Microencapsulation properties of soy protein isolate and storage stability of the correspondingly spray-dried emulsions

The microencapsulating properties of soy protein isolate (SPI) by spray-drying, as affected by pressure level of homogenization, inlet air temperature of drying, core/wall ratio, as well as total solid content were evaluated. The test characteristics included retention efficiency (RE), redispersion behavior (droplet size distribution and mean size of reconstituted emulsions) of spray-dried powders, moisture content, dissolution behavior, and microstructure of particles. The influence of storage at 75% relative humidity for 7 days on these characteristics was also investigated. The results indicated that the RE, redispersion and/or dissolution behaviors, as well as storage stability of spray-dried emulsions were affected by various test parameters, but to a various extent. Among all test parameters, the core/wall ratio was the most pronounced one affecting the properties of the powders, regardless of after storage or not. In general, the RE of the dry powders was higher at increased pressure level, decreased core/wall material, as well as enhanced total solid contents; at a constant total solid content, the redispersion behavior of these powders was closely associated with their RE. At the core/wall ratios of 1:1 or higher, the storage resulted in remarkable decreases in RE of the powders, and impaired redispersion behaviors, while the powder at 1:2 core/wall ratio exhibited an excellent storage stability. Scanning electron microscopy observations confirmed that the differences in RE or storage stability at various core/wall ratios were related to the differences in their particle microstructure. These results would be of great help to understand the microencapsulation properties of SPI, thus providing some valuable information for the development of microencapsulated products using soy proteins as the wall materials.