Effects of cosolvents on the decaffeination of green tea by supercritical carbon dioxide

Due to the adverse effects of the caffeine in a variety of plant products, many methods have been explored for decaffeination, in efforts to remove or reduce the caffeine contained in plant materials. In this study, in order to remove caffeine from green tea (Camellia sinensis) leaves, we have employed supercritical carbon dioxide (SC–CO₂), which is known to be an ideal solvent, coupled with a cosolvent, such as ethanol or water. By varying the extraction conditions, changes not only in the amount of caffeine, but also in the quantities of the principal bioactive components of green tea, including catechins, such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC), were determined. The extraction conditions, including temperature, pressure and the cosolvent used, were determined to affect the efficacy of caffeine and catechin extraction. In particular, the type and concentration of a cosolvent used constituted critical factors for the caffeine removal, combined with minimal loss of catechins, especially EGCG. When the dry green tea leaves were extracted with SC–CO₂ modified with 95% (v/v) ethanol at 7.0 g per 100 g of CO₂ at 300 bar and 70 °C for 120 min, the caffeine content in the decaffeinated green tea leaves was reduced to 2.6% of the initial content. However, after the SC–CO₂ extraction, a substantial loss of EGCG, as much as 37.8% of original content, proved unavoidable.     

Comparison of extraction and isolation efficiency of catechins and caffeine from green tea leaves using different solvent systems

Catechins from green tea (Camellia sinensis L.) have received considerable attention due to their beneficial effects on human health, such as antioxidant and anticancer activities. Optimisation of extraction conditions of the catechins from green tea leaves was performed using different solvents (ethanol or distilled water), different extraction methods (ultrasound‐assisted, room temperature or reflux extractions) and various extraction times (0.5–24 h). The optimal extraction conditions were determined using 40% ethanol with ultrasound‐assisted extraction method for 2 h at 40 °C. In addition, two isolation methods for the recovery of catechins from green tea extracts were compared using different solvent combinations (chloroform/ethyl acetate versus ethyl acetate/dichloromethane). The results showed that the ethyl acetate/dichloromethane system could achieve much higher content of catechins than the other isolation approaches, indicating the method that extract catechins first with organic solvent such as ethyl acetate before removing caffeine is much effective than removing caffeine first when organic solvents are used for the recovery of catechins without caffeine from green tea extracts.     

Extraction behaviors of caffeine and chlorophylls in supercritical decaffeination of green tea leaves

The decaffeination of green tea using supercritical carbon dioxide (SC-CO₂) was optimized by response surface methodology (RSM) for the maximal removal of caffeine, and the coextration of chlorophylls was also monitored during decaffeination. The experimental conditions for the SC-CO₂ extraction of caffeine were set up according to the Box-Behnken design of RSM. The relationships between the extraction yield of caffeine and various parameters used for the SC-CO₂ extraction such as pressure, temperature and concentration of ethanol were studied at a fixed CO₂ flow rate. The extraction yields of caffeine and total chlorophyll were significantly influenced by extraction pressure, temperature and concentration of cosolvent, and their extraction yields behaved almost in parallel at different extraction conditions that were obtained by varying pressure, temperature and ethanol cosolvent concentration. At the optimal decaffeination conditions such as 3.0 g of 95% (v/v) ethanol cosolvent per 100 g of CO₂, 23 MPa, 63 °C and an extraction duration of 120 min for 10 g of green tea leaves, the extraction yields for caffeine and catechins were 96.60% (w/w) and 40.61% (w/w), respectively, and the substantial coextraction of total chlorophyll (43.09% of the total amount) was also observed during the decaffeination process.     

超声辅助室温冲泡绿茶的条件筛选和品质分析

为缩短绿茶室温冲泡的时间并获得较优品质,实验利用超声作为辅助,通过感官审评和主要滋味组分及香气组分的分析,筛选优化冲泡条件,并比较其与标准沸水冲泡的品质差异。结果表明：超声辅助室温冲泡绿茶的优化条件为投茶量5 g、茶水比1∶30（g/mL）、超声时间10 min,该条件下冲泡的绿茶与标准沸水冲泡相比,水浸出物、茶多酚和咖啡碱含量较低,氨基酸含量较高;二者绝大部分香气组分相同,但室温冲泡的缺少了辛醛、反-2-辛烯醛等具有不愉快脂肪气味的物质,增加了α-芳樟醇、己酸-反-2-己烯酯等嫩香清香的物质。实验初步验证了超声辅助室温冲泡绿茶的可行性,所得茶汤滋味鲜醇爽口,香气清鲜高长,整体品质优于标准沸水冲泡。超声法特别适用于工业化萃取茶汤,可大大节省能源,降低废气排放。     

