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Theasinensin A is an important quality chemical component in tea, but its taste characteristics and the related mechanism are still unclear. The bitterness quantification and simulated taste mechanism of theasinensin A were researched. The results showed that theasinensin A was significantly correlated with the bitterness of tea. The bitterness threshold of theasinensin A was identified as 65 μmol/L for the first time. The dose-over-threshold (DOT) value of theasinensin A was significantly higher than that of caffeine in black tea soup. The concentration-bitterness curve and time-intensity curve of theasinensin A were constructed. The bitterness contribution of theasinensin A in black tea was higher than in oolong and green tea. Theasinensin A had the highest affinity with bitterness receptor protein TAS2R16, which was compared to TAS2R13 and TAS2R14. Theasinensin A was mainly bound to a half-open cavity at the N-terminal of TAS2R13, TAS2R14, and TAS2R16. The different binding capacity, hydrogen bond, and hydrophobic accumulation effect of theasinensin A and bitterness receptor proteins might be the reason why theasinensin A presented different bitterness senses in human oral cavity.

Albino tea cultivars are mutant tea plants with altered metabolisms. Current studies focus on the leaves while little is known about the flowers. To evaluate tea flowers from different albino cultivars, the chemical composition and anti-cholesterol activity of tea flowers from three albino cultivars (i.e., Baiye No.1, Huangjinya, and Yujinxiang) were compared. According to the results, tea flowers from Yujinxiang had more amino acids but less polyphenols than tea flowers from the other two albino cultivars. A reduced content of procyanidins and a high chakasaponins/floratheasaponins ratio were characteristics of tea flowers from Yujinxiang. In vitro anti-cholesterol activity assays revealed that tea flowers from Yujinxiang exhibited stronger activity in decreasing the micellar cholesterol solubility, but not in cholesterol esterase inhibition and bile salt binding. It was noteworthy that there were no specific differences on the chemical composition and anti-cholesterol activity between tea flowers from albino cultivars and from Jiukeng (a non-albino cultivar). These results increase our knowledges on tea flowers from different albino cultivars and help food manufacturers in the cultivar selection of tea flowers for use.

Hops provide the characteristic bitter taste and attractive aroma to beer; in this study, hops were replaced by jasmine tea extract (JTE) during late-hopping. The addition of JTE improved the beer foam stability 1.52-fold, and increased the polyphenol and organic acid contents. Linalool was the most important aroma compound in hopped (HOPB) and jasmine tea beer (JTB), but other flavor components were markedly different, including dimeric catechins, flavone/flavonol glycosides, and bitter acids and derivatives. Sensory evaluation indicated that addition of JTE increased the floral and fresh-scent aromas, reduced bitterness and improved the organoleptic quality of the beer. The antioxidant capacity of JTB was much higher than that of HOPB. The inhibition of amylase activity by JTB was 30.5% higher than that of HOPB. Functional properties to beer were added by substituting jasmine tea extract for hops during late hopping.

Background Over the past two decades, the global beverage industry has developed rapidly. Especially, the global tea beverage market reached 37 million tons in 2016, an increase of 40% in five years, and is estimated to reach 45 million tons by 2021. According to the forecast of Statista, a business data platform, the global tea beverage market is estimated to be worth about US $44.3 billion by 2021. In the last 5 years, remarkable progress has been made in the research on tea beverages, including liquid tea beverage, instant tea powder, tea concentrate, kombucha, tea wine and other fermented tea beverages. Scope and approach This article highlights and critically reviews the recent advances in tea beverage research with specific focus on the processing methods for flavor enhancement. An overview on the innovation and development of tea drinks over the world is provided. Key findings and conclusion Cold extraction, ultrasonic extraction and dynamic extraction have been employed in the production of tea beverage. Tannase, β-glucosidase, pectinase, amylase, lyticase and protease have been used to improve the flavor of tea beverage. Chromatography and electrochemical fingerprints and other analytical techniques have been used in flavor evaluation of tea beverages. Many new types of fermented tea beverages have been developed.

