Corncob NaOH Pretreatment and Ethanol and Xylitol Preparation by Simultaneous Saccharification and Fermentation
Corn cob was pretreated with NaOH.Then,Candida tropicalis was inoculated separately,C.tropicalis and Saccharomyces cerevisiae were inoculated simultaneously,and C.tropicalis and S.cerevisiae were inoculated step by step.They were subjected to simultaneous saccharification and fermentation to produce ethanol and xylitol.The results indicated the high temperature and alkaline conditions could result in a large loss of cellulose and xylan.The alkaline conditions at suitable temperature could retain all cellulose and most xylan,remove almost all lignin,and improve enzymatic hydrolysis rate of cellulose.When corn cob was treated with sodium hydroxide solution at 100 ℃,there was no loss of cellulose,the hydrolysis efficiency of cellulase was greatly improved,and 64.5％xylan could be recovered.Inoculating C.tropicalis only and increasing the amount of cellulase could promote the production of ethanol and weaken the production of xylitol.The simultaneous inoculation of C.tropicalis and S.cerevisiae could promote the production of ethanol and xylitol.The production of xylitol could be further promoted by inoculating C.tropicalis and adding xylanase 24 h before adding S.cerevisiae and cellulase.Adding 90 U xylanase and 10％(based on the total volume of fermentation broth)C.tropicalis seeds to 10 g pretreated corn cob(with concentration of 200 g/L),24 h later adding 20 FPU/g cellulase(based on cellulose)and 10％(based on the total volume of fermentation broth)S.cerevisiae seeds,38.4 g/L ethanol and 15.4 g/L xylitol could be produced.
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