Microbial bioconversion of the chemical components in dark tea

Formation of aroma characteristics driven by microorganisms during long-term storage of Liubao tea

Liubao tea (LBT) with longer storage year is believed to have better sensory quality. The aroma characteristics and fungal community succession during the storage process of LBT were studied using LBT stored for 2-15 years as materials. The results showed that the aroma characteristics of LBT showed significant changes in 3 stages. After 10 years of storage, the sensory quality of LBT was notably improved, with herbal aroma beginning to emerge and a distinctly woody aroma. In addition, fungi were involved in the transformation of substances to affect the aroma quality during the storage of LBT. Aspergillus and Penicillium may help reduce musty and green odors and enhancing woody and herbal odors based on correlation analysis. This study provided useful information on the key aroma compounds and core functional microorganisms that drive the aroma characteristics formation of LBT during storage.

Enhancing the quality of dark tea through fermentation with Aspergillus niger: Unveiling aroma and taste characteristics

Amidst the increasing demand for premium dark tea, the utilization of Aspergillus niger-inoculated fermentation has emerged as a potential solution to address the challenges associated with extended processing cycles and inconsistent quality. This study comprehensively investigated the efficacy and mechanisms of A. niger PW-2 inoculation in enhancing dark tea quality compared to spontaneous fermentation, using metabolomics, electronic tongue, molecular docking, and high-throughput sequencing. A. niger PW-2 shaped the fungal community within 7 days, degrading terpene glycosides and lactones while generating terpenoids and unsaturated fatty acids, which enriched the floral aroma of PW-2-inoculated fermentation dark tea (AF). Flavonoid degradation and reduced theaflavins/thearubigins levels in AF decreased astringency, while increased bitter dipeptides and isoflavonoids enhanced bitterness, and the accumulation of umami dipeptides and theabrownins improved umami taste perception of AF. Molecular docking identified key compounds responsible for astringency (kaempferol glycosides), bitterness (6″-caffeoylisoorientin, kaempferol 4'-glucoside 7-rhamnoside, dihydrodaidzein 7-O-glucuronide), and umami (3-O-p-trans-coumaroylalphitolic acid, dihydrodaidzein 7-O-glucuronide, 1-methoxyphaseollidin). Overall, A. niger PW-2 inoculation accelerates fermentation process and enhances flavor characteristics of dark tea, offering a promising approach for high-quality dark tea production.

Characterizing and decoding the dynamic alterations of volatile organic compounds and non-volatile metabolites of dark tea by solid-state fermentation with Penicillium polonicum based on GC-MS, GC-IMS, HPLC, E-nose and E-tongue

Penicillium species is a kind of core fungus involved in Fu brick tea (FBT) production. However, its specific effects on shaping the distinct flavor characteristics and non-volatiles of FBT remain unclear. In this study, Penicillium polonicum, isolated from FBT, was inoculated into primary dark tea for pure-culture fermentation, and investigated its effects on the volatile profile and non-volatile metabolites of dark tea. During fermentation, P. polonicum produced various hydrolytic enzymes, including β-glucosidase, polyphenol oxidase, peroxidase, and tannase, which greatly altered the non-volatile and volatile metabolites of dark tea. GC-MS and GC-IMS identified a total of 185 volatile organic compounds (VOCs), with alcohols (38), ketones (39), aldehydes (33) and hydrocarbons (19) being the most abundant. The changes in VOCs can be divided into three distinct stages. Key aroma compounds, such as (E)-β-Ionoine, (E)-β-damascenone and linalool were prominent in the early stages, while 2-methoxy-3-sec-butyl pyrazine, 2-isopropyl-3-methoxypyrazine, 3-isobutyl-2-methoxypyrazine, and linalool were prominent in the middle and late stages. The formation pathways of key VOCs were primarily involved in amino acids degradation, oxidative degradation of fatty acids, and glycosides degradation. After fermentation with P. polonicum, significant changes were observed in the constituents of catechins, free amino acids, and alkaloids in tea, resulting in an advance while decreased the astringency and bitterness of tea infusion. This research provides novel insight for of the formation of VOCs and non-volatile metabolites of dark tea by P. polonicum, offering important guidance for utilizing P. polonicum as a starter culture to stabilize and enhancing the quality of FBT during production.

Theabrownin: The 'rich hue' of Chinese dark tea, its extraction, and role in regulating inflammation and immune response

Theabrownin (TB) is one of the most representative bioactive components in Chinese dark tea, often referred to as the "gold in dark tea." The complex macromolecular structure of TB is influenced by its source (tea materials), extraction, separation, and purification methods, which affect its final structure and bioactivity. In recent years, research on TB has surged, becoming a hotspot in the field of tea functional components and health research. Extensive studies on its health benefits indicate that TB is a crucial active ingredient in dark tea with substantial potential for application in food, health care, industry, and medical fields. This review summarizes the formation of TB during dark tea manufacturing, especially the "piling" stage, extraction methods, various purification techniques, and the physicochemical properties of TB. Additionally, it comprehensively reviews recent research on TB's role in typical inflammation and immune imbalance-induced diseases such as colitis, atherosclerosis, non-alcoholic fatty liver disease, and innate immune diseases. The review concludes with a comparative summary of the biological activities of TB from the five major types of Chinese dark tea in terms of anti-inflammatory and immune regulatory effects.

Investigation of the classification criteria and flavor compounds in diversified commercially ripened Pu-erh teas

Commercially ripened Pu-erh teas (CRPTs) exhibit a complex flavor profile that poses challenges to standardized production. This study combines traditional sensory evaluation with electronic tongue technology to assess the overall flavor and taste attributes of CRPTs both qualitatively and quantitatively. Multivariate statistical techniques, including Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), and Partial Least Squares Discriminant Analysis (PLS-DA), were used to classify the samples into four categories: Heavy and Thick (HT_CRPT), Heavy and Mellow (HM_CRPT), Mellow and Thick (MT_CRPT), and Mellow and Light (ML_CRPT). HT_CRPT exhibits the highest richness, HM_CRPT demonstrates the greatest astringency and aftertaste-A with the least sweetness (p < 0.05), MT_CRPT presents the most umami and the least richness, while ML_CRPT has the lowest levels of astringency, umami, and bitterness (p < 0.05). CRPTs vary in liquid color from brownish-red to reddish-brown, with HM_CRPT exhibiting the darkest hue, characterized by L* and a* values of 56.15 ± 2.56 and 30.93 ± 1.85, respectively. The principal chemical components of CRPTs encompass theabrownins, phenylpropanoids, polyketides, lipids, and lipid-like molecules. A total of 282 metabolites, including (-)-Epigallocatechin 3,4'-di-gallate, flavonol 3-O-D-glucoside, and isorhamnetin 4'-O-glucuronide significantly influence the flavor of CRPTs (VIP > 1 and p < 0.05). 24 and 35 components underlie liquid color and taste, respectively, with taste compounds interacting with taste receptors primarily through van der Waals forces and hydrogen bonding. A flavor wheel was developed to illustrate in detail the classification criteria and flavor compounds of various CRPTs. The findings establish a scientific foundation for the development of a standardized evaluation system for CRPTs and the creation of a diverse range of products.

Digestive characteristics of Tibetan tea polyphenols and polysaccharides in vitro and their effects on gut microbiota

Tibetan tea contains highly valuable bioactive components like polyphenols and polysaccharides, which can regulate gut microbiota and promote bodily health. This study systematically investigated the gastrointestinal digestion and colonic fermentation behavior of Tibetan tea polyphenols (TPP), polysaccharides (TPS), and their polyphenol-polysaccharide complex (TC). TPP, TPS, and TC demonstrated minimal changes in physicochemical and structural characteristics after gastrointestinal digestion. Following 24 h of fecal fermentation, all components significantly degraded and altered microbial composition (pH decreased to 6.44, 5.76, and 6.14, respectively), promoting dominant flora such as Phascolarctobacterium and Lachnoclostridium. Differentially, TPS and TC demonstrated stronger promotion of dominant Bifidobacterium, Faecalibacterium, and Collinsella, whereas TPP preferentially enriched Megasphaera and Butyricicoccus. Additionally, fermentation markedly increased the concentration of short-chain fatty acids (SCFAs), with TPS yielding the highest total SCFAs (17.29 ± 0.50 mM), particularly acetic and propionic acids. Overall, Tibetan tea polyphenols and polysaccharides may serve as potential prebiotics to improve intestinal health.

