Laser Light Scattering Study of the Fractionation of Casein Micelles in Skim Milk by Controlled Pore Glass Chromatography

Abstract

Casein is a major protein component of milk. It consists of several different polypeptides: α_S1, α_S2, β and к casein, as well as varying amounts of proteolytic fragments of these polypeptides. The polypeptides are bound together by calcium phosphate and citrate to form aggregates of a wide range of sizes (Holt et al, 1978) up to 680 nm in diameter (McGann et al, 1980). The size distribution of these casein aggregates, known as ‘micelles’, in milk may change with different conditions such as variation in Ca²⁺ concentration, pH and history of heat treatment. The nature of the size distribution may affect functional properties of the milk such as enzymic coagulation on addition of rennet (Ekstrand et al, 1980; Dalgleish et al, 1981). It has proved desirable to characterize the size distribution of casein micelles in milk so as to investigate related properties further.