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Journal of Dairy Science Vol. 54 No. 11 1555-1563
© 1971 by American Dairy Science Association ®
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Composition and Properties of Submicellar Casein Complexes in Colloidal Phosphate-Free Skimmilk1

C. V. Morr, R. V. Josephson2, R. Jenness and P. B. Manning

Departments of Food Science and Industries and of Biochemistry, University of Minnesota, St. Paul 55101

ABSTRACT

Colloidal phosphate-free milks prepared from raw or heated (80 C for 30 min) skimmilk by adjustment to pH 4.9 or addition of ethylenediaminetetraacetate followed by dialysis were similar in total and dialyzable nitrogen, calcium, and phosphate. A small amount of inorganic phosphate was not dialyzable and 20 to 25% of the original skimmilk nondialyzable calcium was retained.

Centrifugation of colloidal phosphate-free skimmilk at 150,000 x g for one hour deposited a fraction (~ 4% of the total casein) enriched in {alpha}s-casein. Analytical ultracentrifugation revealed one principal component with sedimentation constant of 7.5 S (20 C) but also showed much size heterogeneity. Electron microscopy confirmed the size heterogeneity and also revealed that the submicellar casein complexes in colloidal phosphate-free skimmilk are smaller, irregularly shaped, and less electrondense than casein micelles in skimmilk. Gel filtration likewise confirmed the size heterogeneity of the submicellar casein particles. Sepharose 4B provided better resolution of submicellar casein particles than either Sephadex G-200 or Sepharose 2B. The successive fractions from filtration on Sepharose 4B were shown by starch gel electrophoresis to increase progressively in ß-casein and decrease in {alpha}s-casein.

FOOTNOTES

1 Scientific Journal Series Paper 7669 Minnesota Agricultural Experiment Station.

2 Present address: Department of Food Science and Nutrition, The Ohio State University, Columbus 43210.






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Copyright © 1971 by the American Dairy Science Association ®.