# Ohmic Heating in the Food Industry: Developments in Concepts and Applications during 2013-2020
## 1 Introduction  
Conventional thermal methods such as pasteurization, sterilization, drying, and evaporation are widely employed commercially to ensure microbiological safety in the food industry [1]. However, these methods cause extensive damage to the nutritional component of food; especially vitamins and heat-sensitive polyphenols that are linked to food quality [2]. These conventional treatments are relatively inefficient in terms of energy requirements, waste recycling, and environmental sustainability. As consumers have increased their demand for healthy foods with fresh properties and longer shelf life, researchers have explored various novel methods to improve food quality and safety [3]. Recently, a lot of research has focused on developing alternatives to conventional thermal technologies, such as reciprocation thermal processing [4], controlled agitation processing [5], microwave, radio frequency [6], and ohmic heating [7]. These alternative technologies have advantages of lower temperature and shorter time requirements than conventional methods, and are also more energy-efficient, sustainable, and environmentally friendly. Amongst these novel technologies, ohmic heating has established itself as one of the most economical alternatives available to the food industries for thermal processing, as it relies only on electricity [8]. Ohmic heating itself has been widely applied for pasteurization [6; 7; 8; 9], drying [7; 8; 9], concentration [8; 9; 10; 11], extraction [9; 10; 11; 12], and nutrient preservation [10; 11; 12; 13]. Ohmic heating results in better nutrient retention and fewer changes in the sensory properties of food [2]. With ohmic heating, heat is generated directly inside the food itself by Joule heating as the electrical current passes directly through the conductive food, and the resulting energy generation induces an increase in temperature [12; 13; 14]. Many liquid and liquid-solid products, in particular, can be processed in a short time through ohmic heating [15]. Many studies have confirmed that ohmic heating effectively pasteurizes juice. Extrinsic factors such as electric field and frequency, and intrinsic factors such as pH and sugar concentration, significantly affect the efficiency of ohmic heating [16; 17]. With ohmic heating, there are no wide temperature gradients in the heated food, which avoids overheating of the surface of the solid food or particles and retains the food's sensory properties [18]. Ohmic heating consumes less energy with a shorter heating time compared to conventional thermal methods used in commercial production. Some studies reported that the shelf life of ohmic treated samples was similar to or longer than that of samples heated conventionally [19]. Numerous studies have indicated that ohmic heating possessed efficient effects in many manufacturing processes and does not lead to significant effects on the nutritional, functional, and synthetic properties and sensory characteristics of food products compared to traditional techniques [14], while improving food quality [20] and inactivating enzymes [21]. Besides, ohmic heating can be widely used to heat liquid food such as citrus juice [22]. [PERSON] et al. [23] analyzed and investigated the impact of the ohmic heating system on the black mulberry juice concentration, and the results were compared to the traditional heating method. The phenolics content of the juice sample using ohmic heating was 3-4.5 times higher than the traditional heating method. The pH value and total phenol content was not significantly affected by using the higher voltage gradient. The consumed energy was (3.33-3.82 MJ/kg water) using ohmic heating compared to the energy consumption by the traditional heating method (17.50 MJ/kg water). This result confirmed that the consumed energy by ohmic heating was 4.6-5.3 times lower than the energy consumption by the traditional heating method [23].