Pu-erh tea tasting in Yunnan, China: correlation of drinkers' perceptions to phytochemistry

Elevated Ozone Reduces the Quality of Tea Leaves but May Improve the Resistance of Tea Plants

Tropospheric ozone (O3) pollution can affect plant nutritional quality and secondary metabolites by altering plant biochemistry and physiology, which may lead to unpredictable effects on crop quality and resistance to pests and diseases. Here, we investigated the effects of O3 (ambient air, Am; ambient air +80 ppb of O3, EO3) on the quality compounds and chemical defenses of a widely cultivated tea variety in China (Camellia sinensis cv. 'Baiye 1 Hao') using open-top chamber (OTC). We found that elevated O3 increased the ratio of total polyphenols to free amino acids while decreasing the value of the catechin quality index, indicating a reduction in leaf quality for green tea. Specifically, elevated O3 reduced concentrations of amino acids and caffeine but shows no impact on the concentrations of total polyphenols in tea leaves. Within individual catechins, elevated O3 increased the concentrations of ester catechins but not non-ester catechins, resulting in a slight increase in total catechins. Moreover, elevated O3 increased the emission of biogenic volatile organic compounds involved in plant defense against herbivores and parasites, including green leaf volatiles, aromatics, and terpenes. Additionally, concentrations of main chemical defenses, represented as condensed tannins and lignin, in tea leaves also increased in response to elevated O3. In conclusion, our results suggest that elevated ground-level O3 may reduce the quality of tea leaves but could potentially enhance the resistance of tea plants to biotic stresses.

Role of Wild Food Environments for Cultural Identity, Food Security, and Dietary Quality in a Rural American State

Wild foods are primary components of traditional and Indigenous food systems that are valued for food security while being vulnerable to global change. This case study examines practices, experiences, and perceptions associated with wild food environments through a household survey in the rural American state of Montana. Findings highlight that wild food environments contribute to cultural identity, sense of place, food security, and dietary quality of surveyed households while being vulnerable to loss of traditional ecological knowledge as well as climate and land-use change. Of the 182 informants, 80% hunt, 83% fish, and 68% forage wild botanicals. More than half of the informants agreed that wild food procurement is part of their cultural identity (66%). Collectively, informants procure more than 172 wild food species with the most prevalent being deer, waterfowl, elk, trout, bass, a range of berries, mushrooms, and botanicals used medicinally. Participants have a multidimensional value system where wild food procurement is valued for diets, recreation, family time, spirituality, and connection to the environment. The majority of participants agreed that the consumption of wild foods contributes to the nutritional quality (87%) and diversity (82%) of their diets while lowering food costs (59%). At least half of the informants reported observing changes in climate patterns over the past decade including increased temperature (50%) and more extreme and variable weather patterns (38%) that they perceive are impacting wild food environments including shifts in wild game, fish, and edible plant populations. Based on findings, we support that wild food environments and associated bio-cultural resources are a critical place to understand, conserve, and promote for nutrition. We thus advance the concept of “conservation for nutrition”. Community engagement, education, and policy plans are called for to promote wild food environments toward supporting sustainable diets and planetary health.

Development and validation of an efficient HILIC-QQQ-MS/MS method for quantitative and comparative profiling of 45 hydrophilic compounds in four types of tea (Camellia sentences)

Hydrophilic constituents are significant for the taste and nutrition of tea, but their simultaneous quantification remains challenging due to the lack of efficient methods. Based on the hydrophilic interaction chromatography coupled with triple quadrupole-tandem mass spectrometry, this work developed and validated an efficient (8.5 min per run), sensitive (LOQ: 0.002-0.493 μg/mL) and accurate method. This method was successfully used to determine the contents of 45 hydrophilic constituents in Yunnan large-leaf tea. Umami amino acids and umami-enhanced nucleotides generally exhibited higher content in green tea and Pu-erh raw tea. By contrast, a few number of amino acids (e.g., proline and γ-aminobutyric acid) and most alkaloids and nucleosides showed significantly higher contents in black tea or Pu-erh ripen tea. By performing the orthogonal partial least squares discriminant analysis, classification models for distinguishing four types of tea, and green tea from Pu-erh raw tea were established.

