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-cyclodextrin (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 mumol of beta-CD/(min.gIE) at 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) maltodextrin 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 coefficient was 3.98, and the particle terminal velocity was 2.4 cm/s. The FBR achieved 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 24 h of reaction, namely, 10.4 mM beta-CD and 2.3 mM gamma-CD.