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Int.J.Curr.Microbiol.App.Sci (2020) 9(9): 118-131

International Journal of Current Microbiology and Applied 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, and Radiowaves are the non ionizing electromagnetic Electromagnetic ranging between 300MHz to 300 GHz and 300 KHz to 300 MHz 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 consists of ionizing thermal effects on human body depending on and non-ionizing radiations (Gava, 1984). distance, power and time. Gamma rays and X rays falls in ionizing part Electromagnetic radiations are used in many of it, however, UV rays, Visible , Infra, fields like Energy Transmission Lines (ETL) Micro and are the part of non- and transformer stations, Electric trains, ionizing radiations. Ionizing Radiations with Cathode Ray Tube (CRT) displays used in (higher than 1014 Hz) have TVs and , Induction furnaces and capability to ionize atomic bonds in cell welding machines used in the industry, all and their excessive exposure to this kinds of electrical household appliances (iron, effect can lead to hazardous conditions such 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, systems (continuous and

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pulsed), communication systems, radar. This led to the development of high Personnel communication systems (Cordless, power microwave sources. According to , Wi-Fi, , 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 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 molecules about these two technologies and their inside the food will rotate according to the contributions to food. alternating . The water is a “” 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 have similar induces molecular motion by 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 range between composition of a food will affect its heating 1mm to 1m and frequency range between 300 inside . 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 heating for domestic use. at a selected frequency bands due to . 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 ) 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 . 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 (Oliveira and Franca, communication, with the development of 2002).

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How a microwave oven works Factors affecting microwave heating

The process starts when electrical energy, in Frequency the form of low-voltage and high-voltage direct current, is converted There are two 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 are 2450 megacyles per second (2.45 GHz). The significant as most interactions between the microwaves are controlled by an at energy and materials take place in that region the top of the magnetron into a . 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 . 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 , 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 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 , or electromagnetic enhances the heating rate. radiation.

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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 change conductivity dissipate heat faster than the during heating and therefore, show combined ones with lower conductivity. Thus, food effect on the dielectric constant, dielectric loss having high thermal conductivity will take factor, loss tangent, and subsequently on the lesser time to attain uniform temperature heating behavior (Khattarpaul, 2005). during holding (Ahmed and Ramaswamy, 2005). Advantages and disadvantages

Moisture content The very first advantage is that heat is generated in the product itself. Microwave The moisture content affects the dielectric penetrates inside the food materials resulting properties of the food product and penetration in entire internal cooking of whole volume of depth of the microwaves. Foods with high food rapidly and uniformly reducing the moisture content shows low microwave processing time and energy. This fast heat penetration depth, and thus results in, uneven transfer in turn results in preservation of heating rate unlike, low-moisture foods which nutrients, vitamins contents, flavor, sensory will have more uniform heating rate due to characteristics, and color of food. Due to the the deeper microwave penetration. During elimination of the hot surfaces microwave heating the initial moisture minimum fouling depositions are found. content of the product and the rate of moisture Microwaves have high heating efficiency evaporation plays an important role (Mudgett, (80% or higher efficiency can be achieved). 1989). They have perfect geometry for clean-in-place (CIP) system. Microwaves are suitable for Mass heat-sensitive, high-viscous, and multiphase fluid as well as low cost in system There is direct relationship between the mass maintenance. One main advantage is that and the amount of absorbed microwave effect of small heat conductivities or heat power, which should be applied in order to transfer coefficients does not play such an achieve the desired heating. For a smaller important role. As a consequence, larger mass generally we use batch oven, however, pieces can be heated in a shorter time and for large capacity equipment conveyors are with a more even temperature distribution. used. These equipments provide great heating These advantages often yield an increased uniformity by movement of product through production. the microwave field. Microwaves need a lot of knowledge or For its efficient operation each microwave experience to understand the moderate effects oven has a critical (minimum) sample mass like uneven heating or the thermal runaway which is usually around 250 ml water load in along with high input of engineering a 1 kW oven. No, significant amount of intelligence. Secondly, microwave heating in microwave power is absorbed into the product comparison with conventional heating needs below this level, and at very low loads they electrical energy, which is its most expensive may damage the magnetron. form.

