Food thawing method based on medium and low frequency oscillating current

Abstract

The present invention discloses a food thawing method based on medium and low frequency oscillating current. The food thawing method includes: applying at least one oscillating current to the frozen food, and the current density of each of the oscillating currents is 0.1 - 200 mA / cm 2 , the frequency of the oscillating current is 200 Hz - 20 kHz, the duty cycle is 1 - 99%, the current density is the effective value, the heat generated by the oscillating current in the frozen food is the same as or slightly greater than the energy required for the ice crystals in the frozen food to be converted into liquid water, so that the frozen food is thawed, and the thawing end temperature of the internal area of the frozen food does not exceed 5°C. The present invention can prevent the phenomenon of excessive energy aggregation in a short time and local overheating on the surface, and the juice loss of the frozen food is less; therefore, the temperature difference in the area of the internal cross-section of the frozen food at the thawing end is smaller, making the quality of the thawed food higher.

Description

Technical Field

[0001] The present invention particularly relates to a food thawing method based on medium and low frequency oscillating current, belonging to the technical field of food thawing. Background Art

[0002] With the development of the national economy and the continuous advancement of industrialization and urbanization, people's demand for food is increasing day by day. Frozen foods have gradually become necessities in people's daily lives due to their convenience and long-term preservation characteristics. The freezing technology only extends the shelf life of food through low temperature, and for perishable, seasonal or regionally specific ingredients, frozen storage can break through the limitations of time and space. However, frozen foods need to be thawed before processing. If the thawing rate is slow, the time is long, and the thawing uniformity is poor, it will affect the sensory quality and food safety of the food.

[0003] Currently, common thawing methods include natural thawing and immersion thawing. These methods do not require special devices or equipment, but they take relatively long time. Therefore, the food surface is easily affected by the external environment, the risk of microbial growth increases, the loss of nutrients is serious, the sensory quality decreases, and ultimately the quality of the thawed food is affected. In recent years, emerging thawing technologies, such as microwave and radio frequency thawing, use high-frequency oscillating electromagnetic waves to act on water molecules, polar biological macromolecules and free ions in the food ingredients, realizing the oscillating friction and heating of internal molecules, and the thawing speed is fast. For foods with irregular shapes, due to the change of penetration depth with frequency, it is extremely easy to cause problems such as uneven thawing, local overheating, surface water evaporation, increased internal and external temperature difference, protein denaturation or degradation.

[0004] In order to maximize the energy utilization rate, a specific medium and low frequency oscillating current can act on the ice crystals inside the food, and this energy is equal to or slightly greater than the energy consumption required for the ablation of ice crystals in frozen foods, thereby realizing the efficient thawing of foods. At the same time, the thawing effect of the oscillating current is closely related to the applied current density and the effective contact area. The greater the current density, the higher the penetration depth. However, when the food has an irregular shape, the parts with smaller thickness at the corners will also cause local overheating due to the continuous application of a relatively large current density. Therefore, an intermittent or staged current density application program needs to be adopted to relieve the instantaneous local overheating phenomenon. At the same time, in order to be applied to household appliances, it must be in a compact and simple form for easy operation by users.

[0005] Currently, among household appliances with thawing functions on the market, there are only microwave ovens, electric ovens, aluminum plate thawers, and radio frequency thawing boxes, and they all exist in the form of single products, thawing respectively by using the principles of microwaves, high temperature, heat conduction, and radio frequency electromagnetic waves. The prices of microwave ovens and radio frequency thawing boxes are relatively high, and due to the use of high-frequency generators and the process being accompanied by the heating of water molecules and biological macromolecules, the device isolation cost is also high, so they cannot be commercially applied in household refrigerators. The radiant heating form of electric ovens is also not suitable for being fixed on refrigerators, and the thawing efficiency of aluminum plate thawing relying on heat transfer properties is low and the practicability is poor. Summary of the Invention

[0006] The main object of the present invention is to provide a food thawing method based on medium and low frequency oscillating current, so as to overcome the deficiencies in the prior art.

[0007] To achieve the foregoing invention object, the technical solutions adopted by the present invention include:

[0008] The present invention provides a food thawing method based on medium and low frequency oscillating current, including: [[ID=1३]]

[0009] Applying at least one oscillating current to the frozen food, the current density of each said oscillating current being 0.1 - 200 mA / cm 2 , the frequency of the oscillating current being 200 Hz - 20 kHz, the duty cycle being 1 - 99%, the current density being the effective value, the heat generated by the oscillating current in the frozen food being the same as or slightly greater than the energy required for the ice crystals in the frozen food to be converted into liquid water, so that the frozen food is thawed, and the thawing end point temperature of the internal area of the frozen food not exceeding 5°C.

