17-17: Characterization of lignin isolated from liquid hot water pretreated hardwood and its effect on the enzymatic hydrolysis

Mixed hardwood pretreated with liquid hot water at severities ranging from 3.05 to 4.41 solubilizes hemicellulose and enhances the enzymatic digestibility of cellulose.  The pretreated solid retains 90% of the lignin that is initially present.  The lignin is hypothesized to hinder the action of the cellulases on cellulose through physical hindrance or non-productive binding of the enzymes.  In order to understand the changes of lignin properties during liquid hot water pretreatment, lignins were isolated from pretreated hardwoods using extensive enzymatic hydrolysis.  Once the cellulose had been hydrolyzed, the remaining solids were treated with proteases to remove any adsorbed protein.  The resulting material, which is principally lignin, was then characterized based on its glass transition temperature (T_g) measured by differential scanning calorimetry.  The T_g of isolated lignins increased from 170°C to 180°C as pretreatment severity increased.  The literature reports T_g after pretreatment may be related to chemical structure, functional groups, intermolecular bonding type and/or molecular size of the lignin.  We measured changes in physical and chemical structure of the lignin using fourier transform infrared spectroscopy (FTIR) analysis and compared these to the T_g.  We found cellulase adsorption onto the lignin surface depends on the source of enzyme and lignin properties (with T_g as an indicator).