DAIRY CHEMISTRY AND BIOCHEMISTRY Figure 2.4 Effect of pH on the rate of mutarotation of lactose. At equilibrium: 894x+35(100-x)=554×100 100-x=62.7 Thus, the equilibrium mixture at 20C is composed of 62.7%B-and 37.3% a-lactose. The equilibrium constant, B/a, is 1.68 at 20C. The proportion of lactose in the a-form increases as the temperature is increased and the equilibrium constant consequently decreases. The equilibrium constant is not influenced by pH, but the rate of mutarotation is dependent on both temperature and pH. The change from a- to B-lactose is 51.1, 17.5 and3, 4% complete at 25, 15 and 0C, respectively, in 1 h and is almost instantaneous at about 75C. The rate of mutarotation is slowest at pH 5.0, increasing rapidly at more acid or alkaline values; equilibrium is established in a few minutes at pH 9.0 (Figure 2. 4)26 DAIRY CHEMISTRY AND BIOCHEMISTRY oL I I I I 2 4 6 8 PH Figure 2.4 Effect of pH on the rate of mutarotation of lactose. At equilibrium: 89.4~ + 35(100 - X) = 55.4 x 100 x = 37.3 100-x = 62.7 Thus, the equilibrium mixture at 20°C is composed of 62.7% 8- and 37.3% a-lactose. The equilibrium constant, P/a, is 1.68 at 20°C. The proportion of lactose in the @-form increases as the temperature is increased and the equilibrium constant consequently decreases. The equilibrium constant is not influenced by pH, but the rate of mutarotation is dependent on both temperature and pH. The change from m- to p-lactose is 51.1, 17.5 and 3.4% complete at 25, 15 and O"C, respectively, in 1 h and is almost instantaneous at about 75°C. The rate of mutarotation is slowest at pH 5.0, increasing rapidly at more acid or alkaline values; equilibrium is established in a few minutes at pH 9.0 (Figure 2.4)