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Radiowaves of several universities (Mitcham et al., 2004; Monzon et al., 2004; Wang et al., 2002). Introduction Equipment Radiofrequency (RF) heating can be defined as electromagnetic heating and other non- The Radiofrequency heating system consists thermal methods that have the ability to of two parts RF generator/ Triode valve for provide high quality foods economically. the radio waves generation and applicator Radiofrequency heating is a type of dielectric which mainly consists of pair of electrodes for heating which uses radio waves as heating RF waves application to the food (Fig 2). source. Radiowaves (RW) are the Food product is placed between the two electromagnetic waves having frequency electrodes and heated without touching the range between 300 KHz to 300 MHz and material. Out of the two electrodes one works wavelength more than 108 nm (Ryynanen, as a capacitor to store energy. These 1995). When food products are exposed to electrodes are used in three configurations, radio waves they gain heated due to ionic first one is through field configuration which depolarization and dipole rotation. RF can be is widely used for thick products and high applied in all the fields of food industry such voltage frequency is applied. Secondly, as pest control in agricultural field and fringefield configuration is used for thin thermal inactivation of pathogenic microbes products and it consists of set of electrodes in processed foods. Mainly, it is used in that are alternatively connected to RF drying of baked goods like crackers, cookies, generator. The third one is staggered through biscuits, pasta etc. (Orsat and Raghavan, field configuration used for medium thick 2005). products (Marra et al., 2009).

History Principle and heating mechanism

In 1895, RF heating was first used as a RF heating system consists of a RF generator medical treatment method, however, which creates an alternating electric field according to Püschner, 1996 development of between two electrodes and heat the material applications in food placed between the electrodes. Ionic industry started in the range depolarization and dipole rotation are the two in the 1930s. In food processing industry, it phenomena responsible for heating. was used firstly for blanching followed by Alternating electric field causes polarization cooking and then dehydrating (Proctor and in molecules so that they will start Goldblith. 1948; Moyer and Stotz, 1947). In continuously reorienting themselves to face the 1960s, there were attempts to use RF to opposite poles. Positive ions will be attracted the frozen foods. These researches led to to negative regions and negative ions will be successful commercial application of RF in moving to positive regions of electric field. thawing of fish blocks. Between 1960s and With continuously changing polarity and high 1980s little research was reported from the frequency heat energy is released throughout university laboratories on radiofrequency its mass as a result of friction due to rotational heating of foods. Later in 1990s, with increase movement of molecules oscillating forward in power, commercially available electric and backward. Polar molecules try to align property, temperature measurement devices, themselves with changing polarity of electric new findings were reported from laboratories field along with the movement of ions.

