ANALYSIS OF BETA-CASEIN AND ITS PHOSPHOFORMS IN HUMAN-MILK

Quantitation of beta-casein was achieved through the use of urea-polya crylamide gel electrophoresis of whole milk and scanning densitometry. This method also provided electrophorectic separation of the differen t phosphoforms of S-casein which were also quantitated. Fifty-eight hu man milk samples collected in 4 different countries were analyzed for beta-casein and beta-casein phosphoform concentrations. The average B- casein concentration obtained using the whole milk methodology was 4.7 2 +/- 1.44 mg/ml. We found that a-casein is found in all the fractions of milk that has been centrifuged to remove the lipid or acid precipi tated to collect the caseins. This study used whole human milk and the refore all the beta-casein present was included in the analysis. The w hole milk analysis of B-casein indicated that on average the phosphofo rms are present in the following order ranked by concentration: tetra- > di- > non- > mono- > tri- > penta-phosphorylated beta-casein. Howev er, the phosphoform distribution of individual donors varied widely. F our different methods were used to determine the concentration of tota l protein in human milk samples. UV absorbance-based and colorimetric methods produced higher values of protein concentration than the Kjeld ahl method. (C) 1998 Elsevier Science Inc.