Yellow Tea Research Articles

Metabolomics in quality formation and characterisation of tea products: a review

SummaryTea is one of the biggest categories of modern non‐alcoholic beverages with health benefits. Through different processes, tea products are divided into six main types: green tea, yellow tea, white tea, oolong tea, black tea and dark tea. Metabolomics is helpful for the comprehensive, accurate and rapid determination of tea metabolites in different types of tea products and tea processing materials. It has been widely applied in studying the relationship of tea metabolites and its quality. Therefore, it is necessary to summarise the application of metabolomics in tea. In this review, we described and summarised (1) the main metabolites of six types of tea and their implications on tea quality with emphasis on the content differences in the main metabolites in different types of tea; (2) the research on optimising the key processing steps of six types of tea based on metabolomics and the discussion of various new strategies for effectively improving their quality and (3) the advanced approach to characterise and distinguish different grades of tea products via metabolomics. The current review offers guidance for the improvement of tea quality by metabolomics and its potential challenges.

Chromatographic Determination of the Mycotoxin Patulin in 219 Chinese Tea Samples and Implications for Human Health.

Patulin (PAT) is a mycotoxin, with several acute, chronic, and cellular level toxic effects, produced by various fungi. A limit for PAT in food of has been set by authorities to guarantee food safety. Research on PAT in tea has been very limited although tea is the second largest beverage in the world. In this paper, HPLC−DAD and GC−MS methods for analysis of PAT in different tea products, such as non-fermented (green tea), partially fermented (oolong tea, white tea, yellow tea), completely fermented (black tea), and post-fermented (dark tea and Pu-erh tea) teas were developed. The methods showed good selectivity with regard to tea pigments and 5-hydroxymethylfurfural (5-HMF) and a recovery of 90–102% for PAT at a 10–100 ppb spiking level. Limit of detection (LOD) and limit of quantification (LOQ) in tea were 1.5 ng/g and 5.0 ng/g for HPLC−UV, and 0.25 ng/g and 0.83 ng/g for GC−MS. HPLC was simpler and more robust, while GC−MS showed higher sensitivity and selectivity. GC−MS was used to validate the HPLC−UV method and prove its accuracy. The PAT content of 219 Chinese tea samples was investigated. Most tea samples contained less than 10 ng/g, ten more than 10 ng/g and two more than 50 ng/g. The results imply that tea products in China are safe with regard to their PAT content. Even an extreme daily consumption of 25 g of the tea with the highest PAT content (124 ng/g), translates to an intake of only 3 μg/person/day, which is still an order of magnitude below the maximum allowed daily intake of 30 µg for an adult.

Effects of ultra-high pressure treatment on structure and bioactivity of polysaccharides from large leaf yellow tea

In this study, the changes of structure and bioactivity of polysaccharides from large leaf yellow tea (LYTP) were investigated under ultra-high pressure (UHP). Native yellow tea polysaccharide were treatmented with ultra-high pressure (200, 400 and 600 MPa) for 5 min to yield yellow tea polysaccharide including 200 MPa-LYTP, 400 MPa-LYTP and 600 MPa-LYTP. It was found that the monosaccharide composition of LYTP changed significantly after the ultra-high pressure treatment. The molecular weight (Mw) of 200 MPa-LYTP (from 563.6 to 11.7 kDa), 400 MPa-LYTP (from 372.2 to 11.8 kDa) and 600 MPa-LYTP (from 344 to 11.6 kDa) sharply decreased upon ultra-high pressure treatment compared with LYTP (771.5 kDa), coincidentally particle size was also significantly reduced for 200 MPa-LYTP (23.2 %), 400 MPa-LYTP (40.2 %) and 600 MPa-LYTP (25.9 %). The results of the scanning electron microscope showed that ultra-high pressure also changed the surface and spatial morphology of LYTP. LYTP after ultra-high pressure treatment (UHP-LYTP) could further ameliorate alcohol-induced liver injury in mice. In addition, UHP treatment can more efficiently remove protein than the Sevages method. With the gradual removal of protein, its hepatoprotective effect increased. These findings demonstrated that UHP treatment could change the primary structure and spatial structure of LYTP, increase the content of acidic polysaccharides, and improve its bioactivity.

