Tuesday, May 3, 2011
This work presents a kinetic study of the enzymatic hydrolysis of three cellulosic substrates: filter paper (FP), used as a de-lignified substrate model; steam exploded sugarcane bagasse (SB); and in natura SB, the last two treated with 4% NaOH. All SB were chemically characterized. Hydrolysis experiments to study the influence of agitation and substrate concentration were performed in shaker, using Accellerase® 1500, Genencor (0.85FPU.mL-1supernatant), at pH 4.8, in 50mM sodium citrate buffer. To verify the substrate concentration effect, cellulose load (weightsubstrate/weighttotal) was 0.5%-13% (for FP) and 0.99%-9.09% (for SB). For FP, the role of the external mass transport resistance was not significant when the agitation speed was in the range 150-300 rpm. It was possible to fit a pseudo-homogeneous Michaelis-Menten model for substrate concentrations up to 13% (w/w). Preliminary tests fitting the model proposed by Chrastil indicated that the role of diffusion through the external film was a more relevant feature for SB than for FP, at higher concentrations of substrate. It was possible to fit a pseudo-homogeneous model for SB, within a range of cellulose concentrations from 0.99% to 3.85% (w/w). Product inhibition had to be considered by the model. Finally, for higher loads of SB, a modified Michaelis-Menten model, appropriate for heterogeneous systems with high diffusion resistance, was fitted. As expected, the complexity of this system regarding to the substrate and to the pool of enzymes acting in synergy, makes difficult the use of one single lumped parameter model for all hydrolysis operation conditions.