Preparation method of sealed food

Abstract

The invention discloses a preparation method of sealed food, and belongs to the technical field of food processing. The preparation method of the sealed food provided by the invention comprises the following steps: S1, pre-packaging the food; s2, performing first-stage microwave sterilization; and S3, second-stage microwave sterilization. According to the invention, a two-stage microwave sterilization method is adopted, the arrangement of the exhaust component is combined, and the combined action of the thermal effect and the non-thermal effect of microwaves is utilized, so that the obtained sealed food can reach a commercial sterile state, and can be stored for a long time without deterioration under the conditions of normal temperature and no preservative; the heating intensity is low, the original sensory performance of the sealed food can be kept, and energy and cost are saved.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a method for preparing sealed food. Background Art

[0002] Foods such as livestock and poultry meat, aquatic meat, soy products and dairy products are rich in protein and other nutrients and are indispensable to people. Since protein-rich foods are nutritious, they are easily contaminated by microorganisms and go bad. In order to prevent protein-rich foods from going bad during storage, transportation and sales, the common methods for preserving protein-rich foods are:

[0003] (1) Protein-rich foods are placed in freezers at -20°C to +5°C and thawed when eaten. This requires a lot of energy to store and is inconvenient to transport, sell and store.

[0004] (2) The protein-rich food is made into traditional canned food. The process is as follows: the protein-rich food is pre-treated and seasoned, placed in a container, the air in the container is evacuated, the container is sealed, and then placed in a high-pressure steam cooker under high temperature (116°C to 130°C) and high steam pressure (1MPa to 2MPa) conditions, the temperature is maintained for 40 to 80 minutes, sterilized, and then cooled to room temperature. The entire sterilization process is a pressure vessel operation, which requires a boiler, a high-pressure steam transmission pipeline system, and a high-pressure cooking system. The investment is large, the heating energy consumption is high, and the impact on the environment is large. In addition, after such high-intensity heating and sterilization, the food has a large thermal denaturation, and the flavor and taste of the canned content are unsatisfactory.

[0005] (3) Using chemicals such as preservatives, sterilizers, acidifiers, and high salt content to treat protein-rich foods is an unwelcome but necessary practice.

[0006] (4) Made into dried meat or tofu food. However, the taste, flavor and texture are no longer the same as the original meat, and the nutritional value is greatly lost.

[0007] A method that can solve the above problems has not yet been found. Summary of the invention

[0008] In order to overcome at least one of the problems existing in the above-mentioned prior art, one of the objects of the present invention is to provide a method for preparing sealed food, which utilizes microwave sterilization technology to achieve effective sterilization and preservation of food without affecting the flavor and taste of the food.

[0009] A second object of the present invention is to provide a sealed food prepared by the above method.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A first aspect of the present invention provides a method for preparing a sealed food, comprising the following steps:

[0012] S1. Food pre-packaging: putting food into a storage container, wherein the storage container is provided with an exhaust component, the interior of the storage container is connected to the outside through the exhaust component, and the storage container is sealed except for the exhaust component to obtain pre-packaged food;

[0013] S2, first stage microwave sterilization: performing a first short section microwave sterilization on the pre-packaged food, heating to a first sterilization temperature, performing a first transition treatment, and then performing a second short section microwave sterilization, and then sealing the exhaust component of the storage container to obtain a first sterilized food;

[0014] The heating time of the first short section of microwave sterilization is 30 to 60 seconds; the first sterilization temperature is 100 to 102°C;

[0015] The first transition treatment does not involve microwave treatment; the first transition treatment lasts for 30 to 90 seconds;

[0016] The temperature of the second section of microwave sterilization is 98-100°C; the holding time of the second section of microwave sterilization is 3-4 minutes;

[0017] S3, second stage microwave sterilization: invert the first sterilized food, perform the third short section microwave sterilization, raise the temperature to the second sterilization temperature, perform the second transition treatment, and then perform the fourth short section microwave sterilization to obtain the sealed food;

[0018] The heating time of the third small section of microwave sterilization is 10 to 40 seconds; the third sterilization temperature is 90 to 96°C;

[0019] The second transition treatment does not involve microwave treatment; the second transition treatment lasts for 30 to 90 seconds;

[0020] The temperature of the fourth section of microwave sterilization is 88-94° C.; the insulation time of the fourth section of microwave sterilization is 2-8 minutes.

[0021] The inventive concept of the present invention is as follows:

[0022] First, regarding food pre-packaging, since the subsequent microwave sterilization will cause the food to heat up and generate steam, if the sealing devices are all sealed at this time, the storage container will burst. Therefore, an exhaust component is provided on the storage container, and during the first stage of microwave sterilization, the interior of the storage container is kept connected to the outside through the exhaust component, so that the steam generated by the food during the heating process can be discharged in time.

