Study On Enzymatic Saccharification And Fermentation Of High-dose Irradiation Pretreated Corn Straw

Biofuels and biochemicals derived from renewable resources have becoming an urgent alternative due to the dilemma of fossil-based fuels and environmental deterioration in recent years.Lignocellulose is a natural rich resource.However,there are many challenges about new technology development and cost-effective process to make an industrial-scale production of lignocellulose ethanol because of its recalcitrant structure.Compared with traditional pretreatment,there are many advantages while using irradiation to treat natural cellulose.It results in degradation of cellulose featured by the decrease in the degree of polymerization,and loose in the structure,increases in the effective reaction area.With the corn straw,the paper studied the new saccharification technology which integrated 1200kGy60Co-?high-energy irradiation with cellulase hydrolysis,and the fermentation process were studied and optimized.The main research results are listed as follows:To study the optimal ratio of enzyme complex formulation,1200kGy60 Co ?-ray irradiation corn straw as raw material,the response surface methodology was applied for analyzing the cellobiohydrolase,the endoglucanase,the?-glucanase and the xylanase.The reducing sugar content was extremely significantly by xylanase dosage but not significantly impacted by cellobiohydrolase,?-glucanase and endoglucanase.The optimum conditions for supplemental levels were found to be hydrolysis at cellobiohydrolase ratio of1.07U/g,endoglucanase ratio of 31.53U/g,?-glucanase ratio of 20.81U/g,xylanase ratio of81.96U/g.The reducing sugar content under these conditions was 372.624mg/g.In order to learn the enzymatic hydrolysis characteristics of irradiation pretreated corn straw by cellulase,the effects of substrate concentration,cellulase concentration,temperature and pH were determined.The kinetics of the hydrolysis reaction could be described with the Michealis-Menten equation,and the hydrolysis reaction obeyed the classical first-order reaction rate in the first three hours.The michealis constant(Km)and maximum rate(Vm)were 8.27g/L and 1.472g/L·h.The kinetic model,including the parameters such as substrate concentration,enzymatic concentration and temperature,was suit for the hydrolysis reaction under the temperature range from 303.15-323.15K(30?-50?).Experimental results showed that with the addition of Tween-80 and PEG6000 cannot raise enzymatic hydrolysis of irradiation corn straw,only improve the initial speed of the enzyme solution.In the process of research on irradiation pretreated corn straw,effects of the three factors on enzymatic hydrolysis under different experimental levels were discussed and the optimal combination of experimental conditions was found out.The results showed thatthe optimal combination was the temperature of 52.38 ?,the added enzyme amount of226.61U/g substrate,the enzymatic hydrolysis time of 45.68 hours,under this combination,reducing sugar content reached 392.16mg/g and reached 93.3% of the theoretical valueCompare the results by fractional step saccharification and fermentation method and simultaneous saccharfication and fermentation method,we can find that SSF has some advantages.After a series of single-factor experiments to optimize the fermentation conditions of ethanol production using irradiation pretreated corn straw by SSF method,the optimum fermentation conditions are as follows:the initial pH value 5,substate and yeast concentration12%.The maximum ethanol concentration reached 9.863g/L obtained after 52 hours SSF of irradiation pretreated corn straw under the optimized conditions.