Ohmic
Back to EFFICIENCY FINDER OF FOOD INDUSTRY
Ohmic heating
Contents
General Information
Overview
The use of the technologies starts in 1900 with resistance heating patents for sterilization. Strict control of operating parameters were not always possible and proper inert material for electrodes were not feasible at that time. The development of the technology go hand in hand with the development of electricity and electronic materials fields.There is a growing interest for treatment of viscous products and product with large particles in liquid medium.
(Goullieaux & Pain, 2014)
Advantages
- The technology enables internal heat generation, the wall temperature can be cooler than the heated medium.
- Volumetric heating and high energy efficiency.
- Higher temperature in particles than in liquid at the same conductivity factor.
- Reduced fouling, it can be kept at minimum.
- Process solid liquid food mixtures.
- Heating of safe ready to eat meals with high retention of nutrients and vitamins avoiding the degradation due to the conventional high processing temperature.
(Goullieaux & Pain, 2014)
Disadvantages
- The control of treatment homogeneity needs better modelling inputs. Variation of the initial process of different food and the variation of electric and thermal properties during the process.
- Food complexity composition enables high temperatures in some part of the product while in others is only a small increase.
- Electrode hygiene: corrosion and cleaning issues.
- Pretreatment may be needed, blanching for example.
- Higher capital investment than for conventional technologies.
(Goullieaux & Pain, 2014)
Base
- The base of the technology is the direct resistance heating enabled by the flow of an electrical current through food material.
- High potential in thermal processing due to the enhance transfer of mass and energy compared with normal material.
- Principle of ohmic heating or joule effect, the dispensation of electrical energy in the form of heat using an electrical conductor.
- The electric conductivity of the material is the main parameter. There is good conductivity (0.05 S/m) in condiments, eggs, yogurt, wine, etc. Low conductivity (<0.0005 S/m) requires high electrical field strength as in margarine, marmalade, powders. Poor conductivity difficult processing in frozen foods, fat and syrup. The conductivity increase with water content, temperature, voltage gradient and frequency but this do not apply to cell food products (membrane as insulator) and dehydrated product solutions.
- Plasmolysis in cells leads to an enhanced mass transfer.
(Goullieaux & Pain, 2014)
Description of techniques
The product is the conductive medium, solid electrodes are common in intimate contact with the product. Electrodes are feed by an electric power supply. The electrodes are separated by a tube or plate insulated. In continuous flow the main stages are heating, holding and cooling.
There are three main generic configurations:
Batch:
It is a static medium used for observations and model validations, adjustment on formulations and also as simulator tester. Used also to find the best conditions for continuous. I can be used for thawing a making new products.
Transverse configuration or constant electric field: the product flows parallel to electrodes. Fluid containing no particles are suitable.
Collinear configurations or at constant current density: the flow is parallel to the electric field. Used for liquid coagulation and cooking.
Treatment of products may be required as checking product suitability and points of improvement (conductivity preparation), stabilization features (speed of heating), microbial lethality (effectiveness) and impact on product quality (less time and less undesirable compound from Millard reaction leads to high quality products).
(Goullieaux & Pain, 2014)
Changes in process (Operation Unit Applications)
Cooking
- The technology enables sensorial quality retention and a higher cooking yield. More uniform, lighter and browner color in general is possible with the technology. Inhibition of microbial growth is possible.
- Toxicological test are needed on meet/electrode contact at high temperature.
- Examination of different kind of meat under wide range of ohmic conditions is needed.
- Results often depends on the fiber muscle direction, the fat content, the type of meat.
(Goullieaux & Pain, 2014)
Cases:
The ohmic heating of meat ball: Modeling and quality determination
Innovative Food Science & Emerging Technologies, Volume 23, June 2014, Pages 121-130 Wassama Engchuan, Weerachet Jittanit, Wunwiboon Garnjanagoonchorn
Blanching
- The technology enables an effective enzymatic deactivation depending on the voltage gradient. Also better color, reduced blistering and crispier texture in the food compared with conventional methods.
