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

The influence of various physico-chemical parameters on Kluyveromyces lacti s beta-galactosidase stability was investigated. The combined effects of te mperature, pressure sand polyols as additive, on the enzyme stability at 25 and 45 degrees C were studied, in the pressure range from 0.1 to 400 MPa, and for polyol concentration between 0 and 2 M. At 25 degrees C, the stabil izing effect of polyols against pressure-induced denaturation increased wit h additive concentration, giving the following ranking of stabilization eff iciency: erythritol > xylitol > sorbitol > glycerol > ethylene glycol, eryt hritol being the most effective agent, whatever the concentration. Moreover , with or without polyols, stabilization against thermal denaturation at 45 degrees C due to the application of moderate pressures (<150 MPa) was obse rved, in the range where pressure alone does not denature the enzyme. The s tabilizing effect of ethylene glycol, glycerol, xylitol and sorbitol at atm ospheric pressure against thermal deactivation was significant and increase d with their concentration. However, erythritol, at atmospheric pressure, w as a strong destabilising agent at 45 degrees 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 degrees C. The application of high hydrostatic pressure, in the range w here pressure alone does not inactivate K. lactis beta-galactosidase, allow s to further increase the level of stabilization achieved at atmospheric pr essure and 45 degrees C, owing to polyols. (C) 1999 Elsevier Science B.V. A ll rights reserved.