JPH07500503A - Thawing frozen food - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] FIELD OF THE INVENTION The present invention relates to thawing of frozen materials, freshly frozen foods.

Background overview The use of quick freezing to preserve food has become widely established in recent years. food to preserve remains in a liquid state in the moisture it contains, and is cooled to a temperature at which the internal portion decreases. frozen. , ~106C to 130'C are typical, e.g. The portion of the freezable moisture content of meat that remains in the liquid state is 1 at -10'C. Typical ranges are 0%, 5% at -20°C, and 3% at -30'C. be. At such temperatures, the quality of food is maintained for a long period of time, i.e. for months or even years. It is often possible to preserve it without significant deterioration.

Foods can be frozen in large blocks with many parts or individually. It can also be frozen in small pieces. Relatively pure ice can be used as food and/or There are things you can do around individual parts.

Food frozen in this way must be thawed before it can be used. Of course Ino is. Some foods (such as fruit) cannot be heated simply by returning them to ambient temperature. Some things (meat, fish, etc.) need to be cooked, that is, cooked for a certain amount of time. temperature and must be maintained at that temperature for a considerable period of time.

(In this book, thawing refers to almost completely converting the water part to a liquid state.

This causes the food to lose its firmness but still contain moisture, leaving it in the form of water. This is different from methods that reach the temperature that exists in the state. )Natural thawing The simplest thawing technique is to simply leave frozen food at ambient temperature, but In this case, the defrosting time is not constant and becomes long.

Thawing time is determined by the ambient temperature, which depends on various factors (e.g. time of year). Therefore, the heat transfer rate to the inside of the frozen food is low. Temperature gradient (low and decreasing as thawing progresses) and food thermal conductivity (this is low and decreases as thawing progresses) It also depends on the length (low).

Most of the heat required for thawing occurs when the water in the food undergoes a phase change (melting) from ice to liquid water. It is, of course, understood that it is absorbed even though the amount of heat is absorbed (latent heat requirement). This fusion The solution occurs gradually over a temperature range, typically around -0,50 Substantially completed by 0. Therefore, the area completely thawed from the surface of the frozen food The temperature gradient between the thawing zone and the substantially completely frozen area is This is the main gradient that affects the thawing time.

The long and inconsistent thawing time caused by this natural thawing technique poses serious problems. Ru.

In many cases, especially if the food needs to be heated or cooked, It is important to ensure that the meat is completely thawed before being cooked. This stage If there are any remaining areas of ice inside the food, remove them. The region effectively has very large thermal inertia due to the latent heat required to melt water. I will do it. Therefore, those areas may remain cold and uncooked. This also impairs the umami flavor of the cooked food.

More importantly, this poses a health risk. Some foods are Do not cook such foods completely as they may contain various bacteria that can cause food poisoning. The importance of doing so is well understood. Raw parts that are not cooked in such food It is extremely undesirable that there is a part, especially if such a part is warm. If it is exposed to water, it may promote the growth of bacteria that may exist inside it. Become.

Given home situations, thawing time can be an inconvenience. commerce In the above situations, minimizing thawing time is essential. Slowly The more food that is thawed, the more it becomes a physical burden on the factory. In the thawing process, the amount of food thawed at once increases, and the thawing time becomes longer. This increases the chance that an item will be used before being properly thawed. It's going to be a big deal.

Therefore, faster and more reliable decompression techniques are needed.

Shikkakuren One possibility is to soak the food in water rather than leaving it in the air.

Controlling water temperature can improve the speed and reliability of the thawing process; The amount of safety that must be tolerated is greater because the time required for freezing can be more precisely determined. This will significantly reduce the rate.

However, this technique provides only modest improvements in decompression speed. . The surface temperature of frozen products can be brought close to the water temperature. (In air, the surface temperature of frozen food is significantly lower than ambient temperature due to the low heat capacity of air, even with forced air circulation. It tends to be very low. ) However, the temperature gradient of frozen foods is relatively low. Until. There is also a risk that food will be contaminated with bacteria and other microorganisms floating in the water. There is sex.

Another possibility is to increase the ambient temperature (with air or water).

This significantly improves thawing time due to the substantially increased temperature gradient across the food. It is possible to However, with this technology, the surface area of frozen food is will be held at an elevated temperature for a period of time such that the portion is partially cooked. This may increase the risk of harmful bacterial growth in such areas. It becomes. This technology is mainly used in situations where frozen foods are heated or cooked immediately. It should be used in a limited manner. 'Thawing technique using air or water called thermal thawing The technique has important drawbacks. Therefore, other thermal thawing methods must be considered.

