Lactoprotein genetic variants in cattle and cheese making ability

Cheese making ability of milk is associated with high contents of protein, casein (CN) and fat, high casein number, short rennet coagulation time (RCT ), high curd firmness (CF) and with a high cheese yield. For the four CN lo ci, as well. as for the beta-lactoglobulin (LG)- and alpha-lactalbumin (LA) locus, more than 60 genetic variants have been observed. However, most of these variants have not yet been investigated with regard to their cheese m aking ability In Holstein Friesian cows kappa-CN BE is associated with a hi gher protein and casein content of milk than kappa-CN AA. However, in Simme ntals and in Brown Cattle this association is not so clear; a higher fat co ntent of milk seems to be related to beta-LG BE when compared with beta-LG AA. In many publications PLG BE also showed a higher casein content than be ta-LG AA. All publications referring to the casein number report that milk containing beta-LG BE has an approximately 3 % (absolute) higher casein num ber than milk containing beta-LG AA. Regarding the genotypes alpha(s1)-CN B C and CC contradictory results for the RCT and CF values have been publishe d when compared with alpha(s1)-CN BE milk. PCN BE showed in all publication s the shortest RCT among all PCN genotypes, whereas the reported results fo r CF of this genotype compared with the types A(1)A(2) or A(2)A(2) are conf licting From the majority of the published data it may be concluded that mi lk containing kappa-CN BE has significantly shorter RCT and higher CF than kappa-CN AA milk. All rare genotypes at the kappa-CN locus, such as AC, BC, AE, BE and EE, had worse RCT values than kappa-CN BE milk. CF of kappa-CN genotypes increases in the order AE/AA<AB/AC<BC/BB. In most investigations involving Parmiggiano-Reggiano, Cheddar and other cheese varieties higher y ields of cheese were found, ranging from 0.3 to 10 %, in favour of kappa-CN BE compared with kappa-CN AA. Due to the higher casein number associated w ith beta-LG BE, higher yields of cheese were reported in literature (range 1 to 10 %) for this genotype than for beta-LG AA. In summary, kappa-CN B an d beta-LG B are the most advantageous variants with respect to cheese makin g ability. However, in most publications attention was focused on the effec ts of a single milk protein locus but due to the tight linkage between the casein loci effects of haplotypes should be studied more extensively.