4. Process and procedure of microwave-assisted extraction

There are two mechanisms in microwave heating: dielectric conduction and ionic conduction. The principle in dielectric heating is to rearrange the molecules in the dipolar structure by rotation in the presence of electrical changes. The dipoles are arranged at 2450 MHz and distributed randomly at 4.9109 times in the second. As a result of this motion, heat is generated by the vibration. In the ionic conduction mechanism, the magnetic field is generated by the movement of ions at the end of the application. The solvent heats up by friction resulting from the resistance of the solvent to the ion flux. In most applications, two mechanisms occur simultaneously.

The frequency, microwave power and heating speed, temperature, mass of food, water content, density, physical geometry, thermal properties, electrical conductivity, and dielectric properties of food are affected by microwave heating. Microwave, which has been used for various applications in food for many years, is also a preferred method for increasing extraction efficiency (Table 2). Contrary to classical heating, in the case of microwave heating, for example, all are heated uniformly and quickly at the same time. The cells are heated by microwave radiation by the moisture in them and apply pressure to the cell wall as a result of evaporation. The cell wall is disrupted by this high pressure, and the passage of the components to the solvent is ensured. One of the most important parameters in extraction process is solvent choice. Solvents with a larger dipole moment will heat up faster. According to the solvent dipole moments, acetonitrile, methanol, acetone, ethyl acetate, water, ethyl alcohol and hexane are the most commonly used solvents for phenolic substance extraction from plant source. The nonpolar solvent hexane (dipole moment <0.1) will not heat up in the microwave.

Microwave extraction is performed with two different systems (Figure 3). The most common system is the closed system extrusion made in a closed container that can control temperature and pressure. The other method is carried out in an open container under atmospheric pressure. The advantage of this method is that the amount of extraction and the amount of solvent used are small at large. The principle of heating using microwave energy is based on the direct effect of the microwave on the molecule through ion conduction and dipole rotation (rotation). In most applications, these two mechanisms come into play simultaneously. Ionic conduction is the electrophoretic migration of ions when a magnetic field is applied. The solution results in


Table 2. Microwave applications in the food industry.

heat production, the electrical conductivity of the food, the composition of the food, the

Preliminary treatment of rice brass raw materials and extraction of oils by solvent extraction are examples of studies in which ohmic heating systems are used as pretreatment in extraction processes. For food samples pretreated using ohmic heating method, the yield varied between

Pulsed electric field (PEF) technology is a food preservation process that is based on the use of the electric field to eliminate food-borne pathogenic microorganisms and to control microorganisms that destroy food, is nonthermal, and does not adversely affect food quality. A typical PEF unit consists of a high-voltage boost generator, application chamber, flow control system, control, and monitor device. The most important one of these is the application chamber, and it

The successful results of PEF technology in liquid foods (especially fruit juice, milk, etc.) are noteworthy and lead to the production of high-capacity systems. In the near future, it is known that in developed countries, high-quality products will be obtained by processing liquid and semiliquid foods with PEF technology. In this context, it will be inevitable that many countries will follow these developments as the result of the conjunctural changes that will take place in the competition of international food trade. For this purpose, attention should be paid to other disciplines (such as machinery, industry, electrical-electronics, materials, and food engineering) to produce PEF technology in our country. Initiation of studies on PEF technology, transmission, and dissemination of this technology in the industry will enable the technology to be

The use of microwave technology, which has been in use since the Second World War, in the analytical laboratory was at the end of the 1970s. Microwaves are electromagnetic radiation that varies in the range of 0.3–300 GHz and are usually extracted at 2.5–75 GHz in natural products. The efficiency of microwave energy depends largely on the content of the solvent, the plant material, and the applied microwave power. The advantage of microwave heating is the decomposition of oxidized weak hydrogen bonds at the poles of the molecules. Extraction with microwave is realized with two different systems. The most common system is the closed system extrusion made in a closed container that can control temperature and pressure. The other method is carried out in an open container under atmospheric pressure. The advantage of this method is that the amount of extraction and the amount of solvent used are largely small.

There are two mechanisms in microwave heating: dielectric conduction and ionic conduction. The principle in dielectric heating is to rearrange the molecules in the dipolar structure by

4. Process and procedure of microwave-assisted extraction

intensity of the electric field, and the duration of the waiting period.

168 Emerging Microwave Technologies in Industrial, Agricultural, Medical and Food Processing

49 and 92%, while for non-pretreated samples, the yield was 53%.

3.2.4. Pulsed electric field extraction

must be treated with care during design.

produced by the domestic industry.

