High-temperature steam sterilization method for large-caliber aluminum two-piece can canned food

Abstract

The invention discloses a high-temperature steam sterilization method for large-caliber aluminum two-piece can canned food. High-temperature steam is adopted for sterilization, and the sterilization process comprises a stepped heating process, a constant-pressure and constant-temperature sterilization process and a stepped depressurization and cooling process. The stepped heating, depressurization and cooling process comprises a plurality of different heating and cooling stages, and the pressure in the kettle needs to be adjusted according to the temperatures of different stages to control the pressure difference between the inside and the outside of the can. Compared with the prior art, the problems that large-caliber (1068 and 1070 can types) aluminum two-piece can canned food is flat in the sterilization process, and the can cover and the can bottom have convex corners can be thoroughly solved.

Description

Technical Field

[0001] This invention relates to the field of food sterilization technology, specifically to a high-temperature steam sterilization method for food packaged in large-diameter (1068, 1070 can type) aluminum two-piece cans, which can avoid the occurrence of can collapse, can expansion, and convex corners. Background Technology

[0002] Currently, large-diameter (1068, 1070 mm) aluminum two-piece cans commonly used in the food industry are prone to problems such as can denting, swelling, bulging corners, and can deformation during sterilization. Existing sterilization methods often refer to those for tinplate cans, because the pressure resistance limit of large-diameter (1068, 1070 mm) aluminum two-piece cans is much lower than that of tinplate cans. During the heating process, the pressure inside the sterilizer increases with the rise in temperature. However, due to the heat exchange time inside the tank, the temperature rises much slower than that inside the sterilizer. Therefore, when the pressure inside the sterilizer increases rapidly, the pressure inside the tank does not change significantly, resulting in a pressure difference between the sterilizer and the tank. When this pressure difference exceeds the deformation pressure of the tank, problems such as tank collapse are likely to occur. During the cooling process, cold water is injected into the sterilizer. The unsaturated water vapor inside the sterilizer liquefies due to the temperature drop, causing a rapid decrease in pressure inside the sterilizer. However, due to the heat exchange time inside the tank, the temperature drops much slower than that inside the sterilizer. Therefore, when the pressure inside the sterilizer decreases rapidly, the pressure inside the tank does not change significantly, resulting in a pressure difference between the sterilizer and the tank. When this pressure difference exceeds the deformation pressure of the tank, problems such as tank expansion are likely to occur. In addition, the 1068 type aluminum two-piece cans are large in volume, and when using tin cans for food sterilization, the cans often have problems such as dents or bulging corners on the bottom and lid, resulting in a low pass rate for canned products. Summary of the Invention

[0003] The present invention aims to overcome the shortcomings of the prior art and solve the problems existing in the existing sterilization methods for large-diameter canned food, and provides a sterilization method for food packaged in large-diameter two-piece aluminum cans.

[0004] The sterilization method for large-diameter aluminum two-piece canned food provided by the present invention is to use high-temperature steam sterilization. The sterilization process includes a stepped heating process, a constant pressure and constant temperature sterilization process, and a stepped pressure and temperature reduction process.

[0005] The stepped heating process includes several heating stages, and the pressure difference between the inside and outside of the container is reduced by adjusting the temperature rise time of different stages.

[0006] The stepped depressurization and cooling process includes several cooling stages, and the pressure inside the vessel is adjusted according to the temperature of different stages to control the pressure difference between the inside and outside of the can.

[0007] Furthermore, during the same heating or cooling phase, the magnitude and rate of change of air pressure are positively correlated with the magnitude and rate of change of temperature.

[0008] Furthermore, the magnitude and rate of change of air pressure during each heating or cooling stage are positively correlated with the magnitude and rate of change of temperature.

[0009] That is, the magnitude and rate of change of air pressure increase with the magnitude and rate of change of temperature, and vice versa.

[0010] The large-diameter aluminum two-piece can is of type 1068 or 1070.

