An integrated cycle freeze-thaw device and its application in fresh food freezing and thawing

Abstract

The present invention relates to an integrated cycle freeze-thaw device and its application in the freeze-thaw of fresh food, belonging to the technical field of food freezing and processing. It includes a freezing chamber, a thawing chamber, a lifting assembly, a temperature acquisition device, a controller, and an argon / krypton / xenon mixed gas combined injection assembly; the freezing chamber and the thawing chamber are vertically distributed up and down and connected by the lifting assembly and a hose, the lifting assembly is composed of a lifting device and a sample tray, the sample tray is connected to the lifting device by a sample tray rack, and the lifting device is used to move the sample tray to the desired position in the cavity; the controller is connected to the inner cavity by the temperature acquisition device, and the controller is also connected to the combined injection assembly. The freezing of the present invention uses a mixed gas composed of liquid nitrogen and argon / krypton / xenon mixed gas to freeze food, and thawing uses the combination of electrostatic field and far-infrared technology, combined with precise temperature control, which is convenient to use and has good effects.

Description

Technical Field

[0001] The invention relates to an integrated cycle freeze-thaw device and application thereof in the freezing and thawing of fresh food, belonging to the technical field of food freezing processing. Background Art

[0002] Freezing is one of the most commonly used technologies for preserving food, and its purpose is to maintain its original nutritional and sensory properties. When frozen, water molecules form ice crystals, which changes the original binding state of food components and water, and the food properties often change significantly. Thawing is the reverse process of freezing, and solid ice is converted back into liquid water. However, since freezing causes irreversible damage to the water binding state, thawed food cannot return to its original state. The cell and tissue structure of frozen and thawed food changes, and is often accompanied by changes in hardness, viscosity, gel structure, etc. Studies have shown that the processing characteristics of some foods are improved after freeze-thaw cycles.

[0003] Fan Liuping et al. (patent number: 202110761738.X) disclosed a method for treating pumpkin pulp by ultrasonic combined cyclic freeze-thaw. Compared with the seed pumpkin pulp product that is directly far-infrared dried without cyclic freeze-thaw, the efficiency of far-infrared drying of seed pumpkin is improved, and the drying time is shortened by 25% to 40%. The product appearance integrity rate is high, closer to the color of fresh seed pumpkin pulp, with small shrinkage rate, moderate hardness and crispness, and the content of free phenols and monomer phenols are significantly higher than conventional far-infrared drying. The research of Wang Lan et al. of Hubei Academy of Agricultural Sciences showed that after starch is treated with freeze-thaw cycles, an ordered network structure will appear, and the network gap will increase with the increase of the number of cycles. The formation and destruction of the network structure correspond to the changes in the properties of the gel part. The water separation rate of starch gel will show a downward trend with the increase of the number of freeze-thaw cycles. The water separation rate of rice starch decreased significantly after two freeze-thaw cycles, indicating that the network structure of gel starch was strengthened, forming a "water cage" structure of a certain strength, which is conducive to reducing the gelatinization temperature of rice during cooking. In addition, due to the effect of thermal expansion and contraction, the cyclic freeze-thaw treatment improves the structure of the brown rice bran layer and changes the surface tissue composition of the brown rice, thereby increasing the water absorption of the brown rice during soaking and reducing the gelatinization temperature of the brown rice during cooking. Yu Yong et al. (patent number: 201711277795.0) disclosed a rapid processing method for cyclic freeze-thaw nutritious, healthy and palatable brown rice, which effectively solves the problems of existing brown rice being difficult to cook and having poor taste. Wu Jinxuan et al. (patent number: 202221014889.5) disclosed a mulberry leaf repeated freeze-thaw device. The mulberry leaves after freeze-thaw operation are used to prepare mulberry leaf tea, which can not only increase the amount of DNJ dissolved in mulberry leaf tea, but also retain the emerald green appearance of mulberry leaf tea. The above studies and patents show the beneficial effects of freeze-thaw operation. However, traditional freezing methods often have adverse effects such as slow speed, low efficiency, large ice crystals formed by freezing, and serious damage to food quality. Traditional thawing techniques include air thawing, vacuum thawing and immersion thawing, which have disadvantages such as low efficiency, high cost and inconvenience. At a slower thawing rate, the quality attributes of frozen food are significantly reduced and microbial growth is significantly accelerated. In addition, it is difficult to achieve integrated operation when freezing and thawing are carried out separately, which is not conducive to freeze-thaw cycles.

[0004] Rapid freezing can effectively reduce the damage of freezing to food. The product temperature can quickly cross the maximum ice crystal formation zone, thereby preventing the migration of water molecules and eventually forming uniform and fine ice crystals. Therefore, rapid freezing is advocated in the field of freezing at home and abroad. The lowest temperature of liquid nitrogen can reach -198℃, which can achieve rapid freezing of food and improve the quality of frozen products. It has been widely used in the rapid freezing of food. However, there are still many problems in the rapid freezing of fresh food materials with liquid nitrogen. For example, due to the rapid freezing speed, some fruits will crack; the inefficient thawing method will cause ice crystal growth and recrystallization during the thawing process of fresh food; the enzyme and microbial activities of fresh food will be enhanced after freezing and thawing, and the product quality will drop sharply; large freezing and thawing equipment occupies a large volume and is inconvenient to use. On the basis of rapid freezing, in recent years, in order to obtain better freezing and thawing effects, more and more research has focused on using physical field technologies to assist freezing and thawing operations, such as ultrasound, microwaves, far infrared, high voltage, electric fields, magnetic fields, radio frequencies, and so on. Effective physical field assisted or coordinated application can accelerate the freezing and thawing process, further improve the product quality of quick-frozen food, and improve the quality of frozen products after thawing. In addition, some research focuses on some new liquefied gases to achieve quick freezing of food.

