Immobilization of a commercial Aspergillus aculeatus enzyme preparation with fructosyltransferase activity in chitosan beads: A kinetic/thermodynamic study and fructo-oligosaccharides continuous production in enzymatic reactor

Pectinex Ultra SP-L, a food-grade enzymatic preparation with high transfructosylating activity, was covalently immobilized on chitosan beads. The highest immobilization yield (95.9%) was obtained using 4.0% glutaraldehyde for 60 min and 80 rpm at 25 ± 1 °C. The immobilized biocatalyst showed good operational stability, being able to retain, after the third cycle of reuse, no less than 100.0 and 73.9% of starting hydrolytic and transfructosylating activities, respectively. Results of residual activity experiments allowed estimating, for irreversible thermal inactivation of both free and immobilized enzyme, the activation energy (E*d = 234.3 and 242.2 kJ·mol−1), enthalpy (234.4 ≤ ΔH*d ≤ 234.2 kJ·mol−1 and 239.4 ≤ ΔH*d ≤ 239.3 kJ·mol−1), entropy (381.2 ≤ ΔS*d ≤ 379.8 J·mol−1·K−1 and 390.4 ≤ ΔS*d ≤ 389.7 J·mol−1·K−1) and Gibbs free energy (109.3 ≤ ΔG*d ≤ 103.9 kJ·mol−1 and 111.3 ≤ ΔG*d ≤ 103.6 kJ·mol−1). The use of the immobilized enzyme in a packed bed reactor allowed obtaining, after 100 min, a fructo-oligosaccharide mixture containing more than 25 g L−1 1-kestose.