[0023] Secondly, regarding the first stage of microwave sterilization, the heating effect of microwaves on food is used to expand the air due to heat and discharge it from the sealing device. In addition, the moisture in the food content also produces water vapor, which squeezes out the air, and uses the dual effect to drive out the air in the device; and after the first stage of microwave sterilization, the exhaust component is sealed to form a fully sealed state, and a vacuum will be formed after cooling, so there is no need to add an additional vacuuming process. During the first stage of microwave sterilization, the moisture contained in the food is in a boiling state, and the boiling point temperature is easy to control, which is conducive to solving the problem of difficult control of microwave sterilization temperature; and the moisture is conducive to the generation of steam, so that the steam fills the entire canned container, so that the meat and the container are also heated evenly.

[0024] The first stage of microwave sterilization is divided into two sections. The first section of microwave sterilization is a short-term rapid heating. In a short period of time, the food has not yet reached a high temperature, but the microorganisms lose their activity in large quantities under the action of the strong microwave electric field, which increases the effect of the microwave non-thermal effect. In this way, the impact of heating on the taste of meat is greatly reduced; and the reduction of microwave sterilization heat is conducive to saving electricity, and the shortening of sterilization time is conducive to improving microwave sterilization efficiency. After reaching the first sterilization temperature, the food is slightly overheated and the heat distribution is uneven. If it continues to be overheated for a long time, the food will swell and explode. Therefore, the first transition treatment without microwave treatment is set up afterwards to redistribute the heat of the food evenly and slightly reduce the temperature before the second section of microwave sterilization.

[0025] Finally, regarding the second stage of microwave sterilization, turning the food upside down for the second stage of microwave sterilization is conducive to more uniform sterilization of various parts of the food. The second stage of microwave sterilization is also divided into two small sections. The third section of microwave sterilization is a short-term rapid heating. Since the temperature of the food drops after the exhaust port is sealed and the inversion process, it is first sterilized for a short time with a high-power strong microwave electric field. In order to make the heating uniform and prevent the food from swelling and bursting, a second transition treatment without microwave treatment is also set, and then the fourth section of microwave sterilization is carried out. The sterilization temperature of the second stage of microwave sterilization is lower than that of the first stage of microwave sterilization, mainly to prevent the thermal expansion of the food and the rupture of the container. The second stage of microwave sterilization is mainly to supplement the sterilization of the exhaust component area and the container, so that the sterilization is thorough and uniform, leaving no sterilization dead corners.

[0026] Preferably, the exhaust component comprises an exhaust port and a sealing component; the exhaust port is connected to the storage container, the sealing component is a movable component, and the sealing component is used to seal the exhaust port.

[0027] Since the steam is discharged from the container through the exhaust component, steam and condensed water will stay in the sealing area of ​​the exhaust component, which will affect the thermal sealing of the container at the exhaust component and cause leakage at the sealing. To solve this problem, the present invention preferably does not adopt the thermal sealing method, but sets the exhaust component as a movable block, and realizes the opening or sealing of the exhaust component by the combination of the exhaust port and the sealing component.

[0028] Preferably, the exhaust port is circular; further preferably, the diameter of the exhaust port is 5 to 30 mm.

[0029] The size of the exhaust port depends on the size of the storage container. If the diameter is too small, the exhaust effect cannot be achieved. If the diameter is too large, the steam is basically discharged from the container before filling the entire container, which will affect the sterilization effect. In addition, if the diameter is too large, the risk of re-contamination of microorganisms will increase.

[0030] Preferably, the sealing component includes at least one of a screw cap and a sealing plug; further preferably, the sealing component is selected from a screw cap.

[0031] Preferably, the sealing member is cylindrical; the shape of the sealing member matches the shape of the exhaust port; further preferably, the bottom surface diameter of the sealing member is 5 to 30 mm.

[0032] Preferably, in step S2, before sealing the exhaust component, the step further includes sterilizing the sealing component.

[0033] Preferably, the method of sterilizing the sealing component is selected from sterilizing agent treatment.

[0034] The sealing components are sterilized by a sterilizing agent, and the steam generated during the drying process serves as the ambient air when the sealing components are sealed, which greatly reduces the microorganisms in the sealed environment of the storage container.

[0035] Preferably, the sterilizing agent is selected from ozone water.

[0036] Preferably, the concentration of the sterilization agent is 0.1-1 mg / L; more preferably, 0.3-0.8 mg / L; more preferably, 0.5-0.6 mg / L.

[0037] Preferably, the sterilization agent treatment time is 1 to 10 minutes; more preferably, it is 1 to 3 minutes.

[0038] Preferably, the sterilization agent treatment is followed by drying; the drying temperature is 100-130°C; more preferably 110-120°C.

[0039] In some specific embodiments of the present invention, the step of sterilizing the sealing component is specifically: immersing the sealing component in a sterilizing agent and drying it. The immersion time is preferably 1 to 3 minutes; the drying temperature is preferably 110 to 120°C; and the drying method is preferably hot air drying. The steam generated by the ozone water during the drying process is used as the ambient air when the sealing component is sealed, so that the microorganisms in the sealed environment are greatly reduced, and then the excess ozone water vapor is discharged.