Discriminant Analysis of Pu-Erh Tea of Different Raw Materials Based on Phytochemicals Using Chemometrics

Pu-erh tea processed from the sun-dried green tea leaves can be divided into ancient tea (AT) and terrace tea (TT) according to the source of raw material. However, their similar appearance makes AT present low market identification, resulting in a disruption in the tea market rules of fair trade. Therefore, this study analyzed the classification by principal component analysis/hierarchical clustering analysis and conducted the discriminant model through stepwise Fisher discriminant analysis and decision tree analysis based on the contents of water extract, phenolic components, alkaloid, and amino acids, aiming to investigate whether phytochemicals coupled with chemometric analyses distinguish AT and TT. Results showed that there were good separations between AT and TT, which was caused by 16 components with significant (p < 0.05) differences. The discriminant model of AT and TT was established based on six discriminant variables including water extract, (+)-catechin, (−)-epicatechin, (−)-epigallocatechin, theacrine, and theanine. Among them, water extract comprised multiple soluble solids, representing the thickness of tea infusion. The model had good generalization capability with 100% of performance indexes according to scores of the training set and model set. In conclusion, phytochemicals coupled with chemometrics analyses are a good approach for the identification of different raw materials.

Analytical Assessment of Bioelements in Various Types of Black Teas from Different Geographical Origins in View of Chemometric Approach

A comprehensive approach to the mineral composition of black teas of different origins was studied using the Flame Atomic Absorption Spectrometry (FAAS) method, supported by chemometric tools including Principal Component Analysis PCA) and Classification and Regression Trees (CART). Significant differences between the teas from seven countries (Japan, Nepal, Kenya, Iran, Sri Lanka, India, and China) were shown. K was the main element determined in all teas, with an average concentration of 11,649 mg/kg, followed by Ca, Mg and Mn. In general, regarding all investigated black teas, the element content was ranked in the following order: K > Ca > Mg > Mn > Fe > Na > Zn > Cu. The applied chemometric methods allowed us to recognize black tea clusters based on their mineral composition and place of cultivation, and allowed us to find correlations between particular elements in black teas. The performed analyses revealed interesting correlations between the concentration of various elements in black teas: K was negatively correlated with Na, Fe, Mn and Cu; K was positively correlated with the content of Ca and Mg. Significant positive correlations between Mn and Fe and Mn and Zn in the studied black tea samples were also revealed. It was shown that mineral composition may be a significant factor regarding the origin of the black tea, not only considering the country, but also the region or province.

Flavor Characteristics of Ganpu Tea Formed During the Sun-Drying Processing and Its Antidepressant-Like Effects

Ganpu tea is a novel type of tea beverage with unique and pleasant flavor that encases Pu-erh tea leaves within an intact mandarin peel. However, to date, no holistic and detail studies on its chemical composition and biological activities have been reported yet. In the present study, by applying UPLC-Q-TOF and UPLC-MS technology, we systematically identified and analyzed 104 water-soluble compounds of Ganpu tea and their variation trend during the sun-drying processing. The results showed that the generation of pigments and gallic acid coincided with a dramatic decrease in catechin content, and a significant increase in alkaloid and flavonoid contents. The conversion of these compounds can contribute to the improvement of sensory attributes of Ganpu tea and maybe indispensable to its unique flavor. Moreover, the mice given orally with high dose of Ganpu tea (0.4 g/kg) showed a significantly reduced immobility duration as compared to that of the negative control group (p < 0.01) both in the forced swimming test and tail suspension test. Together, these results indicate that the sun-drying processing was indispensable to the formation of the unique flavor for Ganpu tea. Multiple types of compounds of Ganpu tea may collectively provide the synergistic attributes to its antidepressant-like properties.

