Effect of soluble additives on enzyme thermo- and/or baro-deactivation

Abstract

The influence of various physico-chemical parameters on Kluyveromyces lactis β-galactosidase stability was investigated. The combined effects of temperature, pressure and polyols as additive, on the enzyme stability at 25 and 45°C were studied, in the pressure range from 0.1 to 400 MPa, and for polyol concentration between 0 and 2 M. At 25°C, the stabilizing effect of polyols against pressure-induced denaturation increased with additive concentration, giving the following ranking of stabilization efficiency: erythritol>xylitol>sorbitol>glycerol>ethylene glycol, erythritol being the most effective agent, whatever the concentration. Moreover, with or without polyols, stabilization against thermal denaturation at 45°C due to the application of moderate pressures (<150 MPa) was observed, in the range where pressure alone does not denature the enzyme. The stabilizing effect of ethylene glycol, glycerol, xylitol and sorbitol at atmospheric pressure against thermal deactivation was significant and increased with their concentration. However, erythritol, at atmospheric pressure, was a strong destabilising agent at 45°C. But when the pressure was increased, considerable stabilization was observed. Indeed, erythritol was the most effective agent at 2 M and 350 MPa against thermal denaturation at 45°C. The application of high hydrostatic pressure, in the range where pressure alone does not inactivate K. lactis β-galactosidase, allows to further increase the level of stabilization achieved at atmospheric pressure and 45°C, owing to polyols.