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.

Chinese Tea Alleviates CCl4-Induced Liver Injury through the NF-κBorNrf2Signaling Pathway in C57BL-6J Mice.

Liver injury is a life-threatening condition that is usually caused by excessive alcohol consumption, improperdiet, and stressful lifestyle and can even progress to liver cancer. Tea is a popular beverage with proven health benefits and is known to exert a protective effect on the liver, intestines, and stomach. In this study, we analyzed the therapeutic effects of six kinds of tea on carbon tetrachloride (CCl4)-induced liver injury in a mouse model. The mice were injected with 10 mL/kg 5% CCl4 to induce liver injury and then given oral gavage of green tea, yellow tea, oolong tea, white tea, black tea, and dark tea, respectively. The serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured, and the expression levels of inflammation and oxidative stress-related proteins in the liver tissues were quantified. All six kinds of tea partly reduced the liver index, restored the size of the enlarged liver in the CCl4 model, and decreased the serum levels of ALT and AST. Furthermore, the highly fermented dark tea significantly reduced the expression levels of NF-κB and the downstream inflammatory factors, whereas the unfermented green tea inhibited oxidative stress by activating the antioxidant Nrf2 pathway. Taken together, tea can protect against liver inflammation, and unfermented tea can improve antioxidant levels. Further studies are needed on the bioactive components of tea to develop drugs against liver injury.

Integrated transcriptome and amino acid profile analyses reveal novel insights into differential accumulation of theanine in green and yellow tea cultivars.

Tea cultivars with yellow- or white-leaf variations have a high economic value due to their high amino acid (especially theanine) concentration. However, the dynamic changes of amino acid components (especially theanine) and related gene expression during new shoot development in these cultivars are still unclear. In this study, 264 tea samples from four representative varieties picked during the harvest period in spring were analyzed for their amino acid profiles. The dynamic change rules of ethylamine and 19 amino acids were summarized in normal green and yellow cultivars during new shoot development. Interestingly, the theanine concentration in the yellow cultivar was significantly higher than that in the green cultivar, and increased gradually as the leaves matured until they reached a maximum in the one bud and three leaves stage. The amino acid concentration in the leaves of the yellow cultivar increased significantly with leaf position, which was generally in contrast to the normal green cultivar. Transcriptome and correlation analyses revealed that CsGS1, CsPDX2, CsGGP5, CsHEMA3 and CsCLH4 might be the key genes potentially responsible for the differential accumulation of theanine in green and yellow tea cultivars. These results provide further information for the utilization and improvement of tea plants.

Screening of α-glucosidase inhibitors in large-leaf yellow tea by offline bioassay coupled with liquid chromatography tandem mass spectrometry

Larger-leaf yellow tea (LYT) is a characteristic type of Chinese tea produced in Huoshan County, Anhui Province, which is made by mature leaves with stems. According to recent report, LYT showed competitive effects in anti-hyperglycemia in comparison to other teas such as green or black tea. However, the bioactive compounds of LYT are still undiscovered so far. For this purpose, 5 fractions of LYT were prepared by sequential extraction. The in vitro bioassay results indicated that the ethyl acetate fraction of LYT had the strongest inhibitory effects on α-glucosidase and α-amylase. Fluorescence-quenching analysis and protein-binding test revealed that the compounds of ethyl acetate fraction could inhibit α-glucosidase and α-amylase activities through binding to enzymes or other mechanisms. All chromatographic peaks of high-performance liquid chromatography (HPLC) of ethyl acetate fraction were separated and collected. The purified compounds were identified by liquid chromatography-mass spectrometry (LC-MS), and subsequently screened by calculating their inhibition ratio on α-glucosidase at the real concentration in LYT infusion. The results showed that (–)-epigallocatechin gallate, (–)-gallocatechin gallate, caffeine, N-ethyl-2-pyrrolidone-substituted flavan-3-ols were effective inhibitors for α-glucosidase.

Effect of Yellowing Duration on the Chemical Profile of Yellow Tea and the Associations with Sensory Traits.

