Comparison of Different Organic Solvents on Antioxidant Activity of Astaxanthin Extracted from Hematococcus pluvialis Using Colorimetric and Non-colorimetric Methods

Astaxanthin is a polar compound with a strong color which might contribute to its reported antioxidant activity as most antioxidant tests are colorimetric assays. The aim of the study was to compare the antioxidant activity of astaxanthin extracted from Haematococcus pluvialis using colorimetric and non-colorimetric methods. The astaxanthin extract was dissolved in solvents with different polarities (40% acetone, dimethyl sulfoxide or methanol). Antioxidant potential was assayed using 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP) and hydroxyl radical scavenging activity (HRSA). Results showed that dimethyl sulfoxide (DMSO) sample had the highest antioxidant activity in DPPH (IC70 = 12.9 mg/ml) and FRAP (389.4 +/- 0.05 mu M TE/g) assays. DMSO was significantly lower than 40% acetone (p<0.05) in Hydroxyl radical scavenging activity (HRSA) assay. DMSO showed highest astaxanthin recovery in high performance liquid chromatography analysis (HPLC). Colorimetric DPPH and FRAP assays gave significantly different results compared to non-colorimetric HRSA assay. This difference could be due to the solubility of astaxanthin and not due to its color.