Biochemical Components Associated With Microbial Community Shift During the Pile-Fermentation of Primary Dark Tea

Comprehensive Analysis of Bacterial Community Structure and Diversity in Sichuan Dark Tea (Camellia sinensis)

Bacteria and fungi present during pile-fermentation of Sichuan dark tea play a key role in the development of its aesthetic properties, such as color, taste, and fragrance. In our previous study, high-throughput sequencing of dark tea during fermentation revealed Aspergillus was abundant, but scarce knowledge is available about bacterial communities during pile-fermentation. In this study, we rigorously explored bacterial diversity in Sichuan dark tea at each specific stage of piling. Analysis of cluster data revealed 2,948 operational taxonomic units, which were divided into 42 phyla, 98 classes, 247 orders, 461 families, 1,052 genera, and 1,888 species. Certain members of the family Enterobacteriaceae were dominant at early stages of fermentation YC, W1, and W2; Pseudomonas at middle stage W3; and the highest bacterial diversity was observed at the final quality-determining stage W4. Noticeably, probiotics, such as Bacillus, Lactobacillus, Bifidobacterium, and Saccharopolyspora were also significantly higher at the quality-determining stage W4. Our findings might help in precise bacterial inoculation for probiotic food production by increasing the health benefits of Sichuan dark tea. This research also falls under the umbrella of the "Establish Good Health and Well-Being" Sustainable Development Goals of the United Nations Organization.

Analysis of the Fungal Diversity and Community Structure in Sichuan Dark Tea During Pile-Fermentation

The fungi present during pile-fermentation of Sichuan dark tea play a pivotal role in the development of its aroma and physical characteristics. Samples of tea leaves were collected on days 0 (YC-raw material), 8 (W1-first turn), 16 (W2-second turn), 24 (W3-third turn), and 32 (W4-out of pile) during pile-fermentation. High-throughput sequencing revealed seven phyla, 22 classes, 41 orders, 85 families, 128 genera, and 184 species of fungi. During fermentation, the fungal diversity index declined from the W1 to W3 stages and then increased exponentially at the W4 stage. A bar plot and heatmap revealed that Aspergillus, Thermomyces, Candida, Debaryomyces, Rasamsonia, Rhizomucor, and Thermoascus were abundant during piling, of which Aspergillus was the most abundant. Cluster analysis revealed that the W4 stage of fermentation is critical for fungal growth, diversity, and the community structure in Sichuan dark tea. This study revealed the role of fungi during pile-fermentation in the development of the essence and physical characteristics of Sichuan dark tea. This study comes under one of the Sustainable Development Goals of United Nations Organization (UNO) to "Establish Good Health and Well-Being."

Black Tea Quality is Highly Affected during Processing by its Leaf Surface Microbiome

Microbiomes can greatly affect the quality of fermented food and beverages, including tea. In this study, microbial populations were characterized during black and green tea manufacturing, revealing that tea processing steps can drive both the bacterial and fungal community structure. Tea leaves were found to mostly harbor Proteobacteria, Bacteriodetes, Firmicutes, and Actinobacteria among bacteria and Ascomycetes among fungi. During processing, tea microbial populations changed especially between sterilized and unsterilized samples. The surface sterilization of fresh leaves before processing can remove many microbes, especially the bacteria of the genera Sphingomonas and Methylobacteria, indicating that these are mostly phylloplane microbes on tea leaves. The surface sterilization removed most fungi, except the Debaryomyces. We also observed a fluctuation in the content of several tea quality-related metabolites during processing. Caffeine and theanine were found in the same quantities in green tea with or without leaf surface sterilization. However, the sterilization process dramatically decreased the content of total catechins and theanine in black tea, indicating that microbes on the surface of tea leaf may be involved in maintaining the formation of these important metabolites during black tea processing.

