Tea Quality Parameters Research Articles

Non-Targeted Metabolomics Reveals the Effects of Different Rolling Methods on Black Tea Quality.

A non-targeted metabolomics approach and sensory evaluation, coupled with multivariate statistical analysis, systematically uncover the impact of the rolling time on the quality parameters of black tea. GC-MS analysis reveals that a moderate extension of rolling time favorably contributes to the accumulation of characteristic aroma components in black tea. The volatile components reach their highest concentration in black tea samples processed during an 80-min rolling period. UHPLC-Q-TOF/MS analysis demonstrates a substantial decrease in the contents of catechins and flavonoids with an increase in rolling time. Simultaneously, the production of theaflavins, coupled with the degradation of green bitterness volatiles (GBVs), significantly contributes to the formation of endogenous aroma components in black tea. These findings underscore the close relationship between rolling time control and black tea quality, emphasizing that a moderate extension of the rolling time fosters the development of improved black tea flavor quality. The comprehensive quality evaluation indicates that the optimal duration is 80 min. However, the initial 0 to 20 min of rolling is a crucial phase for the genesis and transformation of black tea quality. This study offers valuable insights into the influence of rolling time on black tea quality, potentially enhancing future studies of rolling technology. It provides theoretical guidelines for optimizing the processing of Gongfu black tea.

Comparative Study of Biochemical Components in Organic and NonOrganic Black Tea

During the period of 10 September 2020 to 15 September 2021, an experiment was conducted at the Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology (SUST), Sylhet, to compare the biochemical components and quality parameters of organic and nonorganic black tea.

Production and Quality Evaluation of Herbal Tea Mixtures from Phyllanthus Debilis, Osbeckia octandra, and Artrocarpus heterophyllus Leaves

Abstract. Introduction: This study investigated the acceptability and quality of herbal tea mixtures prepared using Phyllanthus debilis, Osbeckia octandra, and Artrocarpus heterophyllus leaves powders in different proportions. Preference for different sensory attributes of tea samples was evaluated using thirty untrained panelists. Proximate composition, tea quality parameters, and microbial counts of tea samples were evaluated as per AOAC and ISO standard methods. The amount of major and trace minerals was evaluated using atomic absorption spectrophotometer. Results revealed that dark-colored samples were much preferred by the consumers. A significant positive correlation (r=0.920) showed among redness (a*) of teas and color preference. Yet, the overall preference was reduced in more bitter and astringent samples. Overall acceptability scores highest for A. heterophyllus tea (M9), yet the color preference was highest in P. debilis tea (M8) and mix of P. debilis and O. octandra (M4). The tea samples were rich in nutrients, yet crude fiber and moisture contents exceed the required maximum limits. Heavy metal concentrations and microbial counts lay within the standard limits. This study showed mixing herbs can enhance the acceptability and quality of herbal infusions. With such optimizations, these novel tea mixtures can thrive commercially in the tea market. Keywords: Herbal tea, Quality parameters, Sensory attributes

Urate oxidase treatment increases the quality of autumn Yellowish Yinghong 9 black tea

Microbes can be used to improve the quality of fermented beverages and food. Colletotrichum camelliae is one of the most dominant fungi associated with tea leaves. In the present study, black tea produced from the autumn leaves of Yellowish Yinghong 9 was treated with C. camelliae urate oxidase (CcUOX) to determine whether this treatment could improve tea quality. The effects of recombinant CcUOX on several black tea quality parameters were assessed, such as liquor color, aroma, and levels of theabrownins, thearubigins, total polyphenols, catechins, caffeine, xanthine, and hypoxanthine. CcUOX treatment significantly affected the aroma composition and volatile compound profiles. Specifically, volatiles in the benzenoid/phenylpropanoid, fatty acid metabolism, and amino acid pathways were increased in CcUOX-treated black tea, whereas levels of volatiles in the terpineol and carotenoid pathways were reduced. This suggested that the balance of aroma constituents in Yellowish Yinghong 9 black tea was affected by treatment with CcUOX. The present study provides evidence that pre-treatment of black tea with a single enzyme from a common tea-associated microbe could significantly improve autumn tea quality, validating this method for use in further studies of tea improvement.

