Cellulose bioconversion by cross-linked cellulase aggregates (cellulase CLEA): Enzymeimmobilization onto magnetic Fe3O4@silica core/shell nanoparticles

Cellulose as a renewable biomaterial for the production of bio-ethanol has forced attention to the use ofcellulose-hydrolyzing enzymes for industrial bioconversion of lignocellulosic materials to glucose. This paper reportsimmobilization of cellulase enzymatic cocktail in the form of cross-linked enzyme aggregates (CLEAs) on the aminefunctionalizedFe3O4@silica core-shell magnetic nanoparticles (MNPs). The incorporation of MNPs enables recoveryand reuse of the enzymes over multiple cycles. The optimum pH of the cellulase cocktail upon immobilization shifted alittle to the acidic side whereas the optimum temperature (65ºC) did not change. CMCase activity of immobilizedcellulase in pH and temperature values higher than optimum conditions, were significantly different from those of freecellulase. Cellulase CLEA-MNP retained about 45% of its maximal activity at pH values higher than 4.8 while freecellulase lost its activity sharply. Immobilized cellulase in contrast to free form retained about 65% of its maximal activityat higher temperature up to 80ºC. Cellulase CLEA-MNP had improved thermal stability at 65ºC relative to free enzyme.Operational stability of immobilized celluase was also noticeable. After a sharp decrease during two cycles of CMChydrolysis, cellulase CLEA-MNP retained 30% of its initial activity through six cycles of reuse.

Keywords:

Cellulase , Magnetic core-shell nanoparticles , Cross-linked enzyme aggregates , Immobilization , Cellulosebioconversion