Tieguanyin is one of the most consumed oolong teas because of its distinctive flavor. The brewing process is crucial for the flavor performance of traditional teas, thus the effects of brewing conditions, including water/tea ratio (R), brewing temperature (T), and time (S) on the sensory traits, chemical composition, and antioxidant activity of Tieguanyin tea infusion were investigated using quadratic orthogonal regression design. Results showed that R affected all the quality variables most, its reduction could lead to the promotion of tea infusion concentration, antioxidant activity, and taste intensity, which was favored by the tea consumers drinking tea almost daily (DTD) but unacceptable for those drinking tea hardly (DTH). Based on the optimization of brewing conditions in response surface methodology (RSM), we recommended several brewing schemes for diverse consume goals: R = 34 mL/g, T = 80 °C, S = 80 s for DTH; R = 39 mL/g, T = 100 °C, S = 127 s for DTO (the consumers drinking tea occasionally); R = 20 mL/g, T = 100 °C, S = 100 s for DTD; R = 26 mL/g, T = 100 °C and S = 127 s for the common consumers seeking for flavor and health benefits. These results would be helpful for tea consumers with multiple demands.

Volatile organic compounds (VOCs) are produced by plants responding to biotic and abiotic stresses. According to their biosynthetic sources, induced VOCs are divided into three major classes: terpenoids, phenylpropanoid/benzenoid, and fatty acid derivatives. These compounds with specific aroma characteristics importantly contribute to the aroma quality of oolong tea. Shaking and rocking is the crucial procedure for the aroma formation of oolong tea by exerting mechanical damage to fresh tea leaves. Abundant studies have been carried out to investigate the formation mechanisms of VOCs during oolong tea processing in recent years. This review systematically introduces the biosynthesis of VOCs in plants, and the volatile changes due to biotic and abiotic stresses are summarized and expatiated, using oolong tea as an example.

Reducing sediment is important for the utilization and production of green tea infusion and concentrate. The effect of tannase on sediment formation in green tea infusion and concentrate was investigated. The results showed that the amount of sediment of green tea infusion significantly decreased after tannase treatment, which was due to the decrease in the concentration of gallated catechins. Significant positive correlations between the sediment amount and the gallated catechin (r = 0.980, p

Tieguanyin oolong tea (TOT), a semi-oxidized tea originating from Anxi county in China, is categorized into jade TOT, medium-baked TOT, and deep-baked TOT, based on different baking processes. To study the effects of baking, chemical analysis, sensory evaluation, and bioactivity assessments of the three TOTs were conducted. The results indicated that the baking process promoted the formation of colored macromolecules (e.g., theabrownins), which affected the color of tea infusion. Free amino acids underwent the Maillard reaction and generated specific Maillard reaction products, such as 5-hydroxymethylfurfural and furfural, which modified the taste and aroma. Floral and fresh volatiles were remarkably reduced, while multiple new volatiles were produced, forming a typically baked aroma. The antioxidant activity and antibacterial activity were reduced after baking, which might be associated with the decrease of monomeric catechins. These results provide a scientific basis for understanding the changes caused by the baking process.

Hydrogen peroxide has a significant effect on the flavor of tea beverages. In this study, the yield of hydrogen peroxide in (–)-epigallocatechin gallate (EGCG) solution was first investigated and found to be significantly enhanced under specific conditions, and the above phenomenon was amplified by the addition of linalool. Then, an aqueous hydrogen peroxide solution was added to a linalool solution and it was found that the concentration of linalool was significantly reduced in the above-reconstituted system. These findings were verified by extending the study system to the whole green tea infusions. The results suggested that the production of hydrogen peroxide in tea beverages may be dominated by catechins, with multiple factors acting synergistically, thereby leading to aroma deterioration and affecting the quality of tea beverages. The above results provided a feasible explanation for the deterioration of flavor quality of green tea beverages with shelf life.

Phenolic acids are important taste components in green tea. The aim of this study was to analyze the taste characteristics of phenolic acids and their influence on the bitterness and astringency of green tea by sensory evaluation and chemical determination. The major tea phenolic acids and quercetin-3-O-rutinoside (Que-rut) were significantly positively correlated with the bitterness (r = 0.757, p r = 0.605, p r = 0.870, p r = 0.576, p

The effects of β-glucosidase on the volatile profiles and aroma stability of black tea juice were evaluated using gas-chromatography-mass spectrometry coupled with sensory analysis. During liquid fermentation of tea leaves, the addition of β-glucosidase increased the concentration of aldehydes, strengthening the undesirable "green grassy" odour. However, the "green grassy" odour was counteracted by adding green tea extract during fermentation. At the same time, "flowery" flavour notes were enhanced, improving the overall aroma quality and strengthening the characteristic "sweet" aroma of black tea. Increased addition of β-glucosidase released more free aroma alcohols from their glucosides. Two "fruity" and "floral" aroma components, benzyl alcohol and phenylethyl alcohol, were not significantly affected by heat treatment (95 °C water bath) and the overall aroma stability was not significantly affected by β-glucosidase treatment. β-Glucosidase treatment improved the aroma, colour and overall suitability of fermented black tea juice as an ingredient for tea-based beverages.