Other heat thawing Vacuum thawing involves boiling water in a container at low temperatures and thawing the resulting water vapor. It consists of condensing on the top and supplying the latent heat of condensation to the food. This is a surface modification. heat, the disadvantages of which are mentioned above.

Infrared heating is essentially surface heating and has similar drawbacks.

Microwave heating may seem desirable, but microwave penetration is low. . It was also found that microwaves are absorbed better by liquid water than by water.

Therefore, microwave thawing creates locally high temperature areas in frozen foods, and these The high temperature part of the frozen food is rapidly heated and cooked while the main body of the frozen food remains frozen. It gets lost. The only way to effectively thaw food using microwaves is to use high temperatures Diffusion of heat from parts to the still frozen parts surrounding them to keep the energy input required to thaw that frozen food volume to the minimum necessary. It is to hold. Therefore, there are few or no advantages over simple natural thawing. Not at all.

Although RF (dielectric) heating achieves better penetration than microwave heating, frozen foods Similar drawbacks include uncontrolled heating of the thawed portion of the

Sonic assisted heat thawing Another method, which has been variously proposed and investigated, uses sonic or ultrasonic vibrations. The material to be thawed is immersed in water into which sonic energy is applied. low audible A variety of frequencies have been proposed, ranging from frequencies up to typical ultra-audio frequencies.

In this technique, sonic energy assists in the thermal thawing process; We will call this wave-assisted thermal thawing. One source of heat for thawing is the water in which the material is soaked. The sonic energy facilitates the transfer of heat into the material being thawed.

The intensity of the sound wave energy itself is generally a small fraction of the total energy required for thawing. be.

Sonic energy significantly improves heat transfer in thawed materials. Irradiation of sound waves The mechanisms that facilitate the transfer of heat into the material undergoing thawing differ. explanations have been given, and different explanations may be valid to varying degrees and/or under different circumstances. Maybe it's true.

In this way, microagitation and/or fluidization Alternatively, convection may increase the rate of heat transfer. Ultrasonic vibrations on the surface of frozen foods and the thawed liquid portion of the layer directly in contact with the wick in its frozen state. agitation to increase the heat transfer properties and thereby thaw the entire frozen product. It is also possible to shorten. The density change during thawing is a movement of liquid mass. , this movement is the flow of liquid toward the solid region of the frozen food, and the associated It is the transport of heat. Therefore, the decompression speed is affected by the movement speed and the decompression speed is affected by the movement speed. The thickness of the phase change region between the minute and the part in the frozen state is is increased to speed up the decompression rate.

Also, different studies have reported different results. One investigation (1959) A, L published in January-December Food Technology Volume 13, pages 109 to 112.

(by A. L. Brody et al.), such techniques do not work. It is concluded. More specifically, if the surface of the material being thawed is It was found that it was heated to a certain degree. However, the pond has excessive addition of surface area. Report or suggest good results with significantly increased thawing speed without heat Ru. The effectiveness of this technique is due to the temperature of the water surrounding the material being thawed. It depends on various factors, such as the nature and the exact nature of the sonic irradiation.

Although sound-assisted thermal thawing techniques reduce thawing time, they also have various drawbacks. With this technology should use lukewarm or boiling water as the main heat source, and the thawing speed should be It is necessary to avoid heating the surface area of the food to a temperature that would cause the surface area to change. limited by necessity. Furthermore, the thawed food may contain at least its outer parts. Let the warm, thawed food sit for quite some time before anything in it is accidentally cooked. -Rosenberg et al., U.S. Pat. No. 3,846,565 When preparing meals, use frozen foods, especially pre-cooked and packaged meals. A heated medium such as water or oil is used to reheat the product. Reheating is , assisted by sonic or ultrasonic vibration wave energy. 20.40.50.7 2.250 and 570 kilohertz (kHz) frequencies particularly reduce reheating time. It is mentioned that frequencies above 100 kilohertz are suitable. It has been removed. However, the purpose of the Rosenberg patent is to In addition to defrosting, you can also create foods that are heated to approximately 750°C (180°F). It is about getting out.

No. 4,464,401 to Kissam, 177 hertz (H Frequencies from z) to 10,000 Hz are disclosed, but this It is intended to provide only a small portion of the low-frequency and low-power sound effects ( acoust 1cs) seems to stimulate heat transfer rather than adding energy. is mentioned. Food Science Journal Vol. 47 (1981), pp. 71-7 The article contributed by Kissam et al. on page 5 is related to this technology. be.