The yellowing process is the crucial step to form the characteristic sensory and chemical properties of yellow tea. To investigate the chemical changes and the associations with sensory traits during yellowing, yellow teas with different yellowing times (0–13 h) were prepared for sensory evaluation and chemical analysis. The intensities of umami and green-tea aroma were reduced whereas sweet taste, mellow taste and sweet aroma were increased under long-term yellowing treatment. A total of 230 chemical constituents were determined, among which 25 non-volatiles and 42 volatiles were the key chemical contributors to sensory traits based on orthogonal partial least squares discrimination analysis (OPLS-DA), multiple factor analysis (MFA) and multidimensional alignment (MDA) analysis. The decrease in catechins, flavonol glycosides and caffeine and the increase in certain amino acids contributed to the elevated sweet taste and mellow taste. The sweet, woody and herbal odorants and the fermented and fatty odorants were the key contributors to the characteristic sensory feature of yellow tea with sweet aroma and over-oxidation aroma, including 7 ketones, 5 alcohols, 1 aldehyde, 5 acids, 4 esters, 5 hydrocarbons, 1 phenolic compound and 1 sulfocompound. This study reveals the sensory trait-related chemical changes in the yellowing process of tea, which provides a theoretical basis for the optimization of the yellowing process and quality control of yellow tea.

Large-leaf yellow tea attenuates high glucose-induced vascular endothelial cell injury by up-regulating autophagy and down-regulating oxidative stress.

Vascular endothelial cell injury induced by high glucose (HG) plays an important role in the occurrence and development of diabetic vascular complications. Yellow tea has a protective effect on vascular endothelial cells. However, the molecular mechanisms underlying this effect are unclear. In this study, the effects of the n-butanol fraction of Huoshan large-leaf yellow tea extract (HLYTBE) on vascular endothelial injury were investigated using human umbilical vein endothelial cells (HUVECs) and diabetic mice. In HUVECs, HLYTBE significantly reduced the production of reactive oxygen species, increased the activity of anti-oxidases (superoxide dismutase and glutathione peroxidase), enhanced the production of reduced glutathione, and decreased the level of oxidized glutathione, thereby improving cell viability. HLYTBE also promoted autophagosome formation, increased the LC3-II/LC3-I ratio, increased the expressions of Beclin1 and Atg 5, and decreased the expression of p62. HLYTBE up-regulated p-AMPK and down regulated p-mTOR, and these effects were reversed by compound C, an AMPK inhibitor. HLYTBE reduced apoptosis and cytochrome C expression, and these effects were attenuated by the autophagy inhibitor 3-methyladenine. In vivo studies showed that HLYTBE improved the impaired pyruvate tolerance, glucose tolerance, and insulin resistance; reduced the concentrations of blood glucose, glycated serum protein, lipids, and 8-isomeric prostaglandin 2α; increased the anti-oxidase activity in serum; and alleviated pathological damage in the thoracic aorta of diabetic mice induced by high sucrose-high fat diet along with streptozotocin. The results suggest that HLYTBE protects the vascular endothelium by up-regulating autophagy via the AMPK/mTOR pathway and inhibiting oxidative stress.

The Change of Mineral Matter Content in Fresh Tea Leaf and Dried Tea According to the Damage of Yellow Tea Mite, Polyphagotarsonemus latus

