Influence of brewing conditions on taste components in Fuding white tea infusions

Correlation analysis and modeling application from objective indicators to subjective evaluation of scented tea: A case study of rose tea

Different scented teas provide various choices for consumers from appearance, aroma, flavor and others. Aiming to define advantages and market positions of different scented teas and promote optimization of market structure, characteristics for scented tea favored by consumers and outstanding attributes of different scented teas should be clarified. Rose tea was taken as study object. Sensory evaluation and consumer acceptance were investigated. GC-MS and HPLC fingerprints were established. Physicochemical characteristics were determined. RGB integration analysis was inventively proposed for correlation analysis. The volatile compounds with spicy, green or herbal odor as camphene, β-phenethyl acetate, eugenol, and physicochemical parameters as antioxidant capacity, reducing sugar content, pH showed positive correlation with popular sensory properties. Six models for consumer preference by objective description were built through GA-SVR (accuracy = 1), and APP was developed. The research mode of scented tea has been successfully established to study multiple subjective characteristics with measurable objective parameters.

Re-rolling treatment in the fermentation process improves the taste and liquor color qualities of black tea

Fermentation is a vital process occurred under the premise of rolling affecting black tea quality. Theoretically, re-rolling during fermentation will remodel the biochemical conditions of tea leaves, and thus influence black tea quality. Herein, we studied the effect of re-rolling on black tea taste and liquor color. Sensory evaluation showed that re-rolling significantly weakened the astringency taste and improved the redness and luminance of liquor. With re-rolling, the color attributes of a* and L* and the contents of theaflavins and thearubigins were significantly improved. Metabolomics analysis showed that the contents of 110 non-volatile compounds were significantly different among black teas with different rolling treatments. In summary, re-rolling accelerated the oxidation of polyphenols into pigments, the hydrolysis of proteins into amino acids, and the metabolism of alkaloids, organic acids, glycosidically-bound volatiles, and lipids during the fermentation period. Our study provided a novel and simple way to improve black tea quality.

Adsorption and desorption characteristics of flavonoids from white tea using macroporous adsorption resin

White tea contains the highest flavonoids compared to other teas. While there have been numerous studies on the components of different tea varieties, research explicitly focusing on the flavonoid content of white tea remains scarce, making the need for a good flavonoid purification process for white tea even more important. This study compared the adsorption and desorption performance of five types of macroporous resins: D101, HP20, HPD500, DM301, and AB-8. Among the tested resins, AB-8 was selected based on its best adsorption and desorption performance to investigate the static adsorption kinetics and dynamic adsorption-desorption purification of white tea flavonoids. The optimal purification process was determined: adsorption temperature 25 °C, crude tea flavonoid extract pH 3, ethanol concentration 80 %, sample loading flow rate and eluent flow rate 1.5 BV/min, and eluent dosage 40 BV. The results indicated that the adsorption process followed pseudo-second-order kinetics. Under the above purification conditions, the purity of the total flavonoids in the purified white tea flavonoid increased from approximately 17.69 to 46.23 %, achieving a 2.61-fold improvement, indicating good purification results. The purified white tea flavonoid can be further used for nutraceutical and pharmaceutical applications.

The types of brewing water affect tea infusion flavor by changing the tea mineral dissolution

The effects of different brewing water samples, including natural drinking water (NDW), pure water (PW), mineral water (MW), distilled water (DW), and tap water (TW) on flavor and quality of green tea infusion were investigated. The results showed the dissolution rate of mineral substances varied greatly depend on the type of water used. Notably, the tea infusion brewed with MW showed the highest taste response and darker but higher brightness in color. Furthermore, the content of volatile compounds was highest in tea infusion brewed with NDW and lowest in tea infusion brewed with MW. The mineral substances content and pH were the main factors affecting volatile compounds in green tea infusion. Thereinto, Ca²⁺ and Fe³⁺ remarkably affected the content of alcohols and aldehydes in volatile compounds. These results suggested that water with a neutral pH value and lower mineral substance content is more conducive for brewing green tea.

