Evaluation of chitosan–coated magnetic nanoparticle-immobilized thermostable hemicellulases for enhanced saccharification and production of bioethanol

Abstract

Enhancing the efficiency of saccharification of pentose and hexose sugars present in lignocellulosic biomass is a major bottleneck for industrial bioethanol production. This problem can be addressed by a concerted effort combining nanotechnology, enzymology and fermentation technology. Functionalized chitosan-coated magnetic nanoparticles (CCMNPs) were prepared and used for co-immobilization of purified xylan hydrolysing xylanase and xylosidase from the thermophilic fungus Thermomyces lanuginosus SSBP for the release of xylose. Stability studies revealed that immobilized enzymes were more stable than free enzymes over a wide range of pH (4.0 – 7.0) and temperature (40 – 90 °C) for xylanase and 30 – 80 °C for xylosidase. The optimum activity of the co-immobilized enzymes shifted slightly as compared to the free enzymes, with coimmobilized xylanase and xylosidase showing optimum activity at pH 6.5 and 6.0, respectively. The study showed sustained production of xylose as the major fermentable sugar under repeated batch and fed-batch saccharification of lignocellulosic biomass. Statistical optimization of saccharification of 1% xylan using response surface methodology indicated the enhanced release of xylose at 50 °C, pH 7.0 and enzyme dose of 60 U/mL xylanase and 30 U/mL xylosidase. Finally, liberated xylose was fermented with Scheffersomyces stipitis to yield bioethanol.