Characterization of rice straw prehydrolyzates and their effect on the hydrolysis of model substrates, using a commercial cellulase cocktail, endo-cellulase and β-glucosidase

Pretreatment and enzymatic saccharification are two major upstream processes that affect the economic feasibility and sustainability of lignocellulosic biofuel production. Cellulase inhibiting degradation products, generated during dilute acid pretreatment, are removed by rinsing, resulting in an increased biorefinery water usage. In an attempt to elucidate which degradation product was most deleterious to enzymatic hydrolysis, hydrolyzates were generated from rice straw and their effect on enzyme activity was determined. Ground rice straw was subjected to the following pretreatments, having a combined severity factor of 1.75: T1– 160°C, pH 1.7; T2– 180°C, pH 2.25; and T3– 220°C, pH 7.0. The liquid prehydrolyzates were freeze-dried and their inhibitory effect on the saccharification of filter paper and cellobiose was determined using a commercial endo-cellulase, β-glucosidase and cellulase cocktail. The addition of only 10 g L^-1 of T1, T2, or T3 freeze-dried prehydrolyzates resulted in decreases of 81%, 86%, and 92% of endo-cellulase enzyme activity, respectively. In the presence of 35 g L^-1 of T1, T2, or T3 prehydrolyzates, filter paper activity of CTec2 was reduced by 64%, 68%, and 82%, respectively. Characterization of the freeze-dried prehydrolyzates showed that T3 had significantly higher xylo-oligosaccharides and total phenolic content than T2 and T1.