New Approaches in Non-thermal Processes in the Food Industry

In terms of product quality and food safety biological and chemical activities must be brought under control and this is usually provided by traditional thermal processing. To provide thermal processes, enzymatic and microbiological inactivations in food are the most basic methods that are used. However, the height of the applied temperature has a negative impact on important parameters, which are the color of food, nutritional value, sensory characteristics and flavor. Therefore, in recent years, producers and consumers are engaged in healthy food in the quest to obtain the quality parameters with less deviation. From this point of view non-thermal new techniques have emerged. This study gives information about new food preservation techniques and the applications that can be used in the food industry. These are hover electric field, ultrasonication, high-pressure application, microfiltration, X-rays, ionizing radiation, high voltage electrical discharge, Pulsed Light, magnetic field heating and moderate magnetic field.


Introduction
Non-thermal technologies, without causing the adverse effects of high temperature on food color, flavor, texture and nutritional value on microorganisms, possess the ability to inactivate room temperature and at temperatures near room temperature. Therefore, intensive research on non-thermal food preservation techniques continue such as heat treatment, ionizing radiation, high hydrostatic pressure (HHP), pulsed electric field (PEF), UV irradiation [108,111].
In recent years, the interest for high-quality food products is constantly increasing due to consumer demand. This situation caused increasing demand for non-thermal food preservation technologies. That's why food industry started to use conventional processing techniques generally carried out at lower temperatures. Thus, the food thermal processing which reduce the negative effect on the quality of non-thermal technologies are began to be used [109,110]. In this study, non-thermal food preservation techniques were given information on.

Pulsed Electric Field
Pulsed Electric Field (PEF) is a process that, high-voltage electric field is applied at very short term, that is used for the preservation of food stuffs with a non-thermal process. It is applied in very low temperatures in order to preserve taste, flavor, and nutritional components. It is aim is to inactivate microorganisms causing very little or no change in the properties that allow prolonging of the shelf life. In the process of PEF, electric field in the range of 12-35 kV cm -1 liquid foods is being implemented with an emphasis on short-term (1-100 µs), inactive enzymes and microorganisms on a physical mechanism [65,66,57]. In the food industry, this process is generally applied during pasteurization process of foods like milk, fruit juice, soups and liquid egg [65,69]. The most popular PEF technology applications are the rectangular pulse model, logarithmic model, decreasing pulse, sudden recycled beats, and pulsating beats model [68].
When the the inactivation of PET technology is investigated, it is obvious that according to the dielectric fragmentation theory, the clamping force of the electrostatic disruption of the cell membrane with the balance between opposite forces are emerging as a result of the deterioration of the balance. The cell membrane thickness is decreasing and as the cell membrane is not influenced. Thus, the ratio of fats in the fatty phase equilibrium between the layers is increasing. 1 As a result of the application of a -10 kV/cm force of 10-15 µs irreversibly to a cell, the cell membranes are breaking up.
To obtain electroporation via the formation of large diameter pipes, there are three incidents, which are the application of electric current intensity and the time of the formation of large diameter pipes and the decrease of the resistance of the ionic environment [68,70]. According to researches done about PEF applications: bacteria, yeasts, moulds and the enzymes that create the distortion effect, applied to liquid foods and the results were successful. It is decided by researchers to be applied to liquid food [71 -74].

Ultrasonication
The term ultrasonication is defined as "vibration per second with sound waves of 20,000 or more that performs energy development" [90,91,99]. Devices developed for ultrasonication are typically at frequencies ranging from 20 kHz to 10 MHz [97,98].The most important advantage of ultrasonication compared to thermal processing of the distortion is the process temperature. It should be low, when providing unwanted and pathogenic microorganisms to activation of enzymes engaged in corruption. Thus, the taste, smell, texture, and nutrients of the product are better preserved and fresh products, which are very close to the state properties, are obtained. [92][93][94]99].
The effect of ultrasonication on microorganisms is expressed in three ways. Low frequency ultrasound applications that are used for food processing purposes can cause cavitation occurrence. At the time of the explosion, a very high degree of heat and pressure takes place in the structure of the cavitation bubbles. This dual effect enables inactivation of microorganisms to be performed [95]. The lethal effect of ultrasonication on bacteria is based on the destruction of the cytoplasmic membrane. Another mechanism for microbial inactivation is explained by free radical formation. During the application of ultrasound the OH-radicals and hydrogen peroxide are formed. Also occurring compounds has significant bactericidal effect [96].
When the studies in which changes in the inactivation of pathogenic microorganisms, quality parameters of food products and products in the activation of enzymes are analyzed, successful results were obtained [100][101][102][103][104][105][106][107].