Effects of Polyphenols in Tea (Camellia sinensis sp.) on the Modulation of Gut Microbiota in Human Trials and Animal Studies

A diet high in polyphenols is associated with a diversified gut microbiome. Tea is the second most consumed beverage in the world, after water. The health benefits of tea might be attributed to the presence of polyphenol compounds such as flavonoids (e.g., catechins and epicatechins), theaflavins, and tannins. Although many studies have been conducted on tea, little is known of its effects on the trillions of gut microbiota. Hence, this review aimed to systematically study the effect of tea polyphenols on the stimulation or suppression of gut microbiota in humans and animals. It was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol. Articles were retrieved from PubMed and Scopus databases, and data were extracted from 6 human trials and 15 animal studies. Overall, large variations were observed in terms of microbiota composition between humans and animals. A more consistent pattern of diversified microbiota was observed in animal studies. Tea alleviated the gut microbiota imbalance caused by high-fat diet-induced obesity, diabetes, and ultraviolet-induced damage. The overall changes in microbiota composition measured by beta diversity analysis showed that tea had shifted the microbiota from the pattern seen in animals that received tea-free intervention. In humans, a prebiotic-like effect was observed toward the gut microbiota, but these results appeared in lower-quality studies. The beta diversity in human microbiota remains intact despite tea intervention; supplementation with different teas affects different types of bacterial taxa in the gut. These studies suggest that tea polyphenols may have a prebiotic effect in disease-induced animals and in a limited number of human interventions. Further intervention is needed to identify the mechanisms of action underlying the effects of tea on gut microbiota.

Metagenomics unveils microbial roles involved in metabolic network of flavor development in medium-temperature daqu starter

As a widely used Asian starter culture, the quality of daqu can significantly affect the organoleptic characteristics of the final products, yet the microbial metabolic network involved in flavor development remains unclear. This study aims to investigate that network based on the dynamics of physicochemical properties, microbial community, and volatile compounds in medium-temperature daqu (MT-daqu) during spontaneous fermentation. Analyses using the metagenomic data set facilitated the gene repertoire overview of this ecosystem, indicating that Lactobacillales (mainly Weissella, Lactobacillus, and Pediococcus), Mucorales (mainly Lichtheimia), and Eurotiales (mainly Aspergillus, Rasamsonia and Byssochlamys) were the potential predominant populations successively responsible for the production of lytic enzymes and flavor precursors/compounds in MT-daqu. Flavor-relevant pathways were found to exist in multiple species, but only bacteria showed the potential to participate in butane-2,3-diol (e.g. Weissella, Lactobacillus, and Staphylococcus) and butanoate (Thermoactinomyces) metabolism, and only fungi were potentially involved in biosynthesis of guaiacol (Byssochlamys) and 4-vinylguaiacol (Aspergillus). Furthermore, a combined analysis revealed that the acidic thermal environment present in early phases was mainly due to the catabolic activities of Lactobacillales and Lichtheimia, which could contribute to the effective self-domestication of microbiota. The study helps elucidate the different metabolic roles of microorganisms and disclose the formation mechanism of daqu's partial functions, namely providing various aromatic substances/precursors and enzymes.

Purification, characterization, and bioactivity of Liupao tea polysaccharides before and after fermentation

The raw tea polysaccharides (RLTPS) and the aged tea polysaccharides (ALTPS) from raw and aged Liupao tea were extracted and purified to afford five refined fractions. Component analysis revealed that the crude polysaccharide content from raw Liupao tea increased from 1.83 ± 0.09 g / 100 g to 3.44 ± 0.28 g / 100 g and the molecular weight decreased after fermentation. Structural analysis indicated that the molar ratio of rhamnose, galactose, and galacturonic acid increased in refined ALTPS. All the refined polysaccharides were glycoprotein complexes contained pyranose ring structure. The thermal stability and asymmetry of refined ALTPS were stronger than refined RLTPS. For activities in vitro, ALTPS had better anticoagulant activity and bile acid binding capacity than RLTPS. Although the activities of the refined ALTPS fractions were lower than ALTPS, they were still higher than the refined RLTPS. Fermentation plays an important role in improving the quality and biological activity of dark tea.

Therapeutic implications of functional tea ingredients for ameliorating inflammatory bowel disease: a focused review

Inflammatory bowel disease (IBD) is a chronic gastro-intestinal disorders of unknown etiology. There are several drugs approved for treating IBD patients with active disease, including first-line use of aminosalicylates, and secondary choices of immunomodulators and other therapies. These medications might manage disease symptoms, but have also shown significant side-effects in IBD patients. Tea is the second largest beverage in the world and its main active ingredients including tea polyphenols, polysaccharides and tea pigments have been shown promising anti-inflammatory and antioxidant properties. In this review, we summarize the influence of different tea varieties including green tea, black tea and dark tea as potential nutritional therapy for preventing and treating IBD, and discuss the mechanisms of tea ingredients involved in the regulation of oxidative stress, inflammation, signaling pathways, and gut microbiota that could benefit for IBD disease management. Our observation directs further basic and clinical investigations on tea polyphenols and their derivatives as novel IBD therapeutic agents.

