Evaluation of antioxidant properties and total phenolic contents of some strains of microalgae

Antioxidant activities of both cells and extracellular substances were evaluated in 12 soil-isolated strains of microalgae according to FRAP and DPPH-HPLC assays. Their total phenolic contents were also determined by Folin-Ciocalteu method. Extractions were performed with hexane, ethyl acetate, and water. The results of FRAP assay showed that algal cells contained considerable amounts of antioxidants from 0.56 +/- 0.06 to 31.06 +/- 4.00 A mu mol Trolox g(-1) for Microchaete tenera hexane extract and Chlorella vulgaris water extract, respectively. In water fractions of extracellular substances, the antioxidants were from 1.30 A +/- 0.15 A mu mol Trolox g(-1) for Fischerella musicola to 73.20 A +/- 0.16 A mu mol Trolox g(-1) for Fischerella ambigua. Also, DPPH-HPLC assay represented high antioxidant potential of water fractions. The measured radical-scavenging activities of the studied microalgae were at least 0.15 A +/- 0.02 in Nostoc ellipsosporum cell mass to a maximum of 109.02 A +/- 8.25 in C. vulgaris extracellular substance. The amount of total phenolic contents varied in different strains of microalgae and ranged from zero in hexane extract to 19.15 A +/- 0.04 mg GAE g(-1) in C. vulgaris extracellular water fraction. Significant correlation coefficients between two measured parameters indicated that phenolic compounds were a major contributor to the microalgal antioxidant capacities.