Seven batches of raw tea leaves, processed by different methods (steaming, pan-frying) and from two different harvesting seasons (spring, autumn), were used to investigate the effect of baking treatment on changes in the composition and content of nonvolatile and volatile compounds. The results showed that baking had a greater impact on sensory and flavor quality, which chemically modified some of taste and aroma components. The aroma concentrations of steamed teas (4,168-10,706 μg/L) were significantly higher than those of pan-fried teas (959-2,608 μg/L), and the aroma concentrations of baked green teas (2,608-10,706 μg/L) were significantly higher than those of unbaked teas (959-4,213 μg/L). Based on VIP 1 and ACI 1, (E, E)-3,5-octadien-2-one, hexanal, β-ionone, 5-methylfurfural, β-cyclocitral, and linalool were identified as the main aroma compounds. Chemical changes resulting from Maillard reaction were greater during baking of steamed, than pan-fried green tea. These results help improve the quality of green tea with baking.

Oral processing (OP), referring to the whole process of food digestion in human mouth, has a major influence on food flavor perception. This study focused on the compositional changes of the four green tea epicatechins (viz., EC, EGC, ECG, EGCG) during OP, based on targeted and nontargeted metabolomics. It was found that the four epicatechins were all extensively lost through transformation undergoing OP, among which EC was the most stable one, whereas EGCG the least. EGCG was further revealed to be susceptible to human oral cavity in the simulated OP in vitro. It could be converted physically by precipitating with mucin in saliva, and chemically through hydrolysis and dimerization, mediated mainly by the neutral pH condition. The OP of epicatechins also caused salivary composition changes possibly involving health benefits of green tea. These findings could raise awareness of the interactions between epicatechins, or any other food materials, with human mouth.

Zijuan tea is a representative anthocyanin-rich tea cultivar in China. In this study, Zijuan tea was used to produce a novel kombucha beverage (ZTK). The physicochemical, sensory properties, and antioxidant activity of ZTK were compared with that of black tea kombucha (BTK) and green tea kombucha (GTK). Results indicated that after fermentation, the color of ZTK changed from yellowish-brown to salmon-pink, because its anthocyanins (4.5 mg/L) appeared red in acidic conditions. Meanwhile no significant changes of color were observed in BTK and GTK. The dynamic changes of pH, biomass, and concentrations of sugars, amino acids, and main organic acids were similar in three kombucha beverages, except catechins showing different trends. Moreover, ZTK showed the highest overall acceptability score, antioxidant activity, and concentration of volatiles among the three kombucha beverages. Therefore, Zijuan tea is suitable for the preparation of kombucha beverage with attractive color and health benefits.

In this study, the fermentation process of black tea wine was optimized, and the changes in catechins, organic acids, and aroma components during fermentation were investigated. The optimal fermentation conditions for tea wine were determined as follows: the addition of 15% sucrose and 0.75% tea leaves, and a fermentation temperature of 25 ºC. Under the optimal conditions, the alcohol content and sensory evaluation score of tea wine were 8.9 %ABV and 88, respectively. The contents of catechins and organic acids in tea wine were 21.29 mg/L and 3.68 mg/mL, which were 1.32-fold and 10.51-fold higher than those of tea infusion, respectively. L-malic acid was the main organic acid in tea wine, which accounted for 56.3% of the total amount of organic acids. A total number of 34 and 33 kinds of aroma components were detected in tea wine and tea infusion, respectively. The main aroma components of tea wine were esters and alcohols, which accounted for 39.7% and 45.9% of the total amount of aroma components, respectively, while the main aroma components of tea infusion were esters and aldehydes, accounting for 34.6% and 33.2%, respectively.

