PRELIMINARY STUDY ON QUANTIFICATION OF aS1-CASEIN VARIANTS IN GIRGENTANA GOAT BREED BY DIRECT CHROMATOGRAPHIC ANALYSIS OF MILK

Abstract

Goat αs1-casein is a highly polymorphic protein, coded by CSN1S1 gene. Nowadays, several alleles were identified and associated with different levels of αs1-casein in goat milk. Polymorphisms at αs1-casein locus have been shown to affect not only the quantity of this casein in goat milk, but also the structural and nutritional characteristics (hypoallergenic properties) and technological properties of the milk (1). The aim of this work was to separate and quantify the most common allelic variants of αs1-casein in milk of Girgentana goat breed, a Sicilian autochthonous breed, and to evaluate the effect of αs1-casein polymorphisms on casein content. The CSN1S1 A/01, B/E, F, and N alleles were simultaneously investigated by PCR-RFLP (2). AS-PCR was used for the detection of the CSN1S1 E (3) and 01 alleles (4). Milk samples were prepared following the method proposed by Bobe et al. (5) and analyzed by RP-HPLC method (6). A reversed-phase analytical column C8 (Zorbax 300SB-C8 RP, 3.5µm,300Å, 150×4.6 I.D.) was used and the detection was made at a wavelength of 214 nm. The procedure was developed using individual raw milk samples of Girgentana goats. For calibration experiments, pure genetic variants were extracted from individual milk samples of animals with known genotypes, considering that commercial standards for goat allelic variants were not available. In particular, were used animals with AA, BB, FF and NN homozygous genotypes. Method validation consisted in testing linearity, repeatability, reproducibility and accuracy. A linear relationship between the concentrations of proteins and peak areas was observed over the concentration range, with low detection limits. Repeatability and reproducibility were satisfactory for both retention times and peak areas.