Oxidation of free and encapsulated oil fractions in dried microencapsulated fish oils

Abstract

The objective of this work was to evaluate oxidation of dried microencapsulated fish oils (DMFO) during storage at ambient temperature, and to examine the influence of oils distribution (free vs. encapsulated oil) in these complex lipidic systems. DMFO were prepared by freeze-drying emulsions containing sodium caseinate, lactose and fish oil, with and without adding the antioxidant mixture ALT (ascorbic acid, lecithin and tocopherol). Samples were stored at 25 or 30°C either in the dark or light with limited, accesible air or under vacuum. The progress of oxidation was followed through quantitation of triglyceride polymers, and oxidation levels of free and encapsulated oil fractions were differentiated. Results showed that oxidation was very rapid both in free and encapsulated oil fractions in all DMFOs exposed to light. In the dark, oxidation was triggered first in the free oil fraction of samples not protected with ALT but, in contrast, samples with ALT showed significantly higher oxidation levels in encapsulated than in free oil fractions, regardless of the limited or free availability of air. These results indicated that addition of the antioxidant system ALT was more effective in the free oil fraction, thus reflecting the great influence of partitioning and/or orientation of antioxidants on their efficacy in complex lipid systems.