Processing and chemical constituents of Pu-erh tea: A review

Effects of Fermentation with Eurotium cristatum on Sensory Properties and Flavor Compounds of Mulberry Leaf Tea

Mulberry leaf tea (MT) is a popular Chinese food with nutrition and medicinal functions. Solid-state fermentation with Eurotium cristatum of MT (FMT) can improve their quality. Differences in chromaticity, taste properties, and flavor characteristics were analyzed to evaluate the improvements of the sensory quality of FMT. After fermentation, the color of the tea infusion changed. The E-tongue evaluation results showed a significant decrease in unpleasant taste properties such as sourness, bitterness, astringency, and aftertaste-bitterness, while umami and saltiness taste properties were enhanced post-fermentation. Aroma-active compounds in MT and FMT were identified and characterized. A total of 25 key aroma-active compounds were screened in MT, and 2-pentylfuran showed the highest relative odor activity value (ROAV). A total of 26 key aroma-active compounds were identified in FMT, and the newly formed compound 1-octen-3-one showed the highest ROAV, which contributed to FMT's unique mushroom, herbal, and earthy flavor attributes. 1-octen-3-one, (E)-2-nonenal, trimethyl-pyrazine, 2-pentylfuran, and heptanal were screened as the potential markers that contributed to flavor differences between MT and FMT. E. cristatum fermentation significantly altered the sensory properties and flavor compounds of MT. This study provides valuable insights into the sensory qualities of MT and FMT, offering a theoretical basis for the development of FMT products.

"Age" of tea: The impact of long-term storage on the aroma of Tuo tea and age prediction

This study investigates the dynamic changes in the aroma profile of Tuo tea during long-term storage, a process not well understood yet critical to the formation of aged tea's unique characteristics. Aroma profiling of Tuo tea samples stored for 2 to 25 years was conducted using sensory evaluation and the HS-SPME/GC × GC-QTOFMS technique, revealing a progressive transition from fresh, fruity, and floral scents to more stale, woody, and herbal notes. Among 275 identified volatiles, 55 were correlated with storage duration (|r| > 0.8, p < 0.05), and 49 differential compounds (VIP > 1, FC > 1.2, FC < 0.833, p < 0.05) were identified across three storage stages (2-4, 5-10, and 13-25 years). Furthermore, theaspirane, eucalyptol, o-xylene, and 1-ethylidene-1H-indene were selected as potential markers of Tuo tea aging, incorporating the implementation of a Random Forest (RF) model. Additionally, our model exhibited high accuracy in predicting the age of Tuo tea within a prediction error range of -2.51 to 2.84 years. This research contributes to a comprehensive understanding of the impact of storage time on tea aroma and aids in the precise identification of tea age.

Recent Advances in the Health Benefits and Application of Tangerine Peel (Citri Reticulatae Pericarpium): A Review

Citrus fruits, renowned for their abundant of phytochemicals and bioactive compounds, hold a prominent position as commercially grown fruits with health-promoting properties. In this context, tangerine peel (Citri Reticulatae Pericarpium, CRP) is garnering attention as a byproduct of citrus fruits. Within the framework of the circular economy, CRP has emerged as a focal point due to its potential health benefits. CRP, extracted from Citrus reticulata cv. and aged for over three years, has attracted increasing attention for its diverse health-promoting effects, including its anticancer, cardiovascular-protecting, gastrointestinal-modulating, antioxidant, anti-inflammatory, and neuroprotective properties. Moreover, CRP positively impacts skeletal health and various physiological functions. This review delves into the therapeutic effects and molecular mechanisms of CRP. The substantial therapeutic potential of CRP highlights the need for further research into its applications in both food and medicine. As a value-added functional ingredient, CRP and its constituents are extensively utilized in the development of food and health supplements, such as teas, porridges, and traditional medicinal formulations.

Bioactive components and mechanisms of Pu-erh tea in improving levodopa metabolism in rats through COMT inhibition

Catechol-O-methyltransferase (COMT) plays a central role in the metabolic inactivation of endogenous neurotransmitters and xenobiotic drugs and hormones having catecholic structures. Its inhibitors are used in clinical practice to treat Parkinson's disease. In this study, a fluorescence-based visualization inhibitor screening method was developed to assess the inhibition activity on COMT both in vitro and in living cells. Following the screening of 94 natural products, Pu-erh tea extract exhibited the most potent inhibitory effect on COMT with an IC50 value of 0.34 μg mL-1. In vivo experiments revealed that Pu-erh tea extract substantially hindered COMT-mediated levodopa metabolism in rats, resulting in a significant increase in levodopa levels and a notable decrease in 3-O-methyldopa in plasma. Subsequently, the chemical components of Pu-erh tea were analyzed using UHPLC-Q-Exactive Orbitrap HRMS, identifying 24 major components. Among them, epigallocatechin gallate, gallocatechin gallate, epicatechin gallate, and catechin gallate exhibited potent inhibition of COMT activity with IC50 values from 93.7 nM to 125.8 nM and were the main bioactive constituents in Pu-erh tea responsible for its COMT inhibition effect. Inhibition kinetics analyses and docking simulations revealed that these compounds competitively inhibit COMT-mediated O-methylation at the catechol site. Overall, this study not only explained how Pu-erh tea catechins inhibit COMT, suggesting Pu-erh tea as a potential dietary intervention for Parkinson's disease, but also introduced a new strategy for discovering COMT inhibitors more effectively.