Optimization of the factors affecting BT-2 black tea fermentation by observing their combined effects on the quality parameters of made tea using Response Surface Methodology (RSM)

This research work aimed to optimize the fermentation time, temperature, and relative humidity of the black tea produced from Bangladesh Tea 2 (BT-2) variety by observing their quality parameters. Total theaflavin (TF), thearubigin (TR), the ratio of TF: TR, total liquor color (TLC), high polymeric substances (HPS), and total phenolic content (TPC) were evaluated for quality measurements of BT-2 black tea. Response Surface Methodology (RSM) with Box-Behnken design (BBD) was applied to optimize fermentation time, temperature, and relative humidity as well as evaluate the effects of optimized conditions on the quality of made tea. The results obtained from the response surface optimization affirmed that under the optimum conditions of time (80.14 min), temperature (28.76 °C), and relative humidity (92.30%), the model showed the value of TF (0.69%), TR (5.57%), HPS (8.61%), TLC (3.05%), and TPC (7.95 GAE g/100g tea). Moreover, the optimized model found that the TF:TR value was 1:9.13, which is close to black tea's optimum quality. The values observed in experiments were highly congruent with the predicted value by the regression model. The Analysis of Variance (ANOVA) test revealed that the model was significant for TF, TR, HPS, TLC, TPC, and TF:TR values of prepared BT-2 black tea at different levels (p < 0.001 to p < 0.01). The composite desirability of the model was 0.93, which suggests that the developed model could be utilized effectively to maintain the quality parameters of BT-2 black tea during fermentation.

Effects of Plant Age, Topography and Processing System On the Biochemical Traits and Quality of Tea

Laboratory experiment was conducted to study the biochemical and quality parameters of tea i.e. Polyphenol, Theaflavin (TF), Thearubigin (TR), Caffeine, Lipid, Total ash, Chlorophyll, Moisture content etc. under different variables designed for age, topography, and processing system imposed on an established tea orchard. Results revealed that plant age and topography do not have any significant effect on most of the studied parameters. In case of plant age, tannin is found to be significantly higher in mature tea plant (39.35 ppm) whereas young plant showed significantly lower total sugar content (28.98 ppm). In case of land elevation, significantly higher tannin (37.41 ppm) and lower carotenoid content (0.74 mg/g) were evident in plants from kunchi topography where flat topography showed significantly higher total sugar (26.62 ppm) in leaves. The handmade tea flavoured with significantly higher amount of polyphenol (58.57 ppm) and caffein (43.30 ppm) but industry made tea showed significantly higher amount of tannin (37.65 ppm), total sugar (15.25 ppm) and TF:TR (1:10). Bangladesh J. Bot. 50(3): 633-639, 2021 (September)

Application of Multispectral Camera in Monitoring the Quality Parameters of Fresh Tea Leaves

The production of high-quality tea by Camellia sinensis (L.) O. Ktze is the goal pursued by both producers and consumers. Rapid, nondestructive, and low-cost monitoring methods for monitoring tea quality could improve the tea quality and the economic benefits associated with tea. This research explored the possibility of monitoring tea leaf quality from multi-spectral images. Threshold segmentation and manual sampling methods were used to eliminate the image background, after which the spectral features were constructed. Based on this, the texture features of the multi-spectral images of the tea canopy were extracted. Three machine learning methods, partial least squares regression, support vector machine regression, and random forest regression (RFR), were used to construct and train multiple monitoring models. Further, the four key quality parameters of tea polyphenols, total sugars, free amino acids, and caffeine content were estimated using these models. Finally, the effects of automatic and manual image background removal methods, different regression methods, and texture features on the model accuracies were compared. The results showed that the spectral characteristics of the canopy of fresh tea leaves were significantly correlated with the tea quality parameters (r ≥ 0.462). Among the sampling methods, the EXG_Ostu sampling method was best for prediction, whereas, among the models, RFR was the best fitted modeling algorithm for three of four quality parameters. The R2 and root-mean-square error values of the built model were 0.85 and 0.16, respectively. In addition, the texture features extracted from the canopy image improved the prediction accuracy of most models. This research confirms the modeling application of a combination of multi-spectral images and chemometrics, as a low-cost, fast, reliable, and nondestructive quality control method, which can effectively monitor the quality of fresh tea leaves. This provides a scientific reference for the research and development of portable tea quality monitoring equipment that has general applicability in the future.