Application of visible-near infrared spectroscopy in tandem with multivariate analysis for the rapid evaluation of matcha physicochemical indicators

Consumer preference for matcha is heavily influenced by its physicochemical properties. The visible-near infrared (Vis-NIR) spectroscopy technology coupled with multivariate analysis was investigated for rapid and non-invasive evaluation of particle size and the ratio of tea polyphenols to free amino acids (P/F ratio) of matcha. The multivariate selection algorithms such as synergy interval (Si), variable combination population analysis (VCPA), competitive adaptive reweighted sampling (CARS), and interval combination population analysis (ICPA) were compared, and eventually, the variable selection strategy of ICPA and CARS hybridization was firstly proposed for selecting the characteristic wavelengths from Vis-NIR spectra to build partial least squares (PLS) models. Results indicated that the ICPA-CARS-PLS models achieved satisfactory performance for the evaluation of matcha particle size (Rp = 0.9376) and P/F ratio (Rp = 0.9283). Hence the rapid, effectual, and nondestructive online monitoring, Vis-NIR reflectance spectroscopy in tandem with chemometric models is significant for the industrial production of matcha.

Yellow tea: more than turning green leaves to yellow

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

A Study on Origin Traceability of White Tea (White Peony) Based on Near-Infrared Spectroscopy and Machine Learning Algorithms

Identifying the geographical origins of white tea is of significance because the quality and price of white tea from different production areas vary largely from different growing environment and climatic conditions. In this study, we used near-infrared spectroscopy (NIRS) with white tea (n = 579) to produce models to discriminate these origins under different conditions. Continuous wavelet transform (CWT), min-max normalization (Minmax), multiplicative scattering correction (MSC) and standard normal variables (SNV) were used to preprocess the original spectra (OS). The approaches of principal component analysis (PCA), linear discriminant analysis (LDA) and successive projection algorithm (SPA) were used for features extraction. Subsequently, identification models of white tea from different provinces of China (DPC), different districts of Fujian Province (DDFP) and authenticity of Fuding white tea (AFWT) were established by K-nearest neighbors (KNN), random forest (RF) and support vector machine (SVM) algorithms. Among the established models, DPC-CWT-LDA-KNN, DDFP-OS-LDA-KNN and AFWT-OS-LDA-KNN have the best performances, with recognition accuracies of 88.97%, 93.88% and 97.96%, respectively; the area under curve (AUC) values were 0.85, 0.93 and 0.98, respectively. The research revealed that NIRS with machine learning algorithms can be an effective tool for the geographical origin traceability of white tea.

Effect of brewing conditions on the chemical and sensory profiles of milk tea

The brewing conditions of beverage milk tea determine the taste of milk tea. This study investigated the changes in sensory characteristics and small molecule compounds in milk tea made from large-leaf yellow tea under different brewing conditions by sensory analysis, colorimeter, and LC-MS. The results show that the tea to milk ratio is the most important process affecting the taste, and the color values of b* (+yellow, - blue) can be used to evaluate the taste of milk tea made from large leaf yellow tea. The composition of small molecular compounds is affected by tea to milk ratio, which can change the taste of milk tea. l-cysteine and 8-methylsulfinyloctyl glucosinolate are significantly positively correlated with taste by metabolomics analysis. l-cysteine was used to verify the analysis results by LC-MS. The total acceptance of milk tea is improved by adding l-cysteine at a low level (0.025-0.035 mM).

Multi-Metabolomics Coupled with Quantitative Descriptive Analysis Revealed Key Alterations in Phytochemical Composition and Sensory Qualities of Decaffeinated Green and Black Tea from the Same Fresh Leaves

