Study On Chemical Conversion And Physical Migration Mechanisms Of Four Polycyclic Aromatic Hydrocarbons In Soybean Oil During Frying French Fries

Polycyclic aromatic hydrocarbons（PAHs）were hydrophobic carcinogens widely presented in the environment and foods.Edible oils and fried foods had higher levels of exogenous polluted and endogenous generated PAHs than other foods due to their higher fat content.The dynamic generation,generating mechanism,and inhibition method development of PAHs in foods during frying had always been a hotspot.However,more than 20 years of exploration had not clarified the generating mechanism of PAHs.The difficulty was that the matrix of foods was extremely complex,and the reaction pathway was not easy to clarify.In this work,it was found that the content of PAHs in frying oil and fried food mostly showed a fluctuating upward trend,and its irregularity was another important reason for the inaccurate calculation of kinetic parameters and the unclear formation mechanism.It was speculated that the reason for the fluctuation may be that PAHs were both generated and lost during the long-term frying.If the fate of the lost PAHs were ignored,the exposure of PAHs would be underestimated.Based on the above problems,this work took the European Unionlimited high toxic Benzoanthracene（BaA）,Chrysene（Chr）,Benzofluoranthene（BbF）,and Benzopyrene（BaP）as the research objects（PAH4）.To make up for the shortcomings of previous research,the loss and fate of PAH4 were characterized by a stable isotope method in soybean oil during frying French fries.The main research contents and results are as follows:（1）Stable isotope-labeled PAH4-d12 showed a similar loss in oil during frying,the higher the ftying temperature and the longer the frying time,the greater the loss rate of PAH4-d12.There were three-loss ways for PAH4-d12:（Ⅰ）PAH4-d12 chemically converted to PAH4-d12 derivatives in oil during frying,（Ⅱ）PAH4-d12 in frying oil migrated to the fried food phase（french fries）,（Ⅲ）PAH4-d12 migrated to the fume phase.（2）Five PAH-d12 derivatives in frying oil were identified by Gas chromatography-Mass spectrometry（GC-MS）.The related results directly proved that the lost BaA-d 12,Chr-d 12,and BaP-d 12 in frying oil would be converted,and the hypothesis proposed in the previous study was verified.There were differences in the degree of chemical conversion of PAH4-d12,among which BaP-d1 2 had the strongest reactivity,followed by BaA-d 12 and Chr-d 12,and BbF-d 12 did not undergo conversion.Based on the identification of structures by GC-MS,the quantum chemical properties of PAHs,and the oxidation mechanism of frying oil,the reaction pathway for the conversion of BaA to Benzanthracene-7,12-one（BaAQ）mediated by free radicals during frying was deduced.（3）PAH4-d12 in oil could migrate to French fries carried by oil during frying.The fluidity of oil rose within 0-6 h,resulting in the slowing down of PAH4-d12 migration,and the total polar compound content exceeding the limit（15%-20%）within 6-10 h resulted in the accelerating of PAH4-d12 migration.Due to the uneven distribution of oil-water in the French fries and the porous structure of the French fries crust,the PAH4-d12 migrated with the oil was mainly distributed in the crust.（4）PAH4-d12 in oil could migrate to the aerosol carried by the heterogeneous fume particles during frying.The particles with a size of<2.5 μm played a major role in carrying and were more stable and less prone to sedimentation in the aerosol.Heterogeneous fume particles were composed of 95.24%-99.77%organic compounds.A total of 27 organic compounds were identified by GC-MS,all of which were products of oil hydrolysis and oxidation.From the perspective of molecular interaction,the main components of fume particles and PAH4 were docked,and it was found that unsaturated fatty acids and conjugated heterocyclic compounds could form electrostatic force andπ-π conjugated force with PAH4,respectively,which were the key to binding PAH4.In this paper,the stable isotope method was used to systematically track the dynamic changes and distribution of PAH4 in the frying oil,food,and fume phase during frying,which made up for the lack of a single research system in the existing literature in breadth.The related mechanisms and the intrinsic effect of thermal oxidation of frying oil on the chemical conversion and physical migration were analyzed in depth.It could lay a theoretical foundation for controlling the generation of highly toxic PAHs derivatives and the exposure to humans through food intake and oil fumes inhalation.