Research On Microbial Oil Production By Oleaginous Yeast With Corn Straw Hydrolysate

Biomasses such as corn straw lignocellulose are abundant,and rational utilization of it can avoid waste of resources and reduce environmental pollution.Oleaginous yeast can convert lignocellulosic hydrolysate into microbial lipid,which can replace traditional animal and vegetable lipid for biodiesel production,and greatly reduce the cost of biodiesel production.However,the lignocellulosic hydrolysate is complex and contains many components that are nocuous for the growth of oleaginous microorganisms and lipid production.In this paper,the hydrolysis method of corn stalk hydrolysate is studied.Then according to the specific hydrolysate,we select the appropriate culture method for lipid production by oleaginous yeast.Finally,the lipid production conditions are optimized and the composition of the lipid is analyzed.For choossing proper method of preparation of corn straw hydrolysate,the corn straw hydrolysis effect of alkaline-hydrogen peroxide method,dilute hydrochloric acid method,dilute nitric acid method and dilute sulphuric acid method are compared.The yield of reducing sugar in the hydrolysis of dilute sulfuric acid is the highest.Dilute sulfuric acid hydrolysate contains 23.57 g/L reducing sugar under the condition of 2% dilute sulfuric acid at 1 h,but the existence of inhibitors and the strong acidity may affect the lipid production of the oleaginous yeast.In order to enhance the resistance of oleaginous yeast to the inhibitors,we chose mixed culture of Lipomyces starkeyi and Trichosporon cutaneum strategy to avoid the toxicity of inhibitors in dilute sulfuric acid hydrolysate.The results show that the biomass of yeast can be improved by the mixed culture strategy,but the production of lipid is low.Therefore,the method of the study is not suitable for the conversion of straw dilute acid hydrolysate to lipid,and anti-toxic production strategy is not further studied.For the strong acidity of dilute acid hydrolysate,resist-acid Cryptococcus curvata is adopted to convert the hydrolysate.The results show that Cryptococcus curvata could grow in acidic environment,and its the lipid content in the p H 3 hydrolysate is higher than that in p H 4 and p H 5 in lipid fermentation medium.The optimum p H for Cryptococcus curvata growth and lipid production is p H 4.4 In the sterilized and detoxified dilute sulfuric acid hydrolysate,five main factors that affect yeast growth and lipid production are studied by single factor experiment.The orthogonal experiment suggested the single factor experiment should be carried out at 30?.The results show that 1.5 g/L of yeast extract,2 times the concentration of inorganic salt,20% of the inoculation amount and 1/4 of the liquid volume is the best lipid-production condition.After optimization,the lipid content and grease concentration are all improved and the lipid concentration increased by about 6%.The lipid produced by Cryptococcus curvata from corn straw hydrolysate contains much C16,C18 fatty acids,the lipid are similar to the vegetable oil composition,and can be used as raw materials for biodiesel.