[0010] Compared with the prior art, the advantages of the present invention include:

[0011] The food thawing method based on medium and low frequency oscillating current provided by the present invention applies a specific oscillating current to each part of the frozen food periodically and / or in stages. Under the scanning processing flow, different parts of the frozen food can intermittently receive energy, that is, a "marquee" - type rapid application, which helps the uniform ablation of ice crystals inside the frozen food; and, the present invention can further prevent the phenomenon of excessive short - time aggregated energy and local overheating on the surface, with less juice loss from the frozen food; therefore, the temperature difference in the area of the internal cross - section of the frozen food at the thawing end point is smaller, making the quality of the thawed food higher.

[0012] The food thawing method based on medium and low frequency oscillating current provided by the present invention is a non - thermal thawing technology that uses micro - currents applied in multiple parts for thawing, and the energy applied by the micro - current to irregular food materials reaches the balance point of the energy to destroy ice crystals, enabling uniform non - thermal thawing and can be popularized to the civilian and industrial ends. Detailed implementation mode

[0013] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solution of the present invention through long-term research and a large number of practices. The following will further explain the technical solution, its implementation process, principle, etc.

[0014] Glossary in the present invention:

[0015] Frozen food: Food frozen at a temperature below -4°C.

[0016] Non-thermal thawing: Thawing food by raising its temperature without relying on heat conduction such as immersion or blowing, that is, thawing the interior of the food without an external heat source.

[0017] The present invention provides a food thawing method based on medium and low frequency oscillating current, including:

[0018] Applying at least one oscillating current to the frozen food, the current density of each said oscillating current being 0.1 - 200 mA / cm 2 , the frequency of the oscillating current being 200 Hz - 20 kHz, the duty cycle being 1 - 99%, the current density being the effective value, the heat generated by the oscillating current in the frozen food being the same as or slightly greater than the energy required for the ice crystals in the frozen food to be converted into liquid water, so that the frozen food is thawed, and the thawing end temperature of the internal area of the frozen food not exceeding 5°C.

[0019] Furthermore, the food thawing method specifically includes: periodically applying the oscillating current to the frozen food.

[0020] Furthermore, the duration of each cycle is within 10 minutes.

[0021] Furthermore, the duration of each cycle is 0 - 10 minutes.

[0022] Furthermore, the food thawing method specifically includes: within each cycle, applying b said oscillating currents to a parts of the frozen food, each part corresponding to at least one of the oscillating currents, and making the current density of the oscillating current applied to each part positively correlated with the thickness of each part, b ≥ a ≥ 1, and a and b are both integers.

[0023] Furthermore, the thickness of the frozen food is within 15 cm.

[0024] Further, the thickness of the selected part of the frozen food is 0.8 - 15 cm, and when the thickness of the selected part is 0.5 - 8 cm, the current density of each of the oscillating currents applied to the selected part is 0.1 - 80 mA / cm 2 ; when the thickness of the selected part is 8 - 15 cm, the current density of each of the oscillating currents applied to the selected part is 80 - 200 mA / cm 2 .

[0025] Further, the current frequencies of the b oscillating currents are the same.

[0026] Further, the method for thawing food specifically includes: within each cycle, simultaneously applying the b oscillating currents to a parts of the frozen food, or sequentially applying the b oscillating currents to a parts of the frozen food, and within the same time period, applying the d oscillating currents to c parts of the frozen food, where c ≤ a, d ≤ b, and c and d are both positive integers.

[0027] Further, the method for thawing food specifically includes: making the current density and / or duty cycle of the oscillating current applied to each part of the frozen food change in a gradient manner with the increase of time.

[0028] Further, the change gradient of the current density of the oscillating current applied to each part of the frozen food is 0.1 - 100 mA / cm 2 / min.

[0029] Further, the change gradient of the duty cycle of the oscillating current applied to each part of the frozen food is 5 - 40% / min.

[0030] Further, the current waveform of the oscillating current is a square wave or a sawtooth wave.

[0031] Further, the duty cycle of the oscillating current is 5 - 95%.

