Thermostable Glycoside Hydrolases in Biorefinery Technologies

Glycoside hydrolases, which are responsible for the degradation of the major fraction of biomass, the polymeric carbohydrates in starch and lignocellulose, are predicted to gain increasing roles as catalysts in biorefining applications in the future bioeconomy. In this context, thermostable variants will be important, as the recalcitrance of these biomass-components to degradation often motivates thermal treatments. The traditional focus on degradation is also predicted to be changed into more versatile roles of the enzymes, also involving specific conversions to defined products. In addition, integration of genes encoding interesting target activities opens the possibilities for whole cell applications, in organisms allowing processing at elevated temperatures for production of defined metabolic products. In this review, we overview the application of glycoside hydrolases related to the biorefining context (for production of food, chemicals, and fuels). Use of thermostable enzymes in processing of biomass is highlighted, moving from the activities required to act on different types of polymers, to specific examples in today’s processing. Examples given involve (i) monosaccharide production for food applications as well as use as carbon source for microbial conversions (to metabolites such as fuels and chemical intermediates), (ii) oligosaccharide production for prebiotics applications (iii) treatment for plant metabolite product release, and (iv) production of surfactants of the alkyl glycoside class. Finally future possibilities in whole cell biorefining are shown. Keywords: Amylase, antioxidant, biofuels, biomass, cellulase, glucanase, glucosidase, hemicellulose, lignocellulose, mannan, pectin, prebiotics, starch, surfactant, xylan, xylanase.