Seasonal variations of phenolic compounds in Australia-grown tea (Camellia sinensis)

Seasonal variations of phenolic compounds in fresh tea shoots grown in Australia were studied using an HPLC method. Three principal tea flavanols [epigallocatechin gallate (EGCG), epicatechin gallate (ECG), and epigallocatechin (EGC)] and four grouped phenolics [total catechins (Cs), total catechin gallates (CGs), total flavanols (Fla), and total polyphenols (PPs)] in fresh tea shoots were analyzed and compared during the commercial harvest seasons from April 2000 to May 2001. The levels of EGCG, ECG, and CGs in the fresh tea shoots were higher in the warm months of April 2000 (120.52, 34.50, and 163.75 mg/g, respectively) and May 2000 (128.63, 44.26, and 183.83 mg/g, respectively) and lower during the cool months of July 2000 (91.39, 35.16, and 132.30 mg/g, respectively), August 2000 (91.31, 31.56, and 128.64 mg/g, respectively), and September 2000 (96.12, 33.51, and 136.90 mg/g, respectively). Thereafter, the levels increased throughout the warmer months from October to December 2000 and remained high until May 2001. In the warmer months, the levels of EGCG, ECG, and CGs were in most cases significantly higher (P < 0.05) than those in the samples harvested in the cooler months. In contrast, the levels of EGC and Cs were high and consistent in the cooler months and low in the warmer months. The seasonal variations of the individual and grouped catechins were significant (P < 0.05) between the cooler and warmer months. This study revealed that EGCG and ECG could be used as quality descriptors for monitoring the seasonal variations of phenolics in Australia-grown tea leaves, and the ratio (EGCG + ECG)/EGC has been suggested as a quality index for measuring the differences in flavanol levels in fresh tea shoots across the growing seasons. Mechanisms that induce seasonal variations in tea shoots may include one or all three of the following environmental conditions: day length, sunlight, and/or temperature, which vary markedly across seasons. Therefore, further studies under controlled conditions such as in a greenhouse may be required to direct correlate flavonoid profiles of green tea leaves with their yields and also to with conditions such as rainfall and humidity.

HPLC analyses of flavanols and phenolic acids in the fresh young shoots of tea (Camellia sinensis) grown in Australia

As part of a 4-year project to study phenolic compounds in tea shoots over the growing seasons and during black tea processing in Australia, an HPLC method was developed and optimised for the identification and quantification of phenolic compounds, mainly flavanols and phenolic acids, in fresh tea shoots. Methanol proved to be the most suitable solvent for extracting the phenolic compounds, compared with chloroform, ethyl acetate and water. Immediate analysis, by HPLC, of the methanol extract showed higher separation efficiency than analyses after being dried and redissolved. This method exhibited good repeatability (CV 3-9%) and recovery rate (88-116%). Epigallocatechin gallate alone constituted up to 115 mg/g, on a dry basis, in the single sample of Australian fresh tea shoots examined. Four catechins (catechin, gallocatechin, epicatechin and epigallocatechin) and six catechin gallates (epigallocatechin gallate, catechin gallate, epicatechin gallate, gallocatechin gallate, epicatechin digallate and epigallocatechin digallate) have been identified and quantified by this HPLC method. In addition, two major tea alkaloids, caffeine and theobromine, have been quantified, while five flavonol glycosides and six phenolic acids, including quinic acids and esters, were identified and quantified. (C) 2003 Elsevier Ltd. All rights reserved.

Phenolic compounds in tea from Australian supermarkets

Phenolic compounds constitute 50-70% of tea water extract and are the main quality parameters for teas. Theaflavins (TF), thearubigins (TR) and theabrownins (TB) are the major polyphenols that determine the quality of black tea. These compounds were measured in 56 leaf teas and teabags sampled from Australian supermarkets in Queensland. The various quantities of TF, ranging from 0.29% to 1.25%, indicate a quality difference that exists among the teas studied. Low TF content in black tea may be due to over-fermenting and/or long periods of storage. The solubility of TR and TB from teabags ranged from 82% to 92%, indicating that the permeability of teabags was variable. Variable quantities of TF in Australian teas show instability and a tendency of TF to oxidize during storage. Total polyphenols in green teas ranged from 14% to 34%, indicating a large variation, which was not reflected in price. The solubility of total polyphenols from teabags has been proposed as a useful quality index of the filtering paper used for the teabags. This chemical analysis of phenolic compounds in commercial teas may be a potential tool for the quality control of Australian manufactured and imported teas in Australian markets. (C) 2005 Elsevier Ltd. All rights reserved.