Role of Phenylalanine in the Formation of Parent and Oxygenated Polycyclic Aromatic Hydrocarbons in Baking Systems

Parent and oxygenated polycyclic aromatic hydrocarbons (PAHs and OPAHs) have gained increasing attention due to their toxicity. However, their formation mechanisms during baking remain unclear. This study aimed to elucidate their formation pathways from amino acids in baking systems. The effects of five amino acids on PAH24 and OPAH12 levels in bread were investigated. Phenylalanine addition (2%) caused the most significant 15-fold increase in the toxic equivalent quotient of PAH36. Stable isotope tracing technology revealed that both the phenyl ring and C3 atom of phenylalanine were incorporated into benzo[a]anthracene and 9-fluorenone, proving the transformation of phenylalanine into PAHs and OPAHs. By nontarget analysis and chemical reactivity analysis, styrene, (E)-stilbene, and benzophenone were identified as key intermediates in the formation of naphthalene, benzo[a]anthracene, and 9-fluorenone, respectively. Overall, this study first proposed the formation pathways of PAHs and OPAHs from phenylalanine, offering guidance for reducing their health risks during baking.