Objectivesα-amylases hydrolyze α-1,4 glycosidic bonds in starch. ILs used as co-solvent in different enzymatic reactions to improve activity, selectivity and stability of enzymes. In this study, fluorescence spectroscopy method was used to explain the effect of [emim][lactate] on kinetic and thermal stability of Aspergillus oryzae α-amylase.MethodsEffect of different concentrations of [emim][lactate] on activity of α-amylases was determined. Kinetic parameters, optimum pH and temperature and thermal stability were determined and compared with absence of [emim][lactate]. Intrinsic fluorescence spectroscopy for Trp residues was performed for both presence and absence of [emim][lactate].ResultsActivity of α-amylase decreases in presence of [emim][Lac]. Moreover, Km of α-amylase in the presence of [emim][lactate] increases while Vm decreased. Optimum temperature in presence of [emim][lactate] increases from 45 to 50 °C while optimum pH decreases from 9 to 7. Thermal stability of α-amylase in the presence of [emim][lactate] is similar to that in the absence of [emim][lactate] at 40 and 50 °C but decreases at 60 °C. Intrinsic fluorescence spectroscopy shows unfolding of native structure of α-amylase is dependent on [emim][lactate] concentration.ConclusionsPresence of [emim][lactate] ionic liquid as co-solvent leads to structural unfolding of α-amylase and loss of its activity and thermal stability.