Kinetic Reactions of Alpha and Beta Lactose. I. Mutarotation

Abstract

Kinetic studies were made of mutarotation of a- and b-lactose by a polarimetric method. Rate constants were determined in the temperature range of 0.5-55 C. The specific optical rotation of an equilibrium solution depended on concentration and temperature. Concentration significantly affected the equilibrium rotation, causing a decrease of 0.01688 degree with each 1 g/100 ml increase in concentration. The following expression applied at equilibrium: [a[degree][degree]]D = 55.23 - 0.01688 c - 0.07283 (t - 25) where c is gram anhydrous lactose /100 ml solution, and t is degrees centigrade. The mutarotation of lactose is a first-order reaction: The velocity constants did not vary significantly from the postulation of the first-order rate law. The velocity constant is independent of reaction time and the concentration of the reactant. A salt solution simulating natural whey in salt composition catalyzes the reaction about 2-fold but does not alter the mechanism.