Bu çalışma, Rize ilinde, Atatürk Çay ve Bahçe Kültürleri Araştırma Enstitüsü Müdürlüğü’nün “Muradiye-10”, “Pazar-20” ve “Tuğlalı-10” çay klonları ile tesis edilmiş parselleri üzerinde, 2013 ve 2014 yıllarında, 3. sürgün döneminde yürütülmüştür. Araştırmada, önemli çay zararlılarından olan, sarı çay akarı (Polyphagotarsonemus latus (Banks) (Trombidiformes: Tarsonemidae)’nın, yaş çay yaprağı ile kuru çayda mineral madde içeriğine olan etkilerinin tespiti amaçlanmıştır. Mineral madde olarak, alüminyum (Al), kalsiyum (Ca), bakır (Cu), demir (Fe), magnezyum (Mg), mangan (Mn), kükürt (S) ve çinko (Zn) değerleri analiz edilmiştir. Deneme tesadüf blokları deneme desenine göre, 3 tekerrürlü olarak planlanmıştır. Sonuçlar, akar ile bulaşık yaş çay yapraklarında en fazla değişim gösteren minerallerin S, Al ve Zn, olduğunu, kuru çayda en fazla değişimin ise, Ca ve Mn içeriğinde gerçekleştiğini göstermiştir. 2013 yılında, yaş çay yapraklarının ortalama S, Al ve Zn içerikleri, kontrol parsellerinde sırası ile, 2648.8- 3122.8 ppm, 1140-1735.4 ppm ve 13.7-18.8 ppm, akar bulaşık parsellerde ise 3099.9-3256.5 ppm, 1102-1909 ppm ve 14.8-18.4 ppm arasında değişim gösterirken, 2014 yılında bu değerler sırası ile kontrol parsellerinde 2613.9-2796.4 ppm, 849-1774.9 ppm ve 16.3-20.3 ppm, bulaşık parsellerde ise 2668.3-2834.6 ppm, 727.9-1678.1 ppm ve 22.2-29.7 ppm kadar olmuştur. Kuru çay nevilerinin, ortalama Ca içeriği ise, 2013 ve 2014 yıllarında sırası ile temiz parsellerde 1377.8-2388,4 ppm ve 1926.8-2240.8 ppm, akar bulaşık parsellerde 1582.8-2167.5 ppm ve 2007.2-2281.6 ppm arasında değişim gösterirken, Mn için bu değerler 2013 yılında temiz ve bulaşık parseller için sırası ile 314.2-827.8 ppm ve 308.3-798.2 ppm, 2014 yılında ise 496.1-668.2 ppm ve 481.9-663.2 ppm olarak tespit edilmiştir. Yaş yaprak içeriği en fazla değişim gösteren Tuğlalı-10 klonu olurken, kuru çay mineral madde içeriği en fazla etkilenen klon Muradiye-10 olmuştur. Sonuç olarak, yaş çay yaprağı ile 5 nevi kuru çaydaki mineral madde içeriklerinin, tek başına klon ya da akarla bulaşıklık durumuna bağlı olarak değil, her iki faktörün birlikte etkisiyle önemli düzeyde değişim gösterdiği, bu durumun yıllara göre de değiştiği ve kuru çaydaki değişimlerin yaş çaydan daha fazla olduğu kanaatine varılmıştır.

Development of Molecular Marker to Detect Citrus Melanose Caused by Diaporthe citri from Citrus Melanose-like Symptoms

It is difficult to distinguish melanose and melanoses-like symptoms with the naked eye because they appear similar. To accurately detect melanose symptoms caused by Diaporthe citri from melanose-like symptoms, we developed PCR-based specific primers Dcitri by aligning the internal transcribed spacer (ITS) region of D. citri with the ITS of Diaporthe cytosporella, Diaporthe foeniculina, Colletotrichum gloeosporioides, Botrytis cinerea, Alternaria citri, and Fusarium oxysporum found on citrus peel. PCR results showed that the specific product was amplified in D. citri but not in other isolates including, C. gloeosporioides, B. cinerea, A. citri, F. oxysporum. In addition, specific products were observed in melanose symptoms caused by D. citri but not in melanose-like symptoms, such as copper-injury, sunscald, damages by yellow tea thrips, and pink citrus rust mite. Using the Dcitri primers developed in this study, it is expected that melanose caused by D. citri could be accurately distinguished from melanose-like symptoms.

Structural Characteristics of Crude Polysaccharides from 12 Selected Chinese Teas, and Their Antioxidant and Anti-Diabetic Activities.

