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Effects of colloidal calcium phosphate content and free calcium ion concentration in the milk serum on the dissociation of bovine casein micelles

  • Carl Holt (a1), D. Thomas Davies (a1) and Andrew J. R. Law (a1)

Summary

The strength of binding of the individual caseins and the nature of the bonding within bovine casein micelles were examined through dissociation of the micelles by dialysis of skim milk either against phosphate-free buffers containing 3 or 6 mm-CaCl2, or against buffers that were nearly saturated with respect to micellar calcium phosphate, but which had a free Ca2+ concentration in the range 0·4–5·9 mm. Dissociation was followed by ultracentrifuging the dialysed milks and determining the partition of the total and the individual caseins between the pellet and serum. During dialysis against the phosphate-free buffers both colloidal Ca and Pi in the milks decreased and about 30 % of the Pi could be removed without significant casein dissociation. With further loss of Pi, however, increasing dissociation occurred and the proportions of the individual caseins retained in the casein pellet were in the order αs2- > αs1- > β- ≈ κ-casein. Dialysis against the calcium phosphate buffers resulted in no loss of colloidal Pi but colloidal Ca increased with the free Ca2+ concentration of the buffer. Little change in the casein partition occurred in the presence of more than 1 mm free Ca2+, but serum casein increased markedly at lower levels, and the strength of binding of the individual caseins in the pelleted casein was in the order αs2-> αs1- > β- > κ-casein. In both types of buffer, dissociation is considered to occur through the breaking of linkages between the caseins and inorganic constituents. Analysis of the amino acids in a calcium phosphate-rich material obtained after exhaustive proteolytic digestion of casein micelles suggests that these linkages involve the phosphate centres of the caseins.

