Cooling crystallization of lactose in the presence of whey protein and lactic acid impurities

Abstract Whey protein and lactic acid are two main impurities affecting the crystallization recovery of lactose from acid whey solutions. This study systematically examined the individual and combined effect of whey protein and lactic acid on the purity of the recovered lactose. From batch cooling stirred tank crystallization experiments, whey protein affected the purity by co-precipitation from the denaturation of protein. In contrast, lactic acid affected the purity by incorporation into the lactose crystal structure. This was primarily due to the similarity in the molecular structure between lactic acid and lactose. The presence of both impurities led to an undesired synergistic effect, which led to a significant increase in the impurity level. The low acidity and enhanced aggregation of protein were the main cause of this undesired synergistic effect. This study highlights the importance of the effective separation of whey protein in acidic whey solutions prior to the recovery of lactose by crystallization.