Short communication: CSN1S1-CSN3 (αS₁-κ-casein) composite genotypes affect detailed milk protein composition of Mediterranean water buffalo
2012
Bonfatti, V. | Giantin, M. | Gervaso, M. | Rostellato, R. | Coletta, A. | Dacasto, M. | Carnier, P.
The aim of the study was to investigate the effect of composite CSN1S1-CSN3 [αS₁-κ-casein (CN)] genotype on milk protein composition in Mediterranean water buffalo. Content of αS₁-CN, αS₂-CN, β-CN, γ-CN, κ-CN, glycosylated and unglycosylated κ-CN, α-lactalbumin, and β-lactoglobulin was measured by reversed-phase HPLC using 621 individual milk samples. Genotypes at CSN1S1 and CSN3 were also obtained by reversed-phase HPLC. Two alleles were detected at CSN1S1 (corresponding to the A and B variants, O62823: p.Leu193Ser,) and at CSN3 (corresponding to the X1 and X2 variants, CAP12622.1: p.Ile156Thr). Increased proportions of αS₁-CN in total casein (TCN) were associated with genotypes carrying CSN1S1 A. Genotypes associated with a marked decrease of the proportion of αS₁-CN in TCN (composite genotypes AB-X1X1 and BB-X1X2) were associated with marked increases in the proportion of αS₂-CN. In addition, composite genotypes carrying the X1 allele at CSN3 were associated with a greater proportion of αS₂-CN in TCN relative to those carrying CSN3 X2. Composite genotypes greatly affected also the variability of ratios of κ-CN to TCN, with genotypes carrying the X1 allele at CSN3 being associated with decreased ratios. The decreased content of glycosylated κ-CN associated with CSN3 X1 was responsible for the overall lower content of total κ-CN in milk of X1-carrying animals. Increasing the frequency of specific genotypes might be an effective way to alter milk protein composition, namely the proportion of αS₁-CN, αS₂-CN, and κ-CN in TCN, and the degree of glycosylation of κ-CN.
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