Various Japanese literature describes the use of air bubbles to generate ultrasonic waves in the water surrounding thawing food. cavitation resulting from the rupture of (Japanese Patent No. 62-245143 and Japanese Patent No. 63-1) No. 57123).

All of the above can quickly and easily remove large chunks of frozen food without raising the temperature excessively. It does not solve the problem of efficient defrosting.

The present invention - principle overview Under the right conditions, directed ultrasonic vibrations on partially thawed frozen food can defrost it. zone between the frozen part and the substantially frozen part (the thawing zone) It was found that it was suitably absorbed by The present invention is based on this discovery. and in its embodiment, the present invention essentially comprises ultrasonic waves under suitable conditions. In a method of defrosting frozen food that directs energy to the frozen food to defrost it, The ultrasonic energy that performs the A method for thawing frozen food in which thawing is achieved by absorption of energy in one zone Consists of. Substantially less of the ultrasound energy reaches the zone where thawing is taking place. All of the frozen food is absorbed and a small portion penetrates the zone and remains in the frozen state of the frozen food. It turns out that it reaches the minute.

As mentioned above, there is a phase change in the water content of frozen foods from ice to liquid water. ange) occurs gradually over a temperature range. Therefore, during thawing, the ideal Rather than a mound surface, a zone of thawing occurs. The effect of thawing is on this zone. depends on the degree of absorption. This we will call the thawing/freezing interface. The front (fully thawed) edge of the zone is where fully thawed (ice-free) food and The trailing edge is defined as the boundary between the food and the food, which naturally contains a significant portion of ice. Generally still liquid and freezable, although not more precisely defined This can be understood as an area where the amount of water has decreased. Absorption of ultrasound energy is It was found that it is actually greatest at the thawing/freezing interface region.

The energy penetrating the thawing zone is, of course, attenuated in the frozen part. to warm up the frozen part and thus perform thawing in the thawing zone. The amount of heat ultimately required is reduced. , however, this effect is due to two It will be small for a reason. One is an ultrasonic wave that reaches the thawing zone. Almost all of the energy is absorbed in the zone and still passes through the zone. It was found that the amount of food that reaches the frozen state is small, which is another reason. The reason is that ultrasonic energy is absorbed by frozen food beyond the thawing zone. This is because the energy absorption is small (albeit greater than the absorption in the thawed region). Ru.

It turns out that there are two main factors that influence the conditions under which this technique is effective. .

The first condition is that the ultrasound energy must be sufficiently coupled to the food being thawed. That means no. For this purpose, a liquid couplant such as water is used. nt) is generally required between the ultrasonic transducer and the food being thawed. Ru. Place frozen food in a thin plastic bag for thawing, so that the liquid in the food is submerged in water. It is desirable to prevent water from being lost to water or from penetrating into the food. This is Once this is done, all you have to do is be careful not to create any air bubbles or voids inside the bag.

This should be done at least before starting thawing, and if possible, also during thawing. This can be achieved by exhausting the air. This way, you can match the bag to the food first. If you continue to vent, even if the shape of the food changes or the voids are destroyed, Furthermore, even if the gases released by defrosting are removed, the conformity of the bag to the food may be poor. The current state will be maintained. To reduce voids in food, in addition to increasing ambient pressure, Compressing the food before and during thawing will only increase the ambient pressure. That might be enough.

Furthermore, the coupling loss is kept moderate compared to the energy transferred into the frozen food. There must be. By using a certain combination of frequency and power density, frozen food can be The energy absorption in the surface area of the product is very high and therefore the frequency/power density It turned out that those areas of the plane had to be excluded. This effect is cavitation, and the term "cavitation" is used to refer to this effect. We will use the word "n".

More specifically, the upper frequency limit at which this effect becomes noticeable is (under easy conditions ) 430 kHz, depending on factors such as power level. This week The wavenumbers were found to be fairly well defined.

This condition is distinct from the sonic assisted defrosting technique discussed above.

Proposals to use this technology include Frequencies in the lower part of the ultrasound range (e.g., up to 100 kilohertz) are generally used. These frequencies all correspond to the frequencies just mentioned for the technology of the present invention. Significantly lower than the wavenumber lower limit.

The second condition is that thawing is effective due to attenuation of ultrasonic energy by thawed food. The depth of implementation is limited. Ultrasonic absorption by thawed food Yield is greatest at the surface of the food, but reaches zones within the food where thawing is progressing. and must be moderate in relation to the amount of energy absorbed in the zone. do not have. This attenuation is frequency dependent; as the frequency increases, It was found that this attenuation also increases.