不同贮藏条件对扁形绿茶货架品质的影响

针对绿茶贮藏环节易氧化、陈变的行业难点问题,以温度、湿度、含氧量、干茶含水量为控制变量,研究差异化调控对绿茶贮藏品质稳定性的影响,以期获得最大限度保持绿茶品质风味和营养价值的贮藏条件。通过均匀设计,结合主成分分析、回归分析优化建立了扁形绿茶的贮藏品质控制参数。结果表明,随着贮藏时间延长,茶多酚和儿茶素含量呈下降趋势,酯型/非酯型儿茶素在贮藏6个月后增加幅度明显,咖啡碱含量变化不显著。优化获得绿茶贮藏协同品控参数:干茶含水量4.5%,温度25 ℃、相对湿度55%、内包装含氧量0.2%,在该条件下绿茶贮藏感官风味和化学物质保留率最为稳定,其中茶多酚、儿茶素和感官评分的综合评分分别为1.28、1.10、2.09。本研究可为绿茶贮藏流通、保鲜控制规程的制定提供技术支撑和参考依据。     

Optimal extraction conditions for simultaneous determination of catechins and caffeine in green tea leaves

The amount of catechins and caffeine in green tea are considered a standard of quality evaluation for green tea. The objectives of this study were to investigate the optimal conditions for simultaneous extraction of catechins and caffeine and to compare their quantity and composition within the exotic tea varieties. Moreover, 8 tea varieties of exotic origin were tested with the optimal extraction conditions found in this study. Regarding the caffeine and catechins contents, a 2 h room temperature extraction using a 2% phosphoric acid-40% EtOH solution was the most suitable simultaneous extraction method. The total catechins and caffeine contents of the tea leaves ranged 44.25–64.80 and 9.26–13.11 mg/g, respectively. The optimal extraction method of catechins and caffeine in tea leaves may be used for further studies and breeding of high quality tea plants.     

超声波辅助提取与电渗析脱盐耦合技术对绿茶茶汤理化性质的影响

本文对比不同功率超声辅助热水提取与传统热水提取的绿茶茶汤理化性质差异,并对其进行电渗析处理,探究电渗析对绿茶茶汤的理化性质及冷却后浊度及沉淀率的影响。结果表明,超声辅助热水提取的绿茶茶汤中可溶性固形物、茶多酚含量、咖啡碱含量均高于传统热水提取,且随超声功率增大先升高后降低,超声功率增加至390 W时,绿茶茶汤中茶多酚及咖啡碱含量达最大值,分别为5903.14、1091.87 mg/kg。电渗析处理能显著降低绿茶茶汤中金属离子含量及电导率,热水提取、130 W超声提取及520 W超声提取的茶汤中钾的脱除率分别为67.46%、80.20%、89.59%,锰的脱除率分别为64.92%、77.35%、88.56%;电渗析处理可显著降低绿茶茶汤的浊度,并对茶汤的“冷后浑”具有抑制效果,且对超声辅助提取的茶汤“冷后浑”的抑制效果较热水提取效果更好。     

Green tea preparation and its influence on the content of bioactive compounds

The effect of different extraction conditions and storage time of prepared infusions on the content of bioactive compounds of green teas and their antioxidant capacity were investigated. The content of total phenols, total flavonoids and total non-flavonoids in green teas was determined spectrophotometrically, while 7 flavan-3-ols, 6 phenolic acids and 3 methylxanthines were identified and quantified by using high performance liquid chromatography (HPLC–PDA). Among the tested green teas bagged green tea Twinings of London was recognized as the richest source of phenolic compounds (3585 mg/L GAE of total phenols). The most abundant phenolic constituents of green tea were flavan-3-ols, of which EGCG was prevailing in all teas (94.54–357.07 mg/L). The highest content of caffeine, as the most abundant methylxanthine, was determined in powdered green tea. The findings of this investigation suggest that extraction efficiency of studied bioactive compounds from green tea depends on the extraction conditions and that maximum extraction efficiency is achieved during aqueous extraction at 80 °C, for 5′ (powder), 15′ (bagged) and 30′ (loose leaf). In order to determine the antioxidant capacity of teas the DPPH, ABTS and FRAP assays were applied. Regardless of the extraction conditions all green teas exhibited significant antioxidant capacity in vitro, which was in correlation with their phenolic content, confirming that green tea is one of the best dietary sources of antioxidants.     

