The Optimization Of Pullulan Polysaccharide Extraction Process In Aureobasidium Pullulans And Development Of Food Preservative Film

Pullulan polysaccharide is a kind of polysaccharide polymerized from Maltotriose.In this thesis,the fermentation broth of Aureobasidium pullulans was used as raw material to optimize the extraction process of Pullulan polysaccharide.Subsequently,the structural analysis of the extracted sample was carried out and the result showed that the sample was the Pullulan polysaccharide.Then the optimization and characterization of pullulan polysaccharide composite membrane were studied.Finally,the application of several composite membranes in fresh-cut apple preservation was compared.The main contents are as follows:(1)The suitable flocculants were optimized and selected from four kinds of biomolecular flocculants through the flocculation and sterilization of biomolecular flocculants.The results showed that chitosan flocculation had the best antibacterial effect.Chitosan flocculation was optimized by the single factor experiment and response surface experiment.The optimum bactericidal conditions were determined as follows:p H was 3.7,time was 20 mins,the temperature was 40℃,chitosan content was 0.96 g/L,the bactericidal rate was 99.19%.Under this condition,the polysaccharide yield could reach91.3%.(2)The isoelectric point of the protein was tested from p H range 7.0～9.0 by the isoelectric point-enzymatic deproteinization method,and the sieve protease was optimized from six proteases.The results showed that p H 8.2 was the optimized isoelectric point of the protein,and the deproteinization rate was 76.84%.The deproteinization efficiency of alkaline protease was the highest.The deproteinization process of alkaline protease was optimized by the single factor experiment and response surface.The best deproteinization condition was p H 8.6,45℃,2.5 h,alkaline protease 83 U/m L,under which the deproteinization rate was 74.70%,and polysaccharide yield was 98.42%.(3)Through the decolorization of macroporous resin and optimizing the selection of resin from 9 kinds of macroporous resin,the results show that the l X-68M resin decolorization effect had the best performance.The decolorization process was optimized by the single factor experiment and orthogonal experiment.The optimal decolorization conditions were as follows:adding 4 g/40 m L resin,20℃,p H 3.0,2 h,220 rpm shaking adsorption decolorization,under which the decolorization rate was 87.88%,and the polysaccharide yield was 88.80%.After the dynamic decolorization experiment,the optimal flow rate was 5 BV/h,the loading volume was 15 BV,and the decolorization rate and polysaccharide rate were 82.51%and 90.39%respectively.The regeneration and adsorption kinetics of macroporous resin was further studied.The results showed that macroporous resin could be reused 4 times after soaking for 2 h with 4%Na OH.The decolorization of Pullulan polysaccharides by LX-68M accords with the Freundlich equation,and the adsorption kinetics of pullulan polysaccharides in the decolorization process mainly accords with the chemical reaction model.(4)Preparation and performance optimization of pullulan polysaccharide composite membrane were determined by using carrageenan,liquid paraffin,glycerin,tween 80 as raw materials,and pullulan polysaccharide were mixed and modified by physical blending.The effects of these four raw materials on the properties of Pullulan polysaccharide membrane were also determined,especially the water resistance,for selecting the best composite ratio of the film.The optimized condition was that pullulan concentration was2.0%(m/v),carrageenan concentration was 0.5%(m/v),liquid paraffin content was 0.5%(m/v),glycerol content was 0.2%(m/v),and tween content was 0.3%(m/v).Under these conditions,the measured water vapor transmittance is 0.38(g·mm/m~2·h·k Pa),water solubility is 48.44%,swelling is 471.54%,elongation at break is 16.88%,and tensile strength is 33 Mpa.(5)The property characterization of Pullulan polysaccharide composite membrane was analyzed by fourier transform infrared spectrometer,thermograying analyzer,and the scanning electron microscope.The results showed that each component is not simply superimposed but with the interaction force to ensure the mechanical properties,stability,and hydrophobic properties of the composite membrane.(6)Pullulan polysaccharide composite membrane was used to preserve fresh-cut apples.The composite membrane was used to cover fresh-cut apples and store them at 4℃.The physical and chemical indexes of fresh-cut apples were determined during storage.The results indicated that the film mulching treatment could maintain the color of fresh-cut apples,slowing down the decrease of titratable acid,increasing the soluble solids,inhibiting the weight and Vc content loss,and increasing the propylene glycol(MDA)content,which had application potential in fresh-cut fruits.