Effect of extraction solvent on total phenolic content, total flavonoid content, and antioxidant activity of Bulung Sangu (Gracilaria sp.) Seaweed

Bulung sangu ( Gracilaria sp.) is commonly consumed as vegetable in Bali. Bulung sangu as other red macroalgae ( Rhodophyta ) is a source of beneficial nutrient for health. In this study, water and various concentrations (50%, 75% and 100%) of methanol, ethanol, and acetone in water were used as solvent in extraction of bulung sangu. The antioxidant activity, total phenolic content, and total flavonoid content of crude extract of bulung sangu were investigated using various in vitro assay. The extract obtained by 75% of aqueous methanol produced higher extraction yield (27.390 ± 0.414 %). Highest total phenolic content was obtained by the using 100% of acetone (36.738 ± 1.062 mg galic acid equivalent/g ). The extract obtained by 100% of ethanol showed highest total flavonoid content (45.933 ± 0.563 mg quercetin equivalent/g). The same extract also exhibited the strongest antioxidant activity indicated by lowest half maximal inhibitory concentration (IC 50 ) (13.603 ± 0.413 µg/ml) evaluated by using DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity. This IC 50 was lower than IC 50 of ascorbic acid (18.593 ± 0.135 µg/ml). These results produce the suitable solvent in obtaining optimum phenolic and flavonoid content of bulung sangu. Likewise, the antioxidant activity results indicate that bulung sangu is useful in dietary application with a potential to reduce oxidative stress.