Milky tea is popular in many countries and its color is an important sensory property. The effects of black tea infusion on the color of milky tea prepared with non-dairy creamer were investigated. The results showed that the redder black tea infusion produced milky tea with more redness, and the color of milky tea was a pleasant pink when the a* value (redness indicator) was in the range of 6.0-7.0. Correlation analysis revealed that the respective theaflavins (TFs), thearubigins (TRs), thearubigins (TBs), (-)-epigallocatechin-3-gallate (EGCG) and chlorogenic acid contents significantly correlated with the a* values of milky tea. A series of complementary experiments were performed to elucidate that TFs and EGCG contributed to the redness of milky tea. The color formation was mainly associated with the binding of phenols to the proteins in the non-dairy creamer. These results contribute to understand the mechanism of color formation in milky tea.

This work aimed at optimizing the extraction of theaflavins for the development of a potentially functional tea beverage using different technological parameters as factors. Green tea leaves treated with tannase provided a beverage with significant higher amount (4.7-fold) of theaflavin (TF) compared to the pure withered leaf fermentation. For black tea, the optimized process conditions to produce a beverage with high TF (0.269 μg/mL) concentration were: 6 g of leaves/400 mL, a low fermentation temperature of 25 °C with the absence of buffer and pH control, an intermediate fermentation time (60 min) and a relatively low aeration rate (0.8–1.0 L/min). The tea liquid produced under optimized fermentation conditions appears to be ideal for making a black tea beverage with surplus summer tea leaves and brings economic benefits.

Highlights • Roasting decreases bitterness, astringency but increases sweet aftertaste. • Roasting degrades flavonoids glycosides and procyanidins. • L-theanine-flavna-3-ols adducts are highly increased after roasting. • Roasting decreases the diversity and intensity of volatile compounds. • Pyrazines, pyrroles and furans highly increase after high temperature roasting., Roasting, a critical process for oolong tea, has been applied to Tieguanyin tea to improve flavor attributes. To investigate the effects of the roasting on the flavor of Tieguanyin, the global metabolomics analysis on the non-volatile and volatile components were proceeded. The weakening of bitterness and astringency, caused by roasting, may be attributed to the decreasing of flavonoids glycosides and procyanidins, whereas the enhancing of sweet aftertaste to the increasing of gallic acid. Besides, l-theanine flavan-3-ols adducts (N-ehtyl-2-pyrrolidinone substituted flavan-3-ols) increased dramatically at 130 °C compared with 105 °C, with the reduction of l-theanine and flavan-3-ols. Meanwhile, high temperature hampered the volatiles’ diversity and intensity, resulting from the lowering of floral volatiles, i.e., β-ionone, jasmine, and nerolidol, yet the nitrogen-containing heterocyclic compounds increased, e.g., pyrroles and pyrazines. The results can help to comprehensively understand the influences of roasting technology on the flavor and chemistry of oolong tea.

The effects of brewing water on the sensory attributes and physicochemical properties of tea infusions made from Chinese teas were investigated. The tea infusions brewed in water with higher pH and total dissolved solids (TDS), generally had a darker color and lower overall sensory acceptability. Moreover, those infusions had less catechins, particularly galloylated-catechins, and lower antioxidant capacity. The teas with less fermentation contained more galloylated-catechins and had higher antioxidant capacity, but were much more susceptible to high mineral brewing water. Green tea was proved to be the most susceptible one, whereas dark tea the most stable one. Green tea infusions prepared with higher pH/TDS water were more rapidly oxidized, resulting in a darker color due to polymerization of catechins, when exposed to the air. These findings suggested that low mineral brewing water was better for Chinese tea, both from the sensory and health benefit perspectives.

The physicochemical characteristics, sensory quality, and antioxidant activity of tea infusions prepared with purified water (PW), mineral water (MW), mountain spring water (MSW), and tap water (TW) from Hangzhou were investigated. The results showed that the taste quality, catechin concentration, and antioxidant capacity of green, oolong, and black tea infusions prepared using MW and TW were significantly lower than those prepared using PW. Extraction of catechins and caffeine was reduced with high-conductivity water, while high pH influenced the stability of catechins. PW and MSW were more suitable for brewing green and oolong teas, while MSW, with low pH and moderate ion concentration, was the most suitable water for brewing black tea. Lowering the pH of mineral water partially improved the taste quality and increased the concentration of catechins in the infusions. These results aid selection of the most appropriate water for brewing Chinese teas.