Effects of bioactive components of Pu-erh tea on gut microbiomes and health: A review

Pu-erh tea is a post-fermentation tea with unique flavor and multiple health benefits. Due to the various microorganisms involved in the post-fermentation process, Pu-erh tea contains highly complex components, which have rich interactions with the gut microbiomes (GMs). Because the structure and homeostasis of GMs are closely related to human wellness and the various diseases progress, the beneficial effects of Pu-erh tea on GMs have a great potential for application in health care. However, there is no systematic summary of the bioactive components of Pu-erh tea, and their effects on the GMs. Here, we review the current studies on the effects of Pu-erh tea and its bioactive components on the structure of GMs as well as on health improvement, and further discuss the relevant quality indicators. This "components - function - indicators" clue will hopefully stimulate the standardization of Pu-erh tea fermentation process and the development of its functional products.

Rutin, γ-Aminobutyric Acid, Gallic Acid, and Caffeine Negatively Affect the Sweet-Mellow Taste of Congou Black Tea Infusions

The sweet-mellow taste sensation is a unique and typical feature of premium congou black tea infusions. To explore the key taste-active compounds that influence the sweet-mellow taste, a sensory and molecular characterization was performed on thirty-three congou black tea infusions presenting different taste qualities, including the sweet-mellow, mellow-pure, or less-mellow taste. An integrated application of quantitative analysis of 48 taste-active compounds, taste contribution analysis, and further validation by taste supplementation experiments, combined with human sensory evaluation revealed that caffeine, γ-aminobutyric acid, rutin, succinic acid, citric acid, and gallic acid negatively affect the sweet-mellow taste, whereas glucose, sucrose, and ornithine positively contribute to the sweet-mellow taste of congou black tea infusions. Particularly, rutin, γ-aminobutyric acid, gallic acid, and caffeine, which impart the major inhibitory effect to the manifestation of the sweet-mellow taste, were identified as the key influencing components through stepwise screening and validation experiments. A modest level of these compounds was found to be favorable for the development and manifestation of the sweet-mellow taste. These compounds might potentially serve as the regulatory targets for oriented-manufacturing of high-quality sweet-mellow congou black tea.

Environmental Factors Variably Impact Tea Secondary Metabolites in the Context of Climate Change

Climate change is impacting food and beverage crops around the world with implications for environmental and human well-being. While numerous studies have examined climate change effects on crop yields, relatively few studies have examined effects on crop quality (concentrations of nutrients, minerals, and secondary metabolites). This review article employs a culturally relevant beverage crop, tea (Camelia sinensis), as a lens to examine environmental effects linked to climate change on the directionality of crop quality. Our systematic review identified 86 articles as relevant to the review question. Findings provide evidence that shifts in seasonality, water stress, geography, light factors, altitude, herbivory and microbes, temperature, and soil factors that are linked to climate change can result in both increases and decreases up to 50% in secondary metabolites. A gap was found regarding evidence on the direct effects of carbon dioxide on tea quality, highlighting a critical research area for future study. While this systematic review provides evidence that multiple environmental parameters are impacting tea quality, the directionality and magnitude of these impacts is not clear with contradictory evidence between studies likely due to confounding factors including variation in tea variety, cultivar, specific environmental and agricultural management conditions, and differences in research methods. The environmental factors with the most consistent evidence in this systematic review were seasonality and water stress with 14 out of 18 studies (78%) demonstrating a decrease in concentrations of phenolic compounds or their bioactivity with a seasonal shift from the spring and /or first tea harvest to other seasons and seven out of 10 studies (70%) showing an increase in levels of phenolic compounds or their bioactivity with drought stress. Herbivory and soil fertility were two of the variables that showed the greatest contradictory evidence on tea quality. Both herbivory and soil fertility are variables which farmers have the greatest control over, pointing to the importance of agricultural management for climate mitigation and adaptation. The development of evidence-based management strategies and crop breeding programs for resilient cultivars are called for to mitigate climate impacts on crop quality and overall risk in agricultural and food systems.

