| China is the country with the largest output and export of apples.However,the pesticide residues found on apples and in processed apple products have become the main hindrance to further internationalization of the apple industry.Pesticide residues on fruits are harmful to human health,while pesticide molecules found in a binding sate within the fruits have a serious impact on the processing quality of apples.Increasing the rate of pesticide residue removal and clarifying the effect of pesticide molecules on the processing of apples are key to improving the commercial quality of apples.In this study,we focused on trichlorfon,carbosulfan,and fluopyram(FLP),three pesticides commonly used in apple cultivation.In this study,the migration and degradation of pesticide residues in postharvest storage and processing of apples were systematically studied by using the theories and methods of food chemistry,quantum chemistry and pharmaceutics.Safe and efficient control measures based on clarifying the degradation and transformation behavior of pesticides were put forward.The main results are as follows:1.Prediction model and degradation analysis of pesticide residues in apple storage.In this work,the degradation data of 100 pesticides were collected,and a correlation analysis was performed.It was found that there was a correlation(|r|>0.3)between the solubility,flash point,and Kow(octanol-water partition coefficient)of pesticides and the degraded RL50.A prediction model for the degradation and toxicity assessment of pesticide residues in fruits and vegetables during storage was then constructed using AI deep learning neural network(DLNN)(R~2=0.74–0.82).The degradation RL50 values of the three pesticides during apple storage were 4.0–11.8d,and the matching degree with the DLNN model was up to 72%–96%.The RL50 of the pesticides was extended to 28.9 days after coating the apples.Molecular dynamics showed that the molecular bond energy in the coating was intense,and the morphology was compact,which hindered the dissipation of pesticides.About 1%–22%of the pesticide was transferred from the peel to the pulp,increasing the risk to food safety.2.Adsorption mechanism and removal technology of pesticide residues on apple surface.The main components of the waxy layer of apple are long-chain aliphatic(65%)and triterpenes(29%).Pesticide molecules could be combined with terpenes in the form of hydrogen bonds identified by pharmacophore technology;the adsorption energy and the monitored three binding fragments verified this conclusion.On the basis of the adsorption behavior of pesticides,the removal rate of ozone fumigation for pesticides was 73%–100%.After ozone and microbubbles were combined(OMBT),the clearance rate increased to 98%–100%,and there was no mechanical injury on the apples.At the same time,the digestion rate of pesticides in water in this technique was more than 90%.The high efficiency of OMBT was attributed to the generation of a large amount of OH(0.03–0.04 mol/L)due to microbubble rupture.Therefore,this technology can remove pesticide residues on the surface of fruits and vegetables and in water simultaneously.3.Analysis of processing factors(PF)of pesticide residues in apple drying.The fresh apple slices were dried by hot air,microwave drying,and natural sun drying.The changes in three pesticide residues were dynamic during the apple-piece drying process,and this phenomenon tended to fit the first-order kinetics and second-order composite model(R~2=0.69–0.98).PF>1after hot-air drying and natural drying indicated that pesticide residues had an enrichment effect.However,microwave drying was less than 1,indicating that the pesticide was degraded,and that the rehydration property of the apple-pieces after microwave drying was better.Therefore,the microwave drying of fruits and vegetables is recommended in production,since it can not only improve efficiency but also reduce the risk of pesticide residue and transformation.4.Effects of pesticide residues on flavor and yield of apple juice.In this study,the flavor and yield of enzymatically hydrolyzed apples were analyzed.The results showed that the three pesticide residues not only reduced esters,alcohols and acids by 3.2%–6.8%but also reduced juice yield by 0.6%–4.8%.Molecular docking showed that some key amino acid residues(such as Lys-358 and Tyr-197)in the catalytic site of Pectinase(PG)complexed with pesticide molecules resulting in conformational changes of PG.Multi-spectral analysis showed that the combination of the two was a static quenching mechanism,and the secondary structure of PG changed.Meanwhile,the degradation rates of the three pesticides during the enzymatic hydrolysis were 28%–96%,and we detected the new degradation product of FLP.5.Transformation pathway and toxicity analysis of pesticides.On the basis of density functional theory,transformation pathways for the three pesticide molecules were proposed,and the products were monitored and verified by high-resolution mass spectrometry.The transformation of pesticide molecules involves hydroxyl substitution,oxidative rearrangement,and other reactions.The combination of theoretical calculation and high-resolution mass spectrometry can avoid the lack of intermediate products and realize the integrity of the transformation pathway.The inhibition degree of pesticides on T3 bacteria luminescence was carbosulfan>FLP>trichlorfon,and the inhibition rate showed a very significant linear correlation with the pesticide concentration(P<0.01).Further evaluation of 21 products from three pesticides using computational toxicology(ECOSAR and T.E.S.T.)revealed that seven products were more toxic than the matrix.Molecular docking found that the pesticide molecule was bonded in the hydrophobic region of the active site of acetylcholinesterase(ACh E),and that the binding energy was-3.5 to-8.4 kcal/mol.It was confirmed by multi-spectral analysis that the pesticides affected the ACh E conformation and that theα-helix decreased by 2.0%–9.0%.6.Bioavailability of pesticides based on apple matrix and standardized food model(SFM).We used apple juice and SFM combined with the bionic digestive system to determine the bioavailability of pesticides.The bioavailability of the three pesticides at the MRL level was not up to 1.0%.However,when the pesticide level is high,the gastrointestinal exposure rate will increase significantly,such as FLP(8 mg/kg)exposure rate up to 19.4%.With the increase in the proportion of SFM,the bioavailability of pesticides in the stomach and intestine was significantly reduced to 0.7%–10.5%and 0.2%–2.9%,respectively.The food matrix was the critical factor affecting the bioavailability of pesticides.The application of a standardized food model can provide new ideas for risk assessment of pesticides and other hazards. |
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