Kinetics of enzymatic hydrolysis of steam-exploded cotton gin waste

The hydrolytic kinetics of cotton gin waste (CGW) at various initial concentrations of two enzymes, Novozymes NS50052 and Spezyme AO3117, was investigated. The experiments showed that the concentrations of reducing sugars increased with increasing initial enzyme concentration for the two enzymes. The reducing sugars produced per gram of Novozymes were higher than those produced by Spezyme. However, the reducing sugars produced per FPU of Novozymes were lower than those produced by Spezyme. The concentrations of reducing sugars reached 6.41 g/ L and 4.93 g/ L after seven hours of hydrolysis at the initial Novozymes enzyme loading of 12.3 filter paper unit ( FPU)/ g substrate and Spezyme loading of 3.68 FPU/ g substrate, respectively. A two-parameter model based on enzyme deactivation and its analytical expression have been derived. The model was used to fit the experimental data of the hydrolytic kinetics of CGW. The enzyme deactivation rate constants in this model decreased as the initial enzyme concentration for the two enzymes increased. The initial product-formation rates were used to determine the maximum hydrolytic rate constant V-m, the half-saturation constant K, and the rate constant k(2) of sugar formation for the two enzymes. In addition, by fitting the kinetic data into a series expression of the partial differential equation of diffusion, the average diffusivities of Novozyme and Spezyme enzymes on the CGW were estimated to be 7.14 x 10(-17) m(2)/ s and 5.58 x 10(-17) m(2)/ s, respectively.