INFLUENCE OF SOME OPERATIONAL PARAMETERS ON THE BIOCONVERSION OF SITOSTEROL WITH IMMOBILIZED WHOLE CELLS IN ORGANIC MEDIUM

Mycobacterium sp. NRRL B-3805 cells immobilized on Celite were used to selectively cleave beta-sitosterol to 4-androstene-3,17-dione (AD), w ith bis(2-ethylhexyl)phthalate as the bioconversion medium. The amount of water retained in the immobilization matrix proved to be a key par ameter for biological activity retention, 0.5 to 0.8 g water/g dry sup port giving the best results. Mechanically stirred batch reactors were effectively used for sterol biotransformation, no increase in bioconv ersion rates being obtained for stirring speeds above 100 rpm. Kinetic studies were performed with beta-sitosterol concentrations up to 30 m M, with different support particle sizes. Kinetic control of the biotr ansformation process becomes apparent for support particle sizes below 0.12-0.2 mm. (C) 1998 Elsevier Science B.V. All rights reserved.