[0040] Preferably, the microwave frequencies of the first small section microwave sterilization, the second small section microwave sterilization, the third small section microwave sterilization and the fourth small section microwave sterilization are each independently selected from 850 to 2600 MHz; further preferably from 900 to 2500 MHz; further preferably from 915 to 2450 MHz.

[0041] Preferably, the food is a protein-rich food; further preferably, the food includes at least one of livestock and poultry meat, aquatic meat, soy products or dairy products.

[0042] Preferably, the storage container is made of at least one of glass, plastic or cardboard.

[0043] Preferably, in step S1, water is added to the storage container before sealing the storage container except the exhaust component; further preferably, the amount of water added is 3-10% of the mass of the food; further preferably, it is 5-8%.

[0044] Since the moisture in the food will boil and evaporate during the subsequent microwave sterilization, resulting in the loss of moisture in the food, in order to compensate for the loss of moisture in the food, this part of moisture is added in the pre-packaging stage.

[0045] The second aspect of the present invention provides a sealed food prepared by the preparation method as described in the first aspect of the present invention.

[0046] The beneficial effects of the present invention are as follows: the present invention adopts a two-stage microwave sterilization method, combined with the setting of the exhaust component, and utilizes the combined effect of the thermal effect and non-thermal effect of microwaves, so that the obtained sealed food can reach a commercially sterile state, and can be stored for a long time without deterioration at room temperature and without preservatives. In addition, due to the unique microwave sterilization method of the present invention, the heating intensity is low, the original sensory properties of the sealed food can be maintained, and energy and cost can be saved.

[0047] Specifically, compared with the prior art, the present invention has the following advantages:

[0048] 1. The present invention utilizes the combined effects of the thermal effect and non-thermal effect of microwaves. The microwave sterilization temperature of the two stages is between 88°C and 102°C, and the duration is less than 12 minutes, which is much smaller than the sterilization heating intensity of traditional canned food (116°C to 130°C, 40 minutes to 80 minutes). Therefore, the flavor and taste of meat will not be greatly affected by the microwave sterilization method of the present invention, and energy consumption can be greatly saved.

[0049] 2. The present invention uses a high-power strong microwave electric field to sterilize in a short time, so that microorganisms lose their activity in large quantities under the action of the strong microwave electric field, increasing the effect of microwave non-thermal effect, and the food has not yet reached a high temperature in a short time, thereby greatly reducing the impact of heating on the taste of meat. In addition, the present invention uses the first stage microwave sterilization, on the one hand, to make the air expand due to heat and run out of the container, and on the other hand, to make the moisture in the food produce water vapor to squeeze out the air. Based on the above dual effects, the air in the container is driven away, and a vacuum is formed after the container is sealed and cooled, thus forming a unique vacuum exhaust method.

[0050] 3. The entire microwave sterilization process of the present invention does not require external steam, boilers, high-pressure steam delivery pipeline systems and high-pressure cooking systems, thereby reducing project investment and daily operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The microwave sterilization process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The content of the present invention is further described in detail below through specific examples. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles set forth in the present invention all belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific data exemplified below. The raw materials, reagents or devices used in the following examples and comparative examples, unless otherwise specified, can all be obtained from conventional commercial sources, or can be obtained by existing known methods.

[0053] Terminology Note:

[0054] 1. Canned food (or canned food): Canned food is a sealed container made of metal sheet, glass, plastic, cardboard or a combination of some of the above materials. It contains commercial food that has been specially treated to achieve commercial sterility and can be kept at room temperature for a long time without spoiling. This type of packaged food is called canned food. Since metal containers affect the penetration of microwaves, the present invention does not include metal container cans.

[0055] 2. Exhaust of canned food: The purpose of exhaust is to remove the air in the canned container, greatly reduce oxygen, and form a vacuum state in the container to inhibit the growth of microorganisms; at the same time, it also reduces the interaction between the food in the container and oxygen, reduces the oxidation reaction of food, and maximizes the color, aroma and taste of food. The method of the present invention uses the heating effect of microwaves on food to make the air expand and run out of the container. In addition, the moisture in the contents also produces water vapor, which squeezes out the air. The dual effect drives away the air in the container. At this time, the container is sealed and a vacuum is formed after the can is cooled.

[0056] 3. Microwave sterilization: The microorganisms in food are subjected to the combined effects of "microwave thermal effect" and "microwave non-thermal effect", causing the proteins and physiological active substances in their bodies to mutate, leading to the delay of growth and development and death of the microorganisms, thus achieving the purpose of food sterilization and preservation.