Matairesinol discovered as a key active ingredient in Chinese dark tea protects against high-fat induced endothelial injury via activating AMPK phosphorylation

ETHNOPHARMACOLOGICAL RELEVANCE

As a traditional health beverage in China, Dark Tea (DT) have been proved to effectively mitigate vascular lesions induced by hyperlipidemia. However, key active ingredient of DT and the potential pharmacological mechanism protecting vascular endothelium is still unclear.

AIM OF THE STUDY

This study aimed to investigate the key active ingredient in DT and reveal underlying mechanism responsible for its protective effect on vascular endothelium.

MATERIALS AND METHODS

The protective effect of DT on vascular endothelium was evaluated using a high-fat diet-induced zebrafish model. The chemical ingredients of DT were analyzed by ultra-high performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UHPLC-Q/TOF-MS), and the active ingredients were identified using a multidimensional molecular data mining approach. Molecular biology experiments were used to explore the underlying mechanisms of DT and its active components.

RESULTS

The results showed that DT could significantly prevent the deposition of circulatory lipids on the vascular wall, inhibit inflammatory cell aggregation, and reduce microvascular hyperplasia in zebrafish models. An integrated multi-dimensional data mining technique was successfully employed to identify a key active lignan in DT, matairesinol. Furthermore, DT and matairesinol significantly protected endothelial cells by activating AMPK phosphorylation, thereby inhibiting downstream HMGCR protein expression and promoting PPARγ phosphorylation.

CONCLUSIONS

Matairesinol has been characterized as a key active ingredient in DT. It protects against high-fat-induced vascular endothelial damage by activating AMPK and downstream signaling pathways. These findings offer new insights into the therapeutic potential of DT as a daily dietary supplement for maintaining vascular health.

Impact of solid-state fermentation inoculated with Eurotium cristatum on the main composition and flavor of three kinds of Pu-erh tea

This study aims to address the problems of strong bitterness, astringency, and inferior taste in Pu'er tea made from young tea trees. First, four strains of Eurotium cristatum were isolated and screened by the static suspension isolation method using tea infusion as the culture medium and identified through morphological and molecular analysis. One of the strains was selected for the solid - state fermentation of raw Pu'er tea, Pu'er black tea, and Pu'er green tea. The fermentation conditions were optimized via response - surface experimental design. The results showed that the optimized fermentation time, temperature, and relative humidity for the three types of tea were 10 days, 30 °C, 45 %; 5 days, 30 °C, 40 %; and 10 days, 35 °C, 40 % respectively. Sensory evaluation indicated that after fermentation, the color of the tea leaves and tea soup deepened. And the freshness of raw Pu'er tea and green Pu'er tea decreased, while a subtle moldy aroma aroma was introduced after fermentation. The astringency and bitterness were effectively reduced. Chemical analysis revealed that, except for the stable caffeine level, the levels of components such as tea polyphenols and catechins changed significantly. Correlation analysis demonstrated a strong correlation between the color, aroma, and taste of the tea and the contents of various chemical components. GC - MS analysis identified 370 volatile compounds, 262 of which showed differences before and after fermentation. In conclusion, solid - state fermentation with E.cristatum can affect the chemical composition of the three types of tea, improve their taste and flavor, and offer a new approach for enhancing the quality of tea from young tea trees.

A Comprehensive Understanding of Camellia sinensis Tea Metabolome: From Tea Plants to Processed Teas

Tea (Camellia sinensis) is one of the most popular nonalcoholic beverages in the world, second only to water. Six main types of teas are produced globally: green, white, black, oolong, yellow, and Pu-erh. Each type has a distinctive taste, quality, and cultural significance. The health-promoting effects of tea are attributed to the complex metabolite compositions present in tea leaves. These metabolite compositions vary in response to different factors. In addition to manufacturing processes in processed tea, the primary factors influencing variations of fresh tea leaf metabolites include genetics, cultivation management, and environmental conditions. Metabolomics approaches, coupled with high-throughput statistical analysis, offer promising tools for the comprehensive identification and characterization of tea leaf metabolites according to growing conditions, cultivation practices, manufacturing processes, seasonality, climate, cultivars, and geography. This review highlights the distinctive variations in fresh tea leaf metabolites, which change in response to various factors, using a metabolomics approach, which are also extended to various processed teas.

Unraveling the flavor formation process of mellow and thick-type ripened Pu-erh tea through non-targeted metabolomics and metagenomics

Ripened Pu-erh tea (RPT) is renowned for its distinctive flavor and health benefits. However, its complex fermentation process poses challenges in ensuring consistency in production. This study investigated RPT flavor formation through sensory evaluation, multi-omics analysis, and multivariate statistical approaches. By day 24, the tea exhibited a reddish-brown infusion and a mellow, thick taste (MT_RPT), achieving the highest sensory score (94.0, P < 0.05). Sixteen flavor-related chemical components exhibited significant changes (P < 0.05). The contents of free amino acids, L-theanine, tea polyphenols, flavonoids, catechins, and thearubigins decreased. In contrast, the contents of total soluble sugars, caffeine, theobromine, epicatechin, and theabrownins (TBs) increased, reaching 74.1 mg/g, 65.38 mg/g, 3.13 mg/g, 3.33 mg/g, and 134.84 mg/g, respectively. Additionally, 33 nonvolatile metabolites (e.g., pelargonidin 3-O-glucoside, dihydroisorhamnetin, and puerarin) were significantly correlated with MT_RPT flavor (VIP > 1, |r| ≥ 0.8, P < 0.05) and influenced by key functional microbes, including Pantoea, Aspergillus, Brachybacterium, and Staphylococcus. By day 30, the infusion darkened, and sensory scores declined (81.4, P < 0.05), attributed to the dominance of Brevibacterium. This microbial shift reduced water-soluble pectin, free amino acids, and 11 metabolites while increasing TBs and theophylline (219.33 mg/g and 0.09 mg/g, respectively). Therefore, TBs were identified as a crucial indicator of optimal fermentation. Moreover, redundancy analysis indicated that the tea pile's central temperature, moisture content, and pH were essential fermentation parameters (P < 0.05). These findings deepen our understanding of MT_RPT flavor development mechanisms and provide valuable insights into precise fermentation control.

Effects of fermented tea by Aspergillus cristatus on the characteristic aroma and non-volatile components of Jiang-flavor baijiu

BACKGROUND

Fu Brick tea (FBT) extract has been demonstrated to lower blood lipids, protect liver, and prevent obesity. Despite these benefits, there are no products on the market that combine FBT with other foods or beverages.

RESULT

In this study, we developed a novel product by combining FBT with high-alcohol Jiang-flavor baijiu, resulting in FBT-baijiu. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis revealed that FBT-baijiu contains health-promoting alkaloids, including eurocristatine (13.60 ± 0.13 mg/L), (-)-neoechinulin A (10.26 ± 0.09 mg/L), neoechinulin D (7.89 ± 0.05 mg/L), variecolorin G (6.94 ± 0.05 mg/L), and echinulin (25.46 ± 0.27 mg/L), which are known to be present in FBT. The aroma compounds of the FBT-baijiu and the base baijiu were analyzed using comprehensive gas chromatography-olfactometry-mass spectrometry (GC-O-MS) technology. The major volatile compounds of two baijiu samples were identified using relative odor activity values (r-OAVs) analysis. The FBT-baijiu showed a significant reduction in ester content, but a remarkable enhancement in aromatic properties. The findings show that combining FBT with baijiu not only offers functional components but also enhances the flavor profile.

CONCLUSION

This study highlights the potential of utilizing FBT as a functional food ingredient or additive, paving the way for the development of new health-promoting products. © 2024 Society of Chemical Industry.

