Oxidative stability index of vegetable oils in binary mixtures with meadowfoam oil
1999
Isbell, T.A. | Abbott, T.P. | Carlson, K.D.
The oxidative stability indices (OSI) of several vegetable oils were determined at 110°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 oleic 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 meadowfoam oil could not be attributed to its tocopherol content since refining did 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 of vegetable oils were also examined for enhanced oxidative stability. Small amounts of crude meadowfoam oil gave enhanced oxidative stability in mixtures with jojoba, triolein and castor oils. Triolein/'crude meadowfoam oil mixtures showed the most dramatic improvements in OSI time with a 5% (w/w) addition of crude meadowfoam causing a 21-fold increase in the OSI time. Meadowfoam 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 stability with respect to olefin position showed that the Δ5 double bond was the most stable by more than an order of magnitude. The oxidative stability of meadowfoam FAMEs at 90°C gave an OSI time of 4.9 h which was the same as methyl erucate and methyl petroselenate, but less than methyl oleate 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.
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