Abstract:

The microbial fermentation in organic-aqueous system is an effective method for the conservation of sterols into AD, but some related problems such as integrity of bacterial membrane and mass transfer resistance still have not been solved. In the present study, the Mycobacterium sp. BD696-6 immobilized on different carriers was used to convert sterols into AD. Compared to the strains immobilized on vegetable sponge, cotton yarn and bubble, the diatomite-immobilized strain resulted in the highest AD yield. Furthermore the conversion conditions of sterols by the fermentation of the diatomite-immobilized strain were optimized by orthogonal test design. The results showed that the optimal conditions were as follows: addition amount of diatomite to seed culture medium 7 g/L, inoculation amount 18% (V/V), concentration of sterols in fermentation medium 3 g/L, and fermentation time 7 d; under these conditions, the AD yield was up to 81.47%, which was 19.52% higher than that by the fermentation of the free strain.

Key words: androst-4-ene-3, 17-dione, sterols, immobilized strain, diatomite