Screening, Cultivation A Marine Microalgae And Extracting Its Polysaccharide With Antioxidant Activity

Polysaccharides are biological macromolecules which mainly exist in forms of glycoproteins, glycolipids and proteoglycan, with some functions, such as anti-tumor, antioxidant, and antibacterial. They have various potential applications in medicine, food and cosmetics industries. Marine microalgae produces some intracellular polysaccharides with unique structure and function, which are different compared to those from terrestrial plants.This paper presents a study on screening, identifying a marine microalgae and then extracting its polysaccharide with ability to resist oxidation.Sea water samples were from Beihai, Guangxi Province, China. After enrichment with TAP-sea water medium,18 microalgae strains were isolated by coated and crossed isolation on the same medium with 2% agar. Among them, the BH95 was selected for its relatively short growth period, more biomass and high polysaccharide content. And then, BH95 was identified as one species of Chlorella, according to its morphological characters and sequence analysis of chloroplast rbcL gene.In single factor experiments, results showed that BH95 accumulated more biomass and polysaccharide under the conditions of photoperiod of 21:3 (lightidark, h), light intensity 4000 lux,25? and initial pH 7.0.After orthogonal experiment, the optimized medium for BH95 growth and polysaccharide accumulation included:1.08 g/L glucose,0.20 g/L urea and 0.125 g/L MgSO4·7H2O. With optimized medium and conditions, the biomass and polysaccharide content rose to 1.416 g/L and 198.050 mg/L,1.85 times and 1.58 times higher than before, respectively.The extraction of intracellular polysaccharide from BH95 cells was performed with hot alkali protocol which was optimized by response surface model. The optimized extraction protocol included:NaOH 1.60%,74.5?,3.00 h, ratio of material to liquor (m/V) 1:25; ethanol 95%, ratio of ethanol to liquor (V/V) 1:3. Under the condition, the extraction rate reached 6.811%, increased by 165.12%than before.The obtained polysaccharide was preliminary purified and subjected to antioxidant analysis. The results showed that polysaccharides in BH95 had the scavenging effect on DPPH free radical, hydroxyl free radical and had certain total reducing power. Therefore, those polysaccharides from marine microalgae BH95 had good oxidation resistance and could be used as a potential source of antioxidants.