[0005] Zhang Min et al. (patent number: 202210166852.2) disclosed a static magnetic field assisted liquefied CO2 pulse spray freezing device and a pressurized high-efficiency freezing method. The quick-freezing device uses liquefied CO2 as the freezing medium and is equipped with a static magnetic field generating device to assist in freezing, which can reduce the size of ice crystals. The freezing method includes evacuation, pre-cooling and CO2 pressurization, magnetic field assisted quick freezing, and deep freezing. However, the refrigeration equipment of the invention uses liquefied carbon dioxide as the refrigerant medium, and the lowest temperature can only reach -78.3°C. When the size of the frozen product is large, it is difficult to achieve a quick freezing effect. The liquefied CO2 of the invention is sprayed through a combined fluid nozzle with a small flow rate, which makes it difficult to achieve the effect of large-scale freezing of materials. In addition, the refrigeration equipment of the invention has only one freezing chamber, which cannot realize the separate pre-freezing pretreatment operation of fresh food materials, and has no thawing function. The sprayed CO2 can only be discharged into the surrounding environment and has no recycling function.

[0006] Regarding food thawing, many studies have shown that infrared and electric fields can play a certain role in the thawing process. Chen et al. compared the thawing effects of infrared and microwave technology on frozen green peppers, carrots and cantaloupe. The results showed that infrared can accelerate the thawing process of frozen fresh food. Bissoyi et al. showed that infrared radiation has more advantages in cell thawing, and the survival rate of thawed cells is higher. Qian Xixun (patent number: 200510088882.2) disclosed a method for preparing fried chestnuts using far-infrared thawing, using far-infrared rays at 170-230℃ for 30-60 minutes to thaw frozen chestnuts to inhibit the occurrence of microorganisms and eliminate odors during the thawing process. Han Qing (patent number: 201721374827.4) disclosed a far-infrared low-temperature thawing device, including a box, a temperature and humidity sensor, a humidifier, a far-infrared generator tube and other parts. The far-infrared generator tube used is a carbon black silk infrared quartz light wave heating tube. Gao Shuomao (patent number: 202121798112.8) disclosed a rapid thawing cabinet based on a low-frequency, high-voltage electric field. The electric field has a protective and penetrating effect on frozen products. The surface and the interior are thawed simultaneously, which improves the thawing speed and quality, and there is no residual frozen area. Su Laijin et al. (patent number: 202011227858.3) disclosed a method for rapid thawing of aquatic products based on electric field synergy, the steps of which include low-temperature, low-voltage electrostatic field thawing treatment, low-temperature, high-voltage electrostatic field thawing treatment, high-temperature, high-voltage electrostatic field thawing treatment, and high-temperature, low-voltage electrostatic field thawing treatment until the aquatic product is completely thawed.

[0007] The above studies and patents show the beneficial effects of far infrared and electrostatic fields in assisting thawing. However, there is no disclosure of patents involving the combined effects of far infrared and electrostatic fields, let alone the invention of a freezer-thawing machine that integrates freezing and thawing functions.

[0008] Argon and krypton are low-cost inert gases. Some studies and patents have reported the beneficial effects of using argon or krypton on the preservation of fresh food. Bi Hongtao (patent number: 201910175956.8) disclosed a method for preserving Cordyceps sinensis by using modified atmosphere packaging containing argon. The use of a mixed gas containing argon for modified atmosphere packaging can significantly inhibit the decrease in the weight loss rate of Cordyceps sinensis, slow down the decrease in soluble protein content, delay the increase in water activity, and delay the increase in polyphenol oxidase activity. Dan Wu et al. (2021) used nano zinc oxide combined with pressurized argon to treat fresh-cut oranges. The experimental results showed that the combined treatment with argon significantly extended the shelf life of fresh-cut oranges. Chen Xiaoxu et al. (Patent No.: 201810945715.2) disclosed a preservation method for fresh-cut fruits and vegetables with rapid water structuring. After peeling and cutting the fruit and vegetable raw materials, they are filled with argon, krypton, nitrogen or carbon dioxide mixed gas, and then treated with high pressure to quickly structure the water on the surface and in the tissues of the fresh-cut fruits and vegetables, reducing the activity of water molecules. Zhang Min et al. (Patent No.: 201710028514.1) disclosed a method for the preservation of shelled and conditioned shrimp with antibacterial activity combined with controlled atmosphere preservation to extend the refrigerated shelf life. The invention provides a controlled atmosphere preservation technology for shrimp based on inert gas, using inert gas argon or krypton instead of conventional nitrogen.

[0009] However, the above disclosed research and patents all use argon or krypton for fresh food preservation, and there is no report on a method and device for freezing and thawing fresh food using argon / krypton / xenon mixed gas. Summary of the invention

[0010] In order to solve the above problems, the present invention provides an integrated cycle freeze-thaw device, including a freezing chamber, a thawing chamber, a lifting component, a temperature collection device, a controller, and an argon / krypton / xenon mixed gas combined injection component;

[0011] The freezing chamber and the thawing chamber are vertically distributed up and down.

[0012] The controller is connected to the temperature acquisition device, and the temperature acquisition device can monitor the temperature in the device and feed back information to the controller;

[0013] The controller controls the movement of the lifting device, and the lifting assembly is placed between the thawing chamber and the freezing chamber and can move freely; the lifting assembly is composed of a lifting device and a sample tray, and the sample tray is connected to the lifting device by a sample tray rack; the lifting device drives the sample tray to move to the freezing chamber or the thawing chamber, and a hose is also provided between the freezing chamber and the thawing chamber, which is used to transmit the remaining mixed gas from the freezing chamber to the thawing chamber.

[0014] The controller is also connected to the combined injection assembly. When a freezing operation is performed, the controller controls the combined injection assembly to inject mixed gas into the freezing chamber.

[0015] The combined injection assembly is connected to the freezing chamber, and the argon / krypton / xenon mixed gas combined injection assembly includes an argon / krypton / xenon mixed gas injection device, a liquid nitrogen injection device, an argon / krypton / xenon mixed gas dynamic ratio adjustment device, an air compressor, a pressure relief valve and a vacuum pump, which can control the dynamic ratio and pressure of the mixed gas according to conditions, and more accurately control the freezing effect; the argon / krypton / xenon mixed gas injection device is also connected to the thawing chamber;

[0016] The thawing chamber comprises a far infrared generating device, an electrostatic field device and a temperature control device.

