Metabolomics Based on UHPLC-Orbitrap-MS and Global Natural Product Social Molecular Networking Reveals Effects of Time Scale and Environment of Storage on the Metabolites and Taste Quality of Raw Pu-erh Tea

Triterpenoid saponins in tea plants: A spatial and metabolic analysis using UPLC-QTOFMS, molecular networking, and DESI-MSI

Triterpenoid saponins, bioactive compounds with pharmaceutical relevance and functional food potential, are abundant in tea plants (Camellia sinensis), yet their structural diversity and tissue-specific distribution remain insufficiently explored. Using high-resolution mass spectrometry, Feature-based Molecular Networking, and imaging mass spectrometry (IMS), we profiled 52 tea saponins, including two novel trisaccharide saponins with unique glycosylation patterns. Aerial tissues, particularly buds and leaves, were enriched with cinnamoyl-decorated tetrasaccharide saponins, whereas roots predominantly accumulated di- and trisaccharide saponins, with significant cultivar-specific variation. IMS further revealed a compartmentalized root distribution, with di- and trisaccharide saponins localized in the epidermis and cortex, while tetrasaccharide saponins were concentrated in the stele. These findings advance understanding of the structural complexity and spatial accumulation of tea saponins, offering insights for bioactive compound extraction and informing breeding strategies to enhance saponin yield and diversity.

Effect of cooking conditions on sea urchin dumplings

The objective of this study was to investigate the changes in flavour and taste of sea urchin dumplings subjected to different cooking methods, utilising gas chromatography-ion mobility spectrometry (GC-IMS), electronic tongue (E-tongue) analysis, free amino acid content assessment and sensory evaluation. The GC-IMS technique successfully detected 69 volatile compounds in the skin and 60 volatile compounds in the filling of the boiled dumplings. From the established fingerprints, it was found that there were significant differences in the flavour compounds of dumplings skins among the groups. 1-Octen-3-ol, 2-methylpropanal, ethyl acetate monomer, methyl 2-methylbutyrate and 2-pentylfuran were found in the skins of dumplings cooked in different ways and were positively correlated with freshness in the E-tongue, and were also positively correlated with aspartic acid and glutamic acid. Sensory evaluations revealed significant differences in dumplings under different cooking methods. The results can provide data support and theoretical reference for the processing of dumplings.

The processing of shaking and standing improves the taste quality of summer black tea

Shaking and standing (SS) enhances the aroma intensity and quality of black tea (BT). However, its contribution to the taste remains unknown, and the interaction mechanism between the aroma and taste perception of black tea is also undisclosed. Here, the metabolomics and sensory evaluation-assisted flavor analysis were employed to investigate the changes in non-volatiles induced by SS, and the interaction mechanism between aroma and taste perception. SSBT exhibited considerable reduced bitterness and astringency intensities compared to BT. Notably, the concentrations of contributing compounds such as catechins, proanthocyanidins, theaflavins, anthocyanins, and flavonol glycosides were decreased in SSBT. Sensory experiments further revealed that nine floral and sweet odorants in SSBT exhibited odor-enhancing interactions. Molecular docking validated the binding affinity and interaction forces between mono/di-ligands and OR1G1/OR52D1. Furthermore, the presence of the nine odorants exerted inhibitory effects on the bitterness and astringency of SSBT. These findings provide a novel perspective on the formation of flavor in SSBT.

Quantitative descriptive analysis, non-targeted metabolomics and molecular docking reveal the dynamic aging and taste formation mechanism in raw Pu-erh tea during the storage

Natural storage promotes raw Pu-erh tea (RaPT) aging along with chemical conversion and flavor evolution. In this study, quantitative descriptive analysis (QDA) and UHPLC-Orbitrap-MS/MS-based non-targeted metabolomics were performed to illustrate dynamic changes of taste compounds across 18 RaPT samples during the storage. Multivariate statistical analyses effectively classified stored RaPT into three groups based on storage stages, confirming that storage duration, rather than environmental conditions, primarily influences the taste profile and the changes in non-volatile compounds. A total of 509 characteristic metabolites (VIP > 1.0, P < 0.05, and FC > 1.50 or < 0.67) including multifarious flavor compounds related to tastes evolution were identified. Notable changes included the reduction, transformation, and condensation of flavonoids (such as catechins, flavonol glycosides, and anthocyanins) and amino acids, alongside an accumulation of organic acids, catechin/amino acid derivatives, flavoalkaloids, and gallic acid. These transformations generated significantly (P < 0.05) decreased umami, bitterness, and astringency, while significantly (P < 0.05) increasing sourness and kokumi. Molecular docking analyses further revealed that certain compounds, notably puerins and N-ethyl-2-pyrrolidone-substituted flavan-3-ols (EPSFs), exhibit high binding affinities with CaSR and OTOP1, contributing to the kokumi and sourness taste profiles.

