Keywords: ohmic heating up equation, ohmic home heating plasma, ohmic heating up food
Ohmic heating system is also known as joule home heating, electric resistance heating system, direct electric warming, electro heating system and electro conductive heat. It is a procedure where alternating electric current is passed through food material to warm up them. Heating is internally made within the materials due to the applied electro-mechanical current. In typical heating, heat transfer occurs from a heated surface to the product interior by the means of convection and conduction and it is time consuming especially with longer conduction or convection pathways that may can be found in the heating process. Elecroresistive or ohmic heat is volumetric in aspect and thus gets the potential to lessen over handling by virtue of its inside-outside heat transfer pattern. Ohmic heating up is distinguished from other electronic heat method by the presence of electrodes getting in touch with the meals by regularity or by waveform.
Ohmic home heating is not really a new technology; it was used as a commercial process in the first twentieth hundred years for the pasteurization of milk. However, the electro pure process was discontinued between the late 1930s and 1960s ostensibly due to prohibitive cost of the electricity and too little suitable electrode material.
Interest in ohmic home heating was rekindled in the 1980s, when researchers were looking for viable methods to effectively sterilize liquid- large particle mixtures, a circumstance that aseptic processing alone was unsatisfactory. (Rahman, 1999)
Ohmic heating up is one of the newest methods of warming foods. It is often desirable to warm up foods in a continuing system such as heating exchanger alternatively than in batches as in a kettle or after sealing in a can. Constant systems have the advantage that they produce less temperature damage in the merchandise, are better, and they can be coupled to aseptic presentation systems. Continuous home heating systems for fluid foods that contain small particles have been designed for many years. However, it is a lot more challenging to safely warm up liquids containing greater debris of food. This is because it is very difficult to see whether a given particle of food has received sufficient heat to be commercially sterile. That is especially critical for low acidity foods such as Beef stew which can cause fatal food poisoning if under heated. Products tend to become over processed if conventional temperature exchangers are being used to add sufficient heating to particulate foods. This concern has hindered the development of aseptic presentation for foods comprising particulates. Ohmic warming may over come a few of these difficulties and limits.
Considerable heat is generated when an alternating electric current is transferred through a conducting solution like a salt brine. In ohmic home heating a low-frequency alternating current of 50 or 60 Hz is combined with special electrodes. Products in a executing solution (almost all polar food fluids are conductors) are consistently handed down between these electrodes. In most cases the merchandise is transferred between several sets of electrodes, each which raise the temperature. After heating, products can be cooled in a continuing temperature exchanger and then aseptically filled up into presterlized storage containers in a manner similar to standard aseptic packaging. Both high and low- acid solution products can be prepared by this method. (Potter et al, 2006)
An improvement in the thermal control is ohmic home heating. In concept, electricenegy is changed into thermal energy uniformly throughout the product. Rapid warming results, and better dietary and organoleptic features are possible when compared with typical in -can sterilization. "Ohmic warming employs electrodes immersed on pipe, '' Quass says. " Product is pumped through the tube as current flows between the electrodes. '' Depth of penetration is not limited. The extent of heating depends upon the electric powered conductivity through the merchandise, plus residence time in the electric field. "ohmic heating up is useful for foods thus burn-on or have particulates that plug up high temperature exchangers, '' continues Quass. "Rather than using a scraped surface high temperature exchanger for stew, for example, ohmic heating can reduce the come-up time, and improve product quality. '
Ohmic heating system is defined as a process wherein (mainly alternating) electric currents are transferred through foods or other materials with the principal purpose of heat them. The home heating occurs in the form of internal energy technology within the material. Ohmic heating system is recognized from other electrical power heating up methods either by the occurrence of electrodes contacting the meals (instead of microwave and inductive heating system, where electrodes are absent), regularity (unrestricted, except for the specially assigned radio or microwave rate of recurrence range), and waveform (also unrestricted, although typically sinusoidal). In inductive warming, electric coils positioned nearby the food product generate oscillating electromagnetic fields that send electric currents through the food, again mainly to heat up it. Such areas may be produced in a variety of ways, like the use of the moving food materials as the secondary coil of your transformer. Inductive home heating may be distinguished from microwave heating up by the rate of recurrence (specifically assigned in the case of microwaves), and the nature of the foundation (the necessity for coils and magnets for era of the field, in the case of inductive home heating, and a magnetron for microwave warming). Home elevators inductive heating is incredibly limited.
