IMPLEMENTATION THEREOF

This invention relates to the ultrarapid freezing technique and allows for maintaining the quality characteristic of fresh food products, freshly cooked dishes and ingredients during their storage and thawing.

Water in a cooked dish is its main part. The value of the mass fraction of moisture and its phase transformations during the cold treatment and storage of a dish largely determine its qualitative indicators, i.e. taste, structure and texture, as well as other organoleptic properties and physical and chemical characteristics.

Water in the initial products and in ready-made food is in bound and free states, and it is also in the form of ice at a temperature below cryoscopic one (freezing point).

Water in complex moisture-containing systems (e.g., ready-made dishes) is bound with other components of the system. Differences exist in the form and energy of bonding. Each form of bonding is characterized by its nature, formation conditions, bonding energy, disbonding conditions and changes in dishes caused by it. The properties of bound water differ in a number of physical and physical and chemical properties from the corresponding properties of free water. This affects the cryoscopic temperatures of different products and the course of ice formation during their freezing.

The density of bound water is greater than the density of free water. The molecules of bound water are spatially oriented, therefore, its dielectric constant is much less than that of free water (2.2 and 81.0 respectively). Bound water is difficult to crystallize - freeze out, and remove - dry. When a product (ready-made dish) is cooled to subzero temperatures, not only free water, but also part of the bound water freezes. In this case, the higher the bonding energy of moisture, the lower temperature separates it (by hydrogen bonds with lattice sites of the already formed ice) from the product molecules. Thus, freezing of a product begins upon reaching the cryoscopic temperature, the value of which depends on the product composition.

Knowledge of cryoscopic temperatures is necessary to justify the conditions of cooling, freezing, storage and transportation of products. These data are also needed in thermal calculations and in calculating the portion of frozen water at different temperatures.

Intense ice formation is observed in the range of cryoscopic temperatures of -1...-8°C (zone of maximum ice formation), as a result of which the portions of frozen water reach their maximum. The intensity of ice formation sharply decreases with further decrease in temperature. The portions of frozen water in a product can increase at -18...-30°C by 10-20% respectively. The remaining water (bound) may be involved in the enlargement of ice crystals in the product during its storage and transportation.

Conclusions : 1. It is impossible to completely transform all water into ice within the specified temperature range, and water in a product (ready-made dish) remains bound. 2. To reduce the portion of bound frozen water, it is necessary to prevent (by external impact) the formation of completed crystal structures of free frozen water and thereby weaken the bonds of bound water molecules with quasi-amorphous conglomerates of free frozen water molecules. 3. A high- frequency inhomogeneous electric field, with which the electric dipoles of the molecules of free and bound water respectively interact differently, may be such an external influence.

There is a known method of quick freezing and a quick freezing device (embodiments) disclosed in patent No. 2270407, IPC F25D 13/00 (2006.01), 20.02.2006, which provides for lowering the temperature around a freezing object to (-30)÷(-100)°C and application of unidirectional magnetic field to it, while the cooling of the object is carried out by a cold air stream having a speed of 1÷5 m/s with the simultaneous application of a sound wave of an audible frequency range on the specified stream of cold air. The strength of the specified unidirectional magnetic field pulsates relative to an arbitrary fixed reference level in the positive and negative direction within a predetermined range. The method provides for the application of an electric field to the specified freezing object.

A quick freezing device comprises a deep-freezer capable of lowering the internal temperature around the object to be frozen to (-30)÷(-100)°C, and a magnetic field generating device for application of a unidirectional magnetic field pulsating in the positive and negative directions to the specified object. Moreover, the specified device includes static magnetic field generating devices for application of a static magnetic field with the strength of an arbitrary fixed level and dynamic magnetic field generating devices for application of a pulsating magnetic field that pulsates within the specified predetermined range.

The above solution is selected as a prototype.

The disadvantage of the known method and the known device is a weak and not evident effect on the crystal formation of free and bound water in the object, the water in the solid phase has a fine-grained polycrystalline structure similar to the ice structure in case of shock freezing, the effect of a finer grain structure is minimized 45 days after the storage of the object under low temperature conditions; a decrease in the object freezing time due to the supercooling of liquid water below the crystallization temperature in comparison with shock freezing is insignificant (15-20%).

The technical result from the use of the invention can be expressed in elimination of the mentioned disadvantages by means of ensuring the absence of formation of a regular (crystalline) structure of free frozen water and the complete retention of bound water in the macromolecular matrices of the object, as well as in significant decrease in the object freezing time (in comparison with shock freezing - up to 70%).

The claimed technical result is achieved by a method of high entropy freezing.

The high entropy freezing method includes the following.

The freezing object is placed in an environment with an air temperature from -18 to -40°C with application of a substantially inhomogeneous electric or electromagnetic field with a power from 0.5 to 2.5 kW to the object.

The duration of the cycles of pulses of impact on the freezing object is from 10 ps to 5 s, the cycle frequency is from 0.2 to 50 Hz, the duration of continuous exposure to an electric or electromagnetic field is comparable to the time of the entire freezing process, while the frequency of electromagnetic radiation is from 0.8 to 3.5 GHz. In particular, inhomogeneous electromagnetic radiation is applied to the freezing object using at least three and preferably four magnetrons located around the freezing object and activated alternatively in a preset mode. The freezing object primarily has a thickness of not more than 2 cm.

A high entropy freezing device comprises a deep-freezer capable of maintaining the temperature around the object to be frozen within -18...-40°C, and an inhomogeneous electromagnetic field generating device comprising at least three magnetrons installed with the possibility of changing the direction and intensity of radiation by moving the reflecting elements of the inhomogeneous radiation generation system. In the best embodiment, the device comprises four magnetrons with reflective elements located around the freezing object equidistant from each other.

