Changes in major catechins, caffeine, and antioxidant activity during CTC processing of black tea from North East India

Pruned tea biomass plays a significant role in functional food production: A review on characterization and comprehensive utilization of abandon-plucked fresh tea leaves

Tea is the second largest nonalcoholic beverage in the world due to its characteristic flavor and well-known functional properties in vitro and in vivo. Global tea production reaches 6.397 million tons in 2022 and continues to rise. Fresh tea leaves are mainly harvested in spring, whereas thousands of tons are discarded in summer and autumn. Herein, pruned tea biomass refers to abandon-plucked leaves being pruned in the non-plucking period, especially in summer and autumn. At present, no relevant concluding remarks have been made on this undervalued biomass. This review summarizes the seasonal differences of intrinsic metabolites and pays special attention to the most critical bioactive and flavor compounds, including polyphenols, theanine, and caffeine. Additionally, meaningful and profound methods to transform abandon-plucked fresh tea leaves into high-value products are reviewed. In summer and autumn, tea plants accumulate much more phenols than in spring, especially epigallocatechin gallate (galloyl catechin), anthocyanins (catechin derivatives), and proanthocyanidins (polymerized catechins). Vigorous carbon metabolism induced by high light intensity and temperature in summer and autumn also accumulates carbohydrates, such as soluble sugars and cellulose. The characteristics of abandon-plucked tea leaves make them not ideal raw materials for tea, but suitable for novel tea products like beverages and food ingredients using traditional or hybrid technologies such as enzymatic transformation, microbial fermentation, formula screening, and extraction, with the abundant polyphenols in summer and autumn tea serving as prominent flavor and bioactive contributors.

The Level of Selected Metals in Made Tea and Tea Infusion from the Roadside Tea Plants and Health Risk Assessment

The effects of human activities are becoming clearer every year, with multiple reports of struggling and eroded ecosystems resulting in new threats of plant and animal extinctions throughout the world. It has been speculated that roadside tea-growing soils impact on metal dynamics from soil to tea plants and subsequently to tea infusion which may be threatened by increasingly unpredictable and dangerous surroundings. Furthermore, heavy metals released from vehicles on the national highway (NH) could be a source of metal contamination in roadside tea soils and tea plants. This study was articulated to realize the effect of NH on a buildup of selected metals (Cu, Cd, Fe, Mn, Ni, and Zn) in made tea along with repeated tea infusion. In general, metal concentration was found significantly higher in made tea prepared from the young shoots collected from the vicinity of NH. The results also showed that distance from the NH and infusion process significantly influenced to content of the analysed metal in tea infusions. The mean average daily intake (ADI) and hazard quotient (HQ) values of analysed tea samples were found in the orderMn˃Fe˃Zn˃Cu˃Ni˃Cd and Mn˃Cu˃Zn˃Fe˃Ni˃Cd, respectively. The HQ values of all analysed metals were found << 1, indicating that ingestion of tea infusion with analysed heavy metals should not cause a danger to human health. However, this study further demonstrates the consumption of tea infusion prepared from made tea around the vicinity of NH may contribute to a significantly higher quantity of metal intake in the human body. From the hierarchical cluster analysis, it has been observed that there are three homogenous groups of analysed heavy metals.

Key Factors of Quality Formation in Wuyi Black Tea during Processing Timing

As the most consumed tea in the world, all kinds of black tea are developed from Wuyi black tea. In this study, quality components, regulatory gene expression, and key enzyme activity during the processing were analyzed to illustrate the taste formation of WBT. Withering mainly affected the content of amino acids, while catechins and tea pigments were most influenced by rolling and the pre-metaphase of fermentation. Notably, regulatory gene expression was significantly down-regulated after withering except for polyphenoloxidase1, polyphenoloxidase2, leucoanthocyanidin dioxygenase, chalcone isomerase, and flavonoid 3', 5'-hydroxylase. Co-expression of flavonoid pathway genes confirmed similar expression patterns of these genes in the same metabolic pathway. Interestingly, rolling and fermentation anaphase had a great effect on polyphenol oxidase, and fermentation pre-metaphase had the greatest effect on cellulase. Since gene regulation mainly occurs before picking, the influence of chemical reaction was greater during processing. It was speculated that polyphenol oxidase and cellulase, which promoted the transformation of quality components, were the key factors in the quality formation of WBT. The above results provide theoretical basis for the processing of WBT and the reference for producing high-quality black tea.