A project was conducted in the mid-1990s at the Technical School of Munich (Rosenbauer 1997), under sponsorship from the ENERGY Research Institute. No data about microbial death kinetics under inductive warming were posted. Thus, the succeeding discussion focuses on ohmic heating. A large number of potential future applications can be found for ohmic heating up, including its use in blanching, evaporation, dehydration, fermentation, and extraction. The present talk, however, concerns mainly its software as a heat treatment for microbial control. With this sense, the main advantages claimed for ohmic home heating are immediate and relatively standard heating. Ohmic heating up is currently being used for processing of complete fruits in Japan and the United Kingdom. One commercial center in america uses ohmic heat for the processing of liquid egg. The principal advantage stated for ohmic heating up is its capacity to heat up materials rapidly and uniformly, including products containing particulates. That is expected to reduce the total thermal maltreatment to the merchandise compared to conventional heat, where time must be allowed for high temperature penetration to occur to the center of a materials and particulates heat slower than the fluid phase of any food. In ohmic home heating, particles can be produced to warm up faster than liquids by properly formulating the ionic material of the liquid and particulate period to guarantee the appropriate levels of electrical conductivity.
Principle of ohmic heat:
Joule heating system is generally known as ohmic warming or resistive home heating because of its romantic relationship to OhmHYPERLINK "http://en. wikipedia. org/wiki/Ohm's_law"'HYPERLINK "http://en. wikipedia. org/wiki/Ohm's_law"s Laws.
Ohm's law states that, at frequent temperature in an electrical circuit, the existing passing through a conductor between two factors is directly proportional to the actual difference (i. e. voltage drop or voltage) over the two points, and inversely proportional to the level of resistance between them.
The mathematical equation that details this relationship is:
I= v/R
Where,
I is the current in amperes, V is the potential difference between two points of interest in volts, and R is a circuit parameter, measured in ohms (which is the same as volts per ampere), and is called the resistance. The actual difference is also known as the voltage drop, and may also be denoted by U, E or emf (electromotive power) instead of V.
The law was named following the physicist Georg Ohm, who, in a treatise printed in 1827, explained measurements of applied voltage and current passing through simple electro-mechanical circuits containing various lengths of wire. He provided a slightly more technical equation than the one above to explain his experimental results (the above equation is the present day form of Ohm's legislation; it might not exist before ohm itself was identified (1861, 1864)). Prior to Georg Ohm's work, Henry Cavendish found experimentally (January 1781) that current varies in direct percentage to applied voltage, but he didn't communicate his results to other scientists at that time.
The resistance of all resistive devices (resistors) is regular over a sizable range of prices of current and voltage. When a resistor can be used under these conditions, the resistor is known as an ohmic device just because a solo value for the amount of resistance suffices to describe the resistive patterns of these devices over the range. When sufficiently high voltages are put on a resistor, forcing a higher current to flow through it, the device is no longer ohmic because its level of resistance, when measured under such electrically pressured conditions, is different (typically increased) from the worthiness assessed under standard conditions (see temperature effects, below).
Ohm's legislation, in the form above, is an extremely useful equation in the field of electrical/electronic engineering because it describes how voltage, current and resisitance are interrelated on the macroscopic level, that is, commonly, as circuit elements within an electro-mechanical circuit.
Advantages of ohmic heating up :
Ohmic heating exhibits several advantages with respect to conventional food handling technologies as follows.
Particulate foods upto 1 in are suitable for ohmic heating system; the flow of any liquid particle blend approaches plug movement when the solids content is extensive (20-70%).
Liquid particle mixtures can warm up uniformly under some circumstances (for example, if fluids and contaminants posses similar electro-mechanical conductivities or if properties such as solids focus, viscosity, conductivity, specific high temperature and movement rate are manipulated appropriately).
Temperatures sufficient for super high temperature (UHT) control can be speedily achieved.