[0032] Further, the method for thawing food specifically includes: making two conductor groups electrically connected to the control power supply be in electrical contact with the frozen food, forming at least one closed loop between the two conductor groups and the frozen food, and applying at least one of the oscillating currents to the closed loop by the control power supply, where the two conductor groups are respectively electrically connected to two different terminals of the control power supply.

[0033] Further, each of the conductor groups includes at least one conductor.

[0034] Furthermore, each of the conductor groups includes a plurality of conductors, and a plurality of closed circuits are formed between the two conductor groups and the frozen food. Each part of the frozen food corresponds to at least one of the closed circuits. Moreover, the food thawing method specifically includes applying a plurality of the oscillating currents into the plurality of closed circuits, wherein the plurality of conductors included in the same conductor group are electrically connected to the same terminal of the control power supply.

[0035] Furthermore, the conductor is a flexible body or a rigid body. Exemplarily, the material of the rigid body can be an alloy formed by any one or more of aluminum, iron, stainless steel, titanium steel, and copper, and the flexible body can be aluminum foil, copper foil, conductive silica gel, etc.

[0036] Furthermore, the thawing end temperature of the internal area of the frozen food is -4 - 5°C.

[0037] Furthermore, the frozen food includes frozen aquatic products, frozen meat products, or frozen flour products, and the frozen meat products include frozen livestock products or frozen poultry products, etc.

[0038] Furthermore, the present invention can be implemented in an appliance with a thawing function. The appliance with a thawing function can be a refrigerator, a microwave oven, a thawing box, an electric grill, etc. Specifically, the appliance with a thawing function can be a small household appliance or a large industrial appliance, etc.

[0039] The technical solution, its implementation process, principle, etc. will be further explained below in conjunction with specific implementation cases. However, it should be understood that within the scope of the present invention, the above technical features of the present invention and the technical features specifically described below (in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be elaborated one by one here.

[0040] The thawing device for implementing the food thawing method based on medium and low frequency oscillating current can be arranged in an appliance with a thawing function, or as a part of the appliance with a thawing function. The appliance with a thawing function can be a refrigerator, a microwave oven, a thawing box, an electric grill, etc. Specifically, the appliance with a thawing function can be a small household appliance or a large industrial appliance, etc. The non-thermal thawing device can be arranged in the thawing space (thawing layer) of the appliance with a thawing function. It should be noted that the circuit connection structure, etc. of the non-thermal thawing device and the appliance with a thawing function are known to those skilled in the art and will not be specifically limited here.

[0041] Specifically, the thawing device adopted in the present invention includes two conductor groups and a control power supply. The two conductor groups are arranged opposite to each other with a gap therebetween, and a receiving space for placing frozen food is formed between the two conductor groups. Two terminals of the control power supply are electrically connected to the two conductor groups. Each conductor group includes at least one conductor. For example, each conductor group includes 1 - 12 conductors.

[0042] Specifically, the conductor is a flexible body or a rigid body. Exemplarily, the material of the rigid body can be an alloy formed by any one or more of aluminum, iron, stainless steel, titanium steel, and copper, and the flexible body can be aluminum foil, copper foil, conductive silica gel, etc.

[0043] Specifically, the control power supply includes an AC power supply and a control circuit board. The control circuit board is electrically connected to the AC power supply. The control circuit board is used to regulate the current frequency, current waveform, current density, current intensity of the oscillating current output by the AC power supply, and monitor the thawing state of the frozen food in the closed loop, etc., so as to make the control power supply output the aforementioned oscillating current. It should be noted that the control circuit board can include PLC control, etc. The numerical control program and the like adopted by the control circuit board can all be obtained through commercial purchase, and the circuit structure and the method of modulating the control duty cycle to achieve constant current output in the control power supply are all implemented by the methods or techniques known to those skilled in the art, and no special limitation is made here.

[0044] Embodiment 1

[0045] The thawing device adopted in this embodiment includes a control power supply and two conductors. One of the conductors is an aluminum plate with a thickness of 2 mm, a length of 30 cm, and a width of 20 cm; the other conductor is household aluminum foil paper. The aluminum plate and the aluminum foil paper are respectively electrically connected to the two terminals of the control power supply.