Rolling forms the diversities of small molecular nonvolatile metabolite profile and consequently shapes the bacterial community structure for Keemun black tea

The detailed dynamics of small molecular nonvolatile chemical and bacterial diversities, as well as their relationship are still unclear in the manufacturing process of Keemun black tea (KMBT). Herein, mass spectrometry-based untargeted metabolomics, Feature-based Molecular Networking (FBMN) and bacterial DNA amplicon sequencing were used to investigate the dense temporal samples of the manufacturing process. For the first time, we reveal that the pyrogallol-type catechins are oxidized asynchronously before catechol-type catechins during the black tea processing. Rolling is the key procedure for forming the small molecular nonvolatile metabolite profile (SMNMetProf), increasing the metabolite richness, and then shaping the bacterial community structure in the KMBT manufacturing process, which decreases both molecular weight and molecular polarity of the small molecular nonvolatile metabolites. The SMNMetProf of black tea is formed by the endogenous enzymatic oxidation of tea leaves, rather than bacterial fermentation.

Compositions and Antioxidant Activity of Tea Polysaccharides Extracted from Different Tea (Camellia sinensis L.) Varieties

Tea polysaccharide (TPS) is a bioactive compound extracted from tea. It has raised great interest among researchers due to its bioactivity. However, few studies focused on the diversity of TPS in its compositions and antioxidant activity. This study collected 140 different tea varieties from four tea germplasm gardens in China, and their TPSs in tea shoots were extracted. The extraction efficiency, composition contents, including neutral sugar, uronic acid, protein, and tea polyphenols, and the scavenging abilities of hydroxyl radical (·OH) and superoxide radical (O2-·) of 140 TPSs were determined and analyzed. The results showed significant differences in the compositions and antioxidant activities of TPS extracted from different tea varieties. By applying hierarchical clustering analysis (HCA), we selected nine tea varieties with high TPS extraction efficiency and 26 kinds of TPS with high antioxidant capacity.

A New Method of Extracting Polygonatum sibiricum Polysaccharide with Antioxidant Function: Ultrasound-Assisted Extraction-Deep Eutectic Solvents Method

Polygonatum sibiricum Polysaccharide (PsP) with antioxidant function is the main active component of Polygonatum sibiricum (P.sibiricum). The currently poor extraction yield and extraction methods of PsP cannot meet the application of that in food industrial production. In this research, an ultrasound-assisted extraction-deep eutectic solvents (UAE-DESs) method, which has never been used in the PsP industry, was first used to extract PsP. The extraction conditions were optimized by the response surface method (RSM). Both the extraction yield and antioxidant function were simultaneously considered during the optimization process. The indicators of PsP's level and antioxidant activity in vitro were used to present the extraction yield of the UAE-DESs method, the purity, and the antioxidant effect of PsP. Under the optimal conditions, which included a liquid-solid ratio of 26:1 (mL:g), extraction temperature of 80 °C, ultrasonic time of 51 min, and ultrasonic power of 82 W, the PsP extraction yield could reach (43.61 ± 0.09)%, which was obviously higher than single DESs (33.81%) and UAE (5.83%), respectively, and the PsP appeared favorably antioxidant function. This research proposed an efficient extraction method for PsP, filled the basic research gap, and further improved the development of PsP as a dietary supplement with antioxidant function in the food industry.

