Kinetic Reactions of Alpha and Beta Lactose. I. Mutarotation

Kinetic studies were made of mutarotation of alpha- and beta-lactose by a polarimetric method. Rate constants were determined in the temperature range of 0.5 to 55C. A complete statistical analysis of the data was made with a computer technique, and interpretation was based on a statistical test of the significance. The specific optical rotation of an equilibrium solution was dependent upon concentration and temperature. Concentration significantly affected the equilibrium rotation, causing a decrease of 0.01688 degree with each 1 g/100ml increase in concentration. The following expression was found to hold at equilibrium: \[ α ∞ \] D = 55.23 − 0.01688 c − 0.07283 \( t − 25 \) where c is gram anhydrous lactose/100ml solution, and t is degrees centigrade. It was shown that the mutarotation of lactose is a first-order reaction: The velocity constants calculated from the experimental data did not vary significantly from the postulation of the first-order rate law. Further evidence supporting this conclusion is that the velocity constant is independent of reaction time and the concentration of the reactant. The same studies where undertaken in a salt solution simulating natural whey in salt composition. The salt solution catalyzes the reaction about twofold, but does not alter the mechanism.