Drying behavior and locking point of single droplets containing functional oil

Inception of the second drying stage called locking point plays a crucial role in the microencapsulation process of functional oils by spray drying. The transition between the first and the second drying periods can directly affect encapsulation efficiency and lipid oxidation by modifying the mechanism of globules migration to the surface of droplet/particles. In this study, the locking point of a single emulsion droplet prepared by incorporating walnut oil into skim milk powder solution was determined using a droplet suspension device. The effects of drying air temperature (80-140 degrees C), total solid content (12-33% w/w), and oil/wall material mass fraction (0.25-1.00 w/w) were assessed on the droplet/particle drying behavior, shrinkage, and locking point. The latter was achieved by plotting the variation of drying rate against moisture content of the droplet/particle. Moreover, confocal laser scanning microscopy (CLSM) was applied in order to investigate the morphology of the produced particles. Finally, a regression function for estimating the locking point from experimental variables was developed. Overall, such research can pave the way towards increasing the encapsulation efficiency and mitigating the lipid oxidation in industrial-scale spray dryers applied for microencapsulation of functional oils. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.