Xylanase covalent binding onto amidated pectin beads: Optimization, thermal, operational and storage stability studies and application

Amidated pectin-polyethylene imine-glutaraldehyde (AP-PEI-GA) immobilizer was prepared. The ideal protocol that should be adopted during the immobilizer preparation was investigated via Box-Behnken design (BBD), and it comprised processing the AP beads with 3.4 % (w/w) PEI solution of pH 9.65 followed by 5.96 % (v/v) GA solution. The obtained AP-PEI-GA immobilizer was efficient, and it acquired 3.03 U.g^-1 of immobilized xylanase (im-xylanase) activity. The computed K_m and V_max values for AP-PEI-GA im-xylanase were 16.67 mg.ml^-1 and 20 g.ml^-1.min^-1, respectively. Through covalent coupling to AP-PEI-GA, Aspergillus niger xylanase thermodynamic properties T_1/2 and D-values were increased by 2.05, 3.08, and 1.35 at 40, 50, and 60 °C, respectively. ΔH_d and ΔG_d for AP-PEI-GA im-xylanase at 40, 50, and 60 °C were higher than those for free form emphasizing more resistance to thermal denaturation. Im-xylanase showed 100 % activity for 20 successive cycles and hydrolyzed different agro-industrial wastes into reducing sugar and xylooligosaccharides (XOS) with more efficiency on pea peel (PP). AP-PEI-GA im-xylanase, PP weight, and hydrolysis time that should be adopted to obtain the highest reducing sugar and XOS yield were optimized through central composite design (CCD). Extracted XOS showed prebiotic and anti-oxidant activities.