Intestinal transport of pure theanine and theanine in green tea extract: Green tea components inhibit theanine absorption and promote theanine excretion

Theanine, an amino acid contained in green tea, is known to possess many pharmacological functions. In this paper, we investigated the absorption of theanine in the human intestinal epithelium, using a Caco-2 monolayer model. Different concentrations of either pure theanine or green tea extracts were administered to Caco-2 cells. The theanine content in the samples was analysed by high-performance liquid chromatography, coupled with fluorescence detection. Cell permeation was also measured. The data revealed that the transport of pure theanine occurred in a manner consistent with passive diffusion. Surprisingly, pure theanine showed good absorption, whereas theanine in the green tea extract was poorly absorbed in the Caco-2 cell model. Furthermore, the transport of theanine in green tea extract in the basolateral (BL) to apical (AP) direction was much greater than that in the AP–BL direction, suggesting that green tea components profoundly affect the trans-epithelial transport of theanine in this Caco-2 cell model.     

Artificial neural network modeling and optimization of ultrahigh pressure extraction of green tea polyphenols

In this study, the ultrahigh pressure extraction of green tea polyphenols was modeled and optimized by a three-layer artificial neural network. A feed-forward neural network trained with an error back-propagation algorithm was used to evaluate the effects of pressure, liquid/solid ratio and ethanol concentration on the total phenolic content of green tea extracts. The neural network coupled with genetic algorithms was also used to optimize the conditions needed to obtain the highest yield of tea polyphenols. The obtained optimal architecture of artificial neural network model involved a feed-forward neural network with three input neurons, one hidden layer with eight neurons and one output layer including single neuron. The trained network gave the minimum value in the MSE of 0.03 and the maximum value in the R² of 0.9571, which implied a good agreement between the predicted value and the actual value, and confirmed a good generalization of the network. Based on the combination of neural network and genetic algorithms, the optimum extraction conditions for the highest yield of green tea polyphenols were determined as follows: 498.8 MPa for pressure, 20.8 mL/g for liquid/solid ratio and 53.6% for ethanol concentration. The total phenolic content of the actual measurement under the optimum predicated extraction conditions was 582.4 ± 0.63 mg/g DW, which was well matched with the predicted value (597.2 mg/g DW). This suggests that the artificial neural network model described in this work is an efficient quantitative tool to predict the extraction efficiency of green tea polyphenols.     

龙井绿茶茶多酚提取工艺研究

为了提高茶多酚的得率和纯度,以龙井绿茶为原料,对茶多酚进行乙醇溶液提取、超声波和微波辅助提取。醇提的最佳条件为乙醇浓度50％,浸提4次,每次45min,温度为70℃,液固比为20：1,最大浸提率为24．45％。微波辅助提取最佳条件为预浸30min,乙醇浓度40％,微波解冻档浸提4min,浸提2次,液固比为40：1,最大浸提率为24．70％。超声波辅助浸提最佳条件为乙醇浓度80％,浸提温度50℃,浸提时间25min,浸提2次,液固比为14：1,最大浸提率为24．72％。结果表明：微波与超声波提取率稍高于醇提,但三者差别不大。     

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:     

Optimising the extraction of tea polyphenols, (−)‐epigallocatechin gallate and theanine from summer green tea by using response surface methodology

In this study, response surface methodology was applied to determine the optimal conditions for the extraction of tea polyphenols, EGCG and theanine from summer green tea. As results, the optimal extraction conditions were determined to be temperature 96 °C, time 40 min and ratio of water to raw material 16 mL g^?1. Under these optimal conditions, the experimental values for tea polyphenols, EGCG, theanine and IC₅₀ for DPPH free radical scavenging activity were 133.41 ± 3.12 mg gallic acid g^?1, 30.23 ± 1.22, 3.99 ± 1.13 mg g^?1 and 724.95 ± 15.12 μg mL^?1, respectively. There was no statistical difference at significant level of 0.05 between the experimental and predicted values. The results suggested that the regression models were accurate and adequate for the bioactives extraction from summer green tea.     

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.     

