Immobilization of casein micelles for probing their structure and interactions with polysaccharides using scanning electron microscopy (SEM)

A new method is described for probing the structure of casein micelles and their interactions with κ-carrageen and λ-carrageenan using scanning electron microscopy (SEM). Immobilization of casein micelles at pH 6.7 to a gold substrate by means of covalent binding resulted in a homogeneous distribution of isolated, spherical casein micelles on the substrate. Detailed images of the casein micelle structure were obtained. Electron micrographs of casein micelle–carrageenan mixtures revealed aggregates, which became larger with increasing carrageenan concentration. Because of the ability of κ-carrageenan to form a gel, in contrast to λ-carrageenan, larger and more aggregates were found with κ-carrageenan at similar carrageenan concentration. Detailed images showed strands of κ-carrageenan to which casein micelles were attached, which was not observed for λ-carrageenan.