The effect of chitosan on the crystallization behavior of lactose has been studied during the spray drying of lactose/chitosan solutions. Solutions with different ratios of lactose and chitosan have been spray dried at an inlet temperature of 160 degrees C using a laboratory-scale spray dryer. Water-induced crystallization, X-ray diffraction analysis and differential scanning calorimetry have been used to study the crystallinity of the spray-dried lactose/chitosan powders. Results show that, despite the ability of chitosan to retain moisture for a longer time during spray drying, the spray-dried powders were in the amorphous form. Moisture-induced crystallization and differential scanning calorimetry results suggest that the presence of chitosan delays lactose crystallization. This finding may be due to the high glass-transition temperature of chitosan, despite its ability to hydrogen bond with water, which was suggested previously by other researchers to be a reason for crystallizing lactose during spray drying in the presence of polyethylene glycol. (C) 2011 Elsevier Ltd. All rights reserved.