Ultrasound extraction of fucoidan and its antioxidant activities from tropical brown seaweeds

This study investigated ultrasound extraction (UE) process parameters (time and solvent) to obtain a high yield of fucoidan extracts and associated antioxidant activities from two tropical seaweeds (Sargassum binderi Sonder and Padina australis). UE parameters were time variable (30 and 60 min), solvent variable (distilled water, 2 % CaCl₂, 0.1 M HCl). Fucoidan's characteristics were evaluated for its total sugar, sulfate content, total phenolic content, and total flavonoid content. Fucoidan extracts were assessed for their antioxidant capabilities by applying 1,1-diphenyl-2-picryl-hydrazyl (DPPH), 2,2-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), and Ferric Reducing Antioxidant Power (FRAP) analyses. UE significantly improved the extraction yield in all seaweeds investigated compared to solvent extraction. Using UE, the highest yield was obtained from S. binderi Sonder using HCl for 60 min (22.40 ± 1.48 %), while the lowest yield was obtained from S. binderi Sonder using water for 30 min (6.82 ± 0.21 %). Bioactivities of fucoidan water extract from S. binderi Sonder obtained from UE extraction time of 60 min exhibited the strongest DPPH scavenging activity (% inhibition of 88.42 ± 0.90), ABTS antioxidant activity (% inhibition of 86.64 ± 0.30), and FRAP (% inhibition of 81.96 ± 0.70). UE under optimum conditions proved an efficient, cost-effective, and environmentally sustainable method for recovering physiologically active polyphenols from two species of brown seaweeds.