RESEARCH OF THE TECHNOLOGICAL PROCESS OF LOW TEMPERATURE STERILIZATION OF FRUIT AND VEGETABLES IN A MICROWAVE FIELD

ABSTRACT

This article discusses the use of microwave energy in fruit and vegetable sterilization technologies and food production in order to find solutions to preserve quality during storage and processing of fresh canned food and reduce losses associated with the growth of microorganisms.

Microwave sterilization allows for simultaneous and uniform heating of each molecule of the food product and completely destroys microorganisms that contaminate it; preserves the protein and vitamin content, taste and organoleptic characteristics as much as possible. The final product does not contain any preservatives, is ready to eat, and can be stored at room temperature for at least 9–12 months from the date of processing. This technology allows you to create a wide variety of recipes for first and second courses from all types of meat, fish, vegetables, and cereals; prepare desserts from fruits and baked goods; Sterilize dairy products, juices and other drinks.

АННОТАЦИЯ

В данной статье рассматриваются применения СВЧ-энергии в технологиях стерилизации плодов и овощей и производстве пищевых продуктов с целью поиска решений сохранения качества при хранении и переработке свежего консерва и снижения потерь, связанных с ростом микроорганизмов.

СВЧ-стерилизация позволяет получить одновременный и равномерный нагрев каждой молекулы пищевого продукта, полностью уничтожает загрязняющие его микроорганизмы; максимально сохраняет содержание протеинов и витаминов, вкусовые и органолептические характеристики. Итоговый продукт не содержит никаких консервантов, готов к употреблению, может храниться при комнатной температуре в течение, как минимум, 9–12 месяцев с момента обработки. Данная технология позволяет составлять самые разнообразные рецепты первых и вторых блюд из всех видов мяса, рыбы, овощей, круп; приготовлять десерты из фруктов, выпечки; стерилизовать молочные продукты, соки и прочие напитки.

Keywords: sterilization, canning, heat treatment, microorganism, microwave energy.

Ключевые слова: стерилизация, консервирование, тепловая обработка, микроорганизм, микроволновая энергия.

Introduction. The most important condition for obtaining high-quality canned fruits and vegetables is strict adherence to the technological requirements for each individual operation. Compliance with these requirements is possible only by organizing on-farm quality control of fruits during the canning process.

One of the ways to intensify the process of sterilization of canned products is the use of microwave processing. Microwave heating allows you to significantly intensify the technological processes of food production, especially when combining it with traditional methods of energy supply, such as baking, frying, roasting, defrosting, sublimation, sterilization, blanching, etc.

The efficiency of a microwave device depends on the operation of the microwave magnetron generator and determining the scope of its use in the technological chain.

Materials and methods. We investigated the possibility of using microwave energy in technologies for sterilization of plant materials and food production in order to find solutions to preserve quality during storage and processing of fresh plant materials and reduce losses associated with the growth of microorganisms. The features of dielectric heating were considered. The advantages of using microwave heating and its effectiveness in the technology of sterilization, pasteurization and disinfection of plant materials are shown. The food industry uses microwave fields operating at frequencies of 915 MHz and 2.45 GHz. The short-term high-temperature microwave sterilization process is used not only to inactivate pathogenic microorganisms, but also to minimize the deterioration of food quality throughout the shelf life. The use of microwave heating helps to inactivate enzymes that reduce the organoleptic qualities and nutritional value of fruits and vegetables. When processing products and raw materials with low humidity, microwave energy supply has the advantage of shorter processing time.

For many types of plant raw materials, prolonged exposure to microwave energy causes irreversible damage, changing quality indicators, including physicochemical ones. The use of pulsed, combined processing may be a solution to this problem. Microwave processing is used both to preserve the quality and prevent diseases of fruits, and in the post-harvest period. This method significantly reduces the overall energy consumption of sterilization, ensuring the preservation of the nutritional value of plant materials, thanks to the effective destruction of dangerous microorganisms such as Salmonella, E. coli, Campylobacter sp., Staphylococcus sp., Listeria, as well as yeast and mold. This analysis is the first part in research to determine optimal food processing modes.

To develop and operate microwave heating installations, it is necessary to justify the parameters of the technological process, have an understanding of the electrophysical properties of products and the basics of process calculations.

However, despite the advantages of microwave heating, traditional methods should not be rejected; on the contrary, their rational combination is the most fruitful and constructive path.

Microwave heating makes it possible to concentrate very high energies in small volumes of material. By varying the geometry and intensity of the electric field, it is possible to create conditions under which the temperature in the center of the product will be higher than on its surface. This allows us to organize and intensify technological processes in a new way, and in some cases create new types of them that cannot be implemented using traditional methods.

During the heat treatment process, food products undergo profound changes that affect their dielectric properties, which, in turn, affects the course of microwave heating.

