Rheological properties of acidified gels of skim milk from cows selected for high or low milk fat concentration

Abstract

Abstract Milk from individual cows from two breeding selection lines, high or low milk fat concentration, was analysed for the concentration of total protein, individual caseins and whey proteins, lactose and fat. The milk samples were defatted and heated (90°C, 4 min) and cooled (to 20°C) in a pilot plate heat exchanger (running volume 5 L). After acidification with 1.6% glucono- δ -lactone (0.03% NaN 3 added), the samples were stored at 20°C for 24 h, thereafter gently stirred and stored for another 96 h at 7°C. Rheological measurements, using a Bohlin VOR Rheometer, showed that skim milk gels from cows with high milk fat concentration and also higher milk protein concentration had an approx. 1.4 times higher elastic modulus ( G′; P ), while the viscous modulus ( G ″) did not differ between the selection lines. The G ′ values positively correlated, in descending order, with the initial milk fat concentration, the total protein and the casein concentrations in the milk. The yield stress of the samples from the cows with high milk fat, however, was not different from that of the low milk fat line cows.