Effects of stir-frying on chemical profile, sensory quality and antioxidant activity of Chrysanthemi Flos: A metabolomics and sensory study

Chrysanthemi Flos has been consumed as floral tea for centuries, but the effects of stir-frying on its chemical profile, sensory characteristics, and bioactivity remain unclear. This study used untargeted metabolomics, sensory assessment (E-eye, E-nose, E-tongue), and antioxidant activity evaluation to investigate compositional changes and their effects. In the metabolomics analysis, a total of 101 non-volatile and 306 volatile differential metabolites were identified. During stir-frying of Chrysanthemi Flos, glycosidic bond rupture in flavonoid glycosides, thermal decomposition of caffeoylquinic acid, Maillard, and caramelization reactions occurred. This led to the formation of 4 flavonoid glycosides (luteolin, diosmetin, apigenin, and quercetin) and 33 roasted aroma compounds like pyrazines, furans, 2-methylbutanal, and 2-furanmethanol. The Spearson's correlation analysis of metabolomics, E-eye, and E-tongue data showed that these compositional changes not only resulted in darkening and scorching of the color of Chrysanthemi Flos after stir-frying, but also improved the bitter and astringent taste of Chrysanthemi Flos tea broths, and enhanced the antioxidant activity of Chrysanthemi Flos. These findings will provide new perspectives on the selection of processing methods for Chrysanthemi Flos.

Effect of tea stems on the quality formation of large-leaf yellow tea: Sensomics and flavoromics approaches

In this study, the stems (ST) and leaves (LT) isolated from Large-leaf yellow tea (LYT) were used for sensory evaluation and quantitative analysis of flavor metabolites by sensomics and flavoromics. The results showed that the flavors of ST and LT in LYT were significantly different, and ST had stronger roasty and nutty aroma and sweet taste, which was mainly due to the accumulation of higher theanine and soluble monosaccharides in ST, and provided more substrates for the production of more pyrazine by the Maillard reaction; whereas LT contributed to the mellow and thick taste quality of LYT, and the abundance of catechins and caffeine were the main reason. The metabolic patterns of flavor metabolites indicated that the flavor differences between ST and LT were mainly due to biological metabolism in tea plants. This study provides the selection of raw materials for LYT in the future and product development of tea stems.

Unlocking Hidden Treasures: LC-MS/MS Molecular Networks for Exploring Novel Passiflora Species with Pharmaceutical Potential

In this study, we report the metabolic profiling of several previously uncharacterized Passiflora species native to Brazil, employing molecular networks to delve deeper into chemical constituents. Using the GNPS platform, in silico tools, and substructure annotation techniques, we expanded the chemical annotations. Principal Coordinate Analysis (PCoA) revealed significant metabolic similarities between several species, including P. incarnata, suggesting shared pharmacological potential. Our identification of metabolic compounds facilitated comparisons between understudied species with medicinal properties. Notably, we documented 25 previously uncharacterized species, paving the way for the development of novel products aimed at improving human well-being. This research focused on several native Passiflora species from Brazil, highlighting their unexplored therapeutic potential.

Metabolomics and electronic-tongue analysis reveal differences in color and taste quality of large-leaf yellow tea under different roasting methods

Roasting is a key process in the production of large-leaf yellow tea (LYT). In this study, we synthesized metabolomics and electronic-tongue analysis to compare the quality of charcoal-roasted, electric-roasted and drum-roasted LYT. Charcoal-roasted LYT had the highest yellowness and redness, drum-roasted LYT had a more prominent umami and brightness, and electric roasting reduced astringency. A total of 48 metabolites were identified by metabolomics. Among these, leucocyanidin, kaempferol, luteolin-7-lactate, and apigenin-7-O-neohesperidoside might affect the brightness and yellowness. Theanine, aspartic acid, and glutamic acid contents significantly and positively correlated with umami levels, and the high retention of flavonoid glycosides and catechins in drum-roasted LYT contributed to its astringency. These findings elucidate the contribution of the roasting method to the quality of LYT and provide a theoretical basis for LYT production.

Investigation of the quality of Lu'an Guapian tea during Grain Rain period by sensory evaluation, objective quantitative indexes and metabolomics

The harvest date is a crucial factor in determining tea quality. For Lu'an Guapian (LAGP) tea, Grain Rain period (GRP) represents a pivotal phase in the transformation of tea quality. The sensory evaluation, computer vision and E-tongue revealed that the liquor color score, B and G values of tea infusion were increased during GRP, while the astringency, bitterness intensities and the R value of the tea infusion were decreased. Consequently, the tea infusion exhibited a greener hue and the taste became appropriate during GRP. Non-targeted metabolomics revealed that the majority of amino acids and derivatives was reduced during GRP. Furthermore, flavonoids, in particular flavonol glycosides, exhibited considerable variation during GRP. Finally, nine metabolites were identified as markers for quality transformation during GRP by PLS and Random Forest. This study investigated the quality of LAGP teas during GRP and filled the gap in the variation of LAGP tea quality during GRP.

Dynamic changes and correlation analysis of microorganisms and flavonoids/ amino acids during white tea storage

White tea stored for various times have different flavors. However, the mechanism of flavor conversion remains elusive. Flavonoids and amino acids are two typical flavor components in tea. Herein, the contents of 46 flavonoids and 40 amino acids were measured in white tea (Shoumei) stored for 1, 3, 5 and 7 years, respectively. L-tryptophan, L-ornithine and L-theanine contribute to the refreshing taste of Shoumei 1 and 3. Quercetin, rutin and hesperidin contribute to aging charm and grain aroma of Shoumei 5 and 7. 306 bacterial OTUs and 268 fungal OTUs core microbiota existed in all samples. Interestingly, white teas contained higher richness of fungi than bacteria. The correlation analysis showed that the cooperation with bacteria and fungi may result in the flavonoids and amino acids composition changes in white teas during storage. Overall, this study provides new insights into flavor conversion of white tea during storage.