Fungal community composition and function in different Chinese post-fermented teas

Chinese post-fermented teas are produced through special fermentation by microorganisms, with fungi significantly contributing to their flavor and sensory characteristics. Here, the fungal community structure and function were investigated using Illumina HiSeq sequencing of the fungal ITS rDNA region across different post-fermented teas, including Fuzhuan, Qingzhuan, Tianjian black, Liupao, and raw and ripened Pu-erh. Additionally, the headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) technology was used to compare the volatile components of tea samples, and moisture content, pH, total nitrogen, carbon-nitrogen ratio, and total sulfur were measured. All the tea samples were slightly acidic, with pH values of 5.56-6.43, and Ascomycota was the most dominant phylum, representing over 90% of the relative abundance. However, there were significant differences at the genus level in the six typical post-fermented teas. Aspergillus was the most dominant genus in Fuzhuan (91.16%), Qingzhuan (54.89%), Tianjian (64.11%), and Liupao (47.43%) teas, whereas Debaryomyces and Blastobotrys were the most dominant genera in raw (35.67%) and ripened (78.88%) Pu-erh tea, respectively. A functional prediction analysis revealed that most fungal gene functions were involved in metabolism. A total of 26 main volatile components were detected, which differed in composition among six tea samples. This is the first comparative analysis of fungal communities and volatile components in different typical Chinese post-fermented teas, and the results will aid the design of better culturing strategies for the specific dominant fungal species and the influence of fungi on aroma types of post-fermented teas.

Roles of Gut Microbiota Metabolites and Circadian Genes in the Improvement of Glucose and Lipid Metabolism in KKAy Mice by Theabrownin

Theabrownin (TB), a prominent pigment in fermented dark tea, exhibits beneficial effects on adiposity reduction. Our study revealed that TB derived from Fu brick tea significantly lowered fasting blood glucose levels and insulin resistance in obese/diabetic KKAy mice. Furthermore, TB demonstrated potent anti-inflammatory effects in the liver, adipose tissue, and intestines, as well as enhancing intestinal integrity. Additionally, TB was found to inhibit hepatic gluconeogenesis and promote fatty acid oxidation. Notably, TB altered gut metabolites, particularly l-palmitoylcarnitine, which showed an elevation in serum, liver, and adipose tissue following TB intervention. l-Palmitoylcarnitine reduced gluconeogenesis in primary hepatocytes and decreased lipid deposition in both primary hepatocytes and 3T3-L1 adipocytes in vitro. However, these effects were abolished when the circadian gene Period 3 (Per3) was knocked down. Our findings suggest that l-palmitoylcarnitine may play a crucial role in improving TB-mediated glucose homeostasis and lipid metabolism by regulating Per3.

Phytochemicals from fractioned dark tea water extract enhance the digestive enzyme inhibition, antioxidant capacities and glucose-lipid balance

Dark tea has long been recognized for its health-promoting benefits, attributed to its complex phytochemical composition. However, the specific bioactive compounds responsible for these beneficial effects remain inadequately characterized. This study aimed to explore the impact of dark tea water extract (DTE) on digestive enzyme activity, antioxidant capacity, and glucose-lipid balance. DTE was fractioned into four fractions using gel separation, followed by analysis with high-performance liquid chromatography and quasi-targeted metabolomics. The 30 % ethanol elution (EEA) and 50 % ethanol elution (EEB) fractions showed stronger antioxidant and enzyme inhibition effects compared to the whole DTE. The EEA fraction was rich in 5 catechins and 26 additional phytochemicals, while the EEB fraction contained high levels of caffeine, ECG, and 29 other phytochemicals. Notably, significant correlations were observed between quercetin-3,4'-O-di-β-glucopyranoside and 3-(2-Naphthyl)-L-alanine with digestive enzyme inhibition. Cellular studies revealed the ability of EEA and EEB to reduce lipid accumulation, improve glycolipid metabolism, and alleviate oxidative stress by increasing SOD, CAT, and GSH levels while decreasing MDA and ROS in HepG2 cells. Furthermore, 34 flavonoids, 2 alkaloids, 2 terpenes, 2 alcohols and polyols, 2 phenylpropanoids and polyketides, 1 organoheterocyclic compound were directly linked to the antioxidant activity and the modulation of glucose and lipid levels. These findings offer valuable insights into the phytochemical profiles of dark tea and its potential health benefits.

Effects of Pile-Fermentation Duration on the Taste Quality of Single-Cultivar Large-Leaf Dark Tea: Insights from Metabolomics and Microbiomics

The pile-fermentation conditions and raw materials used play a vital role in determining the stability and quality of dark tea. In this study, sensory quality evaluation, metabolomics, and microbiomics techniques were used to investigate the effect of pile-fermentation duration on the taste quality of single-cultivar large-leaf dark tea (SLDT) and its underlying metabolite and microbial mechanisms. The study revealed that a 60-day duration resulted in a better SLDT sensory quality, with astringency and bitterness significantly reduced and sweetness increased. Catechins and theaflavins with ester structures, L-epicatechin, methyl gallate, protocatechuic acid, gallic acid, salicin, chlorogenic acid, and neochlorogenic acid were key taste metabolites contributing to the reduction of astringency and bitterness. Salicylic acid and D-sorbitol helped form the sweetness. Correlation analysis found out Aspergillus, Thermomyces, Bacillus, Staphylococcus, and Micrococcaceae were core functional microorganisms linked to these metabolites, helping to foster the higher quality of SLDT. Microorganisms shaped the taste quality of SLDT through metabolic processes and enzyme secretion during pile-fermentation. This study provided insights into the metabolite basis and microbiological mechanisms of SLDT taste formation and offered guidance for optimizing production processes to improve the stability and quality of dark tea.

Flowering in aged white tea: Recovering umami taste and amplifying of stale aroma

Throughout the natural aging process from new to aged white tea, the flavor evolves into a 'stale flavor', despite the initial umami diminishes. The flowering process, inoculation of Eurotium cristatum to white tea, improves the flavor. The impact on sensory qualities and underlying chemical basis of flowering in aged white tea warrant investigation. Sensory analysis, non-targeted metabolomics and volatilomics together deciphered flavor modifications of flowering in aged white tea from different aging years (FAWTs). Findings indicate the flowering process can recover the umami of aged white tea, enhancing the 'stale flavor'. These changes primarily stem from oxidations of catechins and free amino acids, enrichments of flavonols and soluble sugars, and 16 pivotal aroma compounds from degradations of lipids and glycosides. Additionally, 15 volatile and 39 non-volatile compounds were identified as potential biomarkers for FAWTs. These findings offer a viable strategy to improving the quality of aged white tea.

Dynamic changes in flavor characteristics of black tea during solid-state fermentation with Eurotium cristatum

This study employed GC-MS, GC-IMS, and sensory evaluation to investigate dynamic changes in flavor during the solid-state fermentation of black tea by Eurotium cristatum. The results revealed a notable decrease in the bitter and astringent tastes of the black tea infusion following fermentation, while the mellow taste increased significantly. A total of 152 and 129 VOCs were detected by GC-MS and GC-IMS, respectively. And 4 key aroma-active compounds were identified by ROAV. These specific VOCs contributed floral, honey, and sweet scents, which were responsible for the fungal floral aroma in the processed black tea. Furthermore, OPLS-DA identified 31 key VOCs that played a crucial role in differentiating various fermentation stages, with day 4 recognized as a pivotal point for aroma development. The solid-state fermentation with Eurotium cristatum resulted in fermented black tea characterized by a mellow taste and a rich fungal floral aroma, enhancing the flavor quality of the tea.

Metabolic function and quality contribution of tea-derived microbes, and their safety risk in dark tea manufacture

Microbial fermentation, especially the microbes involved, plays a crucial role in the quality formation of dark tea. Over the last decade, numerous microbes have been isolated from dark tea and in turn, applied to dark tea manufacture through pure-strain, mixed-strain, and enhanced fermentation. This article systematically summarizes the specific metabolic function and quality contribution of tea-derived microbes, with special attention paid to their safety risk. Aspergillus niger converts catechins via hydrolysis, addition, oxidative polymerization, and B-ring fission, contributing greatly to the reddish-brown color and mellow taste of dark tea. Aspergillus sydowii and Penicillium simplicissimum are caffeine-degrading microbes, degrading caffeine mainly into theophylline. However, under adverse conditions, Aspergillus, Penicillium, and Fusarium species potentially produce aflatoxins, ochratoxin A, and citrinin, the mycotoxins occurring in dark tea. The in-depth knowledge of tea-derived microbes is important for improving the quality and safety of dark tea, providing a theoretical basis for its industrial modernization.

