Ohmic processing
- 1. OHMIC PROCESSIN GMontica Sawant SY Tech (FET) 13FET1007
- 2. What is ohmic heating?➜ Ohmic heating is an advanced thermal processing method wherein the food material, which serves as an electrical resistor, is heated by passing electricity through it. ➜ Unlike conventional heating where heat transfer occurs from a heated surface to the product interior by means of convection and conduction, Ohmic heating has inside– outside heat transfer pattern ➜ Electrical energy is dissipated into heat, which results in rapid and uniform heating with minimal thermal degradation. ➜ Also called electrical resistance heating, Joule heating, or electro-heating, and may be used for a variety of applications in the food industry. ➜ Similar to HTST processing with the added benefit of uniform and complete heating of particulate food systems like soups.
- 3. PRINCIPLE ➜ Based on the passage of alternating electrical current (AC) through a body such as a liquid-particulate food system which serves as an electrical resistance in which heat is generated. ➜ Foods contain water & ionic salts; capable of conducting electricity, but also have a resistance which generates heat when an electric current is passed through. This resistance produces heat. ➜ Inactivate microorganisms by heat and additional electroporatic effect.
- 4. WORKING ➜ Electrode: Platinized titanium electrode to prevent leaching(ofte coated with a high temp inert plastic material) (if steel stainless steel electrodees are used working at frequencies of above 100khz eliminates this problem) ➜ Temp 40-140 degree C, for <90 sec followed by cooling for 15 minutes ➜ Pressure of up to 4 bar for UHT to prevent product from boiling ➜ Frequency 50-60 Hz ➜ Voltage upto 5000 Vhttp://disciplinas.stoa.usp.br/pluginfile.php/234401/mod_resource/content/1/cr1216_13.pdf
- 5. ➜ A viscous food product containing particulates enters the continuous-flow ohmic heating system via a feed pump hopper. ➜ The product then flows past a series of electrodes in the ohmic column, where it is heated to process temperature. ➜ Then the product enters the holding tubes for a fixed time to achieve commercial sterility. ➜ Next, the product flows through tubular coolers and into storage tanks, where it is stored until filling and packaging ➜ Shelf life of Ohmically processed foods is comparable to canned and sterile, aseptically processed products
- 6. CONTROL PARAMETERS ➜ Electrical conductivity, temperature dependence of conductivity, design of heating device, residence time, thermo physical properties of food, electric field strength. ➜ However, the most important factor is the electrical conductivity of the product and its temperature dependence. ➜ If the product has more than one phase such as in the case of a mixture of liquid and particulates, the electrical conductivity of all the phases has to be considered. ➜ The electrical conductivity increases with rising temperature(resistance of food falls by factor of 2 to 3 over temperature rise of
- 7. Factors affecting ohmic heating ➜ Electrical conductivity of food and food mixture which in turn depends on food components: ionic components (salt), acid, and moisture mobility increase electrical conductivity, while fats, lipids, and alcohol decrease it ➜ Fluid viscosity : higher viscosity fluids shows faster ohmic heating than lower viscosity fluids ➜ In case of liquid + solid mixture, the property difference of the two components also affects ohmic heating, particulate size (upto 25mm ideally ) ➜ Density and specific heat of the food product
- 9. Applications ➜ Ohmic heating can be used for heating liquid foods containing large particulates, such as soups, stews, and fruit slices in syrups and sauces, and heat sensitive liquids. ➜ The technology is useful for the treatment of proteinaceous foods, which tend to denature and coagulate when thermally processed. For example, liquid egg can be ohmically heated in a fraction of a second without coagulating it. ➜ Juices can be treated to inactivate enzymes without affecting the flavor. ➜ Other potential applications of ohmic heating include blanching, thawing, on-line detection of starch gelatinization, fermentation, peeling, dehydration, and extraction. ➜ Currently used in a large number of fruit processing plants in the US and Europe
- 10. Advantages Disadvantages ➜ It can heat particulate foods and Liquid–particle mixtures. (impossible by conventional methods) By ohmic heating, high temperatures can be rapidly achieved(due to uniform heating). For e.g. temperatures for ultra high temperature (UHT) processing ➜ As there are no hot surfaces for heat transfer, there is low risk of product damage due to burning ➜ It has high energy conversion efficiency (90%) ➜ It requires relatively low capital cost. ➜ Very clean and hygienic systems ➜ Minimal thermal deterioration of food resulting in minimal mechanical damage and better nutrients and vitamin retention, shorter operation time ➜ Complex relationship between conductivity and temperature ➜ Leaching of electrode material into the food systems ➜ ohmically processed multi-phase food product Not yet approved by the FDA (as of 2001) ➜ Expensive in terms of installation and equipment manufacture ➜ Low conductivity foods cannot be processed eg. foods having fat globules ➜ Rapid increase of conductivity with temperature may lead to “runaway heating” ➜ Lack of data concerning critical factors affecting heating, including residence time, orientations, loading levels, etc ➜ Lack of data correlating the
Editor's Notes
- #3: The rate of heating is directly proportional to the square of the electric field strength, E, and the electrical conductivity. The electric field strength can be varied by adjusting the electrode gap or the applied voltage. However, the most important factor is the electrical conductivity of the product and its temperature dependence. The electrical conductivity increases with rising temperature, suggesting that ohmic heating becomes more effective as temperature increases.
- #4: The rate of heating is directly proportional to the square of the electric field strength, E, and the electrical conductivity. The electric field strength can be varied by adjusting the electrode gap or the applied voltage. However, the most important factor is the electrical conductivity of the product and its temperature dependence. The electrical conductivity increases with rising temperature, suggesting that ohmic heating becomes more effective as temperature increases.
- #5: http://disciplinas.stoa.usp.br/pluginfile.php/234401/mod_resource/content/1/cr1216_13.pdf