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DIELECTRIC PROPERTIES OF FOODMATERIALS PRESENTED BY:-SAQIB
RASHID [email protected] 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
polarization.The study of dielectric properties concerns storage
and dissipation of electric and magnetic energy in materials.
INTRODUCTIONCont 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 Properties of Food MaterialsDielectric
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 electric fields Water content Temperature Density of the
materialsFactors that Influence Dielectric PropertyThe dielectric
properties of most materials vary with several influencing
factors:The dielectric properties also depend on the:Frequency of
the applied alternating electric field,Temperature of the
material,Density,Composition,Structure of the material. In granular
or particulate materials the bulk density of the air-particle
mixture is another factor that influences the dielectric
properties. 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 foodType of
foodDegree of accuracyFrequencyReflection of transmission
typeMethodsTransmission lineCoaxial probeCavity perturbationFree
space transmission
Dielectric constant of whey protein
Dielectric Measurement Method 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 measured.From
these changes the dielectric constant and loss factor are
determined.Useful in detection processing conditions, or the
quality of foods.The major uses for dielectric properties are
measuring and heating applications. Properly designed electrical
instruments can be used to determined moisture content or water
activity. Knowledge of dielectric properties in partially frozen
material is critical in determining the rates and uniformity of
heating in microwave thawing. Application 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 processes. 5.Dielectric properties are also
important in the selection of proper packaging materials.In design
of microwave and radio frequency heating equipment.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 pressure dryingMeasurement of Dielectric Properties of Pumpable
Food Materials under Static and Continuous Flow
ConditionsContinuous flow microwave sterilization is an emerging
technology that has the potential to replace the conventional
heating processes for viscous and pumpable food products.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 conventional
approach.Cont
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 as well.Conclusion
