Lactose equilibrium in solution

When either isomer is dissolved in water, there is a gradual change from one form to the other until equilibrium is established, i.e. mutarotation. These changes may be followed by measuring the change in optical rotation with time until, at equilibrium, the specific rotation is -1-55.4°. 

the equilibrium mixture at 20 C is composed of 62.7% )S- and 37.3% a-lactose. The equilibrium constant, p/a., is 1.68 at 20°C. 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 )S-lactose is 51.1, 17.5 and 3.4% complete at 25, 15 and 0°C, respectively, in 1 h and is almost instantaneous at about 75°C. 

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