Valorization of Formerly Low-interest Residue: Quince (Cydonia oblonga Mill.) Leaves Phenolic Fractions Obtained by Different Green Extraction Approaches

Abstract

The performance of three advanced green extraction techniques, high voltage electric discharge, microwave-assisted extraction, and subcritical water extraction, was evaluated to valorize quince (Cydonia oblonga Mill.) leaves. High voltage electric discharge was conducted at frequencies of 40–100 Hz for 1–15 min with a solvent-solid ratio of 100 mL/g at 25 °C; subcritical water extraction was performed at temperatures ranging from 100–200 °C with a solvent-solid ratio of 20 mL/g, 30 bar, and for 10 min; and microwave-assisted extraction was carried out at temperatures between 40–120 °C with extraction times of 5 and 10 min and a solvent-solid ratio of 10 mL/g. High voltage electric discharge at 40 Hz for 10 min achieved the highest total phenolic content (985.18 mg gallic acid equivalents/g dry matter) and total flavonoid content (640.72 mg catechin equivalents/g dry matter). However, high-performance liquid chromatography revealed that subcritical extracts were with the highest content of individual phenolic compounds. Fifteen phenolic compounds were identified, including five phenolic acids, six flavan-3-ols, three flavonols, and one flavonol glycoside. Chlorogenic acid (223.86 μg/mL) was the most abundant, followed by epigallocatechin (105.04 μg/mL), rutin (98.78 μg/mL), and epicatechin (60.47 μg/mL). This study highlights the potential of these advanced extraction techniques for the valorization of quince leaves and sets the foundation for further research and development in optimizing extraction processes for attainment of high-value extracts.