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Microbial and enzymatic changes in cigar tobacco leaves during air-curing and fermentation.

ABSTRACT: Metabolic enzyme activity and microbial composition of the air-curing and fermentation processes determine the quality of cigar tobacco leaves (CTLs). In this study, we reveal the evolution of the dominant microorganisms and microbial community structure at different stages of the air-curing and fermentation processes of CTLs. The results showed that the changes in metabolic enzymes occurred mainly during the air-curing phase, with polyphenol oxidase (PPO) being the most active at the browning phase. Pseudomonas, Bacteroides, Vibrio, Monographella, Bipolaris, and Aspergillus were the key microorganisms in the air-curing and fermentation processes. Principal coordinate analysis revealed significant separation of microbial communities between the air-curing and fermentation phases. Redundancy analysis showed that bacteria such as Proteobacteria, Firmicutes, Bacteroidota, and Acidobacteriota and fungi such as Ascomycota and Basidiomycota were correlated with enzyme activity and temperature and humidity. Bacteria mainly act in sugar metabolism, lipid metabolism, and amino acid metabolism, while fungi mainly degrade lignin, cellulose, and pectin through saprophytic action. Spearman correlation network analysis showed that Firmicutes, Proteobacteria, and Actinobacteria were the key bacterial taxa, while Dothideomycetes, Sordariomycetes, and Eurotiomycetes were the key fungal taxa. This research provides the basis for improving the quality of cigars by improving the air-curing and fermentation processes. KEY POINTS: • Changes in POD and PPO activity control the color change of CTLs at the air-curing stage. • Monographella, Aspergillus, Pseudomonas, and Vibrio play an important role in air-curing and fermentation. • Environmental temperature and humidity mainly affect the fermentation process, whereas bacteria such as Proteobacteria, Firmicutes, Bacteroidota, and Acidobacteriota and fungi such as Ascomycota and Basidiomycota are associated with enzyme activity and temperature and humidity.

SUBMITTER: Zhang Q

PROVIDER: S-EPMC10439857 | biostudies-literature | 2023 Sep

REPOSITORIES: biostudies-literature

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Microbial and enzymatic changes in cigar tobacco leaves during air-curing and fermentation.

Zhang Qing Q Kong Guanghui G Zhao Gaokun G Liu Jun J Jin Honggang H Li Zhihua Z Zhang Guanghai G Liu Tao T

Applied microbiology and biotechnology 20230717 18

Metabolic enzyme activity and microbial composition of the air-curing and fermentation processes determine the quality of cigar tobacco leaves (CTLs). In this study, we reveal the evolution of the dominant microorganisms and microbial community structure at different stages of the air-curing and fermentation processes of CTLs. The results showed that the changes in metabolic enzymes occurred mainly during the air-curing phase, with polyphenol oxidase (PPO) being the most active at the browning p ...[more]

PMID: 37458766

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Project description:BackgroundThe air-curing process of cigar tobacco leaves is typically conducted in an open environment, involving the participation of various microorganisms. However, the effect of microbial communities during air-curing process on the formation of flavor components remains unclear. Therefore, this study aims to reveal the dynamics of flavor components and microbial community changes, and explore the potential role of microbial communities in flavor formation during the cigar tobacco air-curing process.ResultsHigh-throughput sequencing analysis showed that Pantoea, Sphingomonas and Pseudomonas were the dominant bacterial genera during air-curing process, while Aspergillus was the dominant fungal genus. Subsequently, volatile flavor analysis shows that alkaloids were the most important volatile compounds in cigar leaves, followed by esters, alcohols and aldehydes. Furthermore, 38 characteristic volatile flavor compounds at different periods of air-curing were identified based on PLS-DA in different periods of air-curing. The correlation analysis between microorganisms and flavor components showed that Pantoea and Staphylococcus might promote the flavor formation from browning to post-air-curing and were positively correlated with specific flavor components like phenylacetaldehyde and acetophenone. Phoma, Mycosphaerella, Wallemia, and Cladosporium were identified as key fungal genera influencing flavor formation, as they showed positive correlations with multiple flavor components. These information enrich our understanding of the flavor formation of cigar tobacco during air curing.ConclusionsThere is a complex correlation between the microbial community and the flavor components, which may have a great influence on the flavor formation during the air-curing process of cigar leaves. Bacterial communities have higher species diversity and richness during air-curing, and have more complex correlation characteristics with volatile flavor, which may play more roles in the flavor formation. This study revealed the potential role of microbial community on flavor formation in cigar tobacco air-curing process, and provided guidance for subsequent screening of specific functional microorganisms to improve and stabilize cigar tobacco flavor.

