Detection and quantification of true proteins, casein fractions and their genetic variants, and whey proteins in goat...

The protein profile of milk is an increasingly important research topic in relation to the technological properties of milk for cheesemaking and its value for human nutrition. Goats are a valuable source of milk worldwide, but there is no precise and rapid method for the simultaneous identification and quantification of the genetic variants of the major protein fractions in goat milk. In this study, we devised a method for the rapid identification and quantification of the main genetic variants of α_S1-, α_S2-, β-, and κ-CN, and of α-LA and β-LG (whey proteins) in caprine milk using an HPLC-UV reverse-phase C8 column. The R² of the calibration equations was >0.99 for all 15 protein fractions identified. A total of 520 milk samples were taken from 260 goats (in duplicates) of 6 different breeds reared on 22 farms operating different farming systems, ranging from traditional or extensive to modern or intensive, and analyzed them to externally validate the method. Milk samples from DNA-genotyped goats were used to identify the genetic variants of the caseins. Compared with other studies, using our method, we were able to separate the main genetic variant of caseins within a total run time of 24 min and with a repeatability >92% for all fractions except the C variant of κ-CN. Farms were found to be the major source of the variability in the contents of true proteins (56.1% of total variance), true caseins (48.6%), κ-CN C (50.6%) and whey proteins (52.9%-62.9%) in goat milk, whereas individual goat within farm was the most important source of variability in the contents of individual caseins and their genetic variants (53.9%-94.7%).