DIELECTRIC PROPERTIES OF FOOD
S A Q I B R A S H I D L O N E
1 4 P F T 0 1 1
L O N E S A Q I B @ G M A I L . C O M
A dielectric material (dielectric for short) is an
electrical insulator that can be polarized by an applied
electric field . when a dielectric is placed in an electric
field, electric charges do not flow through the material
as they do in a conductor but only slightly shift from
their average equilibrium positions causing dielectric
The study of dielectric properties concerns storage and
dissipation of electric and magnetic energy in
• The knowledge of the electrical properties of
the materials to be processed or measured is
important in the design of the equipment.
Dielectric properties determine the behavior
of the materials, when subjected to high
frequency or microwave fields in dielectric
heating processes or cooking.
• This article is a review of the measurement
techniques of the dielectrical properties of
food materials. This study also includes the
classification of electrical properties and
their importance in food processing.
Dielectric property used to explain interactions of
foods with electric fields. It determines the interaction of
electromagnetic waves with matter and defines the charge
density under an electric field.
Major factors that influence these properties of agricultural
and food materials are:
Frequency of the applied radio frequency or microwave
Density of the materials
The dielectric properties of most materials vary with
several influencing factors:
The dielectric properties also depend on the:
1. Frequency of the applied alternating electric field,
2. Temperature of the material,
5. Structure of the material.
In granular or particulate materials the bulk density of the
air-particle mixture is another factor that influences the
The dielectric properties of materials also dependent on
the chemical composition and especially on the presence
of mobile ions and the permanent dipole moments
associated with water and any other molecules making up
the material of interest.
MEASUREMENT OF DIELECTRIC
PROPERTIES IN FOOD
Type of food
Degree of accuracy
Reflection of transmission type
Free space transmission
A microwave signal is generated at the
frequency of interest.
Signal is directed through the sample.
Changes in the signal caused by the sample are
From these changes the dielectric constant and
loss factor are determined.
1. Useful in detection processing conditions, or the quality of
2. The major uses for dielectric properties are measuring and
3. Properly designed electrical instruments can be used to
determined moisture content or water activity.
4. Knowledge of dielectric properties in partially frozen material is
critical in determining the rates and uniformity of heating in
“ Dielectric behavior is important for food technologists and
food engineers to improve quality of microwave foods and to
design microwaveable foods and to develop new microwave
5. Dielectric properties are also important in the selection of
proper packaging materials.
6. In design of microwave and radio frequency heating
7. When selecting equipment for drying low moisture foods
should prevent electric field strength from exceeding a level at
which flash-over would take place.
8. RF energy is mostly used to heat or evaporate moisture from a
product; higher frequency MWs are used for defrosting & low
MEASUREMENT OF DIELECTRIC PROPERTIES OF
PUMPABLE FOOD MATERIALS UNDER STATIC
AND CONTINUOUS FLOW CONDITIONS
• Continuous flow microwave sterilization is an
emerging technology that has the potential
to replace the conventional heating
processes for viscous and pumpable food
• Dielectric properties of pumpable food
products were measured by a new approach
(under continuous flow conditions) at a
temperature range of 20 to 130 °C and
compared with those measured by the
• The food products chosen for this study
were skim milk, green pea puree, carrot
puree, and salsa . Second-order polynomial
correlations for the dependence of dielectric
properties at 915 MHz of the food products
on temperature were developed.
• Dielectric properties measured under static
and continuous flow conditions were similar
for homogeneous food products such as
skim milk and vegetable puree, but they
were significantly different for salsa con
queso, which is a multiphase food product.
This presentation includes information on the influence
of important factors affecting the dielectric properties of
agricultural and food products. It includes examples showing
the nature of the influence of these factors on the dielectric
properties of materials, and thus will be helpful to those
considering applications of dielectric properties for sensing
quality attributes of food products and for those considering
microwave or radio-frequency dielectric heating applications