Project description:Air-curing is the initial step in the processing of cigar tobacco leaves. However, the dynamics of microbial community and metabolic functions in different parts of tobacco leaves during this process remain largely unclear. In this study, amplicon-based high-throughput sequencing revealed that Pseudomonas (9.0 to 29.9%) and Sphingomonas (0.5 to 13.8%) were the dominant bacterial genera in the early stages of air-curing, while Pantoea (1.7-90.4%) became predominant after air-curing. Microbial community diversity analysis indicated that species richness and diversity were significantly higher during the fresh leaf and withering periods. Functional prediction based on PICRUSt2 suggested that the microbial communities in the middle leaves exhibited higher abundances of metabolic pathways related to carbohydrates and amino acids than those in the upper leaves, potentially leading to the formation of more flavor compounds. The volatile flavor compounds were detected during the air-curing process by HS-SPME-GC-MS, with alkaloids and esters being the most prominent, although their accumulation periods differed across leaf parts. Furthermore, based on PLS-DA, 17 and 38 significantly changed flavor components were identified in the upper and middle leaves, respectively. Finally, the potential relationships between characteristic microbes and flavor components were explored based on Spearman correlation coefficient. It was found that multiple bacteria such as Rhodanobacter, Gemmatimonas, and Ramlibacter present in the middle leaves exhibited significant positive correlations with multiple flavor compounds such as 3,3-dimethylacrylic acid, phenylacetone, 2,3-butanedione, and geranylacetone, potentially promoting the flavor formation of cigar tobacco leaves during air-curing process. This study provides scientific insights into the role of microorganisms during the air-curing process of cigar tobacco leaves and offers a scientific basis for screening of specific functional microorganisms to improve and stabilize cigar tobacco flavor in the future.

Project description:IntroductionMicrobiomes of cigar tobacco leaves play a pivotal role during the fermentation, and fermentation temperature is a key factor in shaping the structure and function of the microbial community. This study aimed to investigate the effects of different temperatures (30°C, 35°C, 40°C, 45°C, and 50°C) on the microbiomes of cigar tobacco leaves, providing insights into the complex interactions among temperature, microbes, and physicochemical metabolites.MethodsFirstly, the physicochemical metabolites of cigar tobacco leaves under various fermentation temperatures were detected by gas chromatography-mass spectrometry. Subsequently, the impacts of different temperatures on microbial biomass and community structure were revealed by quantitative real-time PCR and amplicon sequencing, and the biomarkers at different fermentation temperatures were identified by LEfSe analysis. Finally, the functional potential of microbes was predicted by correlation analysis.ResultsThe bacterial biomass increased initially and peaked at 8.4 × 109 copies/g at 35°C, then decreased as the temperature rose. The fungal biomass exhibited a downward trend with increasing temperature, reaching a maximum of 3.9 × 106 copies/g at 30°C. When the fermentation temperature exceeded 45°C, the growth of both bacteria and fungi was significantly restricted. Amplicon sequencing results indicated that Staphylococcus and Aspergillus genera dominated the bacterial and fungal communities, respectively. As the temperature increased, the relative abundance of Staphylococcus decreased first and then increased (46.1%-98.5%), while that of Aspergillus increased first and then decreased (34.9%-77.4%). Additionally, correlation analysis suggested that microbial communities shaped by different temperatures were responsible for the differences in physicochemical metabolites of cigar leaves. The biomarkers identified in the low-temperature fermentation group, including Staphylococcus, Stemphylium, Sampaiozyma, and Filobasidium, were likely responsible for the production of flavor metabolites, the accumulation of sugars, and the elevated ratio of potassium ions to chloride ions contents. Biomarkers in medium and high-temperature fermentation groups, such as Aspergillus, Neodymella, Acinetobacter, Pelomonas, Brevundimonas, and Alkalihalobacillus, might contribute to the degradation of nitrogen-containing substances and alkaloids.DiscussionThis study revealed the unique microbial community structure shaped at different temperatures and its potential correlation with physicochemical metabolites. These findings will help to further optimize the fermentation process of cigar tobacco leaves and develop functional microorganisms suitable for different fermentation temperatures.

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Microbial and enzymatic changes in cigar tobacco leaves during air-curing and fermentation.

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Microbial and enzymatic changes in cigar tobacco leaves during air-curing and fermentation.

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