Impact of the Season on Total Polyphenol and Antioxidant Properties of Tea Cultivars of Industrial Importance in Northeast India

Tocklai vegetative (TV) cultivars are extensively planted in the tea-growing regions of Northeast India. The present investigation explores the impact of season on the total polyphenol (TP) content and the antioxidant activity of thirty-one TV cultivars (TV1-TV31) and four other commercially popular cultivars, namely, Betjan, Kharijan, S.3A/3, and T.3E/3. The TP content of the cultivars was observed to be highest in the monsoon season, with values ranging from 230.57 to 283.53 mg g-1. In the pre-monsoon season and autumn, the TP content ranged from 197.87 to 256.77 mg g-1 and from 169.97 to 223.50 mg g-1, respectively. Antioxidant activity was measured through DPPH, ABTS, FRAP, and lipid peroxidation inhibition assays. The cultivars showed the highest antioxidant activity in the monsoon in tandem with TP content. A bivariate correlation indicated a highly significant (p ≤ 0.01) positive correlation of antioxidant activity with TP content (R2 = 0.83-0.96).

Effect of Fermentation Humidity on Quality of Congou Black Tea

This study investigated the effect of different fermentation humidities (55%, 65%, 75%, 85% and 95%) on congou black tea quality and bioactivity. Fermentation humidity mainly affected the tea's appearance, aroma and taste quality. The tea fermented at low humidity (75% or below) showed a decrease in tightness, evenness and moistening degree, as well as a heavy grassy and greenish scent, plus a green, astringent and bitter taste. The tea fermented at a high humidity (85% or above) presented a sweet and pure aroma, as well as a mellow taste, plus an increase of sweetness and umami. With increasing fermentation humidity, the tea exhibited a drop in the content of flavones, tea polyphenols, catechins (EGCG, ECG) and theaflavins (TF, TF-3-G), contrasted by a rise in the content of soluble sugars, thearubigins and theabrownins, contributing to the development of a sweet and mellow taste. Additionally, the tea showed a gradual increase in the total amount of volatile compounds and in the content of alcohols, alkanes, alkenes, aldehydes, ketones and acids. Moreover, the tea fermented at a low humidity had stronger antioxidant activity against 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) and a higher inhibiting capability on the activities of α-amylase and α-glucosidase. Overall results indicated the desirable fermentation humidity of congou black tea should be 85% or above.

Effect of Extraction Period on Total Phenolics, Total Flavonoids, and Antioxidant Capacity of Ugandan Camellia sinensis (L) Kuntze, Black Primary Grades and Green Tea

Introduction. Globally, the consumption and production of tea are on the rise because of its beneficial constituents. Scarce literature exists on the effects of extraction periods on the contents of the biologically important and protective phytochemicals such as phenolics, flavonoids, and antioxidants in locally produced teas in Uganda. Aim. This study determined the effects of extraction periods on the aqueous total phenolic content (TPC) of local Camella sinensis, black primary grades and green tea, and their ecological differences, their total flavonoid content (TFC), and antioxidant capacities (AOC). Methods. Samples of local tea were collected from Kigezi, Ankole, and Buganda regions, and those of green tea were purchased from a local supermarket in Uganda. Four- and 40-minute infusions were separately prepared for each sample. Total phenolic and flavonoid contents were determined using the Folin–Ciocalteu and aluminium chloride methods using garlic acid and quercetin as standards, respectively. Antioxidant content was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and ferric reducing assay power (FRAP) methods, using ascorbic acid as the standard. Results. Green tea had the highest total phenolic content both with four-minute (9.50 ± 0.25 mgGAE/g) and 40-minute (25.81 ± 1.13 mgGAE/g) extractions, followed by D1 (4.14 ± 0.33 mgGAE/g) at four minutes and PF (23.60 ± 2.37 mgGAE/g) at 40 minutes. Regionally, Kigezi (4.71 ± 0.09 and 22.13 ± 0.85 mgGAE/g) at four and 40 minutes, respectively, gave the highest TPC. In TFC, tea from Buganda (4,371 ± 0.00 μgQE/g) was the highest. In DPPH and FRAP, GT (93.82 ± 0.03%, 39.04 ± 0.02 AAEμg/mL) was the best, followed by Buganda tea (88.71 ± 0.03%, 36.99 ± 0.01 AAEµg/mL), respectively. Conclusion. Longer extraction periods increase TPC in all teas. Green tea generates approximately twice the TPC generated by black tea in four-minute infusions. Green tea gives higher TPC, DPPH, and FRAP but less TFC than some black teas and is perhaps the best in terms of protection against oxidative damage to the body.