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.

Effects of processing technology on tea quality analyzed using high-resolution mass spectrometry-based metabolomics

Fixation is a crucial step in green tea processing that can impact quality. In this study, we explored the differences in the chemical components of steamed and fried green teas made from the same batch of fresh tea leaves using different fixing methods. Results showed that concentrations of sucrose and free amino acids were significantly higher in steamed green tea. Abundances of 12 compounds including purine nucleoside, pyrimidine nucleoside derivatives, and catechins were higher in fried green tea, while 34 compounds such as amino acids and their derivatives, benzofurans and flavonoids were higher in steamed green tea. Thus, steaming retained more compounds associated with sweet and fresh tastes, such as free amino acids, while frying produced more compounds with bitter tastes, such as catechin. This might explain why steamed green tea is mellower than fried tea.

Distinct changes of taste quality and metabolite profile in different tomato varieties revealed by LC-MS metabolomics

Breeding of tomato varieties based on phenotypic traits can potentially lead to a decline in taste and nutritional values, thereby impacting consumer acceptance. However, taste is an intrinsic characteristic of tomatoes. Its decoding requires the identification of crucial compounds and the associated metabolic pathways implicated in taste development and formation. In this study, the taste parameter differences of four tomato varieties were distinguished using an electronic tongue. The content of organic acids and free amino acids, which were closely associated with taste variations, was quantitatively analyzed. Several important taste metabolites and metabolic pathways were identified based on LC-MS metabolomics and enrichment analysis. Through correlation analysis, it was determined that there existed significant associations between the taste, compounds, and metabolites of tomato varieties with different phenotypes. This study could provide references and theoretical basis for tomato breeding, as well as the control and evaluation of taste and quality of tomato varieties.

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.

Biotechnological potential of actinomycetes in the 21st century: a brief review

This brief review aims to draw attention to the biotechnological potential of actinomycetes. Their main uses as sources of antibiotics and in agriculture would be enough not to neglect them; however, as we will see, their biotechnological application is much broader. Far from intending to exhaust this issue, we present a short survey of the research involving actinomycetes and their applications published in the last 23 years. We highlight a perspective for the discovery of new active ingredients or new applications for the known metabolites of these microorganisms that, for approximately 80 years, since the discovery of streptomycin, have been the main source of antibiotics. Based on the collected data, we organize the text to show how the cosmopolitanism of actinomycetes and the evolutionary biotic and abiotic ecological relationships of actinomycetes translate into the expression of metabolites in the environment and the richness of biosynthetic gene clusters, many of which remain silenced in traditional laboratory cultures. We also present the main strategies used in the twenty-first century to promote the expression of these silenced genes and obtain new secondary metabolites from known or new strains. Many of these metabolites have biological activities relevant to medicine, agriculture, and biotechnology industries, including candidates for new drugs or drug models against infectious and non-infectious diseases. Below, we present significant examples of the antimicrobial spectrum of actinomycetes, which is the most commonly investigated and best known, as well as their non-antimicrobial spectrum, which is becoming better known and increasingly explored.

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.

Investigation of the effect of over-fired drying on the taste and aroma of Lu'an Guapian tea using metabolomics and sensory histology techniques

Lu'an Guapian (LAGP) tea, a representative Chinese roasted green tea, undergoes significant changes in taste and aroma during over-fired drying. However, limited studies have been conducted on these effects. This study employed metabolomics and sensory histology techniques to analyze non-volatile and volatile compounds the second drying and pulley liquefied gas drying (PLD) samples. The results revealed that after PLD, the samples exhibited lower umami, bitterness, and astringency; whereas floral, sweet, roasted, cooked corn-like, and cooked chestnut-like aromas became stronger. Among them, the content of (-)-epigallocatechin gallate, glutamic acid, and theogallin, which were closely related to taste, decreased by 4.5 %, 12.3 %, and 10.4 %, respectively. Eight key aroma components were identified as the main contributors to the sample aroma changes: (E)-β-ionone, dimethyl sulfide, (E,E)-2,4-heptadienal, geraniol, linalool, benzeneacetaldehyde, 2-ethyl-3,5-dimethylpyrazine, and hexanal. This study provides a theoretical basis for enhancing the quality of LAGP teas.

