Oxidative stability index of vegetable oils in binary mixtures with meadowfoam oil

The oxidative stability indices (OSI) of several vegetable oils were determ ined at 110 degrees C. Meadowfoam oil, Limnanthes alba, was found to be the most stable oil with an OSI time of 67.3 h for refined oil and 246.9 h for crude oil. Other oils with good oxidative stabilities were refined high ol eic sunflower and crude jojoba oil (Simmondsia chinensis) with OSI times of 49.8 and 34.5 h respectively. The unusually high OSI time of crude meadowf oam oil could not be attributed to its tocopherol content since refining di d not significantly alter the tocopherol content, but significantly reduced the stability. A relationship of iodine value to antioxidant was developed for vegetable oils; however, this linear relationship did not account for the unusually high oxidative stability of meadowfoam oil. Binary mixtures o f vegetable oils were also examined for enhanced oxidative stability. Small amounts of crude meadowfoam oil gave enhanced oxidative stability in mixtu res with jojoba, triolein and castor oils. Triolein/crude meadowfoam oil mi xtures showed the most dramatic improvements in OSI time with a 5% (w/w) ad dition of crude meadowfoam causing a 21-fold increase in the OSI time. Mead owfoam mixtures with jojoba improved the OSI time of jojoba from 31.1 to 52 .7 h, when 10% crude meadowfoam oil was added. A study of oxidative stabili ty with respect to olefin position showed that the Delta 5 double bond was the most stable by more than an order of magnitude. The oxidative stability of meadowfoam FAMEs at 90 degrees C gave an OSI time of 4.9 h which was th e same as methyl erucate and methyl petroselenate, but less than methyl ole ate which had an OSI time of 14.8 h. However, when methyl 5-eicosenoate was isolated in high purity (monoene > 96%) and tested, it gave an OSI time of 69.4 h. (C) 1999 Elsevier Science B.V. All rights reserved.