Green tea from purple leaf coloured tea clones in Kenya- their quality characteristics

The Kenyan tea industry wishes to diversify its tea products, and in line with this, anthocyanin – rich teas were developed at the Tea Research Foundation of Kenya. These teas have purple-coloured leaves and the green colour is masked. In total, 12 accessions of the purple leaf coloured teas and 2 standard tea varieties were studied. Clones Hanlu and Yabukita are Chinese and Japanese tea varieties, respectively, known for good green tea, and they were used as reference standards. Little if any research had been done to characterize the quality of these purple leaf coloured teas and this study investigated their total polyphenols (TPP), catechins, caffeine, gallic acid and theanine. These are the major green tea quality parameters. Results showed that the new Kenyan tea clones had higher total polyphenols than had the reference standard tea varieties, which had 17.2% and 19.7% while the lowest among the Kenyan clones was 20.8%. On catechin quality index, K-purple and TRFK 91/1 showed high index values of 15.9 and 13.3, respectively, while clones TRFK 83/1 and 73/5 showed low index values of 0.74 and 1.0, respectively. Hanlu had the highest caffeine level with 2.42% while clones TRFK KS 3, TRFK KS 2 and TRFK 83/1 had relatively high caffeine levels among the purple leaf coloured teas, with 2.33%, 2.22% and 2.21%, respectively. Clone TRFK 73/5 had the lowest caffeine content, with 1.16%. Theanine analysis showed that most purple leaf coloured teas had more theanine than had the reference standard clones, except TRFK 83/1 and K-purple, which were lower than the reference standard clones. The implication of the green tea chemical quality parameters is also discussed. It is concluded that all the studied clones/varieties have above the minimum 14% of total polyphenols. Clones K-purple and TRFK 91/1 showed high green tea quality indices with the latter doubling with high levels of theanine; hence its highly recommended for green tea manufacture.     

Chemometric evaluation of binary mixtures of alginate and polysaccharide biopolymers as carriers for microencapsulation of green tea polyphenols

In this study principal component analysis and artificial neural networks were used to evaluate the potential of using binary mixtures of sodium alginate and other polysaccharide biopolymers as the carriers for microencapsulation of green tea bioactive compounds. Using binary mixtures of alginate and adjunct biopolymers increased the particle size (from 722 to 1344 µm) and textural parameters of the microbeads. Chemometric techniques revealed the combination of biopolymers and their ratio as the main factors influencing the encapsulation performance. The combination of alginate with hydroxypropyl methylcellulose and locust bean gum enabled to retain the highest (-)-epigallocatechin gallate and caffeine contents, the highest total phenols encapsulation efficiency, and their most retarded release in water, confirming these as the best delivery systems of polyphenol-type active compounds and signifying their potent food applications.     

复合酶辅助浸提绿茶多酚工艺条件优化

采用纤维素酶+果胶酶的复合酶法在较适温度下辅助浸提绿茶多酚,以茶多酚浸提率为考察指标,通过单因素和正交实验优化了酶添加量、料液比、浸提温度和浸提时间等四个浸提条件因素,确定了最佳浸提工艺条件为:纤维素酶和果胶酶分别添加0.3%,料液比1∶40 g/m L,浸提温度50℃,浸提时间45 min;在此条件下茶多酚浸提率可达21.36%,明显高于传统水提法的茶多酚浸提率17.41%。      

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.     

茶叶中茶多糖茶多酚茶咖啡碱的高压脉冲电场快速提取

以10倍质量的0．001MEDTA缓冲液为提取液，应用高压脉冲电场（PEF）技术成功从等外绿茶中提取功能成分茶多糖、茶多酚和咖啡碱，并与水提法的提取率进行了比较。结果表明：在缓冲液pH9．5，场强度为25kV／cm，脉冲数为10的条件下，茶多糖有最大提取率，PEF法提取率是水提法的1．91倍；在缓冲液pH9．5，脉冲电场强度为25kV／cm，脉冲数为12时，茶多酚有最大提取率，提取率是水提法的1．11倍；在缓冲液pH4．0，脉冲电场强度为25kV／cm，脉冲数为10时，咖啡碱有最大提取率，是水提法的1．05倍。     