[0017] In one embodiment of the present invention, the sample tray is a mesh structure, the material is polytetrafluoroethylene, and the tray height is 5 cm; the material of the sample tray rack is polytetrafluoroethylene. The selection of polytetrafluoroethylene material can reduce the interference of the sample tray and the sample tray rack on the electrostatic field and far-infrared rays when the electrostatic field and the magnetic field act on the sample.

[0018] In one embodiment of the present invention, the temperature acquisition device includes a first temperature sensor and a second temperature sensor, the first temperature sensor is suspended in the air and is used to sense the cavity temperature of the freezer or thaw chamber; the second temperature sensor is composed of a 12-way food insertion temperature sensor and a 2.5mm silver-plated waterproof shielded wire, and the temperature error is ±0.15°C. The second temperature sensor is connected to the sample tray and is used to sense the sample temperature at the center of the sample tray.

[0019] In one embodiment of the present invention, the argon / krypton / xenon mixed gas injection device and the liquid nitrogen injection device are both provided with nozzles, flow control valves and air intake insulation pipes and are both controlled to open and close by solenoid valves. The two nozzles spray a mixed gas consisting of argon / krypton / xenon mixed gas and liquid nitrogen into the freezing chamber through the two air intake insulation pipes, and the flow rate is controlled by the flow control valve; the freezing chamber is provided with a rear fan for stirring the gas in the entire cavity to make the temperature evenly distributed; the freezing chamber is also provided with a rear insulation pipe connected to the external environment.

[0020] In one embodiment of the present invention, the far-infrared generating device includes 4 infrared tubes with a maximum power of 700W×4, and the infrared heating working mode is intermittent, all of which are laid on both sides of the inner wall of the thawing chamber; the electrostatic field device is a thorn electrode plate, which discharges outward through each point corona electrode to generate a maximum voltage of 50kV, the thorn plate is 10cm away from the upper and lower sample holders, and the electrostatic field acting on the food is 0-5kV / cm; the outer layers of the far-infrared generating device and the electrostatic field device are both equipped with electrostatic shielding devices and protective devices, so that the far-infrared generating device and the electrostatic field device can work simultaneously without interfering with each other.

[0021] In one embodiment of the present invention, the temperature control device includes a heating plate and a refrigeration compressor, and the temperature control device is also connected to the controller to achieve precise temperature control of 0 to 45° C. in the thawing chamber.

[0022] The present invention also provides an application of an integrated freeze-thaw cycle device, the application comprising the following steps:

[0023] Step 1: pre-treating the food materials by micro-pressurization: first, wash, peel, cut, blanch and protect the color of the food materials, then move the sample tray into the thawing chamber, place the sample on the sample tray, evacuate the entire thawing chamber by a vacuum pump, and use the argon / krypton / xenon gas injection device to introduce a argon / krypton / xenon gas mixture with a relative pressure of 0 to 0.03 MPa into the thawing chamber to achieve micro-pressurization of the fresh food materials with argon / krypton / xenon gas before freezing. The pressurized inert gas argon / krypton / xenon gas mixture and the water molecules in the fresh food form cage-shaped gas hydrates; the formation of gas hydrates in the fresh food will reduce the activity of water molecules and enzyme molecules in the tissue, inhibit the metabolic activity of the fresh food, and thus achieve a protective effect during the freezing and thawing process;

[0024] Step 2: Dynamic quick freezing of food with mixed gas: First, the lifting component moves the food on the sample tray to the freezing chamber, and the controller starts the combined injection component, so that the mixed gas composed of argon / krypton / xenon mixed gas and liquid nitrogen enters the freezing chamber at a preset flow rate V1, until the temperature value fed back by the second temperature sensor reaches the preset temperature T1 in the controller, completing the first stage of the cooling process; secondly, the controller increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the combined injection component, and increases the input mixed gas speed to V2, and when the temperature value fed back by the second temperature sensor reaches the preset temperature T2 in the controller, the quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed; finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the combined injection component, and reduces the mixed gas flow rate input to the insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller, and then closes the liquid nitrogen and argon / krypton / xenon mixed gas input, indicating that all materials in the freezing chamber have been frozen;

[0025] Step 3: Thawing food with argon / krypton / xenon protection: The lifting assembly moves the food on the sample tray to the thawing chamber, and the controller controls the input of argon / krypton / xenon mixed gas for pre-cooling, and uses far-infrared radiation to quickly heat the surface and combine it with an electrostatic field to accelerate the thawing process of the food.

[0026] Step 4: The remaining mixed gas in the freezing chamber enters the thawing chamber through a hose and is used to precool the food during the next pretreatment.

[0027] Step 5: Freeze and thaw other ingredients: repeat the above steps 1 to 4 in a cycle.

[0028] Beneficial effects of the present invention:

[0029] 1. The integrated cycle freeze-thaw device provided by the present invention has both pretreatment and freezing functions and efficient thawing functions. It can realize integrated operation of pre-freezing pretreatment and freeze-thaw cycle of fresh food materials. The pretreatment, freezing and thawing of raw materials can be completed in the same device. The operation is convenient and efficient. It can also be used for rapid freeze-thaw pretreatment before food drying and other processing scenarios.

[0030] 2. The freezing method of the present invention adopts a mixed gas consisting of liquid nitrogen and argon / krypton / xenon mixed gas to freeze food materials, which not only realizes the controllable quick freezing of fresh food materials, reduces the size of ice crystals, and avoids fruit cracking; but also makes the entire freezing and thawing process of fresh food materials under the protection of argon / krypton / xenon mixed gas, and the water migration, enzyme activity, and microbial activity are all restricted, thereby effectively improving the quality of frozen fresh food materials after thawing.

