Effects of solvents on characteristics of crystalline lactose extracted in ternary and quaternary systems

In a technique referred to as lactose extractive crystallisation, a volatile solvent was added to a solution of lactose dissolved in water. As this second solvent was miscible in water, its presence in the saturated or supersaturated lactose solution would reduce the lactose solubility and hence lactose crystals were formed and grew in the ternary system lactose–ethanol–water. It was found that selecting ethanol as a second solvent could produce needle-shaped crystals having the lowest median size of 8 μm, and β-lactose content up to 60% at 60 °C. On the other hand, using two miscible solvents, one non-volatile and one volatile, such as by adding ethanol to the ternary system, lactose–water–glycerol, crystals having large needle-like or trapezoidal shape and β-lactose content up to 90% could be made at 70 °C. The triangle diagram comparing the solubility of lactose in the glycerol and ethanol aqueous solutions at equilibrium and at different temperatures is presented for the first time. Based on this diagram, it is suggested that the weight ratios of two solvents used and reaction temperatures could be manipulated to produce lactose crystals with different characteristic properties.