The Study On Screening Of Microalgae And Extraction Conditions Of Pigment And Polysaccharide

The microalgae has great potential in the development and application of medicine and health products, because of its characteristic of a great power in reproduction, strong adaption to environment, high photosynthetic rate and synthesizing bioactive substances of many unique physiological functions, such as microalgal polysaccharide, pigment, protein, polyunsaturated fatty acid and so on. However, people only use microalgae as the bait of fish, shrimp, shellfish or feed additive for a long time. In recent years, people gradually begin to pay attention to comprehensive utilization of microalgae, and focus on the research and development of microalgae bioactive substances.In this paper, four strains with high biomass were obtained from river and desert in Baotou and Tanggu port in Tianjin. They were named based on the morphological and molecular indentification. The culture conditions were optimized to improve the biomass. At last the microalgal pigment and polysaccharide content were measured to research the comprehensive utilization of microalgae. The major content and results of this paper are shown as follows:1. XJ004and XJ006were isolated from desert in Baotou, XJ012and XJ014were obtained form Tanggu port Tianjin. Cell of XJ004, XJ012and XJ014are unicellular, spheroidal and green. Cells of XJ006are unicellular, swelled in the middle, small in the two ends and living in groups. However the cells of XJ004will become red in late stable phase. With the morphological and molecular identification, XJ004was named Chlorella sp.XJ004, XJ006was named Scenedesmus sp.XJ006, XJ012was named Chlorococcum sp.XJ012, and XJ014was named Nannochloropsis sp.XJ014. Through comparing algae species preservation methods, one of them is able to make the algae live to be one year.2. A single factor experiment and L9(34) orthogonal experiment design was adopted to study effects of three nutrients N, P, and Mg. The best growth conditions for XJ006which was separated from desert were obtained as follows:NaNO32.0g/L, MgSO4·7H2O0.1g/L, K2HPO4·3H2O0.026g/L. At this time XJ006in optimized culture medium grew very well and OD680was2.024. To improve the extraction yield of microalgal chlorophyll, extraction solvent, extraction temperature, extraction time and the ratio of solid to liquid affecting the extraction yield of microalgal chlorophyll were optimized by using the mono-factor and the orthogonal experiment. The optimum extraction conditions were:the use of hand-grinding mortar5min, with95%ethanol as extraction solvent, the extraction temperature is40℃, the extraction time was5h, the ratio of solid was70:1, the extraction times was three. In these conditions chlorophyll extraction yield was5.403%.3. The best growth conditions for salina were obtained as follows:NaNO30.15g/L, MgSO4·7H2O5g/L, K2HPO4·3H2O0.025g/L. The salina in optimized culture medium grew very well and OD680was0.531. Through researching the affection of extraction yield of microalgal β-carotene by extraction solvent, acetone as extraction solvent was best and extraction yield was0.76%.4. The best growth conditions for XJ004were obtained as follows:NaNO30.05g/L, K2HPO4·3H2O0.1g/L, MgSO4·7H2O0.05g/L. XJ004in optimized culture medium grew very well and OD680was1.931. We can get astaxanthin from XJ004, nitrogen deficiency cultured XJ004astaxanthin concent was0.967mg/g, after a high-salt cultured astaxanthin concent was0.508mg/g, after strong light cultured astaxanthin concent was0.911mg/g. So the nitrogen deficiency was the bset way to cultured XJ004for astaxanthin.5. To improve the extraction yield of microalgal polysaccharide, alkali concentration, extraction temperature and extraction time affecting the extraction yield of microalgal polysaccharide were optimized by using the mono-factor and the orthogonal experiment. The optimum extraction conditions were:alkali concentration of0.2mol/L, extraction temperature of80℃, extraction time of180min. Under these conditions, the extraction yield of microalgal polysaccharide was up to13.94%. After optimization, the extraction yield of microalgal polysaccharide was increased by92.01%and9.76%compared with hot water extraction and alkali-alcohol extraction.