Study On Lactic Acid Production From Acidic Catalyzed Steam Exploded Corn Stover By Bacillus Coagulans

Lactic acid and its derivatives are widely used as important organic and finechemicals, among which the polylactic acid used in the manufacture ofbiodegradable materials is the latest and most potential.Currently,the main methodof lactic acid production was microbial fermentation of starch and other food cropsin domestic and foreign. Taking into account the food security issues in China,todevelop biomass lactic acid is of special significance. In this paper,the acidic steamand thermophilic strains of Bacillus coagulans S44exploded cornstalk residue wereselected as raw material and fermentation strains respectively,to study how toefficiently convert lignocellulosic material to lactic acid. Acidic steam explosion ofcorn straw has a higher enzymatic hydrolysis yield,Bacillus coagulans as the strainsof lactic acid fermentation from biomass have industrial application, with theadvantages of high temperature, anaerobic fermentation and L-lactic acid opticalpurity.The main content and results are as follows.In this thesis,firstly the HPLC method for simultaneous determination oforganic acids and sugars in lactic acid fermentation broth from biomass wasestablished. Bio-Rad Aminex HPX-87H was used at column temperature of55oC,themobile phase was5mmol/L sulfic acid solution with flow rate of0.6mL/min, andthe samples were determinated by refractive index detector (RID).The resultsshowed that six organic acids and three sugars in fermentation broth werecompletely separated and determined in17minutes. The linear regression equationwere above0.99997.Under the optimized condition, the recoveries of Rhizopusoryzae and Bacillus fermentation broth at two different spiked levels ranged from96.91%-103.11%,with the relative standard deviations (RSDs,n=6) of0.9568%-4.6144%.By single-factor experiments and Plackett-Burman experimental methods, theconditions (culture conditions and medium factors) for the production of L-lacticacid fermented by thermophilic strains of Bacillus coagulans S44were optimizedand screened.The seed culture of strain S44was12h.Optimum fermentationconditions were as follows: initial pH7.2, the fermentation temperature and cultureshaker were at50°C and180rpm respectively. Fermentation medium to obtain thebest combination by response surface design were(g/L): glucose85,yeast extractpowder2.5,corn steep liquor powder1.2,(NH4)2SO43.0,KH2PO40.22,MgSO47H2O0.4,MnSO4H2O0.03, FeSO47H2O0.03,CaCO370。 Under these conditions,85g/Lglucose was exhausted by72h fermentation,lactic acid production increased from59.09g/L to73.95g/L,25.2%more than the original. The sugar consumption reached 100%, among which86.75%of sugars were converted to lactic acid yield.7L fermenter experiment was be advanced on the basis of shake flaskexperiments,the influence of fermentation pH and feeding on lactic acid productionwas investigated.The results show that:pH of6.3is most suitable for fermentation.85g/L glucose was exhausted by48h fermentation,lactic acid concentration reached71g/L,the lactic acid yield was88.75%. There is a certain degree of substrate inhibitionwhen initial glucose concentrations is above100g/L,fed-batch can effectivelyreduce the substrate inhibition and increase the sugar concentration for fermentation.By a two-batch fermentation of sugar with total concentration of110g/L for72h,L-lactic acid concentration reached82g/L,compared with batch experiments (58g/L), increased by41.38%,the lactic acid yield was75.92%.The study on the technology for the preparation of lactic acid from acidiccatalyzed steam exploded corn stover lactic acid is carried out.Acidic catalyzedsteam exploded corn stover is mainly composed of cellulose and lignin and showed agood effect on enzymatic hydrolysis.With83g/L cellulose concentration,48henzymatic hydrolysis led to85.02%glucose yield and91.14%saccharification yieldusing15FPU/g cellulase and30CBU/g β-glucosidase;PEG addition not only canenhance enzymatic saccharification, but also can reduce the amount of enzyme33.3%. When initially cellulose concentration is110g/L,the highest reducing sugarconcentration of102g/L was obtained for48h hydrolysis in presence of PEG6000,which could be used to lactic acid fermentation directly.This result suggested thatpolyethylene glycol assisted hydrolysis can promote high concentration hydrolysisof acidic catalyzed steam exploded corn stover.Moreover,because of a high sugarconentration, the concentrate step of sugar could be omitted before fermentationprocess and the cost of production could be effectively reduced.Finally, Lactic acid fermentation was investigated using enzymatic hydrolyzateof acidic catalyzed steam exploded corn stover by Bacillus coagulans S44.Ourresluts showed that Bacillus coagulans S44could utilize a variety of carbohydratefrom enzymatic hydrolyzate of acidic steam explosion of corn stalk residue. After72h shake flask fermentation, glucose,cellobiose and xylose utilization reached76.23%,91.37%and100%.At same time,the lactic acid concentration was50.83g/L.7L fermenter batch fermentation experiments showed that4L enzymatichydrolyzate was fermented within42h and the fermentation liquor contained1.07g/L glucose,2.31g/L cellobiose,0.17g/L xylose and61.28g/L L-lactic acid.Feeding0.8L2times concentrated hydrolyzate and continuing to ferment72h, L-lactic acidproduction reached75.03g/L.8.34g/L glucose,1.92g/L cellobiose, and0.16g/Lxylose was remained.As to fermentation with residue the enzymatic hydrolysis ofcorn stover was carried in the fermenter for48h. When the glucose concentrationreached85.64g/L, the inoculum was added to ferment. Lactic acid concentration of57.21g/L and glucose conversion rate of74.11%were reached at72h.