| The vegetables are so important to human life,they provide Vitamin, mineral substance, protein, amino acid, suger and so on. The nitrate is the nitrosamine precutsor which can induce cancers of digesting system. The vegetables are easy to enrich nitrate which can combine with the blood-red protein when entering human body's blood to can not take along the oxygen and then cause the physiology disorder, touching vegetables'quality. The article studies on improvement of rapid detection method of nitrate, nitrate contents in Autumn vegetables in shanghai, with the measures of fertilizer reduction, organic and inorganic fertilizers ,selenium fertilizer to analyze the nitrate content in vegetables, yield, quality and physiological characteristics, in order to provide theoretical basis on vegetables safety control. The results show that:1. Improvement of rapid detection method of nitrate.The results showed that the test results were not obvious difference with ammonia or borax buffer solution; change four factors was no significant effect on the test results. Compare to the national standard method, the two methods had no significant difference either. In the sample recoveries were between 93.77 ~ 104.96% , accuracy and precision meet the test requirements. This study is expected to provide a more simple and efficient method to the detection of nitrate in vegetables.2. Foundation survey and risk assessment on nitrate in vegetables.Analyze the nitrate contents of vegetables collected from the green houses and outdoors in four areas of Shanghai. The results showed that :the content of nitrate in vegetables was in the following descent order: leafy vegetables, root and stem vegetables, melons, egg plants, beans, the nitrate contents in different species differed greatly. According to the assessment of nitrate intake, the average daily intake is 2243.28mg which exceeds ADI 38.42%.3. Effects of fertilizing decreasing on nitrate contents, nutritional quality and biological characteristics of vegetables.(1) Effects of fertilizing decreasing on nitrate contents, nutritional quality and biological characteristics of three vegetables.The results shows that :The nitrate content were reduced effectively with the fertilizer supply decreasing;VC, protein and soluble sugar content did not change significantly with the fertilizer supply decrease;Fertilizer supply decrease caused CAT activity increased, POD and SOD activity decreased, then MDA content decreased, meanwhile NR activity increased, which was correlated with fertilizer supply. So fertilizer supply decrease can reduce nitrate content in vegetables but keep safety.(2) Effects of fertilizer decreasing on the yield,quality and biological characteristics of continuous Greens.The results showed that: Any crop'yield of fertilizer decreasing treatments were less than control, it had no significant influence to the yield of the first and second crop'treatments, but 48.75 kg·hm-2 treatment decreased significantly. Vc and soluble sugar content of the first and second crop and Protein of three crops did not change significant with the fertilizer supply decrease except 56.25 kg·hm-2 and 48.75 kg·hm-2 treatments of the third crop. As for the biological characteristics, using a special concentration of fertilizer on the greengrocery increased MDA, SOD, POD, CAT in greengrocery to different extents. MDA content was reducing with the fertilizer decreasing of first and second crop, but the third crop increasing. SOD activities were not influenced obviously by different fertilizer treatments, CAT changed with an opposite trend to SOD and POD. Nitrate content decreased with the fertilizer concentration decreasing, which was correlation with NR activities. Comprehensive considering the effects of fertilizer decreasing on the yield , quality of greengrocery, as well as food safety for human health,48.75 kg·hm-2 fertilizer decreasing treatment should be lasted the second crop. 4. Effects of application of organic fertilizer combined with chemical fertilizer on yield,quality and biological characteristics of three vegetables.(1) Effects of application of organic fertilizer combined with chemical fertilizer on yield,quality and biological characteristics of Greens.The results showed that:The yield of Greens, Vc content showed a rising trend with the increase of organic fertilizer proportion, protein was highest on 75% organic fertilizer and 25% chemical fertilizer level,soluble sugar content in organic fertilizer was more than 100% chemical fertilizer. SOD ,POD and CAT activities reduced after first increases. Each organic fertilizer group significantly higher than 100% chemical fertilizer on NR activities of greens , showed negative correlation of nitrate content.(2) Effects of application of organic fertilizer combined with chemical fertilizer on yield,quality and biological characteristics of Eggplants and Amaranth interplanting.The results showed that: The yield of eggplants and amaranthes reduced after first increases. Moderating organic fertilizer inhibited nitrate content,Vc and protein contents organic fertilizer treatments were lower than 100% chemical fertilizer of amaranths. There was not significant correlation between nitrate content and the proportion of organic fertilizers of Eggplant, protein content 100% organic fertilizer more than 100% chemical fertilizer significantly.5. Effects of selenium application on the nitrate content,yield,qualities and biological characteristics of Greens and Radish.(1) Effects of selenium application on the nitrate content,yield,qualities and biological characteristics of Greens.The results showed that selenium treatments significantly increased the total Se content in greens. With the increment of application rate of Se, total selenium reach the peak at the 112.725 g·hm-2,and selenium increased most fast at 74.925 g·hm-2.Se application decreased the greens yield compared with CK. However, the vitamin C content was more than control whichever treatment, and it was the highest at 112.725 g·hm-2 ; the protein content of CK was more than other treatments except 149.85 g·hm-2 ;meanwhile selenium application decreased soluble sugar content, 149.85 g·hm-2 had the least; Ca, Mg, Fe, K, Zn, Mn were increased at lower levels, but decreased at higher levels. As for the biological characteristics, using a special concentration of selenium on the greens increased MDA, SOD, POD, CAT in greens to different extents. Nitrate content decreased with the Se concentration increasing , which was correlation with NR activities. Comprehensive considering the effects of selenium application on the selenium content,yields and various quality factors of greens,as well as food safety for human health,the appropriate application rate of Se should not be more than 37.125 g·hm-2.(2) Effects of selenium application on the nitrate content,yield,qualities and biological characteristics of Radishes.The results showed that selenium treatments significantly increased the total se content in radish. With the increment of application rate of se, total selenium reach the peak at the highest application rate.High se application increased the radish yield compared with CK. As for the quality of radish, the vitamin C , Protein content, soluble sugar content and any other quality indexes were not changed significantly.The biological characteristics, using a special concentration of selenium on the radish increased MDA, SOD, POD, CAT in Radishes to different extents. Nitrate content decreased with the se concentration increasing , which was correlation with NR activities.The purpose of this study is putting forward a series of nitrate in vegetables control measures,monitoring vegetables'nitrate content, nutritional quality and physiological characteristics ,which is based on the nitrate content determination of vegetables in Shanghai and intake risk assessment to control fertilizer dose and select different varieties fertilizers to ensure local vegetable safe to eat. |
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