Factors affecting the levels of catechins and caffeine in tea beverage: estimated daily intakes and antioxidant activity

Increased public awareness of health benefits of green tea is generally based on the high polyphenol content of tea leaves and the resulting beverage. A number of factors, such as species, season, agronomic condition and age of the leaves, are known to affect the composition of commercial teas. In the present study the effects of factors associated with domestic preparation and analytical methods, such as brewing time, concentration, solvent and type of tea product, on levels of catechins and caffeine, antioxidant activity and estimated daily intakes were investigated. There were large variations in the levels of total catechins: 43 and 117 mg g^?1 dry matter (DM) (brewed for 30 s and 5 min respectively); 72 and 161 mg g^?1 DM (extracted in boiling water and 50% acetonitrile respectively); 72 and 117 mg g^?1 DM (a tea bag and tea leaves respectively). The effects on caffeine content were comparatively smaller. These variations consequently led to considerable variations in estimated daily intakes based on three cups (600 ml), ranging between 538 and 2014 mg g^?1 DM of total catechins and between 103 and 466 mg g^?1 DM of caffeine. The antioxidant activity was highest (26 680 µmol g^?1 DM) for tea leaves brewed for 5 min and lowest (10 110 µmol g^?1 DM) for a tea bag product brewed for 1 min. Copyright © 2005 Society of Chemical Industry     

原料对茶绿色素提取率的影响

分别以鲜茶、杀青叶、干茶为试材,采用四因素四水平正交试验设计对茶绿色素浸提工艺参数进行了系统的研究。试验结果表明,杀青叶是提取茶绿色素最好的原料;采用100%的乙醇,4.5mL∶1g的醇茶比,75℃水浴浸提25min,浸提效果最佳,提取率为31.50%。茶绿色素含有丰富的茶多酚、咖啡碱、氨基酸等有效成分,是一种优良的天然食用色素。     

Extraction of caffeine and catechins using microwave-assisted and ultrasonic extraction from green tea leaves: an optimization study by the IV-optimal design

In this research, optimal conditions for extraction of caffeine and polyphenols were established from Iranian green tea leaves. In the first step, caffeine was extracted with efficacy about 86% versed to 4.5% of EGC + EGCG. The EGCG + EGC was extracted from partially decaffeinated green tea leaves through microwave-assisted extraction (MAE) and ultrasound-assisted extraction (USE) with efficiency levels of 95 and 85%, respectively. The best results for the MAE process were obtained with 7.8 min and three number of extraction cycles and for the USE process were as followed: time 57 min, temperature 65 °C, and the number of extraction cycles 3. The total phenol content values at the best conditions of MAE and the USE processes were 125 ± 5 and 96 ± 6 mg gallic acid/g DW. The 50% inhibition (IC₅₀) on 1,1-diphenyl-2-picrylhydrazyl (DPPH) were 56 and 66 mg/g of phenol for the MAE and USE processes.     

CO2超临界流体萃取莲子心油最佳工艺条件的研究

应用超临界CO2技术萃取莲子心油。研究了预处理条件(水分含量、粉碎度)、萃取条件(萃取温度与压力、CO2流量、时间)、分离条件(分离温度与压力)对莲子心出油率的影响;然后在单因素分析的基础上,进行正交试验,确定了超临界萃取的最佳工艺条件为:原料水分含量5%左右,粉碎度60目,CO2流量30L/h,时间2h,萃取压力32MPa,萃取温度50℃,分离压力9MPa,分离温度45℃,此时莲子心油的出油率为14.09%。     

Decaffeination of fresh green tea leaf (Camellia sinensis) by hot water treatment

Hot water treatment was used to decaffeinate fresh tea leaf in the present study. Water temperature, extraction time and ratio of leaf to water had a statistically significant effect on the decaffeination. When fresh tea leaf was decaffeinated with a ratio of tea leaf to water of 1:20 (w/v) at 100 °C for 3 min, caffeine concentration was decreased from 23.7 to 4.0 mg g⁻¹, while total tea catechins decreased from 134.5 to 127.6 mg g⁻¹; 83% of caffeine was removed and 95% of total catechins was retained in the decaffeinated leaf. It is considered that the hot water treatment is a safe and inexpensive method for decaffeinating green tea. However, a large percentage of tea catechins was lost if rolled leaf and dry tea were decaffeinated by the hot water treatment and so the process is not suitable for processing black tea.     