Conventional quality results for mushroom but in less time and with a more solid content. Leaching of water soluble substances increases, this can be avoided in vegetable through an immersion in saline solution. Properly designed leads to a more rapid and more energy efficient process.
(Goullieaux & Pain, 2014)
Extraction
- The technology enables an improved mass transfer proportional to the electric field and to the area of the sample (proved in Juice extraction yields improvement). Reduction in extracting time almost 80% is possible.
- Lowering the frequency of alternative current can also improve the yield of extraction.
- Lower energy need.
- Due to the synergy of electrical and thermal effects on cell tissues, a lower temperature is needed for effective membrane damage with a lower electric field applied.
- Simplification equipment is possible compared to pulse electric field.
(Goullieaux & Pain, 2014)
Cases:
Ohmic heating-assisted extraction of anthocyanins from black rice bran to prepare a natural food colourant
Innovative Food Science & Emerging Technologies, Volume 27, February 2015, Pages 102-110
Patiwit Loypimai, Anuchita Moongngarm, Pheeraya Chottanom, Tanongsak Moontree
Drying
- The technology enables from 20 % to 60% less processing time to reach a similar level of results than conventional quality.
- The perme abilization of the structure and the redistribution of water are the main reasons for time reductions.
- With Vacuum impregnation synergy it is possible to increase up to 2 times the shelf life.
- Potential for enabling a significantly lower decrease in processing temperature.
(Goullieaux & Pain, 2014)
Cases:
Effect of pulsed-vacuum and ohmic heating on the osmodehydration kinetics, physical properties and microstructure of apples
Innovative Food Science & Emerging Technologies, Volume 12, Issue 4, October 2011, Pages 562-568
J. Moreno, R. Simpson, D. Estrada, S. Lorenzen, D. Moraga, S. Almonacid
Distillation
Ohmic assisted hydro distillation enables a quicker, more economical and a more environmental friendly process than the conventional methods keeping the quality of the product. The quality and quantity of essential oils extracted from herbs and other raw materials are affected by the extraction method.
(Gavahian, et al, 2012)
Thawing
A major advantage of using the technology for thawing is the way of heating through the conduction of electricity. A combination with conventional methods is beneficial due to the different ways of heating producing a more effective joint effect.
The opportunities for the application of the technology lies on that the electrical conductivity increases with temperature and it is approximately two orders of magnitude lower for frozen food than for thawed food leading to less degradation of the tissues.
Unit equipment with surface temperature sensing avoids the runaway heating problems.
- Thawing processes was faster when the brine concentration increases and the largest surface of the sample was perpendicular to e-field.
Stronger texture of gel is possible. Molecular, cellular and tissues interaction need still to be clarified.
(Goullieaux & Pain, 2014)
Case:
Changes in oxidation, color and texture deteriorations during refrigerated storage of ohmically and water bath-cooked pork
Innovative Food Science & Emerging Technologies, Volume 26, December 2014, Pages 341-346
Yan Dai, Yi Lu, Wei Wu, Xiao-ming Lu, Zhao-peng Han, Yi Liu, Xing-min Li, Rui-tong Dai
Energy Savings
- Focalized production and application of energy due to the internal heating of the samples (lower processing temperatures) leads to a more effective use of energy.
- Reduction of heating time enables important energy savings in the different unit operations.
- Due to the change in physical properties, it can enable energy saving in pumping equipment.
- Saving in energy are possible due to the reductions on the use of solvents due to the enhanced mass transfer properties.
Change in Energy Distribution
- Change from thermal energy sources to electric generation sources as the energy base for ohm heating is electricity.
References
- Gavahian, M., Farahnaky, A., Javidnia, K., Majzoobi, M. (2012) 'Comparison of ohmic-assisted hydrodistillation with traditional hydrodistillation for the extraction of essential oils from Thymus vulgaris L.', Innovative Food Science & Emerging Technologies,14(April), pp. 85-91.
- Goullieaux A., Pain J.P. (2014) 'Part IV: Alternative thermal processing: Chapter 22 Recent Development in Microwave Heating', in Sun, D. (ed.)Emerging Tehcnologies for Food Processing. UK: Academic Press, pp. 361-377.
