Application of the accelerated test Rancimat to evaluate oxidative stability of dried microencapsulated oils

Abstract

The objective of this work was to apply the oxidative test Rancimat to dried microencapsulated oils (DMO), with special emphasis on assessing the efficacy of natural antioxidants. DMO were prepared by freeze-drying emulsions containing sodium caseinate, lactose and fish or sunflower oils, with and without added the antioxidant mixture ALT (ascorbic acid, lecithin and tocopherol). Under the Rancimat working conditions selected for testing DMO (5 g sample, 100oC and 20 L air/h), excellent repeatability was obtained. The antioxidant effect of ALT was much higher in bulk fish oil than in its counterpart DMO, either in Rancimat or at 30oC in the dark. Further experiments using Rancimat showed that the moderate increase in stability of DMO added ALT was only attributable to tocopherol while the synergistic actions of lecithin and ascorbic acid were not observed, their action probably depending on their location and orientation in these complex lipid systems. This test enabled to compare monophasic (bulk oils and DMO-extracted oils) and heterophasic lipidic systems (DMO and DMO devoid of the accessible, free oil fraction), thus offering a rapid means to examine the influence of oil distribution and partitioning of antioxidants on oxidative stability.