A Bottom-Up Approach To Develop a Synthetic Microbial Community Model: Application for Efficient Reduced-Salt Broad Bean Paste Fermentation

Humans have used high salinity for the production of bean-based fermented foods over thousands of years. Although high salinity can inhibit the growth of harmful microbes and select functional microbiota in an open environment, it also affects fermentation efficiency of bean-based fermented foods and has a negative impact on people's health. Therefore, it is imperative to develop novel defined starter cultures for reduced-salt fermentation in a sterile environment. Here, we explored the microbial assembly and function in the fermentation of traditional Chinese broad bean paste with 12% salinity. The results revealed that the salinity and microbial interactions together drove the dynamic of community and pointed out that five dominant genera (Staphylococcus, Bacillus, Weissella, Aspergillus, and Zygosaccharomyces) may play different key roles in different fermentation stages. Then, core species were isolated from broad bean paste, and their salinity tolerance, interactions, and metabolic characteristics were evaluated. The results provided an opportunity to validate in situ predictions through in vitro dissection of microbial assembly and function. Last, we reconstructed the synthetic microbial community with five strains (Aspergillus oryzae, Bacillus subtilis, Staphylococcus gallinarum, Weissella confusa, and Zygosaccharomyces rouxii) under different salinities and realized efficient fermentation of broad bean paste for 6 weeks in a sterile environment with 6% salinity. In general, this work provided a bottom-up approach for the development of a simplified microbial community model with desired functions to improve the fermentation efficiency of bean-based fermented foods by deconstructing and reconstructing the microbial structure and function.IMPORTANCE Humans have mastered high-salinity fermentation techniques for bean-based fermented product preparation over thousands of years. High salinity was used to select the functional microbiota and conducted food fermentation production with unique flavor. Although a high-salinity environment is beneficial for suppressing harmful microbes in the open fermentation environment, the fermentation efficiency of functional microbes is partially inhibited. Therefore, application of defined starter cultures for reduced-salt fermentation in a sterile environment is an alternative approach to improve the fermentation efficiency of bean-based fermented foods and guide the transformation of traditional industry. However, the assembly and function of self-organized microbiota in an open fermentation environment are still unclear. This study provides a comprehensive understanding of microbial function and the mechanism of community succession in a high-salinity environment during the fermentation of broad bean paste so as to reconstruct the microbial community and realize efficient fermentation of broad bean paste in a sterile environment.

Determination of six groups of mycotoxins in Chinese dark tea and the associated risk assessment

Chinese dark tea is widely enjoyed for its multiple health-promoting effects and pleasant taste. However, its production involves fermentation by microbiota in raw tea, some of which are filamentous fungi and thus potential mycotoxin producers. Accordingly, whether mycotoxins pose health risk on dark tea consumption has become a public concern. In this study, a cleaning method of multi-functional column (MFC) and immunoaffinity column (IAC) in tandem combined to HPLC detection was developed and validated for determining ten mycotoxins of six groups (i.e., aflatoxins of B₁, B₂, G₁ and G₂, ochratoxin A, zearalenone, deoxynivalenol, fumonisins of B₁, B₂, and T-2) in dark teas. The interferences from secondary metabolites were effectively reduced, and the sensitivities and recoveries of the method were qualified for tea matrices. Six groups mycotoxins were determined in 108 samples representing the major Chinese dark teas by using the new method. Subsequently, the dietary exposure and health risks were evaluated for different age and gender groups in Kunming and Pu'er in China and Ulan Bator in Mongolia. The occurrence of zearalenone was 4.63% and that of ochratoxin A was 1.85%, with the other four groups mycotoxins were below the limits of quantification. The hazard index values for the five groups' non-carcinogenic mycotoxins were far below 1.0. The deterministic risk assessment indicated no non-carcinogenic risks for dark tea consumption in the three areas. Probabilistic estimation showed that the maximum value of 95th percentile carcinogenic risk value for the aflatoxins was 2.12 × 10^-8, which is far below the acceptable carcinogenic risk level (10^-6). Hereby, six groups mycotoxins in Chinese dark tea showed no observed risk concern to consumers.