Fresh tea leaves were crushed into juice and then fermented (oxidation) to obtain fermented black tea juice, which can be used to prepare black tea beverage. The effects of addition of oolong tea infusion or tossing of tea leaves on the sensory quality and theaflavins (TFs) concentration of fermented black tea juice were investigated. The results showed that both addition of tea infusion and tossing of fresh tea leaves increased the TFs/thearubigins (TRs) ratio and improved the sensory quality of fermented black tea juice. The TFs/TRs ratio was found to be significantly correlated with the scores for flavor (r = 0.98), mouth feel (r = 0.94), and overall acceptability (r = 0.91) of the fermented black tea juices from different processes. This result suggested that a relatively high concentration of catechins and stepwise enzymatic oxidation were the crucial factors that increased the TFs/TRs ratio and improved the sensory quality. The combination of adding tea infusion and tossing fresh tea leaves greatly improved the quality of the fermented black tea juice by markedly increasing the TFs/TRs ratio (87%). Results of the present study provided useful information for improving the quality of fermented black tea juice.

Reducing sediment in green tea concentrate utilized for tea production is an important process. In this study, the effect of saccharides on sediment formation in green tea concentrate was investigated. The results show that the amount of tea sediment significantly decreased (31.4%–86.4%) with the addition of fructose or sucrose and that the ratios of polyphenols and caffeine in the sediment sharply decreased (24.1%–49.7% and 2.4%–6.2%) while the proportion of total sugars markedly increased (20.9%–56.5%) in the sediment. Moreover, fructosyl was found to be a highly effective functional group for preventing sediment formation, on the basis of experimental results for a series of sugars with different numbers of fructosyl groups. This phenomenon was elucidated from the energies of interaction between typical sugars, polyphenols, and caffeine calculated by density functional theory method. Our results open new applications for tea concentrates.

Aroma deterioration is one of the biggest problems in processing tea beverages. The aroma of tea infusion deteriorates fast during heat sterilization and the presence of ferrous ion (Fe2+) aggravates it. The underlying mechanism remains unveiled. In this study, Fe2+ was verified to deteriorate the aroma quality of green tea infusion with heat treatment. Catechins were necessary for Fe2+-mediated aroma deterioration. By enhancing the degradation of catechins, Fe2+ dramatically increased the production of hydrogen peroxide (H2O2). Fe2+ and H2O2 together exacerbated the aroma of green tea infusion with heat treatment. GC-MS analysis revealed that the presence of Fe2+ enhanced the loss of green/grassy volatiles and promoted the formation of new volatiles with diversified aroma characteristics, resulting in a dull scent of green tea infusion. Our results revealed how Fe2+ induced aroma deterioration of green tea infusion with heat treatment and could help guide tea producers in attenuating the aroma deterioration of tea infusion during processing.

The traditional scenting process is complicated and limited by the short flower season. In this study, formulated jasmine essential oil-casein nanoparticles (JEO–CS–NPs) were prepared for scenting green tea, in this case, Huangshan Maofeng. The freeze-dried JEO–CS–NPs (FD-JEO–CS–NPs) with a JEO/CS ratio of 0.25 encapsulated more than 70% of the JEO, and the JEO could be sustainably released for 60 days. After being scented by placing FD-JEO–CS–NPs in the tea package for 50–60 days at room temperature, the tea leaves effectively adsorbed and retained the aromatic compounds and presented a favorable smell of jasmine fragrance with good aroma maintenance. This could be ascribed to the sustained-release of aromatic compounds from the FD-JEO–CS–NPs. The new technology also avoided destroying the color of the soaked tea liquid and infused leaf since the scenting process is performed in the tea package using the antioxidative jasmine essential oil. The research showed that the new scenting technology can be extensively applied for the production of tea leaves scented with various flower fragrances.

Astringency is an important quality attribute of green tea infusion, and (−)-Epigallocatechin gallate (EGCG) is the main contributor to astringency. Turbidity was used to predict the intensity of astringency for EGCG. The interactions between the selected proteins and EGCG, and the impacts of temperature, pH, protein structure, and EGCG concentration were studied. Mucin was selected as the protein in study for the prediction of EGCG astringency intensity. A predictive model (R2 = 0.994) was developed based on the relationship between the astringency of EGCG and the turbidity of EGCG/mucin mixtures at pH 5.0 and 37 °C. The fluorescence quenching analyses showed the interactions between EGCG and the selected proteins, which induced the reversible protein molecule conformational changes. The interactions were considered as the main reason that causes the astringency of tea infusions. The results provided a biochemical approach to explore the sensory qualities of green tea.

