Substrate-specific responses to mixing conditions in high-solids enzymatic hydrolysis: Insights from microcrystalline cellulose and dilute-acid pretreated corncob

This study investigates the mixing effects on the enzymatic hydrolysis of microcrystalline cellulose (MCC) and dilute-acid pretreated corncob substrates under high-solid conditions. Enzymatic hydrolysis experiments were conducted to assess cellulose conversion rates under varying mixing conditions (0, 50, 150, and 250 rpm) and solids loadings (5 %, 15 %, 25 %, and 35 %, w/v), and distinct physicochemical properties of the substrates were characterized. Additionally, the role of mixing conditions and solid loadings on cellulose hydrolysis kinetics and enzyme adsorption on both substrates and lignin were elucidated. Results demonstrated that both substrates exhibited a decrease in cellulose conversion as solid loading increased, with dilute-acid pretreated corncob consistently showing higher conversion rates compared to MCC. Kinetic analysis revealed that both the rate constant k and the fractal exponent h increased with mixing intensity; however, the increase was more pronounced for dilute-acid pretreated corncob's k and MCC's h. Enzyme adsorption studies indicated dilute-acid pretreated corncob had a higher adsorption capacity q_max and a weaker binding affinity K compared to MCC. Furthermore, increased mixing enhanced enzyme adsorption q_max while decreasing binding affinity K, with more pronounced effects on dilute-acid pretreated corncob's q_max and MCC's K. Lower mixing intensities favored cellulase-lignin binding, with an optimal cellulase-to-lignin binding ratio of approximately 1:1.3, suggesting a more stable interaction. These findings underscore the critical role of substrate disparities in high-solid enzymatic hydrolysis, offering valuable guidance for optimizing mixing strategies for efficient conversion of lignocellulosic biomass.