Response surface methodology for the optimization of conventional solvent extraction of flavonoids from Inula viscosa

Flavonoids are bioactive compounds that have countless beneficial health effects and are crucial components of the food-nutraceutical industry. These bioactive molecules are known for their antioxidant effects in addition to other bioactivities. Inula viscosa is a widespread plant throughout the Mediterranean basin in the whole world that has been traditionally used in folk medicine. For instance, its leaves were used as anti-inflammatory drugs and its flowers were used to treat inflammatory diseases and even lung cancer. This study aims for the optimization of conventional solvent extraction of flavonoids from Inula viscosa using response surface methodology (RSM) based on single-factor experiments. The optimized extraction parameters were 63.48 ºC for extraction temperature, 0.5 h for extraction time, 80.20% for ethanol concentration, and 90 mL/g for solid-to-liquid ratio. The extract obtained under these conditions had shown a total flavonoid content of 285.233 ± 0.33 mg QE/100 g Dry Matter (DM), remarkably close to the predicted content of 293.922 mg QE/100 g DM and a total phenolic content of 8097.545 ± 4.878 ± 487.8 mg GAE/g DM. The optimized Inula viscosa extract exhibited strong antioxidant capacities in free radical scavenging with an IC50 (the concentration of the sample required to inhibit 50% of free radicals) of 16.805 ± 1303 µg/mL, and a ferric antioxidant reducing power value (FRAP) of 695.184 ± 22.40 Fe 2 + μmol/g of dry extract. In addition to a significant ABTS scavenging with a value of IC50 9.904 ± 0.003 μg/mL. Phenolic compounds were identified using high-performance liquid chromatography with mass spectrometers. This investigation also carried out the antimicrobial activity of Inula viscosa extract against fourteen bacterial strains and three fungal strains. The Inula viscosa extract had revealed a weak antibacterial and antifungal potential against the different strains, although some strains have been shown to be resistant, especially the Gram-negative strains.