Microbial Degradation Of Carbamate Pesticides In Fermented Foods

Carbamate pesticides are widely used in China's agricultural production,but because of its unscientific use led to pesticide residues,leading to food safety problems.Therefore,the degradation of four carbamate pesticides(aldicarb,isoprocarb,fenobucarb and carbofuran)in the culture medium was studied in this paper.The degradation kinetics of pesticides and the influence of pesticides on the growth of microorganisms,that provided the theoretical basis for the analysis and control of carbamate pesticide residues in food processing.The main contents of this paper were as followed: Firstly,the thermal degradation of carbamate pesticides in raw milk was determined by liquid-liquid extraction combined with gas chromatography,and the kinetic constants were calculated to study the biodegradation of pesticides.Secondly,the degradation of carbamate pesticides by lactic acid bacteria and molds in MRS medium and PDB culture medium was studied.The effects of pesticides on colony growth were measured by plate colony counting and dry weight method.Thirdly,the laboratory simulated fermented milk,rice wine,cheese and dough and other food fermentation process,detected the level of four pesticide residues,revealing the degradation of carbamate pesticides in the fermentation process.At the same time,the safety of different food substrates,different microbes and different fermentation processes were evaluated according to the calculated degradation kinetics parameters.The main results obtained were as followed:(1)The determination of carbamate pesticide residue in samples were extracted by liquid-liquid extraction method,combined with gas chromatography to detect aldicarb,isoprocarb,fenobucarb and carbofuran.The detection limit of this method was 0.006-0.01 mg·kg-1 with correlation coefficient ? 0.996.The recoveries of the four carbamate pesticides in different food substrates were between 70% and 120%,and the standard deviation ? 5.8%.Pretreatment method was simple,gas chromatography could be completed within 22 min,which could satisfy the fast,accurate,green detection requirements.(2)Thermal degradation of carbamate pesticides in raw milk was studied at 63,72 and 90 °C.The half-life of the four carbamate pesticides at 63 °C was reduced to 6.08-9.55 h,72 °C was reduced to 5.59-6.39 h and 4.99-5.72 h at 90 °C,indicating that the residual levels of pesticides decreased with the prolongation of heating time and the temperature increased the degradation of pesticides.The kinetic constants of four carbamate pesticides were carbofuran > fenobucarb >isoprocarb> aldicarb in the case of heating,and the kinetic constants of the carbamate pesticides did not change with the increase of temperature.This showed that carbofuran was not sensitive totemperature,which meant structural stability,fenobucarb and isoprocarbic was followed,aldicarb was the most sensitive to temperature.(3)This paper also studed the degradation of carbamate pesticides in culture medium and the growth promotion of microorganism by pesticides.The results showed that the degrading rate of lactic acid bacteria in MRS medium was 6.06%-20.95%,and the growth of lactic acid bacteria showed obvious retardation period.The degradation rate of fungi in PDB medium could reach52.44%-69.48%.The pesticide had a long-term inhibitory effect on the growth of Penicillium albicans and the growth of Penicillium levoderma had obviously promotion effect.This indicated that lactic acid bacteria and molds promotedthe degradation of carbamate pesticides,and the added pesticides could promote the growth of microorganisms other than Geotrichum candidum.(4)The biodegration of carbamate pesticides in different microbial fermentation process was studied.Laboratory simulation of fermented milk,rice wine,cheese and dough production,four kinds of carbamate pesticides degradation rate had improved significantly.Compared with the control group,the degradation kinetics constants of the carbamate pesticides in the fermentation products of lactic acid bacteria,rhizopus mold,cheese mold and yeast were all improved and the half-life was shortened.The results showed that the fermentation could promote the degradation of carbamate pesticides and improved the safety of food.