Quantification of β-casein in human milk | Journal of Dairy Research | Cambridge Core (original) (raw)

Summary

A method is described for preparing immunologically homogeneous human milk β-casein, against which monospecific rabbit antiserum was prepared. The antiserum was used to quantify β-casein, the major human casein, by rocket Immunoelectrophoresis in individual milk samples. However, it was found that in most samples β-casein occurred together with degradation products originating from its proteolysis by plasmin. Immunological quantification of human β-casein, treated with plasmin for various time periods, showed that rocket height was not affected by proteolysis up to degradation states clearly more advanced than those observed in all samples of fresh human milk tested. Assays of 150 individual milk samples from 80 women, covering a lactation period of up to 730 d, gave an average concentration of β-casein (native+degraded) of 4·67±0·89 standard deviation (g/1); extremes at 2·1 and 7·3 g/1 did not vary significantly during the period under study. Comparison of this average value with an accepted casein content of 4·4 g/1 (Macy & Kelly, 1961) showed that the casein content of human milk is underestimated when obtained by N determinations on milk and on its supernatants at pH 4·6 (whey). Caseins other than β-casein occurred only in minute amounts, if at all.

Type

Original Articles

References

Brignon, G., Ribadeau Dumas, B., Mercier, J. C. & Pelissier, J. P. 1977 Complete amino acid sequence of bovine αs2-casein. FEBS Letters 76 274–279CrossRef Google Scholar PubMed

Chobert, J. M., Mercier, J. C., Bahy, C. & Haze, G. 1976 [Primary structure of the caseinomacropeptide of porcine and human κ-caseins]. FEBS Letters 72 173–178CrossRef Google Scholar PubMed

Greenberg, R., Groves, M. L. & Dower, H. J. 1984 Human β-casein. Amino acid sequence and identification of phosphorylation sites. Journal of Biological Chemistry 259 5132–5138CrossRef Google Scholar PubMed

Gripon, J. C., Desmazeaud, M. J., Le Bars, D. & Bergere, J. L. 1975 [Study of the role of microorganisms and chymosin during cheese ripening]. Lait 548 502–516CrossRef Google Scholar

Groves, M. L. & Gordon, W. G. 1970 The major component of human casein: a protein phosphorylated at different levels. Archives of Biochemistry and Biophysics 140 47–51CrossRef Google Scholar PubMed

Groves, M. L., Gordon, W. G., Kalan, E. B. & Jones, S. B. 1973 TS-A2, TS-B, R- and S-caseins: their isolation, composition and relationship to the β- and α-casein polymorphs A2 and B. Journal of Dairy Science 56 558–568CrossRef Google Scholar

Korycka-Dahl, M., Ribadeau Dumas, B., Chene, N. & Martal, J. 1983 Plasmin activity in milk. Journal of Dairy Science 66 704–711CrossRef Google Scholar

Laemmli, U. K. 1970 Cleavage of structural protein during the assembly of the head of bacteriophage T4. Nature 227 680–685CrossRef Google Scholar PubMed

Laurell, C. B. 1966 Quantitative estimation of protein by electrophoresis in agarose gel containing antibodies. Analytical Biochemistry 15 42–52CrossRef Google Scholar PubMed

Macy, I. G. & Kelly, H. J. 1961 Human milk and cow's milk in infant nutrition. In Milk: The mammary gland and its secretion. Vol. 2 pp. 265–304 (Eds Kon, S. K. and Cowie, A. T.) London: Academic PressCrossRef Google Scholar

Nagasawa, T., Kiyosawa, I. & Kuwahara, K. 1971 Human casein. III. DEAE cellulose-urea chromatography of human casein and dephosphorylation of casein fractions. Journal of Dairy Science 54 987–993CrossRef Google Scholar

Reimerdes, E. H. 1982 Changes in the proteins of raw milk during storage. In Developments in Dairy Chemistry- 1 Proteins pp. 271–288 (Ed. Fox, P. F.) London: Applied Science Publishers.Google Scholar

Scheidegger, J. J. 1955 [An immunoelectrophoresis micromethod]. International Archives of Allergy and Applied Immunology 7 103–110CrossRef Google Scholar PubMed

Swaisgood, H. E. 1982 Chemistry of milk protein. In Developments in Dairy Chemistry - 1 Proteins pp. 1–59 (Ed. Fox, P. F.), London: Applied Science PublishersGoogle Scholar

Uriel, J. 1966 [Electrophoresis in acrylamide-agarose gels]. Bulletin de la Société de Chimie Biologique 48 969–982Google Scholar PubMed