Study On Degradation Of Pesticides Residual And Evaluation Of The Quality Variation In Vegetable

A gas chromatographic method was developed for determining residues of 10 pesticides ( dichlorovos, methamidophos, acephate, omethoate, chlorpyrifos, malathion, methyl-parathion, permethrin, and cypermethrin, fenvalerate ) in leafy vegetables. The applications of ozone, ultrasonic, surfactants and coexpressed detoxifying enzyme (coexpress organophosphorus hydrolase and carboxylesterase B1 ) to the pesticides degradation in baby cabbage were conducted .The influence factors of each degradation technology were studied and the optimum parameters were determined respectively. Degradation efficiency of combination treatments were also studied. Impact on nutrition, color and texture elements of vegetable were analyzed. The following were the main results:(1) A gas chromatographic method was developed for determining residues of 10 pesticides in leafy vegetables. Samples were extracted with acetonitrile and cleaned up with Florisil solid-phase extraction (SPE) cartridges using actone : hexane (1:9, v/v) as eluent.The average recoveries for spiked standards(n=3) were between 85.85% and 108.51% . Precision (expressed as relative standard deviation) was lower than 4.79% and the limit of detection(LOD) was between 0.06 and 2ppb. The method is effective, fast and accurate.(2) The optimum parameter of coexpressed detoxifying enzyme was 30°C, pH 9.0 , OPH 1500 U and 30min respectively. Enzyme could effectively degrade 66.4% dichlorovos, 71.9% malathion, 99.7% methyl-parathion and 30%～40% of others.(3) The optimum parameter of ozone was 35°C, ozone inflow 0.08 m~3/h, pH10.0 and 30min respectively. Dissolved ozone was effective to oxidize 50%-60% of the ten pesticides residue in leafy vegetables, while fenvalerate was only 35.6% . Enhancing media temperature , pH value, ozone level and the reaction time could improve the degradation efficiency.(4) Tween 60 was more effectively in degrading pesticides in vegetables than SE 15 and the content ratio was 0.05%.(5) Ultrasonic combined ozone, tween combined ozone and tween combined enzyme displayed visible synergistic effect. It was most effective by combinations of tween , enzyme plus ozone and tween , enzyme , ozone plus ultrasonic, with 50%～70% degradation in systemic insecticides and pyrethroid pesticides, others were 70%～99% removal expecially 99.6% methyl-parathion.(6) After degradation, baby cabbage still keeps good sensory quality, and the value of L~*, a~*, b~* in vegetable surface were almost constant. However, hardness value ( F_p) and fracture distance of puncture test ( Dp) were inhance but less than 10% and 5% in optimum parameter . The content of ascorbic acid maintained more than 80%. Totally, there was no serious impact on vegetable quality after degradation.(7) Based on field experiments and degradation of pesticides residual in fruits, The results showed that the degradation technologies had high efficiency and significancy.