Integration of non-targeted/targeted metabolomics and electronic sensor technology reveals the chemical and sensor variation in 12 representative yellow teas

Yellow tea is a lightly fermented tea with unique sensory qualities and health benefits. However, chemical composition and sensory quality of yellow tea products have rarely been studied. 12 representative yellow teas, which were basically covered the main products of yellow tea, were chosen in this study. Combined analysis of non-targeted/targeted metabolomics and electronic sensor technologies (E-eye, E-nose, E-tongue) revealed the chemical and sensor variation. The results showed that yellow big tea differed greatly from yellow bud teas and yellow little teas, but yellow bud teas could not be effectively distinguished from yellow little teas based on chemical constituents and electronic sensory characteristics. Sensor variation of yellow teas might be attributed to some compounds related to bitterness and aftertaste-bitterness (4'-dehydroxylated gallocatechin-3-O-gallate, dehydrotheasinensin C, myricitin 3-O-galactoside, phloroglucinol), aftertaste-astringency (methyl gallate, 1,5-digalloylglucose, 2,6-digalloylglucose), and sweetness (maltotriose). This study provided a comprehensive understanding of yellow tea on chemical composition and sensory quality.

Diversity in storage age enables discrepancy in quality attributes and metabolic profile of Citrus grandis "Tomentosa" in China

The folk proverb "the older, the better" is usually used to describe the quality of Citrus grandis "Tomentosa" (CGT) in China. In this study, CGT aged for 6-, 12-, 16-, and 19-years were collected for the investigation of infusion color, main bioactive components, antioxidant activity, metabolic composition, and pathway. The results found that infusion color, the total phenolic and flavonoid, and antioxidant activity of CGT were obviously changed by aging process. Through untargeted metabolomics, 55 critical metabolites were identified to in discrimination of CGT with different storage ages, mainly including phenylpropanoids, lipids, and organic oxygen compounds. Twenty compounds that showed good linear relationships with storage ages could be used for year prediction of CGT. Kyoto encyclopedia of genes and genomes enrichment pathway analysis uncovered important metabolic pathways related to the accumulation of naringin, kaempferol, and choline as well as the degradation of benzenoids, thus supporting that aged CGT might be more beneficial to health. Correlation analysis provided that some key metabolites with bitter taste and biological activity were involved in the darkening and reddening of CGT infusion during aging, and total phenolic and flavonoid were more strongly associated with the antioxidant activity of CGT. This study systematically revealed the quality changes and key metabolic pathways during CGT aging at first time. PRACTICAL APPLICATION: This study reveals the differences in quality attributes and metabolic profile between CGT with different storage ages, providing guidance for consumers' consumption, and also providing more scientific basis for the quality evaluation and improvement of CGT.

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.

Analysis of aroma quality changes of large-leaf black tea in different storage years based on HS-SPME and GC-MS

The reasons for the change in volatile metabolites and aroma of black tea during storage remain unclear. Therefore, we used HS-SPME and GC-MS methods to analyze the aroma compounds of new tea (2021) versus aged tea groups (2015, 2017, and 2019). A total of 109 volatile components were identified. During storage, 36 metabolites mainly with floral and fruity aromas decreased significantly, while 18 volatile components with spicy, sour, and woody aromas increased significantly. Linalool and beta-ionone mainly contributed to sweet and floral aromas of freshly-processed and aged black tea, respectively. Isovaleric acid and hexanoic acid mainly caused sour odor of aged black tea. The monoterpene biosynthesis and secondary metabolic biosynthesis pathways might be key metabolic pathways leading to changes in the relative content of metabolites during storage of black tea. Our study provides theoretical support for fully understanding the changes in the aroma quality of black tea during storage.

Metabolomics analysis reveals the mechanism underlying the improvement in the color and taste of yellow tea after optimized yellowing

In this study, an optimized yellowing process for yellow tea (YT) was developed by response surface methodology. The results showed that increasing the yellowing temperature from 20 °C to 34 °C, increasing the relative humidity from 55% to 67%, and reducing the yellowing time from 48 h to 16 h, caused a 40.5% and 43.2% increase in the yellowness and sweetness of YT, respectively, and improved the consumer acceptability by 36.8%. Moreover, metabolomics was used to explore the involved mechanisms that resulted in the improved YT quality. The optimized yellowing promoted the hydrolysis of 5 gallated catechins, 6 flavonoid glycosides, theogallin and digalloylglucose, resulting in the accumulation of 5 soluble sugars and gallic acid. Meanwhile, it promoted the oxidative polymerization of catechins (e.g., theaflagallin, δ-type dehydrodicatechin and theasinensin A), but decelerated the degradation of chlorophylls. Overall, this optimized yellowing process could serve as a guide to a shorter yellowing cycle.

Estimating the sensory-associated metabolites profiling of matcha based on PDO attributes as elucidated by NIRS and MS approaches

Matcha has been globally valued by consumers for its distinctive fragrance and flavor since ancient times. Currently, the protected designation of origin (PDO) certified matcha, characterized by unique sensory attributes, has garnered renewed interest from consumers and the industry. Given the challenges associated with assessing sensory perceptions, the origin of PDO-certified matcha samples from Guizhou was determined using NIRS and LC-MS platforms. Notably, the accuracy of our established attribute models, based on informative wavelengths selected by the CARS-PLS method, exceeds 0.9 for five sensory attributes, particularly the particle homogeneity attribute (with a validation correlation coefficient of 0.9668). Moreover, an LC-MS method was utilized to analyze non-target matcha metabolites to identify the primary flavor compounds associated with each flavor attribute and to pinpoint the key constituents responsible for variations in grade and flavor intensity. Additionally, high three-way intercorrelations between descriptive sensory attributes, metabolites, and the selected informative wavelengths were observed through network analysis, with correlation coefficients calculated to quantify these relationships. In this research, the integration of matcha chemical composition and sensory panel data was utilized to develop predictive models for assessing the flavor profile of matcha based on its chemical properties.

