The Biotransformation Research Used Corn Cob As Raw Materials Into Xylitol

The biotransformation research used corn cob as raw materials into xylitolXylitol as one of intermediate products of glucose metabolism in the human body,is widely used as a functional sweeteners.In addition,xylitol can improve liver function,therapy acute and chronic hepatitis,acute myocarditis,diabetes,renal failure,etc.It is also used widely in chemical industry,light industry and national defense and other fields.China is a large agricultural country,which products corncob more than 1000 million tons per year,but most of these resources are not fully utilized,and even resulted in different levels of environmental pollution.So how to use these plant fiber resources effective has become one of the important studies for many countries.Expansion of production of bioethanol utilizing lower-value lignocellulose offers a great potential for not only reducing the production cost but also protecting the environment as it produces far less air pollutants than gasline.D-Xylose is the most abundant monosaccharide in lignocellulose hydrolysate after glucose.Consequently,ethanolic fermentation of xylose is of major concern for the efficient utilization of lignocellulosic hydrolysates to produce fuel ethanol.Therefore,to obtain a bacterial strain that can largely use xylose to produce ethanol is always a hot topic within this area.This study was based on microbiology theory.According to habitation of xylose zymogenic,a bacterium,which can ferment xylose to product ethanol,was filtered from natural environment.It was identified by analyzing its physiological and biochemical characteristics and applying several molecule biological means.Then the parameters of technique of fermenting xylose to product ethanol were optimized,to lay a foundation of the cellulose to the alcohol production technique.The main content of this research is as follows.1.After the first riddled of proliferation cultured,separating 36 kinds of bacteria,and then through the resumption of screening and the cell transformation,we found the capacity to product xylitol of the strain e was significantly higher than other strains,whose rate of xylose transformed is 18%,so we select the strain e for further study.Strain e is typical yeast colony morphology,its cell short-oval to spherical,budding reproduction,no ascospores,no ballistospore,formation a large number of pseudohyphal hypha in the coverslip on corn meal agar culture medium.Strain e can assimilate potassium nitrate,ethanol,but cannot produce like-starch.2.Applying modern molecular biology techniques to classify and identify the screened strain e,the results as follow:strain e is the Trichosporon coremiiforme of trichosporon.The registration number of nucleotide sequence of its D1/D2 of rDNA genes is FJ491404 in GenBank.3.Obtained fermentation xylitol best conditions through single-factor test on the shake-flask are as follows:carbon concentration of 40g / 1,nitrogen concentration of 6 g / 1, pH 7,inoculation size 6%,and liquid 60ml,and selected seed age is 23 hours,37℃fermentation for 4 days.4.Based on the single factor experiment,we do orthogonal test,which optimum conditions are carbon source concentration,40g/l;nitrogen source concentration,6g/l;initial pH,7.0;inoculum size,6%,the same to the single factor experiment,under this optimum condition,the conversion rate of xylitol reaches 69.1%.By optimizing the design,the conversion rate of the xylitol advanced 51.1%than initial.The conversion rate of Trichosporon coremiiforme is no significant differences compare to the yeast strains used for xylitol fermentation at domestic and abroad.However,in low-carbon source concentration, Trichosporon coremiiforme has particularly high conversion rate,but the corn cob,straw and other crops after the initial degradation has the low concentrations of monosaccharide,so Trichosporon coremiiforme is more suitable for the biological transformation of the initial degradation products of the corn cob,straw and other crop,which is important in comprehensive utilization of waste and environmental protection.5.In the production process from corn cob to xylose,pretreatment have an important impact on the production of xylose,and bacterial B7 pre-treats corncob for 2 days more appropriate,which process of the optimum content of corn cob is 10%.Through the pretreatment,hemicellulose conversion rate increased from 7.64%to 18.14%,rised 10.5%. Although hemicellulose is not very high conversion rate,only 18.14%,and xylose output is only 6.92g / 1,but the double strains step-by-step approach has a great development prospects, because the method uses two types of bacteria,bacteria B7 and Aspergillus niger,with the advantages of simple raw materials and low cost compare to the traditional enzyme approach and high-temperature cooking method and has the environment protection superiority.Besides this,the double strains step-by-step approach utilizes the scrap corn cob,reached the goal of waste utilization.We believe that after further study,double strains step-by-step approach will attain the satisfactory results in all respects.In this paper,we screen out the strain using xylose produce xylitol,confirm the appropriate conditions for xylitol production,and through corncob xylose conversion to a preliminary study,create the double strains step-by-step approach,based for the multi-strains treatment method.Applying the double strains step-by-step approach not only solve the com cob environment pollution problem,but also obtain high output of xylitol,so it has practical application of high significance.