Microbial and chemical diversity analysis reveals greater heterogeneity of Liubao tea than ripen Pu-erh tea

Liubao tea and ripen Pu-erh tea are representatives of dark tea in southern China. The two dark teas are famous for unique flavors, but confusingly different in development status of tea industry. In this study, microbial DNA amplification sequencing and mass spectrometry-based untargeted metabolomics were applied to observe significant differences in microbial community structure and metabolite profile between the two teas. The Shannon indices of fungi and metabolites in Liubao tea are higher than those in ripen Pu-erh tea. The dominant bacterial and fungal genera, as well as microbial biomarkers of Liubao tea and ripen Pu-erh tea were identified. The combined statistical and molecular networking analysis shows flavan-3-ols as the discriminating features between metabolite profiles of the two dark teas in level of metabolite family. More importantly, the α and β diversity analysis reveals higher pairwise Shannon index differences and Canberra distances of both microbes and metabolites in Liubao tea than those in ripen Pu-erh tea, indicating greater heterogeneity, or lower quality stability of Liubao tea products. These findings illustrate way to improve protocols of Liubao tea processing, and show urgency of involving molecular networking in workflow of metabolomics research.

Effect of Eurotium cristatum fermentation on chemical composition and hypoglycemic and sedative activities of Anji Baicha (Camellia sinensis)

Anji Baicha (Camellia sinensis), one of the top 10 teas in China, possesses old leaves rich in bioactive ingredients yet is frequently discarded due to inferior taste. This study evaluated the effects of fermentation with Eurotium cristatum, a probiotic known to enhance bioactivity, on the primary nutrients and on the hypoglycemic and sedative properties of old leaves of Anji Baicha. Results indicated a considerable reduction in free amino acids and tea polyphenols post-fermentation. Conversely, the concentrations of flavonoids and theabrownins increased significantly, showing a positive correlation with the in vitro hypoglycemic effect. The contents of L-theanine and γ-aminobutyric acid (γ-GABA), known for their sedative effects, increased after fermentation, while caffeine and glutamate, renowned for their neural stimulation effect, decreased. Molecular docking revealed that L-theanine and γ-GABA may act as a sedative and sleep aid by competing for receptors with caffeine and glutamate, specifically NMDAR2A. This study not only introduces a novel approach for utilizing old leaves of Anji Baicha but also establishes a foundation for further investigating the hypoglycemic, sedative, and sleep-aiding effects of tea fermented with Eurotium cristatum. PRACTICAL APPLICATION: This research offers a sustainable solution for repurposing the underutilized old leaves of Anji Baicha, enhancing their market value and contributing to the circular economy within the tea industry. The fermented tea could be integrated into health-conscious food and beverage products, targeting consumers seeking natural hypoglycemic and sleep-aiding alternatives. Additionally, the findings open avenues for the development of functional teas that cater to specific health needs, such as diabetes management and sleep improvement.

A combined drying process involving hot air and roasting for improving summer congou black tea quality

The present study aim to investigate the effects of three drying processes on the flavor-related compounds and sensory quality of summer black tea. A total of 234 flavonoids and 1200 volatile compounds were identified in tea samples by using UPLC-MS/MS and HS-SPME-GC-MS, respectively. It was found that the combining hot-air and roasting drying process increased the level of epigallocatechin, epicatechin, gallic acid, theaflavins, and umami and sweet amino acids in tea samples. Conversely, the contents of epigallocatechin gallate, caffeine, kaempferol and acylated kaempferol glycosides, and quercetin and acylated quercetin glycosides were found to decrease. Analysis of the volatile compounds revealed that combined drying process enhanced the contents of volatile substances with sweet, nutty, and floral properties while reducing those with green attributes. Sensory evaluation results showed that the combined drying process improved the mellow taste and pure aroma, decreased the bitterness and astringency, and weakened the unpleasant flavor of summer black tea. Overall result indicated that the combined drying process could improve the flavor quality of summer black tea. This study may provide data support and feasible strategies for improving summer congou black tea quality.

Multi-Omics analysis reveals the sensory quality and fungal communities of Tibetan teas produced by wet- and dry-piling fermentation

Ya'an Tibetan tea, a dark tea with a rich historical heritage, is typically processed using two primary piling fermentation methods: wet piling with rolled leaves (moisture content around 60%) and dry piling with sun-dried or baked green tea leaves (moisture content below 30%). This study employed sensory evaluation, targeted and non-targeted metabolomics, and fungal Internal Transcribed Spacer (ITS) sequencing to investigate changes in quality components and fungal composition in Tibetan tea processed by both wet and dry-piling methods. The results revealed that 3,7-Dimethyl-1,5,7-octatriene-3-ol and D-limonene were identified as key volatile metabolites contributing to the aroma variations between the dry and wet-piled teas. More pronounced differences were observed in non-volatile components, with 407 differential metabolites identified between the wet- and dry-piled teas. Linear discriminant analysis effect size (LEfSe) identified Rhizomucor, Aspergillus, Thermomyces, Setophoma, and Debaryomyces as the key fungal genera with significant differences between the two piling methods, also dominating in abundance and playing a crucial role in the fermentation process of Tibetan tea. Correlation analysis between microbial communities and differential metabolites showed that Debaryomyces, Thermomyces, and Setophoma were significant contributors to the aroma differences between the teas produced by the two piling methods, while Rhizomucor and Aspergillus had a greater influence on non-volatile metabolites. Since Rhizomucor and Aspergillus were the most dominant fungi in the wet (63.05%) and dry-piled (68.70%) samples, respectively, and showed opposite correlations with major non-volatile differential metabolites, they may underlie the flavor differences between the two piled teas, such as mellowness, thickness, and sweet aftertaste. This study sheds light on the chemical and fungal mechanisms underlying the quality formation of Ya'an Tibetan tea processed by wet and dry piling methods, providing theoretical guidance for the improvement, standardization, and potential enhancement of production efficiency of Ya'an Tibetan tea production.

The aroma formation from fresh tea leaves of Longjing 43 to finished Enshi Yulu tea at an industrial scale

BACKGROUND

Enshi Yulu tea (ESYL) is the most representative of steamed green tea in China, but its aroma formation in processing is unclear. Thus, the ESYL volatiles during the whole industrial processing were investigated using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry.

RESULTS

A total of 134 volatiles were identified. Among these, 31 differential volatiles [P < 0.05 and variable importance in projection (VIP) > 1] and 25 key volatiles [relative odor activity value (rOAV) and/or the ratio of each rOAV to the maximum rOAV (ROAV) > 1.0] were screened out, wherein β-ionone and nonanal were the most key odorants. Besides, the sensory evaluation combined with multivariate statistical analysis of volatiles pinpointed spreading, fixation, first drying, and second drying as the key processing steps that have a pronounced influence on the aroma quality of ESYL. Furthermore, the oxidative degradation of unsaturated fatty acids, synthesis of monoterpenes, and degradation of carotenoids were the main metabolic pathway for the formation of key odorants.

CONCLUSION

The study provides comprehensive insights into the volatile characteristics during the industrial processing of ESYL and promote our understanding of the aroma formation in steamed green teas. © 2024 Society of Chemical Industry.

An integrative multi-omics approach reveals metabolic mechanism of flavonoids during anaerobic fermentation of de'ang pickled tea

Anaerobic fermentation (AF) is critical process for Yunnan De'ang pickled tea production. Therefore, widely targeted metabolomics and metagenomics were integrated to reveal the AF mechanism. Lactic acid bacteria (LAB) (e.g. Lactiplantibacillus plantarum, Lactobacillus vaccinostercus and Lactobacillus paracollinoides) and yeasts like Candida metapsilosis and Cyberlindnera fabianii dominated in the AF. Based on bacterial community succession and metabolites variation, the whole AF processes were divided into two phases, i.e., before and after four months. A total of 327 characteristic metabolites (VIP >1.0, P < 0.05, and FC > 1.50 or < 0.67) were selected from the AF. Besides amino acids increase, LAB and yeasts also promoted non-galloylated catechins, and several simple flavones/flavonols, flavanones/flavanonols and methoxy flavones/flavonols accumulations along with galloylated catechins, flavonol/flavone glycosides and anthocyanins decrease during the AF. This study would improve the understanding about AF mechanism of tea-leaves from the perspectives of flavonoids metabolism and microbial community succession.