[0046] The method for thawing frozen chicken nuggets includes:

[0047] Place a frozen chicken nugget with a thickness of 13 cm, a mass of 600 g, and a surface temperature of -19 °C on the aluminum plate and cover it with aluminum foil paper. The contact area between the aluminum foil paper and the chicken nugget is 10 cm 2 , and the contact area between the aluminum plate and the chicken nugget is 15 cm 2 ;

[0048] Apply a square-wave oscillating current to the frozen chicken nuggets periodically by the control power supply. The frequency of the oscillating current is 1 kHz, and the duration of each period is 2 min;

[0049] In each period, the duration of the first stage is 30 s. The duty cycle of the oscillating current applied in the first stage is 45%, and the effective value of the current intensity of the oscillating current is 1500 mA. At this time, the current density corresponding to the aluminum plate is 100 mA / cm2 , the current density corresponding to the aluminum foil is 150 mA / cm 2 ; the duration of the second stage is 60 s, the duty cycle of the oscillating current applied in the second stage is 30%, the effective value of the current intensity of the oscillating current is 1000 mA, and at this time the current density corresponding to the aluminum plate is 66.7 mA / cm 2 , the current density corresponding to the aluminum foil is 100 mA / cm 2 ; the duration of the third stage is 30 s, the duty cycle of the oscillating current applied in the third stage is 15%, the effective value of the current intensity of the oscillating current at this time is 500 mA, and at this time the current density corresponding to the aluminum plate is 33.3 mA / cm 2 , the current density corresponding to the aluminum foil is 50 mA / cm 2 ;

[0050] After 5 cycles and 10 min of thawing, the chicken nuggets are divided into 4 pieces. A handheld temperature-measuring thermal imager is used to measure the temperatures of different parts of the chicken nuggets, and it is checked whether there are phenomena of local overheating, incomplete thawing, or local cooking on the surface and cut surface of the chicken nuggets; the results show that in this embodiment, the average temperature of the thawed chicken nuggets is -0.9 °C, the highest point temperature is 1.2 °C, the lowest point temperature is -2.6 °C, the regional temperature difference is 3.8 °C, there is no phenomenon of local overheating or cooking, and the weight loss rate is 4.76%.

[0051] Comparative Example 1

[0052] The method for thawing the chicken nuggets in Comparative Example 1, the morphology, size, etc. of the frozen chicken nuggets are basically the same as those in Example 1, and the same thawing device as that in Example 1 is also used. The differences are as follows:

[0053] In each cycle, the duration of the first stage is 30 s, the duty cycle of the oscillating current applied in the first stage is 99%, the effective value of the current intensity of the oscillating current is 3300 mA, and at this time the current density corresponding to the aluminum plate is 220 mA / cm 2 , the current density corresponding to the aluminum foil is 330 mA / cm 2 ; the duration of the second stage is 60 s, the duty cycle of the oscillating current applied in the second stage is 60%, the effective value of the current intensity of the oscillating current is 2000 mA, and at this time the current density corresponding to the aluminum plate is 186.7 mA / cm 2 , the current density corresponding to the aluminum foil is 280 mA / cm 2 ; the duration of the third stage is 30 s, the duty cycle of the oscillating current applied in the third stage is 21%, the effective value of the current intensity of the oscillating current at this time is 700 mA, and at this time the current density corresponding to the aluminum plate is 46.7 mA / cm 2 , the current density corresponding to the aluminum foil is 70 mA / cm 2 ;

[0054] After cycling for 5 periods and thawing for 10 min, the chicken pieces were cut into 4 pieces. The temperature of different parts of the chicken pieces was measured using a handheld temperature-measuring thermal imager, and whether there was local overheating, incomplete thawing, or local cooking on the surface and cut surface of the chicken pieces was checked. The results showed that in this example, the average temperature of the thawed chicken pieces was 4.7 °C, the highest point temperature was 15 °C, the lowest point temperature was -1.3 °C, the regional temperature difference was 16.3 °C, there was local overheating, and the weight loss rate was 10.83%.

[0055] Example 2

[0056] The thawing device used in this example includes a control power supply and four conductors. One of the conductors is a stainless-steel plate with a thickness of 1 mm, a length of 30 cm, and a width of 25 cm, and the other three conductors are household aluminum foils. The stainless-steel plate and the aluminum foil are electrically connected to two sets of terminals of the power supply respectively.

