INTRODUCTIONFresh foods have a limited shelf life and spoil veryquickly due to a high water content and easy availabilityof nutrients for microorganisms. Mechanical, physical,chemical, and microbial processes are the main causesof food spoilage. Therefore, processing of foods is veryimportant in order to maintain their health benefits andquality.Conventional thermal processing is widely used formicrobiological safety and food preservation [1]. Thistechnique effectively inactivates pathogens and spoilagemicroorganisms. However, the application of hightemperatures has a negative effect on the food quality,namely color, texture, flavor, as well as nutritionaland bioactive compounds [2, 3]. Heat transfer in traditionalthermal processing includes three mechanisms,namely convection, conduction, and radiation [4]. Theheterogeneous distribution of heat in different parts offood, which occurs because of internal resistance, addsto the negative impact on the food quality.Therefore, alternative technologies should be used tosolve these problems. Ohmic heating, or Joule heating,is an emerging technique for food processing thatseems to be a suitable alternative to conventional heattreatment. It generates heat by the passage of alternatingcurrent through food and the resistance of food particlesto electrical current. In fact, food forms part of anelectrical circuit in ohmic heating [5, 6].Since ohmic heating converts electrical energy tothermal energy, the temperature inside the food risesuniformly and rapidly [7, 8]. As a result, there are fewersensory changes, less off-flavor, fewer nutritional losses,and less bioactive degradation.217Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226In addition, this new technology ensures themicrobiological safety of the final product [9]. Otheradvantages of ohmic heating include shorter processingtime, higher efficiency, and lower maintenance cost.Ohmic heating has a variety of uses in food processing,namely in pasteurization, peeling, blanching, drying,and concentration [4]. Thus, we aimed to review thelatest studies on the application of ohmic heating in foodprocessing.RESULTS AND DISCUSSIONOhmic heating application in dairy industry.Ohmic heating technology appeared at the end of the19th century. Although it was first utilized to pasteurizemilk, ohmic heating was not commercialized due to theprocess control problems, high cost of electricity, andthe lack of suitable materials for electrode production.Today, it is applied in dairy processing to producesafe, healthy, and high quality dairy products [10].Particularly, it is used to pasteurize lactose-free milksince this product has good electrical conductivity.The material of electrodes used in ohmic heating is animportant issue in dairy production [11]. Less foulinghas been observed in titanium electrodes than instainless steel electrodes. This phenomenon can beexplained by the lower chemical reactivity of titaniumcompared to stainless steel. Also, milk pasteurizedby ohmic heating with titanium electrodes had asafe content of chromium and no iron, while milkpasteurized by ohmic heating with stainless steelelectrodes had more iron and chromium [12]. This is animportant hygienic aspect for designers of food industryequipment.The conditions of ohmic heating (variations offrequencies and voltages) are another factor whichaffects the final product. Costa et al. used ohmicheating with different voltages (2, 4, 5, 7, and 9 V cm−1at 60 Hz) to process sweet whey and compared theresults with conventional heating [9]. The authorsreported that a higher electric field intensity resultedin lower luminosity (L*) and lower color variation(ΔE*). However, a lower electric field intensity led tobetter retention of bioactive compounds. This mightbe due to the relationship between the duration of heatexposure, whey protein denaturation, and the productionof bioactive peptides. Besides, the authors recommendedthe 4 and 5 V ohmic heating for sweet whey, since theseconditions ensured suitable sensory and rheologicalproperties with higher bioactive compounds.In the study of Silva et al., ohmic heating was usedfor Dulce de leche treatment for the first time [13].Dulce de leche is a dairy product which is made byevaporation and sugar addition. The authors indicatedthat the low and intermediate electric field strengthgave the product weaker aroma, more bitter taste, anda higher sandiness score. At higher intensity, Dulce deleche was heated for a shorter time, which resulted in aweaker Maillard reaction and fewer Maillard reactionproducts (such as lactones and furans). Lactones andfurans are compounds which affect the aroma and flavorof sterilized products and may also have a negativeimpact on the quality of Dulce de leche. Furthermore,the ohmic-heated Dulce de leche had a homogeneousaccumulation of whey proteins on a smaller scale. Thisprevented the contact of lactose molecules, as wellas inhibited the growth of lactose crystals in