β-Glucosidase immobilisation on synthetic superparamagnetic magnetite nanoparticles and their application in saccharification of wheat straw and Eucalyptus globulus pulps

Abstract

β-Glucosidase from Trichoderma reesei was immobilised on synthetic superparamagnetic magnetite (Fe₃O₄) nanoparticles with a mean diameter of 10 nm and were used to supplement cellulase in the enzymatic hydrolysis of three substrates: wheat straw pretreated by steam explosion, Eucalyptus globulus pretreated by hydrothermolysis and E. globulus pretreated by hydrothermolysis followed by alkaline extraction. The hydrolysis yields for each pretreated material, using immobilised β-glucosidase (I-βG) and free cellulase, were 76.1%, 83.6% and 75.6%, respectively, and resulted in an improved hydrolysis yields compared with only cellulase. These yields were at most 10% lower than yields reached with free enzymes. The (I-βG) was magnetically recovered and successfully reused twice. The differences in the hydrolysis yields were not significant (p > 0.05) in the case of steam-exploded wheat straw and E. globulus pretreated by hydrothermolysis followed by alkaline extraction. The immobilisation of enzymes provides an opportunity to reduce the costs of enzymes in the bioethanol production process.

Keywords:

• magnetite nanoparticles
• superparamagnetism
• β-glucosidase immobilisation
• saccharification

Acknowledgements

The financial support for this work was provided by FONDECYT (Grants Nos. 1070492 and 7070109). We greatly appreciate the contribution and support in the SQUID measurements provided by Dr S.K. Sharma and Dr M. Knobel from Low Temperature Material Laboratory, Physics Institute, UNICAMP. Roberto Valenzuela thanks the student grants received from the Science and Analytical Technology Program, Pharmacy Faculty and Graduate School of Universidad de Concepción.