An In Vitro Catalysis of Tea Polyphenols by Polyphenol Oxidase

Tea polyphenol (TPs) oxidation caused by polyphenol oxidase (PPO) in manufacturing is responsible for the sensory characteristics and health function of fermented tea, therefore, this subject is rich in scientific and commercial interests. In this work, an in vitro catalysis of TPs in liquid nitrogen grinding of sun-dried green tea leaves by PPO was developed, and the changes in metabolites were analyzed by metabolomics. A total of 441 metabolites were identified in the catalyzed tea powder and control check samples, which were classified into 11 classes, including flavonoids (125 metabolites), phenolic acids (67 metabolites), and lipids (55 metabolites). The relative levels of 28 metabolites after catalysis were decreased significantly (variable importance in projection (VIP) > 1.0, p < 0.05, and fold change (FC) < 0.5)), while the relative levels of 45 metabolites, including theaflavin, theaflavin-3'-gallate, theaflavin-3-gallate, and theaflavin 3,3'-digallate were increased significantly (VIP > 1.0, p < 0.05, and FC > 2). The increase in theaflavins was associated with the polymerization of catechins catalyzed by PPO. This work provided an in vitro method for the study of the catalysis of enzymes in tea leaves.

Effects of Preharvest Shading on Dynamic Changes in Metabolites, Gene Expression, and Enzyme Activity of Three Tea Types during Processing

Preharvest shading significantly influences tea flavor. However, little attention has been given to the mechanism of shading on metabolites, genes, and enzymes in the processing of different tea types. Our study identified 1028 nonvolatile metabolites covering 10 subclasses using a widely targeted metabolome. The results show that shading had a greater effect on the compositions of amino acids, flavonoids, and theaflavins in tea leaves. The combined transcriptomics and enzyme activity analysis results indicate that the upregulated expression of asparagine, aspartate, and tryptophan synthesis genes and proteolytic enzymes promoted the accumulation of amino acids. The downregulated enzyme genes resulted in the reduction of nongalloylated catechins and flavonoid glycosides. Simultaneously, the accumulation of TFs in shaded tea was due to the enhanced enzymatic activities of polyphenol oxidase and peroxidase during processing. Theaflavin-3-3'-di-O-gallate was also significantly positively correlated with the antioxidant and hypoglycemic activities of shaded tea. The results contribute to a better understanding of how preharvest treatments influence summer tea quality.

Comparison of the chemical composition and antioxidant, anti-inflammatory, α-amylase and α-glycosidase inhibitory activities of the supernatant and cream from black tea infusion

Tea cream is a kind of turbid substance commonly existing in tea infusion and tea beverage upon cooling. Herein, a comparative study was conducted on the supernatant and cream from black tea infusion in terms of antioxidant, anti-inflammatory and enzyme inhibitory activities, and chemical composition. Ultraviolet-visible (UV-vis) spectrometry and high-performance liquid chromatography (HPLC) analysis showed that the contents of protein, polyphenols, theaflavins, thearubigins, theabrownins, and caffeine in cream were significantly higher than those in the supernatant. The contents of Al, Ca, Cu, and Fe elements in cream were higher than those in the supernatant. However, higher levels of monosaccharides and free amino acids were detected in the supernatant compared with cream. The ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) based metabolomics analysis revealed that the main marker compounds between the supernatant and the cream were organic acids, phenolic acids, and flavan-3-ols and their oxidation products, flavonol glycosides and amino acids. The cream showed better antioxidant and anti-inflammatory, as well as α-amylase and α-glycosidase inhibitory activities than the supernatant, because it contained higher contents of polyphenols than the supernatant. The present study expanded the new vision towards the cream of black tea infusion.

