Kinetic insights into green extraction of antioxidants from Ficus thonningii: ultrasound-assisted extraction versus maceration
This study aimed to optimize the extraction of total polyphenols and antioxidant compounds from the bark of Ficus thonningii, a medicinal tree widely used in West African ethnopharmacology. Two extraction methods—maceration (MAC) and ultrasound-assisted extraction (UAE)—were compared at three solid-to-liquid ratios (S/L: 1/120, 1/80, and 1/60 g/mL) using an acetone/water solvent system (60:40, v/v). Both processes were carried out at 40 °C for 35 minutes, with kinetic sampling every 5 minutes. Total phenolic content was determined using the Folin–Ciocalteu method, while antioxidant activity was assessed by the FRAP assay. Extraction kinetics followed a biphasic pattern, typical of processes limited by internal diffusion. A second-order kinetic model provided an excellent fit to the experimental data (R² > 0.99; RMSE < 5), allowing accurate estimation of the rate constant (k) and the theoretical equilibrium concentration (Ce). Ultrasound-assisted extraction outperformed maceration in both extraction rate and final yield. At an S/L ratio of 1/60 g/mL, UAE achieved up to 187.43 ± 4.1 mg GAE/g DM of polyphenols and 161.90 ± 2.6 mg TE/g DM in FRAP activity, compared with 162.01 ± 4.2 mg GAE/g DM and 152.80 ± 3.1 mg TE/g DM for MAC. Boxplot and barplot analyses further confirmed the superiority of UAE in terms of reproducibility and efficiency across all tested conditions. The S/L ratio also significantly influenced extraction performance, with lower dilutions leading to higher Ce and k values. These findings highlight the potential of ultrasound-assisted techniques as green, scalable, and efficient alternatives for the valorization of Ficus thonningii bark as a natural source of antioxidants for pharmaceutical, nutraceutical, and cosmetic applications.