Using Cellusic Materials Hydrolyzed By Enzyme To Produce L-lactic Acid

L-lactic acid is one of the three organic acids which possess the largest market inthe world. Biological fermentation is a popular method of producing L-lactic acid,butits high production costs is problem. It can reduce costs to use cellulosic materialsinsteading of the carbon source in the L-lactic acid fermentation. In this paper,Lactobacillus casei NE-19was used as the original strain. Bagasse, corn stalks wereused as raw materials and cellulase and xylanase were degrading enzymes.Enzymatichydrolysis of cellulosic materials and fermentation of enzymatic hydrolyzate toproduce L-lactic acid were studied.Pretreatment experiment was studied to fiber raw material and results showed thatthe best pretreatment parameters as follows:the chemical reagent for3%NaOH,heating time for1h and solid-liquid ratio is1/20. Enzymatic hydrolysis conditionswere optimized and enzymatic hydrolysis rate could be more than88%，The maximumreducing sugar production amounted to44.3g/L when hydrolysis time was14h,temperature50℃, pH4.5, adding amount of cellulase0.3g, adding amount of xylanase0.5g and rotate speed100r/min.Composite mutagenesis of ultraviolet, nitrosoguanidine, diethyl sulfate and lowenergy ion beam were studied. A stable L-lactic acid producing strain NE-86wasobtained and its lactic acid production reached to127.2g/L, increased by15.1%thanthe original strain.Single factor of fermentation medium was optimized and the best fermentationmedium was obtained by response surface optimization: glucose112.5g/L, peptone16.0g/L, beef extract11.4g/L, yeast extract5.6g/L, anhydrous sodium acetate2.25g/L,MgSO47H2O0.1g/L, MnSO40.075g/L, CaCO360g/L, Twain-801mL and pH6.8.By above conditions, the lactic acid production reached to137.86±3.7g/L whenfermented96h and141g/L when120h, the residual sugar5.6g/L only.The results showed that cellulosic materials can be degraded by optimize the enzymatic hydrolysis process parameters.Production capacity of mutant strains wasbetter than the starting strain. The mutant strains could make good use of the reducingsugar and other substances produced by the enzymatic hydrolysis of cellulosicmaterials.