[0057] Microwave thermal effect: Under the action of a certain intensity microwave electric field, the microorganisms in food will absorb microwave energy and heat up due to molecular polarization, thus causing their proteins to denature and lose their biological activity. The thermal effect of microwaves mainly plays a role in rapid heating and sterilization;

[0058] Microwave non-thermal effect: The high-frequency microwave electric field also changes the membrane potential and polar molecular structure of the microorganisms, causing the proteins and physiologically active substances in the microorganisms to mutate, resulting in loss of vitality or death. It plays a special role in sterilization that conventional physical sterilization does not have, and is also one of the causes of bacterial death.

[0059] Microwave sterilization is the result of the combined effect of microwave thermal effect and non-thermal effect. Therefore, the microwave sterilization temperature is lower than the conventional heating method. Under normal circumstances, the conventional method of sterilizing meat is at a temperature of 116-130°C, and the time is about 30 minutes to 80 minutes (depending on the shape and size of the can, the type of food, and the temperature of the can entering the sterilizer), while the microwave sterilization temperature only needs to be 70-103°C, and the total time is about 6-15 minutes. The use of microwave sterilization can greatly reduce the heating intensity.

[0060] 4. Commercial sterility: refers to the state in which food does not contain pathogenic microorganisms and non-pathogenic microorganisms that can reproduce in it at normal temperature after appropriate sterilization treatment. This state is the microbiological inspection indicator of the canning process, ensuring that during the normal commodity circulation and storage of food, residual microorganisms or spores cannot grow and reproduce, thereby not causing food spoilage or the production of toxins by pathogenic bacteria that affect human health. The commercial sterility state allows food to be stored at room temperature for a long time without the addition of preservatives. Commercial sterility is tested in accordance with "GB4789.26-2023 Food Microbiology Inspection Commercial Sterility Inspection".

[0061] In some embodiments of the present invention, the storage container is made of: a cooking bag or other high temperature resistant plastic bag, namely a "soft can" container, or a high temperature resistant container made of other non-metallic materials that do not affect microwave permeability.

[0062] In some embodiments of the present invention, the food is selected from foods rich in protein, including but not limited to livestock and poultry meat, aquatic meat, soy products and dairy products, and is semi-dry or liquid food. In some specific embodiments of the present invention, the food is selected from meat; more specifically pork.

[0063] In some embodiments of the present invention, a method for preparing a sealed food is provided, the flow chart of which is as follows: Figure 1 As shown, the specific steps include:

[0064] S1. Food pre-packaging: Put the processed and seasoned meat into the container. This is a special container with a small round exhaust port with a diameter of 5 to 30 mm and a screw-on sealing structure at the outlet. After the meat is put into the container, seal the other parts except the exhaust port first.

[0065] In step S1, steam is generated in the first stage of microwave sterilization. If the canned container is sealed at this time, the container will burst. Therefore, during the first stage of microwave sterilization, the container is not completely sealed, and an exhaust port is left to allow steam to be discharged out of the container through the exhaust port.

[0066] Steam and condensed water will stay in the sealing area of ​​the exhaust port, which will affect the thermal sealing between the plastic films of the exhaust port and cause leakage at the sealing point. In order to solve this problem, some specific embodiments of the present invention do not adopt the thermal sealing method, but make the exhaust port into a small cylindrical shape, and use a screw cap as a sealing component to seal the outlet end. The diameter of the screw cap seal is 5 to 30 mm, depending on the size of the canned container. If the diameter is too small, the exhaust effect cannot be achieved. If the diameter is too large, the steam will be basically discharged from the container before it fills the entire container, which will affect the sterilization effect. In addition, if the diameter is too large, the risk of re-contamination of microorganisms will increase.

[0067] In the subsequent first stage of microwave sterilization, the moisture in the meat is in a boiling state, and 5 to 8% of the moisture will evaporate. Therefore, in some specific embodiments of the present invention, before the meat is put into the container, 5 to 8% of the moisture of the food is added to the container.

[0068] S2. Microwave sterilization in the first stage: It is divided into two sections of microwave sterilization. The first section is a short-time sterilization with a high-power strong microwave electric field. When the meat enters the microwave sterilizer, the temperature rises rapidly from room temperature (30°C) to 100-102°C, which lasts for 30-60 seconds. At this time, the meat is slightly overheated, and the heat distribution is uneven. If it continues to be overheated for a long time, the meat will swell and burst. Therefore, a 1-minute transition time without microwaves is set afterwards to allow the heat of the meat to be redistributed evenly and the temperature to drop slightly. Then the second section of microwave sterilization is carried out, and the temperature is controlled at 98-100°C, which lasts for 3-4 minutes. The sterilization temperature is adjusted by microwave power, which depends on the type of food and the amount of food to be sterilized. The first stage of microwave sterilization turns a small amount of water into steam, which fills the entire canned container, so that the meat and the container are also heated evenly. Then, the steam and hot air are discharged from the exhaust port.

