Enzymatic hydrolysis of lignocellulosic substrates has been considered as one of the key steps for the biochemical conversion of cellulosic biomass to biofuel and bioproducts. This conversion process starts with the adsorption of cellulase enzymes to the lignocellulose surface. It is believed that hydrophobic interaction forces between cellulase and the biomass surface are responsible for the binding. The activity of the adsorbed enzyme can be inhibited by the presence of lignin in the biomass due to the physical hindrance of lignin and the nonproductive binding of cellulase to lignin. To understand the effect of the hydrophobicity of the biomass surface on cellulase adsorption, a set of reference substrates derived from sulfite and kraft pulping was examined using atomic force microscopy (AFM). The reference substrates used have known surface composition of cellulose and lignin. By measuring the attractive interaction forces between a hydrophobically-functionalized AFM tip and various surface components of the biomass, locations of hydrophobic domains on the surface can be identified.  Our results indicated that the presence of lignin on the surface increased the hydrophobic interactions between the biomass and the CH3-modified cantilever (0.545�0.005 nN, n=8341, 45.53% surface lignin composition versus 0.291�0.003, n=4910, 0% lignin). In addition, with similar surface lignin composition (39.23%), hydrophobic interactions between the methyl-terminated cantilever and kraft lignin (0.545�0.005 nN, n=8341) were higher than those with lignosulfonates (0.419�0.004, n=6713). Cellulase adsorption and batch hydrolysis experiments were also performed. Higher amounts of Celluclast� 1.5 L, a commercial cellulase mixture, was adsorbed to the substrate with kraft lignin on the surface more than the substrate that has lignosulfonate on its surface. Our results confirm that surface lignin increases the hydrophobicity of the surface. Nonproductive binding of cellulase to kraft lignin was higher than lignosulfonate due to the increase in the surface hydrophobicity.

Nanoscale mapping of the surface hydrophobicity of lignocellulosic biomass

247th National Meeting (2014)

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