Valorization of tea waste: Composition, bioactivity, extraction methods, and utilization

Tea is the most consumed beverage worldwide and has many health effects. Although there are many different types of tea, black tea and green tea comprise 98% of total tea production in the world. Tea waste production consists of withering, crushing, fermentation, drying and finally packaging processes. All of the waste generated during this production line is called tea waste. Tea production results in a significant amount of waste that cannot be effectively used for value creation. This waste contains many different components including protein, fiber, caffeine, and polyphenols. Due to its rich composition, it can be revalorized for different purposes. In this study, the general composition and bioactive compounds of tea waste were reviewed. Despite the fact that there have been few studies on the bioactivity of tea waste, those studies have also been discussed. The extraction techniques that are used to separate the compounds in the waste are also covered. It has been indicated that these valuable compounds, which can be separated from tea wastes by extraction methods, have the potential to be used for different purposes, such as biogas production, functional foods, food additives, silages, soluble packaging materials, and adsorbents. Although there are some studies on the revalorization of tea waste, new studies on the extraction of bioactive compounds are necessary to improve its utilization potential.

Monitoring the dynamic changes in aroma during the whole processing of Qingzhuan tea at an industrial scale: From fresh leaves to finished tea

Aroma is one of the most outstanding quality characteristics of Qingzhuan tea (QZT), but its formation is still unclear. Thus, the volatile organic compounds (VOCs) during the whole processing of QZT were investigated by headspace solid-phase microextraction/gas chromatography-mass spectrometry. Based on 144 identified VOCs, the results showed that de-enzyming, sun-drying, and piling fermentation were the key processes of QZT aroma formation. Furtherly, 42 differential VOCs (VIP > 1.0 and p < 0.05) and 16 key VOCs (rOAV > 1.0 and/or ROAV > 1.0) were screened. Especially, sulcatone and β-ionone (rOAV > 100 and ROAV > 10) were considered the most important contributors to the aroma of QZT. The metabolisms of key VOCs were mainly involved in oxidative degradation of fatty acids, degradation of carotenoids, and methylation of gallic acid. This study could help to more comprehensively understand the aroma formation in QZT processing at an industrial scale.

Deciphering the underlying core microorganisms and the marker compounds of Liupao tea during the pile-fermentation process

BACKGROUND

Pile fermentation is one of the key steps in developing the Liupao tea (LBT) quality and unique characteristics. The complex biochemical profile of LBT results from microorganisms present during the pile-fermentation process. However, the critical underlying microorganisms and the marker compounds still need to be determined.

RESULTS

Staphylococcus, Brevibacterium, Kocuria, Aspergillus, and Blastobotrys were the common dominant microorganisms at the end of the pile fermentation of LBT. Staphylococcus, Aspergillus, Blastobotrys, and nine other genera carried by raw tea are the core microorganisms in the LBT during pile fermentation. A total of 29 critical compounds contributed to the metabolic changes caused by the processing of LBT. Of these, gallic acid, adenine, hypoxanthine, uridine, betaine, 3,4-dihydroxybenzaldehyde, and α-linolenic acid could be characterized as potential marker compounds. Correlation analysis showed that the core microorganisms, including Sphingomonas, Staphylococcus, Kocuria, Aureobasidium, Blastobotrys, Debaryomyce, and Trichomonascus, were closely related to major chemical components and differential compounds. Moreover, the mutually promoting Staphylococcus, Kocuria, Blastobotrys, and Trichomonascus were correlated with the enrichment of marker compounds. Integrated molecular networking and metabolic pathways revealed relevant compounds and enzymes that possibly affect the enrichment of marker compounds.

CONCLUSION

This study analyzed the LBT fermentation samples by omics analysis to reveal the stable microbial community structure, critical microorganisms, and markers compounds affecting the quality of LBT, which contributes to a better understanding of pile fermentation of LBT and the fermentation theory of dark tea. © 2023 Society of Chemical Industry.

Metabolic Insights into Caffeine's Anti-Adipogenic Effects: An Exploration through Intestinal Microbiota Modulation in Obesity

Obesity, a chronic condition marked by the excessive accumulation of adipose tissue, not only affects individual well-being but also significantly inflates healthcare costs. The physiological excess of fat manifests as triglyceride (TG) deposition within adipose tissue, with white adipose tissue (WAT) expansion via adipocyte hyperplasia being a key adipogenesis mechanism. As efforts intensify to address this global health crisis, understanding the complex interplay of contributing factors becomes critical for effective public health interventions and improved patient outcomes. In this context, gut microbiota-derived metabolites play an important role in orchestrating obesity modulation. Microbial lipopolysaccharides (LPS), secondary bile acids (BA), short-chain fatty acids (SCFAs), and trimethylamine (TMA) are the main intestinal metabolites in dyslipidemic states. Emerging evidence highlights the microbiota's substantial role in influencing host metabolism and subsequent health outcomes, presenting new avenues for therapeutic strategies, including polyphenol-based manipulations of these microbial populations. Among various agents, caffeine emerges as a potent modulator of metabolic pathways, exhibiting anti-inflammatory, antioxidant, and obesity-mitigating properties. Notably, caffeine's anti-adipogenic potential, attributed to the downregulation of key adipogenesis regulators, has been established. Recent findings further indicate that caffeine's influence on obesity may be mediated through alterations in the gut microbiota and its metabolic byproducts. Therefore, the present review summarizes the anti-adipogenic effect of caffeine in modulating obesity through the intestinal microbiota and its metabolites.

