Study Of Separation And Purification Of Corn Syover Xylo-Oligosaccharides By Membrane Technology

In the separation and purification technology of straw functional oligosaccharides, membrane separation technology because of its low cost, high efficiency, energy saving and other characteristics is widely used in food processing, pharmaceutical and biochemical fields, and attract the attention of the majority of researchers. This study described efficiency and feasibility of membrane technology in separation and purification of straw functional xylo-oligosaccharides(XOS).This paper studied the effects of different pretreatment methods on the purity of xylan, isolation and purification of xylan extract and oligosaccharide solution with different ultrafitration and nanofiltration membrane conbined with activated charcoal.(1) Corn straw as raw materials, comparing the effect of different processes pretreatment, then obtaining xylan main components and impurity content, included colored solute, soluble lignin, salt and other impurities through alkaline extraction could provide the basis for subsequent impurity.(2) The effects of nanofiltration molecular weight cut-off(MWCO) on desalination ratio and recovery ratio of xylan were investigated. When desalination ratio was 94.08% with the DK1812(MWCO150-300), the tatal sugar loss ratio was only 10.53%, showing a high separation efficiency.(3) Nanofiltration and nanofiltration combined with activated charcoal, respectively using straw xylan extract and xylanase enzymatic hydrolyzate as raw materials, the optimal decolorization condition was explored in alkali extraction of xylan solution:activated charcoal dosage of 0.03-0.04 g/mL, temperature of 60-70?, pH of 4, the adsorption time of 40 min.Purification of XOS was done using activated charcoal column.Comparison of different types of activated charcoal, under the same conditions AC-6 dry wood charcoal (powder) showed better performance. When using activated carbon to purificate XOS, adsorption ratio of dry wood charcoal was 84.41% as determined by HPLC.The XOS could be fractioncated by degree of polymerrization according to ethanol concentration in the ethanol/water. When the higher molecular weight XOS, the greater the degree of polymerization, the higher the concentration of ethanol needed to be eluted from the surface of activated carbon.(4) The effect of different MWCO of ultrafiltration membrane on total sugar transmittance,retention, membrane fouling and membrane flux in xylan extract were investigated. The results showed that 3.5 kDa MWCO ultrafiltration membrane, permeate flux decayed with time runned slow.20 kDa MWCO ultrafiltration membrane in low transmembrane pressure (TMP) had high flux, but flux decayed rapidly within a short time. For large aperture membrane, part of xylan molecules entered into the membrane pore causing blockage of membrane pores, the permeate flux decreased rapidly, even increasing TMP, flux increased slightly but would quickly decay again. Therefore, from the viewpoint of flux decaying, small MWCO ultrafiltration membrane is superior to large one.By comparing the clean effect of different cleaning agents,it was concluded:with a compound cleaning agent of NaOH solution (pH10.5-11.5) after 1 h, the ultrafiltration membrane flux recovery ratio increased,10 kDa MWCO ultrafiltration membrane flux recovery ratio was not better than the other two ultrafiltration membranes, MWCO to 3.5 kDa ultrafiltration membrane was best.