More specifically, it turns out that the critical frequency is not clearly defined, but the frequency By raising the temperature to about 740 kilohertz, the depth at which decompression occurs effectively depends on the actual depth of use. It seems like it would be too small to be of any use.

A clear tuning in the prior art that includes frequencies above the limit set by the first condition. There has only been one investigation so far. The frequencies included in this survey were 1 MHz. (MHz), which means that the frequency exceeds the limit set by the second condition. number, and the reported results did not result in effective decompression.

As mentioned above, there are two main factors that influence the conditions under which the technology of the present invention is effective. It has been found that there are two types, cavitation and attenuation. The key to both of these Therefore, what limits the effectiveness of the method of the present invention is that the surface area of the frozen food is This means that a large amount of energy is absorbed.

If we first consider the absorption coefficient factor, absorption will of course occur throughout the thawed region, The energy reaching the thawing zone is a geometric progression with increasing depth. However, the absorption is reduced to the surface area of the frozen food where the energy density is greatest. The maximum value is Absorption at the surface area of frozen food reaches the thawing zone. If the temperature of the surface area of the frozen food is too high relative to the energy reached, become impossibly high.

This effect can be reduced by cooling the surface area of the frozen food, thus Cooling can be achieved by circulating a liquid that couples an ultrasonic transducer to the frozen food. be. If the liquid is water or salt water, heat the surface of the frozen food to near 06C. It is possible to cool down to (The surface of frozen food must be cooled to the point where it freezes. should not be done. ) This effect is due to the ultrasonic wave as the thawing zone moves further through the frozen food. Further reduction is possible by reducing the input of j. This allows the surface By cooling it, it becomes possible to remove much of the heat generated near the surface, but The thawing speed will of course be reduced.

Next, when considering cavitation factors, standard cavitation countermeasures are It is possible to use. Therefore, the ultrasound energy is pulsed. output is fixed Normally, the cavitation effect increases roughly geometrically, and the cavitation effect increases due to pulsations. Vitation effects disappear during off periods, thus increasing the average output level becomes possible. Additionally, the static ambient pressure of the device is increased to reduce cavitation. It is also possible to reduce it.

Using a pulsating output is relatively simple and involves only the device's electronics. However, the permissible range of increase in output is limited. static pressure increases The use of However, it is not subject to any natural restrictions. In fact, peak low pressure is the absolute Assuming that cavitation occurs when becomes negative, the maximum allowable amplitude is The maximum allowable strength will be proportional to the square of the static ambient pressure.

Cavitation limitations impose two limitations on the thawing method of the present invention.

That is, an upper limit is imposed on the power density of the ultrasonic wave, and a lower limit is imposed on the frequency. This way Increase power density by using pulsating power and/or increased static pressure and/or reduce the frequency.

The intensity of ultrasonic energy is limited by the need to eliminate surface heating. Ru. Continuously exceeding 500 kHz with a power density of approximately 5 kilowatts (kW) at atmospheric pressure Although sound waves were output, no evidence of cavitation was observed. This is large Defrosting speed of approximately 1 millimeter (mm) per minute (as thawing progresses through frozen food) (measured as the speed at which a zone moves forward). much faster than this speed If a higher speed is desired, it is assumed that cavitation countermeasures will need to be taken. Ru.

Is the frequency of the ultrasonic energy also necessary to eliminate cavitation? If the power is constant, such cavitation will be limited to a certain amount Occurs below the frequency of As mentioned above (the lower the frequency, the more effective the decompression is) The depth of the results will increase. If the start of cavitation is delayed, The thickness of frozen foods that can reduce the wave number and therefore effectively defrost increases. This reduces the phenomenon of the present invention (in the zone where thawing is progressing). preferential absorption) is much lower (perhaps by two orders of magnitude) than the frequency limits mentioned above. frequency. (One practical factor that limits the range of frequency reduction is , the frequency must be maintained above the audible limit, and the Since the output level is high, it is difficult to believe that sufficient sound insulation is possible. ) unzip monitoring the progress of Impingement imparted to ultrasonic energy by frozen food that is being thawed Dancing and transmitting ultrasonic energy through frozen foods and/or frozen foods Reflections from within are determined by the degree of thawing progress and therefore monitor the thawing progress. It can be used to For this purpose, it is desirable to temporarily turn off the main ultrasonic output. I don't know. Monitor the progress of the defrost at regular intervals and check the specific It may be desirable to establish parametric variables for the block and At the same time, it is possible to determine the completion of decompression.

