Novel Methods For Preparing And Isolating Functional Components From Tea

Tea extracts has been widely used in medicines and functional foods because of their healthy benefits and antioxidant properties. The functional components from tea are confirmed to connected with polyphenolic compounds, especially (-)epigallocatechin gallate (EGCg). Besides the polyphenols, tea also contains a considerable amount of caffeine, which has some undesirable effects for some people. So the demand of decaffeinated tea extracts with high concentration of EGCg are increasingly expanding.It is now an important topic to search for an inexpensive, more efficient and safe methods for isolating and purifying functional components from tea and preparing decaffeinated tea extracts in the tea processing field. The present work was set to investigate novel methods for isolating functional components from dry tea and fresh tea leaf and preparing decaffeinated using fresh tea leaf.Tea was always extracted in hot water during analysis of tea catechins and preparation of tea functional components. The effect of temperature on epimerisation and extractability of tea catechins was investigated. The results showed that epimerization of tea catechins was taken place when tea was extracted in water at 100℃ for 45min, comparing with extracted in 50%(v/v) ethanol solution at room temperature. The tea extract extracted from dry tea in water at 100℃ had lower concentrations of EGCg and ECg. It suggests that the epimerization and oxidation of tea catechins took place in water at high temperature, but were controlled when the tea was extracted in 50%(v/v) ethanol solution. However, fresh tea leaf should be extracted in 75%(v/v) ethanol because it contains a higher moisture content than dry tea.During preparing tea polyphenols, decaffeination was usually carried out after extraction. Decaffeinated tea was always prepared by carbon dioxide supercritical fluid extraction using dry tea. To search for a simple and inexpensive decaffeination method, hot water treatment was used to decaffeinate fresh tea leaf.The results showed that water temperature, extraction time and ratio of leaf to water had statistically significant effect on the decaffeination. A good result was obtained when the fresh tea leaf was decaffeinated with ratio of tea leaf to water 1:20 (w/v) at 100°C for 3 min. It is considered that the hot water treatment is a safe and inexpensive method for processing decaffeinated green tea, and this method could also be used in preparing decaffeinated tea extracts. However, caffeine was not specifically isolated if rolled tea leaf and dry tea were used and so the method was not suitable for the decaffeination of black tea.Chloroform or methylene chloride is an effective solvent for isolating caffeine from crude tea extracts. However, it is not widely accepted by consumers because of its toxicity. Column chromatography was widely adopted to isolate caffeine from tea catechins in which macroporous adsorption resin was usually used for its less residues. However, there were still some problems, such as the high production cost and trace residue when the resin was used.To find inexpensive and safe natural materials for isolating caffeine from tea extracts or catechins, lignocelluloses prepared using 4 species of plants were used for the isolating test and were compared with the macroporous adsorption resin and active carbon. The results showed that the lignocellulose prepared from the sawdust of cedar had the best effects of selectively isolating caffeine and collecting catechin gallate esters, especially EGCg.The adsorption equilibrium of caffeine and catechins on cedar-lignocellulose was determined by static absorption method. The isotherm adsorption was consistent with Langmuir equation. The saturated adsorption was higher at 25 °C than at 40 °C. The saturated absorption of the cedar-lignocellulose to catechins, especially catechin gallate esters such as EGCg, was higher than to caffeine. It suggests that the cedar-lignocellulose can be used to isolating caffeine and collecting catechin gallate esters, specifically. This was confirmed by the adsorption breakthrough curves obtained in the further tests.The macroporous adsorption resin and cedar-lignocellulose were used toisolate caffeine and tea catechins from tea extract by gradient eluviation with ethanol solutions of 0%,5%,10%,20%,30%,60% and 80%(v/v). The results showed that the cedar-lignocellulose has higher capability of isolating caffeine from catechins than the macroporous adsorption resin. Caffeine could be isolated from catechin gallate esters clearly on cedar-lignocellulose by eluviation with 5%(v/v) and 60%(v/v) ethanol solution and high content catechins product with 68.1% EGCg and 0.6% caffeine could be obtained.Novel methods for isolating and purifying functional components from tea and preparing decaffeinated tea were established in this study. The finding of cedar-lignocellulose, a natural, safe and inexpensive adsorption material for isolating and purifying tea catechins, will be of great interests not only in the production of tea catechins, but also in the production of forestry products because it adds value to the by-products of wood processing and alleviates the pollution of the by-products in wood processing.