Hastening of leaf senescence in the processing of green tea leaf to black tea

The current system of processing green tea leaf (Camellia sinensis) to produce black tea involves a long period, especially because of the withering process practised in acquiring leaf senescence which is essential to impart fullness to the resulting tea liquors. Hastening leaf senescence by artificial withering at temperatures favourable to enzymic transformations accelerated the process and considerably shortened the manufacture of black teas.     

Effect of black tea, garlic and onion on corn oil stability and fatty acid composition under accelerated oxidation

Fresh black tea, garlic bulbs and onion skin were macerated in refined corn oil to evaluate their antioxidant properties and the effect of heat on oil stability and fatty acid composition in accelerated oxidation experiments at 55 ° and 140 °C. At the lowest temperature control and onion treatments showed an induction time of 3 days with maximum peroxide values of 62 and 45 meq kg^?1, respectively. Addition of black tea and garlic increased oil stability with peroxide values of 5 meq kg^?1, without appreciable changes in the fatty acid composition. Heating at 140 °C for 48 h produced an accelerated deterioration of corn oil in all treatments. A reduction of polyunsaturated fatty acids of about 40% was observed, with high concentrations of non‐eluted materials which contained thermo‐oxidized substances. It was found that natural extract of black tea and garlic were effective to preserve corn oil under accelerated oxidation at 55 °C which simulates oil behaviour during storage, but cannot reduce the rate of oxidation at frying temperatures.     

Effects of withering on the main physical properties of withered tea leaves and the sensory quality of congou black tea

To explore the relationship between the moisture content of withered tea leaves and their physical properties (i.e., elasticity, plasticity, flexibility, and texture) during withering, texture analyzer was employed to test the elasticity and flexibility of withered tea leaves with different moisture contents. The texture was evaluated by computer vision technology. The withered tea leaves with different moisture contents were used to process congou black tea, which was then subjected to sensory evaluation. Results showed that good elasticity, optimal flexibility, and plasticity were achieved when the moisture content of the withered tea leaves of Fudingdabai comprising two leaves and one bud varied arranging from 65.51 to 61.48%. The sensory evaluation of congou black tea revealed that moderate withering was better than long-term withering and that both moderate and long-term withering were better than no withering during processing. The moisture content was significantly correlated with the flexibility and plasticity of the withered tea leaves. Fresh tea leaves undergoing moderate withering with moisture content of 65.51–61.48% to process congou black tea, good tea shape and liquor color were achieved. This study provided new evidence that the moisture content of withered tea leaves significantly affected the quality of black tea.     

How manufacturing processes affect the level of pesticide residues in tea

Tea (both green and black) is consumed throughout the world, both for pleasure and therapeutic purposes. Most people will be unaware of their involuntary exposure to residues of pesticides lingering in processed tea and so possibly transferring into infusions of tea. The purpose of this work was to study the effect of green tea and orthodox black tea manufacturing processes on the fate of pesticides sprayed onto tea bushes (Camellia sinensis). The fates of residues of dimethoate, quinalphos, dicofol and deltamethrin in these two different types of tea manufacturing processes were compared. For black tea, the manufacturing process involves leaf harvesting, withering, rolling, fermentation and drying; and for green tea, leaf harvesting, microwave heating, rolling and drying. The two processes resulted in the same concentration factor of plant material into the dried commodity, while the decreases in residue levels were different for different pesticides. Initial microwave heating and dehydration in the green tea manufacturing process resulted in greater loss of pesticide residues than did withering and dehydration in black tea; no significant reduction in residue level resulted from the rolling and fermentation steps in black tea. Residue levels in both green and black teas were reduced during final drying. Copyright © 2004 Society of Chemical Industry     

Influence of withering, including leaf handling, on the manufacturing and quality of black teas - a review

Literature on the influence of withering on maceration, fermentation and drying and on black tea quality is reviewed. The importance of including the handling of the leaf in the field and during transportation as an integral part of withering is stressed. The influence of physical and chemical changes in the green leaf, during withering, on the quality of black teas is discussed. Withering practices vary with climate, producing region, the type of manufacturing process and demands by the markets. Mechanised withering may improve quality by reduced handling of the leaf. The influence of plucking standards on withering and the effect of withering on the storage of tea are discussed.     