Revealing the chemical differences and their application in the storage year prediction of Qingzhuan tea by SWATH-MS based metabolomics analysis

It's generally believed that the longer the storage, the better the quality of dark tea, but the chemical differences of Qingzhuan tea (QZT) with different storage years is still unclear. Herein, in this work, an untargeted metabolomic approach based on SWATH-MS was established to investigate the differential compounds of QZT with 0-9 years' storage time. These QZT samples were roughly divided into two categories by principal component analysis (PCA). After orthogonal projections to latent structures discriminant analysis (OPLS-DA), 18 differential compounds were putatively identified as chemical markers for the storage year variation of QZT. Heatmap visualization showed that the contents of catechins, fatty acids, and some phenolic acids significantly reduced, flavonoid glycosides, triterpenoids, and 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) increased with the increase of storage time. Furthermore, these chemical markers were verified by the peak areas corresponding to MS2 ions from SWATH-MS. Based on the extraction chromatographic peak areas of MS and MS2 ions, a duration time prediction model was built for QZT with correlation coefficient R2 of 0.9080 and 0.9701, and RMSEP value of 0.85 and 1.24, respectively. This study reveals the chemical differences of QZT with different storage years and provides a theoretical basis for the quality evaluation of stored dark tea.

Flavor perception and health benefits of tea

As one of the most consumed non-alcoholic beverages in the world, tea is acclaimed for its pleasant flavor and various health benefits. Different types of tea present a distinctive flavor and bioactivity due to the changes in the composition and proportion of respective compounds. This article aimed to provide a more comprehensive understanding of tea flavor (including aroma and taste) and the character of tea in preventing and alleviating diseases. The recent advanced modern analytical techniques for revealing flavor components in tea, including enrichment, identification, quantitation, statistics, and sensory evaluation methodologies, were summarized in the following content. Besides, the role of tea in anti-cancer, preventing cardiovascular disease and metabolic syndrome, anti-aging and neuroprotection, and regulating gut microbiota was also listed in this article. Moreover, questions and outlooks were mentioned to objectify tea products' flavor quality and health benefits on a molecular level and significantly promote our understanding of the comprehensive value of tea as a satisfactory health beverage in the future.

Metabolomics reveals the effects of different storage times on the acidity quality and metabolites of large-leaf black tea

Most aged tea has superior sensory qualities and good health benefits. The content of organic acids determines of the quality and biological effects of aged tea, but there are no reports of the effect of storage on the composition and relative proportion of acidic compounds in black tea. This study analyzed and compared the sourness and metabolite profile of black tea produced in 2015, 2017, 2019 and 2021 using pH determination and UPLC-MS/MS. In total, 28 acidic substances were detected, with 17 organic acids predominating. The pH of black tea decreased significantly during storage from pH 4.64 to pH 4.25 with significantly increased in l-ascorbic acid, salicylic acid, benzoic acid and 4-hydroxybenzoic acid. The metabolic pathways ascorbate biosynthesis, salicylate degradation, toluene degradation, etc. were mainly enriched. These findings provide a theoretical basis to regulate the acidity of aged black tea.

Yellow tea: more than turning green leaves to yellow

Yellow tea (YT), a slightly-fermented tea originated from Ming Dynasty with distinctive "Three yellows," mild-sweet smell, and mellow taste attributed to the unique yellowing process. Based on current literature and our previous work, we aim to comprehensively illustrate the key processing procedures, characteristic chemical compounds, health benefits and applications, as well as the interlocking relationships among them. Yellowing is the most vital procedure anchored on the organoleptic quality, characteristic chemical components, and bioactivities of YT, which is influenced by temperature, moisture content, duration, and ventilation conditions. Pheophorbides, carotenoids, thearubigins and theabrownins are the major pigments contributing to the "three yellows" appearance. Alcohols, such as terpinol and nerol, are attributed to the refreshing and sweet aroma of bud and small-leaf YT, while heterocyclics and aromatics forming during roasting result in the crispy rice-like large-leaf YT. Hygrothermal effects and enzymatic reactions during yellowing result in the decline of astringent substances. Meanwhile, multiple bioactive compounds such as catechins, ellagitannins, and vitexin, endow YT with antioxidant, anti-metabolic syndrome, anti-cancer, gut microbiota regulation, and organ injury protection effects. Future studies focusing on the standard yellowing process technology, quality evaluation system, and functional factors and mechanisms, possible orientations, and perspectives are guaranteed.