There are no heating surfaces for heating transfer, resulting in a low threat of product harm from burning or higher processing.
Energy alteration efficiencies.
Relatively low capital cost. (Biss et al 1989)
Parameters worth focusing on in ohmic home heating:
Product properties :
The most important parameter appealing in ohmic heat is the electrical power conductivity of the meals and food mixture. Large research was conducted on this property in the first 1990s due to importance of electrical power conductivity with regard to heat transfer rate and heat range distribution. The electrical conductivity is set using the following equation:
'= L / AR
Where ' is the precise electrical power conductivity (S/m), A the region of cross portion of the test (m2), L the distance of the sample (m), and R the resistance of the test (ohm). General findings of numerous electronic conductivity studies are as follows.
The electric conductivity is a function of food components; ionic components (sodium), acidity, and moisture range of motion increase electro-mechanical conductivity, while excess fat, lipids, alcohol cut down it. Electrical conductivity is linearly correlated with temperature when the electronic field is sufficiently high (at least 60 V/cm).
Nonlinearities (sigmoid curves) are found with lower electric field durability.
Electrical conductivity increases as the temp and applied voltage raises and lowers as solids content rises.
Lowering the frequency of AC during ohmic heat increases the electro-mechanical conductivity.
The waveform can affect the electronic conductivity; through AC is usually provided in sine waves, sawtooth waves increased the electric powered conductivity in the some cases, while rectangular waves lowered it.
Electrical conductivity as opposed to raw sample revealed increased electro-mechanical conductivity instead of raw examples when both were eventually subjected to ohmic home heating.
The electrical power conductivity of solids and liquids during ohmic heating system of multiphase mixtures is also critically important. In an excellent situation, liquid and stable phases posses essentially equal electric conductivities and would thus (generally) high temperature at the same rate. Whenever there are dissimilarities in the electronic conductivity between a fluid and solid debris, the particles high temperature more slowly a substance when the electrical power conductivity of the sturdy is greater than that of the smooth. Fluid motion (convective heat transfer) is also an important account when there are electrical conductivity dissimilarities between liquids and contaminants.
Other product properties which could affect temperature syndication include the thickness and specific heating of the meals product. When stable contaminants and a fluid medium have similar electric conductivities, the component with the lower temperature capacity will tend to heat faster. Warmth densities and specific heats are conductive to slower home heating. Smooth viscosity also affects ohmic heat; higher viscosity fluids tend to result in faster ohmic home heating than lower viscosity essential fluids.
Texture Examination :
Sensory evaluation is critically important to any practical food operations. Numerous publications have cited the superior product quality that may be obtained through decreased process time, though few written and published studies specifically quantify sensory and texture issues. Six stew formulations sterilized using ohmic home heating before and after three years of storage area were analyzed; the colour, appearance, flavor, feel, and overall food quality scores were excellent. 'Indicating that ohmic heating system technology has the potential to provide shelf-stable foods mechanised properties of hamburgers grilled with a blend of standard and ohmic warming were not not the same as hamburgers cooked properly with conventional warming.
Microbial Loss of life Kinetics:
In terms of microbial loss of life kinetics, substantial attention has been paid to the following question: does indeed electricity result in microbial death, or is microbial loss of life caused solely by heat therapy? The challenge in modeling microbial fatality kinetics is precise matching of time-temperature histories between ohmic heat and standard process. The FDA has posted a comprehensive overview of microbial death kinetics data regarding ohmic home heating.
Initial studies in this field showed combined results, although experimental details were judged insufficient to draw important conclusions. Researches likened death kinetics of candida skin cells under ohmic heating up. Newer work in this area has suggested those decimal decrease times of Bacillus Subtiles spores were significantly reduced when working with ohmic heat at identical temps. These investigators also used a two-step treatment process including ohmic heating, followed by holding and heat therapy, which accelerated microbial fatality kinetics. The inactivation of yeast cells in phosphate buffer by low-amperage immediate current (DC) electrical treatment and normal warming at isothermal heat was examined. These researchers concluded that a synergistic aftereffect of heat and electrolysis was witnessed when the temp became lethal for yeast.
