Dielectric properties of soy protein isolate dispersion and its temperature profile during radio frequency heating

Dielectric properties of soy protein isolate (SPI) dispersions, which were influenced by pH (4-10), concentration (5-15%, w/v) and temperature (20-90 degrees C), were investigated by a response surface methodology. Results showed that the second polynomial model of dielectric properties effected by pH, concentration, and temperature had good correlations (R(2)adj0.850). All the pH, concentration, and temperature significantly contributed to dielectric properties of SPI dispersions at radio frequencies (13.56, 27.12, and 40.68 MHz). The penetration depth (d(p)) value decreased (13,488 to 8,789 cm, 27.12 MHz, 20 degrees C) with the increasing of concentration (5-15%) but decreased (9,558 to 6,027 cm, 27.12 MHz, 15%) with the increasing of temperature (20 to 90 degrees C). The d(p) value had an irregular change near the denaturation temperature of SPI. Radio frequency (27.12 MHz) heating rates of SPI dispersions were decreased with the increasing of protein concentration. Practical applicationsRF heating treatment has been confirmed as an attractive modification method for protein and sterilization method for liquid food. Results from present work could be useful in the development of the protein modification and soy milk sterilization applications.