| Recently, irrational pesticides, unbalanced fertilizers, and emission of industrial wastes have caused agricultural products to be polluted seriously, including that the contents of nitrate, pesticide residues and heavy metals in agricultural products have exceeded corresponding standards to a certain extent. Wuhan is an important vegetable circulation and consumer market with more than 890 million permanent residents. Nitrate which was the significant harmful factor of vegetable quality is worthy paying close attention. In this paper, based on agronomic reduction measures, it was shown that the pollution status of nitrate and nitrite in typical vegetable in Wuhan City, discussed that the influence of storage conditions on the contents of nitrate in vegetables, and definited that effect of reducing nitrate in vegetables by some handling process after collection with the method of combining market sampling and laboratory simulation. Main results were summarized as follows:(1) The present pollution status of nitrate in vegetables were serious in Wuhan City, especially in leaf vegetables, whose average concentration was 3482.2mg·kg-1; the nitrate contents varied significantly in different types vegetables, and the descending sequence was:leaf vegetables, root vegetables, melon and fruit vegetables, beans. Among 81 investigated vegetable samples, the proportion which nitrate contents reached a severe pollution grade which accounted for 35.8%, heavy pollution for 8.6%, moderate pollution for 9.9%, and mild pollution for 45.7%, respectively, and most serious in leaf vegetables, moreover, the vegetables which exceeded the severe pollution grade were all leaf vegetables, and the proportion which nitrate contents exceeded the severe pollution grade accounted for 58.3% in leaf vegetables. All the vegetables were lower than 4mg·kg-1 in nitrite contents in Wuhan City, which were lower than in corresponding hygienic criterion.(2) Temperature conditions influenced the nitrate contents of leafy vegetables and root vegetables significantly. Under the conditions of 0～5℃,10～15℃or 20～25℃, nitrate contents in pakchoi were within 2350.4-3386.6mg·kg-1, 2725.9～4068.9mg·kg-1 and 3188.2～6663.5mg·kg-1, respectively, during four days storage period. The nitrate content of white radish in which initial value was 1695.4mg·kg-1 showed a pesistent ascending trend, nitrate content of white radish were reached 2071.5mg·kg-1,1941.5mg·kg-1 and 1792.3mg·kg-1, respectively, under the conditions of 0～5℃,10～15℃and 20～25℃. Under above three kinds of storage temperature, nitrite contents of both pakchoi and white radish were below 1mg·kg-1, which were below safety standards and will not cause harm to people and livestoke.(3) Under three humidity conditions, the dynamic laws of the nitrate contents in leafy vegetables differed from in root vegetables under the condition of 10～15℃. During the storage period, cabbages were stored under conditions of RH70%～75%, RH80%～85% or RH90%～95% for one day, whose nitrate contents increased by 33.2%,13.2% and 0.6%, respectively; under condition of RH70%～75%, nitrate contents were increased continuous in day 2～5, and increased by 41.0% on day 5, while increased by 13.0% under condition of RH80%～85%; under condition of RH90%-95%, nitrate contents were increased in day 2～4, but decreased by 15.8% on day 5. Under the condition of 10～15℃, white radish were stored for 5 days under the condition of RH70%～75%, whose nitrate contents were increased by 56.6% on day 5; under the condition of RH80%～85%, nitrate contents of white radish were decreased by 6.6% after one day, and which were more than initial value in day 2～5, and the highest yield can reach to 20.0%; nitrate contents kept stable in day 1～4 under condition of RH90%～95%, and which were decreased by 19.3%.(4) Rice washing water, salt solution, vinegar solution and detergent can reduce nitrate contents in vegetables in varying degrees. The optimal treatment decreasing nitrate contents in pakchoi was immersed for 10 minutes in 4%white vinegar solution, which can decrease nitrate contents by 23.4%. The descending sequence of various influencing factors on pakchoi was as follows:detergent types, immersion time, detergent concentration. To optimize experimental factors and levels furtherly, the descending sequence of various factors was as follows:vegetable types, interaction of detergent types and its concentration, detergent types, detergent concentration, interaction of detergent types and immersion time, immersion time. Considering the preferably treatment for decreasing nitrate contents, the treatment for pakchoi was immersed for 30 minutes in 1‰salt solution, whose reduction rate was 32.5%; the treatment for spinach was immersed for 60 minutes in 2‰salt solution, whose reduction rate was 23.7%; however, all above treatments were useless to reduce nitrate contents in white radish.(5) Scalding treatment for a short time can reduce nitrate contents in leafy vegetables just before serving. Results of scalding for 0.5minute, 1.0minute or 2.0minute showed that the effect of 0.5 minute scalding was the best to reduce nitrate contents in vegetables, and through 0.5 minute scalding treatment, nitrate contents of pakchoi and spinach were reduced by 26.9% and 14.5%, respectively. Moreover, nitrite content in scalding vegetables were increased by 6.2-11.6 times, while the amount is no more than 1mg·kg-1.(6) Peeling treatment could be helpful to reduce nitrate or nitrite contents in root vegetables, melon and fruit vegetables. It could reduce the nitrate contents by 3.0%～9.4% for white radishes,10.4%～30.7% for cucumbers. And the nitrite contents could be reduced by 3.6%～75.0% for eggplant. |
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