Resumo

Biosurfactants are amphiphilic compounds produced by living organisms.Bacillus subtilis produces surfactin, which is a cyclic lypopetides, usually growth-associated at later logarithmic phase and natural powerful surface-active agent. Interest in its industrial and environmental applications constantly increases, however some economical strategies, have be applied to improve the yields and attain competitive prices. Cassava wastewater is a residue from flour industry and contains minerals and carbohydrates, thereby it shows good potential as a culture medium, on the other hand, molasses has a higher content of sugar. Therefore, the aim of this work was to evaluate the surfactin production using cassava wastewater as culture medium, supplemented with sugarcane molasse at growth phase. An amount of 100 mL of cassava wastewater was inoculed (7.0 mL) with Bacillus subtilis then, incubated at 150 rpm and 30^oC. At logarithmic phase (24 h) 3.07 g of sugarcane molasses (52.34 % of TRS) was added to each flask. During the fermentation, at 12 hour basis, samples were taken, and had their surface tension (ST), critical micelle dilutions (CMD), glucose content and viable cell count measured. The batch experiments have indicated that transition from growth to stationary phase, took place between 24 and 39 h, besides at 48h, 0 g.L^-1 of glucose was reached. Moreover, as from at 39h the lowest ST value was achieved. The results from fed batch fermentation, have show early stationary phase and a second growth phase after 39h, most like due to the supplementation with molasses. The glucose content has kept around 6g.L^-1 during the process and a subtle increase of that (+/- 2g.L^-1) was observed. The CMD^-2 data indicated that surfactin production was higher, when comparing to batch process. In conclusion, the use of sugarcane molasses in that fed batch process could be an interesting possibility to improve surfactin yields, due to the glucose be the limiting substrate when is used cassava wastewater.