Exploring the mechanism of browning of Rosa roxburghii juice based on nontargeted metabolomics

To explore the mechanism of Rosa roxburghii juice browning, this experiment was based on nontargeted metabolomics to study the effects of browning on the nutrition, flavor, metabolites, and metabolic pathways of R. roxburghii juice before and after storage. The results showed that the total soluble solids, superoxide dismutase (SOD), vitamin C (V_C ), total phenol, and total flavonoid of R. roxburghii juice decreased significantly before and after storage. The color difference value ∆E, browning index, and flavor and taste of R. roxburghii juice changed significantly (p < 0.05). A total of 541 metabolites were detected before and after browning of R. roxburghii juice by nontargeted metabolomics, including 435 differential metabolites, of which 221 were upregulated, and 214 were downregulated. The differential metabolites were mainly amino acids and peptides, carbohydrates, and carbohydrate conjugates. There were a total of 76 metabolic pathways enriched by differential metabolites, involving mainly galactose metabolism; alanine, aspartate and glutamate metabolism; and pantothenate and CoA biosynthesis. The experimental results showed that after browning of R. roxburghii juice, V_C , total phenol, total flavonoid, and SOD activity were seriously lost, and the flavor deteriorated. The contribution of differential metabolites and metabolic pathways to the browning of R. roxburghii juice was sugar metabolism > amino acid metabolism > ascorbate and aldarate metabolism > phenols.

Formation Mechanism of Di-N-ethyl-2-pyrrolidinone-Substituted Epigallocatechin Gallate during High-Temperature Roasting of Tea

Four di-N-ethyl-2-pyrrolidinone-substituted epigallocatechin gallate (EGCG) and two di-N-ethyl-2-pyrrolidinone-substituted gallocatechin gallate (GCG) flavan-3-ols (di-EPSFs) were prepared by the thermal simulation reaction. The effects of reaction temperature and time, initial reactant ratios, and pH values on the content of di-EPSFs were studied. The formation of six di-EPSFs was most favored when the initial reactant ratio of EGCG and theanine was 1:2 and heated under 130 °C at pH 10 for 120 min. The contents of di-EPSF1, di-EPSF2, and di-EPSF5 in large-leaf yellow tea (LYT) increased with the increase of roasting degree. Through quantitative analysis, it was found that EGCG would interact with the Strecker degradation products of theanine to form EPSFs, which further combined with the Strecker degradation products of theanine to form di-EPSFs. This study further improved the understanding of the transformation pathways of EGCG and theanine during tea processing and contributed to exploring the flavor characteristics and health benefits of di-EPSFs.

Guide isolation of guaiane-type sesquiterpenoids from Daphne tangutica maxim. And their anti-inflammatory activities

Using liquid chromatography with tandem mass spectrometry guided molecular networking, 12 undescribed guaiane-type sesquiterpenoids, namely tanguticatins A-L, 19 known analogs and a previously undescribed triterpene (tanguticatin M) were obtained from Daphne tangutica Maxim and characterized. Their planar structures and configurations were elucidated and unequivocally assigned by detailed spectroscopic analyses, electronic circular dichroism spectral calculations and single single-crustal X-ray diffraction analysis. All the isolated compounds were evaluated for lipopolysaccharide-induced nitric oxide production in murine microglial BV2 cells. Tanguticatin E and K exhibited more potent inhibitory effects than minocycline (positive control).

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.

Targeted isolation of diterpenoids and sesquiterpenoids from Daphne gemmata E. Pritz. ex Diels using molecular networking together with network annotation propagation and MS2LDA

Investigation of the whole plant of Daphne gemmata E. Pritz. ex Diels (Thymelaeaceae) using molecular networking coupled to Network Annotation Propagation (NAP) and unsupervised substructure annotation (MS2LDA) led to the discovery of five tigliane diterpenoids, 14 guaiane sesquiterpenoids, one rhamnofolane diterpenoid and three carotene sesquiterpenoids. The structures of the eight undescribed compounds, daphnorbol A and daphnegemmatoids A-G, were characterized by detailed spectroscopic analyses, NMR and ECD calculations, application of Snatzke's method and single-crystal X-ray diffraction analysis. All isolated compounds were evaluated for their cytotoxic activities against HepG2, A549, and MCF-7 cells by MTT assay. Daphnorbol A exhibited significant cytotoxic activity against HepG2 and A549 cells with IC50 values of 4.06 μM and 6.35 μM, respectively. Prostratin showed potent cytotoxic activity against HepG2 and A549 cells with IC50 values of 6.06 μM and 5.45 μM, respectively. Further Hoechst 33,258 and AO-EB staining assays indicated that daphnorbol A and prostratin could induce apoptosis in HepG2 and A549 cells.

Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques

Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.

A novel method for efficient screening and annotation of important pathway-associated metabolites based on the modified metabolome and probe molecules

植物次生代谢物在抵御生物/非生物胁迫、生物间互作以及信息传递等方面发挥重要作用,次生代谢途径解析对植物分子育种、天然产物合成等方面具有重要意义。液相色谱-高分辨串联质谱(LC-HRMS/MS)为次生代谢物鉴定及途径表征提供了技术手段。非靶向LC-HRMS/MS方法可获得丰富的质谱信号,包括一级质谱和二级质谱(MS, MS/MS),但受质谱数据库规模以及次生代谢物复杂性的制约,次生代谢物注释十分困难。该研究以玉米叶片中苯丙烷途径代谢物为例,发展用于非靶向代谢组数据中重要途径代谢物的高效筛选和注释新方法。首先,利用公共代谢途径数据库及文献获取参与苯丙烷代谢途径的61种修饰反应类型,进而从非靶向实验数据中筛选出修饰代谢组。其次,获取开源串联质谱数据中的苯丙烷类化合物作为探针分子,构建探针分子质谱数据库。将探针分子与修饰代谢组共建分子网络,锁定目标途径代谢物并注释结构。该方法在正、负离子模式下分别筛选出玉米叶片中392个和417个苯丙烷途径候选代谢物,去冗余后共注释出129个代谢物,涉及苯丙烷代谢的主要分支途径,如黄酮途径的8个类黄酮、19个氧苷类黄酮和32个碳苷类黄酮,31个羟基肉桂酸途径代谢物以及22个木脂素途径代谢物;其中26个在PubChem和SciFinder数据库中未见收录。该研究利用探针分子结合修饰组可快速锁定途径代谢物,且有助于快速、准确的网络传播注释,可显著提高目标途径代谢物筛选与注释效率,为植物次生代谢途径的深入解析提供分析手段。