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Therefore, in the entire product wherever electrode configuration which affects moisture is present oscillates and generates temperature uniformity. heat uniformly throughout the product. Radiations with lower frequencies The major obstacle in RF technology is non predominantly have ionic polarization as uniform heating of food produce due to heating mechanism while radiations with factors like dielectric properties, size, shape, higher frequencies have both ionic position between the RF electrodes and the polarization and dipole rotation as dominating electrode configuration which affects heating medium (Tang et al., 2005). temperature uniformity. Microwave penetrates inside the food materials resulting Advantages in entire internal cooking of whole volume of food rapidly and uniformly reducing the Radiofrequency heating has many advantages, processing time and energy. This fast heat firstly, dipole rotation and ionic polarization transfer in turn results in preservation of are methods used to generate simultaneous nutrients, vitamins contents, flavor, sensory heat throughout the material resulting in faster characteristics, and color of food. Changes in process and reduction in the chances of sensory attributes and acceptability are overheating and browning. Secondly, it is a minimized during processing as compared to less time consuming rapid method over radio and microwave processing. conventional heating (Jojo and Mahendran, 2013) and other benefits are ease of targeting Application of microwave and the product, not the air surrounding it, tends to drive the moisture from inside out, and Application of microwave hence leveling the moisture, considerably decreasing the processing time, avoiding Drying overheating, dehydration on the surface of the product and heating system can be turned on Application of Microwave energy in or off instantly along with temperature combination with convective air drying in measurement systems (thermocouple). It has three different methods, were explained by low maintenance cost as compared to other Andrés et al., (2004). At the beginning of the methods, greater penetrating depth than drying process, where the interior of the microwaves and high technology tools such product is quickly heated to the evaporation as well design applicators, uniform heating temperature which inturn results in movement pattern and higher energy efficiency makes of large amount of vapor from the inner core this process more suitable for food industry. of the sample towards the outer surface of the product and finally it is removed by the Disadvantages surrounding air. This increases drying rate throughout the process and leads to puffing of Radio frequency heating requires high initial the sample which creates a porous structure capital cost and skilled labours for its which facilitates moisture flow to the surface. handling. Proper shielding is also a major Next, the moisture near the surface of the concern as this method uses electromagnetic product has been removed, while the inner waves as a source of heat (Ferdous et al., core of the food particle remains moist. Thus, 2017). The major obstacle in RF technology microwave energy can be applied when the is non uniform heating of food produce due to drying rate begins to fall. The application of factors like dielectric properties, size, shape, MW energy thus heats this trapped moisture position between the RF electrodes and the to evaporation temperature and facilitates its 123

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movement to the outer layers of the sample. dried tea leaves are sent into a rotary drum Finally, microwave energy can also be with a long-wave infra- heater, installed applied in the final stages of drying to remove below the microwave oven, where they are bound water and to control the effects of roasted into tasty, fragrant, finished tea. product shrinkage, which can decrease drying rate over time. According to Prabhanjan et al., Sterilization and (1995) better rehydration characteristics may be expected in microwave dried products as Ohlsson (1987) reported that microwave the quick energy absorption by water sterilization (128°C and 3 min processing molecules causes rapid evaporation of water, time) produced superior products as compared thus, results in an outward flux of rapidly to conventional processes of canning (120°C escaping vapour. Besides, improving the rate retort temperature and 45 min processing of drying, this outward flux can prevent the time) and retorting foil pouches (125°C and shrinkage of tissue structure, which is 13 min cooking time). According to Tong et common in most conventional air drying al., (1994) no significant change was techniques. Recently, microwave drying has observed in the texture of product or flavor evolved as an alternate drying method for a loss when microwave heating at 915MHz was wide range of food products such as fruits, used to sterilize pouches containing cooked vegetables, snack foods and dairy products. macaroni and cheese. Esteve et al., (1998) Food products like plain yogurt, cranberries, stated that microwave sterilization is a high- carrot slices, model fruit gels, skimmed milk, temperature-short-time (HTST) type process milk, casein powders, butter and fresh pasta which not only used to inactivate spoilage and potato slices (Kim and Bhowmik, 1995; microorganisms in foods but also to minimize Yongsawatdigul and Gunasekaran, 1996a; the quality deterioration of foods Lin et al., 1998; Drouzas et al., 1999 Al-Duri and McIntyre, 1992; Bouraout et al., 1994) Continuous-flow microwave pasteurizer was have been successfully dried by the developed for an experiment by Jaynes, microwave-vacuum application and/or by a (1975) using a Teflon tube (12 cm/0.635 cm) combined microwave assisted-convection placed across a 2450 MHz microwave guide process. Another group of researchers with a holding time of 15 s. proposed a two-stage drying process involving an initial forced air convective However, the effectiveness of pasteurization drying, followed by a microwave drying was considered on the basis of inactivation of (Prabhanjan et al., 1995; Feng and Tang, phosphatase enzyme, standard plate, and 1980). It is however, reported that microwave coliform counts. Villamiel et al., (1996) application can improve product quality such reported microwave pasteurization of milk as better aroma, faster and better rehydration, which results in lower levels of denaturation considerable savings in energy and less time of whey proteins in comparison to consuming as compared with hot air drying conventional thermal processes however alone. Finished tea has to go through denaturation of -lactoglobulin was almost number of processes such as overall finishing, equivalent in both processes. Helmar et al., air stream grading, stem separation, drying (2007) studied the applications of microwave and roasting. Currently, new system uses a pasteurization and sterilization on cover pre- microwave oven for the drying processing packed food like yoghurt or pouch-packed order to reduce the water content of half- meals as well as continuous pasteurization of finished tea from 8-10% to 1-2%. Later these fluids like milk.