Brief description of the drawing Another aspect and feature of the invention is a description of a commercially available thawing device that utilizes the invention. It will be clear from the following description, including and with reference to the accompanying drawings, that the attached In the drawing, FIG. 1 is a simplified perspective view of such a device, and FIG. IA is the transducer assembly of FIG. The details of the body are shown in Figures 2 to 6 for different values of the frequency of ultrasound energy. 1 is a graph showing the effect of the method of the present invention, and FIG. 7 shows the method of the present invention for various values of pressure and frequency of ultrasound energy. This is a graph showing the effect.

Example Thawing can be done by batch or continuous flow methods (a batch or continuous flow method). (nuous flow process). Batch method The zone size of the ultrasonic energy matches the size of the block being decompressed. be given Continuous flow methods include zones for frozen foods to be thawed, e.g. Food is transported by placing it on a belt conveyor, and the width of the zone is The length of the zone is selected to match the width of the frozen food block and the direction of movement ) is selected according to the desired decompression speed.

For continuous flow methods, conditions are usually held constant. The batch method requires Therefore, changing the conditions (e.g. to prevent excessive heating of the block surface) Reduce the sound output or the depth from the surface of the developing zone of thaw. may be desirable.

The apparatus shown in Figure 1 mainly dissolves frozen foods that have been made into blocks of approximately predetermined size. It is intended for freezing and has a typical surface area of 150 mm ( mm) width 150 millimeters (mm) to length 400 millimeters (mm) width 40 0 millimeters (mm), with a typical thickness of 50 millimeters (m m) to 150 millimeters (mm). Frozen foods to be thawed should be It is typically meat or fish with little or no ice.

The device is primarily designed for commercial use, employs a continuous flow method, and uses ultrasonic Wave energy is coupled into the block from both sides by water as couplant.

The device comprises a water tank 10, which comprises a drive and guide wheel and a rotor. A corrugated conveyor belt 11 is driven and guided by a roller 12 and passes through the water tank. have. A pair of transducer assemblies 13 and 1 energized by drive E16 A block 15 of frozen food 4 placed on a conveyor is connected to two such converters. are arranged opposite to each other as shown so as to pass through a zone between them. \ru. Power for the drive 16 is supplied at 19. Frozen food professional is placed on a conveyor on the right side of the device, thawed and comes out on the left side, where it is taken out. The conveyor transports the frozen blocks when they are immersed in water. It includes means such as a clip (not shown) for retaining the lock. the above two The transducer directs ultrasonic energy to opposite sides of the block, effectively decompressing it (or, if the blocks are relatively thin, thaw them) ).

Each of the transducer assemblies 13 and 14 is shown in FIG. It consists of an array of individual ultrasound transducers arranged as shown. illustrated As such, the assembly includes fourteen transducers 17. strength at both ends of the transducer assembly. The transducer density is increased at both ends to minimize losses. . (Alternatively, the middle transducer may be energized lower than the transducers at either end.) One of the limitations regarding the output power of the This is a requirement that they must not be allowed to do so. This is the output strength per unit area. ), so in order to obtain the maximum output, the surface of the converter 2° must be made large. must be closely spaced and closely spaced from each other. Further increase the output of the device Of course, it is also possible to increase the number of rows of converters in order to transducers side by side or staggered (i.e. square or hexagonal) lattice). To increase the cavitation threshold In addition, it is possible to increase the pressure at least in the space between the transducers. Maximize thawing time Of course, it is possible to reduce the strength of the exit if there is no need to minimize it. . It scans or rocks the beam back and forth across the food to thaw the transducer. using a transducer (or transducer assembly) that generates This can be achieved by adopting a method that is deemed most suitable.

If the thawing progress is to be monitored ultrasonically, the transducer assembly may be attached for this purpose. It is possible to periodically stop the program. One of the transducers is used as a monitoring transmitter and another as a monitoring transmitter. It is also possible to use the device as a receiver or separate it for monitoring purposes. It is also possible to provide several transducers.

It is also possible to use the pond influence device to implement the principles of the invention. .

A second decompressor for rectangular blocks includes a pair of plate-like transducer assemblies. , the pair of converter assemblies are similar to the converter assemblies of the apparatus of FIG. The size is matched to the blocks to be decompressed, and the blocks are close together. It is attached so that it can make contact with the top and bottom surfaces of the rack. This allows direct contact Batch methods can be used. However, the air cavity It is desirable to immerse the transducer assembly in a water bath to prevent That's true.