[0057] The method for thawing frozen beef includes:

[0058] A piece of frozen beef with a thickness of 10 cm, a mass of 850 g, and a surface temperature of -18 °C was placed on the stainless-steel plate and covered with 3 pieces of aluminum foil, namely the first aluminum foil, the second aluminum foil, and the third aluminum foil. The contact areas of the first aluminum foil, the second aluminum foil, and the third aluminum foil with the frozen beef were 8 cm 2 , 10 cm 2 , 15 cm 2 , and the average thicknesses of the three regions of the frozen beef covered by the first aluminum foil, the second aluminum foil, and the third aluminum foil were 10 cm, 8 cm, and 4 cm respectively. The contact area between the stainless-steel plate and the frozen beef was 20 cm 2 .

[0059] A square-wave oscillating current was periodically applied to the frozen beef by the control power supply. The frequency of the oscillating current was 3 kHz, and the duration of each period was 30 s.

[0060] In each period, the duration of the first stage was 10 s. In the first stage, a closed loop was formed only between the first aluminum foil and the stainless-steel plate and the first oscillating current was applied. The duty cycle of the first oscillating current was 45%, and the effective value of the current intensity of the first oscillating current was 2000 mA. At this time, the current density corresponding to the stainless-steel plate was 100 mA / cm 2 , and the current density corresponding to the first aluminum foil was 250 mA / cm 2; The duration of the second stage is 10 s. In the second stage, a closed circuit is only formed between the second aluminum foil and the stainless steel plate and a second oscillating current is applied. The duty cycle of the second oscillating current is 30%, and the effective value of the current intensity of the second oscillating current is 1333.3 mA. At this time, the current density corresponding to the stainless steel plate is 66.7 mA / cm 2 , and the current density corresponding to the second aluminum foil is 133.3 mA / cm 2 ; The duration of the third stage is 10 s. In the third stage, a closed circuit is only formed between the third aluminum foil and the stainless steel plate and a third oscillating current is applied. The duty cycle of the third oscillating current is 20%, and the effective value of the current intensity of the third oscillating current is 888.9 mA. At this time, the current density corresponding to the stainless steel plate is 44.4 mA / cm 2 , and the current density corresponding to the third aluminum foil is 59.3 mA / cm 2 ;

[0061] After 20 cycles and 10 min of thawing, the beef is cut into 4 pieces. A handheld temperature-measuring thermal imager is used to measure the temperatures of different parts of the beef, and it is checked whether there are phenomena of local overheating, incomplete thawing, or local cooking on the surface and cut surface of the beef; The results show that in this embodiment, the average temperature of the thawed beef is 0.4 °C, the highest point temperature is 2.3 °C, the lowest point temperature is -1.5 °C, the regional temperature difference is 3.8 °C, there is no phenomenon of local overheating or cooking, and the weight loss rate is 3.22%.

[0062] Comparative Example 2

[0063] The method for thawing beef, the shape, size, etc. of the frozen beef in Comparative Example 2 are basically the same as those in Example 2, and it is also implemented using the thawing device in Example 2. The difference lies in:

[0064] In each cycle, the duration of the first stage is 10 s. In the first stage, a closed circuit is only formed between the first aluminum foil and the stainless steel plate and a first oscillating current is applied. The duty cycle of the first oscillating current is 99%, and the effective value of the current intensity of the first oscillating current is 4400 mA. At this time, the current density corresponding to the stainless steel plate is 220 mA / cm 2 , and the current density corresponding to the first aluminum foil is 550 mA / cm 2 ; The duration of the second stage is 10 s. In the second stage, a closed circuit is only formed between the second aluminum foil and the stainless steel plate and a second oscillating current is applied. The duty cycle of the second oscillating current is 68%, and the effective value of the current intensity of the second oscillating current is 3022.2 mA. At this time, the current density corresponding to the stainless steel plate is 151.1 mA / cm 2 , and the current density corresponding to the second aluminum foil is 302.2 mA / cm 2; The duration of the third stage is 10 s. In the third stage, a closed circuit is only formed between the third aluminum foil and the stainless-steel plate, and a third oscillating current is applied. The duty cycle of the third oscillating current is 45%, and the effective value of the current intensity of the third oscillating current is 2000 mA. At this time, the current density corresponding to the stainless-steel plate is 100 mA / cm 2 , and the current density corresponding to the third aluminum foil is 133.3 mA / cm 2 :

[0065] After 20 cycles of circulation and 10 min of thawing, the beef is cut into 4 pieces. A handheld temperature-measuring thermal imager is used to measure the temperatures of different parts of the beef, and it is checked whether there are phenomena of local overheating, incomplete thawing, or local cooking on the surface and cut surface of the beef; The results show that in this example, the average temperature of the thawed beef is 16.2 °C, the highest point temperature is 28 °C, the lowest point temperature is 8.8 °C, the regional temperature difference is 19.2 °C, there is a phenomenon of local cooking on the surface, accompanied by structural damage caused by protein denaturation and foaming, and the weight loss rate is 13.11%.