The Potential Use of Near Infrared Spectroscopy (NIRS) to Determine the Heavy Metals and the Percentage of Blends in Tea

The following study analyzed the potential of Near Infrared Spectroscopy (NIRS) to predict the metal composition (Al, Pb, As, Hg and Cu) of tea and for establishing discriminant models for pure teas (green, red, and black) and their different blends. A total of 322 samples of pure black, red, and green teas and binary blends were analyzed. The results showed that pure red teas had the highest content of As and Pb, green teas were the only ones containing Hg, and black teas showed higher levels of Cu. NIRS allowed to predict the content of Al, Pb, As, Hg, and Cu with ratio performance deviation values > 3 for all of them. Additionally, it was possible to discriminate pure samples from their respective blends with an accuracy of 98.3% in calibration and 92.3% in validation. However, when the samples were discriminated according to the percentage of blending (>95%, 95-85%, 85-75%, or 75-50% of pure tea) 100% of the samples of 10 out of 12 groups were correctly classified in calibration, but only the groups with a level of pure tea of >95% showed 100% of the samples as being correctly classified as to validation.

Theabrownin: a dietary nutraceutical with diverse anticancer mechanisms

Cancer, a highly deadly disease, necessitates safe, cost-effective, and readily accessible treatments to mitigate its impact. Theabrownin (THBR), a polyphenolic pigment found in Pu-erh tea, has garnered attention for its potential benefits in memory, liver health, and inflammation control. By observing different biological activities of THBR, recently researchers have unveiled THBR's promising anticancer properties across various human cancer types. By examining existing studies, it is evident that THBR demonstrates substantial potential in inhibiting cell proliferation and reducing tumour size with minimal harm to normal cells. These effects are achieved through the modulation of key molecular markers such as Bcl-2, Bax, various Caspases, Poly (ADP-ribose) polymerase cleavage (Cl-PARP), and zinc finger E box binding homeobox 1 (ZEB 1). This review aims to provide in-depth insights into THBR's role in cancer research. This review also elucidates the underlying anticancer mechanisms of THBR, offering promise as a novel anticancer drug to alleviate the global cancer burden.

Lipids: A noteworthy role in better tea quality

New shoots from tea plants (Camellia sinensis) are changed into finished tea after the process, which endows the products with a characteristic flavor. Tea quality is reflected in all aspects, from new shoots to the finished tea that are affected by cultivar, cultivation condition, harvest season, manufacturing methods, and quality of fresh tea leaves. Lipids are hydrophobic metabolites connected with tea flavor quality formation. Herein, we emphasize that the lipids composition in preharvest tea leaves is crucial for materials quality and hence tea flavor. The characterization of lipids in preharvest tea leaves provides a reference to obtain better tea quality. Lipids transformation in postharvest stages of tea leaves differs from varieties of tea types, and lipid oxidations functions in the tea flavor formation. A comprehensive overview of the lipids in tea leaves of preharvest and postharvest stages is necessary to improve tea quality.

The Characteristic Aroma Compounds of GABA Sun-Dried Green Tea and Raw Pu-Erh Tea Determined by Headspace Solid-Phase Microextraction Gas Chromatography-Mass Spectrometry and Relative Odor Activity Value

We aim to improve the product quality of GABA raw Pu-erh tea during development and processing. In this study, headspace solid-phase microextraction gas chromatography-mass spectrometry technology combined with relative odor activity evaluations was used to compare the volatile compounds of GABA sun-dried green tea and GABA raw Pu-erh tea. Sensory evaluation showed a higher aroma score of GABA raw Pu-erh tea than that of GABA sun-dried green tea, with significant differences in aroma type and purity. A total of 147 volatile compounds of 13 categories were detected, which differed in composition and quantity between the two teas. 2-Buten-1-one,1-(2,6,6-trimethyl-1,3-cyclohexadien-1-yl)-,(E)- and beta.-myrcene largely contributed to the aroma formation of both teas. Five volatile compounds were screened as potential markers for tea aroma. Metabolic pathway analysis showed that monoterpenoid biosynthesis may be beneficial to the formation of flowery and fruity aromas in the teas. We suggest that the findings of this study may provide important guidance for the processing and optimization of GABA tea.

Metabolites and metagenomic analysis reveals the quality of Pu-erh "tea head"

Tea head, a derivative product of Pu-erh tea, are tight tea lumps formed during pile-fermentation. The aim of this study was to reveal the differences of quality-related metabolites and microbial communities between ripened Pu-erh tea (PE-21) and tea heads (CT-21). Compared with PE-21, CT-21 showed a more mellow and smooth taste with slight bitterness and astringency, and can withstand multiple infusions. Metabolites analysis indicated CT-21 had more abundant water-soluble substances (47.39%) and showed significant differences with PE-21 in the main compositions of amino acids, catechins and saccharides which contributed to the viscosity of tea liquor, mellow taste and the tight tea lumps formation. Microbial communities and COG annotation analysis revealed CT-21 had lower abundance of Bacteria (84.05%), and higher abundance of Eukaryota (15.10%), carbohydrate transport and metabolism (8.28%) and glycoside hydrolases (37.36%) compared with PE-21. The different microbial communities may cause metabolites changes, forming distinct flavor of Pu-erh.

