Microwave dielectric properties of solid and liquid foods investigated by time-domain reflectometry

Microwave dielectric relaxation measurements by a time-domain reflectometry (TDR) method were performed on solid and liquid foods, covering the frequency range between 100 kHz and 10 GHz. Carrots, radishes, potatoes, rice, milk, cheese, egg whites, egg yolks, fish, chicken, agar aqueous gel, gelatin aqueous gel, and ovalbumin aqueous gel were examined. The relaxation processes caused by the reorientation of free water and bound water, interfacial polarization, and polymer chain motion were discussed. Whiskey, beer, and wine also were examined by TDR, and a relaxation process caused by reorientation of molecular dipoles in water and alcohol was observed. The obtained dielectric parameters for beverages were compared with those of ethanol-water mixtures.