Properties of Aspergillus japonicus β-fructofuranosidase immobilized on porous silica.

β-Fructofuranosidase from Aspergillus japonicus MU-2, which produces fructo-oligosaccharides (1-kestose: O-β-D-fructofuranosyl-(2 → 1)-β-D-fructofuranosyl α-D-glucopyranoside); and nystose: O-β-D-fructofuranosyl-(2 → 1)-β-D-fructofuranosyl-(2 → 1)-β-D-fructofuranosyl α-D-glucopyranoside) from sucrose, was immobilized, covalently with glutaraldehyde onto alkylamine porous silica, at high efficiency (64%). Optimum pore diameter of porous silica for immobilization of the enzyme was 91.7 nm. After immobilization, the enzyme's stabilities to temperature, metal ions and proteolysis were improved, while its optimum pH and temperature were unchanged. The highest efficiency of continuous production of fructo-oligosaccharides (more than 60%), using a column packed with the immobilized enzyme, was obtained at 40% to 50% (w/v) sucrose. The half-life of the column during long-term continuous operation at 55°C was 29 days.