Effect Of Pesticide Residues In Rice And Wheat Flour Food Processing And Risk Assessment

Rice and wheat flour food is an important staple food for Chinese residents,which occupies an important proportion in the diet of residents.In order to reduce disease,insect and grass damage as much as possible and ensure the yield and quality during the growth of rice and wheat,the use of pesticides is inevitable.Although the pesticide residues in rice and wheat can be greatly reduced after initial processing such as peeling and polishing,pesticide residues in rice and wheat flour are still detected from time to time.Long-term consumption of rice and wheat flour containing pesticide residues will pose safety risks to the health of residents,especially infants and young children.In this study,high performance liquid chromatography(HPLC)was used to establish a method for the analysis of multiple pesticide residues in rice and wheat flour,to study the effect of pesticide residues during the processing and storage of rice flour,noodles,steamed bread and bread,calculate processing factors,and evaluate the dietary exposure risk of residents.It provides a reference for clarifying the safety risk of pesticide residues in rice and wheat flour food,guiding residents to consume rice and wheat flour food safely.The main research results are as follows:(1)HPLC was used to improve the pre-treatment method of Qu ECh ERS and optimize the instrument parameters.A method for the detection of five commonly used pesticides,imidacloprid,isocarbophos,methidathion,triazophos and chlorpyrifos,was established and optimized in rice,and a method for the detection of five commonly used pesticides,imidacloprid,triadimefon,fenitrothion,methyl chlorpyrifos and chlorpyrifos in wheat flour.The limits of detection and quantification were 0.0079mg/kg～0.050 mg/kg and 0.0463 mg/kg～0.1440 mg/kg.The recoveries were76.88%～108.24% and the standard deviations were 0.08%～9.70%.Both methods meet the requirements of pesticide residue analysis and can be used for the detection of pesticide residue in rice and noodle food.(2)Rice flour is processed by extrusion and drying on roller,stored at 54℃.The results showed that,on the basis of wet base,the extruding step in extrusion process and soaking step in drying on roller process had better effects on pesticide residues.The five pesticide residues concentration in extruding step were reduced by 20.7%～53.9%,and the five pesticide residues concentration in soaking step were reduced by44.2%～75.9%.During the accelerated storage of rice flour,the residues concentration of five pesticides were all reduced,especially methidathion and chlorpyrifos,which were not detected after 14 days of accelerated storage.In terms of dry base,the five pesticide residues concentration showed a decreasing trend during rice flour processing and storage,and the pesticide residues concentration in extrusion,drying,soaking and drying on roller step decreased significantly,while the other steps had no significant changes.The calculation results of Processing Factor(PF)showed that the PF of imidacloprid and isocarbophos was greater than 1 in the drying step of drying on roller process,while the PF of other pesticides was less than 1 in different processing steps.It could be believed that drying would increase pesticide residues due to concentration to a certain extent.The PF of drying on roller process was lower than that of extrusion process.Compared with extrusion process,drying on roller process was more beneficial to reduce pesticide residues in rice flour.After 14 days of accelerated storage of rice flour,PF of five pesticides were all less than 0.7.(3)Noodles are processed by wet and dry noodles processing process.Dry noodles are stored at 54℃.The results showed that,on the basis of wet base,dough mixing step could reduce the residues concentration of five pesticides by 23%～42%,while dough resting step had no significant effect on the residues of triadimefon,imidacloprid and chlorpyrifos,while the residues concentration of methyl chlorpyrifos and chlorpyrifos were significantly reduced by 24% and 15%,respectively.The residue concentration of chlorpyrifos was increased by 3%,and the residue of other 4 pesticides was increased by 41%～69%.The residues concentration of five pesticides in wet noodles and dry noodles were significantly reduced by 56%～74%.During the accelerated storage of dry noodles,the residues concentration of five pesticides were significantly decreased,especially the fenitrothion,methyl chlorpyrifos and chlorpyrifos,which were decreased by 74%～81%.In terms of dry base,all pesticide residues concentration showed a decreasing trend in noodle processing and storage,and significantly decreased in cooking and cooking,but no significant change in other steps.The results of processing factor calculation showed that PF of five pesticides was greater than 1 in the drying step of dry noodles,and PF of other pesticides was less than1 in different processing steps.The PF range of wet noodles and dry noodles ranged from 0.15 to 0.35,which could effectively reduce pesticide residues concentration.After 14 days of accelerated storage,PF of five pesticides were all less than 0.4,and the longer the storage time,the less pesticide residues concentration.(4)The processing process of bread and steamed bun is similar,including the steps of dough mixing,fermentation and resting.The results showed that,on the basis of wet base,the mixing step of bread and steamed bun can reduce pesticide residues concentration by 33%～46%.Fermentation and resting steps had little effect on pesticide residues concentration,and the residues concentration were reduced by 2%-22% and1%-18%,respectively.The residues concentration of imidacloprid and triadimefon in bread crust were increased by 83% and 65%,respectively.The residues concentration of triadimefon in bread crumb were increased by 14%,and the residues concentration of other pesticides in bread crust and crumb were decreased by 3%-79%.The residue of imidacloprid and triadimefon in steamed bun crust increased by 5% and 52%,and the residue concentration of other pesticides in steamed bun crust and crumb decreased by 4%～38%.In terms of dry base,the pesticide residues concentration in steamed bread and bread processing showed a decreasing trend,and the pesticide residues concentration in flour mixing,steaming and baking were significantly decreased,while the other steps had no significant changes.The results of processing factor calculation showed that the PF of imidacloprid and triadimefon in bread baking and steamed bun steaming was greater than 1,and the PF of other pesticides in different processing steps was less than 1.(5)Follow the principle of maximum risk,choose low risk tolerance of 6～36months infant groups as the target population,calculated according to the study of the processing factors,combined with the feature of the crowd,dietary consumption as well as the pesticide residue limits standard,build the evaluation model,pesticide residues in rice and wheat flour food for infant dietary exposure risk assessment.The results showed that the dietary risk index of pesticide residues in rice flour,noodles and steamed bun were all less than 100,which belonged to the safe exposure level.The risk of dietary exposure of 12-month-old infants among four different infant subgroups was higher,and the risk of pesticide residue exposure in noodles among three rice and wheat flour foods was higher.