Ionizing Radiation
Radioactive substances emit some rays on the environment during the fragmentation of atoms continuously. Ionizing radiation causes the formation of electrically charged ions in the material strikes. Gamma rays, X-rays and accelerated electron beams are used for food preservation. X-rays are manufactured from 5 MeV (million electron volts) and from the resources that are running on low energy [49,51,52]. The results of the study on fresh strawberries against viruses, which are the norovirus, and Tulane, were successful [48]. Although successful results have been obtained as a result of microbial inactivation studies, instead of sterilization by irradiation of food, it is suggested that other suggested food preservation methods may give better results [49][50][51]53]. Extreme high-dose irradiation, especially in foods that contain much fat will result in loss of aroma. Due to negative sensory properties, that effect milk and milk products negatively, these kinds of products are not eligible for teleportation [47].

High Hydrostatic Pressure
High hydrostatic pressure application is a process of solid and liquid foods, as packaged or unpackaged being subjected to a pressure of 100 to 1000 MPa In order to increase their shelf life and to prevent microbial development vegetable products, fruit juice, beverage industry, meat products and crustaceans the application of high hydrostatic pressure is used at room temperature, in the range of 100-900 pressure MPa [7 -9, 12]. At the same time, it is successfully used in the vegetable products, in protection of vitamins, in the fruit juice and beverage industry, for the removal of shellfish meat, for thawing of frozen meat, for removal of the bitterness of grapefruit juice, for the hardening of chocolate and for gelatinization of starch and proteins [10 -13]. The application of high-pressure thermal processes, enzymatic mixtures and usage in connection with antimicrobial substances, and the application of high hydrostatic pressure increase the effectiveness of the method [14 -16].

Plasma Sterilisation
Irving Langmuir first discovered plasma in 1928 and it is regarded as the fourth state of matter due to its features considerably different from the solid, liquid and gaseous states of matter. Gas plasma is regarded as the fourth state of matter by some physicists and defined as, a gas comprised of ion and free electrons [40,44]. There are non-charged particles such as atoms, molecules and radicals in plasma used for sterilisation purposes. It is formed when a gas or gases are left on constant (direct) current or between two electrodes. Electrons and ions are released during plasma generation. This affects cell walls on microorganism. Therefore inactivation takes place and this helps sterilization. Studies show that it produces positive results in microbiological terms in lots of food such as vegetables, fruit and meat products [42,43,45,46]. There are two types of plasmas, which are hot plasma and cold plasma. Ion temperature of cold plasma is near room temperature and more convenient for use in food [42].

Pulse Light
Broad spectrum -wavelenghts (200nm -1 mm) that are close to the infrared region within the UV region are used. A surface, which will be sterilised, is exposed to at least one pulse light, which has about 0,01-50 J/cm2 density of energy. This is the sterilization method which is found suitable for use by FDA (Food and Drug Administration) for food without damaging the content of the product and surface, reducing chemical preservative and the use of disinfectant and giving effect of antimicrobial. The time of pulses ranks between 1 µs and 0,1 s and 1-20 flashes are applied per second. In this application, Chemical change which occurs in microbial inactivation, protein, membrane and other cell components occur through various mechanisms like segregation of DNA chain The cell can repair itself in traditional UV applications under specified conditions but it has been noticed that the cell cannot repair itself and get damaged during the studies carried out via PL method which is applied densely and at a high energy. It has been observed that resistance of mold spores is higher than bacteria's [32, 34, 36, 37]. Successful results have been obtained during the studies carried out recently over the food safety and variations at the nutritional elements. It has been mostly used in meat industry [27][28][29][30][31]. It has made the method used in combination with other protection methods more effective at the studies from the point of food safety.

Microfiltration
Micron inside liquid solution and larger size of particles are divided with microfiltration. Microfiltration membrane's hole varies between 0.05 and 5 mm. When membrane's resistance is low, they are operated under low pressure and they operate approximately up to 2.0 bar. Microfiltration has the ability to selectively allocate particles from the large molecular weights of more than 200 kDa. It's a technique that the pressure changes between 0.1 to 0.5 bar. The pore diameter of the membrane used varies between 0.1-10 µm [22 -26]. Microorganisms and spores from milk or whey, fat globules, somatic cells, large molecules such as phospholipids are used for the separation of the particles. As a result of conducted researches, the milk that is subjected to microfiltration process is stored considerably longer than the duration of pasteurized milk [20-22].