Application of FT-NIR spectroscopy for simultaneous estimation of taste quality and taste-related compounds content of black tea

Fourier transform near-infrared spectroscopy (FT-NIR) coupled to chemometric algorithms such as back propagation (BP)-AdaBoost and synergy interval partial least square (Si-PLS) were deployed for the rapid prediction taste quality and taste-related components in black tea. Eight main taste-related components were determined via chemical analysis and Pearson correlations. The achieved chemical results of the eight taste-related components in black tea infusion were predicted based on 160 tea samples obtained from different countries. Prediction results revealed BP-AdaBoost models gave superior predictions, with all the correlation coefficients of the prediction set (Rp) > 0.76, and the root mean square error values of the prediction set (RMSEP) < 1.7% compared with Si-PLS models (0.71 ≤ Rp ≤ 0.94, 0.08% ≤ RMSEP ≤ 1.73%). This implies that FT-NIR combined to BP-AdaBoostis capable of being deployed for the rapid evaluation of black tea taste quality and taste-related components content simultaneously.

Analytical Assessment of Bio- and Toxic Elements Distribution in Pu-erh and Fruit Teas in View of Chemometric Approach

This study concerns application of flame atomic absorption spectrometry (FAAS) in assessment of macro- and microelement and toxic metal levels (Mg, Ca, K, Na, Mn, Cu, Fe, Zn, Cr, Ni, Co, Cd and Pb) in dark (Pu-erh) and fruit tea leaves and their infusions. Phosphorus was also determined in the form of phosphomolybdate by spectrophotometric method. The reliability of the method was checked using three certified reference materials. The results of analysis were in agreement with the certified values, with analytical recovery ranging from 86 to 113 %. Significant correlations (p < 0.001) were found between concentrations of P, Zn, K, Ni, Fe, Co, Cr, and Pb in Pu-erh tea, whereas in fruit tea, such interdependences were found between Mg, Fe, P, Ni, and Co. Kruskal-Wallis test results have related differences in Pu-erh tea quality as well as technological processing of fruit tea to their mineral composition. In order to characterize tea elemental content, chemometric techniques such as factor analysis (FA) and cluster analysis (CA) were used. Their application allowed on differentiation of samples in view of the fermentation type, technological processing, and overall quality.

In vitro α-glucosidase inhibitory activity of isolated fractions from water extract of Qingzhuan dark tea

BACKGROUND

Natural products have being used as potential inhibitors against carbohydrate-hydrolyzing enzymes to treat diabetes mellitus. Chinese dark tea has various interesting bioactivities. In this study, the active compounds from Qingzhuan dark tea were separated and their anti-diabetic activity was examined using an in vitro enzymatic model.

METHODS

The chloroform, ethyl acetate, n-butanol, sediment and residual aqua fractions of a Chinese dark tea (Qingzhuan tea) were prepared by successively isolating the water extract with different solvents and their in vitro inhibitory activities against α-glucosidase were assessed. The fraction with the highest inhibitory activity was further characterized to obtain the main active components of Qingzhuan tea.

RESULTS

The ethyl acetate fraction had the greatest inhibitory effect on α-glucosidase, followed by n-butanol, sediment and residual aqua fractions (with the IC₅₀ values of 0.26 mg/mL, 2.94 mg/mL, 3.02 mg/mL, and 5.24 mg/mL, respectively), mainly due to the high content of polyphenols. Among the eight subfractions (QEF1-8) isolated from the ethyl acetate fraction, QEF8 fraction showed the highest α-glucosidase inhibitory potential in a competitive inhibitory manner (the K _i value of 77.10 μg/mL). HPLC-MS analysis revealed that (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) were the predominant active components in QEF8.

