Int.J.Curr.Microbiol.App.Sci (2020) 9(9): 118-131 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 9 (2020) Journal homepage: http://www.ijcmas.com Review Article https://doi.org/10.20546/ijcmas.2020.909.015 Microwaves and Radiowaves: In Food Processing and Preservation Kanchan Bhatt*, Devina Vaidya, Manisha Kaushal, Anil Gupta, Pooja Soni, Priyana Arya, Anjali Gautam and Chetna Sharma Dr. Yaswant Singh Parmar University of Horticulture and Forestry, Nauni, Solan (HP), India *Corresponding author ABSTRACT K e yw or ds Drying, Microwaves and Radiowaves are the non ionizing electromagnetic radiations ranging between 300MHz to 300 GHz and 300 KHz to 300 MHz Electromagnetic radiations, respectively. They are used in various fields, however, they are gaining Microwaves, Radiowaves, marked popularity in food technology nowadays. This paper reviewed the Preservation history, basic principles, advantages, disadvantages, uses and applications of microwaves and radiowaves in the field of food preservation and Article Info processing as these technologies have increased the amount of nutrient Accepted: retention in the treated food with increase in shelf life of food along with 04 August 2020 Available Online: less use of preservatives. 10 September 2020 Introduction atomic bonds and are ranged from 1 Hz to 1014 Hz. However, these radiations cause Electromagnetic spectrum consists of ionizing thermal effects on human body depending on and non-ionizing radiations (Gava, 1984). distance, frequency power and time. Gamma rays and X rays falls in ionizing part Electromagnetic radiations are used in many of it, however, UV rays, Visible light, Infra, fields like Energy Transmission Lines (ETL) Micro and Radio waves are the part of non- and transformer stations, Electric trains, ionizing radiations. Ionizing Radiations with Cathode Ray Tube (CRT) displays used in high frequency (higher than 1014 Hz) have TVs and computers, Induction furnaces and capability to ionize atomic bonds in cell welding machines used in the industry, all molecules and their excessive exposure to this kinds of electrical household appliances (iron, effect can lead to hazardous conditions such microwave ovens, cordless phones, electric as damage to living cells and also DNA chain. blankets, refrigerators, etc.) used in our On the contrary, non-ionizing electromagnetic homes, Various RF systems operating in radiations have not enough energy to separate industry, Radar systems (continuous and 118 Int.J.Curr.Microbiol.App.Sci (2020) 9(9): 118-131 pulsed), Satellite communication systems, radar. This led to the development of high Personnel communication systems (Cordless, power microwave sources. According to telephone, Wi-Fi, Bluetooth, etc. (Ozkaya et Decareau, 1985 the first major applications al., 2018). Recently, we have seen the usage were finish drying of potato chips, pre- of electromagnetic waves in the field of food cooking of poultry and bacon, tempering of processing and preservation. Lately, the frozen food and drying of pasta. microwave or radio wave region of the electromagnetic spectrum has been emerged Principle potentially for possible use in food processing and preservation with successful results in A soon as microwave energy is absorbed, microbial inactivation. Here we will discuss polar molecules such as water molecules about these two technologies and their inside the food will rotate according to the contributions to food. alternating electromagnetic field. The water molecule is a “dipole” itself with one Microwaves positively charged end and one negatively charged end. Thus, water molecule acts like Microwaves are nonionizing radiations that magnet, and these dipoles have similar induces molecular motion by ion migration orientation when they are subject to and dipole rotation but does not alter the electromagnetic field. The rotation of these composition of the molecules. Microwave water molecules would generate heat for energy is a part of electromagnetic spectrum, cooking (Ohlsson, 1993). Thus, the and is defined by wavelength range between composition of a food will affect its heating 1mm to 1m and frequency range between 300 inside microwave oven. Due to the dipolar MHz and 300 GHz. These are usually used interaction food with higher moisture content for the industrial processing of foods being will be heated up faster. In nonconductors, between 915 and 2450 MHz and 2450 MHz microwave heating refers to dielectric heating for domestic use. at a selected frequency bands due to polarization. However, coupling of electrical Brief history of microwaves energy from an electromagnetic field in a microwave cavity with the food results in its Microwaves were the result of desired energy heating as well as its