Twelve representative edible Chinese teas (Camellia sinensis L.) from six categories (dark tea, black tea, oolong tea, white tea, yellow tea, and green tea) were selected in this study. Tea polysaccharides (TPs) were extracted with hot water, and their structural properties and biological activities, mainly antioxidant and anti-diabetic activities, were systematically evaluated. Results revealed that the extraction yields of TPs ranged from 1.81% to 6.38%, and Pu-erh tea polysaccharides had the highest extraction yield (6.38 ± 0.28%). The chemical compositions, molecular weight, and compositional monosaccharides of TPs varied among the six categories of tea. It appeared that all TPs were protein-bound acid heteropolysaccharides, and all TPs exhibited obvious antioxidant and anti-diabetic (e.g., α-glucosidase inhibitory and antiglycation) activities. Particularly, Pu-erh tea polysaccharides also contained the highest total phenolic and protein contents, and also exhibited the best antioxidant and anti-diabetic activities. Moreover, for the structural-function relationship, the heat map analysis found that total phenolic and protein contents in TPs were positively correlated with their antioxidant and anti-diabetic activities, indicating that the presence of phenolic compounds and proteins in the TPs might be the main contributors to their bioactivities. The conclusion from this study can help understand the structural-function relationship of crude tea polysaccharides.

Establishment of a HPLC-MS/MS Detection Method for Glyphosate, Glufosinate-Ammonium, and Aminomethyl Phosphoric Acid in Tea and Its Use for Risk Exposure Assessment.

The tea shrub is grown in long-standing orchards, an environment that is suitable for persistent weed growth, which is increasingly controlled by herbicides. Therefore, there is increasing concern that tea consumers may be exposed to herbicide residues. In this study, the levels of glufosinate-ammonium (GLU), glyphosate [N-(phosphonomethyl) glycine; PMG], and its metabolite aminomethyl phosphoric acid (AMPA) were determined in tea samples by HPLC-MS/MS using several current purification methods and a new method that we developed herein. The matrix effect of our proposed method was between -27.3 and 27.7%, which was lower than that in other methods, indicating that this method effectively reduced the interference of tea matrix in the mass spectrometry process. This method was used to determine the levels of PMG, GLU, and AMPA in 780 samples, including six traditional Chinese teas (green tea, black tea, oolong tea, dark tea, white tea, and yellow tea) and a floral tea, from 14 provinces of China. Probability estimates showed that the 95th percentile risk entropy values of the three pesticide residues were far below the acceptable risk level. The risk assessment results showed that exposure to PMG, GLU, and AMPA caused by drinking tea beverages poses no significant risk to human health.

An internet of things (IoT)-based optimum tea fermentation detection model using convolutional neural networks (CNNs) and majority voting techniques

Abstract. Tea (Camellia sinensis) is one of the most consumed drinks across the world. Based on processing techniques, there are more than 15 000 categories of tea, but the main categories include yellow tea, Oolong tea, Illex tea, black tea, matcha tea, green tea, and sencha tea, among others. Black tea is the most popular among the categories worldwide. During black tea processing, the following stages occur: plucking, withering, cutting, tearing, curling, fermentation, drying, and sorting. Although all these stages affect the quality of the processed tea, fermentation is the most vital as it directly defines the quality. Fermentation is a time-bound process, and its optimum is currently manually detected by tea tasters monitoring colour change, smelling the tea, and tasting the tea as fermentation progresses. This paper explores the use of the internet of things (IoT), deep convolutional neural networks, and image processing with majority voting techniques in detecting the optimum fermentation of black tea. The prototype was made up of Raspberry Pi 3 models with a Pi camera to take real-time images of tea as fermentation progresses. We deployed the prototype in the Sisibo Tea Factory for training, validation, and evaluation. When the deep learner was evaluated on offline images, it had a perfect precision and accuracy of 1.0 each. The deep learner recorded the highest precision and accuracy of 0.9589 and 0.8646, respectively, when evaluated on real-time images. Additionally, the deep learner recorded an average precision and accuracy of 0.9737 and 0.8953, respectively, when a majority voting technique was applied in decision-making. From the results, it is evident that the prototype can be used to monitor the fermentation of various categories of tea that undergo fermentation, including Oolong and black tea, among others. Additionally, the prototype can also be scaled up by retraining it for use in monitoring the fermentation of other crops, including coffee and cocoa.

Synthesis and Physicochemical Evaluation of Bees' Chitosan-Based Hydrogels Modified with Yellow Tea Extract.