Future research regarding microbial loss of life kinetics, survivor matters after treatment, and the impact of electricity on cell death kinetics are essential to address regulatory issues. Currently, assuming that microbial death is only a function of heat (warmth) results in an appropriately conventional design assumption.
Vitamin Degradation Kinetics:
Limited information is available regarding product degradation kinetics during ohmic heating. Researchers measured supplement C degradation in orange drink during ohmic and classic heating under nearly identical time-temperature histories and concluded that electricity didn't influence supplement C degradation kinetics. This research was conducted at one electrical field power (E=23. 9 V/cm). Others discovered that the ascorbic acid degradation rate in buffer solution during ohmic heat was a function of vitality, temperature, NaCl awareness, and products of electrolysis. Further research in this area could include the influence of electric field strength, end point temperature and consistency of AC on the degradation of food components during ohmic heating up. The characterization of electrolysis is also critical need in this field.
Mechanisms of Microbial Inactivation
The main mechanisms of microbial inactivation in ohmic heating system are thermal in nature. Occasionally, you can wish to decrease the process requirement or even to use ohmic heating up for a light process, such as pasteurization. It could then be beneficial to identify additional non-thermal mechanisms. Early on literature is inconclusive, since temps had not been completely eradicated as a varying. Recent literature that has taken away thermal distinctions, however, indicates that a mild electroporation device may occur during ohmic warming. The principal cause for the additional effect of ohmic treatment may be its low consistency (50 - 60 Hz), which allows cell walls to build up charges and form pores. This is as opposed to high-frequency methods such as radio or microwave rate of recurrence heating, where the electric field is actually reversed before sufficient charge accumulation occurs at the cell surfaces.
Applications of ohmic heating in food sectors:
Ohmic heating can be applied to wide selection of foods, including liquids, solids and fluid-solid combination.
Ohmic heating is being used commercially to create liquid egg products in United States.
It is being used in the uk and Japan for the control of entire fruits such as Strawberries.
Additionally, ohmic warming has been efficiently applied to wide selection of foods in laboratory including Vegetables & fruits, juices, sauces, stew, meat, seafood, pasta and soups.
Widespread commercial adoption of ohmic heat in america is dependent on regulatory acceptance by the FDA, a scenario that requires full knowledge of the ohmic heating system process in regards to to heat transfer (temperature distribution), mass copy (concentration distribution, which can be inspired by electricity), momentum copy ( fluid stream) and kinetic phenomena (thermal and perhaps electro thermal loss of life kinetics and nutritional degradation)
Researches LINKED TO Effect Of Ohmic Heating up On Food Products:
Ohmic heating system could up juice quality:
Israeli researchers say that ohmic warming of orange juice has proved to be great way of bettering the flavor quality of orange juice while increasing sensory shelf life.
The researchers were seen that sensory shelf life of orange drink could be long to more than 100 days, doubling expectancy compared to pasteurization methods. Ohmic home heating uses electricity to swiftly and uniformly warm up food and drink, resulting in less thermal harm to the product. The technology has been around since the early 1900s, but it was not until the 1980s that food control researchers began looking into the possible benefits to the industry.
The scientists likened pasteurized orange drink, which had been warmed at 9o‹c for 50 sec, with orange that was treated at 90, 120 and 150‹c for 1. 13, 0. 85 and 0. 68 sec within an ohmic heat. The experiment found that for all illustrations retention of both pectin and vit. C was reported similar. In the same way both treatments avoided the progress of micro-organisms for 105 days, compared to fresh orange drink. However, where in fact the ohmic heated examples proved much more powerful was in the preservation of flavours and the overall style quality over a period. The scientists examined five representative taste ingredients- decanal, octanol, limonene, pinene and mycrene. Evaluating showed that levels of these substances were significantly higher in the ohmic treated samples after storage area than in the pasteurized instances.
