Properties of β‐fructosidases (invertases and inulinases) of Fusarium oxysporum grown on an aqueous extract of Cichorium intybus roots

Four different forms of invertase and inulinase named as Invertase, I, II, III, IV and inulinase I, II, III, IV were purified from a culture filtrate of Fusarium oxysporum , grown on a fructan containing medium, by ammonium sulphate fractionation, gel permeation and ion exchange chromatography. Invertases had a higher optimum temperature (55–60°C) as compared to that of inulinases (35–45°C). Of sucrose, raffinose, stachyose and inulin, sucrose was the best substrate for all the four invertases and none of the invertases showed activity with inulin. Inulinases showed maximum activity with inulin. The optimum pH of invertase I and II was 5.5 whereas invertase III and IV showed a maximum activity at pH 4.0. Inulinases I, II, III and IV had an optimum pH of 5.5, 5.5, 6.0 and 6.5, respectively. The thermal stability of invertases was in the order of invertase III > IV > II > I. Inulinase II was more stable than inulinase I whereas inulinase III and IV were the least stable. Inulinases showed a low K m in the range of 10–95 μmol dm −3 of inulin, thereby showing their high affinity for inulin. K m for invertases varied from 2 mmol dm −3 to 4 mmol dm −3 of sucrose. HgCl 2 and CuSO 4 were found to be strong inhibitors for both invertases and inulinases.