Biosynthesis Of β-glycanase And Screening Of Yeast For Xylitol Production From Corn-cob Hemicellulose Enzymatical Hydrolysate

Enzymatical hydrolysis of xylan-rich lignocellulosics followed by fermentation is one of the most important paths to produce xylitol. With pretreated com cob as carbon source and inducer, impacting factors of β-glycanase production by Trichoderma viride LH-011 were systematically studied in this thesis. Moreover, enzymatical hydrolysis of corn cob hemicellulose and screening of xylitol-producing yeast for fermentation of the hydrolysate to xylitol were primarily explored.The experimental results show that the kind and concerntration of carbon source, the kind of nitrogen source and the C/N , the initial pH value and the culture temperature all have some effects on the biosynthesis of β -glycanase. When 15g/L pretreated com cob used as the main corbon source and inducer, mixed (NHU^SQj and urea and peptone as nitrogen source,regulating C/N 6. 4, initial pH value 4. 8, volume charge 50mL in 250 mL flask, 150 r/min, 32±1 ℃ the first 24 hours and 28±1℃ the rear, the CMC-ase activity and the xylanase activity respectively reached 3.76 U/ml and 13.95 U/ml after 96 hours cultivation.The corn-cob hemicellulose hydrolysation has been done under the following conditions: the substrate concerntration was 25g/L, the pH value 4.8, self-made β -glycanases dosage 10% (v/v), 50± water bath,80r/min. As a result, the reducing sugars concentration reached 15.24 g/L after 12 hours and almost kept constantly, and glucose accouting for 3.13%, xylose 19.17% and xylo-oligomers 45.75% oCandida tropicalis AY 91009 was selected by commercial xylose culture medium from the seven xylose-fermenting yeast strains bought from Institute of Microbilogy of Chinese Academy of Science and China Center for Type Culture Collection, which was then adapted to the corn-cob hemicellulose enzymatic hydrolysate (CCHEH) .Through eight-generation gradient CCHEH medium culturing, Candida tropicalis LH-081, a good xylitol-producing strain ,was screened and isolated by high concerntration xylose plate,, Primary study on bioconverting CCHEH into xylitol was carried out using Candida tropicalis LH-081 by 250ml flask batch fermentation process.The best results, a xylitol yield of 0.50g/g reducing sugar with an reducing sugar utilization efficiency of 28.7% , were achieved under the following conditions: reducing sugars concentration of CCHEH 15.24g/L, loading volume 100ml, nitrogen source 1.5g/L yeast extract and 1.5g/L peptone, initial pH value 5.4, inoculum size 10%(volume ratio), the first 24 hours, 160 r/min and the later 48 hours, 100r/min , culture temperature 28±1 ℃ .The result show that bioconversion the CCHEH into xylitol is not a very efficient but a very promising way. in order to realize the simultaneous saccharification and fermentation of the corn-cob hemicellulose for xylitol production, some more things must be done.