The experts' results found that only adverse effect that the ohmic treated orange juice possessed that it increased browning in the drink, although this is not reported to be visible, until after 100 days and nights. Conversely the appearance of the ohmic heated samples was said to be visibly less cloudy. The implications of the results to the juice industry could be huge getting as quality is a significant driving make for something that is often marketed in the top quality category. If the expense of implementation proves competitive then this may become a serious contender to pasteurized methods. (Siman et al 2005)
Ohmic heating patterns of hydrocolloid solutions:
Aqueous alternatives of five hydrocolloids (Carrageenan, 1-3%; xanthan, 1-3%; pectin, 1-5%; gelatin, 2-4% and starch, 4-6%) were heated in a static ohmic heat call at a voltage gradient of 7. 24V cm-1. Time and temperaturedata, noted at selected time intervals, were used to study the result of attentiveness and temp on the ohmic heating system habit of hydrocolloid alternatives. Of the test samples evaluated, carrageenan gave the shortest time to raise the heat from 20 to 100‹c: 4200, 1600 and 1100s at 1, 2 and 3% concentraton respectively. For the same temp raise, xanthan examples required 5500, 2300 and 1400s at 1, 2 and 3% attentiveness levels. Pectin and gelatin samples were found to demonstrate even lower, but similar warming information. At highest concentration (5%), pectin had taken 7300s to attain 100 from 20‹c, and at all other concentrations, the time limit of 10, 000s was exceeded before it reached 100‹c. The heat range of starch solutions never exceeded 62‹c within the given time limit. Home heating was found to be uniform throughout examples for carrageenan, pectin (1-3%) and gelatin examples. For xanthan and starch alternatives, some non-uniformity in temperature profiles was discovered. The noticed ohmic heating action of hydrocolloid solutions corresponded well using their electrical conductivity worth. The homogenesity of heat was related to rheological properties of hydrocolloid alternatives and values. The homogenesity of heating system was related to rheological properties of hydrocolloid solutions and their action at high temperature. (Marcotte et al 1998)
Design and performance analysis of the ohmic heating product for liquid foods:
An experimental ohmic heat unit was designed and fabricated for constant thermal handling of liquid foods. The machine was reinforced by a data acquisition system for sensing the liquid temp distribution, lines voltage and current with time. A separate small ohmic heat unit was also used for batch heating system tests. The info acquisition system performed well and may record temperatures, voltage and current at intervals of two secs. The performance of the ohmic warming unit was assessed predicated on batch and steady state continuous circulation experiments. Testing with 0. 1 M aqueous sodium chloride solution showed the ohmic heat to be fast and uniform. In batch home heating tests, the electric powered conductivity of the liquid could be driven easily as a function of temps using instantaneous ideals of the voltage gradient and current density. In continuous move heating tests, other physical properties, applied voltage gradient and dimensions of product the heat. (Jindal et al, 1993)
4. Persistence of starch gelatinization temps by ohmic
heating :
A way for measuring starch gelatinization temperatures (T), motivated from a change in electric powered conductivity (±), originated. Suspension of indigenous starches with different starch/ water mass ratios and pre-gelatinized starches were prepared, and ohmicallly warmed with agitation to 90‹c using 100V by AC electric power at 50 Hz, and a voltage gradient of 10 V/cm. the results showed that ± of local starch suspensions was linear with temp (R2>0. 999) expect for the gelatinization range, however the linear romantic relationship was always present for the pre-gelatinized starch-water system. It had been seen that the form of d±/dT versus T curve was essentially like the endothermic peak on the DSC thermo gram, and the gelatinization temperature could be handily determined from this curve. Thus, the segment profile on this curve was called the "block peak". The reason behind the reduction in ± of indigenous starch suspension system in the gelatinization range was probably that the region foe motion of the billed debris was reduced by the bloating of stearch granules during gelatinization. ( Tatsumi et al 2003)
5. Ohmic heating of strawberry products: electronic conductivity measurements and ascorbic acid degradation kinetics
The effect of field durability and multiple thermal treatments on electrical conductivity of strawberry products were investigated. Electrical conductivity increase with temperature for all your products and conditions analyzed following linear relationships. Electrical conductivity was found to rely upon the strawberry- based mostly product. , a rise of electronic conductivity with field strength was obvious for just two strawberry pulps and strawberry filling up however, not for strawberry-apple sauce. Thermal treatments caused obvious changes (a lower) in electric powered conductivity worth of both strawberry pulps analyzed, but the use of a conventional or ohmic pre-treatment induces a different patterns of the pulps' conductivity beliefs. Ascorbic acid solution degradation used first order kinetics for both conventional and ohmic heat treatments and the kinetic constants obtained were in the range of the principles reported in the literature for other food systems. The occurrence of a power field does not affect ascorbic acid degradation. (Castro et al, 2003)
