Oxidative modification of cellulosic fibres by lytic polysaccharide monooxygenase AA9A from Trichoderma reesei

Lytic polysaccharide monooxygenases (EC1.14.99.53-56, LPMOs) are oxidative enzymes with the capability to enhance lignocellulose saccharification as well as nanofibrillation of cellulosic fibres. The parameters affecting the efficiency of oxidative modification of cotton linters and softwood kraft fibres by LPMO from Trichoderma reesei (Tr AA9A) were studied here. Circular dichroism experiments were carried out to analyze the thermal stability and to indicate the optimum temperature for the experiments. The enzyme was found to be most thermostable at pH 5 but can tolerate up to 40–50 °C at neutral pH. The enzymatic fibre oxidation efficiency was found to be dependent on reductant (gallic acid) and hydrogen peroxide supply in a pH dependent manner. A high resolution UHPLC-IM-MS method was used for identification of oxidized oligosaccharides released in the enzymatic treatments. A microscopy method was applied for analysis of single fibre dissolution kinetics of Tr AA9A pretreated softwood kraft fibres, demonstrating that the oxidative enzymatic treatment facilitated the fibre dissolution and degraded the fibre surface structures, which prevent swelling.