Sonocrystallisation of lactose in concentrated whey

• Concentrated whey was sonicated at 3–16 J/mL and 20 kHz frequency.
• Sonication initiated rapid lactose sonocrystallisation in concentrated whey.
• The rate of crystallisation slowed at approximately 180 min.
• Ultrasound did not increase the amount of lactose crystallised.
• Sonocrystallised lactose crystals were smaller and more uniform.

Whey concentrated to 32% lactose was sonicated at 30 °C in a non-contact approach at flow rates of up to 12 L/min. Applied energy density varied from 3 to 16 J/mL at a frequency of 20 kHz. 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 180 min but slowed down between 120 and 180 min as the metastable limit was reached. A second treatment with ultrasound at 120 min delivering an applied energy density of 4 J/mL stimulated further nuclei formation and the rate of crystallisation was maintained for >300 min. 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.