Biosynthesis of silica and copper nanoparticles from Trichoderma, Streptomyces and Pseudomonas spp. evaluated against collar canker and red root-rot disease of tea plants

Tea is an important beverage with several health benefits to human beings, but increase in tea diseases is of much concern in recent days. Amongst several stem and root diseases of tea plants, Poria hypolateritia causing red root-rot and Phomopsis theae causing Phomopsis canker diseases are very important in terms of heavy crop loss in young as well as mature tea plantations, respectively. In the present study, indigenous biocontrol agents such as bacteria, fungi and actinomycetes were isolated from southern Indian tea soils collected from different agroclimatic regions and subjected to biosynthesis of copper and silica nanoparticles. Copper and silica nanoparticles were produced using selected indigenous biocontrol agents such as Pseudomonas fluorescens, Trichoderma atroviride and Streptomyces griseus and then characterise for their nature, size, shape, elemental analysis, distribution and functional groups. The results showed that copper and silica nanoparticles were inhibited the growth of P. hypolateritia and P. theae. Nanocopper and nanosilica were subjected to prepare various nanoformulations using suitable inert and eco-friendly carrier materials. Toxicity of nanoformulations was done using zebrafish model. It was confirmed that there was no toxicity of nanocopper and nanosilica when exposed to 0.5, 3 and 30 µg concentrations in terms of viability percentage of embryo, hatching rate, body mass index and heartbeat counts. The present investigation could be a novel approach for the management of root and stem diseases in tea plantations which in turn useful to enhance tea quality parameters.

Changes in Phytochemicals and Determination of Optimum Fermentation Time during Black Tea Manufacturing

Black tea processing consists of four steps, namely withering, CTC, fermentation and drying, while cup quality made tea mostly controlled by fermentation step. This study evaluated biochemical changes at different stages of black tea processing in Bangladesh and determined the optimum fermentation time. Samples were collected from different tea processing stages to measure major phytochemicals and time intervals during fermentation to measure theaflavins and thearubigins ratio. Caffeine content was the least susceptible to processing steps. Biochemical changes started at withering, cell maceration and enzymatic oxidation started at CTC processing, thus the major reduction in the reducing sugar (20.46 to 04.95 ppm), catechin (16.88 to 7.95 ppm) and polyphenol (42.30 to 30.73 ppm) occurred here. The significant changes appeared during fermentation when polyphenol content decreased from 44.66 to 18.23 and catechin from 17.41 to 03.98 ppm due to the breakdown of these compounds to theaflavins (TF) and thearubigins (TR). The TF and TR ratio increased with fermentation time, and the highest of 1:8.4 was found at 50 min, which turned into 1:10 in the final product. The made tea quality parameters were comparable or better at fermentation time of 50 min than the quality of the black tea available in market.

Electronic Nose Technologies in Monitoring Black Tea Manufacturing Process

“Tea” is a beverage which has a unique taste and aroma. The conventional method of tea manufacturing involves several stages. These are plucking, withering, rolling, fermentation, and finally firing. The quality parameters of tea (color, taste, and aroma) are developed during the fermentation stage where polyphenolic compounds are oxidized when exposed to air. Thus, controlling the fermentation stage will result in more consistent production of quality tea. The level of fermentation is often detected by humans as “first” and “second” noses as two distinct smell peaks appear during fermentation. The detection of the “second” aroma peak at the optimum fermentation is less consistent when decided by humans. Thus, an electronic nose is introduced to find the optimum level of fermentation detecting the variation in the aroma level. In this review, it is found that the systems developed are capable of detecting variation of the aroma level using an array of metal oxide semiconductor (MOS) gas sensors using different statistical and neural network techniques (SVD, 2-NM, MDM, PCA, SVM, RBF, SOM, PNN, and Recurrent Elman) successfully.

Development of a mathematical procedure for controlling air flow rate in tea withering

A control system was developed for optimizing the electrical energy consumption while preserving the required quality of withered tea leaves. The electrical energy saving was achieved by controlling the speed of the fan through a variable speed drive (VSD) and controlling the hot and ambient air delivering into the trough. The fan speed was determined based on the theoretical mass flow rate requirement of air calculated by the mathematical model developed for withering, while calculating the thermodynamic properties of withering air and the moisture content of tea leaves in real time. A single board computer, Raspberry pi 3 model B, was used as the controller to run the mathematical model and the software programme to control the VSD for controlling the mass flow rate of air delivered, the air temperature and the relative humidity. Finally, the electrical energy consumption of the fan and the quality parameters of tea were measured through experiments and compared in the withering process with or without control system. The specific energy consumption of withering was in the range of 0.17 to 0.18 kWh/kg of made tea with the control system and it was 0.27 to 0.35 kWh/kg of made tea without control system. The electrical energy consumption was 36 kWh to 39 kWh with the control system and it was in the range of 55 kWh to 67 kWh in without control system. Therefore, 39% of electrical energy was saved by introducing the control system compared to the withering process without control system.