size andsandiness in the final product [14].Ferreira et al. processed raspberry-flavored wheybeverage under different voltages and frequencies ofohmic heating [15]. The authors reported that certainparameters of this process (10, 100, 1000 Hz at 25 Vand 45, 60, 80 V at 60 Hz) had a notable effect on theparticle size, rheological properties, and the color ofthe whey beverage. Overall, ohmic-treated beveragesshowed higher viscosity than conventionally treatedsamples. Among ohmic-heated samples, 10 and 1000 Hzexhibited the highest viscosity due to the largerparticle size and cell aggregation, while voltage-treatedbeverages had lower viscosity. In addition, 10 Hz-treatedsamples exhibited more color changes because of theelectrochemical reaction. The authors proposed 10 and1000 Hz at 25 V as an optimal treatment to achieve thedesired color, physical, and rheological attributes.In another study, Ferreira et al. revealed that underextreme conditions of ohmic heating (80 V at 60 Hz and1000 Hz at 25 V), raspberry-flavored whey beveragehad the lowest antioxidant activity, compared to mildand intermediate conditions (45 and 60 V at 60 Hzand 10 and 100 Hz at 25 V) [16]. Furthermore, theohmic-heated samples showed higher α-glucosidaseand α-amylase inhibition in comparison with theconventionally treated beverages. This could berelated to the tendency of bioactive compounds inwhey proteins to bind to the active sites of enzymes.Reducing the activity of these enzymes can result inlower hydrolysis of disaccharides and polysaccharides,as well as glucose uptake, with blood sugar levels maintained[17].In a study of whey acerola-flavored beverage,Cappato et al. stated that ohmic heating decreased therelaxation period leading to small changes in fattyacid profiles, as well as preserving the nutritionalproperties of processed drink, compared to conventionalheating [18].Rocha et al. examined the quality parameters ofMinas Frescal cheese produced from milk pasteurizedby using ohmic heating [7]. This technique enhancedprotein hydrolysis, resulting in a lower content of proteinand a higher content of small peptides, compared to thecheeses made from conventionally treated milk. Cheesesmanufactured from milk subjected to ohmic heatingat the highest voltage showed the lowest proteolyticactivity and the highest protein levels, similarly to theconventional method. Generally, ohmic heating notablydecreased the hardness, elasticity, and firmness of thecheeses, yet improving their general acceptability. Lowand intermediate electric field intensity (4 and 8 V/cm)increased the production of bioactive compounds and218Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226antioxidant activity. Yet, these voltages altered the fattyacid profile and produced more saturated fatty acids.Therefore, ohmic heating at 8 V/cm was suggestedfor Minas Frescal cheese due to the shorter period ofprocessing.It was evidenced that ohmic heating resulted inlower hydroxymethylfurfural production and higheroverall acceptability of whey dairy drinks, compared toconventional heating at the same temperatures. This wasdue to the shorter time to reach the process temperature,uniform heat, and lack of hot spots formation [19].Thus, ohmic heating could be an innovative method forprocessing whey dairy drinks with improved sensoryproperties [20]. Table 1 summarizes recent applicationsof ohmic heating in food processing.Ohmic heating application in fruit and vegetableprocessing. Fresh fruits and vegetables spoil rapidlyafter harvesting due to their nature (Aw, nutrients, etc.).Thus, it is essential to process and convert them intoproducts which have a longer shelf life [42]. Thetraditional way is to concentrate fruit juices byconventional heating. However, this method impairs thequality of food due to a low coefficient of heat transferand a long processing time [4]. An alternative methodfor concentrating fruit juices is ohmic heating [43].Fruit juices have high electrical conductivity, whichmakes them suitable for the ohmic heating technology.Darvishi et al. reported that the content of total phenolsin ohmic-treated black mulberry juice was 3.0–4.5 timeshigher than in the samples treated conventionally [3].The performance of concentration in ohmic heating wasby about 38–46% greater than in conventional heating.In addition, the authors stated that as the voltageincreased, the process time decreased, resulting in fewerchanges in total phenols and pH.Similarly, high voltages (45 and 50 V) weresuggested by Norouzi et al. for concentration ofsour cherry juice [30]. Although ohmic heatingincreased the turbidity of sour cherry juice comparedto the conventional method, it was still less than theinitial turbidity. This might be due to an increase intotal phenols with enhanced voltage gradient [44].The authors also stated that the application ofdifferent voltages did not have a significant effecton color changes (ΔE) and color parameters such as“L” (lightness) and “b” (blueness/yellowness).Minimal alterations in terms of color have alsobeen detected in ohmic-treated sugarcane juice [25, 45].Fadavi et al. evaluated the impact of ohmic heatingand conventional heating on tomato juice [4]. Theyfound that ohmic heating caused little changes inthe properties of tomato juice (acidity, turbidity, andlycopene) and that these changes would be even lesssignificant in ohmic heating under vacuum.Conventional and ohmic dewatering of grapefruitand orange pulps were investigated by Stojceskaet al. [21]. The authors indicated that the moisturecontent decreased markedly during conventional andohmic drying, while the amount of vitamin C and pHdid not differ significantly.Another study found that the application of ohmicheating for concentration of orange juice under vacuumsignificantly reduced the concentration time and led tothe production of fruit juice with higher viscosity, bettercolor retention, and less decomposition of vitamin C,compared to processing under atmospheric conditions[46].Sabanci and Icier added that the changes in thetemperature of evaporation during the concentration oforange juice had a notable impact on the time to reachFigure 1 The effects of ohmic and microwave treatments on vitamin C content in cantaloupe juice. With the permission of thepublisher, Hashemi et al. [22]Time, sVitamin C, mg/kg 0 10 20 30 40 50 60 70 80 90 100 1108509501050011500125001350014501550016500750219Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226Table 1 Ohmic heating applications in food processingProduct ProcesspurposeOhmic heatingconditionsMain findings ReferencesWhey dairybeveragesThermalprocessing6, 9, 12, and15 V/cm – 500,1000, 1500, and2000 HzSamples processed by increased voltage gradient and frequenciespresented higher overall liking[20]Dulce de leche Thermalprocessing0, 2, 4, 6, 8, and10 V/cm –60 HzLow and intermediate electric field strength resulted in morebitter taste, weaker aroma, and higher sandiness; higher intensityreduced the heating time and weakened the Maillard reaction[13]Whey dairybeverageThermalprocessing6 V/cm – 60 Hz Ohmic heating led to less hydroxymethylfurfural production andincreased overall liking, compared to conventional heating at thesame temperatures[19]Sweet whey Thermalprocessing2, 4, 5, 7, and 9V/cm – 60 HzHigher electric field intensity resulted in lower luminosity andlower color variation; lower intensity led to better retention ofbioactive compounds[9]WheyraspberryflavoredbeverageThermalprocessing10, 100, and1000 Hz – 25 Vand 45, 60, and80 V – 60HzExtreme ohmic heating conditions led to the lowest antioxidantactivity, compared to mild and intermediate conditions;ohmic heating-treated samples showed higher α-glucosidaseand α-amylase inhibition, as well as higher viscosity, thanthe conventionally treated beverages; 10 Hz-treated samplesexhibited more color changes[15]Whey acerolaflavoreddrinkPasteurization 45, 60, and80 V –60 Hz and 10,100, and1000 Hz – 25 VOhmic heating led to small changes in fatty acids profiles orpreservation of nutritional properties, compared to conventionalheating; electric field effects caused small modifications ofnutritional aspects, while frequency had a stronger influence onthe quality of the product; high frequenЦcies (1000 and 100 Hz)resulted in better bioactive compounds and antioxidant capacity[18]Lactose-freemilkPasteurization 8.25 V/cm –50 HzThis product can be subjected to ohmic heating due to itsgood electrical conductivity; less fouling observed in titaniumelectrodes than in stainless steel electrodes[11]Minas Frescalcheese (MFC)Pasteurizationof milkintendedfor MFCmanufacture4, 8, and12 V/cmCheeses manufactured from milk subjected to ohmic heatingat the highest voltage showed the lowest proteolytic activityand highest protein levels, similar to conventional heating;ohmic heating decreased hardness, elasticity, and firmness, butimproved general acceptance of cheeses; production of bioactivecompounds and antioxidant activity increased at low andintermediate electric field intensity (4 and 8 V/cm)[7]Grapefruit andorange pulpsDrying 30 V/cm Vitamin C and pH did not differ significantly between ohmicheating and thermal dehydration[21]CantaloupejuicePasteurization 100 and 200 V Higher voltage resulted in a reduced number of pathogens andlower contents of vitamin C, carotene, and phenolic compounds[22]Pulque Pasteurization 60, 80, 100, and120 V – 60 HzOhmic heating improved the physicochemical and sensory properties,compared to conventional heating[23]Tomato juice Concentration 10.5, 13.2, and15.8 V/cm –50 HzOhmic heating caused slight changes in the properties of tomatojuice (acidity, turbidity, and lycopene) which were even less pronouncedwhen using vacuum[4]Orange juice Concentration 13 V/cm –50 HzOhmic heating treatment under vacuum resulted in better retentionof vitamin C and fewer color changes, compared to treatmentunder atmospheric conditions[24]SugarcanejuicePasteurization 60 