Lactose: Crystallization

Abstract

Lactose crystallization is a key step in the manufacture of whey powders and derivates. Both crystal size and mass of the crystals produced affect the subsequent step of spray-drying and whey powder quality. Consequently, it is essential to control crystallization kinetics, crystal quality, and how these properties are affected by whey components. At an industrial scale, high lactose supersaturations prevail during the crystallization step so that nucleation, crystal growth, and mutarotation occur simultaneously. A kinetic model combining the first-order differential equations representing the three consecutive steps of lactose crystallization, namely, mutarotation, nucleation, and crystal growth, has been developed. Kinetic expressions of each of these steps have been combined into one single model that successfully predicts the different stages of lactose crystallization kinetics and the impacts of process parameters (total solids, seeding, temperature). Following an introduction to spray-drying of whey, this article on lactose crystallization covers different areas: principles and kinetics of lactose crystallization; description of the different steps; and effects of the factors related to the operating conditions on the quality of lactose crystallization and the quality of the whey and derivate powders produced.