of food is also a very efficient prospect for the processing and preservation of food. The most common among them are microwave heating, ohmic heating, combined microwave vacuum-drying, radiofrequency processing, and new hybrid drying technologies.
Hybrid technologies are the recent development in engineering in the operation and design of the dryers to attain dried products with desired characteristics. In hybrid technologies, the drying technologies are combined with the new drying techniques to achieve a new age drying process to reduce energy consumption and enhance product quality. New age drying technologies would be very helpful for the bioproducts in agricultural sectors for all economic, environmental, and product quality aspects. Instant infusion is another new process for the heat treatment of food, depending upon the product requirement providing mild pasteurization and sterilization. For effective and efficient pasteurization and sterilization, the following are the needs: rapid and small heating time, accurate, and small residence time at sterilizing temperature, and rapid cooling time.
For examining the food when it goes under thermal process, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) can be used as they possess some unique properties for the same. Both of them can be used to investigate variation in the food during processing. Both of them are non-invasive and able to detect water mobility. NMR is the most versatile analytical technique used in modern times. It is capable of revealing complicated multivariate information inside the optically opaque and complex food matrix, also the thermal transformation in liquid, suspension, and gels regarding food samples. NMR and MRI are based on the magnetic properties of atomic nuclei and many elements have isotopes with such properties. Both of them are superior to any other instrumental methods because both are non-invasive, non-destructive, both measure volumes instead of surfaces, and are able to extract both physical and chemical information. By both techniques, it can extract knowledge about diffusion, flow, water distribution, and others. Furthermore, processes such as heating, freezing, hydration, dehydration, and salting can be detected and monitored non-invasively.
1.3.1 Infrared Heating
1.3.1.1 Principal and Mechanism
Infrared was discovered by William Herschel in the 1800s. Infrared depicted below red (infra: below); red is the longest wavelength of visible light. IR heating is the transmission of thermal energy in the form of electromagnetic waves. Wavelength between 0.7 and 1000 micrometer, wavelength larger than visible light but smaller than those of radio waves are the infrared waves. Three major types of infrared waves are [39]:
1 Short waves 0.76-2 μm (near IR waves), temperature above 1000°C
2 Medium waves: 2-4 μm (medium IR waves), when the temperature is above 400 - 1000°C
3 Long waves: 4-1000 μm (far IR waves), when the temperature is below 400°C
The working principle of infrared waves includes: IR energy is electromagnetic radiation emitted by hot objects (quartz lamb, quartz tubes, or metal body) by vibrations and rotation of molecules. When it is absorbed, the radiation provides up its energy to heat materials. An object is a “black-body”, if it absorbs (or emits) 100% of incident IR radiation. The quantity of heat emitted from a perfect radiator (blackbody) is expressed by Stefan-Boltzmann law equation:
Where Q is defined as the rate of heat emission, σSB is the Stefan-Boltzmann constant, T is defined as the absolute temperature, and A is defined as the surface area.
When radiant heaters and food products are not perfect absorbers, the Stefan-Boltzmann equation was modified and the concept of “grey body” was found:
Where ɛ defined as the emissivity of the grey body (ranging from 0 to 1).
This property changes with the wavelength of emitted radiation and temperature of the grey body.
The heating level depends on the absorbed energy, which then rely on the composition of food and the radiation frequency.
Mathematically, the transfer of heat rate to food is expressed as,
Where T1 depicts the temperature of the emitter and T2 depicts the temperature of the absorber. Heat transfer rate relies on:
1 Surface temperatures of heating and receiving bodies or materials,
2 Surface characteristics of both bodies or materials,
3 Shapes of the emitting and receiving materials.
Quantities indicate infrared radiations are the perfect source of energy for heating purposes. They indicate the factors such as larger heat transfer capacity, heat penetration directly into the product, no heating of surrounding air, and fast process control. A perfect balance required for optimal heating between the body and surface heating is attained with IR. The parameters that are important to control to achieve optimal heating results are radiator temperature, infrared penetration characteristics, radiator efficiency, and infrared reflection or absorption properties.
1.3.1.2 Advantages of IR Heating
There are several advantages of IR over traditional heating techniques: [1].
Instant heat: Electric IR system forms heat instantly so there is no need for heat build-up.
Reduced operating costs: The energy can reach 50%, depending upon the insulation, types of construction, and other factors. Furthermore, operations maintenance is limited to the cleaning of reflectors and heat source changing.
Clean and safe: Operating IR is a low-risk task and there is no production of by-products.
Zone control: The IR energy is absorbed only where it is directed and does not propagate. Other advantages of IR are as follows:
1 Quick heating rate
2 Shorter residence time
3 Uniform drying temperature
4 A high degree of process control
5 Higher thermal efficiency
6 Cleaner work environment
7 Alternate source of energy
The utilization of IR technique in the food sector is still developing; many attempts are continuously growing for the development of IR technologies and the future research is focusing on process control and equipment design development, expanding the areas of applications of IR heating and understanding the interaction between heating process and product characteristics.
1.3.1.3 Applications of IR Heating
There are wide applications for IR (infrared radiation) which include medical, paper industries dye, automobile, and others. Table 1.1 discusses the several application of IR heating [1]. In industrial applications, medium to long-range wavelengths seem to be beneficial, for all materials to be heated or dried give the largest absorption in the 3-10 mm region. Moreover, the applications in short waves are continuously evolving. Applications of IR are mostly within the area of food for drying and many other processes during the period from the 1950s to the 1970s from the Soviet Union, the United States, and the Eastern European countries. During the 1970s, much research was performed about industrial frying or meat products cooking and the utilization of near-infrared (NIR) techniques is initiated [28, 43]. In the 1970s and 1980s, several types of research were carried out to apply this technique in the sector of food, mostly at [Swedish Institute of Food and Biotechnology] and