Effects of drying-induced fiber hornification on enzymatic saccharification of lignocelluloses

This study investigated the effect of fiber hornification during drying on lignocellulosic substrate enzymatic saccharification. Two chemically pretreated wood substrates and one commercial bleached kraft hardwood pulp were used. Heat drying at 105 and 150°C and air drying at 50% RH and 23.8°C for different durations were applied to produce substrate with various degrees of hornification. It was found that substrate enzymatic digestibilities (SEDs) of hornified substrates made from the same never-dried sample correlate very well to an easily measurable parameter, water retention value (WRV), and can be fitted by a Boltzmann function. The hornification-produced SED reduction at a given degree of hornification as the percentage of the total SED reduction when the substrate is completely hornified depends on two parameters. The first is WRV¯, which is primarily a function of the effective enzyme molecule size, and Δ, which is related to the substrate pore size distribution shape. The low values of SED(CH), SED of a completely hornified substrate, obtained from curve fittings for the three sets of samples studied, suggest that enzyme accessibility to cellulose is mainly through the pores in the cell wall rather than substrate external surface. The SEDs of hornified substrates were found to correlate to Simons' staining measurements well. A new parameter was proposed to better correlate enzyme accessibility to cellulose using the two-color Simons' staining technique.