Enhanced production of diosgenin from Dioscorea zingiberensis in mixed culture solid state fermentation with Trichoderma reesei and Aspergillus fumigatus

Diosgenin is a valuable precursor for the synthesis of steroid compounds and is widely used in the pharmaceutical industry. The production of diosgenin from plant tubers by using microbial transformation is a cheap and environmentally-friendly method. However, the low efficiency of the existing fermentation protocols prevents the large-scale production required to meet the industrial demand. In this work, a solid state fermentation of Dioscorea zingiberensis was performed by using a mixed culture of Trichoderma reesei and Aspergillus fumigatus to increase the bioconversion efficiency. We optimized several parameters of the fermentation process of T. reesei and A. fumigatus monocultures using a response surface methodology. Next, we tested fermentation strategies and different ratios of T. reesei:A. fumigatus (T:A) inoculum. A maximum yield (95.82%) resulted from using a T:A ratio of 1:2 (7.5 x 10(6)T. reesei spores/g pretreated DZW) and a fermentation strategy, in which T. reesei was added at the start of the fermentation and A. fumigatus was added after 24 hours.