Study On The Xylitol Fermentation From Hemicellulosic Hydrolysate

Hemicellulose is a cheap and renewable resource.By contrast with the traditional chemical process,the bioconversion of hemicellulosic hydrolysate to xylitol is a cheaper alternative, and its moderation reaction condition,low energy requirements and environment friendly.To study the key factors in the preparation of hemicellulosic hydrolysate and detoxification,the C. tropicalis electing with induced and educated, xylitol fermentation parameters optimization,decoloration and desalination of ferment liquid and crystal craft of xylitol.Aiming at the problem of harm entironment grievously by the method of acid hydrolyzation,investigating the use of none chem. reagent-physics method:extrusion expansion pretreats the corncob together with steam explosion. In the practice, the optimal processing is as the following:boil the corncob at170℃for2hours after extrusion expansion, and the total content of sugar dissolved reaches19.35%.By way of contrast,counteract methods,evaporation,activated charcoal absorption and anion-exchange resins treatment could remove a given amount of inhibitor.The results have indicated that counteract followed by evaporation could remove51.79%acetic acid and70.65%furfural in hemicellulosic hydrolysate.This process can effectively reduce the detoxification treatment costs, prospect broad industrial applications.For obtaining the C. tropicalis on high xylitol yield, using physics and chemic measure to induce and educate.It is found that xylitol yield is increased5～6%by using ultraviolet radiation inducing70s.At one time, educating the C. tropicalis on three modes that is suitting to the ferment circumstance of hemicellulosic hydrolyzation, high concentration of xylose and low nitrogen fountain and abio-salt to gain the excellent one.The material is high consistency xylose of hemicellulosic hydrolysate with the detoxification craftwork,in the ferment circumstance of low nitrogen fountain and abio-salt,to optimize and investigate the barmy temperature, the quantity of nitrogen fountain and abio-salt buffering, pH value, aeration rate,barmy time,seed condition and inoculation quantity.Researching in sway bottle and ferment jar,the optimum fermentation conditions by C.tropicalis were as follows:xylose concentration:120g/L; yeast cream:0.8～1.0%; corn slurry:2.00%;30℃; initial pH value:6.00,tree-steps dissolved oxygen controlling in ferment craft optimize the ventilated quantity and time. The maximum xylitol yield of corncob hemicellulosic hydrolysate,with and without anion- exchange resins,are76.5%,66.4%,volumetric productivities are2.16g/L/h,2.05g/L/h. The results in similar studies and reports are advanced.Recycling Cells was proved to be an effective method to produce xylitol,the cells have new characteristics in growth and metabolize. To optimize and investigate the initial pH value, the quantity of nitrogen fountain and abio-salt buffering,oxygen accommodate, batch-barmy time and temperature,and obtain the craft of fed-batches fermention in xylitol production that every other supplied the common fermentation culture medium,the other only supplied half of the common fermentation culture medium,the changing craft could gain the well and stable results.The average xylitol yield and batch-barmy time are74.3%and63.8%,43.4h respectively. Cells immobilized on polyurethane foam of the ferment, the average xylitol yield and batch-barmy time are77.13%,66.8%and41.3h respectively.The cells are able to bear the stayer of the hydrolysate, the cost of the product is saved,the cycle of the ferment is shortened,the efficiency of the ferment is enhanced,there is much worth in the practice.Xylitol crystal from ferment liquid is an important step. Activated carbon GH-86performed best in decoloration. The decolored ratio reaches93.6%and the loss of xylitol is3.9%,when using2%, at70℃for50mins. The decolored xylitol ferment liquid is treated with the ion-exchange resin732, then, anion-exchange resin D261, on2BV/h flux to desalt98%salt,the decolored ratio reaches98%together with the activated carbon.The loss of the xylitol is less than8%and the absorption of the remnant sugar is more than30%.0.1%crystal seeds are brought into the condensed xylitol broth after disposal.-10℃preservation for32h.The obtained xylitol crystal has regular tetrahedral shape, its purity reached98.8%.the yield is60.2%.