Hz Ohmic heating and ultrasound did not affect phenolic compounds,whose content was similar to fresh juice; only slight colorchanges were caused by ohmic heating[25]PineapplecubesThermalprocessingElectrical powerwas calculatedbased on theelectricalconductivity ofpineapple cubesLightness and antioxidant properties of the pineapples did notdiffer significantly between ohmic heating and conventionalheating; ohmic heating increased the hardness of the pineapplescompared to the conventional method[26]Blanching 25, 30, and35 V/cmThe highest textural degradation was observed at all electric fieldstrengths at 90 s process time; higher strength (35 V/cm) resultedin a higher drying rate[27]220Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226Continuation of Table 1Product ProcesspurposeOhmic heatingconditionsMain findings ReferencesPear Assisting inlye peeling426, 479, 532,585, and638 V/mOhmic heating enhanced the product yield, efficacy of peeling, aswell as the quality of the final product; peel quality was best atmuch lower concentrations of lye (2% NaOH at 532 V/m and 3%NaOH at 426 and 479 V/m)[28]Mulberry juice Concentration 15, 20, 25, and30 V/cm –50 HzOhmic heating provided greater concentration than the conventionalmethod (about 38–46%); higher voltage reduced the process time,resulting in fewer changes in total phenols and pH[3]Pekmez Evaporation 17.5, 20.0,22.5, and25.0 V/cmEnergy consumption was higher in conventional heating than ohmicheating for all voltage gradients; energy efficiency increased withhigher voltage gradient[29]Sour cherryjuiceConcentration 8.3, 9.7, 122.0,11.1, 12.5, and13.9 V/cm –50 HzAlthough ohmic heating increased the turbidity of sour cherry juicecompared to the conventional method, it was still lower than theinitial turbidity; different voltages did not have a significant effecton color parameters such as “L” (lightness) and “b” (blueness/yellowness)[30]Coconut water Pasteurization 10 and20 V/cm –50 HzOhmic heating could completely inactivate peroxidase but notpolyphenol oxidase; no pink color found in ohmic heating-treatedsamples during cold storage, unlike conventionally pasteurizedsamples[31]Short grainriceCooking 60 Hz Ohmic heating adversely affected color parameters (color intensityand lightness), resulting in softer texture compared to the hotplatecooking system[32]Noodle Cooking 10.0, 12.5,15.0, and17.5 V/cm –60 HzTemperature come-up time decreased significantly with an increasein electric field; 15 V/cm electric field strength with the holdingtime of 90 s was suggested as the best treatment in terms ofdesirable texture and energy efficiency[33]Whole anddecorticatedpearl milletgrainCooking 60 Hz Grain pericarp considered the principal factor influencing thecooking process rather than the method of heating; no significantdifferences observed between conventional open-pan and ohmicheating methods in terms of texture and color[34]Pork Cooking 21 ± 1 V/cm –60 HzShorter cooking time; such important factors as cooking loss,color, and water holding capacity were not significantly affected,compared to pan cooking[35]VacuumpackagedsausagePostpasteurization230 V – 50 Hz Ohmic heating only slightly changed the texture and color ofvacuum packaged sausages, while having no notable impact on pH,water holding capacity, lipid oxidation, or cooking loss[36]Beef Cooking 50 V –20 kHzElectrical conductivity is affected by the amount of fat in themuscle tissue; series electric current reduces electrical conductivity,compared to parallel current[37]Whole egg Pasteurization 20 kHz Ohmic heating improved the hardness and foaming capacitycompared to conventional pasteurization and caused slight changesin color; although ohmic heating increased viscosity, its detrimentalimpact could be reduced by adjusting the process conditions; lowtemperature pasteurization was proposed due to its low impact onprotein denaturation[38]Egg white Pasteurization 20 kHz Fewer proteins denatured during thermally-induced gelation of eggwhite protein under ohmic heating[39]Starch Gelation 7 to 27 V/cm –60 HzThe stability of starch gels strongly depended on the type of starchand was not affected by the type of heat treatment[40]Surimicannedcornmixed gelsThermalprocessing250 V –10 kHzOhmic heating effectively reduced moisture loss in corn and preservedthe texture of corn and surimi gel better than the water-bathheating method[41]221Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226the target values of total soluble solids, performance,and electrical conductivity [24]. They explained thatvarious values of absolute pressure and, consequently,boiling temperatures applied in ohmic heating affectedenergy efficiency, according to the second law ofthermodynamics. Higher boiling temperature decreasedthe process time and had a positive effect on energyefficiency.In some studies, ohmic heating has been used topasteurize fruit juices. Particularly, Hashemi et al.compared the efficiency of ohmic and