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 degrees C. The K-m and V-max values for the enzyme were 8.33 mM and 21.48 mu mol min(-1), respectively. A detailed kinetic study of thermal inactivation has been carried out. Enthalpy of activation (Delta H*) decreased when entropy (Delta S*) of activation increased at higher temperatures. Moreover, free energy of denaturation (Delta 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.