Enhancing the dispersion and dissolution of substrate particles in substrate/water suspen- sion is a feasible way to improve steroid bioconversion. The aim of the present study is to investi- gate the effects of applying surfactant to microbial conversion system on the dispersion, solubiliza- tion and in turn bioconversion of steroid substrate. The model system is hydroxylation of substrate 16α-, 17α-epoxy-4-pregnene- 3 ,20-dine by microbial enzymes from Rhizopus nigricanl. The results show that the presence of substrate leads to an increase in critical micelle concentration ( CMC) of surfactant PSE compared with the normal CMC of PSE in aqueous solution. The grinding time dur- ing substrate suspension preparation affects the substrate aqueous solubility differently with the va- ried surfactant concentrations while barely making any difference in substrate solubility in the ab- sence of surfactant. The properly prolonged grinding time can make up for the loss in substrate so- lubility arising from the reduction in surfactant concentration. The surfactant complexes composed of surfactants PSE and MGE at appropriate ratios are screened out with orthodoxy experiment meth- od, the interaction between PSE and MGE exerts the most prominent effects on substrate biocon- version. and the surfactant complexes show more beneficial effects on steroid bioconversion than the surfactant PSE used alone.
