Reduction of tobacco specific nitrosamines in air-cured tobacco
Antioxidants, such as phenolics, tocopherols and carotenoids in tobacco leaves, are known to interfere with oxidation processes through chain-breaking reactions or through scavenging of free radicals. The induction or up-regulation of these and other antioxidants occur during many types of abiotic and biotic stress. Physical or chemical stresses were tested for their ability to induce an accumulation of antioxidants in harvested tobacco and for the reduction of tobacco-specific nitrosamines (TSNA) during subsequent air curing. The data indicated that root pruning or stalk incision of burley tobacco one week before harvest resulted in an increased accumulation of a-tocopherol, chlorogenic acid, and rutin by 22.2%, 54.4% and 35.4%, respectively, compared with untreated plants. Both physical wounding and chemical spraying also increased the total antioxidant capacity by 25% in both green and cured tobacco. Field experiments performed over three years showed a consistent decrease in nitrite concentration in leaves from stressed tobacco, and the reduction in TSNA was always associated with reduced levels of nitrite. Depending on the climate and curing conditions, curing resulted in significant reductions in TSNA of up to 90% in cured tobacco, as compared with control plants. Thus, the results suggested that higher endogenous antioxidants present during senescence and curing of wounding-stressed tobacco may affect the propensities of those tissues to inhibit TSNA formation by reaction with nitrite.