MILK COMPOSITION AND IDENTIFICATION OF PROTEIN POLYMORPHISM IN MONTBÉLIARDE COWS TO SELECT THE BEST VARIANTS AND IMPROVE CHESSE QUALITY

Cristina Lazăr, Rodica Pelmuş, Elena Ghiţă, M.C. Rotar

Abstract
    The main purpose of this study was to identify the proteins polymorphism in Montbéliarde cows to discover and select the best individuals whit casein variants suitable for a very good ability of making cheese. Milk composition was analysed for fat (3.83%) and protein (3.38%). Fat percentage manifested a high variability and ranged between 6.06% and 1.21%, while milk protein didn’t have the same variation with closed limits (3.89 and 3.28%). SDS-PAGE analysis revealed, after electrophoresis, six protein fractions in milk samples: αs1, αs2, β, k-CN, and β-LG, and α-LA. By densitometry analysis, three levels of expressions of the same type of protein fraction were discovered in each milk sample. The casein group, composed by four fractions αs1-, αs2-, β- and k-casein (32.8%, 7.3%, 34.3%, 17.6%) show in fact that they are 92% of the total milk protein and 8% are albumins similar with other studies for cows. First protein fraction αs1-casein, was with medium expression manifested by 54.54% of the cows, followed by that one with strong (31.82%) and low expression (13.64%). On the third place in milk composition is situated β-casein with strong expression for 4.54% of the cows. Medium expression level of the β-casein was manifested by the majority of the analysed Montbéliarde cows (72.73%) and 22.73% of it had low expression level, while only 4.54% of them have recorded strong expression level. Further investigations will be necessary to confirm the results by PCR-RFLP analysis to identify Montbéliarde cows caseins polymorphism with the genetic variants for each protein locus. This will allow keeping the most suitable animals with strong genetic expression and high content in caseins very well correlated with milk.

Key words: Montbéliarde, dairy cows, milk composition, milk proteins polymorphism