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Allen, R. J. L. 1940 The estimation of phosphorus. Biochemical Journal 34 858865.
Chaplin, L. C. 1984 Studies on micellar calcium phosphate: composition and apparent solubility product in milk over a wide pH range. Journal of Dairy Research 51 251257
Davies, D. T. & Law, A. J. R. 1977 An improved method for the quantitative fractionation of casein mixtures using ion-exchange chromatography. Journal of Dairy Research 44 213221
Davies, D. T. & Law, A. J. R. 1980 The content and composition of protein in creamery milks in south-west Scotland. Journal of Dairy Research 47 8390
Davies, D. T. & Law, A. J. R. 1983 Variation in the protein composition of bovine casein micelles and serum casein in relation to micellar size and milk temperature. Journal of Dairy Research 50 6775
Davies, D. T. & White, J. C. D. 1962 The determination of calcium and magnesium in milk and milk diffusate. Journal of Dairy Research 29 285296
Dickson, I. R. & Perkins, D. J. 1971 Studies on the interactions between purified bovine caseins and alkaline-earth-metal ions. Biochemical Journal 124 235240
Downey, W. K. & Murphy, R. F. 1970 The temperature-dependent dissociation of β-casein from bovine casein micelles and complexes. Journal of Dairy Research 37 361372
Eigel, W. N., Butler, J. E., Ernstrom, C. A., Farrell, H. M., Harwalkar, V. R., Jenness, R. & Whitney, R. Mol. 1984 Nomenclature of proteins of cow's milk: fifth revision. Journal of Dairy Science 67 15991631
Geerts, J. P., Bekhof, J. J. & Soherjon, J. W. 1983 Determination of calcium ion activities in milk with an ion-selective electrode. A linear relationship between the logarithm of time and the recovery of the calcium ion activity after heat treatment. Netherlands Milk and Dairy Journal 37 197211
Ho, C. & Waugh, D. F. 1965 Interactions of bovine caseins with divalent cations. Journal of the American Chemical Society 87 889892
Holt, C. 1982 Inorganic constituents of milk. III. The colloidal calcium phosphate of cow's milk. Journal of Dairy Research 49 2938
Holt, C., Dalgleish, D. G. & Jenness, R. 1981 Calculation of the ion equilibria in milk diffusate and comparison with experiment. Analytical Biochemistry 113 154163
Holt, C., Hasnain, S. S. & Hukins, D. W. L. 1982 Structure of bovine milk calcium phosphate determined by X-ray absorption spectroscopy. Biochimica et Biophysica Acta 719 299303
Lin, S. H. C., Leong, S. L., Dewan, R. K., Bloomfield, V. A. & Morr, C. V. 1972. Effect of calcium ion on the structure of native bovine casein micelles. Biochemistry 11 18181821
Mackinlay, A. G. & Wake, R. G. 1964 The heterogeneity of κ-casein. Biochimica et Biophysica Acta 93 378386
Manson, W. & Annan, W. D. 1971 The structure of a phosphopeptide derived from β-casein. Archives of Biochemistry and Biophysics 145 1626
McGann, T. C. A., Buchheim, W., Kearney, R. D. & Richardson, T. 1983 Composition and ultrastructure of calcium phosphate-citrate complexes in bovine milk systems. Biochimica et Biophysica Acta 760 415420
McGann, T. C. A. & Pyne, G. T. 1960 The colloidal phosphate of milk. III. Nature of its association with casein. Journal of Dairy Research 27 403417
Noble, R. W. & Waugh, D. F. 1965 Casein micelles. Formation and structure. I. Journal of the American Chemical Society 87 22362245
Parker, T. G. & Dalgleish, D. G. 1981 Binding of calcium ions to bovine β-casein. Journal of Dairy Research 48 7176
Reardon, J., Foreman, J. A. & Searcy, R. L. 1966 New reactants for the colorimetric determination of ammonia. Clinica Chimica Acta 14 403405
Rose, D. 1965 Protein stability problems. Journal of Dairy Science 48 139146
Rose, D. 1968 Relation between micellar and serum casein in bovine milk. Journal of Dairy Science 51 18971902
Rose, D. & Colvin, J. R. 1966 Internal structure of casein micelles from bovine milk. Journal of Dairy Science 49 351355
Rowland, S. J. 1938 The determination of the nitrogen distribution in milk. Journal of Dairy Research 9 4246
Schmidt, D. G. 1980 Colloidal aspects of casein. Netherlands Milk and Dairy Journal 34 4264
Schmidt, D. G. 1982 Association of caseins and casein micelle structure. In Developments in Dairy Chemistry – 1. Proteins pp. 6186 (Ed. Fox, P. F.). Barking: Applied Science
Swaisgood, H. E. 1982 Chemistry of milk protein. In Developments in Dairy Chemistry– 1. Proteins, pp. 159 (Ed. Fox, P. F.). Barking: Applied Science
Talbot, B. & Waugh, D. F. 1970 Micelle-forming characteristics of monomeric and covalent polymeric κ-caseins. Biochemistry 9 28072813
Tanford, C. 1961 Physical Chemistry of Macromolecules p. 532. New York: John Wiley
Ter Horst, M. G. 1963 A new theory on the caseinate complex in milk. Netherlands Milk and Dairy Journal 17 185192
Thompson, M. P., Gordon, W. G., Boswell, R. T. & Farrell, H. M. 1969 Solubility solvation, and stabilization of αsl- and β-caseins. Journal of Dairy Science 52 11661173
Toma, S. J. & Nakai, S. 1973 Calcium sensitivity and molecular weight of αs5-casein. Journal of Dairy Science 56 15591562
Visser, J., Schaier, R. W. & Van Gorkom, M. 1979 The role of calcium, phosphate and citrate ions in the stabilization of casein micelles. Journal of Dairy Research 46 333335
Whikehart, D. R. & Rafter, G. W. 1970 Effects of varying protein to protein-phosphate ratios of αs-casein on α-κ-casein micelles. Journal of Dairy Science 53 11711176
White, J. C. D. & Davies, D. T. 1958 The relation between the chemical composition of milk and the stability of the caseinate complex. I. General introduction, description of samples, methods and chemical composition of samples. Journal of Dairy Research 25 236255
Yaguchi, M., Davies, D. T. & Kim, Y. K. 1968 Preparation of κ-casein by gel filtration. Journal of Dairy Science 51 473477

Effects of colloidal calcium phosphate content and free calcium ion concentration in the milk serum on the dissociation of bovine casein micelles

  • Carl Holt (a1), D. Thomas Davies (a1) and Andrew J. R. Law (a1)

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