Studies on freeze-withering in black tea manufacturing

In order to reduce the withering time during black tea manufacture, freeze-withering was attempted, which resulted in flaccid leaves with increased cell membrane permeability in a shorter period of time. The freeze-withered leaves had similar amounts of quality precursors as that of the conventionally withered leaves. The resultant black tea was better in quality than those manufactured without withering and after normal withering. Manufacturing of fresh leaves resulted in comparable levels of theaflavins, but the tea was not acceptable due to its harshness. Increased cell membrane permeability during freeze-withering showed that the leaf attained a sufficient degree of physical wither. The decreases in the levels of chlorophyll showed that chemical withering had also been achieved during freeze-withering, which is supported by the increased levels of caffeine.     

萎凋叶含水量对四川中小叶群体种工夫红茶品质形成的影响

目的探索萎凋程度对重庆工夫红茶品质形成的影响。方法以四川中小叶群体种为研究对象,分析比较了3个萎凋含水量:处理A(69.59%)、处理B(65.17%)、处理C(59.20%)萎凋叶红茶加工过程中色泽、多酚氧化酶(polyphenylene oxide, PPO)活性变化及对后续揉捻效果、生化成分、工夫红茶成茶品质形成的影响。结果随着萎凋水分的降低,萎凋叶L*, b*值呈下降的趋势, a*值呈上升的趋势, 4～6 h时均出现了与总体趋势相反的波动;加工过程中,各处理L*,b*值均呈下降的趋势,a*值在发酵前呈增高的趋势,干燥后值减小。成茶色泽L*a*b*值则均表现为处理A处理C处理B。加工过程中PPO活性呈先升后降的趋势,随萎凋程度的加重,高峰往后延迟且活性越强,处理C在发酵环节中活性最高。揉捻环节随着萎凋叶含水量的降低成条率越高,扁条率越低,细胞破碎率越高,处理C效果最好。内含物质随着萎凋叶含水量的减少,茶多酚先增后减,氨基酸先减后增,咖啡碱呈先减后增再减式起伏变化;水浸出物、可溶性糖差异不明显;成茶中处理C综合感官品质表现最好。结论萎凋叶含水量在60%左右时,有利于发挥四川中小叶群体种品种优势,加工出的工夫红茶品质良好。     

Effect of withering on the polyphenol oxidase level in the tea leaf

The level of polyphenol oxidase in tea leaf (Camellia sinensis) decreased on partial desiccation of the leaf during the withering process of black tea manufacture. However, sufficient activity remained, even after withering, to oxidise the available substrate in the leaf. The loss in activity due to desiccation was restored on rehydration.     

Seasonal variations in theaflavins,thearubigins, total colour and brightness of Kangra orthodox tea (Camellia sinensis (L) O Kuntze) in Himachal Pradesh

Variations in theaflavins, thearubigins, total colour and brightness of orthodox black tea were studied for four consecutive years (1993–1996) with a view to evaluating the effects of changing weather conditions on the quality of Kangra tea. A degree of withering of 600–650 mg g⁻¹ during the first, second and fourth seasons was optimal for the development of significantly higher brightness and total colour characteristics. The quality of rainy season teas suffered owing to high chlorophyll content and low degree of withering. Hot air circulation through the withering troughs to assist evaporation of leaf moisture increased the brightness and total colour of rainy season teas. High atmospheric demand during the dry season assisted loss of green leaf moisture, but withering and brightness exhibited significant negative correlations with high relative humidity and rainfall. Summer season teas were superior in their total colour and brightness. © 2000 Society of Chemical Industry     

