Microwave-assisted Water Extraction of Green Tea Polyphenols

Introduction - Green tea, a popular drink with beneficial health properties, is a rich source of specific flavanols (polyphenols). There is a special interest in the water extraction of green tea polyphenols since the composition of the corresponding extracts is expected to reflect the one of green tea infusions consumed worldwide. Objective - To develop a microwave-assisted water extraction (MWE) of green tea polyphenols. Methodology - MWE of green tea polyphenols has been investigated as an alternative to water extraction under conventional heating (CWE). The experimental conditions were selected after consideration of both temperature and extraction time. The efficiency and selectivity of the process were determined in terms of extraction time, total phenolic content, chemical composition (HPLC-MS analysis) and antioxidant activity of the extracts. Results - By MWE (80 degrees C, 30 min), the flavanol content of the extract reached 97.46 (+/- 0.08) mg of catechin equivalent/g of green tea extract, vs. only 83.06 (+/- 0.08) by CWE (80 degrees C, 45 min). In particular, the concentration of the most bioactive flavanol EGCG was 77.14 (+/- 0.26) mg of catechin equivalent/g of green tea extract obtained by MWE, vs 64.18 (+/- 0.26) mg/g by CWE. Conclusion - MWE appears more efficient than CWE at both 80 and 100 degrees C, particularly for the extraction of flavanols and hydroxycinnamic acids. Although MWE at 100 degrees C typically affords higher yields in total phenols, MWE at 80 degrees C appears more convenient for the extraction of the green tea-specific and chemically sensitive flavanols. Copyright (C) 2009 John Wiley & Sons, Ltd.