a b s t r a c t
Effects of boiling water and microwave blanching methods on the dielectric properties, electrical conductivity
as well as microstructure of stem lettuce cubes (as a model for plant tissue) were studied. The study
also focused on how different blanching methods affect microwave freeze-drying (MFD) in a circular conduit
drying chamber and conventional freeze drying (FD) of stem lettuce cubes. Results showed that the
electrical conductivity of samples blanched by microwave was two times higher than that of boiling
water blanched ones and five times higher than that of unblanched samples. Apart from that, dielectric
constant (e0) and loss factor (e00) of the stem lettuce cubes decreased significantly after freezing. MFD
duration of microwave blanched samples was approximately 4.5 h, reduced by 30% compared to boiling
water blanched ones. MFD process in a circular conduit yielded products of high quality compared to that
in a tray.