Crystallization of ?-lactose is a key step in the processing of whey and permeates. Despite numerous experimental studies, the understanding of the product/process relationships during this unit operation is still poor. In this study, we implemented a kinetics model to study the effects of various mineral and organic compounds commonly found in acid or intermediate wheys and permeates, and which are the most difficult to process, on both the kinetics of lactose crystallization and the size of the resulting crystals. Isothermal batch crystallization of a supersaturated solution of lactose (70 g.100 g-1 water) was studied with and without adjunction of these compounds. Kinetics and crystal size distribution were monitored using refractometry and laser light scattering, respectively. The results were fitted using a model based on population balance and taking into account the particular features of ?-lactose. Various constants were extracted from this model, corresponding to nucleation, crystal growth and mutarotation steps: These constants were the classical nucleation constants, B0 and kn0 (with J (nucleation rate) = kn0 exp (-B0/ (ln S)2), and growth rate constants kg0 (growth rate constant) and g0 (G (growth rate) = kg0 ?Cg0) for the crystal growth. Computing the evolution of the ?-lactose/?-lactose ratio and B0 made it possible to determine the mutarotation kinetics and the interface tension between crystal and solution, respectively. Using Principal Component Analysis (PCA) and Hierarchical Ascendant Clustering (HAC) on the results, it was revealed that the effects of additives in solutions can be scattered in three different classes. The accelerating effect of lactates and citrates were then clearly displayed. The singular effect of whey proteins on lactose crystallization finds a possible explanation, as well as the fact that lactic acid does not behave like lactates. To conclude, the results of this study for the first time to fill the gap between theoretical generalized crystallization and applied lactose crystallization studies in a dairy context. The proposed methodology is thus a way to study lactose crystallization on an industrial scale, where it is most needed.