[0069] In step S2, the benefits of short-time sterilization with a high-power strong microwave electric field include: 1) In a short period of time, the meat food has not yet reached a high temperature, but the microorganisms lose their activity in large quantities under the action of the strong microwave electric field, that is, the effect of the microwave non-thermal effect is increased. In this way, the impact of heating on the taste of meat is greatly reduced. 2) The reduction of microwave sterilization heat saves electrical energy. 3) The sterilization time is shortened, which improves the efficiency of microwave sterilization.

[0070] The first stage of microwave sterilization has the following advantages: the moisture in the meat is in a boiling state, and the boiling point temperature is easy to control, thus solving the problem of difficult control of microwave sterilization temperature; the moisture in the meat is in a boiling state, which will cause the meat and its juice to produce steam, allowing the steam to fill the entire canned container, so that the meat and the container are heated evenly; a highly efficient heating and air exhaust effect is formed to expel the air in the container, reducing the risk of canned meat being oxidized by the reaction with oxygen in the air, and at the same time, inhibiting the growth of microorganisms without the need for an additional vacuuming process.

[0071] S3. Sealing of exhaust port: After the first stage of microwave sterilization, the exhaust port is immediately sealed; the exhaust port is sealed with a screw cap. The screw cap is first soaked in ozone water with a concentration of 0.5-0.6 mg / L for 1-3 minutes, and then the ozone water on the surface of the cap is blown dry with 110-120℃ hot air. The steam generated by the ozone water during the drying process is used as the ambient air when the cap is sealed, which greatly reduces the microorganisms in the sealed environment and discharges the excess ozone water vapor in time.

[0072] S4, inversion process: turn the bottom of the can upside down and then carry out the second stage of microwave sterilization. Inverting the can can make the sterilization of all parts of the can more uniform.

[0073] S5. Second stage microwave sterilization: divided into two small sections of microwave sterilization. The third section of microwave sterilization: the temperature of meat drops after the exhaust port is sealed and the can is turned upside down. First, use a high-power strong microwave electric field for a short time to sterilize. In 10 to 40 seconds, the sterilization temperature rises to 90 to 96°C; then set a 1-minute transition time without microwaves; the fourth section of microwave sterilization: maintain the temperature at 88 to 94°C for 2 to 8 minutes, and use microwave power to adjust the sterilization temperature. The sterilization temperature at this stage is lower than that of the first stage of microwave sterilization, mainly to prevent the can from rupturing the container due to excessive thermal expansion.

[0074] The present invention is further described below in conjunction with more specific embodiments and comparative examples.

[0075] The embodiments and comparative examples of the present invention use pork chops for microwave sterilization at a microwave sterilization frequency of 2450 MHz. During the production of pork chops, no substances that inhibit microorganisms, such as condiments containing preservatives or acidic substances, are added to avoid these substances interfering with the test results.

[0076] Example 1

[0077] This embodiment provides a method for microwave sterilization of pork chops, comprising the following steps:

[0078] (1) Food pre-packaging: 176 grams of pork chop and 20 grams of sauce are placed in a retort bag. The thickness of the entire package is controlled to be no more than 40 mm to ensure that microwaves can penetrate the entire package smoothly. The retort bag has a small round exhaust port with a diameter of 8.5 mm and a screw-on sealing structure at the outlet. After the pork chop is placed in the bag, the other parts except the exhaust port are sealed first. This pork chop package is hereinafter referred to as a pork chop bag.

[0079] (2) The first stage of microwave sterilization: It is divided into two small sections. In the first section, the temperature of the pork chop bag is controlled at 30℃ when it enters the microwave sterilizer, and it is sterilized by high-power microwaves, and the temperature is quickly raised to 100-102℃ for 30 seconds; then the pork chop bag is stopped for 1 minute; then, the second section of microwave sterilization is carried out, and the temperature is controlled at 98-100℃ for 4 minutes; the sterilization temperature is adjusted by the microwave power.

[0080] The first stage of microwave sterilization converts a small amount of water into steam, which fills the entire pork chop bag, allowing the pork chop and the steaming bag to be heated evenly. Then, the steam and hot air are discharged from the exhaust port.

[0081] When using a tunnel-type microwave sterilizer for sterilization, the conveyor belt speed should be stable, and the pork chop packages should be lined up to enter the sterilizer to ensure uniform microwave sterilization.

[0082] (3) Sealing of exhaust port: After the first stage of microwave sterilization, the exhaust port is immediately sealed; the exhaust port is sealed with a screw cap. The screw cap is first soaked in ozone water. The concentration of ozone water is 0.5 mg / L, soaked for 2 minutes, and then the ozone water on the surface of the cap is blown dry with 120℃ hot air; the steam generated by the ozone water during the drying process is used as the ambient air when the cap is sealed, which greatly reduces the microorganisms in the sealed environment. Excess ozone water vapor is discharged in time. The exhaust port is sealed by a screw cap sealing machine.

[0083] (4) Inversion: Turn the bottom of the pork chop bun over and then perform the second stage of microwave sterilization. Inversion can make the sterilization of each part of the pork chop bun more uniform.