[0066] Example 3

[0067] The thawing device used in this example includes a control power supply and two conductors. Both conductors are plates containing stainless-steel, cylindrical pole heads (the pole head can be understood as an electrode contact head, electrode, or conductive contact point, etc., the same below). The length of the cylindrical pole head is 30 mm, the head is hemispherical, with a diameter of 8 mm, the distance between adjacent pole heads is 4 mm, the upper and lower pole heads are paired for output, and are respectively electrically connected to two sets of terminals of the power supply. Each pair can respectively control the current intensity, frequency, and duration of the output oscillating current, and form multiple closed circuits in different parts / regions of the salmon meat.

[0068] The method for thawing frozen salmon meat includes:

[0069] A piece of frozen salmon meat with a maximum thickness of 5 cm, a minimum thickness of 3 cm, a maximum length of 6 cm, a maximum width of 5 cm, a mass of 400 g, and a surface temperature of -18 °C is placed between the two conductors, and its pole head is in close contact with the meat block. Among them, the contact area of a single pole head with the salmon meat is 0.5 cm 2 , and a total of 30 pairs of pole heads are used for thawing. The salmon meat is divided into 3 regions according to the thickness. The first region has a thickness of 4.5 - 5 cm, is in contact with 15 pairs of pole heads, and the contact area is 7.5 cm 2 ; The second region has a thickness of 3.5 - 4.5 cm, is in contact with 10 pairs of pole heads, and the contact area is 5 cm 2 ; The third region has a thickness of 2.5 - 3.5 cm, is in contact with 5 pairs of pole heads, and the contact area is 2.5 cm 2; The 30 pole heads are in an electrically conductive state, and the pole heads cooperating with different regions of the salmon meat are electrically independent of each other. For example, when the 15 pole heads cooperating with the first region are working, they will not cause electrical interference with the pole heads cooperating with the second region;

[0070] Control the power supply to apply a square wave oscillating current to the frozen salmon meat periodically. The frequency of the oscillating current is 5 kHz, and the duration of each period is 10 min;

[0071] In each period, the duty cycle of the oscillating current applied to the first region is 30%, and the effective value of the current intensity of the oscillating current is 525 mA. At this time, the current density corresponding to a single pole head is 70 mA / cm 2 ; The duty cycle of the oscillating current applied to the second region is 17%, and the effective value of the current intensity of the oscillating current is 297.5 mA. At this time, the current density corresponding to a single pole head is 59.5 mA / cm 2 ; The duty cycle of the oscillating current applied to the third region is 6%. At this time, the effective value of the oscillating current intensity is 105 mA. At this time, the current density corresponding to a single pole head is 42 mA / cm 2 ;

[0072] After one cycle of circulation and 10 min of thawing, the salmon meat is divided into 4 pieces. Use a handheld temperature measurement thermal imager to measure the temperatures of different parts of the salmon meat, and check whether there are local overheating, incomplete thawing, or local cooking phenomena on the surface and cut surface of the salmon meat; The results show that in this embodiment, the average temperature of the thawed salmon meat is -0.5 °C, the highest point temperature is 1.8 °C, the lowest point temperature is -1.1 °C, the regional temperature difference is 2.9 °C, there is no local overheating or cooking phenomenon, and the weight loss rate is 4.21%.

[0073] Example 4

[0074] The thawing device used in this embodiment includes a control power supply and two conductors. Both conductors are plates containing stainless steel and cylindrical pole heads. The length of the cylindrical pole heads is 30 mm, the head is hemispherical with a diameter of 8 mm, the distance between adjacent pole heads is 4 mm, the upper and lower pole heads are paired for output, and are respectively electrically connected to two sets of terminals of the power supply. Each pair can respectively control the current intensity, frequency, and duration of the output oscillating current, and form multiple closed loops in different parts / regions of the pork tenderloin.

