Phytosanitary/quarantine regulations for many countries require that certain dried fruit be disinfected
prior to export; however, current technologies involve the use of toxic chemicals and conventional
thermal methods are either undesirable or cause loss of volatile components, browning and texture
change. Newer physical methods including dielectric heating have been considered, but information on
dielectric properties of dried fruits is lacking. Because the loss factor of insect pests, Indian meal moth
(Plodia interpunctella) and navel orangeworm (Amyelois transitella), is several times (26e36) greater than
that of dried fruits, RF treatment in particular has great potential for insect disinfection. In this study, the
dielectric properties of raisins, dates, apricots, figs, and prunes with water contents of 15e30.2 g/100 g,
were determined between 10 and 1800 MHz over a range of 20e60 C. The dielectric constant and loss
factor of all samples decreased with increasing frequency, but increased with increasing temperature at
each frequency. The loss factor of all samples increased with increasing water contents/water activity
(0.5e0.7). The penetration depths (dps) of RF energy in all samples decreased with increasing frequency
and temperature. The deep dp (28.4e103.7 cm) at 27 MHz indicates the potential for developing
continuous and large-scale RF treatments for postharvest insect control in dried fruits.