|Abbott Dr, Thomas|
Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/1998
Publication Date: N/A
Citation: N/A Interpretive Summary: Vegetable oil-based lubricants, foods, and cooking oils suffer from poor oxidative stability. Consequently, methods to improve the oxidative stability of vegetable oils continues with efforts to find new stable oils or novel antioxidants that will stabilize the oil. Crude meadowfoam oil is a very stable oil that might meet some of the desired oxidative stability requirements. Crude meadowfoam oil was found to resist oxidative destruction nearly 18 times longer than the most common vegetable oil, soybean. Because of its good stability crude meadowfoam oil was added in small amounts to other oils in an effort to improve the oxidative stability of other oils. Crude meadowfoam oil improved the stability of other oils such as triolein, jojoba and castor even when only 5% to 10% of crude meadowfoam oil was added. Crude meadowfoam oil stability could not be attributed to common antioxidants. One possible explanation for its stability may be the unusual fatty acid composition that makes up the structure of the oil. The main fatty acid from meadowfoam oil, 5-eicosenoic acid was found to be nearly 5 times more stable than the most common fatty acid, oleic and 16 times more stable than other monounsaturated fatty acids. However, when meadowfoam fatty acids as a whole mixture were tested they gave the same stability as other fatty acids. Because of the poor oxidative performance of the meadowfoam fatty acid mixture, the fatty acid structure must not be the key reason for the unusually high oxidative stability of the crude oil.
Technical Abstract: The oxidative stability index (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 with OSI times of 49.8 h 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. 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 h to 52.7 h when 10% crude meadowfoam oil was added. A study of oxidative stability with respect to olefin position found 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 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 9.9 h. However, when methyl 5-eicosenoate was isolated in high purity(monoene >96%) and tested it gave an OSI time of 69.4 h.