Influence of relative humidity on oxidation of the free and encapsulated oil fractions in freeze-dried microencapsulated oils

The objective of this work was to evaluate the effect of relative humidity (RH) on oxidation of the free and encapsulated oil fractions of dried microencapsulated oils (DMOs) during long-term storage at 30 °C. Sunflower and fish oils with different tocopherol content were encapsulated in a milk-based encapsulation matrix. The total non-volatile oxidation products and tocopherol were quantitated. Results showed that 0% and 32% RH were, respectively, the most unfavourable and favourable conditions against lipid oxidation. The 32% RH atmosphere exerted a great protective effect on the free oil as compared to 0% RH, while no or a negligible effect was found in the encapsulated oil. Except for the samples most susceptible to oxidation, the free oil remarkably oxidized more slowly than the encapsulated oil regardless of RH. Therefore, there were factors other than moisture that determined the oxidation rate in the free and encapsulated fractions of the DMOs.