The relationships between TSNAs and their precursors in burley tobacco from different regions and varieties

Thirty-three air-cured burley tobacco samples produced in 4 main producing areas of China as well as USA and Malawi burley samples were collected and analyzed for the contents of tobacco specific nitrosamine, alkaloids, nitrate and nitrite to investigate the relationship between TSNA and their precursors. The results showed that the TSNA contents in tobaccos from Dazhou and Binchuan were at the low levels comparable to foreign samples. Contents of NNN and total TSNAs varied greatly among samples from different areas, while the differences in NNK, NAT and NAB contents were relatively small. The conversion of nicotine leading to the increase of nornicotine was the main cause for abnormal increase of NNN and total TSNAs in tobaccos from certain areas, and with the increase of total TSNAs, the proportion of NNN increased proportionally. The contents of total TSNAs and NNN had significantly positive correlations with percent nicotine conversion and nornicotine content. Contents of NNK, NAT and NAB correlated significantly with nitrate contents, especially among samples within the same producing area, the correlation coefficient between NNK content and nitrate was much elevated. Nicotine conversion and nitrate contents were two main factors contributing to the increase and accumulation of TSNAs. Comparison among different varieties revealed that Eyan1 and Eyan3 had higher nicotine conversion level, which was the main cause for their higher TSNA contents. The purification and improvement of current cultivars for low nicotine conversion was an essential means to reduce TSNA formation. Lowering of nitrate accumulation to minimize the substrate of nitrate reduction was another important approach for TSNA reduction.