Production of cyclodextrins in a fluidized-bed reactor using cyclodextrin-glycosyl-transferase

Cyclodextrin-glycosyl-transferase (EC2.4.1.19), produced by Wacker (Munich, Germany), was purified by biospecific affinity chromatography with beta-cy clodextrin (beta-CD) as ligand, and immobilized into controlled pore silica particles (0.42 mm). This immobilized enzyme (IE) had 4.7 mg of protein/g of support and a specific activity of 8.6 mu mol of beta-CD/(min(.)g(IE)) a t 50 degrees C, pH 8.0. It was used in a fluidized-bed reactor (FBR) at the same conditions for producing cyclodextrins (CDs) with 10% (w/v) maltodext rin solution as substrate. Bed expansion was modeled by the Richardson and Zaki equation, giving a good fit in two distinct ranges of bed porosities. The minimum fluidization velocity was 0.045 cm/s, the bed expansion coeffic ient was 3.98, and the particle terminal velocity was 2.4 cm/s. The FBR ach ieved high productivity, reaching in only 4 min of residence time the same amount of CDs normally achieved in a batch reactor with free enzyme after 2 4 h of reaction, namely, 10.4 mM beta-CD and 2.3 mM gamma-CD.