An electron microscope study of the ultrastructure of bovine and human casein micelles in fresh and acidified milk

Abstract

SummaryWhen examined under the electron microscope, bovine casein micelles were seen as aggregates of spheroidal granules arranged in spherical symmetry. The granules were of 2 kinds—one transparent in the electron beam and the other relatively opaque. With increasing acidity of the milk the regular arrangements of granules tended to break down, and bridges composed of granules, formed between neighbouring micelles. The average diameter of the granules was about 8 mμ, from which a molecular weight of about 225000 was calculated. Evidence was adduced for the identity of these granules with the macromolecules of native casein in equilibrium with whey.Human casein micelles showed the same structural features. The average diameter of the granules was about 6 mμ, from which a molecular weight of about 100000 was calculated.