Study On The Change Of Quality And Polycyclic Aromatic Hydrocarbons Of Vegetable Oils During Frying And The Binding Mechanism Between Benzo Pyrene And DNA

Fried food is a popular consumer favorite food,widely exists in Chinese and western breakfast,dinner and snack food,however,during the frying process,oil is heated for long period of time and undergoes a series of chemical reactions resulting in the production of toxic or carcinogenic compounds,which have potential negative influences on human health.In this paper,five commonly used frying oils(palm oil,soybean oil,rapeseed oil,sunflower oil and rice bran oil)in our local market were selected to evaluate their frying performance under simulated frying protocol in fast food restaurants in China.The oxidation kinetics of unsaturated fatty acid during frying were explored,and the calibration models using near infrared spectroscopy(NIRS)combined with chemometrics method were also established for evaluating the quality of frying oils.Besides,the change of harmful polycyclic aromatic hydrocarbons(PAHs)during frying was analyzed,and the binding mechanism between calf thymus DNA(ctDNA)and benzo pyrene(BaP),a representative carcinogen of PAHs,was investigated via various spectroscopic methods and molecular docking.The main results were as follows:(1)During the frying process,the acid value(AV)and total polar component(TPC)of the five frying oils increased significantly with the increasing frying time,but far below the Chinese national standard,which was related to filtering and replenishing fresh oil every day.The color deepened gradually with frying time,but the peroxide value(PV)fluctuated.The carbonyl group value(CGV),anisidine value(p-AV)and total oxidation value(TOTOX)increased gradually and tended to be stable with the increasing frying time,and the levels in palm oil was significantly lower than the other frying oils.Iodine value(Ⅳ),oxidative stability index(OSI)and C18:2/C16:0 value decreases gradually with frying time,after frying for 7 days,the five frying oils showed an order of OSI of palm oil(21.07 h)>rice bran oil(9.08 h)>rapeseed oil(7.36 h)>soybean oil(5.10 h)>sunflower seed oil(3.38 h),as well as an order of decreased C18:2/C16:0 value of sunflower oil(60.23%)>rapeseed oil(56.14%)>rice bran oil(33.14%)>soybean oil(28.59%)>palm oil(5.10%).After 7 days of frying,the vitamin E loss rates of the five frying oils were 49.15%(palm oil),34.95%(sunflower oil),32.69%(soybean oil),32.38%(rapeseed oil)and 28.94%(rice bran oil),respectively.The oxidation rates as well as loss rates of vitamin E isomers were different.In a word,palm oil exhibited the best frying stability based on its significantly lower increases in p-AV,TOTOX,CGV and TPC,accompanied by a longer OSI,a lesser decrease in IV and the ratio of C18:2/C16:0 in frying oils tested,as confirmed by principal component analysis(PCA).This may be related to the fact that palm oil contains higher level of saturated fatty acid and lower level of unstable polyunsaturated fatty acid.In addition,77.74%of vitamin E in palm oil is tocotrienol with much stronger antioxidant capacity compared to tocopherol.(2)The correlations between unsaturated fatty acid(linolenic acid,linoleic acid and oleic acid)of five frying oils and frying time during frying were fitted using linear regression and curve prediction analysis.The results showed that linolenic acid levels in soybean oil and rapeseed oil oxidized and agreed with zero-order and first-order kinetics models,that is,conformed to the linear equation and exponential equation at the same time.Similarly,linoleic acid levels in palm oil,rapeseed oil,sunflower oil and rice bran oil oxidized and agreed with zero-order and first-order kinetics models,and linoleic acid levels in soybean oil oxidized and agreed with first-order kinetics models.Oleic acid levels in palm oil,soybean oil,rapeseed oil and sunflower oil oxidized and agreed with zero-order and first-order kinetics models.The correlation coefficients between predictive and experiment values of models were greater than 0.85,indicating a good degree of model fitting.(3)The calibration models of AV and TPC were established using NIRS combined with partial least squares(PLS)to evaluate the quality of frying oil.The results showed that the correction coefficient of calibration model of AV and TPC were both 0.9974.The root mean square error of cross-validation(RMSEC)were 0.111,0.359,respectively.The root mean square error of prediction(RMSEP)were 0.171,0.562,respectively.These indicated that the models of quantitative analysis of AV and TPC of frying oils were good with excellent prediction abilities.(4)PAHs in frying oils were extracted via solid phase extraction,and separated and quantified using gas chromatography-triple quadrupole-mass spectrometry(GC-QqQ-MS).The changes of PAHs in five frying oils were studied.The results showed that the levels of BaP,PAH4,PAH16 and TEQBap in different frying oils were different before and during frying.Before frying,the contents of BaP and PAH4 in palm oil and rice oil were the lowest and the highest,respectively.The levels of BaP and PAH4 in sunflower oil,rapeseed oil and rice bran oil all exceeded the European Union standard.After frying for 7 days,there was a highest increase in the levels of PAH4,PAH16 and TEQBap in soybean oil,while the lowest increase in palm oil.Besides,during frying,the contents of BaP,PAH4 and TEQBap in palm oil were the lowest,while that in rice bran oil was the highest.The proportion and ring number distribution of PAHs were also significantly different between different frying oils before frying and during frying.Overall,the proportion of 3-ring PAHs was the largest,and the contribution rate and increase rate of light PAHs in all frying oils were significantly greater than that of heavy PAHs.From the perspective of food safety,the levels of BaP,PAH4 and TEQBap in palm oil during frying were significantly lower than those of the other frying oils,and the increase of PAH4,PAH16 and TEQBap was the smallest,thus,palm oil exhibited the best performance.(5)The interaction of BaP with ctDNA was studied using multiple spectroscopic methods as well as molecular modeling technique.The main binding mode of BaP to ctDNA was static and hydrophobic interaction.Interaction between BaP and ctDNA was driven principally by groove binding mode,which was revealed by denaturation measurements,ionic strength effects,melting experiments and viscosity studies.The results of molecular docking further corroborated the BaP-ctDNA complexation and showed that BaP preferentially bound to the A-C rich region in the minor groove of ctDNA,which could induce DNA damage at high levels.