How HLEs Differ
HLEs differ from traditional pulping enzymes. Tethys’s novel approach to breaking lignin-hemicellulose bonds has been to discover enzymes that break bonds between lignin and the non-glycosidic carbons of sugars. All other pulping enzymes in use today are glycosidases. Glycosidases do not break lignin-hemicellulose bonds. They only break bonds between the sugars in the hemicellulose, destroying the structure of the hemicellulose and leaving some sugars still attached to the lignin where they are wasted.
Tethys’s strategy is based on current knowledge about the biosynthesis of wood, which implicates non-glycosidic carbons in the hemicellulose as the site of lignin-hemicellulose cross-links.
Typical pulping enzymes (i.e. cellulases and hemicellulases) depolymerize cellulose and hemicellulose in lignocellulosic biomass into sugars by cleaving glycosidic bonds. Cross-links between hemicellulose and lignin are created when hemicellulose is already polymerized and therefore the cross-links between lignin and hemicellulose are largely through non-glycosidic carbons. Hemicellulases depolymerize the hemicellulose so that it does not contribute to the final pulp yield. Any sugar residues directly attached to lignin through non-glycosidic bonds are not removed by hemicellulases. Those sugars go into the lignin stream and are usually wasted.
Tethys’s proprietary and patent pending HLEs break ether bonds between lignin and non-glycosidic bonds. The result is intact hemicellulose left in the biomass that can be used either intact or depolymerized by hemicellulases into sugars. Bonds between sugars and lignin are broken, increasing sugar yields and giving purer lignin fractions.