Thermal Food Engineering Operations. NITIN KUMAR

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СКАЧАТЬ 2.6.5.1 Principle and Mechanism

      The traditional method of heat processes like pasteurization and sterilization follows conduction and conduction methods to injure the microorganisms and reducing the load. As mentioned earlier, these methods also consume much time and energy. To mend these disadvantages and meet the demand of the food and increase the quality of the food ohmic heating is also one of the techniques used for better inactivation methods of microbes [78]. Other names of ohmic heating, electro heating, or joules heating, have gained much interest in the food industry. Any conductive food when heat is passed from within, heat is straightaway produced and simultaneously temperature is increased. This technique is utilized for power products, fruits, and vegetables. The pattern in which heat is generated during ohmic heating causes food products to heat up rapidly in a uniform manner [79]. Overheating is avoided of any food product in this situation as there is not much temperature change or gradient. Therefore this technique consumes less heat and also increases the shelf life of the sample as compared to the traditional method.

      The major process in this method is the thermal effect which is used for the destruction of the cellular structure of the microbes. With this thermal effect, an additional effect added to the mechanism is the chemical effect which helps in free oxygen and hydrogen formation [80]. It also produces radicles of hydroperoxyl and metal ions. Injury of microbes is usually due to the buffer solution used which makes the solution or the product toxic. This toxic formation is the main principle agent to cause the deactivation of microorganisms, and later after the desired state is achieved, toxicity also reduces gradually [81].

When compared to the traditional water bath and ohmic shows a better death effect which is created by electric current. The heating is performed under similar temperature and time parameters. During this process, the permeability of the cell is higher whereas transudation of intracellular materials is also elevated which eventually leads to cell injury of the microorganisms [82]. Cell permeability depends upon several factors such as electric current, increased frequency, and higher potential of threshold, processing time. These factors play a vital role in progressing the inactivation process.

      The augmented permeability might cause irreversible damage to the cell over seepage of cellular compounds, together with proteins, enzymes, amino acids, and nucleic acids. But some studies have also stated that the electroporation method has a specialized effect on the cellular and intracellular effect [83]. Eventually, this can be maintained by fluctuating the parameters so that leakage doesn’t happen beyond the threshold level which automatically leads to death. A connection is formed between thermal and chemical effects because the heat is generated due to the generation of electric current passing through the sample of food [84]. In ohmic heating, with temperature, the heating rate also increases. So it is necessary to carefully experiment and design to match the conditions for thermal and chemical effect. Consequently, there will be an extended method to explain the thermal properties owing to the spirit of ohmic heating where heat is formed due to electric current.

       2.6.5.2 Application for Inactivation in Food Sector

      The effect of inactivation rate and food quality while using the ohmic heating process has been widely studied in several reports. E. coli inactivation was done for goat milk using ohmic heating at 50 Hz where the electric field was adjusted and the whole process was compared with the traditional method [85]. The log reduction was significantly reduced when it was done using ohmic heating as compared to the conventional water bath process. For orange juice, the decontamination was done using ohmic heating for moulds, yeast, and bacteria at 50 Hz with varying temperatures. This was also compared with the traditional one which was done using 90°C for 50 s. The results showed that the reduction or the inactivation processing ohmic heating was 98% with only 15% reduction of vitamin C plus the product did not get degraded any of its qualities and was fresh when compared with the conventional pasteurized one [86]. Shelf life during storage of both the sample treated differently at 48°C extended in case of ohmic heated one up to 100 days which was almost twice as seen in traditionally treated pasteurized process product plus preserving the flavors and nutritional attributes.

[87] showed comparable outcomes in which apple juice was treated through ohmic heating for L. monocytogenes and Salmonella Typhimurium. It was observed the log reduction was 5 CFU/mL at 20Hz which was treated for 30 s without disturbing the superiority of the juice. These conclusions specify that ohmic heating is acceptable for the decontamination of microbes in juices.

      When meatballs were subjected to ohmic heating to inactivate the mesophilic moulds, bacteria, and yeast with the following parameters (75°C, 50 Hz, 0 s holding time, 15.26 V/cm). The inoculation was done for Listeria innocua and the outcome was compared with the conventional process. The traditional process consumed much time, i.e., 150 min as compared to sample treated through ohmic heating which varied from 7-15 min [88]. During and after the storage the sample treated with ohmic heated showed a longer shelf life of 21 days with maintained product quality. From all the above studies it was testified that ohmic heating is considered prominent to yield a higher-end product in terms of quality and safety for both solid and semisolid food with minimum heating time as compared to traditional heating or water bath.

      Similarly, ohmic heating works significantly in inactivation spores from food products. Ohmic heating was used to treat B. licheniformis spores present in cloudberry jam at 50 Hz [85]. The sample was also heated with the water bath and the electric field was adjusted according to that. It was observed that the reduction of log cycles was observed perfectly with the sample heated with ohmic heating rather than a simple water bath at high temperature. B. cereus spores found in doenjang were shrunken when ohmic heating with parameter 26.7 V/cm at 25 kHz was applied for the 60 s [81], though the temperature was maintained up to 105 °C, the quality and color were yet suitable for the customers. The main advantage of ohmic heating is that the time required is reduced to a significant level adding to the efficacy of the inactivation process; additionally, it provides quality preservation assurance, and hence thereby enhanced shelf life. Therefore, gathering all the above context with every study is done to improve the process to attain higher consistency.

2.7 Forthcoming Movements of Thermal Practices in Food Industry

To validate the innovative techniques and products developed from that is the main focus of the food industries to scale it up for the next generation and match the pace. With the continuing year, there are various techniques which emerged and were marketed in varied countries in the world, such as microwave, high-pressure process but commercialization of DIC was very narrow [89]. Many applications are emerging especially for powder food products for debacterization and decontamination which are gaining a huge interest in the food industrial sector. The technology stated in this chapter proved to be great and promising for the inactivation process of the microbes with each of them having some speciality with some advantages and disadvantages. Consequently, it is important to identify and build a specialized amalgamation of these techniques and the specific food products to improve the product characteristics and increase the lethality of the cell of the microbes. The major demerit of these techniques is elevated initial cost for installation and minimum data available for data processing parameters. To minimize this drawback, treatment state is optimized and efficacy and high-end products are processed by adjusting the process parameters. This helps in preserving the nutritional balance and product quality plus ensures the safety of the product while been exposed to high temperature. And also, the result of the studies clarify that these techniques help to enhanced the decontamination process and eradicate the microbial load, ensuring the safety of the product [90]. Henceforward, a detailed calculation of charges related to the setting of the treatment plant to operating and maintain the whole line of the process gives a very authentic and practical approach of the innovative techniques leading to better value products.

2.8 Conclusion

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