Hydrolysis of inulin by immobilized thermostable extracellular exoinulinase from Aspergillus fumigatus

The extracellular thermostable inulinase from Aspergillus fumigatus, which converts inulin into fructose, was immobilized on different supports after partial purification by ammonium sulphate precipitation, and ion exchange chromatography on DEAE-Sephacel. The optimum pH for free and the enzyme immobilized on various supports, was 5.5, whereas temperature optimum was 60 degrees C. The K-m values of various immobilized inulinases, with inulin, varied from 0.2 to 0.5 mM. The heat stability of the enzyme was markedly improved by immobilization on various supports and the immobilized enzyme retained approximately 70% activity after 48 h at 60 degrees C. The operational half-life of the immobilized inulinase at 60 degrees C with 2.5% inulin was 22, 35 and 45 days for QAE-Sephadex, chitin and ConA packed bed column reactors, respectively, which makes this enzyme, in the immobilized form, a potential candidate for production of fructose syrups on industrial scale. (c) 2005 Elsevier Ltd. All rights reserved.