Study On The Immobilization Of Furctosyltransferase And Process Of Fructooligosaccharides

Fructosyltransferase was immobilized with Sodiumalginate to produce fructooligosaccharides(FOS). The preparation of free enzyme selection of carrier, optimization of immobilization,properties of immobilized enzyme and continuousproduction of FOS were mainly investigated in this thesis.Introcellular fructosyltransferase was extracted from the cells of Aspergillus niger with ultrasonic treatment, and the ratio of extraction was up to about50%.Sodiumalginate was selected as a carrier to immobilize fructosyltransferase through absorption and cross linking..400U enzyme per g Sodiumalginate was immobilized for10h at30℃and pH5.5, then crosslinked with0.75%(final concentration)glutaraldehyde for8h at4℃. The highest enzyme activity retained30.2%. The optimum temperature and pH of the immobilized fructosyltransferase were50℃and5.5, respectively,whereas for free enzyme,were50℃and5.0. Thermal and pH stability were both improved by immobilization comparing with the free enzyme. The Kmvalue was0.52mol/L(for sucrose), which was2times higher than that(0.29mol/L)of the free enzyme. This indicated that the affinity between enzyme and substrate decreasedsignificantly.The highest efficiency of production of FOS(50.34%, based on total sugar),using acolumn packed with immobilized fructosyltransferase,was obtained with50%(w/w) sucrose at a flow rate of0.48ml/min at50℃. The volumetric productivity in the reactorwas222.91g FOS/1/h.Influenced by the inhibition from glucose and the invertasefrom Aspergillus niger,the concentration of FOS in the reaction mixture was relativelylow(about50%).After continuous operation of the column packed with immobilized enzyme over13days(more than8h per day),87%of initial enzyme activity was kept. The half-life ofthe immobilized enzyme at50℃was estimated to be21days. Mainly because of thehigher concentration of substrate(50～60%)and operation temperature (50℃), nomicrobial contamination was found during production of FOS(about one month).Inaddition,the mechanical strength of the immobilized enzyme was unchanged.