Xylanase-polymer Conjugates Of W/W Droplet Microfluidic Interfacial Catalysis And Its Application

Interfacial catalysis has advantages of good thermal stability,easy to separate and recycle.It is a kind of high-efficiency catalysis process,which plays an important role in alleviating energy shortage and producing value-added chemicals.However,problems such as limiting interface area,wasting of catalysts and reagents,and reducing catalytic efficiency have severely restricted its industrial application.Therefore,the mode of enzymatic hydrolysis of natural xylan to produce xylooligosaccharides(XOS)was chosen in this thesis.Enzyme-polymer conjugates as interface stabilizers and catalysis were prepared,and a method of W/W droplet microfluidic interfacial catalytic system was constructed to improve the efficiency of interfacial catalysis and obtain high value-added XOS.The main research contents are as follows:(1)XYL-PNIPAAm conjugates biocatalysts were prepared.The N-isopropylacrylamide(NIPAAm)monomer was grafted from xylanase by the grafting-from technology of atom transfer radical polymerization,and xylanase-poly(N-isopropylpropene)conjugates(XYL-PNIPAAm conjugates)were constructed.The results showed that XYL-PNIPAAm conjugates prepared by atom transfer radical polymerization method had a complete protein structure.PH and temperature stability of XYL-PNIPAAm conjugates were increased by24.19% and 20.40% than free xylanase respectively.XYL-PNIPAAm conjugates maintained more than 60% activity after being reused 5 times.Therefore,the stability and reusability of XYL-PNIPAAm conjugates prepared were effectively improved.(2)A new process of Polyethylene glycol(PEG)/Dextran(DEX)Pickering emulsion interfacial catalysis with XYL-PNIPAAm conjugates was established.XYL-PNIPAAm conjugates instead of traditional surfactants were used to construct W/W Pickering emulsion stabilized by XYL-PNIPAAm conjugates.The results showed that when XYL-PNIPAAm conjugates concentration was 20 mg/m L and p H was 6-8,a stable W/W emulsion was obtained with the droplets size of 124.70±10.10 μm.The yield of reducing sugar was reached 78.32% when the reaction condition was at 50 ℃,p H 6,and substrate concentration3%,which was 1.2 times higher than that of the W/W interfacial catalysis process.In addition,XYL-PNIPAAm conjugates maintained 60% activity after recycling for 8 times,indicating that the XYL-PNIPAAm conjugates of W/W emulsion interfacial catalysis system had advanced in emulsion stability,catalytic efficiency and reusability.(3)A process of XYL-PNIPAAm conjugates of W/W droplet-based microfluidic interfacial catalysis was constructed.With PEG as the dispersed phase and DEX as the continuous phase,a W/W droplet-based microfluidic operating system was constructed.The results showed that W/W droplets with controllable sizes were formed when the flow rates of the continuous phase and dispersed phase were 0.29-0.48 μL/min and 0.52-0.80 μL/min respectively.The droplet diameter was power-law related to the radio of the two-phases flow rates from 22.00 μm to 139.00 μm,and the stability of droplets was 15 times higher than the W/W Pickering emulsions.The XOS yield reached the maximum at 75.03%(9.62 mg XOS/m L)under the condition of p H 5,50 ℃ and substrate concentration of 1%,which was 1.25 times higher than W/W Pickering emulsion interfacial catalysis system.In addition,the XYL-PNIPAAm conjugates maintained 60% activity after recycling for 10 times,indicating that XYL-PNIPAAm conjugates of microfluidic interfacial catalysis effectively-highly improved the catalytic efficiency.(4)A system of XYL-PNIPAAm conjugates of W/W droplet-based microfluidic was first applied to the preparation of XOS from mulberry bark.Xylan of mulberry bark was extracted with Na OH solution,and the xylan was hydrolyzed by XYL-PNIPAAm conjugates of W/W droplet microfluidic system.The results showed that the reducing sugar yield was 72.43%,the catalytic rate was increased by 5 times,and the catalytic efficiency was increased by 5.25 times.In addition,a less distribution of XOS(X1,X2 and X3)in mulberry bark was obtained,which was conducive to the later separation and purification.It showed that XYL-PNIPAAm conjugates of W/W droplet microfluidic interfacial catalysis process had the feasibility of high-efficiently degrading natural xylan to prepare XOS.In conclusion,a process of XYL-PNIPAAm conjugates of W/W Pickering emulsion interfacial catalytic was successfully constructed.Around the preparation of enzyme-polymer conjugates,the process of W/W Pickering emulsion interfacial catalysis with XYL-PNIPAAm conjugates,the technology of W/W droplet microfluidic interfacial catalysis,XOS from mulberry bark were successfully prepared,providing a new method for the preparation of XOS by industrial biocatalysis and a new idea for the development and utilization of lignocellulose.