[0011] Furthermore, the tank is a 1068 type aluminum two-piece tank, and the pressure difference between the sterilization autoclave and the tank is between -0.08 MPa and 0.069 MPa.

[0012] Furthermore, the tank body is a 1068 type aluminum two-piece tank, the constant pressure and temperature sterilization pressure is the saturated vapor pressure of 0.106 MPa, and the sterilization time is the time it takes for the contents to reach commercial sterility.

[0013] Furthermore, the deformation pressure value of the 1068 type aluminum two-piece can is -0.08Mpa to 0.069Mpa.

[0014] Furthermore, the stepped heating process includes two stages of pressure and temperature increase:

[0015] Heating stage 1: The temperature of the sterilization autoclave is raised to 95-100℃, the pressure is saturated vapor pressure, and the heating time is 10-30 minutes;

[0016] Stage 2: The autoclave temperature is raised to the sterilization temperature (e.g., 121℃), the pressure is saturated vapor pressure, and the heating time is 15 minutes.

[0017] Furthermore, the constant pressure and constant temperature sterilization process is as follows: sterilization is carried out at the sterilization temperature until the canned food reaches commercial sterility, and then it is cooled by back pressure.

[0018] Furthermore, the stepped depressurization and cooling process includes three depressurization and cooling stages:

[0019] Cooling stage one: The temperature of the sterilization vessel is reduced from 121℃ to 108~112℃, the constant pressure is 0.101~0.106Mpa, and the cooling time is 30~60s;

[0020] Cooling stage two: The temperature of the sterilization autoclave is reduced from 108-112℃ to 95-100℃, the constant pressure is 0.04-0.06 MPa, and the cooling time is 3-4 minutes;

[0021] Cooling stage three: The temperature of the sterilization autoclave is reduced from 95-100℃ to 25-35℃, the constant pressure is 0 MPa, and the cooling time is 15-20 minutes.

[0022] The sterilization process for the aforementioned large-diameter aluminum two-piece canned food is as follows: The large-diameter aluminum two-piece canned food is placed into the sterilizer, and high-temperature steam is introduced into the sterilizer for a stepped heating process: the temperature inside the sterilizer is raised to 95-100℃ in 10-30 minutes, and then raised to 121℃ in another 15 minutes; when both the temperature inside the sterilizer and the cold point temperature of the can reach the sterilization temperature, constant-temperature sterilization is performed, with the temperature reaching the sterilization temperature in 25-45 minutes (the total time of heating stage one and heating stage two); after achieving commercial sterilization at constant temperature, a stepped cooling process using back pressure is employed: first, cold water is injected into the sterilizer (gradually reducing the temperature inside the sterilizer to 108-112℃), while... Inject compressed air to increase the pressure inside the vessel (this pressure is called back pressure), maintaining the pressure inside the vessel at 0.101–0.106 MPa for 30–60 seconds. Continue injecting cold water into the vessel (gradually reducing the temperature inside the vessel to 95–100°C), while simultaneously injecting compressed air to increase the pressure inside the vessel, maintaining the pressure inside the vessel at 0.04–0.06 MPa, ensuring that the pressure difference between the vessel and the tank remains within the critical deformation value of the tank. Maintain this stage for 1–3 minutes. Continue injecting cold water into the vessel, stop injecting compressed air, and open the drain valve and exhaust valve to gradually reduce the pressure inside the vessel to 0 MPa and the temperature to 25–35°C. Maintain this stage for 15–20 minutes.

[0023] The advantage of this invention is that it can completely solve the problems of dented cans, convex corners of can lids and can bottoms that occur during the sterilization process of large-diameter (1068, 1070 can types) aluminum two-piece cans for food packaging. Attached Figure Description

[0024] Figure 1 The image shows the convex corner of an aluminum can after a conventional tin can sterilization process (heating to 100℃, venting for 8 minutes, then heating to sterilization temperature of 121℃, constant temperature sterilization for 80 minutes, and cooling to 40℃).