Widely targeted metabolomics analysis reveals the formation of nonvolatile flavor qualities during oolong tea manufacturing: a case study of Jinguanyin

Background

The manufacturing processes of oolong tea significantly impact its nonvolatile components, leading to the emergence of distinct flavor attributes. Understanding the dynamic changes in nonvolatile components during the manufacturing stages of the Jinguanyin (JGY) cultivar is crucial for unraveling the potential mechanism behind flavor formation.

Methods

Comprehensive metabolomics and sensomics analyses were conducted to investigate the dynamic changes in nonvolatile components throughout various phases of oolong tea processing, focusing on the JGY cultivar.

Results

A total of 1,005 nonvolatile metabolites were detected, with 562 recognized as significant differential metabolites during various phases of oolong tea processing. Notably, the third turning-over, third setting, and high-temperature treatments exhibited the most significant effects on the nonvolatile metabolites of oolong tea. JGY finished tea demonstrated a characteristic flavor profile, marked by mellowness, sweetness in aftertaste, and a significant Yin rhyme. This flavor profile was collectively promoted by the accumulation of amino acids and organic acids, the decrease in flavonols (3-O-glycosides) and sugar substances, the alteration of phenolic acids, and the stabilization of caffeine.

Conclusion

This study contribute to the understanding of the formation of oolong tea flavor qualities. The dynamic changes observed in various types of nonvolatile compounds during oolong tea processing shed light on the intricate interplay of metabolites and their influence on the final flavor characteristics.

A systemic review on Liubao tea: A time-honored dark tea with distinctive raw materials, process techniques, chemical profiles, and biological activities

Liubao tea (LBT) is a unique microbial-fermented tea that boasts a long consumption history spanning 1500 years. Through a specific post-fermentation process, LBT crafted from local tea cultivars in Liubao town Guangxi acquires four distinct traits, namely, vibrant redness, thickness, aging aroma, and purity. The intricate transformations that occur during post-fermentation involve oxidation, degradation, methylation, glycosylation, and so forth, laying the substance foundation for the distinctive sensory traits. Additionally, LBT contains multitudinous bioactive compounds, such as ellagic acid, catechins, polysaccharides, and theabrownins, which contributes to the diverse modulation abilities on oxidative stress, metabolic syndromes, organic damage, and microbiota flora. However, research on LBT is currently scattered, and there is an urgent need for a systematical recapitulation of the manufacturing process, the dominant microorganisms during fermentation, the dynamic chemical alterations, the sensory traits, and the underlying health benefits. In this review, current research progresses on the peculiar tea varieties, the traditional and modern process technologies, the substance basis of sensory traits, and the latent bioactivities of LBT were comprehensively summarized. Furthermore, the present challenges and deficiencies that hinder the development of LBT, and the possible orientations and future perspectives were thoroughly discussed. By far, the productivity and quality of LBT remain restricted due to the reliance on labor and experience, as well as the incomplete understanding of the intricate interactions and underlying mechanisms involved in processing, organoleptic quality, and bioactivities. Consequently, further research is urgently warranted to address these gaps.

Metabolites profiling reveals the dynamic changes of non-volatiles in Pu-erh during Ganpu tea processing

Ganpu is an unique tea product made by Pu-erh tea and citrus peel. In this study, the non-volatiles changes of Pu-erh during Ganpu tea processing were fully analyzed by UPLC-ESI-MS/MS. Total 276 significantly differential metabolites in Pu-erh during Ganpu processing were detected (P < 0.05, VIP > 1), and their change trend were clustered into 8 subclasses by K-means analysis. Metabolites of Pu-erh present at various processes were revealed. 72 differential metabolites (P < 0.05, VIP > 1 and fold change ≥2 or ≤0.5) between any two stages were identified and fixation was the key step with 61 differential metabolites. 39 flavonoids and 2 lignans and coumarins were significantly decreased after fixation, while 5 terpenoids, 3 amino acids, 1 organic acids, 2 nucleotides and derivatives and newly detected jasminoside A (Log2FC = 9.90), picrocrocin (Log2FC = 9.90) and nomilinic acid (Log2FC = 7.56) were significantly increased. The results provided valuable information about the effect of Ganpu processing on dynamic changes of non-volatiles in Pu-erh.

Metabolomic and transcriptomic analyses reveal comparisons against liquid-state fermentation of primary dark tea, green tea and white tea by Aspergillus cristatus

Liquid-state fermentation (LSF) of tea leaves is a promising way to obtain tea-based nutraceutical products rich in various bioactive compounds. In the study, the changes of bioactive compounds, tea pigments and complex metabolites from LSF of primary dark tea, green tea and white tea infusions with Aspergillus cristatus were determined. Chemical analyses revealed that soluble sugars, monosaccharide composition, total polyphenols, total flavonoids, free amino acids, soluble proteins and tea pigments were changed in different ways. An untargeted metabolomic analysis and ribonucleic acid sequencing (RNA-seq) based transcriptomic analysis were performed to investigate the metabolic differentiation and clarify the key differentially expressed genes (DEGs, fold change >2 and p < 0.05), showing that amino acid metabolism, carbohydrate metabolism and lipid metabolism were the most enriched pathways during A. cristatus fermentation of primary dark tea, green tea and white tea infusions. In addition, glycerophospholipid metabolism, linoleic acid metabolism and phenylalanine metabolism were greatly accumulated in the fermentation of primary dark tea and white tea infusions; Pyruvate metabolism, glycolysis/gluconeogenesis, fatty acid degradation, tyrosine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis and valine and leucine, isoleucine degradation were greatly accumulated in the fermentation of primary dark tea and green tea infusions; Starch and sucrose metabolism was greatly accumulated in the fermentation of green tea and white tea infusions; Galactose metabolism was significantly enhanced in the fermentation of primary dark tea infusion; Amino sugar and nucleotide sugar metabolism, sphingolipid metabolism and alanine, aspartate and glutamate metabolism were significantly enhanced in the fermentation of green tea infusion. Besides, some other pathways involving aminobenzoate degradation, biosynthesis of cofactors, pyrimidine metabolism, benzoxazinoid biosynthesis and phenazine biosynthesis, tropane, piperidine and pyridine alkaloid biosynthesis and flavone and flavonol biosynthesis also differed from each other. These findings support that A. cristatus plays a vital role in the biochemical and genetic regulation of metabolite profile, and could be considered a potential prospect for better use of A. cristatus on different kinds of tea materials.

