Dielectric properties of microwave-baked cake and its constituents over a frequency range of 0.915–2.450 GHz

There is a large market for microwave foods, with one of the most prevalent growth areas being low-density bakery products. The dielectric constant and loss factor of Madeira cake batter and its constituents (sugar, cake concentrate, margarine, flour, egg) were measured at a range of moisture contents (0.429–1.000 kg kg−1, dry basis), temperatures (20–80 °C), and over a frequency range of 915–2450 MHz. In general, for a given material, the dielectric properties of samples increased with increasing frequency. Irrespective of frequency and sample moisture content, the dielectric constant of batter and flour was relatively independent of sample temperature, whereas that of the sugar samples increased with increasing temperature, particularly within the lower moisture range. At 2450 MHz the loss factor of batter and flour samples decreased by a limited amount as temperature was increased, whereas at 915 MHz they were relatively unaffected. The sugar samples showed a significant decrease in loss factor with increasing temperature, irrespective of frequency. During microwave baking, the dielectric properties of Madeira cake batter initially increased sharply and then decreased steadily until the end of the baking process.