Effect of Fixation Methods on Biochemical Characteristics of Green Teas and Their Lipid-Lowering Effects in a Zebrafish Larvae Model

Fixation is a key process contributing to different flavors of green tea and pan-fire and steam were the common fixation methods applied conventionally. In this study, pan-fired green tea (PGT) and steamed green tea (SGT) produced by different fixation methods were compared in characteristic biochemicals including volatile compounds, amino acids, catechins and alkaloids, together with evaluating their tastes and lipid-lowering effects. PGT and SGT could be distinguished clearly by orthogonal partial least squares discriminant analysis (OPLS-DA) and heatmap. SGT had higher contents of volatile alcohols (44.75%) with green and floral attributes, while PGT had higher contents of volatile esters (22.63%) with fruity and sweet attributes. Results of electronic tongue analysis showed that PGT and SGT had similar taste of strong umami and sweetness, but little astringency and bitterness. In addition, amino acids were more abundant in PGT (41.47 mg/g in PGT, 33.79 mg/g in SGT), and catechins were more abundant in SGT (111.36 mg/g in PGT, 139.68 mg/mg in SGT). Zebrafish larvae high-fat model was applied to study the lipid-lowering effects of PGT and SGT. Results showed that both SGT and PGT had lipid-lowering effects, and the lipid level was decreased to 61.11 and 54.47% at concentration of 300 mg/L compared to high-fat group, respectively. Generally, different fixation methods of pan-fire and steam showed significant effects on aroma and contents of characteristic chemical compounds (amino acids and catechins) of green tea, but no effects on the taste and lipid-lowering activity.

Recent Advances in Analytical Methods for Determination of Polyphenols in Tea: A Comprehensive Review

Polyphenols, the most abundant components in tea, determine the quality and health function of tea. The analysis of polyphenols in tea is a topic of increasing interest. However, the complexity of the tea matrix, the wide variety of teas, and the difference in determination purposes puts forward higher requirements for the detection of tea polyphenols. Many efforts have been made to provide a highly sensitive and selective analytical method for the determination and characterization of tea polyphenols. In order to provide new insight for the further development of polyphenols in tea, in the present review we summarize the recent literature for the detection of tea polyphenols from the perspectives of determining total polyphenols and individual polyphenols in tea. There are a variety of methods for the analysis of total tea polyphenols, which range from the traditional titration method, to the widely used spectrophotometry based on the color reaction of Folin–Ciocalteu, and then to the current electrochemical sensor for rapid on-site detection. Additionally, the application of improved liquid chromatography (LC) and high-resolution mass spectrometry (HRMS) were emphasized for the simultaneous determination of multiple polyphenols and the identification of novel polyphenols. Finally, a brief outline of future development trends are discussed.

HPLC and high-throughput sequencing revealed higher tea-leaves quality, soil fertility and microbial community diversity in ancient tea plantations: compared with modern tea plantations

BACKGROUND

Ancient tea plantations with an age over 100 years still reserved at Mengku Town in Lincang Region of Yunan Province, China. However, the characteristic of soil chemicophysical properties and microbial ecosystem in the ancient tea plantations and their correlation with tea-leaves chemical components remained unclear. Tea-leaves chemical components including free amino acids, phenolic compounds and purine alkaloids collected from modern and ancient tea plantations in five geographic sites (i.e. Bingdao, Baqishan, Banuo, Dongguo and Jiulong) were determined by high performance liquid chromatography (HPLC), while their soil microbial community structure was analyzed by high-throughput sequencing, respectively. Additionally, soil microbial quantity and chemicophysical properties including pH, cation exchange capacity (CEC), soil organic matter (SOM), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolyzable nitrogen (AN), available phosphorous (AP) and available potassium (AK) were determined in modern and ancient tea plantations.

RESULTS

Tea-leaves chemical components, soil chemicophysical properties and microbial community structures including bacterial and fungal community abundance and diversity evaluated by Chao 1 and Shannon varied with geographic location and tea plantation type. Ancient tea plantations were observed to possess significantly (P < 0.05) higher free amino acids, gallic acid, caffeine and epigallocatechin (EGC) in tea-leaves, as well as soil fertility. The bacterial community structure kept stable, while fungal community abundance and diversity significantly (P < 0.05) increased in ancient tea plantation because of higher soil fertility and lower pH. The long-term plantation in natural cultivation way might significantly (P < 0.05) improve the abundances of Nitrospirota, Methylomirabilota, Ascomycota and Mortierellomycota phyla.

