Study On Screening Of High-yielding Xylitol Strain And Fermentation Technology

The xylitol has many kinds of physiological functions that it can suppress the dental caries, as the nutrition auxiliary therapeutical agent and liver-protecting medicine of diabetic patient.So it was widespread applicated in domains of food, medicine and chemical industry. In this study, biological conversion method was introduced to transform the hemicellulose of vegetable fiber's to xylose, which was transformed to xylitol with the high added value in zymotechnics. Massive farming and forestry vegetable fiber waste will be used effectively. It has important meaning in effective use of plant resources and the environmental protection. This article is mainly worked on assay of strains preserved in our lab, chemistry mutagenesis was used to screen high production strain of xylitol, and the enlargement experiment of this strain was carried out in this research, the result can be described as follows:1.Strain CTD249 was studied by a series of morphological physiological and biochemical characteristics It was found that the bacterium are ovoid or spherical in microscope, contain green ascospore, no throw spores, could assimilation ethanol, do not produce amyloid compound, cannot decompose urea to amine, urease negatie yeast, It can grow in 50% high permeable culture and produce bubbles when ferment glucose and sucrose.2.The molecular biology techniques were introduced for identification of strains CTD249. Extracting ITS sequence genes and sequencing, the results show that the partial sequence of the strain was 544bp (GenBank accept number:HM236292), BLAST analysis was adopt according to the sequencing result of the strains CTD249, The strains CTD249 have high similarity with Pichia guilliermondii and the similarity reaches above 99%, and have the most closest relationship with FJ662408.1,So this strain was identified as Pichia guilliermondii.3.Using the nitrosoguanidine chemical mutagenesis methods to enhance xylitol yield. The chemical mutagenesis results show that:the best diluted times of NTG for 10-4, three rounds NTG optimal adding quantities for 0.14 g/L,0.15 g/L,0.16 g/L. Through the three rounds nitrosoguanidine (NTG) mutation breeding the to get the highest yield xylitol strains, mutations G15 xylitol yield for 16.48 g/L, increasing 4.63 g/L to the former bacteria, revealing better genetic stability in five generations.4.Enzyme extraction method was introduced to extract the crude xylan in corncob, Single factor and the response surface analysis method were used to optimize the hydrolysis process conditions of corncob, determining the optimal conditions:enzyme additive amount 834u/g, hydrolysis time 11.7 h, pH 5.4, hydrolysis temperature 45℃.under the conditions, the hydrolysis content of xylose is 12.30 mg/mL.5. Optimizing xylitol fermentation medium condition and components based on amplifying fermentation medium test.Through single factor optimization and response surface analysis method to determine the optimal condition of xylitol fermentation medium.The best condition:Inoculation quantity by 10.6%, pH 4.7, fermentation time 67.4 h, best combination of xylose medium components:xylose for 33.9 g/L, KH2PO4 for 1.1 g/L, (NH4)2SO4 for 0.5g/L,MgSO4 for 0.5g/L. In the optimized conditions, the maximum value of xylitol for 25.02g/L, xylose conversion rate for 83.43%.The intermediate culture result of 5L fermenter that the best time to produce xylitol is 72h.