Ethnobotanical study on medicinal plants used by Bulang people in Yunnan, China

BACKGROUND

Despite the popularity of modern medicine, medicinal plants remain a cornerstone of treatment for numerous diseases, particularly among ethnic groups and tribal communities around the globe. Ethnomedicine offers advantages such as ease of use, convenience, and economic benefits. Medicinal plant knowledge within Bulang ethnic community of southwest China is a valuable complement to Chinese ethnomedicine systems. Accumulated medical knowledge is due to the extensive length of occupation by Bulang People, considered the earliest inhabitants of Xishuangbanna; this has resulted in the development of various traditional treatment methods with local characteristics and unique curative effects. Therefore, there is exceeding value in exploring the medical knowledge of Bulang.

METHODS

A total of 175 local informants participated in the interviews and distribution of questionnaires in 10 Bulang villages in Menghai County, Xishuangbanna Prefecture, Yunnan Province, China. We documented the community of Bulang's use of medicinal herbs, and we used both the informant consensus factor (ICF) and use value (UV) methodologies to analyze the data. Furthermore, we conducted a comparative study to explore the potential of Bulang traditional medicine by comparing it to traditional Dai medicine.

RESULTS

The study recorded 60 medicinal plant species belonging to 41 families and 59 genera, including 22 species of herb, 22 species of shrub, nine species of trees, and seven species of liana. Araceae, Compositae, Lamiaceae and Leguminosae were found to have the highest number of species. The affordability and cultural heritage of Bulang medicine make it advantageous, Investigated Informants report that increased usage of Western medicine (88%), less availability of herbal medicine (95.43%), and the reduction in medicinal plant resources (80.57%) pose significant threats to Bulang medicine. All Bulang medicinal plants are naturally grown, with only 22 per cent being cultivated. Camellia sinensis (0.94) and Zingiber officinale (0.89) showed the highest UV values, while the function of Phyllanthus emblica L. and Houttuynia cordata Thunb. were also noted. The ICF revealed digestive system related diseases were the most commonly treated, with conditions of the motor system using the highest number of plant species. Finally, a comparison with traditional Dai medicine determined that 22 plants (36.67%) of the 60 surveyed had higher medicinal value in Bulang medicine.

CONCLUSION

Bulang communities primarily source medicinal plants from the wild. Should environmental damage lead to the extinction of these medicinal plants, it could result in a shift toward modern Western medicine as a preferred medical treatment. Bulang ethnomedicine is a vital supplement to China's traditional medicine, particularly aspects of ethnic medicine relevant to daily life. Future research should emphasize inter-ethnic medical studies to reveal the untapped potential of medicinal plants.

Tea (Camellia sinensis (L.) Kuntze) as an emerging source of protein and bioactive peptides: A narrative review

Tea residues represent one of the major agricultural wastes that are generated after the processing of tea. They account for 21-28% of crude protein and are often discarded without the extraction of valuable proteins. Due to various bioactivity and functional properties, tea proteins are an excellent alternative to other plant-based proteins for usage as food supplements at a higher dosage. Moreover, their good gelation capacity is ideal for the manufacturing of dairy products, jellies, condensation protein, gelatin gel, bread, etc. The current study is the first to comprehend various tea protein extraction methods and their amino acid profile. The preparation of tea protein bioactive peptides and hydrolysates are summarized. Several functional properties (solubility, foaming capacity, emulsification, water/oil absorption capacity) and bioactivities (antioxidant, antihypertensive, antidiabetic) of tea proteins are emphasized.

Theogallin-to-Gallic-Acid Ratio as a Potential Biomarker of Pu-Erh Teas

There are two types of Pu-erh tea available on the world market: Raw and Ripe. It is not difficult to tell them apart if the Raw version is relatively young. Researchers have already developed various tools to identify Pu-erh teas. However, they are quite complicated and require advanced statistical analyses. In addition, they are characterized by different levels of accuracy. The aim of the work was to identify relationships or differences that would easily give specific results for identifying types of Pu-erh tea. The content of selected methylxanthines was determined by high-performance liquid chromatography (HPLC) on an Agilent 1200 chromatograph with a UV-VIS diode array detector. The total analysis time was 28 min. A combination of liquid chromatography and a triple quadrupole mass spectrophotometer was used to identify gallic acid and theogallin in the analyzed samples. A multivariate cluster analysis was used to compare the results for single samples, and its results were presented in horizontal hierarchical tree plots. The quantitative determination showed that theophylline is present only in Ripe Pu-erh teas. In addition, it was shown that the ratio of theogallin to gallic acid can be an effective tool to verify the authenticity of Pu-erh varieties.