CONCLUSIONS

Due to the natural cultivation way, the ancient tea plantations still maintained relatively higher soil fertility and soil microbial ecosystem, which contributed to the sustainable development of tea-leaves with higher quality.

Study on In Vitro Preparation and Taste Properties of N-Ethyl-2-Pyrrolidinone-Substituted Flavan-3-Ols

N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) were prepared by an in vitro model reaction, and the taste thresholds of EPSFs and their dose-over-threshold factors in large-leaf yellow tea (LYT) were investigated. The effects of initial reactant ratios, reaction temperatures and time, pH values, and water addition on the yield of EPSFs were explored. The contents of EPSFs during roasting were determined by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS). When the initial ratio of (-)-epigallocatechin gallate (EGCG) to theanine was 1:2 and roasted under 120 °C for 120 min, the contents of EPSFs were the highest. The bitterness and astringency thresholds of four EPSF isomers were measured by the half-tongue method, of which EPSF2 and EPSF3 had higher thresholds than EGCG. In LYT, four EPSFs had lower bitterness and astringency dose-over-threshold factors than EGCG. This study suggested that the reduction of bitterness and astringency of tea after roasting may be mainly due to the formation of EPSFs.

Delving into the Biotransformation Characteristics and Mechanism of Steamed Green Tea Fermented by Aspergillus niger PW-2 Based on Metabolomic and Proteomic Approaches

Aspergillus niger is one of the dominant microorganisms presented in dark tea fermentation. In this study, the biotransformation of steamed green tea leaves fermented by A. niger PW-2 was characterized using metabolomic and proteomic approaches. We observed that, after fermentation, the contents of volatile compounds contributing to the “green” aroma, including linalool, L-α-terpineol and geraniol, decreased significantly. Meanwhile, the astringency taste and contents of metabolites contributing to the taste (catechins) reduced significantly during fermentation. Additionally, the contents of theabrownins, which have health benefits, obviously increased. The bitter and umami tastes were also changed due to the variations in bitter-taste and umami-taste amino acids. We also found that glycoside hydrolases, tannases, catechol oxidases, peroxidases and laccases secreted by A. niger PW-2 were responsible for the metabolism of phenolic compounds and their derivatives (theaflavins, thearubingins and theabrownins). Finally, the metabolic pathways involved in the biosynthesis and degradation of characteristic metabolites were found to reveal the biotransformation characteristics of dark tea fermented with A. niger PW-2.

Study on taste characteristics and microbial communities in Pingwu Fuzhuan brick tea and the correlation between microbiota composition and chemical metabolites

Pingwu Fuzhuan brick tea (PWT) is considered the "Sichuan western road" border-selling tea. The taste and quality of Fuzhuan brick tea (FBT) is greatly influenced by microorganisms. Considering the dearth of studies on the taste and microbial community of PWT, this study aimed to investigate the taste characteristics using electronic tongue system and microbial community structures using high-throughput sequencing, followed by comparison with FBT from other regions and determining the correlation between microbial communities and chemical compositions. The taste strengths of sweetness, bitterness, umami and astringency in PWT were all at lower level compared to other regions FBT. Regarding microbial diversity, the fungal communities in PWT were distinct from those of other regions FBT in terms of taxonomic composition and abundance. Unclassified_k_Fungi and Aspergillus were the most dominant fungal genera in PWT. Candidatus_Microthrix, norank_f_Saprospiraceae, and norank_c_C10-SB1A were dominant bacterial genera in PWT, only distinct from those in Hunan FBT (HNT). Principal component analysis results showed that fungal or bacterial community structures of PWT and other regions FBT were distinctly different. Correlation analysis revealed important links between the top 50 microbial populations and metabolites.

SUPPLEMENTARY INFORMATION

The online version of this article contains supplementary material available at (10.1007/s13197-021-04976-y).

Updates on the chemistry, processing characteristics, and utilization of tea flavonoids in last two decades (2001-2021)

Tea flavonoids are widely recognized as critical flavor contributors and crucial health-promoting bioactive compounds, and have long been the focus of research worldwide in food science. The aim of this review paper is to summarize the major progress in tea flavonoid chemistry, their dynamics of constituents and concentrations during tea processing as well as storage, and their health functions studied between 2001 and 2021. Moreover, the utilization of tea flavonoids in the human body has also been discussed for a detailed understanding of their uptake, metabolism, and interaction with the gut microbiota. Many novel tea flavonoids have been identified, including novel A- and B-ring substituted flavan-3-ol derivatives, condensed and oxidized flavan-3-ol derivatives, and glycosylated and methylated flavonoids, and are found to be closely associated with the characteristic color, flavor, and health benefits of tea. Flavoalkaloids exist widely in various teas, particularly 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols. Tea flavonoids behave significantly difference in constituents and concentrations depending on tea cultivars, plantation conditions, multiple stresses, the tea-specified manufacturing steps, and even the long-term storage period. Tea flavonoids exhibit multiple health-promoting effects, particularly their anti-inflammatory in alleviating metabolic syndromes. Interaction of tea flavonoids with the gut microbiota plays vital roles in their health function.