Canadian tobacco was flue-cured using two different heating systems: direct-fired in which the exhaust gases were in contact with the tobacco and indirect in which only hot air, via a heat exchanger, contacted the tobacco. The concentrations of tobacco-specific nitrosamines (TSNAs) in tobacco cured by indirect heating did not increase during curing and were in the range 0.25-0.35 ppm. There were no changes in TSNA concentrations (range 0.13-0.3 ppm) in tobacco cured by direct firing during the first six days (0-144 h) of curing. However between 168 and 264 h, significant increases in TSNAs occurred (up to 1.91 ppm). TSNA concentrations in leaves at the bottom of the plant were significantly higher than in those found at higher plant position. There were no significant differences in TSNA concentrations in tobacco cured on different farms. The TSNA concentrations in tobacco cured by indirect heat were 87% ± 5% lower than in tobacco cured by direct heat. Subsequent processing of tobacco did not change the relative concentrations of TSNAs.
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