Enzyme-assisted supercritical fluid extraction: an alternative and green technology for non-extractable polyphenols.

Abstract

This contribution proposes an enzyme-assisted eco-friendly process for the extraction of non-extractable polyphenols (NEPPs) from black tea leftover (BTLO), an underutilized tea waste. BTLO hydrolyzed with various enzyme formulations was extracted using supercritical carbon dioxide and ethanol as co-solvent (SC-CO2+EtOH). A conventional solvent extraction (CSE) was performed using EtOH+H2O (80:20, v/v) for comparison purposes. The results revealed that hydrolysis of BTLO with 2.9% (w/w) kemzyme at 45°C and pH5.4 for 98min improved the liberation of NEPPs offering 5-fold higher extract yield (g/100g) as compared with non-treated BTLO. In vitro antioxidant evaluation and LC-MS characterization of extracts revealed the presence of phenolic acids (mainly caffeic and para-coumaric acid) of high antioxidant value. Scanning electron micrograph of the hydrolyzed BTLO samples indicated noteworthy changes in the ultrastructure of BTLO. Moreover, polyphenol extracts obtained by SC-CO2+EtOH extraction were found to be cleaner and richer in polyphenols as compared to CSE. The devised enzyme-assisted SC-CO2+EtOH extraction process in the present work can be explored as an effective biotechnological mean for the optimal recovery of antioxidant polyphenols. Graphical abstract Enzymatic pretreatment can effectively liberate non-extractable polyphenols (NEPPs) while hydrolyzing the cellulosic and hemicellulosic framework of black tea left overs (BTLO).