Study On The Effect And Mechanism Of Tannic Acid Binding On The Thermal Degradation Of Boscalid

Pesticide residues in fruits have always been a food safety issue that has attracted much attention,and the processing process may lead to the degradation and transformation of pesticide residues in fruits,and even generate transformation products that are far more toxic than the parent pesticide,in addition,pesticide residues may combine with fruit matrix to affect degradation and transformation behavior,bringing potentially greater food safety risks.Therefore,this paper takes the pesticide boscalid,which is highly occurring and frequent in fruits,as the research object,explores its mutual binding effect with tannic acid in fruits,focuses on the influence of binding state on the degradation behavior of boscalid during processing,and provides a reference for the accurate monitoring of pesticide residues in processed fruit juices.The main research contents are as follows:Study on the binding effect of boscalid and tannic acid.The combination of boscalid and tannic acid was systematically studied by spectroscopy,thermodynamics and computational chemistry.Compared with tannic acid monomers,the Fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance hydrogen spectroscopy（¹H NMR）of the boscalid-tannic acid complex shifted in the direction of high wavenumber,indicating that hydrogen bonds were formed between the two.The isothermal titration calorimetry（ITC）results showed that the binding constant was 6.0×10⁵ M^-1 at 298 K,and the spontaneous binding was mainly in hydrophobic interactions（ΔG<0,ΔH>0,ΔS>0）.The molecular docking results further confirmed the tendency of boscalid and tannic acid to bind theoretically.In addition,the binding of boscalid significantly affects the antioxidant properties of tannic acid（DPPH radical scavenging capacity decreases by about 16%）.Degradation kinetics of the boscalid-tannic acid bound state.Through univariate experiments,it was found that compared with the free state,with the increase of the concentration ratio of the two,reaction p H（3.5-5.5）and reaction temperature,the degradation rate（k₁）of the bound boscalid decreased,and the corresponding half-life(T_1/2)was greatly extended,all of which were positively correlated with the experimental factors(r（k₁）were0.9820,0.9832,0.6968;r(T_1/2)were 0.9960,0.9755,0.8513,respectively);however,when the p H was 5.5-7.5,k₁and T_1/2 of the bound boscalid were negatively correlated with the p H（r was0.9740,0.9508）,and after the p H was greater than 6.5,there was no significant difference between the degradation of the bound boscalid and the free state;the RSM optimization test was used to obtain the optimal degradation parameter conditions of the bound boscalid,and the actual samples confirmed that the model could effectively predict the degradation of the bound boscalid.The thermal degradation mechanism of bound boscalid and its product toxicity were studied.The identification of UPLC-Q-TOF-MS showed that four identical products were found after thermal degradation of free and bound boscalid,indicating that the binding of tannic acid did not affect the thermal degradation products.Based on density functional theory（DFT）,the structural and reaction characteristics of boscalid pesticides were calculated and analyzed,and it was found that the N-H bond,C=O bond,pyridine ring C-N bond,C-C bond and C-Cl bond of boscalid were more likely to break and were the most likely reaction sites.Combined with high-resolution mass spectrometry data analysis,it was proposed that the degradation pathways of boscalid were hydroxyl substitution and C-N bond and C-C bond breaking.According to the toxicity assessment of T.E.S.T.and ECOSAR,it was found that the toxicity of the thermal degradation products B2 and B3 of boscalid may be higher than that of the parent.The results of this study show that the binding of boscalid and tannic acid will significantly affect the thermal degradation efficiency of boscalid,but will not affect the types of thermal degradation products of boscalid,thereby providing basic data support for the degradation of bound pesticide residues in complex food matrices.