Thermostable Xylanase from <i>Chenopodium album</i>: Thermodynamic and Kinetic Characterization with Sustainable Application in Agro-Industrial Biobleaching

This study focused on the purification and complete biochemical and thermodynamic characterization of a thermostable xylanase derived from <i>Chenopodium album</i><i>.</i> The enzyme exhibited a molecular weight of approximately 48 kDa and retained 85% activity after 2 h at 50 °C and pH 5.0, indicating substantial thermal and pH stability. Kinetic analysis revealed a <i>K</i>_<i>m</i> of 0.26 mM and a <i>V</i>_max of 33 μmol min^-1 mg^-1, confirming high substrate affinity and catalytic efficiency. Thermodynamic analysis revealed enhanced conformational stability of the enzyme, characterized by elevated enthalpy and Gibbs free energy values. The observed negative entropy change (Δ<i>S</i>° = -22.87 J mol^-1 K^-1 at 70 °C) indicates increased molecular ordering during thermal denaturation, particularly in the presence of sorbitol, which acted as a stabilizing polyol, enhancing the conformational rigidity of the enzyme. The enzyme's biotechnological relevance was further validated through kraft pulp biobleaching trials. Treatment with 100 U/g of xylanase led to a 32% reduction in the Kappa number, an increase in brightness from 38.5% to 51.2% ISO, and minimal losses in viscosity (-4.8%) and yield (95.6%), confirming selective delignification without compromising cellulose integrity. These findings underscore the enzyme's promise in reducing chemical load during pulp biobleaching and efficiently producing xylo-oligosaccharides, which possess recognized prebiotic and nutraceutical value.