Comparison of Conventional and Green Extraction Techniques for the Isolation of Phenolic Antioxidants from Sea Fennel

Abstract

In this study, different extraction methods were compared for the isolation of bioactive phenolic compounds from sea fennel: microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), and conventional solvent extraction (CSE). Total phenolics, flavonoids, and tannins were determined spectrophotometrically. In contrast, the determination of individual phenolics was performed by high-performance liquid chromatography coupled with an ultraviolet/visible detector (HPLC-UV/VIS). Two in vitro assays (ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picryl-hydrazyl (DPPH)) were performed to determine antioxidant activity. The maximum extraction of phenolic compounds was achieved with 50% ethanol, while the MAE method showed the highest extraction efficiency, with a total phenolic content of more than 25 mg of gallic acid equivalents (GAE)/mg and a chlorogenic acid content of more than 10 mg/g, respectively. The highest antioxidant potential was also observed in the samples from MAE (the FRAP value ranged from 173 to 185 µmol Fe2+/g, and the DPPH inhibition ranged from 55 to 59%), which was consistent with the extraction results. Although the phenolic antioxidants of sea fennel have been extensively studied recently, to the authors’ knowledge, this study was the first to evaluate the application of the new techniques for their isolation and to show the advantages of MAE compared to the other techniques used.