microwaveprocesses for treatment of cantaloupe juice [22].They indicated that higher voltage of ohmicheating and microwave power markedly decreasedphenolic compounds, vitamin C, and the numberof pathogens. In fact, at high voltages compoundsare produced that catalyze the decompositionpathways of ascorbic acid in the presence of oxygendue to thermal effects, electrode reactions, andthe electrolysis of the solution. Hashemi et al.observed the highest degradation of vitamin C in theohmic treatment at 200 V and the lowest in the microwavetreatment at 400 W (Fig. 1).In another study [47], they found electric current andtemperature to be the major variables which affected thepasteurization of sour orange juice. The authors showedthat heat transfer in orange juice was accelerated by theapplication of a higher electric field (Fig. 2)Alcántara-Zavala et al. reported that ohmic heatingimproved the physicochemical and sensory propertiesof fermented beverage obtained from the agave plant(known as pulque) [23]. Pulque is an alcoholic beveragewith acidic taste. Ohmic heating improved its flavor(alcoholic perception and acidity) and made it morepalatable for consumption, compared to conventionalheating. Due to its mineral content, pulque showed goodelectrical conductivity. Its pasteurization with 120 V at65°C for 5 min was reported as the best treatment.Rinaldi et al. evaluated the physical and chemicalimpacts of ohmic heating and conventional heatingon cubes of pineapple in syrup [26]. They observedinsignificant differences in the lightness (L*) andantioxidant properties between the two methods, whilethe hardness of the ohmic-treated pineapples was higherthan that of those treated conventionally. In addition,Kumar et al. observed the highest textural degradationof pineapple cubes at all electric field strengths at 90 sprocess time [27]. They also found that higher electricfield strength resulted in a higher drying rate.Ohmic heating can be used as an alternative toconventional blanching prior to drying and storageof vegetables and fruits. Kanjanapongkul and Baibuaapplied ohmic heating to pasteurize coconut water andfound that it could completely inactivate peroxidase,but not polyphenol oxidase [31]. In addition, no pinkdiscoloration was reported in the ohmic-heated samples,while the conventionally pasteurized samples featured apink color during cold storage.Another application of ohmic heating is in thepeeling process. Removing the skin of fruits andvegetables is one of the most common treatments infood processing. The conventional peeling methods (lye,steam, and mechanical method) have several drawbacks,including high peeling losses, high consumption ofenergy, and environmental issues. Therefore, there is agrowing demand for alternative methods [48]. Gupta andSastry employed ohmic heating to remove the skin ofpear [28]. Furthermore, a combination of ohmic heatingand CO2 laser drilling has been used to remove tomatoskins [49]. These studies have shown that ohmic heatingenhances the product yield, efficacy of peeling, aswell as the quality of the final product. However, someparameters should be considered to optimize the peelingprocess, such as temperature, composition of peelingmedium, and electric field strength [28, 50].Ohmic heating application in grain processing.The boiling of food products, such as rice and noodles,is a time-consuming process. Today, as the people’slifestyles have altered, there is a growing demand forrapid cooking methods and alternatives to traditionalmethods. Gavahian et al. investigated the impact ofohmic heating and traditional cooking on the texturaland physical attributes of short grain rice [32]. Theyreported that although ohmic heating adversely affectedthe color parameters (color intensity and lightness),it resulted in softer texture in comparison with thehotplate cooking system. In this regard, the corrosionof electrodes and electrochemical reactions have beenexpressed as factors affecting the color of ohmic-heatedfoods [32].Ohmic heating has also been found to markedlyreduce the cooking time, fouling, and consumptionof energy, compared to the traditional method [51].Similarly, Jo and Park utilized different electric fields(10.0, 12.5, 15.0, and 17.5 V/cm) for cooking instantnoodles [33]. They observed that heat transfer betweennoodles and soup was expedited at higher electric fields.Therefore, the authors suggested 15 V/cm with theFigure 2 Temperature profile of sour orange juice duringohmic heating for 120 s and three different voltages(100, 150, and 200 V). With the permission of the publisher,Hashemi et al. [47]Time, sTemperature, °C0 20 40 60 80 100 1202535455575859510565100 V 150 V 200 V222Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226reduces the electrical conductivity during ohmic heating,as well as uniform heating. The authors also found thatseries electric current reduced electrical conductivity,compared to parallel current. Reduction of shrinkageand