The supercritical CO₂-based decaffeination (SCD) method can be used to prepare decaffeinated tea, but its overall effect on the phytochemicals, volatiles, and sensory qualities of green and black teas is still unclear, and its suitability to prepare decaffeinated green and black teas still needs to be compared. This study revealed the effect of SCD on phytochemicals, volatiles, and sensory qualities in black and green tea prepared from the same tea leaves, and compared the suitability of preparing decaffeinated green and black teas using SCD. The results showed that the SCD could remove 98.2 and 97.1% of the caffeine in green and black tea, respectively. However, it can cause further losses of phytochemicals in green and black teas, specifically the loss of epigallocatechin gallate, epigallocatechin, epicatechin gallate, and gallocatechin gallate in green tea and the loss of theanine and arginine in green and black teas. After the decaffeination, both green and black teas lost some volatiles but also generated new volatiles. Especially, the fruit/flower-like aroma, ocimene, linalyl acetate, geranyl acetate, and D-limonene, were generated in the decaffeinated black tea, while herbal/green-like aroma, β-cyclocitral, 2-ethylhexanol, and safranal, were generated in the decaffeinated green tea. The overall acceptance of decaffeinated green tea decreased due to the substantial reduction in bitterness and astringency, while the overall acceptance of decaffeinated black tea significantly increased. Therefore, SCD is more suitable for the preparation of decaffeinated black tea.

Optimization of brewing conditions for Tieguanyin oolong tea by quadratic orthogonal regression design

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.

Physicochemical indicators coupled with multivariate analysis for comprehensive evaluation of matcha sensory quality

The sensory quality of matcha is a pivotal factor in determining consumer acceptance. However, the human sensory panel test is difficult to popularize by virtue of professional requirements and inability to evaluate large samples. The analysis showed that physicochemical indicators of matcha were significantly related to sensory quality. Hence, principal component analysis (PCA) based on selected key physicochemical indicators was proposed to evaluate the sensory quality of matcha in this research. The eight key indicators were selected from twenty-four physicochemical indicators based on least absolute shrinkage and selection operator (LASSO) for the establishment of the PCA comprehensive evaluation model. The results demonstrated that the PCA comprehensive evaluation model achieved superior performance, with -0.895 r_c (correlation coefficient in calibration set) and -0.883 r_p (correlation coefficient in prediction set) for overall sensory quality. This work demonstrated that LASSO-PCA comprehensive evaluation as an objective protocol has great potential in predicting matcha sensory quality.

Effects of brewing water on the sensory attributes and physicochemical properties of tea infusions

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.

Simultaneous quantification of chemical constituents in matcha with visible-near infrared hyperspectral imaging technology

This study aimed to assess the feasibility of identifying multiple chemical constituents in matcha using visible-near infrared hyperspectral imaging (VNIR-HSI) technology. Regions of interest (ROIs) were first defined in order to calculate the representative mean spectrum of each sample. Subsequently, the standard normal variate (SNV) method was applied to correct the characteristic spectra. Competitive adaptive reweighted sampling (CARS) and bootstrapping soft shrinkage (BOSS) were used to optimize the models. They were built based on partial least squares (PLS), creating two models referred to as CARS-PLS and BOSS-PLS. The BOSS-PLS models achieved best predictive accuracy, with coefficients of determination predicted to be 0.8077 for caffeine, 0.7098 for tea polyphenols (TPs), 0.7942 for free amino acids (FAAs), 0.8314 for the ratio of TPs to FAAs, and 0.8473 for chlorophyll. These findings highlight the potential of VNIR-HSI technology as a rapid and nondestructive alternative for simultaneous quantification of chemical constituents in matcha.

Distinct variation in taste quality of Congou black tea during a single spring season

The quality of Congou black tea fluctuates greatly with the changing seasons. However, variations in the taste quality of Congou black tea manufactured during a single spring season are far from clear. Here, we analyzed the taste quality of HuangJinCha (HJC) Congou black tea using sensory evaluation and found the taste quality of black tea manufactured in the early spring was better than that manufactured in the late spring. Principal component analysis (PCA) and cluster analysis for the data from the electronic tongue confirmed the variation and revealed that April 4 may be the critical time point at which variations in taste quality become apparent. The contents of tea polyphenols (TP), total catechins (TC), total flavones, (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), and gallic acid (GA) showed increasing trends, whereas total amino acids (TAA) declined over time. Moreover, the variations in total amino acids (r = 0.846) and total flavones (r = - 0.858) were highly significantly correlated with the average taste quality score (p < .01), suggesting these compounds were the primary factors responsible for the fluctuation in taste quality of Congou black tea processed during a single spring season.