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Fig.1 Structure of microwave heating device (Canadian Centre for Occupational Health & Safety)

Fig.2 Schematic diagram of radio frequency treatment (Solar et al., 2005)

Microwave blanching controls and faster start-up and shut-down times has been reported by Kidmose and Proctor and Goldblith (1948) reported the first Martens (1999). For retention of nutritional microwave blanching using 3000 MHz for quality of food products, several researchers some green vegetables, and it was revealed suggested the use of microwave heating as an that vegetables can retain maximum amounts alternative to conventional blanching method of vitamin C. However, many results indicate for food products (Giami, 1991; Ponne et al., that microwave blanching was more efficient 1994; Sánchez-Hernández et al., 1999 and in retaining water-soluble vitamins in Ramesh et al., 2002). According to Lin and vegetables as compared to conventional Brewer (2005) for effective heat transfer in blanching methods. Muftugil (1986) observed food microwave blanching requires little or better retention of vitamin C in microwave no water thus it can reduce the amount of blanched samples as compared to hot water nutrients lost by leaching in comparison to hot blanched samples of green beans. Advantages water immersion. The study on microwave of microwave blanching as compared with blanching of peanuts has been conducted by conventional heating methods include speed Schirack et al., (2007) and reported that of operation, energy savings, precise process microwave blanching was better than 125

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traditional blanching techniques in terms of impact of RF heating to control Mexican fruit energy and time savings. However, it was also fly larvae on Fuyu persimmons fruit and observed that high temperature microwave observed that the treatments used at (48–52 blanching of peanuts resulted in the ˚C) followed by holding times of 0.5 to occurrence of stale/floral and ashy-off flavors. 18min) had no significant effect on firmness, Patricia et al., (2011) studied a clear positive soluble solids content, titratable acidity or effect of microwave blanching on the product weight loss. An efficient RF nutritional quality of broccoli and reported treatment protocol has been developed for that the amounts of protein, ashes, vitamin C, almonds for uniform heating and occurrence iron and phosphorus found in broccoli of RF in differential heating of insects. blanched by microwave were much more than the sample treated by hot water blanching as processing well as they were much closer to fresh broccoli. Minute difference in color, volatile The comparison of the rate of heating, time– aroma compounds, and sensory attributes temperature profiles and quality of three meat between fresh dill and dried dill was observed products (ground, comminuted and non- by Straumite et al., (2012) which was hot comminuted muscle) cooked in a water bath water blanched at 90°C temperature for 30 s or by a 1.5 kW and 27.12MHz RF heater (a followed by microwave pretreatment at 900 cylindrical chamber set between two W for 30 s. Overall quality was good due to electrodes wrapped around the RF applicator) synergistic effect of hot water blanching was conducted by Laycock et al., (2003) and assisted with microwave pretreatment. reported that the cooking time was reduced by up to 1/25 and the surface of the RF cooked Application of radiowave frequency in food products became heated at a faster rate than processing the centre, with differences of 10–20 C. However, juice losses in the RF cooked food Pest control samples were less and thus were acceptable in terms of colour and water-holding capacity. Conventional fumigation agents such as Lagunas-Solar et al., (2005) reported that the methyl bromide infect fruits and nuts thus Radio frequency process operated at 70-90ºC they are replaced by RF radiation. As per range with high efficiency (50%), compares study the conducted by Tang et al., 2000 and well with the 10-15% efficiency for Birla et al., 2008, intrinsic thermal mortality conventional surface heating methods as they of insect pests showed the potential to are uniform and show deep penetration of RF develop high-temperature–short-time thermal waves which results in rapid and treatments in order to control codling moth in homogeneous heating as well as provide fruits. A Lab-scale fruit-mover which is greater than 99.999% reduction in infection capable of continuously rotating the fresh levels for Salmonella sp., and for Escherichia fruit (with an and an apple as test coli O157:H7 when compared to control. samples) through a series of water jets in Wang et al., (2012) reported that the RF order to achieve uniform RF heating was heating at 27MHz and application of an developed by Birla et al., (2008) and found alternating current of 6kW can be used for that apples with typical geometry (oval and processing of pre-packaged heterogeneous dimples on ends) showed more temperature foods (meat lasagna in large polymeric variation as compared to the almost spherical containers (295 x 253 x 42 mm) for retaining oranges. Monzon et al., (2007) studied the product quality as compared to conventional

