GROWTH CHARACTERISTICS AND ANTIOXIDATIVE STATUS OF Cylindrotheca closterium (BACILLARIOPHYCEAE) FROM JEJU ISLAND, KOREA

Abstract

Benthic diatoms are a commonly used food source in shellfish aquaculture. The Cylindrotheca closterium Ehrenberg is commonly available throughout the year with higher abundant in the winter to spring on the coast of Jeju Island, Korea. We isolated an axenic strain of C. closterium, estimated its growth characteristics under 27 different combinations of temperature, salinity, and nutrients, and determined its biochemical composition and antioxidant activities. The antioxidant properties of C. closterium were determined from the extracts of methanol, water and enzymes (protease and carbohydrase).The maximum specific growth rate (µmax), defined as the increase in cell density per unit time, was 0.63–0.97 day-1, and the maximum biomass, 7.20 104 cells mL-1, was reached at 0.82 day-1 µmax, 20°C, 30 psu salinity, and F nutrient concentration on day 10 of the culture period. The proximate composition was as follows: protein 11.11%, lipid 1.18%, carbohydrate 18.51%, ash 61.86%, and moisture 7.34%. The scavenging rates for 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical was 72.5% and 69.4% from Viscozyme and methanol extracts, respectively. The extracts from AMG and Viscozyme showed 45.8% and 45.5% nitric oxide scavenging rate which was slightly lower than the activity of -tocopherol and more than BHT, and the extract from methanol and water showed 44.8% and 44.6% scavenging rate which was statistically similar with BHT. The metal-chelating activities of the Kojizyme, Alcalase, methanol, Viscozyme and Neutrase extracts were 67.1 %, 53.9%, 53.2%, 52.1% and 50.2 %respectively, five to six times higher than commercial antioxidants. The AMG, Viscozyme and Neutrase extracts showed the highest linoleic acid peroxidation inhibition, exceeding BHT and also statistically similar with -tocopherol.