Heat-tolerant nitrite-degrading bacterial strains: isolation, identification, and applications in reducing nitrosamines in cigar tobacco leaves

Abstract:

[Background] Tobacco-specific nitrosamines (TSNAs) are produced by the nitrosation of tobacco alkaloids with nitrogen oxides during the processing of tobacco, especially during the modulation and fermentation stages. [Objective] To mine the microorganisms that can tolerate high-temperature fermentation of cigar tobacco leaves and reduce the accumulation of TSNAs. [Methods] We examined the high-temperature tolerance, nitrite degradation, and nitrite tolerance of the bacterial strains derived from cigar tobacco leaves that could efficiently degrade nitrite and tolerate high concentrations of nitrite at 50 ℃. A efficient strain was then selected and used for a 35-day high-temperature fermentation of cigar tobacco leaves. We determined the levels of nitrite, TSNAs, conventional chemical components, and neutral aromatic components before and after fermentation to analyze the effects of the strain on TSNAs and tobacco quality during the fermentation process. [Results] Three bacterial strains capable of degrading nitrite at 50 ℃ were isolated and identified, which were Bacillus mojavensis NY7, B. halotolerans NY8, and B. subtilis NY9. Among them, B. halotolerans NY8 exhibited the strongest nitrite-degrading capacity. The high-temperature fermentation of cigar tobacco leaves with NY8 reduced nitrite by 96.86% and TSNAs by 67.14%. Moreover, the nicotine reduction caused by the inoculation of NY8 was significantly higher than that of the control group, and the total neutral aromatic components (except neophytadiene) were slightly increased. [Conclusion] The isolated strains are suitable for high-temperature fermentation of cigar tobacco leaves and demonstrate high efficiency in degrading nitrite and reducing the accumulation of TSNAs. The findings provide inspiration for reducing the harm of cigar tobacco leaves.