|
Abstract
The dielectric behavior of a semi-solid food was essentially predicted
at 3 GHz,
25 °C, for a range of moisture contents and water activities,
by an electrophysical model for two-phase heterogeneous mixtures based on
lumped-circuit analysis. The model involved an active aqueous ionic phase and
an inert solids phase whose properties were estimated from proximate analysis
data. A critical level of water activity was seen for activation of
conductive loss mechanisms which appeared to be related to the availability
of water in mobile forms. This is seen to involve ionization of salts below
saturation levels and salts bound to food solids at low moisture contents.
Observed dielectric behavior was primarily
associated with water and ion activities and is believed to result from the
ionization and subsequent dilution of aqueous ions as moisture contents were
increased by sorbing samples at progressively
higher water activities. The state of water in semi-solid foods is seen in
terms of relative mobilities which appear to be
related to the kinetics of microbial growth and biochemical reactions of
foods in prolonged storage at low and intermediate moisture contents. Results
of this and previous work suggest that bound water relaxations are negligible
at microwave frequencies.
|