Temperature Dependence of 4-Hydroxy-2-Trans-Nonenal (HNE), a Toxic Aldehyde, in Coconut, Palm, Safflower and Grape Seed Oils

Abstract

The temperature dependence of the formation of 4-hydroxy-2-trans-nonenal (HNE), the most toxic aldehyde among the four α, β-unsaturated-4- hydroxyaldehydes, was investigated in commercial coconut, palm, safflower and grape seed oils. These oils were heat treated at different temperatures (165, 185 and 218°C) for different length of heating time, such as 0, 1, 3 and 5 hours. The detection and identification of HNE was by using high-performance liquid chromatography (HPLC) of HNE-DNPH and measured by 378 nm UV absorption. The four commercial vegetable oils for this study were selected based on their different degrees of unsaturation according to their fatty acid distributions. Experiments such as peroxide value, fatty acid distribution, and trolox equivalent antioxidant capacity (TEAC) assay were performed in the unheated commercial oils to obtain general information on their properties. The thiobarbituric acid (TBARS) assay, measuring secondary oxidation products such as aldehydes, and related carbonyl compounds of oils was conducted at 165, 185 and 218°C heating temperature for 0-6 hours. The oils were heated at 165, 185 and 218°C for 1, 3, and 5 hours to measure the formation of the HNE as 2,4-dinitrophenylhydrazone derivatives using high-performance liquid chromatography (HPLC). It was found that HNE formation was dependent on the heating temperature, the heating time and the level of linoleic acid concentration in four oils. HNE concentration was found higher heating at 185°C compared to heating at 165°C. At 218°C heating, some decomposition of HNE happened in most of the oils. The highest HNE formation was found in grape seed oil, followed by safflower oil, palm oil and coconut oil.