A comprehensive review of polyphenol oxidase in tea (Camellia sinensis): Physiological characteristics, oxidation manufacturing, and biosynthesis of functional constituents

Polyphenol oxidase (PPO) is a metalloenzyme with a type III copper core that is abundant in nature. As one of the most essential enzymes in the tea plant (Camellia sinensis), the further regulation of PPO is critical for enhancing defensive responses, cultivating high-quality germplasm resources of tea plants, and producing tea products that are both functional and sensory qualities. Due to their physiological and pharmacological values, the constituents from the oxidative polymerization of PPO in tea manufacturing may serve as functional foods to prevent and treat chronic non-communicable diseases. However, current knowledge of the utilization of PPO in the tea industry is only available from scattered sources, and a more comprehensive study is required to reveal the relationship between PPO and tea obviously. A more comprehensive review of the role of PPO in tea was reported for the first time, as its classification, catalytic mechanism, and utilization in modulating tea flavors, compositions, and nutrition, along with the relationships between PPO-mediated enzymatic reactions and the formation of functional constituents in tea, and the techniques for the modification and application of PPO based on modern enzymology and synthetic biology are summarized and suggested in this article.

Understanding of formation and change of chiral aroma compounds from tea leaf to tea cup provides essential information for tea quality improvement

Abundant secondary metabolites endow tea with unique quality characteristics, among which aroma is the core component of tea quality. The ratio of chiral isomers of aroma compounds greatly affects the flavor of tea leaves. In this paper, we review the progress of research on chiral aroma compounds in tea. With the well-established GC-MS methods, the formation of, and changes in, the chiral configuration of tea aroma compounds during the whole cycle of tea leaves from the plant to the tea cup has been studied in detail. The ratio of aroma chiral isomers varies among different tea varieties and finished teas. Enzymatic reactions involving tea aroma synthases and glycoside hydrolases participate the formation of aroma compound chiral isomers during tea tree growth and tea processing. Non-enzymatic reactions including environmental factors such as high temperature and microbial fermentation involve in the change of aroma compound chiral isomers during tea processing and storage. In the future, it will be interesting to determine how changes in the proportions of chiral isomers of aroma compounds affect the environmental adaptability of tea trees; and to determine how to improve tea flavor by modifying processing methods or targeting specific genes to alter the ratio of chiral isomers of aroma compounds.

Widely targeted metabolomics and HPLC analysis elaborated the quality formation of Yunnan pickled tea during the whole process at an industrial scale

Yunnan pickled tea is produced from fresh tea-leaves through fixation, rolling, anaerobic fermentation and sun-drying. In this study, widely targeted metabolomics using UHPLC-QQQ-MS/MS and HPLC analysis were carried out to elaborate its quality formation during the whole process. Results confirmed the contribution of preliminary treatments and anaerobic fermentation to the quality formation. A total of 568 differential metabolites (VIP > 1.0, P < 0.05, FC > 1.50 or < 0.67) were screened through OPLS-DA. (-)-Epigallocatechin and (-)-epicatechin significantly (P < 0.05) increased from the hydrolyzation of ester catechins, such as (-)-epigallocatechin gallate and (-)-epicatechin gallate in anaerobic fermentation. Additionally, the anaerobic fermentation promoted vast accumulations of seven essential amino acids, four phenolic acids, three flavones and flavone glycosides, pelargonidin and pelargonidin glycosides, flavonoids and flavonoid glycosides (i.e. kaempferol, quercetin, taxifolin, apigenin, myricetin, luteolin and their glycosides) through relevant N-methylation, O-methylation, hydrolyzation, glycosylation and oxidation.

Ultrasonication Effects on Quality of Tea-Based Beverages

Tea is the most popular consumed drink after water. Teas and tea-based beverages have grown in popularity due to bioactive compounds. Tea-based beverages have started to take their place in the market. Extraction is a crucial step for the production of functional tea-based beverages. Compared to conventional methods, ultrasound is attractive due to its lower energy requirements, and shorter extraction time. This review aimed to discuss recent marketing aspects of tea-based beverages as well as the potential and challenges of a novel infusion technique. This review describes the health benefits and technological aspects of tea-based beverages in relation to how to best solve nutritional and microbial concerns. Current and future challenges and opportunities of the novel infusion technique and its scaling-up for the extraction of bioactive compounds are also covered in the present review.

Effects of Microbial Action and Moist-Heat Action on the Nonvolatile Components of Pu-Erh Tea, as Revealed by Metabolomics

Microbial action and moist-heat action are crucial factors that influence the piling fermentation (PF) of Pu-erh tea. However, their effects on the quality of Pu-erh tea remain unclear. In this study, the effects of spontaneous PF (SPPF) and sterile PF (STPF) on the chemical profile of Pu-erh tea were investigated for the first time, and sun-dried green tea was used as a raw material to determine the factors contributing to the unique quality of Pu-erh tea. The results indicated that the SPPF-processed samples had a stale and mellow taste, whereas the STPF-processed samples had a sweet and mellow taste. Through metabolomics-based analysis, 21 potential markers of microbial action (including kaempferol, quercetin, and dulcitol) and 10 potential markers of moist-heat action (including ellagic acid, β-glucogallin, and ascorbic acid) were screened among 186 differential metabolites. Correlation analysis with taste revealed that metabolites upregulated by moist-heat and microbial action were the main factors contributing to the staler mellow taste of the SPPF-processed samples and the sweeter mellow taste of the STPF-processed samples. Kaempferol, quercetin, and ellagic acid were the main active substances formed under microbial action. This study provides new knowledge regarding the quality formation mechanism of Pu-erh tea.

