The Production Of Isomaltooligosaccharides By Immobilized Aspergillus Niger Or Immobilized α-Transglucosidase

The production of isomalto-oligosaccharides by immobilized Aspergillus niger cell produced a-transglucosidase and immobilized the enzyme was investigated respectively in this paper.Aspergillus niger cells produced a-transglucosidase were entrapped in polyvivyl alcohol ( PVA )—cryogel beads by a freezing-thawing method. Due to the povosity of PVA—cryogels, high molecular-weight substances can penetrate beads of the biocatalyst. The immobilization in cryoPVA-gel stabilized the enzyme and ensured high mechanical and chemical stability of the biocatalyst, which could be used many times for α-D-Glucopyranoside hydrolysis. Various characteristics of immobilized cells such as thermal and pH optimum, pH and thermal storage stability were evaluated. Among them the pH optimum of free and immobilized cell were found to 6.0 and the thermal optimum of free cell was 55℃ whereas that of immobilized cell was 60 ℃. Immobilization increased in V_m value from 1.17 to 2.84 ( μM / min· g cell ) and the K_m value of immobilizeda-transglucosidase (11.88 mM ) was higher than that of free enzyme ( 20.50 mM ). It was observed that operational, pH, and thermal stabilities of the membrane-bound enzyme were increased with immobilization. The yield of isomalto-oligosaccharides catalyzed by immobilized cell ( 70.7% ) is as much as that of isomaltooligosaccharides catalyzed by free cell ( 71.9% ). And yield of effect contants is54.11% with immobilized cell, which is a little lower than that of effect contants with free cell (57.1%).Many different methods have been used to immobilizeda-transglucosidase but either the yields of immobilization were low or immobilized enzyme was not stable or last a large portion of activity within a short time. The only successful method for immobilization of a-transglucosidase was entrapment in alginate beads, a-transglucosidase was immobilized into alginate beads coated with chitosan film, where the protein is remained in a liquid core. Various characteristics of immobilized a-transglucosidase such as pH and thermal optimum, operational stability were evaluated. Among them the thermal optimum of free and immobilized a-transglucosidase were found to 65 °C and the pH optimum of freea-transglucosidase was 5.0 whereas that of immobilized a-transglucosidase was 5.5. Immobilization increased in Km value from 9.3 to 12.7 (mM/min- mg protein) and the Vm value of immobilized a-transglucosidase (0.63 mM) was lower than that of free enzyme (0.81 raM ). It was observed that pH, operational, thermal and storage stabilities of ,the enzyme were increased with immobilization. The yield of isomaltooligosaccharides catalyzed by immobilized enzyme ( 49.92 % ) is lower than that of isomaltooligosaccharides catalyzed by free enzyme ( 65.26% ). But yield of effect contants is 44.10% with immobilized cell, which is not lower than that of effect contants with free cell ( 42.28% ).