Evaluation of carbohydrates and quality parameters in six types of commercial teas by targeted statistical analysis

The content of low molecular weight carbohydrates (LMWC) of six types of tea produced from the leaves of Camellia sinensis were analyzed by hydrophilic interaction chromatography (HILIC) coupled to mass spectrometry. Quantities of sucrose, glucose, fructose, myo-inositol, maltose, mannitol, raffinose, galactinol, and stachyose were determined in samples of white, yellow, green, black, oolong, and dark tea. Sucrose was the most abundant carbohydrate in all types of tea. The concentration of all measured carbohydrates except mannitol was lowest in dark tea samples. Correlation analyses using quantitative data of LMWCs, antioxidant activity, and color parameters were performed on black tea samples to evaluate the interaction of different quality parameters. Carbohydrates depletion was observed during tea processing with formation of Amadori compounds with theanine.

Health Functions and Related Molecular Mechanisms of Tea Components: An Update Review

Tea is widely consumed all over the world. Generally, tea is divided into six categories: White, green, yellow, oolong, black, and dark teas, based on the fermentation degree. Tea contains abundant phytochemicals, such as polyphenols, pigments, polysaccharides, alkaloids, free amino acids, and saponins. However, the bioavailability of tea phytochemicals is relatively low. Thus, some novel technologies like nanotechnology have been developed to improve the bioavailability of tea bioactive components and consequently enhance the bioactivity. So far, many studies have demonstrated that tea shows various health functions, such as antioxidant, anti-inflammatory, immuno-regulatory, anticancer, cardiovascular-protective, anti-diabetic, anti-obesity, and hepato-protective effects. Moreover, it is also considered that drinking tea is safe to humans, since reports about the severe adverse effects of tea consumption are rare. In order to provide a better understanding of tea and its health potential, this review summarizes and discusses recent literature on the bioactive components, bioavailability, health functions, and safety issues of tea, with special attention paid to the related molecular mechanisms of tea health functions.

Simultaneous Determination of Four Aflatoxins in Dark Tea by Multifunctional Purification Column and Immunoaffinity Column Coupled to Liquid Chromatography Tandem Mass Spectrometry

Dry tea matrix contains an abundance of caffeine and polyphenols which are different from the food matrix (e.g., protein, lipid, and carbohydrates), and only a few studies have tried aflatoxins determination with tea samples. Here, a specific, accurate, and sensitive method was developed and validated for the simultaneous determination of aflatoxin B1, B2, G1, and G2 in dark teas. Aflatoxins were extracted by acetonitrile/water, press-filtered, and cleaned by multifunctional purification column (MFC) and immunoaffinity column (IAC) in tandem. The cleaned extract was analyzed by liquid chromatography tandem mass spectrometry. The matrix interference was effectively reduced by MFC-IAC cleaning method. Recoveries at the spiking concentrations of 5-60 μg/kg ranged from 77.5 to 93%, with relative standard deviations <11.0%. The correlation coefficients of aflatoxins standard were >0.998. The limits of detection were 0.024-0.21 μg/kg and the limits of quantification were 0.08-0.74 μg/kg. The intra- and interday accuracy ranged from 74 to 87%, and the intra- and interday precisions ranged from 0.4 to 3.1%. After the method validation, the aflatoxins contaminations in 100 collected dark teas were detected, and the results were compared with those of other methods.

Mycotoxin Contamination of Beverages Obtained from Tropical Crops

This review is mainly centered on beverages obtained from tropical crops, including tea, nut milk, coffee, cocoa, and those prepared from fruits. After considering the epidemiological data found on the matrices above, the focus was given to recent methodological approaches to assess the most relevant mycotoxins. Aspects such as singularities among the mycotoxin and the beverage in which their were found, and the economic effects and repercussions that the mycotoxin-tainted ingredients have on the beverage industry were pointed out. Finally, the burden of their consumption through beverages, including risk and health effects on humans, was addressed as well.