Sonocrystallisation of lactose in concentrated whey

Abstract

Whey concentrated to 32% lactose was sonicated at 30°C in a non-contact approach at flow rates of up to 12L/min. Applied energy density varied from 3 to 16J/mL at a frequency of 20kHz. Sonication of whey initiated the rapid formation of a large number of lactose crystals in response to acoustic cavitation which increased the rate of crystallisation. The rate of sonocrystallisation was greater than stirring for approximately 180min but slowed down between 120 and 180min as the metastable limit was reached. A second treatment with ultrasound at 120min delivering an applied energy density of 4J/mL stimulated further nuclei formation and the rate of crystallisation was maintained for >300min. Yield on the other hand was limited by the solubility of lactose and could not be improved. The crystal size distribution was narrower than that with stirring and the overall crystal size was smaller.

Keywords: Concentrated whey; Lactose; Sonocrystallisation; Ultrasound.