Prediction of suitable brewing cuppages of Dahongpao tea based on chemical composition, liquor colour and sensory quality in different brewing

Oolong tea is famous for its characteristic of durably brewing. To explore suitable brewing cuppages and the scientific methods to brew Oolong tea in multiple steeping process. Dahongpao tea (Zhengyan, Banyan and Zhouyan tea) is well known Oolong tea variety, brewed at 14 times and assessed its chemical composition, infusion colour and sensory quality in different brewing intervals. The results showed that Zhengyan tea (A3) had the best quality of steeping among the chosen tea. It could be brewed up to 10 cuppages with 80% sensory score. The chemical composition and tea infusion colour strength were higher in Zhengyan tea. Though, 70% caffeine leached within first three steeping. The Forest regression model revealed that the suitable brewing time ranges between 4 and 10 in the chosen Dahongpao tea variety. This study provides a scientific method and suitable steeping times for the drinking of different Dahongpao tea through dynamic analysis of quantity of chemical composition, infusion colour strength and sensory quality.

Effects of β-glucosidase and α-rhamnosidase on the Contents of Flavonoids, Ginkgolides, and Aroma Components in Ginkgo Tea Drink

Ginkgo tea is a kind of health food produced from Ginkgo biloba leaves. The market of Ginkgo tea encountered many difficulties because of its bad palatability and vague function statement. In this study, two kinds of glycosidase were used to improve the flavor of Ginkgo tea, and three kinds of bioactivities were selected to investigate the health care function of the tea infusion. The aroma components extracted by headspace absorb (HSA) method during the making of Ginkgo tea were analyzed by GC-MS. The flavonoids and ginkgolides released into the tea infusion were studied by HPLC. A combination of β-glucosidase (β-G) and α-rhamnosidase (α-R) was applied during the making of the tea. The contents of characteristic aroma components and the release of total flavonoids and ginkgolides were increased significantly by adding β-G and α-R. The composition of flavone glycosides was changed greatly. The free radical scavenging, inhibition of inflammatory cell activation, and tumor cytotoxicity activities of the tea were demonstrably improved. According to the release of active components, Ginkgo tea can be brewed repeatedly for at least three times. The enzymes used here show potential application prospects in the making of Ginkgo tea or tea drink to get higher contents of flavonoids, ginkgolides, and aroma components.

Comprehensive Investigation of the Effects of Brewing Conditions in Sample Preparation of Green Tea Infusions

Chemical and biological investigation of green tea has been generally performed while using different infusions that are prepared without consideration of the effects of sample preparation conditions. In this study, for the first time, the effects of green tea brewing conditions on the antioxidant activity and chemical profiles of metabolome and catechin compounds were examined at 60 °C and 95 °C for a period of 5-300 min. The antioxidant capacities of the tea infusions, which were assessed as per 2,2-diphenyl-1-picryl-hydrazyl hydrate (DPPH) radical scavenging activity, depended more on temperature than time. Metabolomics study that was based on ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF/MS) revealed that the metabolic profiles, including 33 differential metabolites, were significantly changed by temperature and time, with the effects of time being more evident at 95 °C starting after 30 min. Infusions that were brewed at 95 °C for greater than 30 min yielded distinct profiles in the hierarchical clustering analysis. The quantification of eight catechins by UHPLC-QqQ/MS showed that the total catechin level peaked at 95 °C brewing at 10 min, after which the levels of four epi-forms of catechins decreased and those of four non-epi-forms increased, implying the epimerization of catechins over time. These results suggest that the brewing conditions for sample preparation of green tea should be put into careful consideration in studies where green tea extracts are applied as aqueous infusions.

Effects of brewing conditions on the phytochemical composition, sensory qualities and antioxidant activity of green tea infusion: A study using response surface methodology

Green tea is a highly consumed beverage, and the phytochemical composition, sensory qualities, and antioxidant activity of tea infusion are significantly affected by brewing conditions. However, the simultaneous effects of brewing conditions on the infusion are unknown. This study aimed to model the effects of brewing conditions (temperature, time, water/tea ratio and particle size) on the phytochemical composition, sensory profiles and antioxidant activity of green tea infusion using response surface methodology. The regression models describing the brewing of detected indexes were significant (p ≤ 0.01) and reliable (R² ≥ 0.854). Particle size had the greatest negative effects on the phytochemical composition and antioxidant activities of tea infusion. Optimization of brewing conditions performed for five types of needs and preferences for consuming were verified to be credible. In particular, optimal conditions of overall acceptance were 82 °C (temperature), 5.7 min (time), 70 mL/g (water/tea ratio), and 1100 µm (particle size).