Flavor stability is important for the quality of tea beverages. Baking is a typical processing technology to improve the flavor of tea leaves. In present study, seven raw tea materials, including steamed spring and autumn tea leaves, pan-fired spring tea leaves, and their corresponding baked tea leaves, were used to investigate the effect of baking on flavor stability of green tea beverages. The results showed that tea beverages prepared with baked tea had better flavor stability. The baking process obviously changed the concentrations of some important flavor substances, especially the aromatic pyrrole substances from 0 (unbaked) to 338.13 μg/L (baked) in tea beverages. Heat treatment had little influence on the flavor of tea beverages prepared from baked tea, but caused great changes in non-volatile and volatile components in those prepared from unbaked leaves. These results could help guide the processing of tea beverages which would improve their flavor quality stability.

Castanopsis lamontii is used as functional herbal tea in southwest China. Usually, only buds rather than mature leaves are applied. To figure out whether mature leaves were suitable for producing herbal tea, chemical composition, sensory properties and bioactivities of Castanopsis lamontii bud infusion (CLB) and mature leaf infusion (CLM) were investigated. According to the results, CLB and CLM had similar non-volatile composition, but in different proportion. Meanwhile, CLB contained more types of volatiles than CLM, leading to distinguishable volatile profiles between them. Sensory assessment showed that CLB had sweet aftertaste and floral aroma. CLM tasted astringent and smelled grassy. Bioactivity evaluation indicated that CLB exhibited higher activities in scavenging free radicals and suppressing lipopolysaccharide-induced inflammation. Taken together, CLB had better overall acceptability in sensory quality and higher bioactivity, implying that Castanopsis lamontii buds were more suitable for producing herbal tea.

The physicochemical changes of the instant green tea powders added with β-cyclodextrin and sodium ascorbate stored at 4°C and 25°C were investigated by determining moisture, polyphenols, caffeine, amino acids, catechins, color, sensory quality, and the total microbial count. The results showed that addition of both β-cyclodextrin (6%, w/w) and sodium ascorbate (2%, w/w) reduced the changes of moisture, polyphenols, and catechins contents, helped to maintain the sensory quality, and limited the microbial count. The low temperature (4°C) was also found to maintain the sensory quality and limit of the microbial count of instant green tea powder. The combination of low temperature and addition of β-cyclodextrin with sodium ascorbate were the best treatment for the storage of instant green tea powder. These results could provide useful information for the quality improvement of instant green tea powder during storage.

The present study aims to improve the sweet aftertaste and overall acceptability of green tea infusion by hydrolyzing (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) with tannase. The results showed that the intensity of the sweet aftertaste and the score of overall acceptability of the green tea infusion significantly increased with the extension of the hydrolyzing treatment. (-)-Epigallocatechin (EGC) and (-)-epicatechin (EC) were found to be the main contributors for the sweet aftertaste, based on a trial compatibility with EGCG, ECG, EGC, and EC monomers, and a synergistic action between EGC and EC to sweet aftertaste was observed. A 2.5:1 (EGC/EC) ratio with a total concentration of 3.5 mmol/L gave the most satisfying sweet aftertaste, and the astringency significantly inhibited the development of the sweet aftertaste. These results can help us to produce a tea beverage with excellent sweet aftertaste by hydrolyzing the green tea infusion with tannase.

