Recovery of lactose from simulated delactosed whey permeate by a low-temperature crystallization process

Abstract

Delactosed whey permeate is the mother liquor/by-product of lactose manufacture, but it still contains around 20 wt% lactose. The high mineral content, stickiness, and hygroscopic behavior prevent further recovery of lactose in the manufacturing process. Therefore, its use is currently limited to low-value applications such as cattle feed, and more often it is seen as waste. This study investigates a new separation technique operating at sub-zero conditions. At low temperature, precipitation of calcium phosphate is expected to be reduced and the lower solubility at sub-zero temperature makes it possible to recover a large portion of the lactose. We found that lactose could be crystallized at sub-zero conditions. The crystals had a tomahawk morphology and an average size of 23 and 31 µm. In the first 24 h, the amount of calcium phosphate precipitated was limited, whereas the lactose concentration was already close to saturation. The overall rate of crystallization was increased compared with the crystals recovered from a pure lactose solution. Mutarotation was rate limiting in the pure system but it did not limit the crystallization of lactose from delactosed whey permeate. This resulted in faster crystallization; after 24 h the yield was 85%.