Secondary Metabolites Produced by the Dominant Fungus Eurotium cristatum in Liupao Tea and Their Hypolipidemic Activities by Regulating Liver Lipid Metabolism and Remodeling Gut Microbiota

Liupao tea is a postfermented dark tea with hypolipidemic activity. Research on the active substances in Liupao tea has primarily focused on those derived from the tea itself, overlooking the secondary metabolites produced by its predominant fungus, Euirotium cristatum. In this study, E. cristatum CPCC 401251, the predominant strain found in Liupao tea under investigation, was isolated and analyzed. A total of 19 representative metabolites, including prenylbenzaldehydes, diketopiperazines, and anthraquinones, were obtained from its culture. Subsequent analysis revealed the presence of multiple secondary metabolites of E. cristatum CPCC 401251 in Liupao tea. The 19 compounds significantly reduced the lipid content in free fatty acid (FFA)-stimulated hepatocyte AML-12 cells to varying degrees. Considering the content, chemical class, and biological activity of secondary metabolites from E. cristatum CPCC 401251, compounds 1, 7, and 13 were selected to detect their hypolipidemic activities and potential mechanisms in hyperlipidemia golden hamsters. Compound 1 exerted a hypolipidemic effect by activating the AMPK signaling pathway, decreasing Scd1, and improving intestinal flora. Compounds 7 and 13 played a role in the hypolipidemic activity by regulating the gene expression related to lipid synthesis and degradation, including upregulating the mRNA levels of Pparα, Hsl, and Atgl, and decreasing the mRNA level of Scd1. These findings help us understand the dominant fungus E. cristatum secondary metabolites presenting in Liupao tea and their potential hypolipidemic contributions. This work improves the understanding of the active substances in Liupao tea and highlights the health-promoting effects of microorganisms in the fermented tea.

Blended Tea Ameliorates T2DM via Modulation of Gut Microflora

Increasing evidences suggest that type 2 diabetes mellitus (T2DM) is closely related to gut microflora dysbiosis, which can be improved by dietary intervention. Four natural plant products, including Cyclocarya paliurus, Fu brick tea, Ampelopsis grossedentata, and Lithocarpus litseifolius, were blended to form a blended tea product for obtaining the better flavor. The blended tea was also expected to have excellent pharmacological activity. Therefore, the ameliorative effect of blended tea on T2DM and underlying mechanisms were studied in this study. The results showed that the blended tea extract effectively attenuated the symptoms of glucose and lipid metabolism-related disorders in T2DM mice fed by high-fat and high-sucrose diet. Furthermore, blended tea extract intervention significantly attenuated gut microbiota dysbiosis, the abundance of bacteria such as Bacteroidetes and Firmicutes, which aid in the hydrolysis and utilization of carbohydrates, significantly increased, while the abundance of pathogenic bacteria such as Proteobacteria significantly decreased. Certain core microorganisms involved in energy metabolism, including Ruminococcaceae_UCG-005, Butyricimonas, Roseburia, Oscillibacter, [Eubacterium]_nodatum_group, Muribaculaceae, Prevotellaceae UCG 001, were also found to be improved by blended tea extract. Collectively, our results demonstrated that the blended tea may ameliorate T2DM through modulation of gut microflora. The blended tea may serve as novel functional drink for the treatment of T2DM and dysbiosis of gut microbiota.

Combining non-targeted and targeted metabolomics to study key bitter and astringent substances of Liupao tea

Liupao tea is a post-fermented dark tea with bitterness and astringency as key sensory traits, though its chemical composition is not fully understood. Six Liupao tea samples with significant differences in bitterness and astringency were analyzed using non-targeted metabolomics and sensory evaluation. Thirty finished and five semi-finished Liupao tea samples were analyzed using UHPLC-MS-PRM for targeted quantification of bitter and astringent compounds. The results show that 477 non-volatile compounds were detected, including 18 potential bitter compounds and 22 potential astringent compounds. Six key bitter compounds (epigallocatechin gallate, catechin gallate, caffeine, quinic acid, neochlorogenic acid, and caffeic acid) and 11 key astringent compounds (e.g., epigallocatechin gallate, gallic acid, chlorogenic acid, ellagic acid) were identified. After fermentation, flavonoid glycosides and flavanols were reduced by 62.41 % to 97.46 %, while phenolic acids showed varied trends. Different rates of change in key compounds during fermentation resulted in variations in bitterness and astringency. This study offers insights for improving Liupao tea quality.

Enhanced Fermentation of Pu-Erh Tea with Aspergillus niger: Quality and Microbial Community Analysis

Post-fermented Pu-erh tea (PFPT) is a microbial fermented tea characterized by unique sensory attributes and multiple health benefits. Aspergillus niger is the dominant fungus involved in the fermentation process and plays a significant role in imparting the distinct characteristics of PFPT. To investigate the role of Aspergillus niger in the fermentation of Pu-erh tea, this study inoculated unsterilized sun-dried green tea with Aspergillus niger isolated from Pu-erh tea to enhance the fermentation process. Metabolites and microbial communities in sun-dried green tea (CK), fortified fermented tea (TF), and naturally fermented tea (NF) were analyzed using non-targeted metabolomics, 16S rDNA, and internal transcribed spacer sequencing. Non-targeted metabolomics revealed that Aspergillus niger significantly altered the metabolite profile of the tea samples, identifying a total of 200 different metabolites, with 95 showing significant increases and 105 significant decreases, predominantly enriched in metabolic pathways associated with amino acid biosynthesis and degradation. High-throughput sequencing revealed that although the relative abundance of the fungal community remained largely unchanged, the inoculation of Aspergillus niger significantly increased the abundance of Bacillales and Pseudomonas within the bacterial community, thereby influencing the dynamic balance of the microbial ecosystem. Collectively, the inoculation of Aspergillus niger altered the composition of the microbial community and metabolic activities, resulting in changes to the content of amino acid-dominated metabolites, thereby enhancing the flavor profile and overall quality of Pu-erh tea. These findings provide important insights for optimizing the production processes of Pu-erh tea and the application of microorganisms in other fermented foods.

Are there any differences in the quality of high-mountain green tea before and after the first new leaves unfold? A comprehensive study based on E-sensors, whole metabolomics and sensory evaluation

High-mountain green tea, where the first new leaf hasn't yet unfurled, is prized for perceived superior quality, but this hasn't yet been verified by experimentation. Electronic sensors, whole metabolomics and sensory evaluation were employed to assess the quality of yymj (tea buds with a newly unfurled leaf) and qymj (tea buds without new leaves). The qymj proved to have significant advantages in aroma, color and shape, but still had some shortcomings in umami, bitterness and sourness. Differences in the content of volatile organic compounds (including alcohols, hydrocarbons and lipids) and nonvolatile organic compounds (flavonoids, amino acids, sugars, and phenolic acids) quality of high-mountain green teas with different maturity levels and provides well explained these quality differences. This study establishes a systematic approach to study the quality of high-mountain green tea at different maturity levels, and provides important reference information for consumers, governments and tea farmers.

Fu brick tea polysaccharides: A state-of-the-art mini-review on extraction, purification, characteristics, bioactivities and applications

Fu brick tea (FBT), a post-fermented dark tea, is highly esteemed for its abundant nutritional and medicinal values. Fu brick polysaccharides (FBTPs) are acidic heteropolysaccharides primarily composed of galactose and galacturonic acid, which are crucial components of FBT. FBTPs exhibit multiple bioactivities, including immunomodulatory, antioxidant, anti-inflammatory, regulatory effects on intestinal microbiota, anti-obesity, among others. Owing to their significant marketing potential and promising development prospects, FBTPs have attracted considerable attention from researchers worldwide. However, the specific mechanisms and underlying structure-function relationships of FBTPs are not well understood. Consequently, this review aims to provide comprehensive and cutting-edge information on the extraction, purification, structural characteristics, and biological activities of FBTPs, with an emphasis on exploring how their structural characteristics influence biological activities and therapeutic potential. We found that different materials and extraction techniques could result in differences in the structure-activity relationship of FBTPs. Furthermore, monosaccharide composition and molecular weight could also significantly impact the bioactivities of FBTPs, such as lipid-lowering effects and immunomodulatory activity. This review would further facilitate the applications of FBTPs as therapeutic agents and functional foods, thereby laying a solid foundation for their further development and utilization.