6. Polyphenoloxidase deactivation kinetics during ohmic heating of grape juice
The heating up method affects the temperature distribution inside a food and immediately modifies the time-temperature marriage for enzyme deactivation. Fresh grape drink was ohmically warmed at different voltage gradient (20, 30 and 40 V/cm) from 20‹C to conditions of 60, 70, 80 or 90‹c and the change in the experience of polyphenoloxidase enzyme (PPO) was assessed. The critical deactivation temps were found to be 60‹c or lower for 40V/cm were fitted to the experimental data. The easiest kinetic model affecting one step first-order deactivation was much better than more technical models. The activation energy of the PPO deactivation for the heat range selection of 70-90‹c was found to be 83. 5 kJ/mol. (Baysal et al, 2006)
7. Handling and stabilization of cauliflower by ohmic heating technology:
Cauliflower is a brittle product which does not resist standard thermal treatments by warmth. The feasibility of processing cauliflower by ohmic warming was investigated. Cauliflower florates were sterilized in 10 kW APV continuous ohmic heating pilot flower with various configurations of pre-treatments and processing conditions. The balance of last products was analyzed and textural qualities were examined by mechanised measurements. Ohmic heat treatments gave something of attractive appearance, with interesting firmness properties and percentage of debris >1cm. stabilities at 25‹c and 37‹c were confirmed and in one case, the merchandise was even secure at 55‹c. Low temperatures precooking of cauliflower, higher rate and sufficient electro-mechanical conductivity of florates seem to be to be optimal conditions. The interest of using this electronic technology to process brittle products such as ready foods formulated with cauliflower was high lightened. (Sandrine et al, 2006)
The commercial development of ohmic heating up processes
The creators discuss the problems of heat transfer techniques in cook-chill food control. These include damage of flavours and nutrition, and particle harm due to high shear often utilized to improve warmth copy rates. These high temperature transfer problems have been overcome with the development of ohmic heat technology. The ohmic heat result occurs when an electric current is approved via an electrically performing product. In practice, low frequency alternating electric current (50 or 60 Hz) from the public mains supply is used to eliminate the likelihood of adverse electro-chemical reactions and minimise power difficulty and cost. Electrical energy is changed into thermal energy. The depth of penetration is nearly endless and the magnitude of warming is governed only by the spacial uniformity of electric powered conductivity throughout the merchandise and its residence time in the heating unit. The authors quickly discuss the look features, temperatures control and market popularity of ohmic warming. (Skudder et al 1992)
8. Electro-mechanical conductivity of apple and sour cherry juice concentrates during ohmic heating
Ohmic heating is based on the passing of electrical current through a food product that functions as a power resistance. In this research, apple and sourcherry concentrates having 20-60% soluble solids were ohmically heated up through the use of five different voltage gradients (20-60 V/cm). The electrical conductivity relationships depending on heat range, voltage gradient and concentration were obtained. It was detected that the electronic conductivities of apple and sourcherry juices were significantly afflicted by heat and focus (P < 0. 05). The ohmic heat performance coefficients (SPCs) were described utilizing the energies directed at the system and adopted by the juice examples. The SPCs were in the number of 0. 47-0. 92. The unsteady-state heat conduction equation for negligible inner resistance was fixed with an ohmic heating up era term by the finite difference technique. The numerical model results considering system performance coefficients were weighed against experimental ones. The predictions of the numerical model using obtained electric conductivity equations were found to be very appropriate.
(Coskan et al 1999)
CONCLUSION:
The studies discuss the problems of heat copy techniques in cook-chill food control. These include devastation of flavours and nutrition, and particle destruction due to high shear often hired to improve high temperature copy rates. These temperature transfer problems have now been overcome with the development of ohmic heat technology.
The Energy efficiency is more and also the price of preservation is also low so, it is effective to work with the this system.