3.2.5. Microwave-assisted extraction

appropriate if it is a fugitive compound. However, in closed containers it is necessary to wait for the temperature to fall before opening the container after extraction. The main difference is the heat. The extraction process begins with the extraction cell being loaded, for example. Microwave radiation is applied, and the pre-extraction step is started to heat the solvent to the set values. Normally, heating takes less than 2 min. The specimen is then irradiated and

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The advantages of microwave-assisted extraction are reduction in solvent consumption, increase in extraction efficiency, high recovery, ease of use and low cost, wide solvent, and solvent blends. The disadvantages are that if the target component or solvent is polar or volatile, the efficiency of the microwave is too weak, and it is applied at high temperatures such as 110–150C, which requires additional filtration or centrifugation to separate the solids

5. Applications of MAE as a green extraction technique in food industry

MAE is usually used in environmental analyses. Extraction of polyaromatic hydrocarbons, polychlorobiphenyls, and organochlorine pesticides from matrices such as sediment and soil has been studied. MAE has also been applied to food analyses. Extraction of 16 organochlorine insecticides in sesame seeds, use of microwave confinement in drug extraction from seed, and extraction and testing of lidocaine, methadone, diazepam, nordiazepam, proxifene, and norproxifen materials as model medicines are the main applications in which the MAE technique is used. At the same time, extraction of natural products such as drugs (pentobarbital, ketamine, diazepam); extraction from skeletal tissues; extraction of natural products such as terpenes, alkaloids, volatile oils, and carotenoids; extraction of color pigments in the paprika; identification of pesticide residues in sunflower seeds; discovery of a rapid method using

generally extracted at intervals of 10–30 min [17–19].

Figure 4. MAE apparatus.

as compared to supercritical fluid extraction.

Figure 3. Schematic view of the microwave-assisted extraction system (closed system and open system).

a resistive friction (friction) to this ion flow, and thus the solution heats up. Extraction is usually carried out in a closed container. In this case the pressure increases, and the solvent can be heated to higher temperatures than the boiling point. For most solvents (such as acetone, acetone hexane, acetone), the temperature in the container is two to three times the boiling point of the solvent. Two main types of MAE systems can be used: closed-vessel system (under controlled temperature and pressure) and open-vessel system (atmospheric temperature). Both systems and MAE apparatus (DKSH Australia Pty. Ltd.) are shown in Figures 3 and 4, respectively.

While the cells are being irradiated simultaneously in the closed-vessel system, the vessels are successively irradiated in the open system. In open vessels the temperature is limited by the atmospheric pressure boiling point of the solvent, while in closed vessels, the temperature can be increased by the applied pressure. The closed container system seems to be most Microwave-Assisted Green Extraction Technology for Sustainable Food Processing http://dx.doi.org/10.5772/intechopen.76140 171

Figure 4. MAE apparatus.

a resistive friction (friction) to this ion flow, and thus the solution heats up. Extraction is usually carried out in a closed container. In this case the pressure increases, and the solvent can be heated to higher temperatures than the boiling point. For most solvents (such as acetone, acetone hexane, acetone), the temperature in the container is two to three times the boiling point of the solvent. Two main types of MAE systems can be used: closed-vessel system (under controlled temperature and pressure) and open-vessel system (atmospheric temperature). Both systems and MAE apparatus (DKSH Australia Pty. Ltd.) are shown in Figures 3

Figure 3. Schematic view of the microwave-assisted extraction system (closed system and open system).

170 Emerging Microwave Technologies in Industrial, Agricultural, Medical and Food Processing

While the cells are being irradiated simultaneously in the closed-vessel system, the vessels are successively irradiated in the open system. In open vessels the temperature is limited by the atmospheric pressure boiling point of the solvent, while in closed vessels, the temperature can be increased by the applied pressure. The closed container system seems to be most

and 4, respectively.

appropriate if it is a fugitive compound. However, in closed containers it is necessary to wait for the temperature to fall before opening the container after extraction. The main difference is the heat. The extraction process begins with the extraction cell being loaded, for example. Microwave radiation is applied, and the pre-extraction step is started to heat the solvent to the set values. Normally, heating takes less than 2 min. The specimen is then irradiated and generally extracted at intervals of 10–30 min [17–19].

The advantages of microwave-assisted extraction are reduction in solvent consumption, increase in extraction efficiency, high recovery, ease of use and low cost, wide solvent, and solvent blends. The disadvantages are that if the target component or solvent is polar or volatile, the efficiency of the microwave is too weak, and it is applied at high temperatures such as 110–150C, which requires additional filtration or centrifugation to separate the solids as compared to supercritical fluid extraction.
