Ultrasound-assisted extraction for maximizing total phenolics, flavonoid content, and antioxidant activity in Thymus algeriensis: Box-Behnken experimental design

This study investigates the optimization of extraction parameters for antioxidant compounds in Thymus algeriensis, a medicinal plant known for its therapeutic effects against respiratory infections, gastrointestinal disorders, and inflammatory conditions. The plant was harvested periodically every five days in 2022, starting from the day of growth (April 1) until yellowing (August 18), with the flowering sample selected on May 30 for the optimization of extraction parameters for antioxidant compounds. Ultrasound-assisted extraction (UAE) was employed to enhance the extraction efficiency of total phenolic content (TPC) and total flavonoid content (TFC), thereby improving antioxidant activity by controlling temperature, extraction time, and solvent volume as independent variables. To optimize the extraction parameters, the results were analyzed using the Box-Behnken design (BBD) of response surface methodology (RSM). The optimal values obtained, corresponding to the best desirability of 0.919, were TPC = 2.961 g GAE/100 g, TFC = 0.887 g QE/100 g, IC50 (DPPH) = 0.016 mg/mL, and IC50 (FRAP) = 0.426 mg/mL, under the conditions of temperature = 60 °C, time = 36.74 min, and solvent volume = 32.825 mL. Finally, a one-way ANOVA test was conducted on the results for all samples, revealing that the optimal values for the four dependent variables (TPC, TFC, DPPH•, and FRAP) were achieved in May during the flowering period.