Investigation of the presence and significance of theanine in the tea plant

Theanine was determined in black teas and tea plants by a combination method of thin-layer chromatography (t.l.c.) and densitometry. It was shown that in 20 samples of black tea from different qualities and sources the amount varied from 0.33 to 1.59 g 100 g^?1 dry wt. The highest quality black teas possessed the lowest amount of theanine, but it is subject to chemical degradation during black tea manufacture. The investigation of physiological function of theanine in the tea plant showed that during germination the theanine level reached a maximum after 45 days. This indicates that at this period of the growth of the tea plant theanine acted as a source of nitrogen and as a starting point for the synthesis of the carbon skeletal compounds of the tea plant. Theanine was found to exist in all parts of the tea plant but it accumulated more in young and active tissues and also in younger plants, which emphasises its metabolic role in the tea plant. The distribution of theanine in the shoots indicated that the first leaf was the principal site for the synthesis of polyphenolic compounds from theanine.     

Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine

The effect of different extraction set-ups that influence the extraction efficiency of catechins and caffeine from green tea leaves (variety Fanning Belas, China) were studied using different aqueous and pure solvents (acetone, ethanol, methanol, acetonitrile, water), different temperatures (60, 80, 95 and 100 °C) and times (5–240 min). Raw extracts were analysed for contents of major catechins (EC, EGC, ECG, EGCG), caffeine, proanthocyanidins and flavonols (myricetin, caempherol, quercetin). Starting material was found to contain 191 g major catechins/kg material, 36 g caffeine/kg material and 5.2 g flavonols/kg material on a dry mass basis. The content of major catechins in green tea extracts varied from approximately 280–580 g/kg dry extract, with extraction efficiencies of major catechins varying from 61% to almost 100%. Content of caffeine in extract was in the range of 75 g/kg, where its extraction efficiency varied from 62% to 76%. Average extraction yield was 30% with exceptions when using pure acetone and acetonitrile, where extraction yield was about 3%. Contents of flavonols and proanthocyanidins were in the ranges 6–20 and 12–19 g/kg, respectively. Different extraction procedures with water were also investigated and optimal conditions determined: maximum achieved extraction efficiency of catechins with water was obtained at 80 °C after 20 min (97%) and at 95 °C after 10 min of extraction (90%). Degradation of catechins was observed at higher extraction temperatures and with prolonged extraction times. Using a lower ratio of solvent to material, extraction efficiencies were increased by applying a multi-step extraction procedure. Optimal extraction procedure was then performed using decaffeinated green tea leaves, which were obtained by high-pressure extraction with CO₂, when 98% of caffeine was selectively isolated without significant impact on valuable catechins.     

Analysis of some selected catechins and caffeine in green tea by high performance liquid chromatography

Green tea seems to have a positive impact on health due to the catechins-found as flavanols. Thus, the present study was aimed to develop a low cost reversed phase high performance liquid chromatographic (HPLC) method for simultaneous determination of flavanol contents, namely catechin (C), epicatechin (EC), epigallocatechin (EGC), epicatechin 3-gallate (ECG) and epigallocatechin 3-gallate (EGCG) and caffeine in 29 commercial green tea samples available in a Saudi Arabian local market. A C-18 reversed-phase column, acetonitrile–trifluoroacetic acid as a mobile phase, coupled with UV detector at 205 nm, was successfully used for precise analysis of the tested analytes in boiled water of digested tea leaves. The average values of N (No. of theoretical plates), HETP (height equivalent of theoretical plates) and R_s (separation factor) (at 10 μg ml⁻¹ of the catechins EC, EGC, EGCG and ECG) were 2.6 × 10³ ± 1.2 × 10³, 1.7 × 10⁻³ ± 4.7 × 10⁻⁴ cm and 1.7 ± 5.53 × 10⁻², respectively. The developed HPLC method demonstrated excellent performance, with low limits of detection (LOD) and quantification (LOQ) of the tested catechins of 0.004–0.05 μg ml⁻¹ and 0.01–0.17 μg ml⁻¹, respectively, and recovery percentages of 96–101%. The influence of infusion time (5–30 min) and temperature on the content of the flavanols was investigated by HPLC. After a 5 min infusion of the tea leaves, the average concentrations of caffeine, catechin, EC, EGC, ECG and EGCG were found to be in the ranges 0.086–2.23, 0.113–2.94, 0.58–10.22, 0.19–24.9, 0.22–13.9 and 1.01–43.3 mg g⁻¹, respectively. The contents of caffeine and catechins followed the sequence: EGCG > EGC > ECG > EC > C > caffeine. The method was applied satisfactorily for the analysis of (+)-catechin, even at trace and ultra trace concentrations of catechins. The method was rapid, accurate, reproducible and ideal for routine analysis.     

