Column-chromatographic extraction and separation of polyphenols, caffeine and theanine from green tea

A highly efficient column-chromatographic extraction (CCE) followed by sequential adsorption to extract and separate bioactive compounds from green tea was developed. Tea powder was loaded into columns with 4-fold solvents and eluted through a cyclic CCE. High-quality tea extracts with greater than 90% extraction efficiencies of polyphenols, epigallocatechin-3-gallate, caffeine, theanine and polysaccharides were obtained with 4-fold water circulated five times among different columns at 70 °C. Similar results, except for low polysaccharide extraction (35.5%), were obtained with 4-fold 30% ethanol circulated three times at room temperature. The highly concentrated water extraction was directly passed through columns of polyamide, DM130 macroporous and 732 ion exchange resins, resulting in high-purity polyphenols (99%), caffeine (98%) and theanine (98%) after simple purification of the eluates from each column. This method uses simple equipment, minimum solvents and can be used for both quantitative analysis and continuous preparation of high-quality tea extracts and bioactive compounds.     

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.     

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.     

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.     

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.     

抗酒精化学损伤的茶氨酸复合配方筛选与体外抗氧化活性研究

通过流动注射化学发光法筛选以茶氨酸为主要成分的强抗氧化性配方,研制以茶氨酸、γ-氨基丁酸等茶叶特征成分为主要配方的复合氨基酸颗粒剂(以下简称功能修饰因子)。采用不同溶解载体溶解不同浓度的功能修饰因子,通过对.OH、DPPH.、H2O2清除能力和过氧化脂质抑制作用的测定,研究功能修饰因子的抗氧化性能。结果表明,以水、42%乙醇、42%茶酒作为溶解载体溶解的功能修饰因子,均具有较好的抗氧化性能,其中功能修饰因子的42%茶酒溶液在较低浓度就显示出很好的清除效果,且浓度与清除能力呈现明显的量效关系,表明茶酒中以儿茶素为主体的茶叶功效成分与功能修饰因子具有较强的协同增效作用。当浓度为4g/mL、1g/mL、2.5g/mL、5g/mL时,对.OH、DPPH.、H2O2、过氧化脂质的清除率最高,分别为61.8%、61.92%、51.05%、85.93%。     

Measurement of theanine using reverse-phase ion-pair liquid chromatography with photodiode array detection

There is increasing demand for theanine as a taste-enhancing additive and as a supplement for improving and maintaining human health. We describe the development of an ion-pair reversed-phase liquid chromatographic method for the analysis of theanine in tea. Samples may be directly analysed after sonication for 10 min. The mobile phase consists of an aqueous 2 mM solution of pentadecafluorooctanoic acid (ion pair reagent) and acetonitrile (82:18, v/v). The theanine peak is detected using a UV detector at 200 nm. The limit of detection is 5.1 ng and the limit of quantitation is 15.6 ng. The method is accurate with recoveries higher than 97%.