CONCLUSION

These results indicated that Qingzhuan tea extracts exerted potent inhibitory effects against α-glucosidase, EGCG and ECG were likely responsible for the inhibitory activity in Qingzhuan tea. Qingzhuan tea may be recommended as an oral antidiabetic diet.

Comparative analysis of volatiles difference of Yunnan sun-dried Pu-erh green tea from different tea mountains: Jingmai and Wuliang mountain by chemical fingerprint similarity combined with principal component analysis and cluster analysis

BACKGROUND

Modern instrumental analysis technology can provide various chemical data and information on tea samples. Unfortunately, it remains difficult to extract the useful information. We describe the use of chemical fingerprint similarities, combined with principal component and cluster analyses, to distinguish and recognize Pu-erh green teas, which from two tea mountains, Wuliang and Jingmai, in the Pu-erh district of Yunnan province. The volatile components of all 20 Pu-erh green teas (10 Wuliang and 10 Jingmai teas) were extracted and identified by headspace solid-phase micro extraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS).

RESULTS

Sixty-three volatiles (including alcohols, hydrocarbons, ketones, and aldehydes) were identified in the 20 Pu-erh green teas, and differences in compound compositions between them were also observed. Through fingerprint similarity, combined with principal component and cluster analyses, the 20 Pu-erh green teas were differentiated successfully based on their volatile characteristics.

CONCLUSIONS

This study demonstrates that the GC-MS combined with chemical fingerprint and unsupervised pattern recognition method is suitable for the investigation of the volatile profiling and evaluating the quality and authenticity of teas related to the different origins.Graphical abstractDifferentiate Pu-erh green teas from different tea mountains by using chemical fingerprint similarity and multivariate statistical methods.

Effects of Pu-erh tea aqueous extract (PTAE) on blood lipid metabolism enzymes

Effects of Pu-erh tea aqueous extract (PTAE) on blood lipid metabolism enzymes (e.g.HMGR) are assayedin vitro.

Application of gas chromatography-mass spectrometry and chemometrics methods for assessing volatile profiles of Pu-erh tea with different processing methods and ageing years

A method was developed based on head-space solid phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) combined with multivariate statistical methods to assess volatile profiles in different types of Pu-erh teas.

Significant elevation of antiviral activity of strictinin from Pu'er tea after thermal degradation to ellagic acid and gallic acid

Compared with abundant catechins, strictinin is a minor constituent in teas and has been demonstrated to possess inhibitory potency on influenza virus. In this study, strictinin was found as the major phenolic compound in Pu’er teas produced from leaves and buds of wild trees. Due to its thermal instability, strictinin, in tea infusion or in an isolated form, was completely decomposed to ellagic acid and gallic acid after being autoclaved for 7 minutes. A plaque reduction assay was employed to compare the relative inhibitory potency between strictinin and its thermally degraded products against human influenza virus A/ Puerto Rico/8/34. The results showed that the antiviral activity of ellagic acid regardless of the presence or absence of gallic acid was significantly higher than that of strictinin. Thermal degradation of strictinin to ellagic acid and gallic acid seems to be beneficial for the preparation of Pu’er teas in terms of enhancing antiviral activity.

Effects of extreme climate events on tea (Camellia sinensis) functional quality validate indigenous farmer knowledge and sensory preferences in tropical China

