Xylanase immobilization using activated carrier of gellan gum-agar beads: Improved stability and catalytic activity for the production of antioxidant and anti-proliferative xylooligosaccharides

Abstract

Immobilization of xylanase produced by the fungus, Aspergillus flavus, was achieved utilizing the activated gellan gum-agar as a carrier. The immobilization conditions were optimized based on Box-Behnken design which comprised the addition of agar (1.23%) to gellan-gum (GL) and processing the obtained beads at pH 7.7 with 1.62% polyethyleneimine (PEI) as the optimum conditions. Alteration of the surface morphologies and elemental constituents of the carrier during the synthesis and immobilization process were inspected using energy-dispersive X-ray analysis (EDX) and scan electron microscope (SEM). The yield and efficiency of the immobilization process were 45.85% and 97.41%, respectively. The immobilized enzyme possessed the highest activity at pH 5–8 and temperature up to 70 °C with activation energy lower than half that of the free form. Higher half-lives and Gibbs free energy were achieved for the immobilized enzyme, sustaining the suitability of the used carrier for promoting enzyme stability. Moreover, the negative entropy values for both free enzyme and the immobilized forms estimated the high stability of the enzyme during the thermal deactivation process. The Km value of the immobilized form was lower than that of the free enzyme, reflecting its enhanced affinity toward xylan substrate. Furthermore, the immobilized enzyme retained 99.3 and 85.7% of its initial xylan hydrolyzing activity after 7, and 11 cycles, respectively. Finally, the applicability of the immobilized form in the hydrolysis of xylan and production of antioxidant and breast cancer anti-proliferative xylooligosaccharide mixture was also estimated.