Impact of refining on the levels of 4-hydroxy-trans-alkenals, parent and oxygenated polycyclic aromatic hydrocarbons in soybean and rapeseed oils

•4-HAEs, PAHs and oxy-PAHs were monitored during oil refining.•PAHs, PAH4 and PAH8 decreased to legal levels after refining.•Bleaching contributed most to total reductions of 4-HNE, PAH4, PAH8 and oxy-PAHs.•Neutralization contributed most to the removal and the reduction rate of PAHs.•These results will help the quality control of PAHs, oxy-PAHs and HAEs in oils.

4-Hydroxy-2-trans-hexenal (4-HHE), 4-hydroxy-2-trans-nonenal (4-HNE), polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (oxy-PAHs) are harmful compounds that commonly occur in edible oils. In this study, we assessed the levels of these compounds in soybean and rapeseed oils during refining. The concentrations of 4-HHE, 4-HNE, 16 PAHs and five oxy-PAHs in soybean oil decreased from 16.27, 644.19, 48.72 and 20.04 μg/kg to 5.65, 260.01, 19.71 and 2.04 μg/kg, respectively, after refining. In rapeseed oil they decreased from 21.46, 246.44, 38.02 and 6.56 μg/kg to 0.00, 37.35, 17.25 and 2.04 μg/kg, respectively. Furthermore, the compounds were sequentially reduced throughout the refining process. The most significant reduction in PAHs was attributed to neutralization (up to 54.79% of the total reduction), while the most significant reduction in oxy-PAHs was attributed to bleaching (up to 84.83% of the total reduction), which also notably reduced 4-HHE and 4-HNE in the soybean oil refining. These results may be helpful for quality and process control with regards to minimizing the levels of harmful compounds in edible oils.