Transformation of polycyclic aromatic hydrocarbons during frying stinky tofu

Reductions in polycyclic aromatic hydrocarbon (PAH) concentrations have been observed during frying. However, transformation mechanisms of PAHs remain unclear. We hypothesize that PAHs may be oxidized into oxygenated polycyclic aromatic hydrocarbons (OPAHs) and other derivatives during frying. First, the levels of 24 PAHs and 12 OPAHs during frying stinky tofu were evaluated. Among the OPAHs, 9,10-anthraquinone exhibited the greatest increase in frying oil, with an increase rate of 55 %. The transformation of anthracene into 9,10-anthraquinone was further confirmed through stable isotope tracing. Targeted and untargeted mass spectrometry analyses suggested that anthrone, heavy PAHs, and alkyl derivatives were also produced from anthracene. Theoretical calculations revealed that radical addition was kinetically and energetically more favourable than hydrogen abstraction in the initial reaction of anthracene. This study systematically elucidates, for the first time, the transformation mechanisms of anthracene in frying oil, paving the way for reducing health risks associated with PAHs.