Abstract
A pelleted morphological form of Rhizopus nigricans, which might be regarded as a naturally immobilized biomass, enabled development of a continuous process of progesterone 11α-hydroxylation in a laboratory-scale stirred tank bioreactor. β-Cyclodextrin was used to enhance steroid solubility in aqueous transformation media and consequently to increase the rate of steroid hydroxylation. Batch and continuous processes were performed with pellets of different average diameters, ranging from less than 1 mm to 7.5 mm. Mathematical model simulations of both operational modes confirmed the previously defined Michaelis–Menten kinetics for the biotransformation. A decrease in overall hydroxylation rate was noticed when pellets larger than 5 mm were used, which correlated with the lower area of outer surface of agglomerates where, presumably, most of the enzyme induction had taken place.
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