Flavor characteristics and chemical compositions of Tieguanyin oolong tea processed using different semi-fermentation times were investigated. Six flavor attributes of the teas, namely, astringency, bitterness, umami, sweet aftertaste, floral flavor, and green fruity flavor, were analysed. With extended semi-fermentation time, the taste intensity of sweet aftertaste increased, and the aroma intensity of floral and green fruity flavors increased, while the intensities of astringency, bitterness, and umami showed no clear trend. With increasing semi-fermentation time, the concentrations of gallated catechins, myricetin-rhamnose, quercetin-rutinoside, myricetin, and theanine greatly decreased, while those of total theaflavins, vitexin-rhamnose, kaempferol-galactose, kaempferol-rutinoside, vitexin, quercetin, and kaempferol increased significantly. The intensity of bitter taste was positively correlated with the concentrations of total catechins and gallated catechins. The intensity of astringent taste strongly correlated with the flavonoid concentrations, and that of sweet aftertaste positively correlated with the concentrations of (−)-epigallocatechin and (−)-epicatechin. However, dose-over-threshold analysis revealed that catechins, theaflavin, flavonol glycosides, and caffeine are the main taste-active compounds contributing to the taste of Tieguanyin oolong tea. The concentrations of total volatiles and most of the esters increased markedly with the semi-fermentation time, while the concentrations of low aldehydes showed a significant decrease. The flavor index was consistent with the intensity of floral aroma, increasing from 0.59 (12 h) to 0.84 (24 h) and then decreasing to 0.63 (32 h). Results of this work suggest that the flavor change is mainly due to the variation of taste-active and aroma-active compounds in oolong tea.

Bitterness and astringency are two important quality attributes of green tea infusion, and catechins are the main contributor to the bitterness and astringency. The aim of this work was to quantitatively analyse the bitterness and astringency of green tea infusion according to the concentrations of catechins. The concentration–taste curves of catechins showed a pattern that fit the cubic functions, and their R2 values were higher than 0.956. The bitterness of green tea was highly correlated with the concentrations of (−)-epigallocatechin gallate and (−)-epicatechin gallate (ECG) (R2 = 0.7769, p

The physicochemical properties of tea extracts are significantly affected by the extraction method. The aim of this study was to compare the effects of static and dynamic extractions on the concentrations of chemical components and taste quality of green tea extracts. Our results show that extraction of chemical components using static extraction follows a pseudo-second-order reaction, while that of dynamic extraction follows a first-order reaction. The concentrations of the solids, polyphenols, and free amino acids in green tea extract prepared by dynamic extraction were much higher, although the overall yields were not significantly different between the two extraction methods. Green tea extracts obtained via dynamic extraction were of lower bitterness and astringency, as well and higher intensities of umami and overall acceptability. These results suggest that dynamic extraction is more suitable for the processing of green tea concentrate because of the higher concentration of green tea extract.

The effects of Ca2 + on the taste of green tea infusions and solutions of the main taste compounds were studied. Increasing the Ca2 + concentration influenced the appearance and the taste of the tea infusions prepared from instant green tea by weakening the bitter, umami and sweet tastes and by strengthening the astringent taste. Ca2 + enhanced the astringent taste of EGCG, caffeine and theanine solutions and weakened the bitter taste of EGCG and caffeine solutions, the umami taste of the theanine solution and the sweet taste of theanine and sucrose solutions. Synergistic or countervailing actions were found among the taste substances: EGCG and caffeine could strengthen each other's astringent and bitter tastes; theanine could weaken the astringent taste of the EGCG solution, and caffeine could strengthen the umami taste of the theanine solution. The results suggest that green tea infusion prepared from instant green tea should use water with low Ca2 + concentration.

The formation of irreversible tea sediment (IRS) and its chemical components in green tea infusions were investigated. The results showed that the amounts of IRS in the green tea infusions from various tea cultivars ranged from 0.10 to 1.47 mg/mL. The amount of IRS was influenced remarkably by the chemical components in the green tea infusion. Principal component analysis and regression analysis indicated that gallated catechins, Mn, Ca, caffeine, Na, and (−)-gallocatechin gallate (GCG) were the principal components. IRS (mg/mL) =−4.226 + 0.275 gallated catechins + 79.551 Na + 7.321 Mn + 21.055 Ca + 0.513 caffeine − 0.129 GCG (R2= 0.697). The contents of the main chemical components in the reversible tea sediment (RTS) and IRS were markedly different, especially the minerals. Large amount of minerals participated in the formation of irreversible green tea sediment. The amount of IRS increased with the extraction temperature. Practical Application: The results of this paper will help select the right tea cultivars, which have less RTS and IRS. This paper also helps understand the chemical components of IRS in green tea infusions and to find the right method to prevent its formation.

