Post-harvest treatment and the accumulation of nitrite and N'-nitrosonornicotine in burley tobacco.

Concentrations (dry-weight basis) of nitrate, nitrite and N'-nitrosonornicotine (NNN) in Burley tobacco were determined during successive processing stages of experimental homogenized-leaf-cured (HLC) material, after conventional air curing and during prolonged storage ('ageing') of HLC and air-cured tobaccos. During homogenized leaf curing, less than 6 micrograms/g nitrite-N and less than 10 micrograms/g NNN were found in tobacco frozen immediately after aerobic incubation of homogenates at 40 degrees C for 0, 4, 8, 20 and 25 h. Up to 550 micrograms/g nitrite-N and 850 micrograms/g NNN occurred in tobacco incubated similarly for 20 h, then allowed to stand 1 h without aeration. Samples of two genetic Burley lines of high and low alkaloid content were similarly incubated, allowed to stand 1 h, dried and 'aged' for up to one year in partially anaerobic environments. NNN contents were positively correlated with 'at-harvest' alkaloid content, and NNN increased at each subsequent stage of processing, reaching a maximum of 1 800 micrograms/g in the high-alkaloid line after one year of 'ageing'. Small increases of NNN that reached a final concentration of 50 micrograms/g occurred in tobaccos that were air-cured, then 'aged'.