Climate change is impacting agro-ecosystems, crops, and farmer livelihoods in communities worldwide. While it is well understood that more frequent and intense climate events in many areas are resulting in a decline in crop yields, the impact on crop quality is less acknowledged, yet it is critical for food systems that benefit both farmers and consumers through high-quality products. This study examines tea (Camellia sinensis; Theaceae), the world's most widely consumed beverage after water, as a study system to measure effects of seasonal precipitation variability on crop functional quality and associated farmer knowledge, preferences, and livelihoods. Sampling was conducted in a major tea producing area of China during an extreme drought through the onset of the East Asian Monsoon in order to capture effects of extreme climate events that are likely to become more frequent with climate change. Compared to the spring drought, tea growth during the monsoon period was up to 50% higher. Concurrently, concentrations of catechin and methylxanthine secondary metabolites, major compounds that determine tea functional quality, were up to 50% lower during the monsoon while total phenolic concentrations and antioxidant activity increased. The inverse relationship between tea growth and concentrations of individual secondary metabolites suggests a dilution effect of precipitation on tea quality. The decrease in concentrations of tea secondary metabolites was accompanied by reduced farmer preference on the basis of sensory characteristics as well as a decline of up to 50% in household income from tea sales. Farmer surveys indicate a high degree of agreement regarding climate patterns and the effects of precipitation on tea yields and quality. Extrapolating findings from this seasonal study to long-term climate scenario projections suggests that farmers and consumers face variable implications with forecasted precipitation scenarios and calls for research on management practices to facilitate climate adaptation for sustainable crop production.

Occurrence of 15 + 1 EU priority polycyclic aromatic hydrocarbons (PAH) in various types of tea (Camellia sinensis) and herbal infusions

For the analysis of 15 + 1 EU priority PAH in tea and herbal infusions, an online-SPE-LVI-GC-MS method was developed. This method includes sample extraction of the tea and herbal infusions with saponification followed by an automated SPE clean-up step. For brews a liquid-liquid extraction with cyclohexane was performed before an automated SPE clean-up. Gas chromatographic separation was done using an Agilent J&W Select PAH (15 m × 0.15 mm × 0.10 µm) column, which allows the separation of the three benzofluoranthenes as well as triphenylene from chrysene. Method performance criteria such as method linearity, limit of quantitation (LOQ) and repeatability were determined and demonstrated that the method was fit for purpose. The method was used to analyse 15 + 1 EU priority PAH in 91 tea and herbal infusion samples. The levels of PAHs ranged from below 0.5 (LOQ) to 460 µg kg⁻¹, with a median of 4.7 µg kg⁻¹ and a mean of 39 µg kg⁻¹ for BaP, and from below 1.0 (LOQ) to 2700 µg kg⁻¹, with a median of 39 µg kg⁻¹ and a mean of 250 µg kg⁻¹ for total PAH, which were in good agreement with other studies reported in the literature. For the brews prepared under normal house preparation (20 g material in 2 L boiling tap water for 10 min), no total 15 + 1 PAH could be detected above the LOQ. With an extended brewing time of 30 min, a transfer rate between 0.25% and 0.52% could be determined, which results in no exceeding of the maximum limits given by the European Union directive for drinking water (EU Council Directive 98/83/EC).

New Phenylpropanoid-Substituted Flavan-3-ols from Pu-er Ripe Tea

Pu-er ripe tea is a special microbial post-fermented tea made from Pu-er raw tea, a kind of green tea produced from the leaves of Camellia sinensis var. assamica. It is one of the most consumed teas in the past two decades in China, due to its special flavor, taste, and beneficial effects. This work aimed to obtain diverse catechin structures from Pu-er ripe tea, which led to the isolation of four new phenylpropanoid-substituted flavan-3-ols, puerins C-F (1-4), together with four known flavan-3-ols, (+)-catechin (5), (-)-epicatechin (6), (±)-gallocatechin (7), and (-)-epigallocatechin (8). Their structures were elucidated on the basis of detailed spectroscopic analysis, including 1D and 2D NMR, mass and CD spectra. Compounds 1-4, which could be formed in the post-fermentative process of Pu-er tea, were isolated for the first time from tea and Theaceae plant.

