OPTIMIZATION, SCALE-UP AND KINETIC PROFILES OF ETHANOL FERMENTATION WITH BARU (Dipteryx alata) WASTES IN A FIVE LITERS BIO-REACTOR.

Seeds of baru (Dipteryx alata) are commonly consumed in the central region of Brazil as toasted nuts, flour, fermented drinks and others, while the woody and non edible shells and pulps are discarded, generating a big amount of wastes. Previous studies described nutrient content of both shell and pulp, as well as the lack of toxic compounds and the potential of such baru’s wastes as a suitable substrate for ethanol production in a fermentation process. This work was aimed to optimize fermentation conditions in 100 mL Erlenmeyer flasks, using an experimental design which combined two factors (shell/pulp concentration and fermentation time), at three chosen levels each (1, 5, 9% and 24, 48, 72 hours, respectively), while three responses were measured for each level combination: cell growth, substrate consumption and ethanol yield. Optimal conditions obtained from response surfaces were used in scale-up experiments run during 48 hours in a mechanically stirred bio-reactor with an effective volume of five liters, coupled to temperature, pH and stirring control. Samples from fermentation broth were taken at intervals of 6 hours to construct kinetic profiles for cell growth, carbohydrate consumption and ethanol production and to calculate their specific rates and global yield values for biomass/substrate and product/substrate. Optimal fermentation conditions previously determined out of response surfaces from optimization experiments, were fixed as fermentation time of 48 hours, using 5% of shell/pulp substituting carbohydrates in broth formulation. Specific rate values ranged from 0.002 to 0.096 h-1for biomass growth, 0.051 to 3.23 h-1 for substrate consumption and 0.115 to 2.933 h-1 for ethanol production. Calculated yield values were 0.038 (biomass/substrate) and 0.337 (product/substrate), while ethanol final concentration was 7.15 mg/mL. These results confirm the technical suitability of using baru’s wastes as a substrate for ethanol production at larger scale.