[0031] 3. The mixed gas produced in the freezing chamber of the present invention can also be transported to the thawing chamber through a hose for recycling, and the controller can be used to control the input of the argon / krypton / xenon mixed gas to pre-cool and protect the food.

[0032] 4. The present invention is provided with a controller, a temperature collection device, a temperature control device and a lifting assembly, so that the user can adjust the operation according to the temperature feedback, avoid direct hand contact when performing different steps, and the operation is convenient.

[0033] 5. The thawing process of the present invention utilizes the combination of electrostatic field and far infrared technology to accelerate the thawing of food.

[0034] 6. The sample tray of the present invention has a mesh structure so as to better receive mixed gas, electrostatic field discharge, and far infrared generation, and at the same time facilitate uniform temperature distribution.

[0035] 7. The present invention is provided with shielding and protection devices for the electrostatic field device and the far infrared generating device, so that the electrostatic field and the far infrared rays do not interfere with each other and have a good synergistic effect.

[0036] 8. The present invention divides the freezing process into three stages, which has a thorough freezing effect.

[0037] 9. The thawing chamber of the present invention is also provided with a temperature control device, which can realize accurate temperature control of the thawing chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic structural diagram of an integrated cycle freeze-thaw device in one embodiment of the present invention.

[0039] In the figure, 1: thawing chamber, 2: freezing chamber, 3: far-infrared generating device, 4: lifting assembly, 5: electrostatic field device, 6: sample tray, 7: rear fan, 8: air compressor, 9: liquid nitrogen injection device, 10: controller, 11: argon / krypton / xenon mixed gas injection device, 12: vacuum pump, 13: first temperature sensor, 14: second temperature sensor. DETAILED DESCRIPTION

[0040] Example 1

[0041] like Figure 1 As shown, the present invention provides an integrated cycle freeze-thaw device, including a freezing chamber 2, a thawing chamber 1, a lifting assembly 4, a temperature collection device, a controller 10, and an argon / krypton / xenon mixed gas combined injection assembly;

[0042] The freezing chamber 2 is located at the lower layer of the thawing chamber 1, and an openable and closable partition is provided between the freezing chamber 2 and the thawing chamber 1; the lifting assembly 4 is placed between the thawing chamber 1 and the freezing chamber 2 and can move freely.

[0043] The lifting assembly 4 is composed of a lifting device and a sample tray 6. The sample tray 6 is a mesh structure made of polytetrafluoroethylene and has a tray height of 5 cm. The sample tray 6 is connected to the lifting device by a sample tray rack. The lifting device drives the sample tray 6 to move to the freezing chamber 2 or the thawing chamber 1. A hose is also provided between the freezing chamber 2 and the thawing chamber 1 for transmitting the remaining mixed gas from the freezing chamber 2 to the thawing chamber 1.

[0044] The thawing chamber 1 includes a far infrared generating device 3, an electrostatic field device 5 and a temperature control device.

[0045] The far infrared generating device 3 is 4 far infrared tubes laid on the inner walls of both sides of the thawing chamber 1, with a maximum power of 700W×4, and the infrared heating working mode is intermittent.

[0046] The electrostatic field device 5 is a barbed electrode plate placed in the middle area of ​​the thawing chamber 1, which discharges outward through each point corona electrode to generate a maximum voltage of 50kV. The distance between the barbed plate and the upper and lower sample holders is 10cm, and the electrostatic field acting on the fresh food sample is 0-5kV / cm.

[0047] The outer layers of the far infrared generating device 3 and the electrostatic field device 5 are both equipped with electrostatic shielding devices and protective devices. On the one hand, the far infrared is not interfered by the electrostatic field, and the far infrared and the electrostatic field can work simultaneously; on the other hand, the generated electrostatic field acts on the sample in a directional manner to achieve efficient thawing.

[0048] The thawing chamber 1 is also provided with a temperature control device connected to the controller 10, including a built-in heating plate and a refrigeration compressor, which can achieve precise temperature control of 0 to 45°C in the thawing cavity.

[0049] The controller 10 is connected to the temperature acquisition device, which includes a first temperature sensor 13 and a second temperature sensor 14. The first temperature sensor 13 is suspended and is used to sense the cavity temperature of the freezing chamber 2 or the thawing chamber 1; the second temperature sensor 14 is composed of a 12-way food insertion temperature sensor and a 2.5mm silver-plated waterproof shielded wire, and the temperature error is ±0.15°C. The second temperature sensor 14 is connected to the sample tray 6 and is used to sense the sample temperature at the center of the sample tray.

[0050] The controller 10 controls the movement of the lifting device, and moves to the thawing chamber 1 or the freezing chamber 2 through the controller 10 according to user needs.

[0051] The controller 10 is also connected to the combined injection assembly. When a freezing operation is performed, the controller 10 controls the argon / krypton / xenon mixed gas combined injection assembly to inject the mixed gas into the freezing chamber 2 .

[0052] The argon / krypton / xenon mixed gas combination injection assembly is connected to the freezing chamber 2 .

[0053] The argon / krypton / xenon mixed gas combined injection assembly comprises an argon / krypton / xenon mixed gas injection device 11 , a liquid nitrogen injection device 9 , an air compressor 8 , and a vacuum pump 12 .

[0054] The argon / krypton / xenon mixed gas injection device 11 is also connected to the thawing chamber 1; the argon / krypton / xenon mixed gas injection device 11 includes an argon / krypton / xenon mixed gas cylinder controlled by a solenoid valve, a nozzle, a flow control valve and an air intake insulation pipe, and the argon / krypton / xenon mixed gas injection device 11 is also connected to the thawing chamber 1.

[0055] The freezing chamber 2 is provided with a rear fan 7 for stirring the gas in the entire cavity to make the temperature distribution uniform; the freezing chamber 2 is also provided with a rear insulation pipe connected to the external environment.

[0056] The liquid nitrogen injection device 9 comprises a liquid nitrogen dewar tank controlled by a solenoid valve, a nozzle, a flow control valve and an air intake insulation pipe.