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method of heating. RF cooking effects the The dough has low heat conductivity thus, the quality, temperature distribution and heating traditional baking process is slow and can rate of chicken breast meat at 27.12 MHz require as long as 30 min. On the other hand, until the center of the breasts reached to 74 in RF processing of bread, dough pieces are °C. After this heating method is compared to placed inside pans made of heat-resistant, RF the conventional one it is explained that, the compatible, food-grade polymers and time to reach end point temperature in the RF introduced into the RF baking oven with oven was significantly less compared with controlled-temperature air flow and exhaust water bath (conventional method), where fans in order to remove excess moisture yield, moisture content, pH, expressible released during the baking process. Total time moisture, shear value of RF and water bath for baking is reduced to 8–10 min for (WB) cooked chicken breast meat were commercial bread loaves, and the bread statistically the same (Kirmaci et al., 2012). develop a crust when it comes out of the RF oven (Awuah et al., 2014). Drying and baking Liquid foods A simulation model for RF-assisted convective drying for the seed quality of In order to evaluate the effect of system broad bean was developed by Ptasznik et al., parameters such that flow rate and RF power (1990). Drying of alfalfa using a combination at 1.5 kW, 27.12 MHz. continuous heating of of RF power at 27MHz with heated forced air starch and guar solutions was investigated has been reported by Murphy et al., (1992). respectively by Awuah et al., (2002) and Mermelstein, (1998) observed that RF drying Piyasena and Dussault (2003), however, to provides uniformity in moisture content of find optimum conditions to inactivate final products and reduces the possibility of surrogates of both Listeria and E. coli cells in mould growth, which consequently increases milk under continuous laminar flow the shelf-life. Later, Jumah (2005) prepared a conditions, Awuah et al., (2005) used a 2 kW, theoretical analysis of simultaneous heat and 27.12 MHz, RF applicator. The effect of RF mass transfer in the RF-assisted fluidized bed treatment on microbial inactivation in orange drying of corn particulates. This model and apple juices and in apple cider was worked efficiently as a tool for - studied by Geveke and Brunkhorst (2004, aided optimization of RF-enhanced fluidized 2008) and by Geveke et al., (2007). Mainly bed drying processes. The main problem they focused on microbial inactivation and associated with post baking is surface quality of beverages processed using the cracking which occurs during traditional system which provides a RF heating source of drying processes due to moisture gradients in 15 kHz to a maximum of 41 kHz and varied the product. RF drying can solve this problem with the product type and increasing the because of its uniform penetration minimizing product temperature to maximum of 65˚C at moisture gradients. Not only this, RF is highly the outlet. Experimentally this method was energy efficient for removing final moisture effective as compared to traditional one. from dry baked products. Conventional Along with this, maximum microbial baking is carried out in forced-air convection inactivation the RF treated samples are found ovens where the heat is transferred to the to be similar in its color and flavor property to surface of the dough by convection, the natural juices with negligible loss in conduction, and irradiation, and then from the ascorbic acid or enzymatic browning in RF surface toward the inside by heat conduction. treated juices. Inactivation of Bacillus subtilis

