Recent work showed that 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was present in some cured tobacco and was more carcinogenic than N′-nitrosonomicotine (NNN). In the present investigation, the concentration relationships of NNK, NNN, and their probable precursors, i.e., nitrite, nitrate, and alkaloids, were determined: (a) after the growth of Ky 14 burley tobacco under different shade conditions followed by air curing; and (b) during preparation of air-cured and homogenized-leaf-cured (HLC) burley tobaccos from conventionally grown tobaccos of different alkaloid genotypes. A capillary gas chromatography-nitrogen-phosphorus detector procedure was developed and utilized for quantitative determinations of NNK and NNN.

NNK contents ranged from 0.2 to 0.5 µg/g in air-cured Ky 14 tobacco lamina from leaves grown under 0 to 65% shade (100, 65, and 35% of natural daylight). The highest NNK concentrations were from 45% shade-grown lamina from lower leaf positions on stalks. Concentrations of NNK did not correlate significantly with those of either nitrate or total alkaloids calculated over all shade treatments and stalk positions.

During HLC tobacco processing, the following significant correlations of NNK with precursor content changes were found for each of four burley alkaloid genotypes calculated over the four successive stages of processing: NNN (r = 1.0); and nitrate (r = -0.9). NNK also correlated negatively with nicotine concentration changes (r = -0.9) in the low-alkaloid and high-alkaloid isolines during processing. After a 20-h incubation period under aerobic conditions followed by a 1-h standing period without aeration, substantial increases of NNK were observed in each burley line. The increased NNK contents ranged from 9-fold for the low-alkaloid isoline to 99-fold for the nornicotine-converter line. Increases in NNK content (27 to 69%) also occurred during the air drying stage; further increases occurred during a 15-month storage period at ambient conditions. After the HLC process and prolonged storage, maximal NNK contents were observed in each tobacco genotype in the following order of increasing NNK content: Ky 14 cultivar, 79 µg/g; low-alkaloid line, 80 µg/g; nomicotine converter line, 102 µg/g; and high-alkaloid line, 177 µg/g. At the beginning of a controlled environmental storage period used for high-alkaloid and low-alkaloid isoline air-cured and HLC tobaccos, NNK contents correlated with nitrite (r = 1.0) and nitrate (r = -0.9) calculated over the two curing regimens. Increased NNK contents were observed in HLC high-alkaloid line tobacco but not in the air-cured high-alkaloid line after 52 weeks of storage at 20°C and 12% moisture.

NNK accumulation varied among tobacco alkaloid genotypes and occurred mainly during the following HLC processing steps: standing period following incubation; forced-air drying and prolonged storage (“aging”) for HLC tobaccos. It seems probable that low levels of NNK and NNN in burley tobacco could be achieved by growth of a low-alkaloid genotype and use of postharvest treatment procedures that minimize nitrite formation and nitrate and alkaloid conversion (disappearance).

1

This investigation is in connection with a project at the Kentucky Agricultural Experimental Station, and the results are published as KAES Journal Article 85-3-10-55. Part of the work was presented at the 75th Annual Meeting of the American Association for Cancer Research, May 9 to 12, 1984, Toronto, Ontario, Canada (1).

This content is only available via PDF.