[0057] Example 2

[0058] The device in Example 1 is applied to the freeze-thaw process of fresh food, and the specific method is as follows:

[0059] Step 1: Pre-processing the food: first, wash, peel, cut, blanch and protect the color of the food, then move the sample tray 6 into the thawing chamber 1, and the mixed gas transmitted from the freezing chamber 2 through the hose after the last use can be used for rapid cooling and pre-cooling of fresh food, and the temperature is regulated by the temperature control device to maintain at 0-4°C;

[0060] A fresh food sample is placed on the sample tray 6, the entire thawing chamber 1 is evacuated by a vacuum pump 12, and an argon / krypton / xenon mixed gas with a relative pressure of 0 to 0.03 MPa is introduced into the thawing chamber 1 by the argon / krypton / xenon mixed gas injection device 11, so that the fresh food material is slightly pressurized by argon / krypton / xenon gas before freezing, and the pressurized inert gas argon / krypton / xenon mixed gas and the water molecules of the fresh food form cage-shaped gas hydrates; the formation of gas hydrates in the fresh food will reduce the activity of water molecules and enzyme molecules in the tissue, inhibit the metabolic activity of the fresh food, and thus achieve a protective effect during the freezing and thawing process.

[0061] Step 2: Freezing the food: First, the lifting assembly 4 moves the food on the sample tray 6 to the freezing chamber 2, and the controller 10 starts the combined injection assembly, so that the mixed gas consisting of the argon / krypton / xenon mixed gas and liquid nitrogen enters the freezing chamber at a preset flow rate V1 until the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T1 in the controller 10, completing the first stage of the cooling process;

[0062] Secondly, the controller 10 increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the argon / krypton / xenon mixed gas combination injection assembly, and increases the input mixed gas velocity to V2, and when the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T2 in the controller 10, the second stage of quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed;

[0063] Finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the argon / krypton / xenon mixed gas combination injection assembly, and reduces the mixed gas flow rate in the input insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller 10, and then turns off the liquid nitrogen and argon / krypton / xenon mixed gas input, indicating that all materials in the freezing chamber 2 have been frozen.

[0064] Step 3: Thawing food: The lifting component 4 moves the food on the sample tray 6 to the thawing chamber 1, and the controller 10 controls the input of argon / krypton / xenon mixed gas for pre-cooling, and adopts far-infrared radiation surface rapid heating and combined with electrostatic field method to accelerate the thawing of food. The far-infrared power used is 0-700W / root, the infrared working time is 30-80s, and the intermittent time is 30-60s; the electrostatic field strength used is 0-50kV, and the electric field strength acting on the sample is 0-5kV / cm, which accelerates the thawing process of food.

[0065] Step 4: The remaining mixed gas in the freezing chamber 2 enters the thawing chamber 1 again through the hose to precool the food during the next pretreatment.

[0066] Step 5: Freeze and thaw other ingredients: repeat the above steps 1 to 4 in a cycle.

[0067] Example 3

[0068] The device in Example 1 is applied to the freeze-thaw process of Hami melon, and the specific method is as follows:

[0069] Step 1: Pre-treating Hami melon: First, wash, peel and cut the ingredients, place the Hami melon on the sample tray 6, then move the sample tray 6 into the thawing chamber 1, and the mixed gas transmitted from the freezing chamber 2 through the hose after the last use can be used to quickly cool down and pre-cool the Hami melon, and the temperature is regulated by the temperature control device to maintain at 4°C;

[0070] The Hami melon sample is placed on the sample tray 6, the entire thawing chamber 1 is evacuated by the vacuum pump 12, and the argon / krypton / xenon mixed gas injection device 11 is used to introduce an argon / krypton / xenon mixed gas with a relative pressure of 0.03 MPa into the thawing chamber 1, and the temperature is 4°C, the relative humidity is 85%, and the relative pressure of the argon / krypton / xenon mixed gas is 0.03 MPa. The mixture is maintained for 20 minutes.

[0071] Step 2: Freezing food: First, the lifting assembly 4 moves the cantaloupe on the sample tray 6 to the freezing chamber 2, and the controller 10 starts the combined injection assembly to allow the mixed gas consisting of argon / krypton / xenon mixed gas and liquid nitrogen to enter the freezing chamber at a preset flow rate V1 until the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T1 in the controller 10, completing the first stage of the cooling process;

[0072] Secondly, the controller 10 increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the argon / krypton / xenon mixed gas combination injection assembly, and increases the input mixed gas velocity to V2, and when the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T2 in the controller 10, the second stage of quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed;

[0073] Finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the argon / krypton / xenon mixed gas combination injection assembly, and reduces the mixed gas flow rate in the input insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller 10, and then turns off the liquid nitrogen and argon / krypton / xenon mixed gas input, indicating that all materials in the freezing chamber 2 have been frozen.

[0074] Step three: thawing food: the lifting component 4 moves the food on the sample tray 6 to the thawing chamber 1, the controller 10 controls the input of argon / krypton / xenon mixed gas for pre-cooling, and adopts far-infrared radiation surface rapid heating and combined electrostatic field method to accelerate the thawing of food. The far-infrared power used is 300W×4, the infrared working time is 70s, and the intermittent time is 60s; the electrostatic field intensity used is 50kV / cm, and the electric field intensity acting on Hami melon is 5kV / cm; far-infrared surface radiation combined with electrostatic field treatment can act on the inside and outside of the Hami melon sample at the same time to accelerate the thawing process.

[0075] Step 4: The remaining mixed gas in the freezing chamber 2 enters the thawing chamber 1 again through the hose to precool the food during the next pretreatment.

