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Dielectric PROPERTIES OF FOOD

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DIELECTRIC

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Dielectric PROPERTIES OF FOOD

  1. 1. DIELECTRIC PROPERTIES OF FOOD MATERIALS PRESENTED BY:- 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
  2. 2.  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 polarization. The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. INTRODUCTION
  3. 3. CONT… • 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.
  4. 4. 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 electric fields  Water content  Temperature  Density of the materials
  5. 5. 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, 3. Density, 4. Composition, 5. Structure of the material.
  6. 6. 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.
  7. 7. MEASUREMENT OF DIELECTRIC PROPERTIES IN FOOD Type of food Degree of accuracy Frequency Reflection of transmission type Methods Transmission line Coaxial probe Cavity perturbation Free space transmission
  8. 8. DIELECTRIC CONSTANT OF WHEY PROTEIN
  9. 9. 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.
  10. 10. 1. Useful in detection processing conditions, or the quality of foods. 2. The major uses for dielectric properties are measuring and heating applications. 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 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. ”
  11. 11. 5. Dielectric properties are also important in the selection of proper packaging materials. 6. In design of microwave and radio frequency heating equipment. 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 pressure drying
  12. 12. 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 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.
  13. 13. 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.
  14. 14. 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.

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