Optimization Of The Lipid Extraction Method And Oil-rich Culture Conditions Of Nannochloropsis Sp.

Algal oil extraction method and oil enriching algal culture conditions were optimizedwith Nannochloropsis sp. cultured in flat plate photobioreactors. Influences of solvents,fragmentation ways, extraction times and extraction temperatures on the extraction rate ofalgal oil were compared. The differences of the specific growth rates, maximal cell densitiesand biomasses under the culture conditions of different illuminations, temperatures, salinities,nitrogen concentrations and optical paths of reactors were compared. Products, harvestedfrom the stationary phase culture under different culture conditions, were analyzed on thecontents of polysaccharide, soluble protein, pigments, and lipid. Orthogonal experiments weredesigned and carried out for optimization of the culture conditions of enriching oil inNannochloropsis.The results showed that the influence of different extraction solvents, fragmentation ways,extraction times and extraction temperatures on extraction rates of algal oil were different.The influence of the extraction solvents was the highest, followed by the extractiontemperatures, extraction times, fragmentation methods. The best method of oil extractionfrom Nannochloropsis was optimized as follow: industrial alcohol was the best extractant; andrepeated freezing and thawing,2h extraction time,65℃extraction temperature. Under theseconditions, the oil extraction rate of Nannochloropsis was34.62%. The method from thisexperiment coule be used to the oil extraction from high density microalgae.Different culture conditions had different influence on the growth of Nannochloropsis.The influence of illuminations on the growth of Nannochloropsis was very significant(p<0.01). The illuminations within1000lx and50000lx, the specific growth rate, maximalcell densities and biomasses increased at first and reached the maximum under20000lx, thendecreased. The results indicated that the high illumination can significantly promote thegrowth of Nannochloropsis. High illumination could induce the increase of the cell densityand biomass. Temperature had a significant effect (p<0.05) on the growth of Nannochloropsis.In the range of temperatures set by the experiment, Nannochloropsis grew normally. Thespecific growth rate, maximal cell densities and biomasses reached the maximum under30℃,then decreased. Too high and too low of the temperature were not conducive to the growth ofNannochloropsis. The optimal temperature was28-32℃. Salinity had a significant influence on the growth of Nannochloropsis (p<0.05). During the range of10‰-30‰of salinity,Nannochloropsis could grow. The specific growth rate, maximal cell densities and biomassesincreased with the increase of the salinity during this range. When the salinity was40‰, thegrowth and cell density of Nannochloropsis decreased, and all of the parameters had sharplydeclined. The influence of nitrogen concentration on the growth of Nannochloropsis was verysignificant (p<0.01). The nitrogen concentration was set within o mmol/L and3.53mmol/L.The specific growth rate increased at low concentration of nitrogen and reached the maximumunder2.35mmol/L nitrogen. The cell density and biomass increased at first and reached themaximum under1.18mmol/L. Conclusion including the economic factors, the optimalnitrogen concentration maybe1.18mmol/L. The optical path of photobioreactors had a verysignificant effect on the growth of Nannochloropsis (p<0.01). The optical path within5cmand20cm, the specific growth rate, maximal cell densities and yield per unit volumedecreased; the yield per unit area increased. Within the optical path set by the experiment, theoptimal optical path was5cm.Under different culture conditions, the contents of organic matters in cells ofNannochloropsis were different. In different illumination conditions, with the enhancement oflight intensity, the contents of crude fat and polysaccharides increased at first and thendecreased. The maximal contents of them were reached under2000lx. The contents ofsoluble protein and carotenoids increased at first then decreased, and reached the maximumunder5000lx. The content of chlorophyll increased with the increasing of the light. Underdifferent temperature conditions, within20℃and32℃, the contents of crude fat andchlorophyll decreased; the content of carotenoids increased; the content of soluble proteinincreased at first and then decreased, the maximum was reached under28℃; the content ofpolysaccharides decreased at first and then increased, and the maximum was reached under20℃and32℃. Under different salinity conditions, with the increase of salinity during10‰-30‰, the contents of crude fat, chlorophyll and carotenoids increased; the content ofsoluble protein increased at first and then decreased, and reached the maximum under30‰;the content of polysaccharides increased at first and then decreased, and the maximum wasreached under20‰. The difference of protein contents between10‰and20‰groups werenot significant. Under different conditions of nitrogen concentrations, the contents of crude fatand soluble protein decreased with the increased; in contrast, the contents of polysaccharides and chlorophyll increased with the increase of nitrogen concentration; the content ofcarotenoids increased at first and then decreased, and reached the maximum under2.35mmol/L. Comparison of the influence by the optical path within5cm and20cm, thecontents of crude fat, soluble proteins, and polysaccharides decreased; but the contents ofchlorophyll and carotenoid increased. The increase trend of carotenoids was more obviousthan that of chlorophyll.Among various factors, the effect of illumination on the content of crude fat was thegreatest, and then followed by the temperature, the nitrogen concentration and optical path.The results showed that the best culture conditions of Nannochloropsis were:5cm optical pathof photobioreactor,5000lx illumination,24℃temperature, and deficiency of nitrogen. Underthis culture conditions, the content of lipid could reach46.72%of dry weight of the cell. Theresults of this experiment provided a reference value for the practical application of oil-richcultivation of Nannochloropsis.