Comparison of the main compounds in Fuding white tea infusions from various tea types

The purpose of this study was to compare the main components, and particularly catechins, caffeine, theanine, free amino acids, and water extracts, in Bai Hao Yin Zhen, Bai Mu Dan, and Shou Mei Fuding white tea infusions brewed at different temperatures, and their contributions to taste were estimated by dose-over-threshold value. Infusion temperature had a distinct effect on the main components extracted, and 100 °C was found to be optimal for extracting catechins and caffeine. However, the effect of temperature on theanine, free amino acids, and water extracts varied with tea type. Bai Mu Dan and Shou Mei yielded a higher content of the major compounds than did Bai Hao Yin Zhen. Thus, infusion temperature had a large effect on extracting the main compounds, and the differences in content between the three white teas presumably reflected differences in the harvest time, processing method or leaf shape.

Scientific opinion on the safety of green tea catechins

The EFSA ANS Panel was asked to provide a scientific opinion on the safety of green tea catechins from dietary sources including preparations such as food supplements and infusions. Green tea is produced from the leaves of Camellia sinensis (L.) Kuntze, without fermentation, which prevents the oxidation of polyphenolic components. Most of the polyphenols in green tea are catechins. The Panel considered the possible association between the consumption of (-)-epigallocatechin-3-gallate (EGCG), the most relevant catechin in green tea, and hepatotoxicity. This scientific opinion is based on published scientific literature, including interventional studies, monographs and reports by national and international authorities and data received following a public 'Call for data'. The mean daily intake of EGCG resulting from the consumption of green tea infusions ranges from 90 to 300 mg/day while exposure by high-level consumers is estimated to be up to 866 mg EGCG/day, in the adult population in the EU. Food supplements containing green tea catechins provide a daily dose of EGCG in the range of 5-1,000 mg/day, for adult population. The Panel concluded that catechins from green tea infusion, prepared in a traditional way, and reconstituted drinks with an equivalent composition to traditional green tea infusions, are in general considered to be safe according to the presumption of safety approach provided the intake corresponds to reported intakes in European Member States. However, rare cases of liver injury have been reported after consumption of green tea infusions, most probably due to an idiosyncratic reaction. Based on the available data on the potential adverse effects of green tea catechins on the liver, the Panel concluded that there is evidence from interventional clinical trials that intake of doses equal or above 800 mg EGCG/day taken as a food supplement has been shown to induce a statistically significant increase of serum transaminases in treated subjects compared to control.

The synergistic potential of various teas, herbs and therapeutic drugs in health improvement: a review

Tea is one of the most widely consumed non-alcoholic beverages in the world next to water. It is classified as Camellia sinensis and non-Camellia sinensis (herbal teas). The common bioactive compounds found mainly in green teas are flavan-3-ols (catechins) (also called flavanols), proanthocyanidins (tannins) and flavonols. Black tea contains theaflavins and thearubigins and white tea contains l-theanine and gamma-aminobutyric acid (GABA), while herbal teas contain diverse polyphenols. Phytochemicals in tea exhibit antimicrobial, anti-diabetic and anti-cancer activities that are perceived to be helpful in managing chronic diseases linked to lifestyle. Many of these phytochemicals are reported to be biologically active when combined. Knowledge of the synergistic interactions of tea with other teas or herbs in terms of biological activities will be of benefit for therapeutic enhancement. There is evidence that various types of teas act synergistically in exhibiting health benefits to humans, improving consumer acceptance and economic value. Similar observations have been made when teas and herbs or medicinal drugs were combined. The aim of this review is to highlight potential beneficial synergies between combinations of different types of teas, tea and herbs, and tea and medicinal drugs. © 2017 Society of Chemical Industry.