Kinetics of lactose crystallization and crystal size as monitored by refractometry and laser light scattering: effect of proteins

Abstract

Lactose crystallization is a key step in the manufacture of whey powders. Both the crys- tal size and mass of crystals produced affect the subsequent step of spray drying and whey powder quality. Consequently, it is essential to control crystallization kinetics, crystal quality and how these properties are affected by whey components. For this purpose, two suitable and simple methods were developed. Refractometry was used to follow the kinetics of lactose crystallization in super- saturated solution of lactose. The extent of crystallization and the overall crystallization rate con- stant were then deduced. Laser light scattering was used to follow the crystal growth in the solid phase by measuring crystal size over time. The two methods were used to determine the impact of whey proteins on lactose crystallization from supersaturated solution. Our first results showed that the presence of whey proteins (5g·100 g-1 water) did not significantly modify the overall crystalli- zation rate constant but had a large lowering effect on the final size of crystals during the non-seeded crystallization process (~30 µm against ~105 µm in the absence of protein). lactose crystallization / whey proteins / refractometry / laser light scattering