[0076] Example 4

[0077] The device in Example 1 is applied to the freeze-thaw process of broccoli, and the specific method is as follows:

[0078] Step 1: Pre-treat Hami melon: First, wash, cut and blanch the ingredients (select fresh broccoli without mechanical damage and pests, wash it clean, cut the inflorescences of uniform size, and then blanch it in 95°C hot water for 1 minute, then cool it in cold water, and take it out to drain the water), put the broccoli on the sample tray 6, and then move the sample tray 6 into the thawing chamber 1, and the mixed gas transmitted from the freezing chamber 2 through the hose after the last use can be used to quickly cool down and pre-cool the broccoli, and the temperature is regulated by the temperature control device to maintain it at 4°C;

[0079] The broccoli sample is placed on the sample tray 6, the entire thawing chamber 1 is evacuated by the vacuum pump 12, and the argon / krypton / xenon mixed gas injection device 11 is used to introduce an argon / krypton / xenon mixed gas with a relative pressure of 0.02 MPa into the thawing chamber 1, and the temperature is 4°C, the relative humidity is 90%, and the relative pressure of the argon / krypton / xenon mixed gas is 0.02 MPa. The conditions are maintained for 20 minutes.

[0080] Step 2: Freezing food: First, the lifting assembly 4 moves the broccoli on the sample tray 6 to the freezing chamber 2, and the controller 10 starts the combined injection assembly, so that the mixed gas consisting of argon / krypton / xenon mixed gas and liquid nitrogen enters the freezing chamber at a preset flow rate V1 until the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T1 in the controller 10, completing the first stage of the cooling process;

[0081] Secondly, the controller 10 increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the argon / krypton / xenon mixed gas combination injection assembly, and increases the input mixed gas velocity to V2, and when the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T2 in the controller 10, the second stage of quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed;

[0082] Finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the argon / krypton / xenon mixed gas combination injection assembly, and reduces the mixed gas flow rate in the input insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller 10, and then turns off the liquid nitrogen and argon / krypton / xenon mixed gas input, indicating that all materials in the freezing chamber 2 have been frozen.

[0083] Step three: thawing food: the lifting assembly 4 moves the food on the sample tray 6 to the thawing chamber 1, the controller 10 controls the input of the argon / krypton / xenon mixed gas for pre-cooling, and adopts the method of rapid surface heating by far-infrared radiation and combined with the electrostatic field to accelerate the thawing of the food. The far-infrared power used is 250W×4, the infrared working time is 60s, and the intermittent time is 60s; the electrostatic field intensity used is 30kV, and the electric field intensity acting on the sample is 3kV / cm; the far-infrared surface irradiation combined with the electrostatic field treatment can act on the inside and outside of the broccoli sample at the same time to accelerate the thawing process.

[0084] Step 4: The remaining mixed gas in the freezing chamber 2 enters the thawing chamber 1 again through the hose to precool the food during the next pretreatment.

[0085] Example 5

[0086] The equipment in Example 1 is applied to the freeze-thaw process of yellow peaches, and the specific method is as follows:

[0087] Step 1: Pre-treatment of yellow peaches: Raw material screening and cleaning: select yellow peaches of uniform size, moderate maturity, and no mechanical damage, and then clean them; peeling: use a peeling machine to peel and pit the washed yellow peaches; cut: cut the washed and pitted yellow peaches into pieces; color protection: transfer the cut yellow peaches into a color protection solution and soak them for 2 hours. The color protection solution consists of 0.1% to 0.5% (w / v) sodium isoascorbate, 0.1% to 0.5% (w / v) citric acid, and 0.5% to 1% (w / v) sodium chloride. Then remove and drain the water.

[0088] Place the yellow peach on the sample tray 6, then move the sample tray 6 into the thawing chamber 1, and the mixed gas transmitted from the freezing chamber 2 through the hose after the last use can be used to quickly cool down and pre-cool the yellow peach, and the temperature is regulated by the temperature control device to maintain at 4°C;

[0089] The yellow peach sample is placed on the sample tray 6, the entire thawing chamber 1 is evacuated by the vacuum pump 12, and the argon / krypton / xenon mixed gas injection device 11 is used to introduce an argon / krypton / xenon mixed gas with a relative pressure of 0.03 MPa into the thawing chamber 1, and the temperature is 4°C, the relative humidity is 80%, and the relative pressure of the argon / krypton / xenon mixed gas is 0.03 MPa. The mixture is maintained for 20 minutes.

[0090] Step 2: Freezing the food: First, the lifting assembly 4 moves the yellow peach on the sample tray 6 to the freezing chamber 2, and the controller 10 starts the combined injection assembly to allow the mixed gas consisting of argon / krypton / xenon mixed gas and liquid nitrogen to enter the freezing chamber at a preset flow rate V1 until the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T1 in the controller 10, completing the first stage of the cooling process;

[0091] Secondly, the controller 10 increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the argon / krypton / xenon mixed gas combination injection assembly, and increases the input mixed gas velocity to V2, and when the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T2 in the controller 10, the second stage of quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed;

[0092] Finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the argon / krypton / xenon mixed gas combination injection assembly, and reduces the mixed gas flow rate in the input insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller 10, and then turns off the liquid nitrogen and argon / krypton / xenon mixed gas input, indicating that all materials in the freezing chamber 2 have been frozen.

[0093] Step three: thawing ingredients: the lifting assembly 4 moves the ingredients on the sample tray 6 to the thawing chamber 1, the controller 10 controls the input of the argon / krypton / xenon mixed gas for pre-cooling, and adopts the method of rapid surface heating by far-infrared radiation and combined with the electrostatic field to accelerate the thawing of the ingredients. The far-infrared power used is 300W×4, the infrared working time is 70s, and the intermittent time is 60s; the electrostatic field intensity used is 50kV, and the electric field intensity acting on the sample is 5kV / cm; the far-infrared surface irradiation combined with the electrostatic field treatment can act on the inside and outside of the yellow peach sample at the same time to accelerate the thawing process.

[0094] Step 4: The remaining mixed gas in the freezing chamber 2 enters the thawing chamber 1 again through the hose to precool the food during the next pretreatment.

