Study On Single Cell Oil Production Using Cassava Starch As Feedstock By Trichosporon Fermentans

With the problem of global energy shortage and environmental deteriorationbecome more and more seriously, development of renewable biofuels become anecessity. Oleaginous microorganisms with its high lipid content and widely carbonutilization, become a good substitute raw materials for biodiesel production. In thiswork, microbial lipids product by T. fermentans using glucose as raw material wasstudied. First, preliminary optimization of the medium was studied by Single FactorExperiment in shaker. Then, the batch and feed-batch fermentation in the2Lfermenter was investigated respectively, the biomass, lipid content were23.06g/L,68.49%and61.18g/L,45.34%. Gas chromatography analysis showed that the lipidfatty acid composition containing mainly palmitic acid, palmitoleic acid, stearic acid,oleic acid and linoleic acid, its composition was similar to vegetable fats, can be usedas the raw materials for biodiesel production.Presently, the industrial application of microbial lipids is hampered by the highcost of nitrogen-limited mediums used in microbial oil production. In order to reduceproduction costs, cassava starch hydrolysate as a fermentation carbon source wasselected to replace expensive carbon source glucose. The possibility of production ofmicrobial lipids with cassava starch hydrolysate was explored in this dissertation, andthe effects of related factors on cell growth and lipid accumulation weresystematically examined. Response surface methodology was employed to optimizethe fermentation conditions related on lipid yield (fermentation temperature, carbonand nitrogen ratio, inoculum size, pH value, rotation speed, inorganic saltconcentration), through the response surface analysis, the optimal flask fermentationconditions were obtained as follows: fermentation temperature28.78°C, C/N ratio126.18, pH6.69, inoculum size8%, rotation speed200r/min, inorganic saltconcentration of1times, the predicted value of lipid yield reached15.01g/L. Underthe optimum conditions, the average of the verification tests value was close to thepredicted value, and the lipid yield was28.61%increased under the optimizedconditions compare to the control. Then the effect of batch and fed-batch culture in2L fermenter by T. fermentans using cassava starch hydrolysate as the raw materialswas investigated. The biomass, lipid content of batch and fed-batch culture wererespectivelya as follow:26.32g/L,38.87%and78.27g/L,45.29%. Gas chromatography analysis showed that the lipids fatty acid composition containingmainly palmitic acid, palmitoleic acid, stearic acid, oleic acid and linoleic acid, whichwas similar to the composition of vegetable oils, indicating it can be used as feedstockfor biodiesel production.To further reduce production costs and improve the efficiency of lipidsproduction, the effect of adding a small amount of oxygen-vectors to enhance oxygentransfer in fermentation on cell growth and lipid accumulation by T. fermentans wasstudied.1%(v/v) n-dodecane was selected to be better adding volume, and base onthe flask fermentation, the application of oxygen-vectors in2L fermenter forfed-batch fermentation was preliminary studied. When the application of theoxygen-vector fed-batch in2L fermentor, biomass, lipid content were greatlyimproved to be102g/L and50.85%respectively. Gas chromatography analysisshowed that the lipid fatty acid composition containing mainly palmitic acid,palmitoleic acid, stearic acid, oleic acid and linoleic acid, which was similar to thecomposition of vegetable oils, indicating it can be used as feedstock for biodieselproduction.The study is of great significance for reducing the cost of production of microbiallipids, helps to solve the bottleneck problem of lipids raw material which hinders thelarge-scale production and wide application of biodiesel.