Combinative effect of pulsed-light irradiation and solid-state fermentation on ginkgolic acids, ginkgols, ginkgolides, bilobalide, flavonoids, product quality and sensory assessment of Ginkgo biloba dark tea

Pulsed light (PL) is a prospective non-thermal technology that can improve the degradation of ginkgolic acid (GA) and retain the main bioactive compounds in Ginkgo biloba leaves (GBL). However, only using PL hasn't yet achieved the ideal effect of reducing GA. Fermentation of GBL to make ginkgo dark tea (GDT) could decrease GA. Because different microbial strains are used for fermentation, their metabolites and product quality might differ. However, there is no research on the combinative effect of PL irradiation fixation and microbial strain fermentation on main bioactive compounds and sensory assessment of GDT. In this research, first, Bacillus subtilis and Saccharomyces cerevisiae were selected as fermentation strains that can reduce GA from the five microbial strains. Next, the fresh GBL was irradiated by PL for 200 s (fluences of 0.52 J/cm2), followed by B. subtilis, S. cerevisiae, or natural fermentation to make GDT. The results showed that compared with the control (unirradiated and unfermented GBL) and the only PL irradiated GBL, the GA in GDT using PL + B. subtilis fermentation was the lowest, decreasing by 29.74%; PL + natural fermentation reduced by 24.53%. The total flavonoid content increased by 14.64% in GDT using PL + B. subtilis fermentation, whose phenolic and antioxidant levels also increased significantly. Sensory evaluation showed that the color, aroma, and taste of the tea infusion of PL + B. subtilis fermentation had the highest scores. In conclusion, the combined PL irradiation and solid-state fermentation using B. subtilis can effectively reduce GA and increase the main bioactive compounds, thus providing a new technological approach for GDT with lower GA.

Effects of solid-state fermentation with Aspergillus cristatus (MK346334) on the dynamics changes in the chemical and flavor profile of dark tea by HS-SPME-GC-MS, HS-GC-IMS and electronic nose

Aspergillus cristatus, the predominant microbe of Fuzhuan brick tea (FBT), is responsible for the creation of distinctive golden flower and unique floral aroma of FBT. The present study examined the alterations in chemical and aromatic components of raw dark tea by solid-state fermentation using A. cristatus (MK346334), the strain isolated from FBT. As results, catechins, total ployphenols, total flavonoids, theaflavins, thearubigins and antioxidant activity were significantly reduced after fermentation. Moreover, 112 and 76 volatile substances were identified by HS-SPME-GC-MS and HS-GC-IMS, respectively, primarily composed of alcohols, ketones, esters and aldehydes. Furthermore, the calculation of odor activity values revealed that 19 volatile chemicals, including hexanal, heptanal, linalool and methyl salicylate, were the main contributors to the floral, fungal, woody and minty aroma of dark tea. The present research highlights the pivotal role played by the fermentation with A. cristatus in the chemical composition, antioxidant property and distinctive flavor of dark tea.

Dark Tea Wine Protects Against Metabolic Dysfunction-Associated Steatotic Liver Disease In Vivo Through Activating the Nrf2/HO-1 Antioxidant Signaling Pathway

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a complex and multifactorial disease. Dark tea exhibits great potential for various bioactivities for metabolic health. In this study, we aimed to evaluate therapeutic effects and the underlying mechanisms of dark tea wine (DTW) on MASLD with obesity. A rat model of MASLD was established by high-fat diet and administered with different doses of DTW as an intervention. The biomarkers of lipid metabolism and oxidative stress in rats were tested. The weight of organs and adipose tissues and the expressions of nuclear factor erythroid 2-like 2 (Nrf2) and heme oxygenase-1 (HO-1) were investigated based on the pathology and western blot analysis. We found that DTW enhanced antioxidant capacity via activating the Nrf2/HO-1 signaling pathway, further markedly triggering inhibition of weight gain, reduction of lipid dysfunction, and improvement of pathological characteristics to ameliorate MASLD induced by high-fat diet. These results suggest that DTW is a promising functional supplement for prevention and treatment of MASLD and obesity.

Dark tea consumption is associated with a reduced risk of dysglycaemia and increased urinary glucose and sodium excretion in Chinese adults

AIM

To examine the associations of tea consumption (both frequency and type) with (1) prediabetes and diabetes and (2) urinary glucose and sodium excretion in Chinese community-dwelling adults.

MATERIALS AND METHODS

In 1923 participants (457 with diabetes, 720 with prediabetes, and 746 with normoglycaemia), the frequency (occasional, frequent, daily, or nil) and type (green, black, dark, or other) of tea consumption were assessed using a standardized questionnaire. Morning spot urinary glucose and urine glucose-to-creatinine ratios (UGCRs) were assessed as markers of urinary glucose excretion. Tanaka's equation was used to estimate 24-h urinary sodium excretion. Logistic and multivariate linear regression analyses were performed.

RESULTS

Compared with non-tea drinkers, the corresponding multivariable-adjusted odds ratios (ORs) for prediabetes and diabetes were 0.63 (95% confidence interval [CI] 0.48, 0.83) and 0.58 (95% CI 0.41, 0.82) in participants drinking tea daily. However, only drinking dark tea was associated with reduced ORs for prediabetes (0.49, 95% CI 0.36, 0.66) and diabetes (0.41, 95% CI 0.28, 0.62). Dark tea consumption was associated with increased morning spot urinary glucose (0.22 mmol/L, 95% CI 0.11, 0.34 mmol/L), UGCR (0.15 mmol/mmol, 95% CI 0.05, 0.25 mmol/L) and estimated 24-h urinary sodium (7.78 mEq/day, 95% CI 2.27, 13.28 mEq/day).

CONCLUSIONS

Regular tea consumption, especially dark tea, is associated with a reduced risk of dysglycaemia and increased urinary glucose and sodium excretion in Chinese community-dwelling adults.

Rapid identification of the aging time of Liupao tea using AI-multimodal fusion sensing technology combined with analysis of tea polysaccharide conjugates

Identifying the aging time of Liupao Tea (LPT) presents a persistent challenge. We utilized an AI-Multimodal fusion method combining FTIR, E-nose, and E-tongue to discern LPT's aging years. Compared to single-source and two-source fusion methods, the three-source fusion significantly enhanced identifying accuracy across all four machine learning algorithms (Decision tree, Random forest, K-nearest neighbor, and Partial least squares Discriminant Analysis), achieving optimal accuracy of 98-100 %. Physicochemical analysis revealed monotonic variations in tea polysaccharide (TPS) conjugates with aging, observed through SEM imaging as a transition from lamellar to granular TPS conjugate structures. These quality changes were reflected in FTIR spectral characteristics. Two-dimensional correlation spectroscopy (2D-COS) identified sensitive wavelength regions of FTIR from LPT and TPS conjugates, indicating a high similarity in spectral changes between TPS conjugates and LPT with aging years, highlighting the significant role of TPS conjugates variation in LPT quality. Additionally, we established an index for evaluating quality of aging, which is sum of three fingerprint peaks (1029 cm-1, 1635 cm-1, 2920 cm-1) intensities. The index could effectively signify the changes in aging years on macro-scale (R2 = 0.94) and micro-scale (R2 = 0.88). These findings demonstrate FTIR's effectiveness in identifying aging time, providing robust evidence for quality assessment.

Technological quality and fungal community of Kombucha fermented with hemp leaves and milky mushroom flour (Calocybe indica)

Kombucha is traditionally a non-alcoholic beverage whose production is dependent on culture and the various ingredients used as substrates for fermentation. The goal of our study was to apply hemp leaf and milky mushroom (Calocybe indica) flour as functional ingredients to enhance phytonutrient quality, along with using a microbial consortium highly symbiotic with these ingredients. The study determined the content of phytonutrients (phenolic and flavonoids content), antioxidant activity through percentage inhibition of DPPH radical scavenging activity (%), and microbial communities changes during fermentation. The microbial changes were evaluated by cell viable count (total bacteria, Lactic Acid Bacteria, and Yeast & Mold) and ITS in prepared kombucha (using red tea leaves, pandan leaves, and sucrose) supplemented with functional ingredients: T1 (hemp leaves (control)) and T2 (hemp leaves with milky mushroom flour). The results indicated that microbial consortium changed during fermentation. In the first 7 days, the levels of yeast and mold increased to 6.17 and 6.18 log CFU/mL, respectively. By day 21, the levels of both T1 and T2 continued to rise, reaching 7.78 and 7.82 log CFU/mL, respectively. The viable count of lactic acid bacteria in T1 and T2 gradually increased to 6.79 and 6.70 log CFU/mL, respectively, by day 14. These changes resulted in a marked decrease in pH value, reaching 3.63 and 3.23 in T1 and T2, respectively, by the end of the process (21 days). The total bacterial viable count decreased with an increase in the fermentation time. During fermentation, unique genera of tea fungus observed in T1 and T2 were 64% and 19%, respectively. At the beginning (0 days), the top five genera found in T1 were: g__Setophoma (25.91%), g__Macrocybe (14.88%), g__Cladosporium (7.81%), g__Phaeosphaeria (7.12%), g__Malassezia (6.63%), while the top five genera in T2 were g__Macrocybe (94.55%), g__Setophoma (1.87%), g__Cladosporium (0.77%), g__Phaeosphaeria (0.40%), g__Cordyceps (0.38%). However, on day 21 (end of the process), it was found that g__Dekkera had the highest relative abundance in both T1 and T2. In addition, the supplementation of the two ingredients affected the total phenolic and total flavonoid content of the treatments. At the end of the process, T2 showed values of 155.91 mg GAE/mL for total phenolics and 1.01 mg CE/mL for total flavonoids, compared to T1, which had 129.52 mg GAE/mL and 0.69 mg CE/mL, respectively. Additionally, the DPPH inhibition was higher in T1 (91.95%) compared to T2 (91.03%). The findings suggest that kombucha fermented with these innovative ingredients exhibited enhanced phytonutrients, and served as substrate for LAB and tea fungus fermentation, while limiting the growth of fungal genera and diversity of microbial consortium.

