GROWTH CHARACTERISTICS AND ANTIOXIDANT PROPERTIES OF THE BENTHIC DIATOM NAVICULA INCERTA (BACILLARIOPHYCEAE) FROM JEJU ISLAND, KOREA1

Benthic diatoms are a commonly used food source in shellfish aquaculture. Diatoms of the genus Navicula are the most abundant benthic diatoms occurring year-round on the coast of Jeju Island, Korea. We isolated an axenic strain of N. incerta Grunow; estimated its growth characteristics under 27 different combinations of temperature, salinity, and nutrients; and determined its biochemical composition and antioxidant activities. The maximum specific growth rate (lmax), defined as the increase in cell density per unit time, was 0.81‐1.04 AEd )1 , and the maximum cell density, 7.99 · 10 5 cells AEmL )1 , was reached at 0.88 AEd )1 lmax ,2 0� C, 30 psu salinity, and F ⁄2 nutrient concentration on day 12 of the culture period. The approximate cellular composition was as follows: 7.0 ± 0.04% protein, 1.7 ± 0.28% lipid, 12.8 ± 0.85% carbohydrate, 68.4 ± 0.09% ash, and 10.1 ± 0.44% moisture. The antioxidant properties of N. incerta were determined for various extracts. The rates of 1,1-diphenyl-2-picrylhydrazyl (DPPH) free-radical scavenging for Neutrase and methanol extracts were 81.6% and 62.8%, respectively. Flavourzyme extract had a superoxidescavenging rate of 57.7%. Kojizyme and Ultraflo extracts had nitric-oxide-scavenging rates of 42.2% and 40.6%, respectively, significantly higher than commercial antioxidants, such as a-tocopherol and butylated hydroxytoluene (BHT). The metalchelating activities of the methanol, Neutrase, and Termamyl extracts were 68.5%, 45.2%, and 41.2%, respectively, four to six times higher than commercial antioxidants. The Termamyl extract showed the highest linoleic acid peroxidation inhibition, exceeding a-tocopherol and on par with BHT.