The non-incubated enzyme was considered as control (100%). The following buffer systems were used: sodium acetate buffer for pH 5.0–6.0, Tris–HCl buffer for pH 7.0–8.0, glycine–NaOH buffer for pH 9.0–11.0,Na2HPO4–NaOH buffer for pH 12.0 and KCl buffer for pH 13.0.