JOURNAL OF APPLIED RESEARCH ON MEDICINAL AND AROMATIC PLANTS, vol.25, 2021 (SCI-Expanded)
The current investigation aims to optimize the extraction of leaf phenolics of Centaurea sp. and to propose a scientific basis for an optimal collection of this plant. Centaurea sp. samples were collected regularly over seven months from January to July 2017 (the non-estivation period). They were then subjected to preliminary ultrasound-assisted extraction (UAE) assays employing four solvents at different polarity (methanol, ethanol, ethyl-acetate, and acetone). April samples extracted in methanol, which revealed maximum recovery of phenolic content, were selected for UAE optimization employing the Box-Behnken design (BBD) technique under the category of the response surface methodology (RSM). In this step, three parameters including time X-1 (min), temperature X-2 (degrees C) and sample-to-solvent ratio X-3 (g/mL) were used to maximize three responses including total phenolic compounds (TPC) content and two different antioxidant capacity assays, DPPH and FRAP. The results under the optimum conditions were significant: TPC 46.44 "mg GAE/g dm", DPPH 38.91 "mg AAEAC/g dm", and FRAP 41.71 "mg AAEAC/g dm". Moreover, 14 phenolic acids were detected and quantified under optimum conditions after running high-performance liquid chromatography analysis (HPLC-DAD). Protocatechuic acid was found at the highest concentration (564.62 +/- 0.44 mu g/g dm) followed by p-coumaric acid (277.89 +/- 0.90 mu g/g dm) and ferulic acid (121.52 +/- 3.83 mu g/g dm). On the other hand, both predicted and experimental BBD responses were in accordance, which points the success of the optimization.