| Free radicals,which are produced during the organism’s normal metabolism,can be harmful to organisms because it contains unpaired electrons.Owing to the antioxidant system of organisms could quench the free radicals rapidly,it usually does not produce obvious injury of organism.Human can avoid harmfulness caused by excessive free radicals via taking antioxidant-rich foods.As one of the necessities of our daily life,vegetables contain various antioxidants.However,because of its high cropping index and stubbles,occurrence variety, and high frequency of plant diseases and insect pests, pesticides are usually overused.To date, the effect of the non-enzymes of vegetables,the change of the ability of scavenging free radicals in vitro, and the relationship between changes of free radicals and pesticide residues are rarely investigated and poorly understood. In this study, the negative impacts of pesticide, the ability of scavenging free radicals in vitro, and the relationship between changes of free radicals and pesticide residues in Lactuca sativa were investigated.1. To evaluate the effects of free radicals in Lactuca sativa when treated by different concentrations and times of beta-cypermethrin, the activity of superoxide dismutase and catalase,the content of flavonoids and total phenolic were investigated using methods of specific kits and spectrophotometry.The results showed that the increase of pesticide amount could increase the activity of CAT, decrease the activity of SOD, and also increase the ascending descending range.The content of flavonoids and total phenolic increased in samples treated only once with the low concentration; the content of flavonoids and total phenolic decreased in group treated once with the medium and high concentration, as well as the group when treated twice with the low, medium,high concentration.This result revealed that Lactuca sativa treated by beta-cypermethrincouldproduce redundant hydroxyl radicals,but restrained other free radicals,and the amount enhanced with the increase of concentration and treatment times of pesticide.2. The effects of free radicals in the Lactuca sativa treated with different concentrations and times of imidacloprid were investigated. The results showed that the activities of CAT decreased and the activity of SOD increased, and the range of the increase and decrease became bigger with the increase of pesticide amount, which suggested that Lactuca sativa treated with imidacloprid could overproduce superoxide anion radical, but restrained hydroxyl radicals, and the amount enhanced with the increase pesticide treatment. The content of flavonoids increased in group treated once with different concentrations of imidacloprid, and the range of the increase became bigger with the increase of concentration. The content of flavonoids increased in the group treated twice with low concentration of imidacloprid, but the content of flavonoids decreased in the group treated twice with medium and high concentration of imidacloprid, and the range of the decrease became larger with the increase of concentration. The content of total phenolic increased which group treated once with different concentration of imidacloprid, the content of total phenolic decreased in the group treated twice with different concentration of imidacloprid, and the range of the increase and decrease became larger with the increase of concentration. Hence, this result supported that Lactuca sativa disposed only one time by imidacloprid with the recommended concentration could produce abundant free radicals, however, when the samples treated with high concentration(applying pesticide twice) of imidacloprid will restrain the production of redundant free radical, but restrain hydroxyl radicals. Further research on whether only superoxide anion radical and hydroxyl radicals were restrained or not is needed.3. The scavenging activity of hydroxyl radicals, superoxide anion radical and DPPH in vitro were determined, respectively, via methods of salicylic acid, kit and spectrophotometry. The results showed that when the Lactuca sativa samples treated with beta-cypermethrin and imidacloprid with different concentrations and times, the scavenging activity of hydroxyl radicals,superoxide anion radical and DPPH in vitro was decreased, and with the increase of concentration and treatment time, the range of the decrease became larger.4. With the extension of time, the activity of antioxidants of Lactuca sativa and the ability of scavenging free radicals in vitro gradually approached the blank control. However, with the increase of concentration and time of pesticide, it took a much longer time to approach the blank control. Comparison of the recovery time of antioxidants(except CAT) and the ability of scavenging free radicals in vitro between the two pesticides identified that Lactuca sativa took a much shorter time when treated with beta-cypermethrin.5. The effect of boiling of scavenging free radicals in vitro of Lactuca sativa treated withpesticide was investigated. The results showed that the scavenging activity of hydroxyl radicals,superoxide anion radical and DPPH in vitro of Lactuca sativa disposed by pesticide after boiling were restrained, and the range of the restrain became larger with the increase of concentration. As for the Lactuca sativa samples treated with beta-cypermethrin and imidacloprid with different concentrations, the scavenging activity of hydroxyl radicals in vitro decreased by 25.02-33.87%,the scavenging activity of superoxide anion radical in vitro decreased by52.98-59.13%, and the scavenging activity of DPPH in vitro decreased by 42.35-52.1%. Given the evidence that a greater influence on enzymes under a higher temperature, it is reasonable to propose that enzymes antioxidants play a major role of the scavenging activity of superoxide anion radical and DPPH in vitro of Lactuca sativa, non- enzymes antioxidants play a major role of the scavenging activity of hydroxyl radicals.6. As for the Lactuca sativa samples treated with beta-cypermethrin and imidacloprid, the investigation of residues showed that with the extension of time, the residues of the Lactuca sativa disposed by beta-cypermethrin and imidacloprid gradually decreased, and the digestion dynamic conformed to the first order kinetics reaction model. Based on the digestion dynamic curve of two pesticides, it can be concluded that imidacloprid dissolved quickly within the first 5days, the rate of digestion obtained 75.68% at the 5 d, the digestion became relatively slow after5d; during 0-7d, beta-cypermethrin dissolved quickly, the rate of digestion obtained 76.41% at 7d,the digestion relatively became slow after 7d. It showed that the degradation characteristics of the two pesticides in the Lactuca sativa were different. The half life of imidacloprid and beta-cypermethrin were 2.85 and 3.98 d, respectively, which showed that the two pesticides could be easily decomposed(half life<10d). Is the specification of the potion, two kinds of drug safety interval for 14d; According to the research result shows that with the degradation of pesticides, the lettuce in vivo and in vitro antioxidant capacity were gradually restored, after 14 d, return to ck levels.Thus, It has certain negative correlation between the residues of two kinds of drugs and antioxidant capacity of Lactuca sativa which treated by drug. |
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