VARIATION IN SIZE OF GOAT MILK CASEIN MICELLES RELATED TO CASEIN GENOTYPE

Casein (CN) micelle size was determined in 2 goat milks from animals w ith different genotype for alpha(s1)CN. One milk lacked alpha(s1)GN, t he other had an alpha(s1)CN content of 4.7 g kg(-1). In comparison, th e goat bulk milk has 3.3 g kg(-1) alpha(s1)CN. The mean diameter of mi celles in milk without alpha(s1)CN was found to be 280 nm, while the d iameter was 199 nm in milk with a high content of alpha(s1)CN, ie a de crease by 29%. Micellar sizes were estimated by photon correlation spe ctroscopy (PCS) and by transmission electron microscopy (TEM) associat ed with negative staining. Micellar volume distribution according to s ize showed that milk without alpha(s1)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 formin g the large micelles. In contrast, milk with a high level of alpha(s1) CN showed a narrow unimodal distribution of frequency. The chemical an alysis of milks, total casein, individual caseins, total and soluble m inerals showed that the only difference is the alpha(s1)CN level. The results might imply a role of alpha(s1)CN in micelle size regulation.