Resumo

Proteolytic enzymes are found in all living organisms and are usually essential for microbial growth and cell differentiation. They show a widespread application in various industrial sectors, making them responsible for about 30% of total enzyme sales worldwide. Even though, thermostable proteases produced by Bacillus sp are among the most industrially important,some strategies have to be applied to attain competitive prices and to improve the yields. Therefore, the aim of this work was to evaluate the feasibility of continuous production of proteases by Bacillus subtilis using cassava wastewateras substrate. The experiments were carried out in bench bioreactor containing 2.8L of cassava wastewater and 1.2L of distilled water as culture medium, 7% (v/v) of inoculum, 4vvm of aeration, 30 ^°C and 150 rpm of agitation. The fermentations were done in duplicate and were carried out using one of the following dilution rates 2.10^-2, 4.10^-2 and 6.10^-2 h^-1. The foam was collected during its production at the top of the bioreactor. Samples of the culture medium were taken at 12h basis, and protease activity, glucose content and viable cell count were determined. In all fermentations, the production of foam started before 24h and the feeding began only around 36h, enabling the establishment of a continuous process until 120h. It is worth observingthat, for all the dilution rates, the viable cells count was stable after 24h and the glucose concentration fell dramatically after that time, reaching values near to zero after 48h throughout the remainder of the fermentations, indicating that any glucose added to the system is readily consumed by the cells. Protease activity, at all rates, showed a peak at 24h and then values with relative litte levariation after the beginning of feeding. The activities for the rates 4.10^-2 and 6.10^-2 h^-1 were very similar after 72h (4U), whereas for 2.10^-2 h^-1 values were mostly around 2U. In conclusion, these results show that the use of dilution rates above 4.10^-2 h^-1 apparently had no influence in protease production in this process, besides, the number of viable cells analyzed during the fermentation, was stable and its amount is related to the dilution rate used.