Application of a magnetic immobilizedβ-glucosidase in the enzymatic saccharification of steam-exploded lignocellulosic residues

Aβ-glucosidase preparation derived fromAspergillus niger was immobilized onto a magnetic support and used in the enzymatic saccharification of a lignocellulosic material. The enzyme was immobilized onto polyethyleneimine-glutaraldehyde activated magnetite (PAM) and also onto titanium (IV) oxide (TiO₂)-coated magnetite (TAM). Although > 80% of the protein applied was immobilized, only 15–27% of the enzyme activity was recovered after immobilization. Theβ-glucosidase immobilized onto TiCO₂-coated magnetite suffered from enzyme being removed from the matrix under hydrolysis-use conditions, whereas the PAM enzyme remained attached to the matrix. The physicochemical properties of the immobilizedβ-glucosidase preparations are described. Both immobilizedβ-glucosidase preparations were capable of completely hydrolyzing cellobiose. Recycling of the immobilized enzymes (IME) resulted in reduced rates of hydrolysis with each recycling of the enzyme, although cellobiose was still capable of being completely hydrolyzed. The reduced hydrolysis performance was attributable to physical losses of IME during recovery and, in the case of TAM, enzyme loss from the matrix. Supplementing cellulase digests of steam-explosion pretreatedEucalyptus regnons pulps with immobilizedβ-glucosidase resulted in enhanced hydrolysis. Cellulose-to-glucose yields of 80% of theoretical predictions resulted within 24 h. The magnetically immobilizedβ-glucosidase could easily be recovered from the lignocellulose solids suspension in a stirred batch reactor by applying a magnetic field. The recycled immobilized enzyme continued to convert cellobiose into glucose in 80% yields over a 24-h period. This is the first report of a magnetically immobilizedβ-glucosidase preparation used in the enzymatic saccharification of a lignocellulosic material.