Immobilized Cyclodextrin Glycosyl Transferase for the Continuous Production of Cyclodextrins

Cyclodextrin glycosyl transferase (E.C: 2.4.1.19) from Bacillus, macerans and from a Bacillus sp. isolate was immobilized by two methods, viz. to epoxy-activated Sepharose and to alkylamine silica treated with glutaraldehyde. Because of the ready availability, low cost ($0.01/g), good surface area (30 M²/g) and ease of operation of a continuous cylindrical reactor, the high silica fabric was chosen. The immobilized enzyme had a pH optimum shifted to the alkaline side (from 6.5 to 7.5) and had a reduced temperature optimum (from 60°C to 50-55°C). Reuse efficiency showed 65% reduction in the overall activity of the immobilized enzyme after 10 cycles of 48 h each. Continuous operation at 55°C of a cylindrical reactor of 141 ml capacity, using the immobilized enzyme (80 g of high - silica fabric containing 114 mg of purified enzyme) gave a maximum productivity of 10.2 g of cyclodextrins L^-1 h,^-1, at a dilution rate of 0.32 h^-1 and a substrate concentration of 20 g L^-1. The half life of the biocatalyst was found to be 22 days, which could be further improved by using a lower operating temperature. Over the useful life time of the immobilized biocatalyst (22 days), the total Cyclodextrin produced was of the order of 88 Kg.