[0084] (5) Second stage microwave sterilization: divided into two small sections of microwave sterilization. The first section of microwave sterilization: the temperature of the pork chop bag drops after the "exhaust port sealing" and "inversion" processes. First, use a high-power strong microwave electric field for a short time for microwave sterilization. In 10 to 15 seconds, the sterilization temperature rises to 92 to 94°C; then the pork chop bag stops microwave sterilization for 1 minute; the second section of microwave sterilization: maintain the temperature at 90 to 92°C for 6 minutes, and use microwave power to adjust the sterilization temperature. The sterilization temperature of this stage is lower than that of the first stage of microwave sterilization to prevent the pork chop bag from excessive thermal expansion and rupture; at this time, it is normal for the entire pork chop bag to expand slightly. Then slowly cool down to below 40°C and leave the conveyor belt. When it drops to room temperature, a vacuum is formed in the pork chop bag. The final average net weight of the pork chop bag is 180 grams per bag, and about 16 grams of water is evaporated per bag.

[0085] Example 2

[0086] This example provides a method for microwave sterilization of pork chops, which differs from Example 1 in that: in step (3), the cap is not immersed in ozone water, in order to test the microwave sterilization capability of the second stage. The remaining steps are the same as those of Example 1.

[0087] Comparative Example 1

[0088] This example provides a method for microwave sterilization of pork chops, comprising the following steps:

[0089] (1) Food pre-packaging: 176g pork chop and 20g sauce are placed in a retort bag. This pork chop package is referred to as a pork chop bag. The thickness of the entire package is controlled to be no greater than 40mm to ensure that microwaves can penetrate the entire package smoothly. The bag opening where the pork chop is placed, i.e. the feed opening, is not sealed temporarily and is used as an exhaust port. No small round exhaust port is provided (this is the purpose 1 of the process arrangement in this example).

[0090] (2) First stage microwave sterilization: When the pork chop enters the microwave sterilizer, the temperature is controlled at 30°C, then raised to 94-96°C in 2-3 minutes, and then maintained for 16 minutes, and the sterilization temperature is adjusted by microwave power. (Compared with Example 1, this example does not have a high-power strong magnetic field and short-time microwave sterilization, but relies on extending the sterilization time to increase the sterilization intensity, but the sterilization time cannot be too long to avoid long-term heating affecting the flavor and taste of the pork chop.)

[0091] In this stage, the sterilization time is extended a lot, but the sterilization temperature is lowered, less steam is generated, and there is less condensation water in the heat-sealed areas between the plastic films at the exhaust port, which is conducive to the heat-sealed areas between the plastic films. (This is the purpose of the process arrangement in this case 2)

[0092] When using a tunnel-type microwave sterilizer for sterilization, the conveyor belt speed should be stable, and the pork chop packages should be lined up to enter the sterilizer to ensure uniform microwave sterilization.

[0093] The first stage of microwave sterilization also has a slight degassing effect.

[0094] (6) Sealing of exhaust port: Use thermal sealing method to seal the feed port. (Since there is no screw capping of the exhaust port, the process of screw capping and soaking in ozone water is omitted, which is the purpose of the process arrangement in this example 3)

[0095] (7) Inversion: Turn the bottom of the pork chop bun over and then perform the second stage of microwave sterilization. Inversion can make the sterilization of each part of the pork chop bun more uniform.

[0096] (8) Second stage microwave sterilization: It is divided into two small sections of microwave sterilization. The first section of microwave sterilization: the temperature of the pork chop bag drops after the "exhaust port sealing" and "inversion" processes. First, a high-power strong magnetic field is used for short-term microwave sterilization. In 10 to 15 seconds, the sterilization temperature rises to 92 to 94°C; then the pork chop bag stops microwave sterilization for 1 minute; the second section of microwave sterilization: the temperature is maintained at 90 to 92°C for 6 minutes, and the microwave power is used to adjust the sterilization temperature. The sterilization temperature of this stage is lower than that of the first stage of microwave sterilization to prevent the pork chop bag from excessive thermal expansion and rupture; at this time, it is normal for the entire pork chop bag to expand slightly. Then slowly cool down to below 40°C and leave the conveyor belt. When the product drops to room temperature, a small amount of vacuum has been formed in the pork chop bag. The final average net weight of the pork chop bag is 192 grams per bag, and about 4 grams of water is evaporated per bag.

[0097] Comparative Example 2

[0098] Since the microwave sterilization method is similar to the traditional canning sterilization method, they are comparable. The pork chops in this example are made by using the traditional canning sterilization process, and then compared with the microwave sterilized pork chops to analyze their results. This example provides a traditional canning sterilization method for pork chops, including the following steps:

[0099] (1) Food pre-packaging: 176g pork chop and 20g sauce are placed in a retort bag. The retort bag has a small round vent with a diameter of 8.5mm and a screw-on sealing structure at the outlet. After the pork chop is placed in the bag, seal the rest of the bag except the vent. This package is hereinafter referred to as a pork chop bag.

