| Eicosapentaenoic acid(EPA)is a kind of polyunsaturated fatty acids that cannot be spontaneously synthesized in the human body.And the intake of EPA can effectively reduce the risk of cardiovascular disease and cancer.Nannochloropsis sp.is considered to be one of the most appropriate microalgae for large-scale production.Due to its advantages in high photosynthetic efficiency,fast growth rate,high EPA content,and easy expansion of production,the Nannochloropsis sp.has attracted wide attention in the current researches of algae lipid production.However,there still exist certain limitations during the process of producing EPA-rich lipid from microalgae,such as low EPA yield,difficulty in lipid extraction,and large losses in refining process.In this context,this thesis focused on the Nannochloropsis sp.and conducted in-depth research on microalgae cultivation,lipid extraction,cell disruption,lipid refining,and evaluated the economic benefits of the lipid production from microalgae.First,ultrasound and addition of polyethylene glycol were leveraged to increase the EPA productivity of Nannochloropsis sp.in the cultivation process.Besides,the influence of temperature was investigated.The results showed that lowering the temperature in an appropriate range could increase EPA productivity,and 18? was the best setting point,which yielded a result of 30.81 mg/(L·d).The results also dedicated that ultrasound for 1 minute per day or the addition of 2%polyethylene glycol could increase the EPA productivity by about 20%.Second,extrusion technology was applied to break the cell wall of Nannochloropsis sp.to increase the extraction efficiency.Through the optimization of the extrusion conditions,the result showed that several principal parameters,such as ?)the die structure;?)the distance between the screw and the die(?),and ?)the water content of the material,both had a significant impact on the extrusion effect.Extrusion treatment ruptured most of the Nannochloropsis sp.cells,thus reduced the time of the lipid extraction and the usage of solvents,which also had a positive impact on the quality of the lipid.Besides,the extraction solvents of microalgae oils were screened,and the fixed bed was applied in process of the microalgae lipid extraction.The results showed that the low-toxic hexane/ethanol solvent could replace the chloroform/methanol solvent with an extraction efficiency of over 95%.The new extraction process of fixed bed combined with extruded microalgae could obtain an improved lipid yield of 21.55%with a low solvent consumption of 2.17 mL/g and a short time of 2 h.Then,modified Fick's law model was leveraged to fit the extraction process of neutral lipids,glycolipids,and phospholipids in n-hexane or ethanol.The results indicated that after the microalgae cell wall broke,the lipid diffusion coefficient increased by 4 orders of magnitude.When n-hexane was used as the extraction solvent,the diffusion speed of neutral lipids was significantly faster,2 to 4 times higher than that of glycolipids and phospholipids.When ethanol was used as the extraction solvent,there was little difference in the diffusion coefficient of different lipids.Based on the differences of different lipid diffusion coefficients,a sequential extraction with two steps was employed to obtain lipid products.In the first step,extraction with n-hexane was conducted for 15 minutes,the result showed that the lipid contained 45%?50%of neutral lipids.In the second step,extraction with ethanol was conducted for 60 minutes,and obtained a lipid with phospholipid content of 47%-50%.The packed bed maceration extraction method could be adopted in the two-step extraction process,which had the advantages of convenient operation and low solvent consumption.Thin-layer chromatography combined with gas chromatography was utilized in order to clarify the composition of the crude lipid obtained by n-hexane/ethanol from Nannochloropsis sp..The results showed that the total content of glycerides in crude lipid reached 51.49%,and the more content components were monogalactose diglycerides(MGDG,14.03%),triglycerides(TAG,9.27%),and phosphatidylethanolamine(PE,6.22%),digalactose diglyceride(DGDG,5.81%),free fatty acid(FFA,5.79%),phosphatidylcholine(PC,3.53%).Fatty acid composition analysis showed that EPA was mainly distributed in polar lipids,mainly in the form of MGDG,DGDG,and PE.Next,this thesis employed microcrystalline cellulose as the adsorbent for deacidification treatment.The effects of ultrasonic,microwave,and alkali treatments on microcrystalline cellulose were investigated in the case studies.The results showed that alkali treatment caused significant changes in the structure and properties of microcrystalline cellulose,such as destroying hydrogen bonds,decreasing crystallinity,and increasing chemical reactivity.Compared with other adsorbents,the alkali-treated microcrystalline cellulose had a good adsorption and deacidification effect,with a 95.11%lipid recovery rate and a 97.83%phospholipid preservation rate,respectively.Compared with traditional alkali refining,the lipid recovery rate and phospholipid preservation rate of adsorption deacidification by alkali-treated microcrystalline cellulose were higher,which was helpful for retaining more EPA in the lipid.Finally,this thesis investigated the economic effects of EPA-rich lipid production from Nannochloropsis sp.based on the production data from the algae factory and the pilot test results.The estimated cost of EPA-rich microalgae lipid was 170.96 yuan/kg,of which the cultivation cost accounted for the largest proportion,accounting for 33.77%of the total cost,followed by the microalgae harvesting(22.23%)and drying steps(19.41%),respectively.Through market research,the market value of this algae lipid was about 300-400 yuan/kg,indicating that the production process proposed in this thesis had good economic benefits and was appropriate for large-scale production. |
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