NITIN KUMAR

Thermal Food Engineering Operations


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Recent work is experimental in nature and performed in Japan, Taiwan, and several other countries. Applications are mostly from areas such as dehydration, drying of vegetables, fish, rice, roasting of coffee, cocoa, and cereals, heating of floor, frying of meat, baking of pizza, biscuits, and bread, enzymes, and pathogens inactivation. Also, for thawing, blanching, sterilization, pasteurization of packing materials, and surface pasteurization, these techniques have been used.

      The major effects on food involve the quick heating of food surfaces sealed in moisture and aroma compounds. Variation to components of food surfaces is equivalent to those that happen during baking.

      1.3.2 Microwave Heating

       1.3.2.1 Principal and Mechanism

      With the increasing demand for healthy foods, there is a repeated effort given to enhance and optimize different processing techniques in food, to meet the expectations of consumers. With the advancement of emerging technologies, microwave energy has become an indispensable part of every household system. The use of microwave has expanded from heating and defrosting to thawing, blanching, sterilization, drying, etc., in food industries [20, 69]. Microwave is electromagnetic waves with a frequency which ranges from 300 Mhz to 300 GHz. Frequency of microwave used for domestic purposes is 2.45 GHz, whereas the frequency for industrial purposes is 915 MHz [8].

Industry Methods
Agriculture Incubation and warming
Bottling Drying
Glass Drying, curing the varnish or paint on back—mirrors and tempering layers
Medical-applications Incubation and warming
Environmental chambers Heating
Food Toasting, cooking, food warming, drying, broiling, and melting
Pharmaceutical Drying water from powder—tablets
Metal treatment Preheating—aluminum; steel
Paper Laminating Calendaring—rolls Adhesive—labelsDrying water from—towels
Paint Primer, topcoat alkyd, acrylic—steel panels, Drying—bicycles, vehicles bodies, aluminiumbodies
Textiles Moisture elimination—carpets Latex and PVC backingMoisture elimination from dyes
Plastics Laminating Annealing FormingEmbossing

      The microwave energy is transferred to food through the contactless transmission of the wave. This system ensures the uniform heating of food samples during the operation. The equipment comprises a magnetron which is the generator, guide waves which are the aluminium tubes, and for a continuous operation, it has a tunnel attached with a conveyor or a metal compartment for batch operation. These chambers and tunnels are sealed by absorbers or traps to prevent the microwave from escaping and causing injury to the operator [11].

      Microwaves are defined by two mechanisms:

      (a) Ionic polarisation: ions present in the solution, when suspended to the electric field, orient themselves, experiencing acceleration and an upsurged kinetic energy. When ions collide with each other it gets converted into heat. This frequent collision increases the density or the concentration of the solution which is also known as the ionic polarization effect [3], whereas in gases the collision becomes difficult due to the spacing between the molecules. In food material, cations are generated by the presence of salts of sodium, potassium, or calcium whilst chlorine produces anions.

      (b) Dipole rotation: When the polar molecule strives to situate itself into the fluctuating electric field caused by the microwave, the dipole rotation is created, where the oscillation of the dipolar species leads to the collision with the surrounding producing heat [80]. With the increase in temperature, the dipole movement decreases, whereas ionic conduction increases hence, food samples with both the compounds when heated by the microwave, first governed by the dipole rotation and then with the increase in temperature governed by ionic conduction. The comparative involvement of these methods of heating hinges on the concentration and flexibility of sample ions, plus on the sample’s relaxation time [36].

       1.3.2.2 Advantages of Microwave in Food Industry