Purification and immobilisation of inulinase fromAspergillus candidus for producing fructose

A high-inulinase-producing strain of Aspergillus candidus (10 units cm−3 of medium) for producing fructose from inulin has been identified. The extracellular inulinase from this fungi was purified 56-fold by ammonium sulphate fractionation, DEAE cellulose and Sephadex G-150 column chromatography. Invertase to inulinase ratio of 1.8 in culture filtrate was reduced to 0.14 in the purified preparation. The pH and temperature optima were 5.5 and 45°C, respectively. The molecular weight of inulinase was determined as 54±4 kDa. Km of inulinase with inulin as a substrate was 3.8 mmole dm −3. The purified preparation produced only fructose as the product of inulin, indicating that inulinase has primarily exo-inulinase activity. Inulinase was immobilised on chitin and casein using glutaraldehyde as a linking agent and on cellulose using FeCl3-HCl as a metal chelation agent. Maximum immobilisation of 45.8% was achieved on cellulose. All three immobilised preparations had a higher temperature optima of 55°C. The inulinases immobilised on cellulose and casein were stable at pH 5–7. The cellulose-immobilised preparation was more stable than the other two preparations after heating for 1 h at 55°C.