红茶加工过程中纤维素酶和主要品质成分的动态变化

为探究红茶在日光萎凋、揉捻、发酵等加工工序中纤维素酶和主要品质成分的变化规律,本研究以凫早2号(C.sinensis cv.Fuzao2)为原料,测定红茶加工过程中β-葡萄糖苷酶、内切葡聚糖酶及外切葡聚糖酶的活性,同时分析了可溶性糖、儿茶素、咖啡碱、游离氨基酸等主要品质成分含量的动态变化。结果表明,β-葡萄糖苷酶活性、儿茶素总量、氨基酸总量在日光萎凋阶段结束后达到最高值,分别是0.091 U(10 min)-1·mL-1、97.6 mg/g、38.9315 mg/g,揉捻阶段迅速下降后趋于稳定;内切葡聚糖酶活性在日光萎凋开始至发酵结束呈持续上升趋势,从0.19 U(10 min)-1·mL-1增加至0.51 U(10 min)-1·mL-1;可溶性糖含量在揉捻、发酵期间下降迅速,而外切葡聚糖酶活性和咖啡碱含量在红茶加工过程中变化不显著。     

Changes undergone by free amino-acids during the manufacture of black tea

(1) An increase in total free amino-acids during the withering stage of tea manufacture was confirmed, and was found to be dependent on storage conditions which promote the onset of senescence in plucked tea shoot tips (especially desiccation). The rate of increase was positively related to temperature up to the point where the tissues were killed, after which no further changes took place. Individually, all the major amino-acids increase during withering except the most abundant amino-acid, theanine, which shows an appreciable decrease. (2) During the fermentation stage of black tea manufacture the concentrations of leucine, isoleucine, serine, glutamic acid, glutamine, threonine and phenylalanine are appreciably reduced. Other free amino-acids undergo little change in concentration. (3) During the drying stage of tea manufacture there is a small general decrease in free amino-acid concentration. (4) There is an active metabolism of free amino-acids in plucked tea shoot tips. Within 3 h of feeding glycine-¹⁴C, radioactivity could be detected in all the free amino-acids and especially in serine which contained about ten times as much ¹⁴C as did glycine after this period. Caffeine increased in concentration and in degree of labelling with time from feeding of glycine-¹⁴C which suggests that the amino-acids are the precursors of this purine compound in tea shoot tips. (5) The effect of these changes on the organoleptic properties of black tea are discussed.     

Effect of Storage on Anthocyanin Degradation in Black Mulberry Juice and Concentrates

Anthocyanins present in fruits and vegetables are receiving increased attention because of their potential antioxidant activity but are very susceptible to degradation during processing and storage. Effect of storage on kinetics of anthocyanin degradation and hydroxymethylfurfural (HMF) formation in black mulberry juice and concentrate was determined during 8 months of storage at temperatures of 5°, 20°, 30°, and 40 °C. The monomeric anthocyanin degradation was in accordance with the first-order reaction kinetics and the activation energies of anthocyanin degradation in black mulberry juice and concentrate were found as 56.48 and 49.75 kJ mol^?1, respectively. HMF formation in black mulberry juice and concentrate increased linearly with storage time and temperature and followed zero-order reactions. The activation energies of HMF formation in black mulberry juice and concentrate were found as 75.70 and 104.11 kJ mol^?1, respectively. The losses of antioxidant activity for black mulberry juice and concentrate during storage at different temperatures were in the ranges of 4.87–16.01 and 4.47–33.57 %, respectively. Antioxidant activity in black mulberry juice and concentrate was correlated with total monomeric anthocyanins.     

Characterization of Tannase Activity on Tea Extracts

Assay of tannase activity was performed directly, using extracts of black tea leaf, by a pH stat method at the pH optimum of the enzyme (6.0). Reaction rates were calculated from the initial rates of the volume of titrant vs. time plots, and activity was expressed as μmoles/min. The enzyme was unstable to pH levels above 6.0 and temperatures above 40°C. Optimum temperature was 35°C. Using saturating amounts of enzyme, the pH stat was also used to determine total hydrolyzable gallate for kinetic studies and to determine the effect of gallated polyphenols on loss of solids in instant tea processing.     