[0075] The method for thawing frozen pork tenderloin includes:

[0076] Place a frozen pork tenderloin with a maximum thickness of 6 cm, a minimum thickness of 4 cm, maximum length and width of 6 cm, a mass of 400 g, and a surface temperature of -18 °C between two conductors, making its electrode heads in close contact with the meat block. The contact area of a single electrode head with the pork tenderloin is 0.5 cm 2 . A total of 35 pairs of electrode heads are used for thawing, and the frozen pork tenderloin is divided into 3 regions according to its thickness. The first region has a thickness of 5.5 - 6 cm and is in contact with 15 pairs of electrode heads, with a contact area of 7.5 cm 2 ; the second region has a thickness of 4.5 - 5.5 cm and is in contact with 12 pairs of electrode heads, with a contact area of 6 cm 2 ; the third region has a thickness of 3.5 - 4.5 cm and is in contact with 8 pairs of electrode heads, with a contact area of 4 cm 2 ; all 35 pairs of electrode heads are in a conducting state, and the electrode heads cooperating with different regions of the frozen pork tenderloin are electrically independent of each other and will not generate electrical interference;

[0077] Apply a square-wave oscillating current to the frozen pork tenderloin periodically by controlling the power supply. The frequency of the oscillating current is 8 kHz, and the duration of each cycle is 1 min;

[0078] In each cycle, the duration of the first stage is 20 s. The duty cycle of the oscillating current applied to the first region is 32%, the effective value of the current intensity of the oscillating current is 560 mA, and the current density corresponding to a single electrode head at this time is 74.7 mA / cm 2 , the duty cycle of the oscillating current applied to the second region is 22%, the effective value of the current intensity of the oscillating current is 385 mA, and the current density corresponding to a single electrode head at this time is 64.2 mA / cm 2 , the duty cycle of the oscillating current applied to the third region is 13%, the effective value of the current intensity of the oscillating current at this time is 227.5 mA, and the current density corresponding to a single electrode head at this time is 56.9 mA / cm 2 ; the duration of the second stage is 20 s. The duty cycle of the oscillating current applied to the first region is 24%, the effective value of the current intensity of the oscillating current is 420 mA, and the current density corresponding to a single electrode head at this time is 56 mA / cm 2 , the duty cycle of the oscillating current applied to the second region is 16%, the effective value of the current intensity of the oscillating current is 280 mA, and the current density corresponding to a single electrode head at this time is 46.7 mA / cm 2 , the duty cycle of the oscillating current applied to the third region is 10%, the effective value of the current intensity of the oscillating current at this time is 175 mA, and the current density corresponding to a single electrode head at this time is 43.8 mA / cm 2; The duration of the third stage is 20 s. The duty cycle of the oscillating current applied to the first region is 17%, and the effective value of the current intensity of the oscillating current is 297.5 mA. At this time, the current density corresponding to a single pole tip is 39.7 mA / cm 2 , the duty cycle of the oscillating current applied to the second region is 11%, the effective value of the current intensity of the oscillating current is 192.5 mA, and the current density corresponding to a single pole tip is 32.1 mA / cm 2 , the duty cycle of the oscillating current applied to the third region is 6%, the effective value of the current intensity of the oscillating current at this time is 105 mA, and the current density corresponding to a single pole tip is 26.3 mA / cm 2 ;

[0079] After 10 cycles and 10 min of thawing, the pork tenderloin is cut into 4 pieces. A handheld temperature measurement thermal imager is used to measure the temperatures of different parts of the pork tenderloin, and it is checked whether there are phenomena of local overheating, incomplete thawing, or local cooking on the surface and cut surface of the pork tenderloin; the results show that in this embodiment, the average temperature of the thawed pork tenderloin is 0.5 °C, the highest point temperature is 2.5 °C, the lowest point temperature is -0.6 °C, the regional temperature difference is 3.1 °C, and there are no phenomena of local overheating or cooking, and the weight loss rate is 3.94%.

[0080] A food thawing method based on medium and low frequency oscillating current provided by the present invention applies specific oscillating current to each part of the frozen food periodically and in stages. Under the scanning processing flow, different parts of the frozen food can receive energy intermittently, that is, a "marquee" - type rapid application, which helps to uniformly melt the ice crystals inside the frozen food; moreover, the present invention can further prevent the phenomenon of excessive short - time aggregated energy and local overheating on the surface, and less juice of the frozen food is lost; therefore, the temperature difference of the cross - sectional area inside the frozen food at the thawing end point is smaller, making the quality of the thawed food higher.