The novelty of the research involves designing the measurement methodology aimed at determining the structure–property relationships in the chitosan-based hydrogels containing yellow tea extract. Performed investigations allowed us to determine the swelling properties of hydrogels in selected time intervals, evaluate the mutual interactions between the hydrogels and simulated physiological liquids via pH measurements and directly assess the impact of such interactions on the chemical structure of hydrogels using Fourier transform infrared (FT-IR) spectroscopy and their wettability by the measurements of the flatness of the drop on the surface of the tested samples via the static drop method. Next, the surface morphology of hydrogels was characterized by the Scanning Electron Miscorcopy (SEM) and their elasticity under the tension applied was also verified. It was proved that incubation in simulated physiological liquids resulted in a decrease in contact angles of hydrogels, even by 60%. This also caused their certain degradation which was reflected in lower intensities of bands on FT-IR spectra. Further, 23% v/v yellow tea extract in hydrogel matrices caused the decrease of their tensile strength. An increase in the amount of the crosslinker resulted in a decrease in the sorption capacity of hydrogels wherein their modification caused greater swelling ability. In general, the investigations performed provided much information on the tested materials which may be meaningful considering their application, e.g., as dressing materials.

The Effect of Yellow Tea Leaves Camellia sinensis on the Quality of Stored Chocolate Confectionery

Chocolate and tea leaves are considered the most valuable sources of highly bioactive polyphenols due to their potential anti-cancer properties and beneficial effects on the cardiovascular and nervous systems. The objective of the present study was the development of a sensory profiling modality that is correlated with the taste of the chocolate enriched with yellow tea phytochemicals. The additive concentration was optimized in white chocolate and the designed product was evaluated using the sensory profiling method. It was shown that the yellow tea extract in chocolate had a significant effect on the taste and color of the product. Addition of 2.0% yellow tea powdered extract increased the value of color acceptance and caused an intensification of the aromas, particularly the leafy taste, compared to the control samples. The next step of the study was to determine the influence of tea addition in white, milk and dark chocolate subjected to 6 months of storage. The designed chocolates were tested for their activity as antioxidants (DPPH, ABTS and ORAC assay) and cholinesterase inhibitors (AChE, BChE assay). It was confirmed that the yellow tea addition affected the activity of prepared chocolates with respect to radical scavenging activity and was highest for dark chocolate with yellow tea where the values were as follows: 4373 mg Tx/100 g (DPPH), 386 mg Tx/100 g (ABTS) and 4363 µM Tx/100 g (ORAC). An increase in the anti-radical activity of chocolate with yellow tea was found after 3 months of storage, but the subsequent 3 months of storage resulted in its reduction. AChE values ranged from 0.118 to 0.730 [µM eserine/g dw] and from 0.095 to 0.480 [µM eserine/g dw] for BChE assay. Total capacity to inhibit AChE and BChE differed depending on the type of chocolate and was negatively influenced by the half-year storage. Summarizing tested values for individual samples were higher, with increasing content of cocoa liquor and yellow tea extract in the product. The results of the research show that the use of yellow tea in confectionery is promising and may appoint a new direction in functional foods.

Volatile components and key odorants of Chinese yellow tea (Camellia sinensis)

In the present study, volatile compounds from 15 yellow tea samples were extracted and examined using stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS), and the key odorants were identified by gas chromatography-olfactometry (GC-O) analysis. Results revealed 74 volatile compounds in these yellow teas, geraniol (3.89 μg/g) being the most abundant aroma compound. Alcohols and esters were the dominant volatiles, accounting for approximately 52.44% of the total volatiles in content. Moreover, 25 key odorants were identified by GC-O method, and were considered to be responsible for the unique aroma quality of yellow tea. Major key odorants included (E, E)-3,5-octadien-2-one, (Z)-linalool oxide (furanoid), (E)-2-heptenal, naphthalene, geraniol, (E)-linalool oxide (furanoid), styrene, linalool, α-ionone, 1-octen-3-ol, trans-β-ionone, and (E, Z)-3,5-octadien-2-one. In addition, huge differences were observed among the content levels of key odorants in three types of yellow tea samples, namely MengDingHuangYa (MDHY), WeiShanHuangCha (WSHC), and PingYangHuangTang (PYHT). This is an important study describing the characterization of aroma and key odorants in yellow tea. The results obtained from this study advance our understanding of the aroma quality of yellow tea, thereby providing a theoretical basis for the processing and quality control of yellow tea aroma quality.