The third thawing device acts as a water tank and contains a sea of ultrasonic energy in the tank. sea) consisting of a vessel fitted with a convenient number of transducers to produce J. this device By simply holding an irregularly shaped block immersed in it, the surrounding ultrasonic energy It is suitable for exposure to ghee and is like an ultrasonic washing bath. ultrasonic energy are sized, shaped, or positioned so that microwaves are absorbed in the microwave. Understand that water-containing parts of frozen foods absorb water with reasonable efficiency, no matter where they are placed. It will be. However, if a microphone is used, such as using a stirrer, It is also desirable to employ radio frequency distribution techniques.

The devices of the second and third forms are pressurized to reduce the occurrence of cavitation. It is possible to conveniently configure it so that it can be used.

The third type of device is suitable for both commercial and domestic use. For home use Generally speaking, the power level provided by a normal domestic electricity supply, i.e. 3 kilowatts, is It is convenient to use a level that does not significantly exceed kW.

The cavitation limit can be increased, for example by increasing the static ambient pressure of the thawing device. This makes it possible to significantly shorten the thawing time. over temperature at elevated pressure heating is often low, but normal precautions to prevent overheating may be taken. need to pay. Other methods of increasing cavitation limits, e.g. transducers It is possible to apply a method such as making the energization pulsating.

The exact relationship between increased pressure, frequency, efficiency and thawing time remains to be seen. That's not to say. However, the pressure is 300 kilopascals (kPa) and 60 When raised to 0 kilopascals (kPa), both pressures thaw 5 times and 10 times. If the time is shortened, that is, the pressure is increased, the thawing time will be shortened. Increase the pressure once The variation of the thawing time corresponding to the frequency in the dredging is that the frequency is 520 kilohertz (k[ If the pressure is lowered to the range of stomach. Efficiency increases pressure to approximately 600 kilopascals (kPa) and increases pressure to approximately 300 kg It seems to increase as the temperature decreases to Pascal (kPa), but this aspect was measured. It's not easy to do.

The power used to thaw a small sample of frozen meat is approximately 1 watt/sq. Meter (wat t/cm. Approximately 1 watt/square centimeter ( Values exceeding watt/cm are associated with low frequencies (approximately 300 kilohertz) and high pressures (approximately 300 kilohertz). It is believed that it can be used for up to 600 kilopas. at normal ambient pressure has an output of approximately 0.51 watts/cm2 without the risk of overheating. (It is thought that it will not exceed watt/cm.

2 to 6 are graphs illustrating some of the conditions under which the present invention is effective.

These graphs show the behavior of continuous ultrasound signals at atmospheric pressure.

Figure 2 shows the attenuation A of ultrasound energy in meat plotted against temperature t. (This graph was published in Volume 1, 1978, D4:3 to D4:6) Delivered at the 24th Meat Research Workers Convention in Kulmbach. C, A, Mi Ies and a (D, 5h ``Change of ultrasonic attenuation in meat during freezing'' conducted by sin the attenuation of ultrasound in It is based on Meat During Freezing) J. ) unzip It can be seen that the attenuation is small in the cooked meat and is almost independent of temperature. meat is frozen At the point where it begins (1 degree below 0°C), the attenuation rises rapidly to a peak.

As the temperature decreases further, the attenuation drops from its peak until the meat is almost completely cooled. By the time the meat is frozen, the attenuation is small (approximately twice the attenuation of thawed meat) and temperature effects are reduced. The fruits are also small.

This graph is valid for low energy levels. The absolute value of attenuation depends on the nature of the food. e.g., the fibers are aligned parallel to the direction of propagation of the ultrasound energy. The attenuation in a muscle is approximately 2 times that in a muscle where the fibers are aligned perpendicular to the direction of propagation. It's double. The absolute value is also roughly proportional to frequency.

Figure 3 shows that a block of frozen food plotted against frequency f has a given surface temperature. A graph showing the depth X to which thawing occurs before reaching the limit (e.g. 20°C) It is. It is assumed that a uniform ultrasound field is incident perpendicularly to the block.

FIG. 4 shows a graph showing the temperature t of the block plotted against the depth X into the block. It's rough. The thaw/freeze interface is at point 23. The area 24 to the left of this point is The degree is highest at the surface (x=0) and drops to just below 060 at the interface. It shows. The temperature then drops sharply just beyond this interface (point 25) and the temperature drops to the initial freezing temperature (point 26).

Figure 5 shows a graph showing the attenuation of the block plotted against the depth X into the block. It is f. This horizontally compresses the left (hot) part of the curve in Figure 2 and compresses the right (low temperature) part of the curve in Figure 2 horizontally. ) can be obtained by enlarging the part. Similarity between the curves in Figure 2 and the curves in Figure 5 The similarity is that both the left and right parts of the curve in Figure 2 are almost horizontal, so the above This is because its shape does not change even when it is expanded or compressed.