不同萎凋和发酵处理对“汝城白毛茶”加工红茶品质的影响

近年来国内红茶,尤其是一些特色优质红茶备受青睐,汝城白毛茶作为湖南特色茶树资源,所加工的红茶特色鲜明。为充分发挥汝城白毛茶特色资源的特色,探明其红茶适宜性、个性化加工技术,该研究以春季一芽一叶为原料,从萎凋(A因子4水平)和发酵(B因子7水平),进行2因素不同水平的L₂₈(4¹×7¹)共28个处理,对在制品叶象指标、成品感官审评、各单项评分、品质成分等进行分析,重点探讨萎凋、发酵对汝城白毛茶红茶品质特征的影响及工艺优化。结果表明汝城白毛茶加工红茶采用中、偏重萎凋,萎凋至含水量56%～60%为佳,发酵时间以6～8 h为宜。通过该参数萎凋和发酵加工而成的红茶呈现出金毫满披,花蜜香浓郁,红浓明亮,滋味浓、强(醇)、厚、鲜、爽、甘等优质红茶特点,具湖南红茶"花蜜香、甘鲜味"核心品质特征。     

Survival of toxigenic Escherichia coli on chamomile,peppermint, green,black, ginger,and cinnamon teas during storage and brewing

In this study, the persistence of toxigenic Escherichia coli (E. coli) on dried chamomile, peppermint, ginger, cinnamon, black and green teas stored under 4, 10, and 25°C was determined. The E. coli survival rate in ginger and cinnamon teas decreased below 0 on Day 5. In the other tested teas, E. coli survivability showed a downward trend over time, but never dropped to 0. Chamomile tea retained the greatest population of viable E. coli. Meanwhile, die-off of E. coli was higher at 25°C compared to lower temperatures. Additionally, fate of E. coli during brewing at 60, 70 and 80°C was evaluated. The E. coli population was reduced to below 2 Log colony forming units (CFU)/g after 1 min at 80°C, At the same time, the E. coli survival at 60°C was higher than that at 70°C in all tested teas. The data indicated that if E. coli survives after storage of prepared teas, it may also survive and grow after the brewing process, especially if performed using temperatures <80°C. Finally, we analyzed the correlations between temperature, time, tea varieties and E. coli survival, and successfully constructed a random forest regression model. The results of this study can be used to predict changes in E. coli during storage and fate during the brewing process. Results will form the basis of undertaking a risk assessment.     

Polyphenols Extracted from Black Tea (Camellia sinensis) Residue by Hot‐Compressed Water and Their Inhibitory Effect on Pancreatic Lipase in vitro

Abstract: Polyphenols, retained in black tea wastes following the commercial production of tea beverages, represent an underutilized resource. The purpose of this study was to investigate the potential use of hot‐compressed water (HCW) for the extraction of pancreatic lipase‐inhibiting polyphenols from black tea residues. Black tea residues were treated with HCW at 10 °C intervals, from 100 to 200 °C. The resulting extracts were analyzed using high‐performance liquid chromatography‐mass spectrometry and assayed to determine their inhibitory effect on pancreatic lipase activity in vitro. Four theaflavins (TF), 5 catechins, 2 quercetin glycosides, quinic acid, gallic acid, and caffeine were identified. The total polyphenol content of extracts increased with increasing temperature but lipase inhibitors (TF, theaflavin 3‐O‐gallate, theaflavin 3′‐O‐gallate, theaflavin 3,3′‐O‐gallate, epigallocatechin gallate, and epicatechin gallate) decreased over 150 °C. All extracts inhibited pancreatic lipase but extracts obtained at 100 to 140 °C showed the greatest lipase inhibition (IC₅₀s of 0.9 to 1.3 μg/mL), consistent with the optimal extraction of TFs and catechins except catechin by HCW between 130 and 150 °C. HCW can be used to extract pancreatic lipase‐inhibiting polyphenols from black tea waste. These extracts have potential uses, as dietary supplements and medications, for the prevention and treatment of obesity. Practical Application: Active forms of lipase inhibitors can be recovered from black tea residues. They could be used as dietary supplements or medications.     

Effect of extraction temperature on cream and extractability of black tea [Camellia sinensis (L.) O. Kuntze]

Summary Tea cream and haze in black tea infusions increased with the rise in the tea extraction temperature. The temperature at which substances involved in cream and haze formation began to be extensively extracted into the tea infusion was between 50 and 60 °C. The tea cream particle volume concentration in infusions extracted at 50 °C or below formed less tea cream particles, and their particle sizes were larger and more heterogeneous than those extracted at 60 °C and second infusions extracted at 90 °C from the residual leaves that were previously extracted at 40–50 °C. High‐performance liquid chromatography confirmed that constituents with pyrogallol groups are involved in tea creaming, and the effect of caffeine on tea cream and haze depends on whether these constituents are sufficiently present. The extractability of tea increased with the rise in extraction temperature. Two‐stage extraction of tea in ready‐to‐drink tea processing and its effects on colorimetric indicators were also examined.     