Regulation of fungal community and the quality formation and safety control of Pu-erh tea

Pu-erh tea belongs to dark tea among six major teas in China. As an important kind of post-fermented tea with complex microbial composition, Pu-erh tea is highly praised by many consumers owing to its unique and rich flavor and taste. In recent years, Pu-erh tea has exhibited various physiological activities to prevent and treat metabolic diseases. This review focuses on the fungi in Pu-erh tea and introduces the sources, types, and functions of fungi in Pu-erh tea, as well as the influence on the quality of Pu-erh tea and potential safety risks. During the process of fermentation and aging of Pu-erh tea, fungi contribute to complex chemical changes in bioactive components of tea. Therefore, we examine the important role that fungi play in the quality formation of Pu-erh tea. The associations among the microbial composition, chemicals excreted, and potential food hazards are discussed during the pile-fermentation of Pu-erh tea. The quality of Pu-erh tea has exhibited profound changes during the process of pile-fermentation, including color, aroma, taste, and the bottom of the leaves, which are inseparable from the fungus in the pile-fermentation of Pu-erh tea. Specifically, the application prospects of various detection methods of mycotoxins in assessing the safety of Pu-erh tea are proposed. This review aims to fully understand the importance of fungi in the production of Pu-erh tea and further provides new insights into subtly regulating the piling process to improve the nutritional properties and guarantee the safety of Pu-erh tea.

Antihyperlipidemic effect and increased antioxidant enzyme levels of aqueous extracts from Liupao tea and green tea in vivo

Liupao tea (fermented dark tea) may improve the active function of hyperlipidemia. Utilizing a hyperlipidemia Sprague-Dawley model and UPLC-MS/MS metabolomics, we examined how the effect of Liupao and green tea extracts on hyperlipidemia and antoxidant enzyme levels and compared their constituents. The results showed that the two types of tea could reduce the levels of total cholesterol (TC), total triglyceride, and low-density lipoprotein cholesterol (LDL-C); increase the contents of bile acids and cholesterol in feces; and improve catalase and glutathione peroxidase (GSH-Px) activities. Compared with the model control group, Liupao tea effectively reduced TC and LDL-C levels by 39.53% and 58.55% and increased GSH-Px activity in the liver by 67.07%, which was better than the effect of green tea. A total of 93 compounds were identified from two samples; the amounts of alkaloids and fatty acids increased compared with green tea, and ellagic acid, hypoxanthine, and theophylline with relatively high contents in Liupao tea had a significantly positive correlation with antihyperlipidemic and antioxidant effects. Therefore, Liupao tea had better antihyperlipidemic and antioxidant activities in vivo than green tea, which might be related to the relatively high content of some active substances.

Aromatic Profiles and Enantiomeric Distributions of Chiral Volatile Compounds in Pu-Erh Tea

Pu-Erh tea, as a typical post-fermented tea, can be divided into raw Pu-Erh tea (RAPT) and ripened Pu-Erh tea (RIPT) according to the processing technology. It is famous for its unique aroma after aging. Although previous research on the aroma characteristics of Pu-Erh tea mostly focused on the aroma compounds, little research on chiral compounds in RAPT and RIPT has been performed. Therefore, the current work aims to explore the aroma characteristics of Pu-Erh tea from the perspective of enantiomers of chiral compounds. A total of 15 enantiomers were determined in this study, among which (R)-(-)-2,2,6-trimethylcyclohexanone, (R)-(-)-linalool, (S)-(+)-linalool, (R)-(+)-δ-octanolactone, (R)-(+)-γ-nonanolactone, (2R,5R)-(+)-theaspirone A, and (R)-(-)-dihydroactinidiolide were identified as enantiomeric compounds that play an important role in the aroma of RAPT and RIPT. Furthermore, (2S,5R)-trans-linalool oxide and (R)-(+)-α-terpineol were important contributors to the aroma profile of RAPT, while (S)-(+)-2-methylbutanal, (S)-(-)-limonene, S-(-)-α-terpineol, and (1R,2R)-(-)-methyl jasmonate contributed to the characteristic aroma of RIPT. The addition of these enantiomeric compounds brings the aroma closer to that of the original tea sample. In addition, the analysis of chiral enantiomers of linalool, limonene, theaspirone A, and γ-nonanolactone can provide guidance for the quality and flavor control of Pu-Erh tea aroma.

Microbiota drive insoluble polysaccharides utilization via microbiome-metabolome interplay during Pu-erh tea fermentation

Polysaccharides are abundant components in Pu-erh tea, yet the utilization of insoluble polysaccharides under the actions of microbiota has rarely been studied. The aim of this work was to study how insoluble polysaccharides were utilized during fermentation through the investigation of the variations and correlation of microbiota with polysaccharides degradation products. Genomics study revealed the significant changes of microbiota. Metabolomics analysis showed monosaccharides (types 1 and 3) were consumed during early and middle fermentation stages, while carboxylic acids and other monosaccharides (type 2) were accumulated at middle and late pile-fermentation stages. Correlation revealed that type 1 and 3 monosaccharides, which act as energy providers, were positively associated with Aspergillus, while type 2 monosaccharides possessing multiple bioactivities and carboxylic acids influencing tea taste were positively related to Rasamsonia, Thermomyces, Bacillaceae, and Lactobacillaceae. This study would be beneficial to improve production efficiency and provide basis for quality control of Pu-erh tea fermentation.

