Study of cyclodextrin production using cyclodextrin glycosyltransferase immobilized on chitosan

Abstract

Abstract Cyclodextrin glycosyltransferase (CGTase EC.3.2.1.19) was immobilized on chitosan through covalent bonding using glutaratdehyde. Various characteristics of immobilized CGTase (ICGTase) such as the pH—activity curve, the temperature—activity curve, pH and thermal stability, batch re‐usability and continuous operation stability were evaluated. Among them, the pH optimum and temperature optimum of CGTase were shifted from pH 7.5 and 55°C to pH 8.5 and 60°C after immobilization. No increase of pH stability was observed, whereas the thermal stability of ICGTase was superior to that of free CGTase. ICGTase retained 83 % of relative activity in converting liquefied starch (5% (w/v)) to cyclodextrins (CDs) under the conditions of four times of repeated use of 23 h conversion by the batch system at 55°C and pH 8.5. The half‐life of ICGTase under the same conditions by the continuous operation system was about 6 days. About 46 % of the liquefied potato starch solution (5 % (w/v)) was converted to CDs by ICGTase. Addition of ethanol in starch solution was found to increase the formation of β‐CD, and 58‐3 % yield of CDs was obtained by the addition of 16 % (v/v) ethanol in starch. The kinetic constants K m and V max of ICGTase and free CGTase were also examined.