Face-Centered Central Composite Design for the Optimization of the Extraction of Phenolic Compounds from Kernels and Shells of Raphia farinifera and Evaluation of the Antioxidant, Antimicrobial, and Anti-Inflammatory Activities

Abstract

This study reports the extraction of phenolic compound from shells and kernels of the Raphia farinifera fruit and the biological activities of the extract. A face-centered composite design was established to optimize the extraction conditions: ethanol/water ratio (0-100%), solvent/powder ratio (10-30 mL/g), and extraction time (90-180 min). Subsequently, the extracts obtained under the optimal conditions were used for the evaluation of the radical scavenging capacity, the capacity to chelate ferric ions, and the antimicrobial and anti-inflammatory activities. The optimal extraction conditions for the shells are an extraction time of 134.24 min, 65% ethanol in water, and a solvent/substrate ratio of 21.16 mL/g, and for the kernel, an extraction time of 180 min, 94.3% ethanol in water, and a solvent/substrate ratio of 18.6 mL/g. In these conditions, the phenolic compounds were 95.36 mg EAG/L for the shell extract and 139.72 mg EAG/L for the kernel extract. The antioxidant activity revealed that the half-maximal inhibitory concentrations (IC50) of the kernel extracts are 22.32 μg/mL and 55.73 $\mu$g/mL for the shells. A reducing activity of Fe 3+ ions with an activity of 308.39 μg EAA/mg for the kernel extracts and 293 μg EAA/mg for the shells was observed. B. cereus was the most sensitive microorganism with a minimum inhibitory concentration (MIC) equal to the minimum bactericidal concentration (MBC) with a value of 156.25 ppm for the kernel extract while the shell extract showed MIC of 625 ppm and MBC of 2500 ppm. The IC50 values for the denaturation of proteins by extracts of shells and kernels are 0.76 μg/mL and 0.56 $\mu$g/mL, respectively. Membrane stabilization revealed IC50 values of 1054.54 $\mu$g/mL and 1339 $\mu$g/mL for the shell and kernel extracts, respectively. This work has shown the potential of Raphia farinifera extracts for the food industry and cosmetics.