[0025] Figure 2 This is a diagram of the convex corner of the bottom of an aluminum can after a conventional tinplate can sterilization process (heating to 100℃, venting for 8 minutes, then heating to sterilization temperature of 121℃, sterilizing at a constant temperature for 80 minutes, and cooling to 40℃).

[0026] Figure 3 This is a diagram showing the intact, easy-to-open aluminum can after the sterilization process in Embodiment 1 of the present invention.

[0027] Figure 4 This is a diagram showing the intact bottom of an aluminum can after the sterilization process in Embodiment 1 of the present invention. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0030] This invention discloses a high-temperature steam sterilization method for large-diameter aluminum two-piece cans containing food, employing steam sterilization and back-pressure cooling. The sterilization process includes stepped heating, constant pressure and temperature sterilization, and stepped depressurization and cooling. Each of the stepped heating and depressurization / cooling processes includes multiple different heating stages and multiple different cooling stages. The internal pressure needs to be adjusted according to the temperature at different stages to control the pressure difference between the inside and outside of the can. During the same heating stage, the magnitude and rate of change of gas pressure are positively correlated with the magnitude and rate of change of temperature; that is, the magnitude and rate of change of gas pressure increase with increasing temperature and rate of change, and vice versa. Furthermore, the magnitude and rate of change of gas pressure during each heating stage are positively correlated with the magnitude and rate of change of temperature; that is, the gas pressure is higher during stages with higher temperatures and lower during stages with lower temperatures. The canned goods are placed in a sterilizing autoclave, and high-temperature steam is introduced into the autoclave to heat and sterilize the cans. Once the temperature inside the autoclave and the cold point temperature of the cans both reach the sterilization temperature, constant-temperature sterilization is performed. A heating time of 25–45 minutes to reach the sterilization temperature is suitable. The constant-temperature sterilization time depends on the type of contents and the type of sterilization, generally ranging from 10 to 90 minutes, with commercial sterility as the standard. A stepped depressurization and cooling stage is then employed: after constant-temperature sterilization, a step-down cooling method using back pressure is used. First, cold water is injected into the autoclave, and simultaneously, compressed air is introduced to increase the pressure inside the autoclave (this pressure is called back pressure), maintaining the pressure inside the autoclave at 0.101–0.106 MPa. The purpose of the back pressure is to replenish the cold water injected into the autoclave. The instantaneous pressure drop caused by internal steam condensation keeps the pressure difference between the vessel and the tank within the critical deformation limit of the tank, preventing tank collapse and convex corners. This stage is maintained for 30-60 seconds. Cold water is then continuously injected into the vessel while compressed air is introduced to increase the pressure inside the vessel (this pressure is called back pressure), maintaining the pressure inside the vessel at 0.04-0.06 MPa. This keeps the pressure difference between the vessel and the tank within the critical deformation limit of the tank, preventing tank collapse and convex corners. This stage is maintained for 1-3 minutes. Cold water is then continuously injected into the vessel, and the introduction of compressed air is stopped. The drain valve and exhaust valve are opened to gradually reduce the pressure inside the vessel to 0 MPa and the temperature to 25-35°C. This stage is maintained for 15-20 minutes.

[0031] Using the above-mentioned stepped heating method to heat the canned goods can effectively prevent the cans from collapsing. The reason is as follows: the temperature rise rate inside the can is always slower than the temperature rise rate inside the sterilizer, especially when steam is initially added for heating. The temperature rise rate inside the sterilizer is faster and the pressure rises rapidly, while the pressure inside the can remains almost constant. Therefore, stepped heating is required. The temperature inside the sterilizer is raised to 95-100℃ in the first 10-30 minutes, and then raised to 121℃ in the next 15 minutes. Heating the can in stages ensures that the pressure difference between the sterilizer and the can remains within the critical value for deformation in each heating stage, preventing the can from deforming.

