Tailor-made enzyme consortium segregating sclerenchyma fibre bundles from willow bark

Abstract

We report for the first time that pectin-degrading enzymes could be tailored for wood bark based on the chemical features of pectin. Besides wood, stems of trees contain 10–20% bark that remains one of the largest underutilized biomasses on the planet. Unique extractive compounds, suberin, pectin, sclerenchyma fibres, etc. form a major part of the bark that is today mainly combusted for energy production. In certain trees, such as willow, lignified sclerenchyma fibres organize in continuous, thin bundles or bast fibres which are surrounded by the non-lignified ground tissue. Random screening of lignocellulose-degrading enzymes is the mainstream, suitable for uniform and simple substrates like cellulose, but the pectin chemistry is more complex. The structure of pectin was first elucidated after which pectin-degrading enzymes were tailored. Surprisingly, the applied pectinases alone were able to fully liberate the fibre bundles from the bark under mild conditions. When the pectinases were used together with hemicellulases, fibre bundles with an abnormally low surface lignin content of 10% were obtained. Overall, the novel findings of this study give promise for commercial valorisation of the underappreciated bark biomass in the future without the need to build huge plants with their expensive chemical recovery systems. Most importantly, the “tailor-made enzyme consortium based on the structural features of the substrate” concept may be a revolutionary breakthrough in precisely designing biochemical degradation strategies particularly for the recalcitrant macromolecule component (such as pectin) of lignocellulosic biomass.