Optimization Of Culture Conditions Of Nannochloropsis Sp.and Extraction And Alcoholysis Of Algal Oil

Functional oils and biodiesel have always popular in the research and development microalgae applications.The former is a class of oils rich in polyunsaturated fatty acids,and is considered to be a“golden oil”beneficial to human health,the latter refers to regenerated fatty acid methyl ester or ethyl ester,a kind of new fuel for environmental and resource sustainability.In this paper,the improved f/2 medium was used to investigate the biomass and oil production of six strains of N.sp.FJ-5,and the best algae strain was screened for the further work.Then,the dynamical model of growth and product accumulation of N.sp.FJ-5 under different culture conditions were established using a bubble column photoreactor.After that,a three-phase separation technology?TPP?for extracting oil from algae powder was optimized by single factor analysis.The oil-containing organic solvent separated by TPP is further utilized to optimize the conditions of oily alcoholysis using liquid lipase TL IM?TL?.The main contents and results of this paper are as follows:1.Six strains of Nannochloropsis sp.were cultured in modified f/2 medium,and their biomass,chlorophyll a,oil,protein and polysaccharides contents were compared and analyzed.The results show that strain N.sp.FJ-5 has a great potential in various aspects of growth and products accumulation.After ten days of culture in nitrogen-containing medium,its biomass was 0.49±0.01 g L^-1,the chlorophyll a content is 3.67±0.08 mg L^-1,and the oil content is 33.27±0.72%.After four days of culture in the nitrogen-deficent medium,the biomass decrease slightly to 0.46±0.01 g L^-1,and the chlorophyll a content didn't change significantly,which was 3.79±0.02 mg L^-1,and the oil content increase to 35.10±1.12%.The soluble protein content of the collected algal power was 6.15±0.27 mg g^-1,and the polysaccharide content was 29.55±1.63 mg g^-1.The total fatty acids in per gram of algal power can reach to 328.80±39.03 mg,and the saturated fatty acids and unsaturated fatty acids accounted for 41.6%and 58.4%of total fatty acids respectively,of which EPA accounts for 13.7%.2.The dynamical models between growth and product accumulation of N.sp.FJ-5under autotrophic and mixculture conditions were quantitatively established by using a bubble column photoreactor and adding glycerol as a carbon source.The experimental results show that the increase of glycerol concentration in the concentration range of 0⁴g L^-11 glycerol has a significant effect on the growth of N.sp.FJ-5 and the synthesis of total fatty acids?TFAs?.Compared with the biomass of 5.01 g L^-11 under autotrophic culture conditions,the biomass can be increased up to 6.22 g L^-11 under the mixculture condition of adding 4 g L^-11 glycerol.In addition,the effect of glycerol on TFAs production was more obviously,the TFAs content only reached 0.59 g L^-11 under autotrophic conditions,and 1.77 g L^-11 under the mixculture conditions of adding 4 g L^-1glycerol.The experimental data were then subjected to dynamical models analysis,and the results showed that the model fitting goodness R² high than 0.9,excepting for that in4 g L^-11 glycerol culture where the sodium nitrate consumption model had the R² of 0.86.The results therefore suggested that Logistic and Luedeking-Piret equation as well as the equation models for substrate consumption could fit well with the growth of N.sp.FJ-5,the accumulation of TFAs and the consumption of sodium nitrate.3.The method of extracting algae oil from algae powder was optimized using a new three-phase paration technology?TPP?with K₂HPO₄-ethanol system to make algae oil separated from algae powder to greater extent,and the material-buffer ratio is 1:30,the mass of K₂HPO₄ is 30%of the buffer volume,the volume of ethanol is twice the volume of the buffer,and the best temperature is under 80°C.318.60 mg of crude oil can be extracted from each gram of algal powder.The optimal extraction reaction conditions were applied to the algae powder of N.sp.FJ-5 collected by the bubble column photoreactor,and the changes of oil accumulation and fatty acid composition under different glycerol concentrations were compared.The results showed that the addition of1 g L^-11 glycerol in the medium was beneficial to the accumulation of oil,the oil content reached to 65.05%,higher than the 61.21%in the non-glycerol group,and the higher glycerol concentration inhibited the accumulation of oil.When the glycerol concentration was increased to 2 g L^-11 and 4 g L^-1,the oil content decreased to 43.49%and 34.97%.From the perspective of fatty acid composition and content,the addition of glycerol has no effect on the fatty acid composition,but it is worth noting that the amount of glycerol added has a great influence on the EPA content.As the glycerol concentration increases,the EPA content gradually decreases.4.The suitable conditions for alchholysis of algae oil under excessive ethanol environment were preliminarily investigated by using lipase TL.The optimum conditions were as follows:the enzyme loading was 1%of the system,the water content was 0.5%of the system,the reaction temperature was 30?,and the reaction time was 6 h.The higher alcoholysis rate obtained was 76.35%.