Effects of different drying, extraction methods, and solvent polarity on the antioxidant properties of Paeonia daurica subsp. mlokosewitschii leaves

The study presents the effect of drying methods (microwave-drying and freeze-drying), different solvents (80% methanol, 99% methanol, 80% ethanol), and different extraction methods on the antioxidant activity of Paeonia daurica subsp. mlokosewitschii leaves, estimated based on DPPH free radical scavenging activity. The highest antioxidant activity was revealed in the freeze-dried leaves. The drying method significantly influenced the antioxidant activity: the thermal microwave-drying resulted in lower antioxidant potential. The solvent polarity also played a significant role in the determination of the antioxidant activity of Paeonia daurica subsp. mlokosewitschii leaves: the lowest IC50 values (specific concentration of the sample required for 50% inhibition) were revealed for freeze-dried plants extracted with 80% methanol, followed by IC50 values obtained for the extraction with 80% ethanol, and the highest IC50 values were revealed for extracts of microwave-dried plants extracted with 99% methanol. The subsequent drying of freeze-dried plant extracts had no significant effect on the antioxidant activity of the extract. The subsequent drying of the methanol extract from microwave-dried plants at room temperature or 40°C significantly reduced IC50 value, however, the results were comparable with those, obtained for the methanol extracts of freeze-dried plants without subsequent drying of the extract. Thus, the optimal method of drying and extraction of Paeonia daurica subsp. mlokosewitschii leaves for preserving the antioxidant activities was established: freeze-drying of leaves followed by 24 h extraction with 80% methanol.