drip loss were observed in both types of meatduring ohmic cooking at 50 V and 20 kHz [37].Additionally, ohmic heating can be applied to cookpork since it shortens the cooking time without havinga significant impact on the water holding capacity,color, and cooking loss, compared to the traditional pancooking [35]. Similarly, ohmic heating has no significanteffect on the properties of scallops (texture, shrinkage,and water release) and reduces the denaturation of actinby shortening the heating time [53].Inmanee et al. investigated the impacts of ohmicheating on Listeria monocytogenes contamination andthe quality of sausages during post-pasteurization [36].They showed that the ohmic process effectivelyinactivated L. monocytogenes (≥ 5-log reduction). Theauthors compared the electrical conductivity of sausage,salt solution, and collagen casing. They found that thecollagen casing had a higher electrical conductivity thanthe sausage and attributed it to the presence of fat, whichmade up to 20% of the sausage. The salt solution actedas a conductor, with lower conductivity than the sausageand casing.The study also showed that the ohmic process onlyslightly changed the texture and color of the vacuumpackagedsausages. At the same time, it had no notableimpact on pH, water holding capacity, lipid oxidation,and cooking loss. However, these slight changes intexture and color were not detectable by sensoryevaluators. Therefore, ohmic heating has the potential tobe applied in the meat and meat products industry withthe least impact on their quality.Other food products. Several studies haveinvestigated the technological attributes of eggs underohmic heating. Since fresh-laid eggs can be a cause ofsalmonella infection, manufacturers prefer pasteurizedegg for both its safety and ease of handling [54].holding time of 90 s as the best treatment in terms ofdesirable texture and energy efficiency.Dias-Martins et al. compared the impact ofconventional open-pan and ohmic heating on wholeand decorticated pearl millet grains [34]. They foundthe grain pericarp to be the principal factor influencingthe cooking process, rather than the method of heating.Regarding pearl millet grain, no significant differenceswere observed between the two cooking methods interms of texture and color. However, the ohmic-heateddecorticated grains exhibited greater lightness andharder texture, compared to the conventionally cookedgrains.Waziiroh et al. examined the basic aspects of usingohmic heating for baking gluten-free bread [52]. Theystated that the changes in the physical properties ofgluten-free bread during heating depended on theingredients and their interaction in the dough. Theybelieved that two major factors affected the porosityand viscosity of dough during baking by ohmicheating, namely dough ingredients and their properties(e.g., non-ionic and ionic compounds, particle size,surface hydrophobicity, emulsification ability, etc.) anddough structural properties (foam formation, proteindenaturation, and starch gelatinization).Ohmic heating application in meat industry.It has been investigated that ohmic heating can beused for processing meat and meat products. Severalfactors affect the electrical conductivity and thereforethe efficiency of the ohmic process, including meatstructure (type of meat, amount of fat and moisture),lean-to-fat ratio, and electric current direction [35].Llave et al. studied the impact of meat type (Japanesebeef and Australian beef) and the direction ofelectric current (series and parallel) on the electricalconductivity during ohmic cooking [37]. They reportedthat Japanese meat had lower electrical conductivitythan Australian meat due to its higher fat content.Having low electrical conductivity, fat prevents thepassage of current by covering lean particles, whichFigure 3 Various applications of ohmic heating in food processing223Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226Eggs are a rich source of protein and dueto their sensitivity to high temperature, greatcare must be taken during egg pasteurization toprevent proteins denaturation and coagulation.Alamprese et al. reported that ohmic heatingimproved the hardness and foaming capacity of thewhole egg, compared to conventional pasteurization,and caused slight changes in its color [38].The authors stated that although ohmic heatingincreased viscosity, its detrimental impact could bereduced by adjusting the process conditions. In general,they proved that ohmic treatment could be used as adesirable method for whole egg treatment and proposedlow temperature pasteurization due to its low impact onprotein denaturation.Similarly, Llave et al. examined color alterationsof egg yolk under ohmic treatment and evaluated thecorrelation between color changes and the degree ofprotein denaturation [54]. They found that increasingtemperatures caused the egg yolk color to gradually turnfrom plain orange to vivid yellow, while the egg whitegradually changed