[0095] Example 6

[0096] The device in Example 1 is applied to the freeze-thaw process of beef, and the specific method is as follows:

[0097] Step 1: Pre-process beef: Take fresh beef leg meat, remove irregular parts and excess fat and connective tissue, and then cut into square pieces of uniform size, each weighing about 125g;

[0098] The temperature is set to 4°C, and the controller starts the mixed gas tail gas to flow into the thawing chamber to achieve rapid precooling of the material. The controller turns on the vacuum pump to evacuate for 1 minute and then turns it off, opens the argon / krypton / xenon mixed gas valve, fills the cavity with argon / krypton / xenon mixed gas and pressurizes it to 0.02 MPa; maintains it for 20 minutes under the conditions of temperature 4°C, relative humidity 85%, and argon / krypton / xenon mixed gas relative pressure 0.02 MPa.

[0099] Step 2: Freezing food: First, the lifting assembly 4 moves the beef on the sample tray 6 to the freezing chamber 2, and the controller 10 starts the argon / krypton / xenon mixed gas combination injection assembly, so that the mixed gas composed of the argon / krypton / xenon mixed gas and liquid nitrogen enters the freezing chamber at a preset flow rate V1 until the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T1 in the controller 10, completing the first stage of the cooling process;

[0100] Secondly, the controller 10 increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the argon / krypton / xenon mixed gas combination injection assembly, and increases the input mixed gas velocity to V2, and when the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T2 in the controller 10, the second stage of quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed;

[0101] Finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the argon / krypton / xenon mixed gas combination injection assembly, and reduces the mixed gas flow rate in the input insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller 10, and then turns off the liquid nitrogen and argon / krypton / xenon mixed gas input, indicating that all materials in the freezing chamber 2 have been frozen.

[0102] Step three: thawing food: the lifting component 4 moves the food on the sample tray 6 to the thawing chamber 1, the controller 10 controls the input of argon / krypton / xenon mixed gas for pre-cooling, and adopts far-infrared radiation surface rapid heating and combined with electrostatic field method to accelerate the thawing of food. Under the protection of argon / krypton / xenon mixed gas, far-infrared radiation surface rapid heating combined with electrostatic field treatment is adopted. The far-infrared power used is 300W×4, the infrared working time is 80s, and the interval time is 50s; the electrostatic field intensity used is 30kV, and the electric field intensity acting on the sample is 3kV / cm; far-infrared surface radiation combined with electrostatic field treatment can act on the inside and outside of the beef sample at the same time to accelerate the thawing process. The temperature of the thawing chamber is adjusted to 4°C, and the thawing is completed when the center temperature of the sample drops to 0°C.

[0103] Step 4: The remaining mixed gas in the freezing chamber 2 enters the thawing chamber 1 again through the hose to precool the food during the next pretreatment.

[0104] Example 7

[0105] The device in Example 1 is applied to the freeze-thaw process of fish meat, and the specific method is as follows:

[0106] Step 1: Select a fresh hairtail fish weighing about 1kg as the test material. Remove the head, tail, and internal organs, and cut the middle into evenly-spaced sections, each 10cm long.

[0107] The temperature is set to 4°C, and the controller starts the mixed gas tail gas to flow into the thawing chamber to achieve rapid precooling of the material. The controller turns on the vacuum pump to evacuate for 1 minute and then turns it off, opens the argon / krypton / xenon mixed gas valve, fills the cavity with argon / krypton / xenon mixed gas and pressurizes it to 0.02 MPa; maintains it for 20 minutes under the conditions of temperature 4°C, relative humidity 85%, and argon / krypton / xenon mixed gas relative pressure 0.02 MPa.

[0108] Step 2: Freezing food: First, the lifting assembly 4 moves the fish on the sample tray 6 to the freezing chamber 2, and the controller 10 starts the argon / krypton / xenon mixed gas combination injection assembly, so that the mixed gas composed of the argon / krypton / xenon mixed gas and liquid nitrogen enters the freezing chamber at a preset flow rate V1 until the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T1 in the controller 10, completing the first stage of the cooling process;

[0109] Secondly, the controller 10 increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the argon / krypton / xenon mixed gas combination injection assembly, and increases the input mixed gas velocity to V2, and when the temperature value fed back by the second temperature sensor 14 reaches the preset temperature T2 in the controller 10, the second stage of quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed;

[0110] Finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the argon / krypton / xenon mixed gas combination injection assembly, and reduces the mixed gas flow rate in the input insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller 10, and then turns off the liquid nitrogen and argon / krypton / xenon mixed gas input, indicating that all materials in the freezing chamber 2 have been frozen.

[0111] Step three: thawing food: the lifting component 4 moves the food on the sample tray 6 to the thawing chamber 1, the controller 10 controls the input of argon / krypton / xenon mixed gas for pre-cooling, and adopts far-infrared radiation surface rapid heating and combined electrostatic field method to accelerate the thawing of food. Under the protection of argon / krypton / xenon mixed gas, far-infrared radiation surface rapid heating combined with electrostatic field treatment is adopted. The far-infrared power used is 300W×4, the infrared working time is 60s, and the interval time is 60s; the electrostatic field intensity used is 30kV, and the electric field intensity acting on the sample is 3kV / cm; far-infrared surface radiation combined with electrostatic field treatment can act on the inside and outside of the beef sample at the same time to accelerate the thawing process. The temperature of the thawing chamber is adjusted to 4°C, and the thawing is completed when the center temperature of the sample drops to 0°C.

[0112] Step 4: The remaining mixed gas in the freezing chamber 2 enters the thawing chamber 1 again through the hose to precool the food during the next pretreatment.

[0113] Comparative Example

[0114] Two control groups were set up with the food materials used in Examples 3, 4, 5, 6 and 7 and compared with the method of the present invention:

[0115] Control group (1): quick freezing in a -40℃ forced air freezer and natural thawing in a 4℃ cold air cabinet;

[0116] Control group (2): quick freezing in liquid nitrogen and natural thawing in a 4°C cold air cabinet;

[0117] The sample processing method and freezing and thawing temperature range are consistent with those of Example 3, Example 4, Example 5, Example 6, and Example 7.

