Dielectric properties of milk during ultra-heat treatment

Dielectric properties are important for predicting dielectric heating of foodstuffs. The dielectric properties of three types of milk (raw, skimmed and concentrated non-fat) were analyzed at high frequencies between 10 MHz and 2450 MHz for producing temperatures between 20 °C and 150 °C. The study of cow milk dielectric constants (ε′ and ε″) at conditions above 100 °C is needed to evaluate dielectric sterilization of milk. The dielectric constant (ε′) was found to decrease with frequency at all temperatures but increase with temperature at low frequencies and decrease with temperature at high frequencies. The dielectric loss factor (ε″) decreased with frequency and increased with temperature in almost the entire range of frequencies. Ionic conduction was the dominant mechanism across most of the frequency range. For milk samples with higher ash content (related to salt content), ε′ was higher at low frequencies and lower at high frequencies, whereas ε″ was higher for all frequencies. Penetration depth was lower for milk samples with higher ash content.