Accumulation of polycyclic aromatic hydrocarbons (PAHs) in rice subjected to drying with different fuels plus temperature, industrial processes and cooking

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic compounds produced naturally in the environment or during pyrolysis of organic fuels for thermal applications. The effect of four heating sources (wood, rice husk, liquefied petroleum gas (LPG), and electric heating) on the PAHs content in rice grains during different treatments was evaluated. The treatment conditions included three drying temperatures (40, 60, and 80 °C), three different industrial processes (dehusking, polishing, and parboiling), and cooking. The drying air temperature had little influence on the PAHs content. Of the sixteen PAHs monitored, nine were detected in the different treatments. Highest total PAH concentration was found when drying with wood (131.6 μg kg−1), followed by rice husk (45.7 μg kg−1), LPG (15.9 μg kg−1), and electric heating (7.7 μg kg−1). Parboiling increased the PAHs content, mainly the phenanthrene content, with an increase of 120.6% (wood), 236.4% (rice rusk), 663.3% (LGP), and 471.4% (electric heating) when compared with brown rice. On the other hand, polishing reduced the PAHs content and upon subsequent cooking, no residual PAHs were detected. The solubility and adsorption capacity of the individual compounds affected directly the PAH contamination in parboiled rice.