Ultrasound-assisted extraction of compounds from Stevia leaf pretreated with ethanol

Abstract

In this study, ultrasound-assisted extraction (UAE) of Stevia rebaudiana leaf compounds previously treated with ethanol was investigated. Ultrasound power intensity was evaluated and an experimental design was applied to examine the effect of temperature, solvent to leaf ratio and ethanol percentage in the solvent on mass (YM) and sweeteners (YS) yield, total phenolic content (TPC) and antioxidant activity (AA). The application of the maximum power (165 W) provided the obtaining of greater YM and YS, and extracts with higher TPC contents and AA. The increase in the solvent/leaf ratio provided the highest YM and YS, as the increase of ethanol in the solvent, while the temperature promoted an increase only in the YM. Maximum values of YM (44.7 wt%) and YS (88.50 wt%) were obtained using solvent with 40 % ethanol, 50 °C and 15 mL g−1 (solvent/leaf). The extract obtained is constituted by ∼26 wt% of steviol glycosides (GS), corresponding to 9.5, 4.1 and 12.0 wt% of Stevioside, Rebaudioside C and Rebaudioside A, respectively. The analysis of the principal components indicated a high correlation of the variables ethanol percentage in the solvent and solvent to leaf ratio in obtaining extracts with higher TPC content and AA.