Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2003
Publication Date: 10/20/2003
Citation: Knothe, G.H., Dunn, R.O. 2003. Influence of compound structure, concentration and presence of metals on oxidative stability of fatty compounds by the oil stability index method. Journal of the American Oil Chemists' Society. 80(10):1021-1026.
Interpretive Summary: It is well-known that vegetable oils can react with air to form undesirable products. Usually when referring to edible products, this phenomenon is referred to as rancidity. Similarly, industrial products, such as biodiesel or lubricants, derived from vegetable oils can react with air to form such undesirable products. These undesirable products have negative impact on performance and properties of the vegetable oil-derived industrial products. The degree to which vegetable oil-derived products form these undesirable products depends on the structure of the components of the vegetable oil, in other words, on the stability of the components towards oxygen in the air, as well as some other factors. This work investigates how an index (termed the oil stability index), developed for describing the stability of vegetable oils and their derivatives, depends on some features of their structure and other parameters such as metals present as extraneous materials and relative amounts of the components.
Technical Abstract: During storage and use, vegetable oil-derived industrial products such as biodiesel and lubricants can be subjected to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant issue facing these vegetable oil-derived products. Enhanced understanding of the influence of various components of vegetable oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of mono-alkyl esters of fatty acids by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for assessing the influence of compound structure and concentration. The results support the observation that small amounts of more highly unsaturated compounds have a disproportionately strong effect on oxidative stability. This observation also affects the use of the outdated parameter iodine value used in fatty acid chemistry. Free acids showed decreased OSI times in comparison to alkyl esters. The influence of three metals, copper, iron and nickel, was also investigated. They were shown to also reduce oxidative stability but their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest catalytic effect on oxidation as determined. OSI can therefore be an alternative to long-term storage tests for determining the influence of extraneous materials.