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

Abstract

Casein (CN) micelle size was determined in 2 goat milks from animais with different genotype for OEs1CN.One milk lacked OEs1CN,the other had an OEs1CNcontent of 4.7 9 kg-l, ln comparison, the goat bulk milk has 3.3 9 kg-1 OEs1CN.The mean diameter of micelles in milk without OEs1CNwas found to be 280 nm, while the diameter was 199 nm in milk with a high content of OEs1CN, ie a decrease by 29%. Micellar sizes were estimated by photon correlation spectroscopy (PCS) and by transmission electron microscopy (TEM) associated with negative staining. Miceilar volume distribution according to slze showed that milk without OE s lCN 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 case in forming the large micelles. In contrast, milk with a high level of OEs1CNshowed a narrow unimodal distribution of frequency. The chemical analysis of milks, total casein, individual caseins, total and soluble minerais showed that the only difference is the OEs1CN level. The results might imply a role of OEslCN in miceile size regulation.