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IntroductionFermentation is a crucial process in cigar manufacturing. Exogenous addition of functional microorganisms for fortified fermentation can further improve cigar tobacco leaves fermentation quality.MethodsIn this study, five Cyberlindnera fabianii strains were isolated from cigar tobacco leaves. Their fermentation effects were assessed by analyzing flavor components and major chemical compositions.ResultsAmong these five isolates, four C. fabianii strains demonstrated the ability to enhance the overall flavor profile, particularly by increasing esters and chlorophyll degradation products. Additionally, several strains, particularly F3 and F4, also reduced total alkaloid and nitrogen content. Among these, C. fabianii strain F4 exhibited the most significant improvements. Sensory evaluation revealed that strain F4 could enhance mellowness, richness and sweetness while reducing irritation and off-flavors in fermented cigar tobacco leaves.DiscussionOur findings indicate that C. fabianii strain F4 can significantly improve the overall quality of cigar tobacco leaves through fermentation. This study provides a promising microbial fermentation agent for potential application in the cigar industry.

IntroductionThe fermentation process plays an important role in enhancing the quality of cigar tobacco leaves. Through fermentation, microbial metabolism can degrade aromatic precursors and macromolecules, which increases the content of aroma compounds and reduces irritancy of tobacco leaves.MethodsTo further enhance the fermentation effect of cigar tobacco leaves, a Rhodotorula strain (Rh3), capable of producing carotenoids and improving fermentation quality, was isolated from cigar tobacco leaves. Subsequent genetic engineering techniques introduced the carotenoid cleavage dioxygenase 1 (CCD1) gene into the isolated Rh3.ResultsThe modified Rh3 exhibits a significant increase in carotenoid degradation products compared with the original Rh3 in culture medium (from 0.29 μg/mg to 15 μg/mg). Subsequent cigar tobacco leaf fermentation experiments revealed that the modified Rh3 produced 65.9% more carotenoid degradation products compared to the control group, outperforming the original strain, which achieved a 41.4% increase. Furthermore, the modified strain preserves its ability to improve the intrinsic chemical composition of cigar tobacco leaves.DiscussionWe show here that modified Rh3 can increase the content of carotenoid degradation products, thereby enhancing the fermentation effect of cigar tobacco leaves. This study presents a beneficial exploration to improve the quality of cigar tobacco leaves for future use and offers a promising strategy for producing flavor compounds from discarded tobacco leaves.

Underground coal fires, which are widely distributed and cause serious resource waste and environmental hazards, have become a common concern of the international community. This paper aims to reveal the mechanism of coal spontaneous combustion and the expansion law of underground coal fires. A void rate model from the goaf to the ground surface and a multi-field coupling model for underground coal fires were established. Based on which, the combustion process from the beginning of oxidation to the formation of large-scale fire of the remaining coal in goaf was analyzed. Furthermore, the evolution law of underground coal fire after nitrogen injection and the influence of different nitrogen injection parameters were analyzed. The results show that the coal spontaneous combustion can be divided into three stages: slow reaction stage (stage Ⅰ), violent combustion stage (stage Ⅱ), and stable combustion stage (stage Ⅲ), and the transformation of different stages is mainly controlled by the oxidation reaction rate of coal. To obtain the optimal parameters for nitrogen injection for fire suppression, the fire extinguishing efficiency concerning nitrogen injection time, nitrogen injection amount and nitrogen injection position, as well as the distribution law of nitrogen in rock strata were analyzed. Through range analysis, it is determined that the most effective fire extinguishing occurs with the injection rate of 0.15 m3/s in stage I, and the injection position has little influence on the fire extinguishing effect. This understanding contributes to a deeper understanding of the multi-field coupling mechanism of underground coal fires and provides a guidance for extinguishing and preventing underground coal fires.

Abstract With the large-scale mining of coal resources, the huge economic losses and environmental problems caused by underground coal fires have become increasingly prominent, and the research on the status quo and response strategies of underground coal fires is of great significance to accelerate the green prevention and control of coal fires, energy conservation and emission reduction. In this paper, we summarized and sorted out the research status of underground coal fires, focused on the theoretical and technical issues such as underground coal fire combustion mechanism, multiphysics coupling effect of coal fire combustion, fire prevention and extinguishing technology for underground coal fires, and beneficial utilization technology, and described the latest research progress of the prevention and control for underground coal fire hazards. Finally, the key research problems in the field of underground coal fire hazards prevention and control were proposed in the direction of the basic theory, technology research, comprehensive management and utilization, with a view to providing ideas and solutions for the management of underground coal fires.

Coal seam mining will lead to the movement and fissures of the overlying strata, which makes a complex void condition between the mining area and the ground surface. The void condition plays a key role in the occurrence and expansion of underground coal fires. In this study, the void rate model and the coupled thermal-hydro model of the underground coal fire were constructed. The COMSOL Multiphysics was used to study the coupling law of the temperature field and gas flow field of coal seam spontaneous combustion. By setting different oxygen content and inlet gas velocity, the influence of the external environmental parameters on the expansion law of underground coal fire is analyzed. The results show that the void characteristics of the mining area and the overlying strata have an obvious influence on the expansion of underground coal fire, and there is also a two-way coupling effect of the temperature field and gas flow field. The analyses of the influencing parameters show that reducing the oxygen content or increasing the inlet gas velocity will have a certain inhibitory effect on the expansion of underground coal fires, which can reduce the risk of spontaneous combustion.