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

The objective of this work was to apply the oxidative test Rancimat to drie d microencapsulated oils (DMO), with special emphasis on assessing the effi cacy of natural antioxidants. DMO were prepared by freeze-drying emulsions containing sodium caseinate, lactose and fish or sunflower oils, with and w ithout added the antioxidant mixture ALT (ascorbic acid, lecithin and tocop herol). Under the Rancimat working conditions selected for testing DMO (5 g sample, 100 degreesC and 20 L air/h), excellent repeatability was obtained . The antioxidant effect of ALT was much higher in bulk fish oil than in it s counterpart DMO, either in Rancimat or at 30 degreesC in the dark. Furthe r 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 prob ably depending on their location and orientation in these complex lipid sys tems. This test enabled to compare monophasic (bulk oils and DMO-extracted oils) and heterophasic lipidic systems (DMO and DMO devoid of the accessibl e, free oil fraction), thus offering a rapid means to examine the influence of oil distribution and partitioning of antioxidants on oxidative stabilit y.