Study On The Response Of Three Newly Isolated Filamentous Microalgae To Light Intensity And Nitrogen Concentration And The Oxidation Resistance Of Lipid

Nowadays,most of the microalgae used for commercial application are single-celled microalgae,the high energy consumption of harvesting is one of the main reasons hindering the industrialization of microalgae.Compared with single-celled microalgae,filamentous microalgae have longer algal filaments,which could not only resist the consumption of zooplankton,but also improve the harvesting efficiency of algal,thus reducing the production cost of microalgae.Hence in this study,three newly isolated filamentous microalgae were used as experimental materials to study the growth,physiological and biochemical regularity under different conditions of light intensity,initial nitrogen concentration and medium,the strain possess highest productivity of lipid was screened,amplified it in the plate reactor under optimum culture condition,then expand extract lipid,the oxidation resistance assay of lipid was carried in the end.The following experimental results are mainly obtained:(1)Zygnema sp.JNU40 belongs to Zygnema,Zygnematophyceae,Streptophyta family.The effects of two different light intensities(100 and 300?mol/(m~2·s))and six initial nitrogen concentration gradients(3,6,9,12,15 and 18 mmol/L)on the growth and biochemical composition of Zygnema sp.JNU40 are investigated.The highest biomass was observed at 300?mol/(m~2·s)light intensities and 12 mmol/L initial nitrogen concentration culture condition, which was 6.60 g/L.The 3 mmol/L initial nitrogen concentration was conducive to the accumulation of total lipid and fatty acids of Zygnema JNU40,and the highest total lipid content reached 32.13%of total dry weight.The main components of fatty acid were palmic acid,oleic acid,linoleic acid and?-linolenic acid,and the oleic acid content accounted for 55.01%of total fatty acid.Under 100?mol/(m~2·s)light intensities culture condition,the highest protein and carbohydrate content was obtained under 18 mmol/L initial nitrogen concentration,which was16.35%and 37.70%of total dry weight,respectively.Meanwhile,the total lipid content accounted for only 10.16%of total dry weight.(2)Barranca multiflagellata JNU39 belong to the Barrancaceae fam.nov.,Chaetophorales,Chlorophyceae family.The effects of three different light intensities(100,300 and bilateral light illumination of 300?mol/(m~2·s))and seven initial nitrogen levels(1,3,6,9,12,15 and 18 mmol/L)on the growth and biochemical composition of B.multiflagellata JNU39 are investigated.The results showed that,under bilateral light illumination of 300?mol/(m~2·s)culture condition,the highest biomass was observed at 9 mmol/L initial nitrogen concentration,which was 6.92 g/L.The1 mmol/L initial nitrogen concentration was conducive to the accumulation of lipid and fatty acids,and the highest total lipid content reached 53.13%of total dry weight.The main components of fatty acid in B.multiflagellata JNU39 were palmic acid,oleic acid,linoleic acid and eicosaenoic acid,and the maximum content of oleic acid accounted for 60.80%of total fatty acid,the highest absolute content accounted for 25.44%of the total dry weight.B.multiflagellata JNU39 turn to red in the later period of culture and pigment analysis showed that it could accumulate high content of canthaxanthin and lutein.The highest content of canthaxanthin and lutein reached 1.50 mg/g and 3.33 mg/g,respectively.In addition,under 100?mol/(m~2·s)light intensities culture condition,the highest protein and carbohydrate content was obtained under 18 mmol/L initial nitrogen concentration,which was 20.89%and 37.43%of total dry weight,respectively.Under 100?mol/(m~2·s)light intensities culture condition,the highest protein and carbohydrate content was obtained under 18 mmol/L initial nitrogen concentration,which was 20.89%and 37.43%of total dry weight,respectively.(3)Klebsormidum sp.JNU41 is aerial filamentous microalgae,belongs to genus Klebsormidium,Streptophyta family.The alga was grown with modified BG11 and BBM medium under three light intensities(100,300 and bilateral light illumination of 300?mol/(m~2·s))and six initial nitrogen concentration gradients(3,6,9,12,15 and 18 mmol/L).Under the conditions of m BBM medium and bilateral light illumination of 300?mol/(m~2·s),the maximum biomass reached 8.38 g/L when initial nitrogen concentration set 6 mmol/L;total carbohydrate content reached a maximum of36.96%of total dry weight.Under the conditions of m BG11 medium and bilateral light illumination of 300?mol/(m~2·s),the maximum total lipid content reached 55.12%of total dry weight when initial nitrogen concentration set 6 mmol/L;the main components of fatty acids were palmitic acid,oleic acid,linoleic acid and linolenic acid,the highest relative content of linoleic acid was 65.87%of total fatty acids,and the highest absolute content accounted for 30.21%of total dry weight;the highest total protein content was 37.69%of total dry weight;the maximum lutein content reached 1.64 mg/g when initial nitrogen concentration set 15 mmol/L.(4)By comparing the yield per unit volume of total lipids in different filamentous microalgae under different conditions,the optimal alga strain was Klebsormidum sp.JNU41,and the optimal culture condition was bilateral light illumination of 300?mol/(m~2·s)and 6 mmol/L initial nitrogen concentration on the m BBM medium.Then amplified culture K.flaccidum JNU41 by plate reactor,which the highest biomass was 5.34 g/L.In the optimization experiment of lipid extraction,it is found that under ultrasonic pretreatment,the extraction solvent was 10%DMSO anhydrous ethanol:hexane(1:2,v/v),and the extraction rate was 82.31%.The antioxidant and free radical scavenging experiments were carried out on the extracted,it was found that the antioxidant and free radical scavenging ability of the oil were positively correlated with the concentration and showed strong ability in scavenging ABTS~+and OH~-free radicals.On the whole,Klebsormidum sp.JNU41 has the advantage of strong photosynthetic efficiency,fast growth,easy cultivation,easy harvest,and could obtain the competitive yield of lipid and linoleic acid,which is expected to become a new plant resource for mass production of linoleic acid.