[0118] Referring to Table 1, the freeze-thaw machine of the present invention can significantly reduce the freezing time (0 to -5°C) and freezing time (4 to -18°C) of five kinds of fresh foods, with significant differences. The freezing time (0 to -5°C) is the time it takes for the product to pass through the maximum ice crystal formation zone when it is frozen. A shorter time leads to the formation of smaller ice crystals, which helps to maintain the quality of frozen fresh foods. The freeze-thaw machine of the present invention can significantly shorten the thawing time (-18 to 0°C) of five kinds of fresh foods, with significant differences. Fresh foods frozen and thawed using the freeze-thaw machine of the present invention have less juice loss and better hardness.

[0119] Table 1 Effects of different freezing and thawing methods on the freezing and thawing characteristics of five fresh foods

[0120]

[0121]

[0122] Different lowercase letters after the same number indicate significant differences (P < 0.05)

[0123] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. An integrated freeze-thaw cycle device, characterized in that: It includes a freezing chamber, a thawing chamber, a lifting assembly, a temperature collection device, a controller, and an argon / krypton / xenon mixed gas combination injection assembly; The freezing chamber and the thawing chamber are vertically distributed up and down and connected by a hose; The lifting assembly is placed between the thawing chamber and the freezing chamber and can move freely. The lifting assembly is composed of a lifting device and a sample tray. The sample tray is connected to the lifting device by a sample tray rack. The controller is connected to the temperature acquisition device and the combined injection assembly; The combined injection assembly is connected to the freezing chamber, and the argon / krypton / xenon mixed gas combined injection assembly includes an argon / krypton / xenon mixed gas injection device, a liquid nitrogen injection device, an argon / krypton / xenon mixed gas dynamic ratio adjustment device, an air compressor, a pressure relief valve and a vacuum pump; the argon / krypton / xenon mixed gas injection device is also connected to the thawing chamber; The thawing chamber comprises a far infrared generating device, an electrostatic field device and a temperature control device; the far infrared generating device and the electrostatic field device are both provided with shielding and protection devices.

2. An integrated freeze-thaw cycle device according to claim 1, characterized in that: The sample tray is a mesh structure, and the material is polytetrafluoroethylene.

3. The integrated freeze-thaw cycle device according to claim 1, characterized in that: The sample tray frame is made of polytetrafluoroethylene.

4. The integrated freeze-thaw cycle device according to claim 1, characterized in that: The temperature acquisition device is connected to the lifting assembly, and includes a first temperature sensor and a second temperature sensor. The first temperature sensor is suspended in the air, and the second temperature sensor is connected to the sample tray. The second temperature sensor is composed of a 12-way food insertion temperature sensor and a 2.5mm silver-plated waterproof shielded wire.

5. The integrated freeze-thaw cycle device according to claim 1, characterized in that: The argon / krypton / xenon mixed gas injection device and the liquid nitrogen injection device are both provided with a nozzle, a flow control valve and an air intake insulation pipe.

6. The integrated freeze-thaw cycle device according to claim 1, characterized in that: The freezing chamber is provided with a rear fan and a rear insulation pipe, and the rear insulation pipe is connected to the external environment.

7. The integrated freeze-thaw cycle device according to claim 1, characterized in that: The far-infrared generating device comprises four far-infrared tubes, which are all laid on both sides of the inner wall of the thawing chamber, and the electrostatic field device is a thorn electrode plate.

8. The integrated freeze-thaw cycle device according to claim 1, characterized in that: The temperature control device comprises a heating plate and a refrigeration compressor, and the temperature control device is also connected to the controller.

9. Application of an integrated cycle freeze-thaw device as claimed in claim 1 in high-quality freeze-thaw of fresh food, characterized in that The application comprises the following steps: Step 1: pre-treating food materials by micro-pressurization: first, wash, peel, cut, blanch and protect the color of the food materials, then move the sample tray into the thawing chamber, place the sample on the sample tray, evacuate the entire thawing chamber by a vacuum pump, and introduce argon / krypton / xenon mixed gas with a relative pressure of 0 to 0.03 MPa into the thawing chamber by the mixed gas injection device, so as to achieve micro-pressurization treatment of fresh food materials with argon / krypton / xenon gas before freezing; Step 2: Dynamic quick freezing of food with mixed gas: First, the lifting component moves the food on the sample tray to the freezing chamber, and the controller activates the combined injection component to allow the mixed gas consisting of argon / krypton / xenon mixed gas and liquid nitrogen to enter the freezing chamber at a preset flow rate V1 until the temperature value fed back by the second temperature sensor reaches the preset temperature T1 in the controller, completing the first stage of the cooling process; Secondly, the controller increases the input amount of liquid nitrogen and argon / krypton / xenon mixed gas of the combined injection assembly, and increases the input mixed gas velocity to V2, and when the temperature value fed back by the second temperature sensor reaches the preset temperature T2 in the controller, the quick freezing process of crossing the maximum ice crystal formation zone of the sample is completed; finally, the controller reduces the input amount of liquid nitrogen and argon / krypton / xenon mixed gas valve of the combined injection assembly, and reduces the mixed gas velocity input into the insulation hose to V3, until the temperature value fed back by the second temperature sensor meets the material freezing temperature value preset in the controller, and then closes the input of liquid nitrogen and argon / krypton / xenon mixed gas, indicating that all materials in the freezing chamber have been frozen; Step 3: thawing food with argon / krypton / xenon protection: the lifting assembly moves the food on the sample tray to the thawing chamber, the controller controls the input of argon / krypton / xenon mixed gas for precooling and protection, and uses far-infrared radiation to quickly heat the surface and combine with an electrostatic field to accelerate the thawing process of the food; Step 4: The remaining mixed gas in the freezing chamber enters the thawing chamber through a hose to precool the food during the next pretreatment; Step 5: Freeze and thaw other ingredients: repeat the above steps 1 to 4 in a cycle.

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