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spores in soybean milk by radio-frequency frequency (RF) heating. Innovative flash heating at 28MHz by heating up to Food and Emerging 115ºC for 0.4sec was studied by Uemura et Technologies. 6 (4):396–402. al., (2011). They further stated that Fouling of Awuah, G.B., Ramaswamy, H.S., Piyasena, P., the electrode surface by the protein from the (2002). Radio frequency (RF) heating of soybean milk became a problem with high starch solutions under continuous flow electric- field on continuous treatment, which conditions: effect of system and product was later corrected by covering electrode parameters on temperature change surface with a Teflon film. across the applicator tube. Journal of Food Process Engineering, 25 (3):201– It is concluded, nowadays, people are more 223. Birla, S.L., Wang, S. and Tang, J. 2008. health conscious, they want ready to eat food Computer simulation of radio frequency inclusive of all essential nutrients with less heating of model fruit immersed in preservatives. Electromagnetic waves are very water. Journal of Food Engineering. useful for the food industry and have made 84:270–280. processing easy and effective as compared to Bouraout, M., Richard, P., and Durance, T. conventional methods Radiowaves have more 1994. Microwave and convective drying penetration as compared to microwaves of potato slices. Journal of Food whereas, both of them are less time Process Engineering. 17:353–363. consuming and highly efficient, on the other Canadian centre for occupational Health and hand, effective learning is needed to handle safety. 2018. Microwave Ovens and them. Thus, we can conclude that thorough their Hazards. Accessed on: 26/05/2020. learning of each method and better Decareau, R.V. Microwaves in the Food understanding of operations can be helpful in Processing Industry. 1985. Orlando, achieving our goals in near future. Academic. Drouzas, A.E., Tsami, E. and Saravacos, G.D. References 1999; Microwave/vacuum drying of model fruit gels. Journal of Food Ahmed, J., and Ramaswamy, H. 2014. Engineering. 39(3):117–122. Handbook of food preservation In: Esteve MJ, Frigola A, Martorell L, Rodrigo C. Rehman S (ed). Microwave 1998. Kinetics of ascorbic acid Pasteurization and Sterilization of degradation in green asparagus during Foods. 2nd edn. CRC, London . heat processing. J Food Prot. 61: 1518- Al-Duri, B., and McIntyre, S. 1992. 1521 Comparison of drying kinetics of foods Feng., H. and Tang, J. 1998. Microwave finish using a fan-assisted convection oven, a drying of diced apples in a spouted bed. microwave oven, and a combined Journal of Food Science. 63, 679–683. microwave/convection oven. Journal of Ferdous, M.S., Koupaie, E.H., Eskicioglu, C. Food Engineering. 15: 139-155. and Johnson, T. 2017. An experimental Awuah, G. B., H. S. Ramaswamy, and J. Tang. 13.56 MHz radio frequency heating 2014. Radio Frequency Heating in Food system for efficient thermal Processing: Principles and pretreatment of waste water sludge. Applications. Boca Raton: CRC Press. Progress in Electromagnetics Awuah, G.B., Ramaswamy, H.S., Economides, Research.79:83-101. A., Mallikarjuanan, K., (2005). Fito, P., Chiralt, A. and Eugenia, M. 2005. Inactivation of Escherichia coli K-12 Current state of microwave applications and Listeria innocua in milk using radio to food processing, In: Novel Food Processing Technologies (Ed by G.V. 128

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How to cite this article:

Kanchan Bhatt, Devina Vaidya, Manisha Kaushal, Anil Gupta, Pooja Soni, Priyana Arya, Anjali Gautam and Chetna Sharma. 2020. Microwaves and Radiowaves: In Food Processing and Preservation. Int.J.Curr.Microbiol.App.Sci. 9(09): 118-131. doi: https://doi.org/10.20546/ijcmas.2020.909.015

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