Dielectric properties of beta-lactoglobulin dispersions were measured at the selected microwave frequency range (915 and 2450 MHz) by the open-ended coaxial probe method using a network analyzer. The effects of temperature (20-90 degrees C), concentration (5-15% w/w) and pH (4-10) on dielectric properties were investigated using a response surface methodology and it was found to follow 2nd order polynomial models. Temperature and concentration significantly contributed on dielectric characteristics of beta-lactoglobulin dispersion and pH of the dispersion exhibited the least effect. Dielectric parameters (epsilon' and epsilon '') increased significantly at the close vicinity of denaturation temperature. Penetration depth (D(p)) decreased with an increase in concentration and non-systematic with temperature. (C) 2009 Published by Elsevier Ltd.