[0032] The above-mentioned stepped pressure and temperature reduction method for cooling canned goods can effectively prevent can deformation. The reasons are as follows: the temperature inside the can decreases more slowly than the temperature inside the sterilizer, especially in the initial 6 minutes of filling with cold water. During the first 3 minutes, the temperature and pressure inside the can remain almost constant at the sterilization temperature and pressure, while the pressure inside the sterilizer drops sharply. Therefore, compressed gas needs to be injected at the same time as cold water to increase the pressure inside the sterilizer. The pressure is maintained at the constant temperature sterilization stage for the first minute of cooling. After 4-5 minutes of cooling, the temperature inside the can gradually decreases. The amount of compressed gas injected is controlled to allow the pressure inside the sterilizer to slowly decrease to 0.04-0.06 MPa within 1-3 minutes. After 5-6 minutes of cooling, the cold spot temperature inside the can gradually decreases. After 15-20 minutes, the pressure inside the can basically reach 0 MPa. The amount of compressed gas injected is reduced, and the drain valve is opened to keep the pressure difference between the sterilizer and the can within the can deformation limit range, thus preventing can deformation.

[0033] This invention employs a high-temperature steam sterilization method. During the heating process, steam is directly introduced, causing the temperature and pressure inside the sterilizer to rise rapidly. The temperature inside the tank, heated more slowly by convection heat transfer, leading to a pressure difference between the sterilizer and the tank, potentially causing the tank to collapse. A stepped pressurization and heating process, controlling the heating time according to the different contents, slows the pressure rise within the sterilizer, stabilizing the pressure difference between the sterilizer and the tank and keeping it below the tank's deformation pressure limit. During the cooling process, cold water is introduced into the sterilizer to cool the tank. To prevent the steam inside the sterilizer from rapidly contracting upon contact with the cold water, creating a vacuum inside the sterilizer, the external pressure of the tank is controlled. The rapid decrease in pressure causes the tank to form a convex angle. A stepped pressure and temperature reduction is used to simultaneously inject compressed air into the sterilizer to control the pressure inside. This stabilizes the pressure difference between the sterilizer and the tank, ensuring it remains below the tank's deformation pressure limit. For example, at a sterilization temperature of 121℃ and a tank pressure of 0.106 MPa, the pressure inside the sterilizer is monitored using a pressure display device. The pressure difference between the sterilizer and the tank is maintained within -0.08 to 0.069 MPa, ideally within 0 to 0.05 MPa. This effectively prevents the convex angle caused by rapid pressure reduction in the sterilizer and slow cooling in the tank.

[0034] The sterilization method of this invention employs a constant temperature sterilization process, with the sterilization temperature and time varying depending on the contents. Large-diameter (1068, 1070 mm) aluminum two-piece cans have better heat conduction than tinplate cans; therefore, this sterilization method is more effective than traditional tinplate can sterilization methods. After sterilization, the canned goods meet commercial sterility standards, and after 12 months of storage at room temperature, they also meet commercial sterility standards.

[0035] Example 1: High-temperature steam sterilization method for packaged preserved mustard greens and pork in large-diameter 1068-type aluminum two-piece cans.

[0036] Net weight is 480g, solid weight is 85%. Steam is introduced into the sterilization autoclave for heating. The autoclave is vented at 100℃ for 10 minutes, and the tank is heated for 10 minutes to lower the pressure difference between the autoclave and the tank below the critical deformation pressure of the tank. The temperature inside the autoclave and the tank reaches 121℃ after 15 minutes, at which point the pressure inside the autoclave and the tank reaches 0.101–0.106 MPa. Sterilization is then carried out at a constant temperature of 121℃ for 80 minutes. After the constant temperature is reached, the small inlet valve is opened to introduce compressed gas into the autoclave, maintaining the pressure at 0.106 MPa for 1 minute. Then, cold water is introduced through the large valve over the next 3 minutes, controlling the compressed gas to slowly reduce the pressure inside the autoclave to 0.05 MPa. This pressure is maintained for 18 minutes until the pressure inside the tank reaches approximately 0 MPa. The amount of compressed gas introduced is reduced, and the drain valve is opened to maintain the pressure difference between the autoclave and the tank within the tank's deformation limit. The temperature is then lowered to 30℃, and the autoclave is allowed to cool naturally to room temperature.