Fundamentally, a microwave apparatus consists of the following elements: power source: microwave energy converter; devices for supplying microwave energy; communication device transmitting energy to the load (product); a device that creates a uniform distribution of energy during heating; the heating chamber itself with a transport device; systems of microwave traps and sealing seals that prevent radiation into the environment, as well as control systems with feedback between elements.

Currently, these preservation methods have been supplemented with new, more effective methods such as short-term sterilization at elevated temperatures, aseptic preservation, sterilization with ionizing radiation, treatment with high-frequency currents, antibiotics, chemical preservatives, etc.

The theoretical study of ongoing phenomena, namely the technological process, is presented in the form of an object of study, which is characterized by input and output parameters.

The technological process of sterilization of fruits and vegetables, as an object of research, can be presented in the form of a flow diagram (Fig. 1).

The group of parameters Y, Z are input, and X, U are output indicators characterizing the technological process of sterilization.

Figure 1. Process flow diagram

Group of parameters Y characterizes the design parameters of the microwave sterilizing apparatus. These include: dimensions and magnetron generating microwave emitter, etc.

The group of parameters Z characterizes the properties of fruits and vegetables entering the microwave heater for processing: the chemical composition of the product, the size of the product, etc.

Group of parameters X, U: mass flow, temperature, product processing time.

The task of theoretical research is to establish patterns of connections between the input and output parameters of an object.

If the effects of input parameters on an object do not change over time, then the output parameters are also unchanged, and the process is called stationary. If at least one input effect changes over time, then the process of corresponding change in the output parameters of the object is called dynamic; after the end of the transition process, it becomes stationary. For a theoretical study of the static and dynamic characteristics of the object, a mathematical model of the process is compiled. In general, to simulate heating with microwave processing, a variety of heat transfer models and the impact of electrical energy are used. This method involves placing a food product in an electromagnetic field, in which, by changing the direction of the external field, the orientation of its molecules changes. From the above, it is clear that in an electromagnetic field of high frequency current, the product will be heated throughout its entire thickness simultaneously and evenly, which is the main advantage of this method. Based on this method, VNIIKOP created a high-frequency continuous sterilizer with a productivity of 0.13-0.27 bps.

However, its introduction into industry is hampered by its low efficiency (η=0.25+0.3).

When sterilizing with high frequency currents, heat is generated inside the product, which makes it possible to successfully use this method for processing solid and mushy food products. Heat is generated in them in two ways: in non-thermally conductive ones - due to friction under the influence of molecular polarity, in thermally conductive ones - due to changes in acceleration under the influence of a changing potential.

The amount of heat generated as a result of the conversion of electrical energy depends not only on the installation, but also on the properties of the product being processed:

where Q is the heat generated under the influence of high-frequency currents; f – frequency (according to international agreement, the following frequencies are accepted: 13.56, 27.12 and 40.08 MHz); V – voltage; d – distance between capacitor plates; ε – dielectric constant (for meat ε=145; peas at 230C ε=9, and in the frozen state ε=2.5); tanδ – loss coefficient (depends on the relationship between the frequency and dipole moment of the molecule); proteins have a high dipole moment, so their loss coefficient has a maximum at a lower frequency; γ – specific gravity.

 The main condition for dielectric heating is the homogeneity of the heated mass, otherwise a fairly high temperature difference occurs. When measuring temperature with thermocouples its lowest value was noted at the walls of the jar, and the greatest temperature difference reached 350C. The varying degrees of heat generation were especially noticeable during fruit processing. The heating rate is much higher than with other sterilization methods that rely on external heat. During sterilization of fruits at a frequency of 9 MHz, heating the mass of 1 liter jar to 700C took 6 minutes.

Further expansion of high-frequency sterilization is constrained by economic considerations and can be expected to find use in processing products that cannot be rapidly sterilized by steam or hot water. We note that the cost of thermal energy obtained using a high-frequency generator with a power of 15 kW at efficiency converting electricity into heat is about 56%, 2.8 times the equivalent cost of steam.

Conclusion. Experiments, as a rule, are multifactorial and are associated with optimizing the quality of materials, finding optimal conditions for carrying out technological processes, developing the most rational equipment designs, etc. The systems that serve as the object of such research are very often so complex that they cannot be theoretically studied in a reasonable time. Therefore, despite the significant amount of research work performed, due to the lack of a real opportunity to sufficiently study a significant number of research objects, as a result, many decisions are made on the basis of random information and are therefore far from optimal.

In practice, the very need to measure most quantities is caused by the fact that they do not remain constant, but change as a function of changes in other quantities. In this case, the purpose of the experiment is to establish the type of functional dependence y=f(X). To do this, both the values ​​of X and the corresponding values ​​of y ̅ must be simultaneously determined, and the task of the experiment is to establish a mathematical model of the dependence under study. In fact, we are talking about establishing a connection between two series of observations (measurements).

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