Detailed protein fraction profile of goat milk of six breeds

The protein profile of goat milk is very different from cow milk in terms of proportion of the different protein fractions and especially for its much higher genetic polymorphism. The aim of this study was to investigate breed effect on the detailed protein profile of goat milk. This research is part of the GOOD-MILK project which involved 1,272 goats from 6 different breeds reared in 35 farms located in Sardinia (Italy). The breeds are divided in two categories: the Alpine breeds (ALP: Camosciata delle Alpi and Saanen); and the Mediterranean breeds (MED: Murciano-Granadina, Maltese, Sarda, and Sarda Primitiva). A total of 1,090 individual milk samples from 23 farms (823 samples + 267 duplicates) were analysed for identification and quantification of milk protein fractions by RP-HPLC method. The data were analysed using a linear mixed model with the classes of days in milk (DIM), parity, and breed as fixed effects, while the flock effect was included as random. In a second model, the fixed effects of casein genotypes were also included. Breed affected all milk protein fractions, while DIM and parity had small effects. The main differences in protein profile among breeds were between ALP and MED types, being the former richer in whey proteins and lower in caseins than the latter; within MED, Sarda and Sarda Primitiva showed higher concentration in caseins than the other breeds, and no significant differences from each other. The inclusion of casein genotypes did not change relevantly the breed effect estimates but it decreased the residual variance, especially for αS1- and β-caseins. Further investigation about the relationships between milk protein profile and milk quality and cheese-making ability in different goat breeds are envisaged.