Effect of altitude, shooting period, and tea grade on the catechins, caffeine, theaflavin, and thearubigin of Turkish black tea

The effect of altitude, shooting period, and tea grade on the catechins and caffeine contents of Turkish black tea was investigated. The experimental factors significantly affected all of the parameters analyzed. Epigallocatechin gallate was the major catechin of black tea (0.719-1.007 g 100 g-1 dm) followed by epigallocatechin (0.627-0.791 g 100 g-1 dm). Additionally, caffeine (1.810-2.175 g 100 g-1 dm), theaflavin (3.201-6.000 μmol g-1), and thearubigin (8.577-12.635 g 100 g-1 dm) contents were determined. Samples of tea grown at high altitude generally produced a considerably greater amount of the catechins that improve tea quality. Shooting period, which is specific to tea cultivation in Turkey, significantly affected almost all of the quality parameters of black tea. Tea produced in the first shooting period contained more catechins than the samples plucked in the following shooting periods. Dust and orange pekoe 1 contained the most catechins of the tea grades analyzed.

Effect of Seasonal Variations and Growth Conditions on Carbohydrate Partitioning in Different Organs and the Quality of Bush Tea

Bush tea (Athrixia phylicoides DC.) is a root perennial shrub used as indigenous tea and medicinal tea in South Africa. Thus, concurrent trials were conducted under different growing conditions as follows: in the glasshouse, field planted and wild, naturally grown, to investigate the effects of seasonal harvests and growing environments on carbohydrate reserves and quality parameters of bush tea. Of 50 plants, 25 single plants were allotted to each respective environment in a field and glasshouse conditions—and were arranged in a randomized complete block design. These were then harvested in summer, autumn, winter, and spring, respectively. For the wild bush tea trial, 25 single plants were randomly selected. Selected sugars and starch were quantified together with other quality parameters [total polyphenolic content (TPC), total flavonoid content (TFC), total tannin content (TTC), and total antioxidant activities). The study revealed that the glucose content of bush tea plant organs was significantly higher during winter, followed by autumn, as compared with the other seasons. Similar fructose and sucrose trends were evident. However, the content of amylopectin was also significantly higher during summer, followed by autumn, compared with the other seasons. In winter, plants exhibited higher amylopectin content when compared with other seasons. No significant differences were found in the amylose content. Both wild and cultivated bush tea plants yielded the highest specific sugars in the study. The phytochemicals present in the leaves of field-grown bush tea and wild bush tea during winter were higher than in those grown in summer, autumn, and spring. No significant difference in tannin contents was observed, irrespective of seasons and growing conditions. Regardless of growing conditions, autumn yielded lower total antioxidant activities using both the DPPH and ferric reducing antioxidant power (FRAP) assays when compared with other seasons. To better resolve the metabolomic data, principal component analysis (PCA) was used and the first principal component showed a strong correlation within all parameters recorded over PC2. Future ecophysiological studies are recommended to establish region- and season-specific metabolomic biomarkers with canonical distinction on beverage, pharmacological, and organoleptic attributes of bush teas.

Catechins and Plain Black Tea Parameters Variations in Selected Tea Growing Agro-Ecological Zones in Kenya

