Chapter 41
Accumulation of Tobacco-Specific Nitrosamines during Curing and Aging of Tobacco Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on July 22, 2018 at 16:07:10 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
H. R. Burton and L. P. Bush Department of Agronomy, University of Kentucky, Lexington, KY 40546-0091
Review of the literature on the tobacco-specific nitrosamines (TSNA) content of cured and processed tobacco has led to some conflicting conclusions. Brunnemann et al. (1) and Fischer et al. (6) reported there was a direct correlation between nitrate and TSNAs. Djordjevic et al. (5) reported no relationship between nitrate and TSNA's but there was a significant, positive correlation between secondary amine alkaloid content in cured tobacco and individual TSNA accumulation. It would seem there should be a better relationship between TSNAs and the level of nitrite in cured tobacco than either nitrate or alkaloid concentrations. This is based on the knowledge that nitrate concentration is 10 greater and alkaloid levels are 5 x 10 greater than TSNAs in cured tobacco (3). We propose that nitrite levels are rate limiting because of low levels in tobacco. Therefore, studies were initiated to determine if there was a correlation between nitrite and TSNAs in tobacco. In a study on accumulation of TSNAs during curing, Burton et al. (3) reported there was a direct relationship between nitrite and TSNAs when tobacco was cured at high relative humidity. The large increase in TSNAs and nitrite occurred between the sixteenth and nineteenth day after harvest of stalk-cut tobacco. This observed increase was documented when cured tobacco was exposed to 32°C and 90% RH over a three week interval (3). It should be noted the levels of TSNAs and nitrite were approximately 1,000 ppm in the tobacco. Because these high levels of nitrosamines and nitrite do not reflect levels found in conventionally cured tobaccos, one would not expect to observe elevated levels of nitrite and TSNAs in tobaccos cured under ambient conditions. A three year study was initiated in 1988 to determine if there was a direct correlation between nitrite and TSNAs in conventionally cured tobaccos. Three different tobacco varieties were grown and cured using cultural practices for the production of burley tobacco. A flue variety (G28) was selected because flue cured varieties contain low levels of TSNAs. A burley variety (Ky14) also was grown along with a dark variety (Ky171). TSNA values for cured burley midvein rangedfrom1ppmto 10ppm while nitrite-N values ranged from 2ppm to 140ppm. A significant correlation coefficient (r = 0.77) was obtained between nitrite and TSNA. Comparison of nitrite and NNNfromthe lamina 3
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0097-6156/94/0553-0361$08.00/0 © 1994 American Chemical Society
Loeppky and Michejda; Nitrosamines and Related N-Nitroso Compounds ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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and midrib also resulted in significant correlation coefficient. In general lamina contained the lowest levels of nitrite and NNN in comparison to levels contained in midvein tissue. When data regarding nitrite and TSNA levelsfromthe three tobacco types were combined (n = 162) after three years of study, a significant correlation coefficient (r = 0.59) was obtained which indicated nitrosamine accumulation was limited by the plant's ability to accumulate nitrite during curing. The distribution of the alkaloids and nitrite in the cured leaf also could limit TSNA accumulation. Under normal curing conditions TSNAs should accumulate when the reactants are in proximity to each other. There was no information available on the distribution of the precursors or products within the cured tobacco leaf. Recently Burton et al. (4) reported the distribution of TSNAs, individual alkaloids, nitrite, and nitrate in air-cured tobacco leaf. This study was achieved by segmenting air-cured tobacco lamina and midvein. The combined segmentsfrom20 leaves were analyzed for TSNAs, alkaloids, nitrate, and nitrite. Results of this study showed alkaloid concentration was greatest at the periphery of the lamina and lowest at the basal portion of the midvein. This profile was obtained for all secondary amine pyridine alkaloids. If alkaloids were limiting TSNA accumulation, the TSNA concentration should be greatest at the periphery of the leaf. Nitrate concentration was highest along the center portion of the midvein. If nitrate were limiting one would predict TSNA and nitrite concentration be highest along the midvein portion of the leaf. The nitrite profile was quite different from the nitrate profile in the cured leaf. Nitrite was lowest at the tip of the leaf and highest at the base of the leaf including the midvein. The tip of leaf midvein contained the lowest concentration of nitrite. If nitrite was limiting nitrosamine accumulation, the TSNA distribution should be seemlier to the nitrite distribution in the cured leaf. The distribution profiles for TSNAs were almost identical to the nitrite distribution profile. This study indicated the accumulation of TSNAs in cured lamina is dependent on the ability of the senescing leaf to produce nitrite. The origin of nitrite most likely is due to microflora reduction of nitrate to nitrite. Acknowledgments: The investigation reported in this paper was supported by the U.S. Department of Agriculture, Agricultural Research Service, under cooperative Agreement 58-6430-1-121 and is published with the approval of the Director of the Kentucky Agricultural Experiment Station (92-3-193). REFERENCES 1. Brunnemann, K.D.; Masaryk, J.; Hoffmann, D. J. Agric. Food Chem. 1983, 31, 1221-1224. 2. Burton, H.R.; Bush, L.P.; Djordjevic, M.V. J. Agric. Food Chem. 1989, 37, 1372-1377. 3. Burton, H.R.; Childs, G.H., Jr.; Andersen, R.A.; Fleming, P.D. J.Agric.Food Chem. 1989, 37, 426-430. 4. Burton, H.R.; Dye, N.K.; Bush, L.P. J. Agric. Food Chem. 1992, 40, 10501055. 5. Djordjevic, M.V.; Gay, S.L.; Bush, L.P.; Chaplin, J.F. J. Agric. Food Chem. 1989, 37, 752-756. 6. Fischer, S.; Spiegelhalder, B.; Preussmann, R. Carcinogenesis 1989, 10, 15111517. R E C E I V E D January 26,
1994
Loeppky and Michejda; Nitrosamines and Related N-Nitroso Compounds ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