from transparent to cloudy.In addition, the egg color changes were correlatedwith the non-denaturation ratio of the second peaktemperature. In this regard, Joeres et al. indicated thategg white protein did not fully denature during ohmicheating [39]. They believed that this could be related tothe oscillatory electric field which partially interferedwith the complete denaturation and development ofintermolecular beta-sheet structures during thermalgelation of ovalbumin. Also, according to the resultsof scanning electron microscopy, the ohmic-heatedgels had a more open and porous network structure,compared to conventional treatment which exhibiteddenser gels.In another study, da Silva et al. investigated theimpact of ohmic heating on the rheological attributesand stability of gels produced from starch [40].Particularly, they examined the effect of starch source(cassava and maize) and type of treatment. They foundthat the stability of starch gels strongly depended on thetype of starch and was not affected by the type of heattreatment. The researchers revealed that ohmic heatinghad several advantages over conventional heating. Inparticular, it reduced energy and water consumption, aswell as wastewater production, and did not affect theproperties of the final product.In a study by Jung et al., ohmic heating was usedto process surimi-corn mixture [41]. The authorsreported that this technique effectively reduced theamount of moisture loss in corn and preserved thetexture of corn and surimi gel better than the water-bathheating method.Limitations and advantages. Ohmic heating hasrevealed its potential for processing various foods inindustrial applications. Apart from heat treatment, itcan also be used as an assisted treatment for otherprocesses like peeling, concentration, and drying(Fig. 3). Although recent studies have indicated thatohmic heating can improve the physical and chemicalproperties of foods, compared to conventional heating,there are some limitations regarding its application.Operator safety, high capital cost, and corrosion ofelectrodes are major concerns of food manufacturers tocommercialize this novel technology.Studies have shown that ohmic-treated foods havebetter texture, better aroma, lower color variation,higher bioactive compounds, and better sensoryproperties, compared to conventionally treated foods [3,7, 9, 13, 16, 18, 20, 23, 26, 30, 33, 36, 49]. However, forsome foods, there are no significant differences betweenthe two methods in terms of quality [21, 26, 40].In contrast, some studies have revealed that ohmicheating can adversely affect some physical propertiesof food such as color [32]. Electrode corrosion and someelectrochemical reactions are among its limitations thatcan affect the food quality. Besides, ohmic heating isnot a suitable method for processing foods with a highfat content since fat has low electrical conductivity.Therefore, the ohmic process conditions must beoptimized according to the food properties in order toachieve the best result.Other advantages of ohmic heating are a shorter timeto reach the process temperature, lower consumptionof energy, uniform distribution of heat, and a shortertotal heating period [7, 10, 29, 40, 43]. Although thisnovel technology has some limitations and drawbacks,its advantages make it a suitable alternative to thetraditional heating process.CONCLUSIONOhmic heating follows the Joule’s law to heat foodsquickly and evenly, effectively and volumetrically. Thismethod is markedly influenced by different properties offoods, including the amount of fat, type of food material,particle size, pH, viscosity, the content of chargedions, etc. In addition, variations of frequencies andvoltages also play an important role in the performanceof ohmic heating during food processing. Our reviewconcludes that the processing of food materials by ohmicheating can be carried out in a shorter time, comparedto conventional heating. In addition, the quality offoods can be effectively affected by ohmic treatmentthrough both thermal and non-thermal impacts. Whileits thermal impacts on the food quality have beenextensively studied, there is limited information on thenon-thermal impacts of this technology on various foodproperties, such as texture, color, taste, etc. Therefore,a more detailed study is needed to fully realize thethermal and non-thermal impacts of ohmic heating fordifferent foods and under various operating conditions.The ohmic process has many benefits for food industry,including process energy and time savings. Furthermore,this technology provides more reliable process control,compared to the traditional technique. These benefitssuggest that ohmic heating can be a superior alternative224Jafarpour D. et al. Foods and Raw Materials. 2022;10(2):216–226CONTRIBUTIONThe authors were equally involved in writing themanuscript and are equally responsible for plagiarism.CONFLICT OF INTERESTThe authors have declared no conflict of interest.