Production, purification and thermal characterisation of invertase from a newly isolated Fusarium sp. under solid-state fermentation

Production of invertase employing a newly isolated Fusarium sp. under solid-state fermentation was optimised. Different process parameters were optimised. The maximum enzyme activity under optimum conditions was 47.23 ± 2.12 U gds⁻¹ with nitrogen additives. The enzyme was purified by ammonium sulphate precipitation, diethylaminoethyl cellulose ion-exchange chromatography and Sephadex gel filtration. This protocol gave 20.25-fold purification and 5.53% recovery. The optimum pH and temperature for activity were 5.0 and 50 °C. The K _m and V _max values for the enzyme were 8.33 m m and 21.48 μmol min⁻¹, respectively. A detailed kinetic study of thermal inactivation has been carried out. Enthalpy of activation (Δ H *) decreased when entropy (Δ S *) of activation increased at higher temperatures. Moreover, free energy of denaturation (Δ G *) increased at higher temperature making the enzyme thermally stable. A possible explanation for the thermal inactivation of invertase at higher temperatures is also discussed.