Effects of Temperature and Heating Time on the Formation of Four Toxic α,β-Unsaturated-4-Hydroxyaldehydes in Vegetable Oils

The formation of four α,β-unsaturated hydroxyaldehydes, 4-hydroxy-2-trans-hexenal (HHE), 4-hydroxy-2-trans-octenal (HOE), 4-hydroxy-2-trans-nonenal (HNE), and 4-hydroxy-2-trans-decenal (HDE), was detected in commercial corn, soybean, peanut, and canola oils heated for 1, 3, and 5 hours at 145, 165, and 185 °C. These four toxic aldehydes were investigated using high-performance liquid chromatography (HPLC). These oils were selected based upon different degrees of unsaturations, especially their linoleic and linolenic acid concentrations. To select the appropriate conditions of temperatures and heating times, preliminary experiments were conducted using the thiobarbituric acid assay, which detects the formation of secondary-oxidation products such as aldehydes and related carbonyl compounds. After various heat treatments, the formation of HHE, HOE, HNE, and HDE was detected as 2,4-dinitrophenyl hydrazine derivatives using HPLC. In general, HHE, HOE, HNE, and HDE formation increased in all four oils with higher temperatures, longer heating times, and higher concentrations of linoleic and linolenic acids in the oils. The formation of HNE in the oils was mostly much higher than the other three 4-hydroxyaldehyde isomers under the same conditions.