Effects of Microbial Proteins on Qingzhuan Tea Sensory Quality during Pile Fermentation

To determine the effects of microbial proteins on Qingzhuan tea sensory quality during tea pile fermentation, tea leaf metabolomic and microorganism proteomic analyses were performed. In total, 1835 differential metabolites and 443 differentially expressed proteins of the microorganisms were identified. Correlation analysis between metabolomics and proteomics data revealed that the levels of microbial proteins EG II and CBH I cellulase may play important roles in cell wall construction and permeability, which were crucial for the interaction between tea leaves and microorganisms. Microbial proteins heat shock proteins (HSP), alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and CuAO related to detoxification and stress responses showed a positive correlation with tea theanine, glutamine, γ-aminobutyric acid, glutamic acid, catechin, (-)-gallocatechin gallate, and (-)-catechin gallate, suggesting their effects on tea characteristic compound accumulation, thus affecting Qingzhuan tea sensory quality.

Insights into the airborne microorganisms in a Sichuan south-road dark tea pile fermentation plant during production

Introduction

Sichuan south-road dark tea (SSDT) is generally produced through a series of processes, including fixing, rolling, pile fermentation, and drying, with microbial action during pile fermentation playing a crucial role in determining tea quality. The air within the SSDT pile fermentation plant (SSDTPP) is considered an important source of these microbes, but research in this area has been limited.

Methods

In this study, air samples from SSDTPP were collected on the 1st (SSDT1), 12th (SSDT2), and 24th (SSDT3) days of pile fermentation and comprehensively analyzed by high-throughput sequencing.

Results and discussion

The results revealed the presence of 2 and 24 phyla, 9 and 49 classes, 18 and 88 orders, 28 and 153 families, 38 and 253 genera, and 47 and 90 species of fungi and bacteria, respectively, across all samples. SSDT1 and SSDT2 individually had the highest fungal and bacterial diversity, while Aspergillus was the dominant genus throughout the pile fermentation with an abundance of 34.6%, 91.17%, and 67.86% in SSDT1, SSDT2, and SSDT3, respectively. Microbial populations in SSDT1 were predominantly involved in xenobiotic biodegradation and metabolism, amino acid metabolism, the biosynthesis of other secondary metabolites, etc. However, SSDT2 exhibited a higher prevalence of human disease-related functions. SSDT3 primarily focused on the metabolism of other amino acids and carbohydrate metabolism. Additionally, 104 genera and 22 species coexisted in both SSDTPP air and piled SSDT, suggesting that frequent microbial exchange may occur between them. These findings pave the way for microbial traceability during SSDT production and provide a foundation for further functional microbial research.

Discrimination and prediction of Qingzhuan tea storage year using quantitative chemical profile combined with multivariate analysis: Advantages of MRMHR based targeted quantification metabolomics

The duration of storage significantly influences the quality and market value of Qingzhuan tea (QZT). Herein, a high-resolution multiple reaction monitoring (MRMHR) quantitative method for markers of QZT storage year was developed. Quantitative data alongside multivariate analysis were employed to discriminate and predict the storage year of QZT. Furthermore, the content of the main biochemical ingredients, catechins and alkaloids, and free amino acids (FAA) were assessed for this purpose. The results show that targeted marker-based models exhibited superior discrimination and prediction performance among four datasets. The R2Xcum, R2Ycum and Q2cum of orthogonal projection to latent structure-discriminant analysis discrimination model were close to 1. The correlation coefficient (R2) and the root mean square error of prediction of the QZT storage year prediction model were 0.9906 and 0.63, respectively. This study provides valuable insights into tea storage quality and highlights the potential application of targeted markers in food quality evaluation.

Dynamics changes in metabolites and pancreatic lipase inhibitory ability of instant dark tea during liquid-state fermentation by Aspergillus niger

Instant dark tea (IDT), prepared by liquid-state fermentation using Aspergillus niger, is known for its high theabrownins content and lipid-lowering effect. To explore the impact of fungal fermentation on IDT compositions and its pancreatic lipase inhibitory ability (PLIA), untargeted and targeted metabolomic analysis were applied to track the changes of metabolites over a 9-day fermentation period, and correlation analysis was then conducted between metabolites and PLIA of IDT. There were 54 differential metabolites exhibited significant changes from day 3 to day 5 of fermentation. The concentrations of theabrownins and caffeine increased during fermentation, while phenols and free amino acids decreased. The PLIA of IDT samples significantly increased from day 5 to day 9 of fermentation. Theabrownins not only positively correlated with the PLIA but also exhibited a high inhibition rate. These findings provide a theoretical basis to optimize the production of IDT as functional food ingredient.

Formation, physicochemical properties, and biological activities of theabrownins

Theabrownins (TBs) are heterogeneous mixtures of water-soluble brown tea pigments, and important constituents to evaluate the quality of dark tea. TBs have numerous hydroxyl and carboxyl groups and are formed by the oxidative polymerization of tea polyphenols. Many biological activities attributed to TBs, including antioxidant, anti-obesity, and lipid-regulating, have been demonstrated. This review summarizes the research progress made on the formation mechanism and physicochemical properties of TBs. It also discusses their protective effects against various diseases and associated potential molecular mechanisms. Additionally, it examines the signaling pathways mediating the bioactivities of TBs and highlights the difficulties and challenges of TBs research as well as their research prospects and applications.

A cooperative combination of non-targeted metabolomics and electronic tongue evaluation reveals the dynamic changes in metabolites and sensory quality of radish during pickling

Pickled radish is a traditional fermented food with a unique flavor after long-term preservation. This study analyzed the organoleptic and chemical characteristics of pickled radish from different years to investigate quality changes during pickling. The results showed that the sourness, saltiness, and aftertaste-bitterness increased after pickling, and bitterness and astringency decreased. The levels of free amino acids, soluble sugars, total phenols, and total flavonoids initially decreased during pickling but increased with prolonged pickling. The diversity of organic acids also increased over time. Through non-targeted metabolomics analysis, 349 differential metabolites causing metabolic changes were identified to affect the quality formation of pickled radish mainly through amino acid metabolism, phenylpropane biosynthesis and lipid metabolism. Correlation analysis showed that L*, soluble sugars, lactic acid, and acetic acid were strongly associated with taste quality. These findings provide a theoretical basis for standardizing and scaling up traditional pickled radish production.

Pruned tea biomass plays a significant role in functional food production: A review on characterization and comprehensive utilization of abandon-plucked fresh tea leaves

Tea is the second largest nonalcoholic beverage in the world due to its characteristic flavor and well-known functional properties in vitro and in vivo. Global tea production reaches 6.397 million tons in 2022 and continues to rise. Fresh tea leaves are mainly harvested in spring, whereas thousands of tons are discarded in summer and autumn. Herein, pruned tea biomass refers to abandon-plucked leaves being pruned in the non-plucking period, especially in summer and autumn. At present, no relevant concluding remarks have been made on this undervalued biomass. This review summarizes the seasonal differences of intrinsic metabolites and pays special attention to the most critical bioactive and flavor compounds, including polyphenols, theanine, and caffeine. Additionally, meaningful and profound methods to transform abandon-plucked fresh tea leaves into high-value products are reviewed. In summer and autumn, tea plants accumulate much more phenols than in spring, especially epigallocatechin gallate (galloyl catechin), anthocyanins (catechin derivatives), and proanthocyanidins (polymerized catechins). Vigorous carbon metabolism induced by high light intensity and temperature in summer and autumn also accumulates carbohydrates, such as soluble sugars and cellulose. The characteristics of abandon-plucked tea leaves make them not ideal raw materials for tea, but suitable for novel tea products like beverages and food ingredients using traditional or hybrid technologies such as enzymatic transformation, microbial fermentation, formula screening, and extraction, with the abundant polyphenols in summer and autumn tea serving as prominent flavor and bioactive contributors.

