Growth characteristics and antioxidant properties of the benthic diatom Navicula incerta (Bacillariophyceae) from Jeju Island, Korea

摘要

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 (mu(max)), defined as the increase in cell density per unit time, was 0.81-1.04 center dot d(-1), and the maximum cell density, 7.99 x 10(5) cells center dot mL(-1), was reached at 0.88 center dot d(-1) mu(max) 20 degrees 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 superoxide-scavenging 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 metal-chelating 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 alpha-tocopherol and on par with BHT.