Effects of phosphorus supply on the quality of green tea

Self-rooted, 10-month-old, uniform tea [Camellia sinensis (L.) O. Kuntze cv. Huangguanyin] plants were supplied with 0, 40, 80, 160, 400 or 1000 μM phosphorus (P) for 17 weeks to determine how P-deficiency affects the quality of green tea. Leaf P concentration increased with increasing P supply. Whole plant dry weight (DW) increased as P supply increased from 0 to 160 μM, then remained little changed with further increasing P supply. The P-deficient green tea displayed decreased concentrations of water extract, total polyphenols, flavonoids, total free amino acids, theanine (Thea) and asparagic acid (Asp) + glutamic acid (Glu), increased concentrations of water soluble sugars, valine (Val), γ-aminobutyric acid (GABA), proline (Pro) and cysteine (Cys), and ratio of total polyphenols to total free amino acids, but unchanged concentrations of total catechins and epigallocatechin gallate (EGCG). In conclusion, the sensory and biochemical qualities of green tea were lowered by P-deficiency.     

Survival and metabolic activity of probiotic bacteria in green tea

The aim of this study was to determine the enzymatic activity and survival of three probiotic strains (Lactobacillus paracasei LAFTI-L26, Lactobacillus acidophilus LAFTI-L10 and Bifidobacterium animalis ssp. lactis LAFTI-B94) during incubation in six different varieties of green tea extracts. The polyphenol content, antioxidant, antimicrobial and antihypertensive properties in green tea (variety Wu Lu Mountain) and in two standards (epigallocatechin-3-gallate and rutin) were also investigated before and after incubation with B. animalis B94. The green tea extracts permitted the survival of the selected probiotic strains better than the saline solution, with B. animalis B94 maintaining the highest levels of viable cells. These selected probiotic bacteria exhibited β-glucosidase, β-galactosidase and α-rhamnosidase activity. The antioxidant and antihypertensive properties of standard solutions of epigallocatechin-3-gallate and rutin increased after incubation with B. animalis B94, caused by polyphenol content reduction and the formation of other more highly biologically active metabolites. However, during the incubation of green tea with B. animalis B94, changes in the concentration of the most abundant green tea polyphenols did not enhance the biological activity.     

微波法提取低档绿茶多酚工艺研究

该研究采用微波法提取低挡绿茶多酚,在单因素试验的基础上,选择乙醇浓度、微波时间、微波功率、料液比为自变量,茶多酚提取率为评价指标,设计L9(34)的正交试验,研究各自变量交互作用及其对茶多酚提取率影响,确定最佳组合方案为:A2B1C3D2,即乙醇浓度60%、料液比1∶6、微波时间25 s、微波功率为360 W,在此工艺条件下,茶多酚提取率达27.64%。     

绿茶中没食子酸提取工艺的研究

通过离子化萃取分离法提取了绿茶中没食子酸,采用单因素实验和正交试验,考察了浸提温度、NaHCO3浓度、料液比和浸提时间对绿茶中没食子酸提取率的影响。结果表明提取没食子酸的最佳工艺条件是：浸提温度80℃,NaHCO3浓度0.15%,料液比1∶80,浸提时间50min,在此条件下没食子酸提取率为0.8443%。     

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%。     

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。