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.

Enzymatic Oxidation of Tea Catechins and Its Mechanism

Tea (Camellia sinensis, Theaceae) is one of the most widely consumed beverages in the world. The three major types of tea, green tea, oolong tea, and black tea, differ in terms of the manufacture and chemical composition. Catechins, theaflavins, and thearubigins have been identified as the major components in tea. Other minor oligomers have also been found in tea. Different kinds of ring fission and formation elucidate the major transformed pathways of tea catechins to their dimers and polymers. The present review summarizes the data concerning the enzymatic oxidation of catechins, their dimers, and thearubigins in tea.

Impact of processing method on selected trace elements content of green tea: Does CTC green tea infusion possess risk towards human health?

This study reported the content of selected metals, viz. cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), lead (Pb) and zinc (Zn) as well as non-carcinogenic risks of orthodox green tea and CTC (crush, tear and curl) green tea (Camellia sinensis L.) in India. Results revealed that significantly higher amount of Cr (1.26-10.48 mg kg-1), Cu (13.40-22.73 mg kg-1), Fe (54.14-99.65 mg kg-1), Ni (3.43-7.09 mg kg-1), and Zn (25.04-38.04 mg kg-1) in CTC green tea than orthodox one. However, no definite trend was observed for Cd and Pb, with overall contents ranged from 6.68 to 23.32 µg kg-1 and 0.04 to 0.13 mg kg-1, respectively. The extraction of the elements in tea infusion was higher for CTC green tea. The hazard quotient and hazard index values of all the studied metals were less than unity, confirming no significant health effect for consumers assuming drinking of 750 mL tea infusion prepared from 10 g green tea per day per person.

Revealing the profound meaning of pan-firing of oolong tea - A decisive point in odor fate

The delicate aroma of Bao-chung tea comes from oxidation, followed by fixation in the pan-firing step. Traditionally, the timing of pan-firing has been based on odor perception by tea masters and lacks relevant scientific research. Pan-firing at three different green-note intensities and three stirring sequences was used to explore the relationship between the compositions of volatile organic compounds (VOCs) before pan-firing and in the finished tea. Pan-firing decreased green leaf volatiles and increased the ratio of terpenoid volatiles. The characteristic VOCs of the finished tea were highly related to VOCs before pan-firing (R² = 0.97). Principal component analysis revealed that the traditional judgment of the pan-firing step is based on nonanal, β-linalool, and cis- and trans-linalool oxides. The timing of pan-firing is crucial for VOCs, and VOC composition before pan-firing can be used to predict desired tea aroma.

Chemical and biological properties of cocoa beans affected by processing: a review

Cocoa (Theobroma cacao L.) is widely cultivated in tropical countries. The cocoa beans are a popular ingredient of confectionery. Cocoa beans contain various chemicals that contribute to their bioactivity and nutritional properties. There has been increasing interest in developing cocoa beans for "healthy" food products. Cocoa beans have special combination of nutrients such as lipids, carbohydrates, proteins and other compounds of biological activities. The bioactive phytochemicals include methylxanthines, polyphenols, biogenic amines, melanoidins, isoprostanoids and oxalates. These phytochemicals of cocoa are related to various in vivo and in vitro biological activities such as antioxidation, anti-cancer, anti-microbial, anti-inflammation, anti-diabetes, cardiovascular protection, physical improvement, anti-photoaging, anti-depression and blood glucose regulation. The potential of bioactive compounds in cocoa remains to be maximized for food and nutritional applications. The current processing technology promotes the degradation of beneficial bioactive compounds, while maximizing the flavors and its precursors. It is not optimized for the utilization of cocoa beans for "healthy" product formulations. Modifications of the current processing line and non-conventional processing are needed to better preserve and utilize the beneficial bioactive compounds in cocoa beans.