The effect of process parameters on seasonal development of flavour in black tea

Analysis by g.l.c. of ether–extractable steam volatile constituents of black tea from a high elevation tea estate in the Western Region (Dimbulla District) of Sri Lanka during seasonal flavour development, indicated the presence of trans-2-hexenal, n-butyraldehyde, cis-3-hexenol, 1-octen-3-ol linalool, methyl salicylate and geraniol as the main flavour constituents. Of these, trans-2-hexenal and linalool showed appreciable seasonal changes in black tea. Leaf quality and manufacturing practices, particularly withering and fermentation, influenced the production of these compounds during black tea manufacture. It is suggested that the relative concentration of these compounds may be partly responsible for the typical flavour quality of Sri Lanka black teas and these may be used as indices of flavour development.     

Identification of microbial contaminants present during the curing of honeybush tea (Cyclopia)

Honeybush tea (Cyclopia) is produced over a wide area of the Western and Eastern Provinces of South Africa and exported to several countries worldwide. It is traditionally manufactured by curing honeybush material for several days at relatively high temperatures and moisture contents and this results in extensive mould and bacterial growth. This leads to a product with inferior leaf colour and organoleptic quality as well as health concerns. Unlike during the manufacture of black tea, honeybush curing temperatures do not reach levels where these contaminants are eliminated. The microbial contaminants and the minimum temperatures necessary to eliminate these organisms were thus investigated. Yeast-Glucose (YG), Yeast-Starch (YpSs) and Czapek media were evaluated for the isolation of contaminants that developed during the curing of honeybush tea. YG and YpSs gave good results, while the Czapek medium was found to be unsatisfactory for the detection of microbial contaminants. A low pH (pH 5.0) favoured mould growth, while bacteria proliferated at pH 7.0. Honeybush material fermented in a curing heap and material fermented under controlled conditions at 40 and 50 °C showed microbial contamination, but no contaminants were detected on or in material fermented at higher temperatures (60, 70 and 80 °C). Two thermophilic moulds, Humicola grisea var thermoida and Humicola lanuginosa, a thermotolerant mould, Rhizomucor pusillus, and five endospore-forming species of the genus Bacillus were isolated. The data indicated that R pusillus was the predominant microbial contaminant. © 1999 Society of Chemical Industry     

光质萎凋对不同茶树品种红茶品质的影响

本文以室内自然萎凋为对照,比较红光、黄光、蓝光的不同光强（1000、1500、2000 lx）对不同品种红茶感官品质和主要成分的影响。结果表明,与对照相比,光质萎凋能保持或提升福鼎大白茶、蜀永1号萎凋叶游离氨基酸含量,保持或提高了四川中小叶种红茶茶黄素含量;蓝光可提升蜀永1号、四川中小叶种红茶可溶性糖含量,还可降低福鼎大白茶、蜀永1号红茶茶褐素含量。黄光光强与福鼎大白茶红茶可溶性糖含量呈显著正相关,与四川中小叶种茶褐素含量存在极显著正相关,与蜀永1号萎凋叶和红茶茶多酚含量呈较大负相关,但不显著,而蓝光光强与四川中小叶种红茶可溶性糖含量呈较大正相关,但不显著。综合感官品质,福鼎大白茶红茶最佳的萎凋光质为1500 lx黄光、2000 lx黄光,茶红素含量较高,分别为2.211%、2.049%,而茶褐素含量较低,分别为3.081%、3.025%;蜀永1号红茶最佳的萎凋光质为1500 lx黄光,游离氨基酸含量最高,为2.8%;四川中小叶种红茶最佳的萎凋光质为1500 lx黄光、1500 lx蓝光,前者游离氨基酸含量较高,为3.4%,后者茶黄素含量较高,为0.280%,茶褐素含量较低,为2.937%。所以1500 lx黄光有利于提升所选品种红茶品质。