扩散相和胶束相之间的交换依赖于温度。采用响应面分析法研究了钙和磷对酪蛋白胶束形成和性质的影响。结果表明，钙和磷在扩散相和胶束相之间的交换进行缓慢，酪蛋白胶束中的钙和磷的比例是难以交换的。