Anti-Oxidative Effect of Pu-erh Tea in Animals Trails: A Systematic Review and Meta-Analysis

This study adopted systematic literature review and meta-analysis methodology to explored anti-oxidative effect of pu-erh tea. Study authors have systemically searched seven databases up until 21 February 2020. In performing the literature search on the above-mentioned databases, the authors used keywords of pu-erh AND (superoxide dismutase OR glutathione peroxidase OR malondialdehyde). Results derived from meta-analyses showed statistically significant effects of pu-erh tea on reducing serum MDA levels (SMD, −4.19; 95% CI, −5.22 to −3.15; p < 0.001; I2 = 93.67%); increasing serum SOD levels (SMD, 2.41; 95% CI, 1.61 to 3.20; p < 0.001; I2 = 91.36%); and increasing serum GSH-Px levels (SMD, 4.23; 95% CI, 3.10 to 5.36; p < 0.001; I2 = 93.69%). Results from systematic review and meta-analyses validated that various ingredients found in pu-erh tea extracts had anti-oxidation effects, a long-held conventional wisdom with limited supporting evidence.

Tea Infusions as a Source of Phenolic Compounds in the Human Diet

Phenolic compounds are components with proven beneficial effects on the human body, primarily due to their antioxidant activity. In view of the high consumption of tea and the numerous factors that affect the nutritional value of its infusions, the aim of this study was to identify the effects of tea type and duration of leaf extraction with water on the levels of phenolic compounds and other components that determine biological activity (oxalates, Ca, Na, Cu, and Mn). Based on assays, infusions of red tea prepared for 20 min were found to be the best source of phenolics (202.9 mg/100 mL), whereas the lowest level of these compounds was determined in infusions of black tea extracted from leaves for 30 min (46.9 mg/100 mL). The highest degree of increase in polyphenol content (by approx. 50%) was noted in red and green tea infused for between 10 and 20 min, whereas for black tea, polyphenol levels decreased with time. The biological activity of tea infusions appears to be determined to the greatest extent by the interactions between phenolic compounds and oxalates (r = 0.6209), calcium (r = 0.8516), and sodium (0.8045). A daily intake of three to four mugs (1 L) of tea infusions provides the human body the entire amount of phenolics recommended for health reasons (as regards red tea, this is possible at 1/3 of the volume) and covers the daily requirement for manganese, as well as (partially) copper.

Moisture contents and product quality prediction of Pu-erh tea in sun-drying process with image information and environmental parameters

In this study, moisture contents and product quality of Pu-erh tea were predicted with deep learning-based methods. Images were captured continuously in the sun-drying process. Environmental parameters (EP) of air humidity, air temperature, global radiation, wind speed, and ultraviolet radiation were collected with a portable meteorological station. Sensory scores of aroma, flavor, liquor color, residue, and total scores were given by a trained panel. Convolutional neural network (CNN) and gated recurrent unit (GRU) models were constructed based on image information and EP, which were selected in advance using the neighborhood component analysis (NCA) algorithm. The evolved models based on deep-learning methods achieved satisfactory results, with RMSE of 0.4332, 0.2669, 0.7508 (also with R ² of .9997, .9882, .9986, with RPD of 53.5894, 13.1646, 26.3513) for moisture contents prediction in each batch of tea, tea at different sampling periods, the overall samples, respectively; and with RMSE of 0.291, 0.2815, 0.162, 0.1574, 0.3931 (also with R ² of .9688, .9772, .9752, .9741, .8906, with RPD of 5.6073, 6.5912, 6.352, 6.1428, 4.0045) for final quality prediction of aroma, flavor, liquor color, residue, total score, respectively. By analyzing and comparing the RMSE values, the most significant environmental parameters (EP) were selected. The proposed combinations of different EP can also provide a valuable reference in the development of a new sun-drying system.

UHPLC-Q-TOF-MS/MS-based Metabolite Profiling of Ganpu Tea in Rat Urine and Feces

Ganpu tea is a novel type of beverage produced from Pu-erh tea stuffed in the pericarp of Citrus reticulata “Chachi”. It has gained considerable popularity in China owing to its inviting flavor and health effects. However, the in vivo metabolites of Ganpu tea, which may contribute to its overall health effects, are still unclear. In the present work, rat urine and feces samples were collected after oral administration of Ganpu tea extract (GTE), and then subjected to ultra-high-performance liquid chromatography/quadrupole-time-of-flight tandem mass spectrometry (UHPLC-Q-TOF-MS/MS)-based metabolite profiling. As a result, 27 prototype compounds and 41 metabolites derived from caffeic acid, gallic acid, p-coumaric acid, xanthine, catechin, polymethoxyflavone, (PMF) flavanone, and flavone were identified in rat urine and feces. Based on the detected metabolites, the ingested prototype compounds derived from Ganpu tea were found to undergo extensive phase II metabolism in rats, especially and sulfation. These results will be valuable for interpreting the health effects of Ganpu tea.