Surface Oil Measurement for Spray-dried Fish Oil Microcapsules Using Nile Red and Confocal Laser Scanning Microscopy

The objective of this study was to analyze the surface oil ratio and distribution measurement of spray-dried powders during hexane washing, in order to evaluate the properties of fish oil-encapsulated powders. Two types of spray-dried powders were prepared from two differently sized emulsions, namely: (i) nano and (ii) microsized oil droplets. A matrix composed of maltodextrin and sodium caseinate was used as the wall material to encapsulate the fish oil, and Nile red was used to stain the oil. The extraction of the surface oil releases a threshold amount of oil on the surface of the particle. The study of the fluorescence intensity using confocal laser scanning microscopy (CLSM) indicates good correlation between the oil content and fluorescence intensity. It was difficult to remove the surface oil of the nano-sized oil droplets in the spray-dried powders by hexane washing because the smaller oil droplets had higher stability in the spray-dried powders.