Ultraviolet Light
Ultraviolet (UV) light is an electromagnetic radiation with a wavelength between 10-400 nanometers. Ultraviolet light is divided to three categories according to its wavelength: UV-A 400-320 nm, UV-B 320-290 nm and it has two wavelenght between UV-C 290-200 nm [54,57]. The usage of UV-C light in food has an effect on the microorganisms within a broad spectrum. Furthermore, it is known that UV-C has posovote effect on food products. Ultraviolet light demonstrates antimicrobial (germicidal) wave length effect from 100 nanometers to 280 nanometers. The sub-division of ultraviolet light in this part is UV-C [55,58]. Generally, ultraviolet light causes damage to nucleic acids when it effects microorganism. Thus, it leads to prevention of reproduction. Nucleic acid absorbs the ultraviolet light between 200-310nm. As a result of damage microorganism becomes inactive [56,57]. Effectiveness of the application of ultraviolet light depends on characteristics of light, feathures of foodstuff, microorganism types, processing conditions, and products being solid or liquid [57,59]. UV light for inactivation of microorganisms on food surfaces is ever increasing and the technology required to be successful have been identified in many studies [60 -64].

Magnetic Field Heating and Moderate Field Heating
Magnetic field has a potential impact in microbial inactivation of foods. Static Magnetic Field (SMF) and mobile magnetic field (MMF) have a potential effect in microbial inactivation in foods. As in SMF, magnetic field intensity can change as sinusoidal waves. DNA synthesis of the magnetic field causes change in the sequence of biomolecules or biyomembranes, ionic movement between the plasma membrane. As a result, it causes change in the cell proliferation rate [76,77]. It's applied in the processing of liquid, solid and packaged foodstuffs. Pressured Electric Field (PEF) and Static Magnetic Field (SMF) are both used for food freezing processes and successful results are obtained [75].
Moderate Magnetic Field (MMF) depends on the completion of the electrical circuit based on the principle of the food by passing the electrical current through. Generally, it is used for breaking down the cell wall to affect the efficiency of the fruit juice [82 -84]. The voltage gradiyen below 100 V/cm is used for component extraction from microorganisms, fermentation yield, and combined with other methods to prolong the shelf life [78 -81].

High-Voltage Electrical Discharge and Gliding Arc Discharge
Recently, new technologies like high-voltage electrical discharges (HVED) are used to remove the valuable compound like polyphenols which are obtained from plant material [86,87]. It leads to degradation by forming damage in cell walls and tissues with electrical and mechanical effects of technology HVED (0-400 kJ/kg). A study was conducted about pressed rapeseed. As a result, in order to decrease the loss of high components high voltage electrical discharges and solid-liquid ratio (1:5-1:20, w/w) were used. Successful results have been obtained. Cayman arc discharge (CAD) is one of the new conservation methods in food. It is the technology that used with electric arc discharge [89]. A study of the slip arc discharge, the contaminated water with Escherichia coli , the first 10, 13 and 16, and 25 minutes along treated with GAD for 25 min and the best results 16 minutes of plasma treatment (approximately 2.7 log decrease) was inactivated [88].

Discussion
Literature review shows that there are new techniques in food processing. As a result of these new techniques, new alternative and non-thermal methods gained importance, which will have less impact on the overall quality and nutritional value of foods. In order to extent shelf life of foods ultrasonication, microfiltration, High Hydrostatic Pressure (HHP) Technology, and Hover Electric Field (PEF) applications have been developed. Nowadays, in the production of foodstuff, microbiologically safe and thermal process techniques are becoming increasingly important. Pulsed Light Technology is a method widely available on food surfaces, but it was concluded that more research is required. It has been identified in the literature that high-voltage electrical discharge in a magnetic field and heating of other technologies such as food practices are not adequate. UV and PEF technologies are especially found in the fruit juice and liquid foods. Studies demonstrate that usage of non-thermal preservation methods with other food preservation methods has been found to be more effective in the activation of other destructive microorganisms and enzymes.

Conclusion
The negative effects of thermal processes on the product have led manufacturers to avoid using these methods. The exploration of new techniques because of the new food processing methods that will have less impact on overall quality and nutritional value of food, are requested by the consumer. As a result of researches, non-thermal processes which are one of the new technologies are regarded as techniques that can be used successfully in obtaining a quality product in terms of sensory and nutritional content. Also it can be used on their own and other preservation methods. With these methods, loss of nutrients released by the effect of high temperatures in the food structure and the changes occurring in the sensory properties can be minimised. It is found that the applications of electrical field has increased and it has been seen as promising.

References
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