Dielectric behavior of apple (var. Granny Smith) at different moisture contents: Effect of vacuum impregnation

The dielectric properties of vacuum impregnated (VI) and non-vacuum impregnated (NVI) apple, var. Granny Smith, were measured at 2.45 GHz and 25 °C using the open-ended coaxial probe method and a network analyzer (HP-85070B) connected to a computer with suitable software. The effect of moisture content, water activity and porosity on the dielectric constant and loss factor was evaluated. The results suggest a water activity value near 0.9 (0.6 water content, dry basis) from which dielectric loss mechanisms seems to be notably increased, related to the availability of mobile water.