Variation in size of goat milk casein micelles related to casein genotype

Abstract

Casein (CN) micelle size was determined in 2 goat milks from animals with different genotype for αauthorCN. One milk lacked αauthor CN, the other had an αauthor CN content of 4.7 g kg-1. In comparison, the goat bulk milk has 3.3 g kg-1 αauthorCN. The mean diameter of micelles in milk without αauthor CN was found to be 280 nm, while the diameter was 199 nm in milk with a high content of αauthor CN, ie a decrease by 29%. Micellar sizes were estimated by photon correlation spectroscopy (PCS) and by transmission electron microscopy (TEM) associated with negative staining. Micellar volume distribution according to size showed that milk without αauthor CN had the typical distribution of goat milk, ie a large spread of diameters from 20 to 270 nm without any clear maximum in frequency and a high proportion of casein forming the large micelles. In contrast, milk with a high level of αauthor CN showed a narrow unimodal distribution of frequency. The chemical analysis of milks, total casein, individual caseins, total and soluble minerals showed that the only difference is the αauthor CN level. The results might imply a role of αauthor CN in micelle size regulation. © 1995 Elsevier/INRA.