[0081] A food thawing method based on medium and low frequency oscillating current provided by the present invention is a non - thermal thawing technology that uses micro - currents applied to multiple parts for thawing. And the energy of the micro - current applied to irregular food materials reaches the energy balance point for destroying ice crystals, which can achieve uniform non - thermal thawing and can be popularized to the civilian and industrial sectors.

[0082] The current generator on which the food thawing method based on medium and low frequency oscillating current provided by the present invention is based is simple, low - cost, easy to control in the process, has high energy utilization rate, and no significant thermal effect is generated when thawing food materials. Therefore, it can be fixed in household appliances and can also become a new type of thawing household appliance single product.

[0083] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, rather than to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A food thawing method based on medium and low frequency oscillating current, characterized in that Including: Periodically applying at least one oscillating current to the frozen food. In each period, applying b of the oscillating currents to a parts of the frozen food, and making the current density and / or duty cycle of the oscillating current applied to each part of the frozen food change in a gradient manner with the increase of time. Each part corresponds to at least one of the oscillating currents. The current frequencies of the b oscillating currents are the same, and making the current density of the oscillating current applied to each part be positively correlated with the thickness of each part. The duration of each period is within 10 min; The current density of each of the oscillating currents is 0.1 - 200 mA / cm 2 , the frequency of the oscillating current is 200 Hz - 20 kHz, the duty cycle is 1 - 99%, the current density is the effective value, the heat generated by the oscillating current in the frozen food is the same as or slightly greater than the energy required for the ice crystals in the frozen food to be converted into liquid water, so that the frozen food is thawed, the thawing end temperature of the internal area of the frozen food does not exceed 5°C, b ≥ a ≥ 1, and both a and b are integers.

2. The food thawing method according to claim 1, characterized in that: The duration of each period is 0 - 10 min.

3. The food thawing method according to claim 1, wherein Specifically including: The thickness of the frozen food is within 15 cm.

4. The food thawing method according to claim 3, wherein The thickness of the selected part of the frozen food is 0.8 - 15 cm, and when the thickness of the selected part is 0.5 - 8 cm, the current density of each of the oscillating currents applied to the selected part is 0.1 - 80 mA / cm 2 ; when the thickness of the selected part is 8 - 15 cm, the current density of each of the oscillating currents applied to the selected part is 80 - 200 mA / cm 2 .

5. The food thawing method according to claim 3 or 4, characterized in that Specifically including: In each period, simultaneously applying b of the oscillating currents to a parts of the frozen food, or sequentially applying b of the oscillating currents to a parts of the frozen food, and within the same time period, applying d of the oscillating currents to c parts of the frozen food, where c ≤ a, d ≤ b, and c and d are both positive integers.

6. The food thawing method according to claim 1, wherein: The change gradient of the current density of the oscillating current applied to each part of the frozen food is 0.1 - 100 mA / cm 2 / min.

7. The food thawing method according to claim 1, wherein: The change gradient of the duty cycle of the oscillating current applied to each part of the frozen food is 5% - 40% / min.

8. The food thawing method according to claim 1, wherein: The current waveform of the oscillating current is a square wave or a sawtooth wave.

9. The food thawing method according to claim 1, wherein: The duty cycle of the oscillating current is 5 - 95%.

10. The food thawing method according to claim 1, wherein, Specifically including: Making two conductor groups electrically connected to the control power supply be in electrical contact with the frozen food, forming at least one closed loop between the two conductor groups and the frozen food, and applying at least one of the oscillating currents to the closed loop with the control power supply, where the two conductor groups are respectively electrically connected to two different terminals of the control power supply.

11. The food thawing method according to claim 10, characterized in that: Each of the conductor groups includes at least one conductor.

12. The food thawing method according to claim 11, wherein: Each of the conductor groups includes multiple conductors, forming multiple closed loops between the two conductor groups and the frozen food. Each part of the frozen food corresponds to at least one of the closed loops, and specifically, the food thawing method includes applying multiple oscillating currents to the multiple closed loops, where the multiple conductors included in the same conductor group are electrically connected to the same terminal of the control power supply.

13. The food thawing method according to claim 11, characterized in that: The conductor is a flexible body or a rigid body.

14. The food thawing method according to claim 1, characterized in that: The thawing end temperature of the internal area of the frozen food is -4 - 5 °C.

15. The food thawing method according to claim 1, characterized in that: The frozen food includes frozen aquatic products, frozen meat products or frozen flour products.