As the depth of the zone of progressive thawing increases, the ultrasonic energy increases accordingly. The total attenuation experienced when reaching such a zone increases, and the energy reaching such a zone increases. energy amount will decrease. Therefore, the rate at which such zones advance is uniformly reduced.

Energy absorption near the surface of the meat is constant and therefore thawing is progressing. The surface becomes uniformly hotter as the zone progresses deeper into the block. block The internal temperature drops from the surface towards the thawing zone, but this One reason is that some time has elapsed since thawing was completed in the area near the surface. Because it has been in a state where it has to absorb energy for a long time compared to the other parts. In addition, one reason is that the strength of the energy becomes deeper due to attenuation in the thawed region. This is because it uniformly decreases as the temperature increases.

Portion 24 of the graph in FIG. This means that the energy absorption is lower than that in the zone where thawing is progressing. However, the temperature rises considerably toward the surface of the food that is being thawed. It shows. This is because the specific heat of thawed food (roughly the specific heat of water) Because it is small compared to the latent heat required for thawing ice to water in the advancing zone of It is.

For example, when the surface of the frozen food passes water at or near 0°C over the surface. If the temperature/distance curve is cooled by Branches 24 branch downward toward the surface of the frozen food. Therefore, such cooling is By lowering the peak temperature obtained in frozen foods, it is possible to cool them at a predetermined limit peak temperature. Allows frozen food to be thawed further inside.

As mentioned above, almost all the ultrasonic energy that reaches the interface is absorbed by the interface. is converted into heat. Some of this energy is absorbed by the melting of the ice (latent heat) at the interface. ), and some are used in the developing zone of thaw on the cold side of the interface. into the zone, where it melts the moist portion of the zone and warms the zone. Used to bring the zone to a fully thawed state.

Returning to FIG. 3, line 20 indicates that the fibers are parallel to the direction of propagation of the ultrasound energy, i.e. , for muscles aligned perpendicular to the surface of the block. This line is unzipped The depth is shown to decrease as the frequency increases. With increasing frequency This downward slope of line 20 is due to the ultrasonic wave in the decompressed confession with increasing frequency. This is because the rate of energy decay is increasing. Depth X is approximately 740 km in frequency. The frequency drops below a practical value at Rohrtz (kHz).

Line 21 is for a muscle whose fibers are aligned "vertically". This line becomes line 20 Although similar, it is located higher than line 20. The attenuation in this alignment is called “parallel ” is lower than the attenuation of the alignment, so the depth of decompression is larger.

Line 22 shows an abrupt cutoff that occurs at normal ambient pressure. It occurs between 430 kilohertz (kHz) and 460 kilohertz (kHz). this Very high surface heating occurs at frequencies and pressures. Effective at normal ambient pressure To cause proper decompression, the frequency must be increased above this point.

FIG. 6 is a graph showing the decompression efficiency E plotted against frequency, where the efficiency is Absorption of ultrasound energy in the zone of progressive thawing and total ultrasound energy It is defined as the ratio of absorption to absorption. Two lines are shown, line 30 is in a “vertical” orientation. Line 31 represents a "parallel" arrangement. The two lines are the critical low frequency share a common cutoff line 32. The position of this line is It depends on the strength of Lugie, and if the strength is low, it will move slightly to the right. This is The point at which cavitation occurs depends not only on frequency but also on strength. It is.

Figure 7 shows a 30 millimeter (mm) diameter cold cut perpendicular to the muscle fibers. Figure 2 shows the thawing of a half-I11''M muscle tissue sample of frozen beef.Sample length was 75 millimeters (mm). The thermocouple is placed at various depths into the sample under test. It was inserted in d). Various converters are used to convert radio frequency power amplifiers to Forced. Measurements of the power supplied were made. The sample is placed in an insulated block. was held and the transducer was pressed against the sample. The sample in the block is enclosed in a pressure vessel. It was covered and the pressure could be increased if necessary. Increase in pressure is pressure This was achieved by pressurizing the air inside the container.

Each thermocouple is at 11°C (considered the zone position where thawing is progressing). The time (T), expressed in hours, is applied to various frequencies and ambient pressures. shown on the graph. The curve marked Th is stationary in the decompressed region. The conductivity of heat conduction is K, and the depth from the surface at a temperature Δθ higher than the initial frozen fish is d. This represents the theoretical behavior assuming that. ΔH is at jK/kg It is the enthalpy of frozen meat with respect to the enthalpy of specific gravity ρ in OoC.

If ■ is the time it takes for the thawed zone to reach the depth d, then T=ΔHρd2 Δθ to /2 , which gives the curve Th.