Effect of the roasting degree on flavor quality of large-leaf yellow tea

Roasting is crucial for producing large-leaf yellow tea (LYT) as it substantially affects chemical composition and sensory quality. However, the effect of roasting degree on LYT flavor quality is not clear. To investigate the effect of roasting degree on LYT flavor, the odor profiles and sensory evaluations of LYTs produced with small fire, medium fire and old fire roasting (OF) were determined. The OF was essential for the formation of LYT flavor with strong roasted, nutty, woody odors and weak fatty, fruity odors, and retaining high levels of GCG, total volatiles and heterocyclic compounds. Furthermore, the characteristic crispy-rice-like odor was only found in LYT with OF treatment and burnt flavor was missing. 2,3-Diethyl-5-methylpyrazine, trans-β-ionone with odor activity value above 1600 and 39 respectively offered roasted, floral odors, respectively in LYT. The current results provide a scientific basis for understanding the reactions that occur during the conventional production of LYT.

Yellow Tea Stimulates Thermogenesis in Mice through Heterogeneous Browning of Adipose Tissues.

Large-leaf yellow tea (YT) exhibits interesting beneficial metabolic effects in previous studies. Here, the authors elucidated the actions of YT on thermogenesis, energy metabolism, and adipocyte metabolic conversion. Five-week-old male C57BL/6 mice are fed low-fat diet, high-fat diet (HFD), and HFD supplemented with 0.5% or 2.5% YT. After treatment for 10 or 14 weeks, YT enhances energy expenditure, O2 consumption and CO2 production. YT strongly boosts thermogenic program in brown adipose tissue (BAT) and subcutaneous adipose tissue (SAT), while only weakly in epididymal adipose tissue (EAT). These are accompanied by higher body temperature, increased mitochondrial copy numbers, and upregulation of thermogenic genes (Ucp1, Pgc1α, etc.) and proteins. The classic brown adipocyte markers (Eva1, Zic1) are induced only in BAT, while beige adipocyte markers (Tbx1, Tmem26) are boosted only in SAT. Furthermore, subcutaneous-originated preadipocytes are induced by YT in vitro to differentiate to brown-like adipocytes - a browning effect. Dietary YT induces adaptive thermogenesis through increasing mitochondrial biogenesis in EAT, inducing beigeing in SAT and enhancing browning in the BAT.

Characterizing relationship between chemicals and in vitro bioactivities of teas made by six typical processing methods using a single Camellia sinensis cultivar, Meizhan

ABSTRACT Processing method is considered as a major factor that affects biotransformation of phytochemicals in tea and leads to diverse flavor and bioactivity of tea. In the present work, six typical tea manufacturing processings were employed to compare the effect on chemical composition of teas through using leaves of the single tea cultivar – – Camellia sinensis var. Meizhan. And in vitro antioxidant activity, inhibition against α-glucosidase and three lipid metabolism enzymes of these teas were also investigated, the relationships among them were analyzed further. As fresh leaves were processed into six categories of teas, the content of total catechins (TCs) has decreased in varying degrees while theaflavins (TFs) has increased. The antioxidant capacity composite index (ACCI) from high to low were green tea, yellow tea, oolong tea, white tea, dark tea, and black tea with the range from 98.44 to 58.38, which dominated by the content of TCs. Furthermore, all categories of teas possessed an inhibition effect on the pancreatic lipase (PL), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-COA reductase), lecithin cholesterol acyltransferase (LCAT), and α-glucosidase. The inhibition rate of PL and α-glucosidase appears to be positively influenced by TFs content (r =0.863, r =0.857, p < 0.05) while that of LCAT showed significant positive correlations with the content of tea polyphonels (TPs) (r = 0.902, p < 0.01). These results provide a better understanding of the relationships between processing method and chemical components of tea. It is suggested that various tea categories possess potential healthy effects which could serve as promising nutritional supplements.