Over 60% of tea in Kenya is produced by smallholder tea farmers distributed in the East and West of the Rift Valley. With all smallholder tea farmers using the same production technologies including planting materials, the quality of tea from different agro-ecological zones should be the same. However, black teas attract different prices. This study compared levels of leaf quality, catechins, and polyphenols in green leaf and quality parameters of black tea from twelve factories in three different agro-ecological zones in Kenya and assessed the relationships between the green leaf quality parameters and black tea quality parameters. The catechins contents, the black tea quality parameters, and sensory evaluations changed (p less than or equal to0.05) between the factories and with an agro-ecological zone of production. All black teas had high antioxidant activities, which differed (p less than or equal to0.05) across the factories and zones. Despite the use of same agronomic inputs in the smallholder tea growing zones in Kenya, the quality of resultant black teas was largely influenced by the environmental factors in the different regions. It is therefore not possible to produce black teas of the same quality across the country. Despite the variations, all regions exhibited high levels of black tea quality parameters and sensory evaluation, re-affirming the Kenyan smallholder black teas are of high quality. The high antioxidant activities suggest possible beneficial pharmacological activities from consumption the teas. The green leaf quality (leaf count) were significantly (p less than or equal to0.05) correlated with black tea brightness and all sensory evaluation parameters, demonstrating high benefits from good plucking standards. Green leaf gallic acid, epigallocatechin, epicatechin, epigallocatechin gallate, and total catechins levels were related (p less than or equal to0.05) to black tea total polyphenols and all sensory evaluation parameters. In addition, the green leaf caffeine, epicatechin, epigallocatechin gallate, and total catechins influenced (p less than or equal to0.05) theaflavins in black tea. These green leaf parameters are therefore key drivers of Kenyan plain black tea quality.

Response of Plain Black Tea Parameters, Individual Theaflavins and Yields Due to Location of Production and Clones within Lake Victoria Basin

Tea (Camellia sinensis) is a major cash crop and leading foreign exchange earner, contributing to poverty alleviation by providing employment and livelihood to many stakeholders in the producing countries. Production has increased faster than consumption causing price stagnation, especially for CTC black teas. Kenya is the third-largest tea producer and Lake Victoria Basin produces over 60% of her tea. Selection of tea cultivars in Kenya has been cantered in one location before the selected clones are introduced to other growth environments. This study evaluated if tea clones maintain their yield and plain black tea quality attributes when grown at different locations within Lake Victoria Basin. The basin produces mainly plain black teas whose quality is due to levels of polyphenolic compounds, especially green leaf flavan-3-ols that are oxidized to theaflavins and thearubigins during black tea processing. The theaflavins and thearubigins contribute to the color and brightness of black teas. The trials were done in two sites Timbilil and Kipkebe using twenty clones. All the plain tea quality parameters including individual theaflavins and yields varied (p less than 0.05) with clones, demonstrating diversity in the cultivars used. The levels of the parameters and yields also changed (p less than 0.05) with the location of production. These results demonstrated that clonal tea quality and yields vary depending on the geographical location of production. There were also significant interactions effects between the clones and location of production in the quality parameters and clones showing the extent of the changes varied from clone to clone. Indeed the relative ranking of the clones varied with location. No clone retained its relative superiority ranking at the two locations. Both the Spearman correlation coefficients (rs) and the Pearson correlation coefficients (r) between the individual parameters were positive but low and insignificant, except for theaflavin-3-gallate. These results demonstrate the need for location-specific evaluation of both new and old clones to establish clonal yield and quality potentials in new locations of cultivation.

Clonal Variations in the Response of Hard Physically Withered Leaf to Rehydration Following Long Chemical Wither Durations

Long chemical wither durations and hard physical wither reduce the quality of plain black tea, through reduction in total theaflavins production while encouraging thearubigins formation. Such quality reduction may vary with genetic makeup of the tea plant. However, rehydration reactivates activities of oxidative enzymes responsible for producing plain black tea quality parameters. Influence of rehydrating hard physically withered leaf that had undergone long chemical wither durations on two clonal plain black tea quality parameters were assessed. Rehydration restored the formation of plain tea quality parameters from hard physically withered leaf. However, quality deterioration due to long chemical wither duration could not be reversed by rehydration. The patterns of responses of the clones used were similar. Thus in the processing of plain black tea, efforts should be made to maintain chemical wither durations to below 30 hours. However, rehydration reverses reduced plain black tea quality parameters by hard physical withers to equivalent of chemical wither.

