Effect of ethanol on the synthesis of large-ring cyclodextrins by cyclodextrin glucanotransferases

Cyclodextrin glucanotransferase (EC 2.4.1.19, CGTase) synthesizes cyclodextrins (CD) composed of 6 to more than hundred glucose units from amylose by an intramolecular transglycosylation reaction. The addition of ethanol to the reaction medium resulted in an increase of the yield of large-ring CD obtained with a CGTase from Bacillus sp. BT3-2 and Bacillus macerans. The presence of 15% ethanol in the reaction mixture with the CGTase from Bacillus sp. BT3-2 resulted in a 30% increase of the amounts of CD10-CD13 synthesized after 5 h of reaction. The addition of 20% ethanol increased the yield of CD14-CD21 up to 1000%. The hydrolysis of the large-ring CD by the CGTases was suppressed in the presence of ethanol. The ring-opening coupling cyclization reactions of the CGTase were effected differently by the organic solvent which may contribute to the observed increase of the yield and size of the CD obtained in the synthesis reactions.