Food Structure


C. Holt


This review considers the average size and size distribution of bovine casein micelles as measured by electron microscopy, light scattering and controlled pore glass chromatography, and the origin and biological function of the size distribution.

Recent work by electron microscopy has given average sizes in reasonable agreement with measurements on the same milk sample by light scattering . It is suggested that natural variations in averaqe micelle size and overestimation of micelle radii by light scattering methods as well as deficiencies in electron microscopical methodology were responsible for past discrepancies.

Electron microscopy and controlled pore glass chromatography provide evidence that in some milks the differential weight or volume distribution curve is bimodal with a main peak at 90-180nm and a lesser peak at >200nm diameter.

The largest micelles in the size distribution are too large to have been formed fully within the Golgi vesicles of the mammary secretory cell, so a second stage of aggregation may occur in the alveolar lumen.

Using a model of the casein micelle in which the particles have a hairy outer layer, it is shown how the size distribution can influence the structure of a milk gel.

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