INFLUENCE OF TEMPERATURE ON CRYSTALLIZATION OF LACTOSE IN ICE-CREAM

Sandiness in ice-cream due to lactose crystallization can still be a p roblem in many circumstances. Lactose crystallization occurs in ice-cr eam as the unfrozen phase becomes supersaturated. However, the effects of storage temperature and temperature fluctuations on lactose crysta llization have not been very well quantified. In this work, an acceler ated storage apparatus was used to determine the effects of thermal fl uctuations (from +/- 0.01 degrees C to +/- 2.0 degrees C), at several mean storage temperatures (from -5.0 to -20.0 degrees C), on the onset of lactose nucleation and subsequent crystal growth in a standard van illa ice-cream. The induction time for nucleation initially decreased as temperature was lowered (for temperature oscillations of +/- 1.0 de grees C), until a minimum induction time of 3 h was found between -10. 0 and -12.0 degrees C. Further decreases in storage temperature caused the induction time to increase. The induction time for nucleation inc reased as the extent of temperature fluctuations increased, from 0.01 to 2.0 degrees C, while initial lactose crystal growth rate showed the opposite trend. The initial growth rate increased as temperature decr eased between -5.0 and -10.0 degrees C, but then decreased for tempera tures below -10.0 degrees C. At -20.0 degrees C lactose crystals grew very slowly. At -10.0 degrees C the rate of growth decreased with incr easing amplitude of temperature oscillations.