Effects of water availability and pest pressures on tea (Camellia sinensis) growth and functional quality

Extreme shifts in water availability linked to global climate change are impacting crops worldwide. The present study examines the direct and interactive effects of water availability and pest pressures on tea (Camellia sinensis; Theaceae) growth and functional quality. Manipulative greenhouse experiments were used to measure the effects of variable water availability and pest pressures simulated by jasmonic acid (JA) on tea leaf growth and secondary metabolites that determine tea quality. Water treatments were simulated to replicate ideal tea growing conditions and extreme precipitation events in tropical southwestern China, a major centre of tea production. Results show that higher water availability and JA significantly increased the growth of new leaves while their interactive effect was not significant. The effect of water availability and JA on tea quality varied with individual secondary metabolites. Higher water availability significantly increased total methylxanthine concentrations of tea leaves but there was no significant effect of JA treatments or the interaction of water and JA. Water availability, JA treatments or their interactive effects had no effect on the concentrations of epigallocatechin 3-gallate. In contrast, increased water availability resulted in significantly lower concentrations of epicatechin 3-gallate but the effect of JA and the interactive effects of water and JA were not significant. Lastly, higher water availability resulted in significantly higher total phenolic concentrations but there was no significant impact of JA and their interaction. These findings point to the fascinating dynamics of climate change effects on tea plants with offsetting interactions between precipitation and pest pressures within agro-ecosystems, and the need for future climate studies to examine interactive biotic and abiotic effects.

Flavor characteristics of seven grades of black tea produced in Turkey

Seven grades of black tea [high-quality black tea (grades 1-3) and low-quality black tea (grades 4-7)], processed by ÇAYKUR Tea Processing Plant (Rize, Turkey), were compared for their differences in descriptive sensory analysis (DSA), aroma-active compounds (volatile compounds), and taste-active compounds (sugar, organic acid, and free amino acid compositions). Ten flavor attributes such as 'after taste', 'astringency', 'bitter', 'caramel-like', 'floral/sweet', 'green/grassy', 'hay-like', 'malty', 'roasty', and 'seaweed' were identified. Intensities for a number of flavor attributes ('after taste', 'caramel-like', 'malty', and 'seaweed') were not significantly different (p > 0.05) among seven grades of black tea. A total of 57 compounds in seven grades of black tea (14 aldehydes, eight alcohols, eight ketones, two esters, four aromatic hydrocarbons, five aliphatic hydrocarbons, nine terpenes, two pyrazines, one furan, two acids, and two miscellaneous compounds) were tentatively identified. Of these, aldeyhdes comprised more than 50% to the total volatile compounds identified. In general, high-grade quality tea had more volatiles than low-grade quality tea. With respect to taste-active compounds, five sugars, six organic acids, and 18 free amino acids were positively identified in seven grades of black tea, of which fructose, tannic acid, and theanine predominated, respectively. Some variations (p < 0.05), albeit to different extents, were observed among volatile compounds, sugars, organic acids, and free amino acids in seven grades of black tea. The present study suggests that a certain flavor attributes correlate well with taste- and aroma-active compounds. High- and low-quality black teas should not be distinguished solely on the basis of their DSA and taste- and aroma-active compounds. The combination of taste-active compounds together with aroma-active compounds renders combination effects that provide the characteristic flavor of each grade of black tea.

Commercial teas highlight plant DNA barcode identification successes and obstacles

Appearance does not easily identify the dried plant fragments used to prepare teas to species. Here we test recovery of standard DNA barcodes for land plants from a large array of commercial tea products and analyze their performance in identifying tea constituents using existing databases. Most (90%) of 146 tea products yielded rbcL or matK barcodes using a standard protocol. Matching DNA identifications to listed ingredients was limited by incomplete databases for the two markers, shared or nearly identical barcodes among some species, and lack of standard common names for plant species. About 1/3 of herbal teas generated DNA identifications not found on labels. Broad scale adoption of plant DNA barcoding may require algorithms that place search results in context of standard plant names and character-based keys for distinguishing closely-related species. Demonstrating the importance of accessible plant barcoding, our findings indicate unlisted ingredients are common in herbal teas.