The group of curves marked 0 kPa indicates that the power level is at a level that prevents sample overheating. Represents the actual time of four different frequencies at ambient pressure when the bell is held It is something that Mark the points on the 300 kilohertz (kHz) curve with a circle. , a square for the 350 kilohertz (kHz) curve, and a square for the 415 kilohertz (kHz) curve. ) curve is marked with a triangle, and the 520 kilohertz (kHz) curve is marked with a diamond. .

The family of curves marked 300/600 kilopascals (kPa) corresponds to the high pressures mentioned above. This represents the actual time of the above frequencies.

These results demonstrate that commercially available frozen beef professional fibers with a thickness of 150 millimeters (mm) This shows that when Tsuku applied ultrasonic waves to both sides, it took about 45 minutes to thaw the food. Out The force level is lower than the cavity at the lower frequency required to achieve this decompression rate. If high pressure is used to form a formation, excessive heating should be avoided. This is considered to be low enough to eliminate the Typical maximum temperature is around 7°C Ru. When using high pressures of several hundred kilopascals, typically 300 to 600 A suitable frequency is approximately 300 kilohertz (kHz) to 350 kilohertz (kHz). ). Even if the frequency is less than 300 kilohertz (kHz), High pressure of about 100 kilopascals (kPa), i.e. about 1 atmosphere higher than ambient pressure The cavitation limit is effectively increased at lower pressures. Part of the electricity supplied is Some refrigeration is not required to thaw the meat and therefore remove wasted heat. need to be rejected.

The important point is that when increasing the pressure above ambient pressure, it is better to use a lower frequency. was found to be effective, but harmful cavitation occurs at normal ambient pressures. This means that it is easy to cause

,,,, PCT/Gll 9210203G International Search Report

Claims (20)

[Claims] 1. (a) The ultrasonic energy applied to the frozen food is and (b) within the thawed food. decompressed, provided that the frequency is low enough not to be unduly attenuated. the zone between the part and the substantially frozen part, i.e. where thawing is progressing. The decompression occurs primarily from the absorption of the ultrasonic energy in the zone. A method for thawing frozen foods characterized by the generation of energy. 2. A further condition is to increase the cavitation threshold. A method according to claim 1, characterized in that: 3. Claim characterized in that the frequency is less than 740 kilohertz (kHz). The method described in Section 1. 4. A claim characterized in that the frequency is 430 kilohertz (kHz) or more. The method described in Section 3. 5. further characterized in that the ultrasonic energy is pulsated. 2. The method according to claim 1. 6. Claim 1 characterized in that the defrosting is carried out at static pressure elevated above ambient pressure. The method described in. 7. The static pressure is increased to 600 kilopascals (kPa), which is higher than atmospheric pressure. 7. The method according to claim 6, characterized in that: 8. The static pressure is increased to at least 300 kilopascals (kPa) above atmospheric pressure. 8. The method according to claim 7, characterized in that: 9. characterized in that when said increased pressure is applied said frequency is reduced; 7. The method according to claim 6, wherein: 10. Defrosts food by detecting when ultrasonic energy has completely passed through the frozen food. According to any of the preceding claims, characterized in that it comprises means for determining completion. How to put it on. 11. characterized in that the frozen food is directly exposed to a beam of ultrasonic energy. A method according to any of the preceding claims. 12. The frozen food is exposed to a beam of ultrasonic energy directed in two opposite directions. The method according to any one of claims 1 to 10, characterized in that it applies to a system. Law. 13. Particularly characterized in that the frozen food product is subjected to almost any amount of ultrasonic energy. 11. The method according to any one of claims 1 to 10. 14. said at least one said ultrasonic energy source by direct contact with said ultrasonic energy source; Claims 11 and 10, wherein ultrasonic energy is supplied to the frozen food product. 13. A method according to any of claims 12. 15. the frozen food is traversed through at least one of the ultrasonic energy beams; According to any one of claims 11 and 12, the apparatus is moved in a cross-sectional direction. How to put it on. 16. characterized in that the ultrasonic energy is coupled to the frozen food by an aqueous liquid; 14. The method according to any one of claims 11 to 13, wherein the method comprises: 17. The frozen food is housed in a jacket with a matching shape. A method for thawing a frozen food according to any one of claims 1 to 16. 18. said jacket is configured to be at least initially evacuated; 18. The method according to claim 17, characterized in that: 19. 18. The method of claim 17, wherein evacuation of the jacket is continuous during thawing. How to put it on. 20. Thawing a frozen food by the method according to any one of claims 1 to 19 equipment.