Biochemical characterization and kinetic comparison of encapsulated haze removing acidophilic xylanase with partially purified free xylanase isolated from Aspergillus flavus MTCC 9390

摘要

An extracellular xylanase from the culture supernatant of isolated soil- borne Aspergillus flavus MTCC 9390 grown on well optimized medium was purified using neutral salt fractionation and size exclusion column chromatography. The elution profile of the fractionated sample showed major xylanolytic protein that was further characterized. The activity of isolated enzyme was optimum at pH 5.0 and temperature 55 A degrees C. The enzyme was stable at pH between 4.5 and 6.5 and temperatures between 45 and 75 A degrees C. The enzyme showed a K-m of 1.5 % for xylan with a V-max of 200 UmL(-1). The molecular mass of protein was found to be 35 kDa with cysteine residue at or near the active site of enzyme. After encapsulation in alginate beads, a change in kinetic and biochemical properties of xylanase was recorded. Better thermostability, wider pH optima and enhanced temperature optima were the key determinants of significant immobilization. The activity of free and bound enzyme having different specific activities, induced different clarification behavior of reconstituted or fresh pineapple juice at different expressed units. The retention of recovered enzyme after successive reaction cycles with xylan confirmed the effective immobilization. The bound enzyme with lower specific activity clarified juice faster than the free enzyme due to its operational stability and reusability. Samples of pineapple juice showed relatively less viscosity, suspended solids and more clarity with immobilized enzyme treatment.