[0100] (2) Exhaust: The pork chop buns are steamed in an exhaust box for 12 minutes to make the center temperature of the pork chop buns reach above 85°C so that the air in the pork chop buns can be exhausted.

[0101] (3) Sealing the exhaust port: After the exhaust process is completed, use a capping machine to screw the cap into the exhaust port and seal it tightly. (Due to post-high temperature sterilization, a small amount of microorganisms are allowed to exist in the capping, and no aseptic operation such as soaking in ozone water is required.)

[0102] (4) Put the pork chop bag into a high pressure steam cooker, keep the temperature for 50 minutes under the circulation of hot water at 121°C for sterilization, then cool it down to 40°C and take it out. During the heating, sterilization and cooling process, a certain amount of hot air must be added into the high pressure steam cooker to ensure that the pressure inside and outside the pork chop bag is balanced in order to prevent the pork chop bag from bursting due to heat.

[0103] (5) The pork chop buns were then cooled to room temperature. When the product dropped to room temperature, a small amount of vacuum was formed inside the pork chop buns. The final average net weight of the pork chop buns was 197 grams per bun. (During the exhaust process, a small amount of external steam entered the buns, forming water droplets, so the total net weight increased slightly)

[0104] Sample inspection

[0105] The pork chop buns prepared in Examples 1-2 and Comparative Examples 1-2 (hereinafter referred to as samples) were placed in an incubator at 36°C ± 1°C for 90 days, and the samples were observed and tested.

[0106] (1) For the swollen samples, pick them out in time and directly judge them as "non-commercially sterile" according to the national standard GB4789.26-2023, 5.3.3, and count the number. (Note: If there are living microorganisms in the pork chop bag, these microorganisms will grow and produce gas, and the gas will accumulate in the pork chop bag to cause swelling. Even if the cooking bag leaks, the leakage hole will be blocked by liquid or tiny contents, and the gas will still not escape, and it will still swell.)

[0107] (2) For the inspection of vacuum samples: After being stored in an incubator at 36°C ± 1°C for 90 days, take samples of 10% of the total amount of vacuum samples for commercial sterility inspection, and count the number of "commercial sterile" samples and the number of "non-commercial sterile" samples.

[0108] (3) Sensory comparison of commercial sterile samples in each example: After all samples were stored for 90 days, one package of commercial sterile samples was taken in each example for sensory inspection, comparison, and recording.

[0109] (4) Two packages of vacuum samples were randomly selected from the samples in Example 1 and commissioned to Guangzhou Inspection and Certification Group Co., Ltd. (a third party) to conduct commercial sterility testing in accordance with GB4789.26-2023. The test results were: commercial sterility.

[0110] The test results of the above samples are statistically shown in Table 1.

[0111] Table 1 Statistical table of test results of examples and comparative examples

[0112]

[0113] Result analysis:

[0114] (1) The sample prepared in Example 1 was not non-commercially sterile, and had a vacuum and no leakage. This was due to the use of high-power strong microwave electric field for short-time sterilization and other technical measures. The sample tasted good and maintained the original flavor of the pork chop. This technical solution is feasible.

[0115] (2) The screw cap of Example 2 was not immersed in ozone water. Although there was a second stage of microwave sterilization, a small amount of non-commercial sterile samples still existed, indicating that it was necessary to immerse the screw cap in ozone water. However, compared with Comparative Example 1, the method of Example 3 can obtain a good taste while keeping the number of leakage samples small, which is not achievable by traditional sterilization methods.

[0116] (3) Comparative Example 1 does not have a small round exhaust port, but directly exhausts the air from the side of the cooking bag feed port. After exhausting the air, the plastic films at the exhaust port are thermally sealed. The commercial sterile sample obtained by this method has a good taste and can maintain the original flavor of the pork chop. However, in order to avoid contamination of a large number of water droplets on the sealing edge, Comparative Example 1 had to reduce the microwave sterilization temperature in the first stage to reduce water evaporation. In order to compensate for the insufficient sterilization intensity, the sterilization time had to be greatly extended, but the number of leaking and swollen samples was still relatively large. Compared with Example 1, Comparative Example 1 adopts a thermal sealing method. Due to slight water droplets on the sealing edge, some samples will leak. Therefore, the thermal sealing quality between the plastic films at the exhaust port is not as good as the screw cap sealing method adopted in Example 1.

[0117] (4) Comparative Example 2 uses a traditional canning sterilization process, which is mature in technology. The obtained samples are not non-commercially sterile and have vacuum and no leakage. However, since the pork chop is subjected to 12 minutes of steam heating and exhaust and 50 minutes of high-pressure cooking at 121°C for sterilization, its sensory properties are significantly deteriorated and the amount of heat energy used is also high.

