Characterizing and improving the thermostability of purified xylanase from Aspergillus niger DFR-5 grown on solid-state-medium

 The thermostability of absolutely purified xylanase from Aspergillus niger DFR-5 was improved using polyols. Supplementation of sorbitol at 2M concentration was found to increase the half-life and D-value of xylanase at elevated temperatures (45-70ºC). Thermodynamic parameters associated with the process were analyzed revealing that the stability at higher temperatures was due to the increased enthalpy (∆Hº) and free energy (∆Gº) change of enzyme denaturation in the presence of sorbitol. The negative values of ∆Sº (-150.093 Jmol-1K-1 at 70ºC) clearly indicated that enzyme underwent a significant process of aggregation during denaturation. The enzyme required divalent cations for maximum activity and inhibited by chelator. The diminution of activity by various thiol-binding agents and enhancement by reducing agents like β-ME confirmed the essentiality of cysteine for catalysis. The enzyme had a half-life and D-value of 277 and 921 days when stored at 4 ºC.