Growth characteristic, mono-strain mass culture and antioxidant effects of two benthic diatoms Amphora coffeaeformis and Achnanthes longipes from Korea

Abstract

Amphora coffeaeformis and Achnanthes longipes are commonly found as dominant benthic microalgae in Jeju coastal water throughout the year. In order to investigate pharmaceutical uses of these diatoms, each single species was isolated with micropipette under phase contrast microscope and subcultured with artificial seawater media which was enriched with F/2 media, trace metal solution and meta-silicate anhydrous crystal (Na2SiO3). Growth characteristics of these species were also determined with different combination of salinity, nutrients concentration and temperature. Thereafter, mass culture of each species was done based on the maximum growth condition. Biomass was collected after two weeks of mass culture and freeze dried for antioxidant study. The antioxidant properties of different fractions (n-hexane, chloroform and ethylacetate) obtained by solvent fractionation of 80% methanolic extract of two microalgae were investigated for free radical, reactive oxygen species scavenging (Super oxide, Hydrogen peroxide, Hydroxyl radical and Nitric oxide), metal chelating and lipid peroxidation inhibition activities. All fractions of A. longipes showed higher DPPH• (free radical) scavenging activities (n-hexane: 89.0%, Chloroform: 76.0%, Ethylacetate: 66.0%, Methanol: 90.6% and aqueous residue: 63.0%). N-hexane fraction of A. longipes showed significantly higher activity (49.0%) on nitric-oxide. Ethyl acetate fraction of A. longipes and aqueous residue of A. coffeaeformis exhibited 64.0% and 75.6% metal chelating activity which was higher than commercial antioxidants (-tocopherol: 18.0% and BHT: 16.0%). The n-hexane fraction of A. coffeaeformis had 67.5% activity on DPPH•. Chloroform and n-hexane fractions of A. coffeaeformis exhibited 46.2% and 47.6% H2O2 scavenging effects which were closely similar to commercial antioxidants (-tocopherol: 49.2% and BHT: 58.6%). Chloroform and ethyl acetate fractions of A. longipes and fraction of n-hexane