The relationship between the amount of tea cream and the chemical components contents in the original green tea infusion was investigated. The results showed that the amounts of tea cream in the green tea infusions obtained from different cultivars and different parts of new shoots were varied. There were many chemical components participating in the formation of green tea cream. However, there were only the contents of caffeine (Y=0.85, P

The formation of tea cream in the green tea concentrates of different solid concentrations (5, 10, 20, 30, 40, 50 and 60°Brix) was investigated. The results showed a good positive correlation (γ = 0.98, p ≤ 0.05) between the amount of tea cream and the solid concentrations from 5 to 40°Brix, while the amount of tea cream in the tea concentrates of 50 and 60°Brix decreased acutely. Total sugar, caffeine and catechins were found to be the main chemical components of tea cream in the green tea concentrate. The large decrease of the amount of tea cream in the tea concentrates of 50 and 60°Brix may be induced by a sharp increase of the viscosity of the tea concentrates, which helped to improve the stability of tea concentrate. It may be indicated that the stability of green tea concentrate enhanced when the concentration higher than 50°Brix, which helped to restrain the formation of tea cream.

The formation of green tea cream and its chemical components were investigated. The green tea infusions were processed from different parts of new shoots: the bud and the first leaf, the second leaf and its implicative stem, the third leaf and its implicative stem, and the fourth leaf and its implicative stem, which were named as first part, second part, third part and fourth part, respectively. The results showed that the formation of tea cream and its settlement slowed down gradually from the first part to the fourth part, and that the amount of tea cream also decreased accordingly. The amount of tea cream was influenced remarkably by the chemical components in the green tea infusion. The main components of green tea cream were polyphenols (29.86 –78.66%), total sugar (14.47–27.62%) and caffeine (2.35–10.43%). Catechins (12.8–42.5%) were the main components of polyphenols which participated in tea cream formation. The main components in the catechins were found to be (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCG), (−)-epicatechin (EC) and (−)-epicatechin gallate (ECG). Seven minerals were found in the tea cream, including Ca2+, K+, Mg2+, Mn2+, Na+, Zn2+ and Ni2+.

The formation and the main chemical components of sediments, including reversible tea sediments (RTS) and irreversible tea sediments (IRS), in concentrated green tea during low-temperature storage were studied. RTS was mainly formed in the first 10 days, and IRS was mainly formed between 20 and 40 days of storage. The RTS were the primary sediment, contributing more than 90% of the total sediment. The RTS comprised of polyphenols, total sugar, caffeine, flavones and proteins, while the IRS mainly comprised of oxalates of Ca, Mg, Ga and Mn. The total mineral content in the IRS (17.1%) was much higher than that in the RTS (2.6%) after 80 days of storage. The Ca, Mg, Mn and Ga contents in IRS were over 1.0% (w/w) each. About 75% of the IRS was soluble in 0.1 M aqueous HCl, with the oxalate accounting for 68%. Minerals and oxalic acid were the crucial factors in the IRS formation.

The effect of Ca(2+) in brewing water on the organic acid content, turbidity, and formation of tea cream and sediment in green tea infusions was studied. When the Ca(2+) concentration of the brewing water was40 mg L(-1), the green tea infusion became more turbid. The turbidity of the tea infusion was highly negatively correlated with the contents of oxalic acid (R=-0.89, p0.01), quinic acid (R=-0.90, p0.01) and tartaric acid (R=-0.82, p0.01). Oxalic acid on its own interacted with Ca(2+) at low concentrations, whereas polyphenols and protein did not. In conclusion, Ca(2+) in brewing water influences the quality of a tea infusion by inducing tea cream and sediment formation from combination of Ca(2+) and organic acids, such as oxalic acid, quinic acid and tartaric acid. Ca(2+) and oxalate are the main metal ion and anion, respectively, involved in tea cream and sediment formation on tea infusion cooling or concentrating.

Free amino acids are important chemical components which impact the taste of green tea infusion. The hydrolysis of water-insoluble protein in the green tea residue helps to increase the contents of free amino acids components except theanine. Studies indicate that the hydrolysis of the tea protein could be restricted due to interaction of polyphenols with protein. The experiment indicates that the hydrolysis of tea protein by protease is the main trend when the polyphenols concentration is lower than 5 mg ml(-1), however, the proteins (including tea protein and protease) would interact with polyphenoles instead of hydrolysis when the concentration of polyphenols is higher than 5 mg ml(-1). The hydrolysis of tea protein is absolutely restrained when concentration comes to 10 mg ml(-1).