When an inhomogeneous electromagnetic field interacts with a physical medium, energy losses occur in it due to electrical resistance and viscosities: in the first case - dielectric losses, and in the second one - conductivity losses. As a result of these effects, changes occur in the state of electric charges of this medium, which results in the release of heat in the substance and at the same time in the change in the positions of molecular dipoles relative to each other or their fixation in a certain position (pseudo-viscosity) without changing the physical and chemical properties of the product.

Most food products and media are imperfect dielectrics from an electrophysical point of view. They usually have a sufficiently high dielectric constant and low electrical conductivity, caused, as a rule, only by free ions of a substance. Such products and media may be subject to dielectric heating, which is based on the displacement of charges and molecules bound with them (polarization), when a substance (product) is exposed to an alternating electromagnetic field. In this case, in an inhomogeneous electromagnetic field, additional work is spent on the movement of the dipoles, which due to the presence of internal intermolecular friction turns into heat.

The dipole polarization is due to the presence of constant dipoles (polar molecules) of the substance, which, as a result of the action of the field, can rotate from random directions in the directions of the field force lines, thereby causing polarization due to the orientation of the constant dipoles. In addition, in an inhomogeneous electromagnetic field, the polar dipoles are shifted towards the thickening of the field force lines.

The heat energy released in a unit of a substance volume as a result of dielectric heating is usually characterized by specific power (P _spe c., W/m ³ ), which according to the Joule-Lenz’s law is determined by the following formula:

where e' is the relative dielectric constant of the substance;

E is an electric field strength in the considered volume of the substance, V/m;

d is a dielectric loss angle;

f is a frequency, Hz.

This formula shows that the specific power P _spe c. depends on the frequency of the electromagnetic field and the square of the electric field strength.

The depth of penetration of the electromagnetic field into the product (medium) means the distance D (m) from the surface of the product inside, at which the power of the internal heat sources decreases by e times and which is determined by the following formula:

D = 9.55 · 10 ¹¹ / (f · (e')1/2 · tg d) (2)

The following is an example of calculating the amount of sufficient electromagnetic field strength with a constant exposure of the product to the electromagnetic field during freezing: With a temperature difference of 30°C after 1 m ² we can divert 150 W. Assume that, when the product interacts with microwave radiation, absorbed power shall not exceed 15 W (by an order less than the heat removal), then from the formula (1) with e = 50, tg d =1, f = 2.5 x 10 ⁹ GHz, we obtain the following:

Thus: E = 10.28 V/m at the frequency f = 2,500 MHz.

The speed of freezing is affected by the following: temperature of the product; thickness (shape); heat transfer coefficient from the surface to the medium. The choice of freezing speed is determined by practical feasibility, technology and economic reasons. The following is an example of a high entropy freezing device.

A high entropy freezing device comprises three units:

A. A freezer with air ducts supplying cold air;

B. Fittings for the placement of the objects to be frozen and installation of the systems of power (electromagnetic) impact on objects during freezing;

C. A controlled system of electromagnetic impact on the sample to be frozen.

A. A freezer is a heat insulated cube with edge length of 1 m. The degree of heat insulation and sealing ensures low heat losses in the freezer at a level of not more than 10 degrees per hour at a temperature difference of not higher than 70 degrees (-40°C is the temperature inside the freezer, + 30°C is the ambient temperature) due to all types of heat exchange with the environment. The freezer is cooled by continuously supplying air cooled to -40°C from any source.

The freezer has a door to accommodate the power device and the objects to be frozen as well as sealed feedthroughs for connection of the following:

- power supply of the system for electrical and electromagnetic impact on the objects to be frozen;

- low-current signals of monitoring and control of the system of power impact on the objects to be frozen.

The design of the freezer ensures protection for personnel working with the device against exposure to electromagnetic radiation.

B. The unit for placement of objects to be frozen and installation of systems for impact on the samples during freezing shall ensure the installation of the impact system and placement of samples in the area of an inhomogeneous electric or electromagnetic field. The fitting material shall be neutral to electromagnetic radiation.

C. The controlled system of electromagnetic impact on the object comprises magnetrons, a power supply unit and a control unit.

Waveguides and magnetrons are installed in an amount of up to 8 pieces around the object and are controlled centrally. In this case, the operation of each magnetron is synchronized according to the following parameters:

- operating time of one magnetron (pulse duration)

- time of deactivated state of the magnetron

- time of the operation start shift relative to the operation start of the first of the magnetrons Control of the power of electromagnetic radiation impact on the sample to be frozen is carried out by operating the Hertzian radiator in the pulse mode. The control unit is installed outside the freezer and ensures the control of the duration and ratio of electromagnetic radiation pulses, as well as the display of temperature in the freezer and in the object.

The power supply unit is located outside the freezer, and ensures power supply of the radiator and control unit.

For example, a 187x137x35 tray with fruit and berry slices was selected as the freezing object; the thickness of the slicing layer was up to 20 mm. An electromagnetic field was created by alternating activation of 8 magnetrons of the power device (magnetron power was 700 W). The exposure parameters in this case were as follows: total cycle duration was 2.4 s, cycle frequency was 0.2 Hz.

The storage time of frozen samples was 12 months. After thawing, an examination of the organoleptic properties of the samples and their comparison with the reference samples frozen without exposure to an inhomogeneous electromagnetic Held were performed.

Examination results were as follows: slicing fruits and berries had organoleptic properties and physical and chemical characteristics of a fresh product without traces of freezing of bound water and destruction of cell membranes.