Microwave-assisted extraction of tea polyphenols and tea caffeine from green tea leaves

A microwave-assisted extraction (MAE) method is presented for the extraction of tea polyphenols (TP) and tea caffeine from green tea leaves. Various experimental conditions. such as ethanol concentration (0 - 100%, v/v), MAE time (0.5 - 8 min), liquid/solid ratio (10:1 - 25:1 ml g(-1)), pre-leaching time (0-90 min) before MAE and different solvents for the MAE procedure were investigated to optimize the extraction, The extraction of tea polyphenols and tea caffeine with MAE for 4 min (30 and 4%) were higher than those of extraction at room temperature for 20 h. ultrasonic extraction for 90 min and heat reflux extraction for 45 min (28 and 3.6%), respectively. From the points of extraction time, the extraction efficiency and the percentages of tea polyphenols or tea caffeine in extracts, MAE was more effective than the conventional extraction methods studied. (C) 2002 Elsevier Science B.V. All rights reserved.