Antioxidant Activity of Microalgae Extract Cosmarium sp. Using 2.2-Azinobis-(3-Ethylbenzothiazoline)-6-Sulfonic Acid (ABTS) Radical Cation Assay

The demand for natural antioxidants has increased due to the harmful effects of synthetic antioxidants, such astoxicity and carcinogenic properties. Microalgae face this requirement as they can produce numerous substances that havepotential as an antioxidant. This study aimed to evaluate the antioxidant activity of Cosmarium extracts using ABTS radicalcation assay and identify compounds probably responsible for it. Dried biomass was extracted using hexane, ethyl acetate,and ethanol solvents using the maceration method. Extracts were partially purified with TLC and column chromatography.Compounds identification were conducted using GC-MS analysis. The result showed that ethanol extract has the best activitywith the IC 50 at 55.95 ppm, followed by hexane and ethyl acetate extracts with IC 50 as much as 104.339 ppm and 180.07 ppm,respectively. Two active fractions were the selected fraction after partial purification with chromatographic analysis. Fraction1 gave IC 50 at 99.6 ppm while fraction 2 gave better IC 50 at 53.562 ppm, both categorized as strong antioxidants. Compoundsidentification by GC-MS revealed that both fractions contain fatty acids compounds with 9.12-octadecadienoic acid (linoleicacid) and hexadecanoic acid (palmitic acid) as the dominant compound in fractions 1 and 2, respectively. This study gaveinsight into the potential of ethanol fraction from Cosmarium sp. as a natural antioxidant.