Appearance and Size of Micelles from Bovine Milk

Electron micrographs of a number of milks from individual cows were prepared by a replica method technique, and average micelle diameters determined by appropriate calculations based on visual counts of the number of micelles in various size ranges. The milks were also analyzed for several inorganic constituents and proteins, and their stability at 140C determined. Results indicate that the major factors influencing micelle size were total soluble calcium and κ-casein (as a per cent of total casein). Citrate concentration was also related to micelle diameter, but this is thought to be an indirect effect, as citrate was the major factor influencing the concentration of soluble calcium. Ionic calcium was not significantly related to average micelle diameter. Heat stability (140C) was not significantly related to average micelle diameter. The appearance of replicas prepared from cold milk and from milk chilled and rewarmed to 35C suggested that the β-casein which dissolved from micelles of cooled milk did not re-enter the micelles as the milk was rewarmed but merely deposited on the surface of the micelles.