Some Physico-Chemical Properties of Lactose

Lactose contains a free aldehyde group, and therefore it is capable of existing in two different isomeric modifications. When either of these is dissolved in water, it is partially transformed into the other until an equilibrium is reached. The transformation is slow at low temperatures. This fact is of practical importance because the rate of mutarotation sets an upper limit to the rate of solution, or of crystallization of lactose. The fact that the two forms have quite different solubilities is responsible for the recent production of beta lactose on a commercial scale.