Abstract: The effects of different drying processes on the structural and physicochemical properties of fish oil microcapsules were analyzed. The microcapsules were prepared by preparing a nanoemulsion an ultrasonic technique using deep-sea fish oil, susceptible to oxidation, heat-sensitive and photosensitive, as the core material and soy protein isolate (SPI) and phosphatidylcholine as the wall material, and drying it using spray drying, vacuum freeze drying or microwave drying. The results showed that spray dried microcapsules were spherical particles with a compact structure, no oil droplet aggregation, small particle size, good solubility and high stability against oxidation and heat, as well as good entrapment efficiency (95.54%). Both vacuum freeze-dried and microwave dried microcapsules were irregular in shape with a porous surface, having high surface oil contents and entrapment efficiencies of 86.70% and 74.28%, respectively, and exhibiting a certain degree of oil droplet aggregation, larger particle size and poor solubility. The release rates of free fatty acids from the microcapsules prepared by spray drying, vacuum freeze-drying and microwave drying were 20.03%, 25.98% and 75.91% in simulated gastric juice, and 78.73%, 71.78% and 22.91% in simulated intestinal juice, respectively. The in vitro digestion experiments showed that release rate of free fatty acids from spray dried microcapsules was relatively low in simulated gastric juice, but higher in simulated intestinal juice. Therefore, the performance of spray dried microcapsules is better than that of microcapsules prepared by the other two drying processes. This study provides a theoretical basis for developing an evaluation system for the application of various drying processes in the preparation of microcapsule products.

Key words: fish oil, microcapsule, drying process, structure, product properties, physicochemical properties