Effects of genetic variants of kappa-casein and beta-lactoglobulin and heat treatment on coagulating properties of milk
Choi, J.W.; Ng-Kwai-Hang, K.F.
Asian-Australasian Journal of Animal Sciences 16(8): 1212-1217
ISSN/ISBN: 1011-2367 Accession: 066169923
Fifty-two Holstein cows with different phenotypes Of K-casein (K-CN) and beta-lactoglobulin (beta-LG) were selected to provide weekly milk samples for heating at 30, 70, 75 and 80degreesC for 2 min. Coagulating properties of heated milk samples measured as rennet clotting time, rate of curd firming and curd firmness at cutting were determined by a Formagraph. Milk samples were analysed for fat and casein. Least squares analyses of data, after adjustments were made for effect of milk casein and fat contents, indicated that although an increase in heating temperatures resulted in less desirable coagulating properties, the effect of milk types was inherent irrespective of heating temperatures. The shortest rennet clotting time (6.06 min), fastest rate of curd firming (5.61 min) and firmest curd (38.05 nun) were obtained from milk with the B variant for K-CN and B variant for beta-LG when preheated at 30degreesC. It appears that milk bearing K-CN B is more resistant to heat perturbation. All milk samples having the K-casein AA (milk types AA/AA, AA/AB, AA/BB) did not have a measurable K20 value when preheated at 70degreesC. This effect was observed for K-cascin AB (milk types AB/AA, AB/AB, AB/BB) at 75degreesC and K-casein BB (milk types BB/AA, BB/AB, BB/BB) at 80degreesC.