Stimulation in primary and secondary metabolism by elevated carbon dioxide alters green tea quality in Camellia sinensis L

Rising CO2 concentration, a driving force of climate change, is impacting global food security by affecting plant physiology. Nevertheless, the effects of elevated CO2 on primary and secondary metabolism in tea plants (Camellia sinensis L.) still remain largely unknown. Here we showed that exposure of tea plants to elevated CO2 (800 µmol mol−1 for 24 d) remarkably improved both photosynthesis and respiration in tea leaves. Furthermore, elevated CO2 increased the concentrations of soluble sugar, starch and total carbon, but decreased the total nitrogen concentration, resulting in an increased carbon to nitrogen ratio in tea leaves. Among the tea quality parameters, tea polyphenol, free amino acid and theanine concentrations increased, while the caffeine concentration decreased after CO2 enrichment. The concentrations of individual catechins were altered differentially resulting in an increased total catechins concentration under elevated CO2 condition. Real-time qPCR analysis revealed that the expression levels of catechins and theanine biosynthetic genes were up-regulated, while that of caffeine synthetic genes were down-regulated in tea leaves when grown under elevated CO2 condition. These results unveiled profound effects of CO2 enrichment on photosynthesis and respiration in tea plants, which eventually modulated the biosynthesis of key secondary metabolites towards production of a quality green tea.

Rapid assessment of black tea quality using diffuse reflectance spectroscopy

Tea quality assessment methods generally require elaborate sample preparation steps and often yield in consistent results. Over the last two decades, the diffuse reflectance spectroscopy (DRS) is emerging as a rapid and non-invasive tool for assessing quality parameters of several materials. In this study¸ we examined the DRS approach by creating a reflectance spectral imaging of 81 black crush, tear and curl (CTC) tea samples and eight tea quality parameters. Spectral models for each parameter were developed using the partial-least-squares regression (PLSR) approach. The ratio of performance deviation (RPD) was used to assess such spectral models. Results showed that moisture content, thearubigin components of TRSI and TRSII, total polyphenol contents and liquor brightness were accurately predicted with RPD values 3.63, 2.32, 2.24, 2.23 and 2.02, respectively. Prediction accuracies were moderate for thearubigin, total liquor color and theaflavin. The variable important projection (VIP) showed the wavelengths around near-infrared and shortwave-infrared regions strongly influence spectral reflectance of black tea.

Clonal plain back tea quality parameters responses of hard physical withered leaf to rehydration and fermentation durations

Hard physical withers in tea processing result in reduced plain black tea quality parameters, but improve flavoury black tea quality. Chemical withers with minimal moisture loss improve plain black tea quality parameters. But chemical withered leaf is normally bulky and not flaccid thus reducing maceration rates. Hard physical withers reduce polyphenol oxidase activity, thereby impairing ability of the leaf to produce high amounts of plain black tea quality parameters, especially theaflavins and thearubigins. This study examined if rehydrating hard physical withered leaf could improve its fermentability and influence fermentation duration, and if such changes are cultivar dependent. Rehydrating hard physical withered leaf increased (p≤0.05) total theaflavins, thearubigins, brightness, total colour and sensory evaluation of resultant black teas. The patterns of the responses did not vary with cultivars or fermentation duration. The theaflavins and brightness declined (p≤0.05) while thearubigins and total colour increased (p≤0.05) with long fermentation durations irrespective of withering regime. Results demonstrate that problems of plain black tea quality reduction due to hard physical withers can be partially reversed by rehydration to chemical wither standard, but the withering regime does not influence when maximum plain black tea quality parameters are produced.

Change of enzyme activity and quality during the processing of Turkish green tea

This study was performed to investigate the effect of process parameters on polyphenol oxidase (PPO), peroxidase (POD) and quality parameters (total phenolics, catechins, color and sensorial attributes) of green tea. Tunnel steam system (TSS) and drum steam system (DSS) were used to inactivate the enzymes for green tea production. POD was inactivated 99%, whereas PPO was partially inactivated in all exposure times of applications. In TSS, the highest inactivation ratios were achieved at 3 min (T2) and 5 min (T3) of steam treatment, however, the highest sensory quality was obtained for 3 min application. In DSS, although the highest PPO inactivation (34%) was achieved in the “moderate rate steam-moderate time” application (D2: 65 L/h for 45 s), the best quality parameters were obtained in the “high rate steam-short time” (D1:70 L/h for 30 s) application. DSS provided higher inactivation rates than TSS at shorter time of steam treatment. The leaves were exposed to drying process (100–120 °C, 60–90 min) after steaming and residual amounts of PPO were inactivated after completing the final drying step. The process parameters should be optimized not only considering the enzyme inactivation ratios during steaming but also the quality properties of the final green tea product.