subsequent dissipation transfer rate enhancement which led to an within food product. This in turn results in a increased frequency. During 1946, a self sharp increase in temperature within the taught engineer Dr. Percy Spencer was testing product. MW energy is transferred at a magnetron (a new vacuum tube) and while molecular level through interaction of working on it surprisingly the candy bar in his molecules with the electromagnetic field, pocket melted. The occurrence of this incident particularly, through molecular friction which lead to the implementation of microwave results from dipole rotation of polar solvents energy into the food industry (Fito et al., and from the conductive migration of 2005). However, the first patent was issued in dissolved ions. Second major mechanism of 1952 (Spencer, 1952) describing an industrial heating with microwaves is through the conveyor belt microwave system and its first polarization of ions which results in the application started 10 years later. Whereas, backward and forward movement of the ionic during the Second World War, microwave molecules trying to align themselves with the technology was principally used for oscillating electric field (Oliveira and Franca, communication, with the development of 2002). 119 Int.J.Curr.Microbiol.App.Sci (2020) 9(9): 118-131 How a microwave oven works Factors affecting microwave heating The process starts when electrical energy, in Frequency the form of low-voltage alternating current and high-voltage direct current, is converted There are two frequencies allocated for into direct current. Magnetron (heart of microwave heating (915 and 2450 MHz) for microwave) after using this direct current, the application of food having frequencies of generates microwaves with a frequency of 0.328 and 0.122 m. These wavelengths are 2450 megacyles per second (2.45 GHz). The significant as most interactions between the microwaves are controlled by an antenna at energy and materials take place in that region the top of the magnetron into a waveguide. and generate immediate heat due to molecular The waveguide streamlines microwaves to a friction. fan like device called a stirrer which disperses them inside the oven cavity. Later on the Dielectric properties microwaves are reflected by the metal walls of the oven's interior and are absorbed by The electrical properties of microwave and molecules in the food. Because each wave is radiofrequency heating are classified as made up of a positive and negative dielectric properties, which provide details, component, the molecules in the food are how food materials interact with pushed back and forth at twice the rate of the electromagnetic energy. Initially when we microwave frequency (4.9 billion times a preheat microwave it reaches higher second). temperature than the preset temperature, to compensate the effect of higher initial Working of magnetron temperature, the power of MW oven should be reduced or a higher sample mass should be The magnetron is also known as heart of used or the product should be heated for a microwave oven which converts electrical shorter duration (Mudgett, 1989). energy to microwave radiation. Magnetron uses low-voltage alternating current and high- Geometry and location of foods voltage direct current. The shape of the food affects the depth of Later on, a transformer changes the incoming microwave penetration, heating rate and voltage to the required levels and a capacitor, uniformity. Due to the difference in product in combination with a diode, filters out the thickness, irregular-shaped products are high voltage and converts it to direct current. subjected to non uniform heating. The closer Electrons are emitted from a central terminal the size and wavelength ratio, the higher will called a cathode, inside the magnetron and are be the center temperature. attracted by positively charged anode surrounding the cathode. Smaller particulates require less heat than larger ones. Moreover, regularity in the shape Rather a straight line movement, permanent increases the uniformity of heat distribution magnets force the electrons to take a circular within the product. A food of a spherical or path. As soon as, they pass by resonating cylindrical shape heats more evenly than a cavities, there is generation of continuous square. A higher surface-to-volume ratio pulsating magnetic field, or electromagnetic enhances the heating rate. radiation. 120 Int.J.Curr.Microbiol.App.Sci (2020) 9(9): 118-131 Thermal properties Temperature Thermal conductivity of food plays a pivot Depending upon the material, dielectric role in microwave heating. During microwave properties may vary with temperature. Both heating foods with higher thermal moisture content and temperature can