[0037] After sterilization, the canned pork with preserved mustard greens was in good condition, with no issues such as bursting, denting, or protruding corners. Figure 3 , Figure 4 As shown in the figure, the canned food meets the commercial sterility standard after sterilization and meets the commercial sterility standard after 12 months of storage at room temperature.

[0038] Example 2: A high-temperature steam sterilization method for spiced chicken wings packaged in a large-diameter 1068-type aluminum two-piece can.

[0039] Net weight is 460g, solid weight is 87%. Steam is introduced into the sterilization autoclave for heating. The autoclave is vented at 100℃ for 30 minutes, and the tank is heated for another 30 minutes to lower the pressure difference between the autoclave and the tank below the critical deformation pressure of the tank. The temperature inside the autoclave and the tank reaches 121℃ after another 15 minutes, at which point the pressure inside the autoclave and the tank reaches 0.101–0.106 MPa. Sterilization is then carried out at a constant temperature of 121℃ for 60 minutes. After the constant temperature period ends, a small inlet valve is opened to introduce compressed gas into the autoclave, maintaining the pressure at 0.106 MPa for 1 minute. Then, cold water is introduced through the large valve over the next 3 minutes, controlling the compressed gas to slowly reduce the pressure inside the autoclave to 0.05 MPa. After the final 20 minutes, the pressure inside the tank reaches approximately 0 MPa. The amount of compressed gas introduced is reduced, and the drain valve is opened to maintain the pressure difference between the autoclave and the tank within the tank's deformation limit. The temperature is then lowered to 25–35℃, and the autoclave is allowed to cool naturally to room temperature.

[0040] After sterilization, the canned spiced chicken wings are in good condition with no issues such as bursting, denting, or protruding corners. The canned food meets commercial sterility standards after sterilization and is stored at room temperature for 12 months.

[0041] Example 3: High-temperature steam sterilization method for enoki mushrooms packaged in large-diameter 1068-type aluminum two-piece cans.

[0042] Net weight is 500g, solid weight is 60%. Steam is introduced into the sterilization autoclave for heating. The autoclave is vented at 100℃ for 25 minutes, and the tank is heated for another 25 minutes to lower the pressure difference between the autoclave and the tank below the critical deformation pressure of the tank. The temperature inside the autoclave and the tank reaches 121℃ after another 15 minutes, at which point the pressure inside the autoclave and the tank reaches 0.101–0.106 MPa. Sterilization is then carried out at a constant temperature of 121℃ for 60 minutes. After the constant temperature period ends, a small inlet valve is opened to introduce compressed gas into the autoclave, maintaining the pressure at 0.106 MPa for 1 minute. Then, cold water is introduced through the large valve over the next 3 minutes, controlling the compressed gas to slowly reduce the pressure inside the autoclave to 0.06 MPa. Finally, after 15–18 minutes, the pressure inside the tank reaches approximately 0 MPa. The amount of compressed gas introduced is reduced, and the drain valve is opened to maintain the pressure difference between the autoclave and the tank within the tank's deformation limit. The temperature is then lowered to 25–35℃, and the autoclave is allowed to cool naturally to room temperature.

[0043] After sterilization, the canned enoki mushrooms were in good condition with no issues such as bursting, denting, or protruding corners. The canned goods were tested to be commercially sterile after sterilization and were tested to be commercially sterile after 12 months of storage at room temperature.

