Extent of deterioration and formation of toxic substances in cooking oil (Coconut oil) when heated repeatedly above smoke point

Abstract

Commercial cooking oil sample (Refined, Bleached and Deodorized-Coconut Oil or RBD-CNO) was subjected to heat treatments. Twelve samples of four treatments and three replicates for each treatment: namely, the untreated (UN), heated once (T1), heated twice (T2) with intermittent cooling and, heated thrice (T3) with intermittent cooling were analyzed for fatty acid profile, free fatty acid value, peroxide value and the presence of PAH. Data were statistically analyzed using one way analysis of variance (ANOVA). Significant treatment mean differences were established using DMRT. The fatty acid profile showed that only linoleic acid decreased in quantity constantly up to the third heating. Free fatty acid and peroxide values showed an increasing trend. All of the 22 PAH included in the analysis were present in all treatments in small quantities. The only PAH which showed an increasing trend in the 4 treatments was 1, 6, 7-trimethylnaphthalene, the quantities of the rest remained the same. The decrease in the amount of linoleic acid in the free fatty acid profile indicated that unsaturated fatty acids decompose on heating and this could be the source of peroxides, but saturated fatty acid components were stable at high temperature.