the promising next-generation food [62]. The development, research, and large-scale set-up of these novel technologies are taking place internationally. It is evident from the number of publications on the benefits of novel thermal technologies in food processing in various food and agriculture processing research journals [51].
Microwave: The most popular and extensive technology studied worldwide both domestically and industrially is microwave processing due to its various advantages such as easy operation, lower maintenance requirement, and cleaner environment [77]. But despite all the advantages, microwave is facing two main hurdles, i.e., irregular distribution of temperature within the food product and high cost of energy regarding this technique [6]. Furthermore, the set-up operated at 2450 MHz may give rise to serious boundary and surface overheating of the food to outstretch the desired elevated temperature in cold spots. For those cases, continuous microwave systems have been used to provide uniform temperatures for the heating of foods. Some authors have suggested fusion with water as the heating medium, pulsed microwave [24, 51]. The most common technology is microwave-assisted thermal sterilization system (MATS™) based on 915MHz single-mode cavities using a shallow bed with water food immersion; it penetrates deeper in food and water offers to reduce the edge heating. It got approval in 2009 by the Food and Drug Administration (FDA) [72].
Infrared heating: Proved by many researchers, Infrared heating (IRH) is an efficient process for the purification of pathogenic microorganisms in food. Many operational variables such as food temperature, size and kind of food materials, IR power intensity, IR power intensity, and others are necessary for microbial inactivation. At a commercial scale, IRH had been found as the replacement or substitute to decrease non-uniform temperature distribution which occurs in microwave heating [6]. Internationally, IRH is used for blanching, drying, baking, roasting, and peeling. At the industrial level IRH has considerable advantages such as a large heat delivery rate, no medium required, high energy efficiency, low environmental footprint, and others [39]. But because of less penetration depth, this technology is not successful at the commercial level; for example, it cannot be utilized in in-packaging food processing. The major successful large-scale (commercial) applications of IRH is drying of low-moisture foods (grains, pasta, tea, etc.), also the applications in baking (e.g., pizzas, biscuits, and others) and in the oven for roasting of cereals, coffee, etc.
Radiofrequency: Another thermal technology is Radiofrequency heating (RFH), used from the 1940s. Earlier applications were to warm bread, dry up and blanch vegetables and others. RFH has a greater industrial interest because of its unique properties such as deeper penetration due to its lesser frequencies, uniform electric field distribution, and longer wavelength. Major applications are in the food-drying sectors for pasta, snacks, and crackers and sterilization or pasteurization process, treatment of seeds and disinfection of product [19]. As compared to microwave heating, RF has the potential to reduce surface overheating and can also give better results at a commercial scale [81]. On a commercial scale, such as for treating bulk materials, sterilization of packaged foods is successful because they are simple to construct, have a more uniform heating pattern, and have greater penetration depth. Drawbacks of this technology include, at industrial scale, the design equipment is complicated, there is a high investment cost and technical issues such as dielectric failure and thermal runaway heating that can damage package and product [1]. Another common thermal technique is ohmic heating (OH) where internal heat generation takes place by passing a current into the materials.
Ohmic heating (OH): Compared to other technologies, ohmic heating has advantages such as larger temperature in particles than in liquid, decreased fouling, energy-efficient, uniform heating (achieved by thermal, physical, and rheological properties), and lower cost [64]. The drawbacks include the requirement of aseptic packing after OH heating, the possibility of corrosion, direct exposure of the electrode with food.
Major utilization of OH are blanching, sterilization, evaporation, dehydration, extraction, and evaporation. The basic procedure involved in OH of microbial inactivation is thermal harm and in some cases by electroporation. In comparison to traditional heating, OH heating can attain lesser heating times, can keep away from hot surfaces, and can decrease the temperature gradients.
Since the 1990s, OH is now utilized in developing countries and all over the world. Almost a hundred processing plants have been placed all over the world. The market is in the developing stage and evolving constantly. OH equipment is installed all over the world such as in Italy, France, Spain, Greece, and Mexico [54]. The application of OH is not much commercialized for solid food products. For liquids, viscous liquids, and pumpable multiphase products, the installed set-ups perform the sterilization and pasteurization of numerous food products with great characteristics with main applications in vegetables and fruit areas.
Overall, the major issue involved in commercialization of electromagnetic techniques for numerous food applications is the lack of heat uniformity, which has a major impact on key variables of food processing and safety. To avoid this downside, hybrid systems are proposed, i.e., the combination of traditional and volumetric heating [54, 63]. The hybrid system offers advantages such as safety, improved process efficiency, and product properties. Successful hybrid techniques are IR-convective drying, a combination of IRH, IR-heat pump drying, and microwave heating, and many others are still in progress because of the magnified energy throughput.
1.2.1 Environmental Impact of Novel Thermal Technologies
The emergence of novel thermal technologies and non-thermal processes in food processing industries is capable of producing high-quality and standardized products. Both of them are environmentally sound and efficient in nature as compared to conventional technologies. Here we will consider more on the environmental footprints of novel thermal technologies. The primary objective in the food industry is food safety which requires high energy consumption, but novel thermal technologies are successfully able to balance energy saving and energy consumption.
The high value of hygiene and safety of food requires large use of water in both hot and cold cycles in production which consequently increases the environmental footprint. Processes such as cooking, sterilization, drying, and pasteurization require various types of energy. Novel thermal technologies are promising, attractive, and efficient in nature. They are capable of providing improved quality and reduced environmental effects which will eventually reduce environmental footprints. Novel thermal technologies can reduce processing costs followed by improving and maintaining the value-added products. Overall the primary types of energy used based on conventional thermal processing techniques are fossil fuel and electricity, majorly utilized in refrigeration and mechanical power in pumps. A heat exchanger is commonly used in the pasteurization of beverages where the pathogens are killed when heated to a particular residence time. During thermal treatment, convection and conduction play a major role to transfer heat to the products. For viscous fluids, directing heating process is applied, e.g., steam injection and steam infusion are utilized for thermal treatments. In the food and beverages industry, regarding the distribution of energy in 2002, Denmark suggests that total consumption of energy (TJ/Year) is 135,200 including the amount of heating and power. Adapted from [58].
This concludes that major heat is used in frying, evaporation, drying, and heating for thermal processes. Until the present moment, this trend is still functioning. Novel thermal technologies such as radio frequency, ohmic heating, microwave, etc., for food processing being continuously evolving. These novel thermal technologies have reduced emissions, reliability, improved productivity, high product quality, energy saving, water saving and consequently have less impact on the environment; [45] investigated that for Orange juice and cookies manufacturing, radio frequency drying (RF) can range up to 0 to 73.8 TJ per year in terms of primary energy saving. The major kinds of gas emissions from food industries are linked to power and heat production particulate matter and gases such as SO2, CO2, NO, from combustion processes. The particulate matter and volatile organic compounds (VOCs) and other chemical emissions are from methods such as size reduction, heating, refrigeration system, and cooking methods.
Conventionally 33% of the overall energy consumed in food processing corresponds to the production of steam. The steam is commonly used in drying, concentrating liquids, cooking, sterilizing, etc., in the processing of