Fermentation process plays an important role in the biochemical properties and quality of cigar tobacco leaves (CTLs). In industry, exogenous additive (EA) was usually adopted for improving the quality of CTLs during fermentation. However, the mechanism of enhanced quality of CTLs fermented with EA was confused. Herein, the chemical compositions and microbial communities of CTLs during fermentation with EA were analyzed. The increased contents of total nitrogen and total sugar, as well as the improved consumption rate of reducing sugar in CTLs were found with the addition of EA. Besides, fermentation with EA reduced the content of total nonvolatile organic acid, especially unsaturated fatty acid. The contents of total and several representative aroma components were improved. Additionally, the increased abundance of Staphylococcus and decreased abundance of Aspergillus were detected. Combined with the changes of chemical compositions and microbial communities, it was confirmed that the carbohydrates and alcohols originated from EA promote the enrichment of Staphylococcus and accelerate biochemical reactions, such as Maillard reaction and esterification reaction, thus improving the contents and quality of aroma components in CTLs. This study demonstrated the mechanism of enhanced quality of CTLs fermented by EA, which provides more ideas for developing novel and efficient EAs.

IntroductionThe main goal of tobacco fermentation technology is to minimize the alkaloid content while improving flavor substance content.MethodsThis study revealed the microbial community structure and their metabolic functions during cigar leaf fermentation by high-throughput sequencing and correlation analysis, and evaluated the fermentation performance of functional microbes based on in vitro isolation and bioaugmentation fermentation.ResultsThe relative abundance of Staphylococcus and Aspergillus increased first but then decreased during the fermentation, and would occupy the dominant position of bacterial and fungal communities, respectively, on the 21st day. Correlation analysis predicted that Aspergillus, Staphylococcus and Filobasidium could contribute to the formation of saccharide compounds, Bacillus might have degradation effects on nitrogenous substances. In particular, Candida, as a co-occurring taxa and biomarker in the later stage of fermentation, could not only degrade nitrogenous substrates and synthesize flavor substances, but also contribute to maintaining the stability of microbial community. Moreover, based on in vitro isolation and bioaugmentation inoculation, it was found that Candida parapsilosis and Candida metapsilosis could significantly reduce the alkaloids content and increase the content of flavor components in tobacco leaves.DiscussionThis study found and validated the critical role of Candida in the fermentation of cigar tobacco leaves through high-throughput sequencing and bioaugmentation inoculation, which would help guide the development of microbial starters and directional regulation of cigar tobacco quality.

Exogenous additives applied for cigar tobacco leaves fermentation played an important role in sensory quality of cigar. In this study, effects of additives including coffee and cocoa on the quality of cigar tobacco leaves were explored. The changes of sensory quality, conventional chemical components, nonvolatile organic acids, and aroma compositions in tobacco leaves were studied. Results showed that the richness, mellowness and matureness of aroma, as well as the fluentness and sweetness of smoke in cigar were improved with the introduction of coffee or cocoa. According to chemical composition analysis, fermentation with coffee or cocoa increased the contents of alkaloids and sugar in tobacco leaves, which endowed the tobacco a relatively good performance on the sweetness and aroma richness. Besides, the decrease of citric acid, as well as the increase of saturated fatty acid and aroma components were found with additives, which was beneficial to improve the mellowness and aroma richness of cigar. It was suggested that coffee and cocoa exhibited positive effects on the chemical composition, especially increased the contents of sugar, saturated fatty acids and aromatic components, thus improving the sensory quality of tobacco leaves.

The addition of medium during industrial fermentation can improve the quality of cigar tobacco leaves after agricultural fermentation. In this study, the cigar filler tobacco “Brazilian Frogstrips YA14” was used as the test material to determine the contents of main chemical components in cigar tobacco leaves after fermentations with the additions of water (control group) and a medium (test group), and the changes in the community structure and abundances of bacteria on tobacco leaves during the fermentation process were analyzed. The results of the study were as follows: 1) During the fermentation process, the protein content of tobacco leaves fluctuated slightly, basically stabilized at 19%–20%. 2) Under the impact of the medium, the total content of main amino acids in tobacco leaves showed a downward trend, and the difference of which between the control group and the test group was the most obvious on the fourth day of fermentation. 3) The change trend of the content of petroleum ether extract in cigar leaves for the control group was not obvious, and the content of petroleum ether extract in the tobacco leaves for the test group decreased by 12.4% under the impact of the medium. 4) After fermentation, the relative content of saturated fatty acids for the control group and the test group all increased, while the relative content of unsaturated fatty acids all decreased. 5) After the addition of the medium, the diversity of bacteria on tobacco leaves changed significantly, the number of OTUs in tobacco leaves increased, and the bacterial community structure changed. This research indicates that after adding the medium to ferment cigar filler, the changes of bacterial community and dominant bacterial group on cigar tobacco leaves have impacts on the contents of chemical components in tobacco leaves, and the fermentation with the addition of medium has a positive effect on improving the quality of tobacco leaves.

The cigar market is growing rapidly in China. However, insufficient aroma value and quality, as well as confused subject fragrance were found in cigar tobacco leaves (CTLs), which has greatly restricted the development of Chinese cigar. In this study, several new and effective additives, including coffee, cocoa, ginger, cumin, and rhodiola rosea, were screened out for facilitating the fermentation process. Significant improvements on the aroma and sensory quality of CTLs were detected. The above-mentioned additives can increase the contents of total sugar, alcohols, alkenes, ketonic and acid aroma components in tobacco leaves. Besides, the content of representative aroma component, such as neophytadiene, increased by 1~2 times. Moreover, abundant new aroma components were introduced into CTLs. As a result, the performances on aroma richness, aroma and smoke characteristics, as well as aftertaste and combustion of CTLs were enhanced. The findings provide a promising strategy for enhancing sensory quality of domestic CTLs and the flourishment of Chinese cigar.