Octanoate: An assay for oxidative deterioration in oils and fats

Abstract

AbstractThe assay of octanoate, a predicted residue remaining bound to glycerol after the thermal decomposition of oxidised oils and fats, has been used to follow the autoxidation of sunflower and linseed oil triglycerides. Alkali catalysed transmethylation gave methyl octanoate which was determined by gas chromatography using methyl nonanoate as added internal standard. The autoxidation of the oils was also followed by peroxide value. For both oils linear relationships were found between the peroxide value and the amount of octanoate produced after thermal decomposition of the oil samples under vacuum. Thus the assay of octanoate is a useful measure of oxidative deterioration under conditions where the first formed peroxides have been destroyed, (e.g. the refining and deodorisation of oxidised crude oils or the deterioration of frying fats during use). Oils freshly extracted from seed had very low octanoate values. The assay is not applicable however to ‘laurate’ oils or to butterfat which have high levels of endogenous octanoate.