The influence of rare genetic variants of milk proteins on compositional properties of milk, rennetability, casein micelle size and content of non-glycosylated kappa-casein
1997
Lodes, A. (Kraft Jacobs Suchard Research and Development, Muenchen (Germany)) | Buchberger, J. | Krause, I. | Klostermeyer, H.
Milk samples of individual cows were analysed for milk composition (n = 801) and rennetability (n = 870). The following genotypes were included: alphas1-Cn BB/ BC and CC, beta-Cn A1A1, A1A2, A1B, A2A2, A2B, A2C and BB, kappa-Cn AA, AB, AC, AE, BB, BC and BE and beta-Lg AA, AB, AD, BB, BC, BD and BW. The data were evaluated by least squares analysis. With regard to the beta-Cn locus, the protein and casein content decreased in the order: beta-Cn A2C more than A1A1 more than A1B more than A1A2 more than A2B more than A2A2 more than BB. The seven kappa-Cn genotypes investigated did not show significant effects on the values of protein and casein. The casein number was significantly influenced by the beta-Lg genotypes; it increased from 75.7 to 79.0 per cent in the order beta-Lg AA less than AD less than AB less than BW less than BD less than BB less than BC. Of all loci tested, kappa-Cn had the greatest influence on the rennetability of milk. Rennet coagulation time increased from 9.8 to 13.0 min (BE less than BB less than AB less than AE/AA less than BC less than AC). Milk with the rare types kappa-Cn AE or BE was characterized by a very weak curd similar to that of kappa-Cn AA milk, whereas kappa-Cn BB and BC milk formed a strong curd. Curd firmness of kappa-Cn AB and AC milk took an intermediate position. The relationship between the genetic variants and the micelle size and the content of non-glycosylated kappa-casein, respectively, was examined on 203 milk samples. Micelle size increased from 190 to 229 nm in the order: kappa-Cn BC/BB less than AB less than AC less than BE less than AA less than AE, whereas the content of non-glycosylated kappa-casein increased as follows: kappa-Cn AC/AE less than AA less than AB less than BE less than BC less than BB.
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