[0118] The above experimental results show that the method provided by the embodiment of the present invention has a good sterilization effect, the obtained sample has a good sterilization effect, the heating intensity is low, the original sensory organoleptic properties of the meat food can be basically maintained, energy is saved, and the cost is low; in particular, the method of Example 1 can fully meet the requirements of commercial sterility, and has little effect on the sensory properties of the sample such as color, smell, taste and mouthfeel.

[0119] The embodiment of the present invention utilizes the combined effect of the thermal effect and the non-thermal effect of microwaves. The microwave sterilization temperature of the two stages is between 88°C and 102°C, and the duration is less than 12 minutes, which is much smaller than the sterilization heating intensity of traditional cans (116°C to 130°C, 40 minutes to 80 minutes). Therefore, the flavor and taste of meat will not be greatly affected by the microwave sterilization method of the present invention, and energy consumption is greatly saved. The embodiment of the present invention adopts a high-power strong microwave electric field for short-time sterilization, so that microorganisms lose their activity in large quantities under the action of the strong microwave electric field, and the effect of the microwave non-thermal effect is increased. In a short time, the food has not yet been able to rise to a high temperature, thereby greatly reducing the effect of heating on the taste of meat. In addition, the embodiment of the present invention utilizes the first stage of microwave sterilization, which, on the one hand, causes the air to expand due to heat and run out of the container, and on the other hand, causes the moisture in the food to generate water vapor and squeeze out the air. Based on the above dual effects, the air in the container is driven away, and a vacuum is formed after the container is sealed and cooled, thereby forming a unique vacuum exhaust method. The entire microwave sterilization process of the present invention does not require external steam, boilers, high-pressure steam delivery pipeline systems and high-pressure cooking systems, thereby reducing project investment and daily operating costs.

[0120] In summary, the present invention adopts a two-stage microwave sterilization method, combined with the setting of the exhaust component, and utilizes the combined effect of the thermal effect and non-thermal effect of microwaves. The obtained sealed food can reach a commercially sterile state. It can be stored for a long time without deterioration at room temperature and without preservatives. In addition, due to the unique microwave sterilization method of the present invention, the heating intensity is low, which can maintain the original sensory properties of the sealed food and save energy and cost.

Claims

1. A method for preparing a sealed food, characterized in that: The following steps are involved: S1. Food pre-packaging: putting food into a storage container, wherein the storage container is provided with an exhaust component, the interior of the storage container is connected to the outside through the exhaust component, and the other parts of the storage container except the exhaust component are sealed to obtain pre-packaged food; S2, first stage microwave sterilization: performing a first short section microwave sterilization on the pre-packaged food, heating to a first sterilization temperature, performing a first transition treatment, and then performing a second short section microwave sterilization, and then sealing the exhaust component of the storage container to obtain a first sterilized food; The heating time of the first short section of microwave sterilization is 30 to 60 seconds; the first sterilization temperature is 100 to 102°C; The first transition treatment does not involve microwave treatment; the first transition treatment lasts for 30 to 90 seconds; The temperature of the second section of microwave sterilization is 98-100°C; the holding time of the second section of microwave sterilization is 3-4 minutes; S3, second stage microwave sterilization: invert the first sterilized food, perform the third short section microwave sterilization, raise the temperature to the second sterilization temperature, perform the second transition treatment, and then perform the fourth short section microwave sterilization to obtain the sealed food; The heating time of the third small section of microwave sterilization is 10 to 40 seconds; the third sterilization temperature is 90 to 96°C; The second transition treatment does not involve microwave treatment; the second transition treatment lasts for 30 to 90 seconds; The temperature of the fourth section of microwave sterilization is 88-94° C.; the insulation time of the fourth section of microwave sterilization is 2-8 minutes.

2. The preparation method according to claim 1, characterized in that: The exhaust component comprises an exhaust port and a sealing component; the exhaust port is connected to the storage container, the sealing component is a movable component, and the sealing component is used to seal the exhaust port.

3. The preparation method according to claim 2, characterized in that: The exhaust port is circular; the diameter of the exhaust port is 5 to 30 mm.

4. The preparation method according to claim 2, characterized in that: In step S2, before sealing the exhaust component, the sealing component is sterilized.

5. The preparation method according to claim 4, characterized in that: The method of sterilizing the sealing component is selected from sterilizing agent treatment.

6. The preparation method according to claim 5, characterized in that: The sterilizing agent is selected from ozone water; and / or the concentration of the sterilizing agent is 0.1-1 mg / L.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The microwave frequencies of the first small section microwave sterilization, the second small section microwave sterilization, the third small section microwave sterilization, and the fourth small section microwave sterilization are each independently selected from 850 to 2600 MHz.

8. The preparation method according to any one of claims 1 to 6, characterized in that: The food is a food rich in protein; Preferably, the food comprises at least one of livestock and poultry meat, aquatic meat, soy products or dairy products.

9. The preparation method according to any one of claims 1 to 6, characterized in that: The material of the storage container includes at least one of glass, plastic or cardboard.

10. A sealed food prepared by the preparation method according to any one of claims 1 to 9.

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