Oxidation rate of the non-encapsulated- and encapsulated oil and their contribution to the overall oxidation of microencapsulated fish oil particles.

Microencapsulation of fish oil by spray drying is an established method to protect polyunsaturated fatty acids against oxidation by separating the environmental O2 from encapsulated lipids. Some oil droplets are not fully embedded within the matrix and are exposed to the environmental O2. The aim of the study is to determine the oxidation rate of the non-encapsulated- and encapsulated oil as well as the contribution of each lipid fraction to the overall oxidation of the encapsulates. The amount of non-encapsulated oil was varied by changing the preparation of the O/W emulsions (18% fish oil; 27% solids) regarding protein to oil ratio (0.02-0.22 (w/w)) and applied homogenization pressure (0.5/0.1-25/5 MPa). Emulsions were spray dried using a pilot plant drier with a maximal water evaporation rate of 30 kg h-1 operated at an inlet and outlet temperature of 160 °C and 85 °C, respectively. The obtained particles were analyzed in terms of water content, aw, particle size, non-encapsulated oil concentration and encapsulation efficiency. The amount of hydroperoxides in the total-, encapsulated- and non-encapsulated oil was determined over a storage period of 6 weeks. The non-encapsulated oil concentration was in the range of 2.20 and 18.45% which corresponds to an encapsulation efficiency between 53.82 and 93.56%. The sum of hydroperoxides in the non-encapsulated- and encapsulated oil equaled the amount detected in the total oil. The non-encapsulated oil oxidized on average 7.4 ± 2.0 times faster than the encapsulated lipids, whereas its contribution to the overall oxidation was minor, due to its low amount. The encapsulated oil was the main contributor to the overall oxidation and oxidized, even though it was fully embedded within the matrix.