Lactose crystallization as affected by presence of lactic acid and calcium in model lactose systems

• Acid whey is a hard to process stream due to failure of lactose to crystallize.
• The presence of lactic acid (LA) restricts lactose to crystallize.
• Presence of moderate levels of Ca improves lactose crystallisation.
• Behaviour of water molecules around lactose governs the overall crystallisation.
• Removal of some Ca from acid whey may improve the lactose crystallisation.

Acid whey is considered a hard to process stream mainly due to failure of lactose to crystallize, apparently attributed to the presence of lactic acid (LA) and calcium (Ca). Understanding the physical state and the thermal behaviour of lactose during crystallization in the presence of LA and Ca is important in order to develop adequate strategies to improve processability of acid whey and thus was the objective of this study. Presence of high concentration of LA (1% w/w) resulted in a decline in lactose crystal yields (∼59%). This was alleviated by lowering the LA content (0.2% w/w) which improved the yield (∼77%). At high LA content, small amounts of Ca (0.072% w/w) appeared to diminish the negative impact of LA presence by increasing the yield. Pure L solution yielded lactose particles of ∼84 μm. Crystal size slightly increased to ∼91 μm in the system containing high concentrations of LA along with low Ca concentration and although the presence of low concentrations of both LA (0.2% w/w) and Ca (0.072% w/w) resulted ∼ 163 μm sized crystals. Water molecules in the hydration layer around lactose molecules appeared to play a significant role governing the crystallisation behaviour and characteristics of lactose crystals in the presence of LA and Ca and/or in combination. Hence, the removal of some Ca to concentrations ≤0.072% w/w from acid whey may improve the crystallisation of lactose and thereby improve the processability of acid whey.