Green Extraction Approach for Phenolic-Rich Peppermint Extracts Using Ultrasound: Impact of Solvent and Time Variables.

Abstract

This study investigated the effects of solvent composition and sonication time on the ultrasound-assisted extraction of phenolic-rich peppermint extracts using ethanol-water mixtures. Ethanol concentrations of 0%, 50%, 75%, and 95% were applied for extraction periods of 15 and 30 min, and the resulting extracts were evaluated for total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities using DPPH and ABTS assays. Two-way ANOVA revealed that ethanol concentration, sonication time, and their interaction significantly affected all measured parameters (p < 0.01). The optimal extraction condition was 50% ethanol for 15 min, which produced the highest TPC (141.64 ± 3.34 mg GAE/g extract) and TFC (256.20 ± 2.43 mg RE/g extract), together with the strongest antioxidant activities, as indicated by the lowest IC₅₀ values for DPPH (0.123 ± 0.001 mg/mL) and ABTS (0.023 ± 0.001 mg/mL) radical scavenging activity. Correlation analysis demonstrated strong negative relationships between phytochemical contents and antioxidant IC₅₀ values, indicating that increased phenolic and flavonoid contents were associated with enhanced antioxidant activity. Prolonged sonication generally reduced extraction efficiency under certain solvent conditions, particularly at intermediate ethanol concentrations, suggesting possible degradation of sensitive phytochemicals during extended cavitation. These findings demonstrate the importance of balancing solvent polarity and extraction duration to maximize phytochemical recovery and antioxidant activity under green extraction conditions.