The utilization of a data fusion approach to investigate fingerprint profiles of dark tea from China's different altitudes

Dark tea refers to a kind of post-fermented product, and its quality and price vary owing to the distinct altitudes at which it grows. In this study, a novel method based on high performance liquid chromatography with a diode-array detector (HPLC-DAD) and an evaporative light scattering detector (HPLC-ELSD) was proposed for the classification of dark teas from distinct altitudes in China. Through implementing a strategy fusing feature-level data to construct a combined dataset, the classification performance of dark teas from distinct altitudes in China was evaluated after preprocessing. The results suggested that, through the feature fusion strategy, the identification accuracy rate increased from <70% of a single detector to 76.923%. After the implementation of preprocessing, the identification accuracy rate was further improved. Typically, the model identification accuracy rate after short-time Fourier Transform (STFT) treatment reached 92.85%, and the AUROC value was higher than 0.84, exhibiting a favorable generalization ability. This study provides a new thinking for the identification technology of dark teas from different altitudes in China.

Probiotic Bacillus as fermentation agents: Status, potential insights, and future perspectives

Probiotic Bacillus strains can solve the problems of single flavor and long fermentation time of fermented products caused by the lack of certain functional genes and insufficient metabolism ability of fermenter strains (Lactobacillus and Bifidobacterium) at the present stage. There is a lack of systematic evaluation and review of probiotic Bacillus as food fermentation agents. In this paper, it is observed that probiotic Bacillus strains are involved to varying degrees in liquid-state, semi-solid state, and solid-state fermentation and are widely present in solid-state fermented foods. Probiotic Bacillus strains not only produce abundant proteases and lipases, but also effective antifungal lipopeptides and extracellular polymers, thus enhancing the flavor, nutritional value and safety of fermented foods. Bacillus with probiotic qualities is an underutilized group of probiotic food fermentation agents, which give a potential for the development of fermentation technology in the food business and the integration of ancient traditional fermentation techniques.

Bacillus licheniformis-based intensive fermentation of Tibetan tea improved its bioactive compounds and reinforced the intestinal barrier in mice

Tibetan tea changes during microorganism fermentation. Research on microorganisms in Tibetan tea has focused on their identification, while studies on the influence of specific microorganisms on the components and health functions of Tibetan tea are lacking. Bacillus licheniformis was inoculated into Tibetan tea for intensive fermentation, and the components of B. licheniformis-fermented tea (BLT) were detected by liquid chromatography with tandem mass spectrometry (UHPLC-TOF-MS), and then the effects of BLT on intestinal probiotic functions were investigated by experiments on mice. The results revealed the metabolites of BLT include polyphenols, alkaloids, terpenoids, amino acids, and lipids. Intensified fermentation also improved the antioxidant capacity in vivo and the protective effect on the intestinal barrier of Tibetan tea. In addition, the enhanced fermentation of Tibetan tea exerted intestinal probiotic effects by modulating the relative abundance of short-chain fatty acid-producing bacteria in the intestinal flora. Therefore, intensive fermentation with B. licheniformis can improve the health benefits of Tibetan tea.

The carbohydrate metabolism and expression of carbohydrate-active enzyme genes in Aspergillus luchuensis fermentation of tea leaves

Introduction

Carbohydrates, which make up 20 to 25% of tea beverages, are responsible for their flavor and bioactivity. Carbohydrates of pu-erh tea change during microbial fermentation and require further research. In this study, we examined the carbohydrate metabolism and expression of carbohydrate-active enzyme genes during the fermentation of tea leaves with Aspergillus luchuensis.

Methods

Widely targeted metabolomics analysis, high-performance anion-exchange chromatography measurements, and transcriptomics were used in this study.

Results

After fermentation, the levels of soluble sugar, hemicellulose, lignin, eight monosaccharides, and seven sugar alcohols increased. Meanwhile, the relative contents of polysaccharides, D-sorbitol, D-glucose, and cellulose decreased. High expression of 40 genes encoding 16 carbohydrate enzymes was observed during fermentation (FPKM>10). These genes encode L-iditol 2-dehydrogenase, pectinesterase, polygalacturonase, α-amylase, glucoamylase, endoglucanase, β-glucosidase, β-galactosidase, α-galactosidase, α-glucosidase, and glucose-6-phosphate isomerase, among others.

Discussion

These enzymes are known to break down polysaccharides and cell wall cellulose, increasing the content of monosaccharides and soluble sugars.

Insight into the chemical compositions of Anhua dark teas derived from identical tea materials: A multi-omics, electronic sensory, and microbial sequencing analysis

Anhua dark teas (DTs), including Tianjian tea, Qianliang tea, Hei brick tea, and Fu brick tea, are unique fermented teas from China's Anhua County; yet their chemical composition differences remain unclear. Herein, metabolomics, volatolomics, and electronic sensory assessments were employed to analyze and compare chemical compositions and sensory characteristics of five types of Anhua DTs. All of these teas were derived from identical tea materials. Chemical compositions differed significantly among Anhua DTs, with Tianjian tea remarkable. Long-lasting fermentation and complex processing methods led to transformation of multiple compounds, particularly catechins. Eighteen volatile compounds with OVA > 1 were key aroma contributors in Anhua DTs. Internal transcribed spacer and 16S ribosomal DNA sequencing showed that Eurotium, Pseudomonas, and Bacillus are dominant microorganisms in Anhua DTs. Furthermore, this study unveiled notable differences in chemical compositions between Anhua DTs and five other traditional types of tea. This research enhances our understanding of Anhua DTs processing.

Effects of Monascus purpureus on ripe Pu-erh tea in different fermentation methods and identification of characteristic volatile compounds

The present study aimed to explore the key volatile compounds (VCs) that lead to the formation of characteristic flavors in ripe Pu-erh tea (RIPT) fermented by Monascus purpureus (M. purpureus). Headspace solid-phase microextraction coupled with gas chromatography/mass spectrometry (HS-SPME-GC-MS), orthogonal partial least square-discriminant analysis (OPLS-DA) were employed for a comprehensive analysis of the VCs present in RIPT fermented via different methods and were further identified by odor activity value (OAV). The VCs 1,2-dimethoxybenzene, 1,2,3-trimethoxybenzene, (E)-linalool oxide (pyranoid), methyl salicylate, linalool, β-ionone, β-damascenone were the key characteristic VCs of RIPT fermented by M. purpureus. OAV and Gas chromatography-olfactometry (GC-O) further indicated that β-damascenone was the highest contribution VCs to the characteristic flavor of RIPT fermented by M. purpureus. This study reveals the specificities and contributions of VCs present in RIPT under different fermentation methods, thus providing new insights into the influence of microorganisms on RIPT flavor.

Changes in amino acids, catechins and alkaloids during the storage of oolong tea and their relationship with antibacterial effect

The storage process has a significant impact on tea quality. Few is known about effect of storage on quality of oolong tea. This study aimed to assess the effect of different storage times on the key chemical components of oolong tea by measuring changes in catechin, free amino acid, and alkaloid content. Variation in the main substances was determined by principal component analysis and heat map analysis. The results revealed notable effects of the storage process on the levels of theanine, epigallocatechin gallate (EGCG), and glutamine. These findings suggest that these compounds could serve as indicators for monitoring changes in oolong tea quality during storage. Additionally, the study observed an increase in the antibacterial ability of tea over time. Correlation analysis indicated that the antibacterial ability against Micrococcus tetragenus and Escherichia coli was influenced by metabolites such as aspartic acid, threonine, serine, gamma-aminobutyric acid, ornithine, alanine, arginine, and EGCG. Overall, this study presents an approach for identifying key metabolites to monitor tea quality effectively with relatively limited data.