[0044] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A sterilization method for food packaged in a large-diameter aluminum two-piece can, wherein high-temperature steam sterilization is used, and the sterilization process includes a stepped heating process, a constant pressure and constant temperature sterilization process, and a stepped pressure and temperature reduction process. The stepped heating process includes several heating stages; The stepped depressurization and cooling process includes several cooling stages; Furthermore, during the stepped heating and cooling process, the pressure inside the vessel is adjusted according to the temperature at different stages to control the pressure difference between the inside and outside of the vessel. In the stepped heating process, the temperature gradually increases from the initial temperature to the sterilization temperature, and the pressure gradually increases from 0 MPa to 0.106 MPa. The pressure difference between the sterilization autoclave and the tank body is kept less than or equal to the limit pressure value of the tank body deformation. During the step-down pressure and temperature reduction process, the temperature gradually decreases from the sterilization temperature to 25-35℃, and the pressure gradually decreases from 0.106Mpa to 0Mpa. The pressure difference between the sterilization autoclave and the tank body is kept less than or equal to the limit pressure value of the tank body deformation.

2. The sterilization method according to claim 1, characterized in that, The stepped heating process includes two heating stages: Heating stage 1: The temperature of the sterilization autoclave is raised to 95-100℃, the pressure is saturated vapor pressure, and the heating time is 10-30 minutes; Heating stage two: The autoclave temperature is raised to the sterilization temperature, the pressure is saturated vapor pressure, and the heating time is 15 minutes; The constant pressure and constant temperature sterilization stage involves maintaining the temperature at the sterilization temperature until the contents reach commercial sterility, followed by back pressure cooling. The stepped pressure and temperature reduction includes three cooling stages: Cooling stage one: The temperature of the sterilization autoclave is reduced from the sterilization temperature to 108-112℃, the constant pressure is 0.101-0.106Mpa, and the cooling time is 30-60s; Cooling stage two: The temperature of the sterilization vessel is reduced from 108-112℃ to 95-100℃, the constant pressure is 0.04-0.06 MPa, and the cooling time is 3-4 minutes; Cooling stage three: The temperature of the sterilization vessel is reduced from 95-100℃ to 25-35℃, the constant pressure is 0 MPa, and the cooling time is 15-20 minutes.

3. The sterilization method according to claim 1 or 2, characterized in that, The tank is a 1068 type aluminum two-piece tank, and the pressure difference between the sterilization autoclave and the tank body is between -0.08Mpa and 0.069Mpa.

4. The sterilization method according to any one of claims 1-3, characterized in that, The deformation pressure value of the 1068 type aluminum two-piece can is -0.08Mpa to 0.069Mpa.

5. The sterilization method according to any one of claims 1-4, characterized in that, The constant temperature sterilization pressure is 0.106 MPa saturated vapor pressure, and the sterilization time is the time required for the contents to reach commercial sterility.

6. The sterilization method according to any one of claims 1-5, characterized in that, The sterilization process is as follows: Large-diameter aluminum two-piece cans containing food are placed into the sterilizing autoclave. High-temperature steam is introduced into the autoclave for a stepped heating process: the temperature inside the autoclave is raised to 95-100°C over 10-30 minutes, and then raised to the sterilization temperature over another 15 minutes. When both the temperature inside the autoclave and the cold point temperature of the cans reach the sterilization temperature, constant-temperature sterilization is performed, with the temperature raised to the sterilization temperature over 25-45 minutes. After achieving commercial sterility through constant-temperature sterilization, a stepped cooling process using backpressure is employed: first, cold water is injected into the autoclave, and simultaneously, compressed air is introduced to increase the pressure inside the autoclave. The pressure inside the vessel is maintained at 0.101–0.106 MPa for 30–60 seconds. Cold water is then continuously injected into the vessel while compressed air is introduced to increase the pressure inside, maintaining it at 0.04–0.06 MPa. The pressure difference between the vessel and the tank is kept within the critical deformation value of the tank. This stage is maintained for 1–3 minutes. Cold water is then continuously injected into the vessel, and the introduction of compressed air is stopped. The drain valve and exhaust valve are opened to gradually reduce the pressure inside the vessel to 0 MPa and the temperature to 25–35°C. This stage is maintained for 15–20 minutes.

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