茯砖速溶茶喷雾干燥工艺优化

以茯砖茶为原材料,茶水比1︰20(g/mL)浸提,在单因素试验基础上,通过正交试验优化茯砖速溶茶喷雾干燥工艺。研究进风温度、物料流速及风机功率对茯砖速溶茶出粉率及品质的影响。结果表明,茯砖速溶茶喷雾干燥最佳工艺条件为:进风温度180℃、物料流速15%、风机功率40 m³/h。在此条件下,所得的茯砖速溶茶含水量为5.19%,出粉率为17.2%,呈淡黄色,粉末均匀细小,无结块,溶解性好,营养物质丰富,茶多酚含量为27.6%、游离氨基酸为3.4%、咖啡碱为8%。     

龙井绿茶咖啡碱的提取工艺研究

通过研究龙井绿茶中咖啡碱的几种提取方法,选择和优化工艺条件,为从绿茶中提取咖啡碱的工业化提供一定的参考,首先验证了索氏抽提法提取龙井绿茶中咖啡碱的有效性,其次分别研究了微波辅助和超声波辅助提取茶叶中咖啡碱的优化工艺。结果表明：微波浸提咖啡碱的最佳浸提条件为：液固比20∶1,微波解冻档辐照3min,浸提3次,最高浸提率为3.69%;超声波最佳浸提条件为：超声功率100%,超声波处理时间为25min,浸提2次,液固比为25∶1,超声温度为80℃,最高浸提率为3.77%。微波和超声波浸提效果明显高于索氏浸提,但微波浸提与超声波浸提的提取率相差不大。     

FT-NIR spectroscopy for caffeine estimation in instant green tea powder and granules

The feasibility of measuring caffeine content in instant green tea and granules was investigated by Fourier Transform Near-Infrared (FT-NIR) spectroscopic technique. A calibration model was developed using pure caffeine standards of varying concentrations in the near-infrared region (4000-12000 cm⁻¹). The developed model was validated using test validation technique. FT-NIR spectroscopy with chemometrics, using the PLS-first derivative plus straight line subtraction method could predict the caffeine content in tea samples accurately up to an R² value greater than 0.98 and a standard error of prediction (SEP) value less than 2.0 with 6 factors in the prediction model. The developed model was applied to predict caffeine content in tea samples within 2-5 min. The developed procedure was further validated by recovery studies by comparing with UV spectroscopic method of caffeine determination.     

真空升华法脱除绿茶中咖啡碱工艺研究

根据咖啡碱升华的理化性质,本文采用真空升华法脱除炒青绿茶中的咖啡碱,并研究了其最佳工艺参数及此工艺对炒青绿茶品质的影响。结果表明,茶样中的咖啡碱处于结合态,不易升华,所以直接对茶样进行真空升华处理,茶样中咖啡碱的脱除率未超过15%。研究不同预处理对咖啡碱脱除效果的影响,发现水浸润预处理结合超声-微波协同萃取仪预处理,对咖啡碱的脱除最为有效。真空升华最佳工艺为:将茶样用2倍于其质量的水浸润后,采用超声-微波协同萃取仪在微波功率300W、超声功率50W条件下处理60s后在90℃条件下真空升华处理4h,所得茶样咖啡碱脱除率为62.24%,主要有效成分茶多酚损失率低于10%,且非酯型儿茶素的损失量大于酯型儿茶素。     

微波辅助循环萃取法脱除茶叶咖啡因研究

探讨了利用微波辅助萃取技术高选择性脱除茶叶中咖啡因的新方法,在料液比1∶50,微波功率160W,微波时间6min的条件下,以沸水为溶剂,咖啡因脱除率高达80.56%,茶多酚损失率为40.16%。优化工艺以茶叶萃取液为溶剂,采用循环萃取的方式,则可以控制茶多酚损失率降至12%。进一步探索性尝试4℃冷藏静置12h的方法进行萃取液循环利用,促使咖啡因以络合物的形式沉淀、脱除。在最优条件下,连续生产茶叶9批次后仍可保持47.02%的脱除率,并且茶多酚的损失率小于11.74%。     

茶树花中茶多酚和茶皂素综合提取技术研究

为了实现对茶树的综合利用,以茶树的花为实验材料,在单因素实验的基础上,采用正交实验方法对茶树花中茶多酚和茶皂素的综合提取工艺进行优化。分析了浸提时间、料液比、浸提温度、乙醇浓度和超声波功率对浸出率的影响。结果表明,乙醇浓度70%,超声波功率350W,浸提温度60℃,浸提时间10min,料液比1∶30g/mL时,茶多酚和茶皂素的综合得率最高,分别达到了28.38%和23.69%。     

从残次茶中制备茶多酚的关键技术研究

现今对残次茶的利用和茶多酚的提取工艺不完善,以至于造成残次茶的浪费。因此,研究从残次茶中提取茶多酚的关键技术是很有必要也很有意义的。试验以黑毛茶为原料,乙醇为提取溶剂,采用超声辅助提取的方法提取茶多酚,并通过响应面分析得到最佳工艺条件：超声功率70 W,乙醇体积分数70%,浸提温度65 ℃,浸提时间30 min,料液比1∶25（g∶mL）。在此条件下,茶多酚提取率为7.44%。 关键词：中图分类号：TS202.3 文献标识码：A 文章编号：0254-5071（20１5）06-0094-05 doi: