Effect Of Nitrate Nitrogen Level In Tobacco Leaves And Nitrate Scavenger On TSNA Formation During High Temperature Storage

In order to investigate the effect of nitrate nitrogen content on TSNA formation during high temperature and reveal the mechanism of TSNA formation in stored tobacco leaves,several experiments were conducted.Different concentration of nitrate was applied in tobacco growing season.Field experiment and pot experiment was conducted with different ratio of nitrate-N to ammonium-N applied in tobacco growing season.Tobacco samples from different tobacco fields with different yields and samples from lamina and midrib of both burley and flue-cured tobacco were also collected.All the samples had different levels of nitrate nitrogen content.Lab experiment was conducted in a temperature-controlled chamber at 45℃ and 10℃ for 15 d.Nitrate nitrogen and TSNA contents of all samples were determined.Effect of different nitrogen forms on quality of tobacco was also studied.In order to screen the substances which inhibit TSNA formation,effect of oxidants and antioxidants on TSNA formation in burley tobacco stored at high temperature was investigated.Ozone was employed as the oxidant while Vitamin C(VC),vitamin E(VE),caffeic acid,green tea,ginger juice and kiwi fruit juice were selected as antioxidants to treat burley tobacco leaves before high temperature storage in order to test their promoting effect and inhibitory effect on the formation of TSNAs.Results indicated that nitrate nitrogen content increased with the increment of yield and the amount of nitrogen fertilizer.Content of nitrate nitrogen and TSNA had a low correlation in newly cured tobacco.However,after high temperature storage for 15 d,the correlation significantly increased.Nitrate nitrogen content and TSNA increment during high temperature storage showed a significant positive correlation.Results of pot experiment with different nitrogen forms showed that nitrate nitrogen contents of burley tobacco increased with the increment of the ratio of nitrate-N to ammonium-N.Contents of 4 types of TSNAs and total contents of TSNAs after curing also significantly increased with the increase of the ratio of nitrate-N to ammonium-N.In the process of air-curing,nitrate nitrogen contents significantly increased.After 45℃ storage for 15 d,the contents of 4 types of TSNAs and total contents of TSNAs were all significantly higher than that stored at low temperature.The net increase of TSNA contents also increased with the ratio of nitrate-N to ammonium-N.In the process of maturing and curing of flue-cured tobacco,nitrate nitrogen contents decreased.Flue-cured tobacco leaves contained low contents of nitrate nitrogen after curing.Nitrate nitrogen contents and TSNA contents before and after high temperature storage in flue-cured tobacco had no relationship with the ratio of nitrate-N to ammonium-N,while the TSNA level was the lowest under the treatment with the nitrate-N to ammonium-N ratio of 50 to 50 for middle leaves and under the treatment of 100% nitrate-N for upper leaves.With the increase of ammonium-N to nitrate-N ratio,the contents of nicotine,total nitrogen and protein of burley tobacco increased significantly.Chemical composition of flue-cured tobacco showed no relationship with nitrogen source,but the flue-cured leaves under treatment of nitrate-N to ammonium-N ratio of 50:50 had the highest sugar content and well-balanced chemical composition.Results of field experiment with different nitrogen forms showed that the nitrate nitrogen content in burley tobacco leaves and flue-cured tobacco leaves both significantly increased with the increase of the ratio of nitrate-N to ammonium-N.The nitrate nitrogen content in burley tobacco leaves was dozens to hundreds of times as much as that of flue-cured tobacco leaves.After stored at 10℃ for 15 d,the contents of 4 types of TSNAs and total contents of TSNAs in burley tobacco leaves and flue-cured tobacco leaves increased with the increase of the ratio of nitrate-N to ammonium-N.After stored at 45℃ for 15 d,the contents of 4 types of TSNAs and total contents of TSNAs significantly increased than that of CK.The net increase of TSNA contents increased with the ratio of nitrate-N to ammonium-N.There was a significant positive correlation between the nitrate nitrogen content and net increase of total TSNA content.The research on the economic characters and quality of flue-cured tobacco showed that the treatment with the nitrate-N to ammonium-N ratio of 50 to 50 had high economic benefit and the chemical components were more harmonious,and the aroma was enough,and the sensory quality was better.Nitrate nitrogen content in midrib was much higher than that in lamina in both burley and flue-cured tobacco.After high temperature storage for 15 d,TSNAs increment in midrib was significantly higher than that in lamina.The experiment of oxidants and antioxidants showed that the TSNA contents in burley tobacco leaves significantly increased after the treatment,and the promoting effect was significantly enhanced with the duration of ozone treatment.Total TSNA contents in air-cured burley tobacco leaves after the oxidant treatment for12h/d for 15 days was 6.83 times higher than that without ozone treatment.The difference in total TSNA contents between the two groups reached extremely significant level.Among the selected antioxidants,3% VC solution presented the most inhibitory effect on TSNAs formation in burley tobacco during high temperature storage.Further experiment was set up to investigate the effect of VC concentration on TSNAs formation and the the results showed that the inhibitory effect in samples treated with of 3% VC solution was better than that treated with 1% VC solution.Therefore,reduction of leaf nitrate content through agronomic measures is effective in reducing TSNA formation during storage.