Solid biological culture medium sterilization system and sterilization method thereof

Abstract

The invention discloses a solid biological culture medium sterilization system and a sterilization method thereof. The system comprises a spiral feeding device (1), a microwave sterilization device (2), a constant-pressure transit bin (3), a spiral discharging device (4) and a cooling discharging device (5) which are arranged in sequence. According to the invention, efficient and uniform microwave thermal effect and non-thermal effect sterilization can be continuously carried out on the wet and soft solid biological culture medium, the sterilization system is simple and reliable, continuous flow line production can be realized, the labor intensity of workers is reduced, and the investment cost is saved.

Description

Technical Field

[0001] This invention belongs to the field of solid biological culture medium sterilization technology. Background Technology

[0002] In modern agricultural production, solid substrates used for aseptic plant cultivation and edible fungi cultivation all require sterilization. Currently, the common method involves sealing the substrate in bags and then placing it in an autoclave. Fuel or electricity is used as a heat source to heat the water inside the autoclave, generating high-temperature steam. This steam then heats the substrate, sterilizing it for approximately 60 minutes at a pressure greater than one atmosphere and a temperature of around 120°C. The substrate is then cooled in the autoclave until the pressure drops to ambient pressure and the temperature approaches room temperature before being removed for use. This sterilization method has at least the following drawbacks: firstly, it is energy-intensive; secondly, the process of transferring the sealed bags of substrate into and out of the autoclave is cumbersome and labor-intensive; thirdly, the cooling and depressurization process after sterilization is lengthy, taking at least 20 hours, which affects production efficiency; and fourthly, industrial sterilization equipment is complex, bulky, and expensive.

[0003] Microwave heating eliminates the need for a heat transfer medium, directly heating the culture medium as a whole without core-surface temperature difference. This results in rapid heating and high thermal efficiency. Furthermore, the non-thermal effects of microwave energy destroy the proteins and genetic material of bacteria and microorganisms, inhibiting their growth and reproduction, which is beneficial for sterilizing the culture medium. Chinese Patent Application No. CN104470022A discloses a microwave heating device for powders and its method of use. While it achieves ideal results for heating fine and dry powders, the sterilization temperature of microwave heating at atmospheric pressure does not exceed the boiling point of water due to the high moisture content of the culture medium, making it difficult to guarantee sterilization effectiveness.

[0004] Currently, microwaves are used in the sterilization of culture media as follows: the culture media to be sterilized is sealed in bags made of microwave-transparent material to form substrate sticks (such as culture sticks for artificial bacteria), and then placed in a fixed microwave resonant cavity or moved on a transmission device through multiple microwave sources. The bacteria and microorganisms in the culture media are killed by the thermal and non-thermal effects of microwave energy.

[0005] Further, based on whether the sterilization environment pressure is higher than the external environment pressure, it is divided into two cases: atmospheric pressure sterilization and high pressure sterilization. 1. In atmospheric pressure sterilization, the sterilization environment pressure is the same as the external environment pressure. Since the culture medium is rich in water, the sterilization temperature cannot be too high (if the temperature is too high, the water in the culture medium will vaporize, and the internal pressure of the sealed culture medium bag will be too high, which will easily cause the bag to bulge and break, contaminating the culture medium). The sterilization time can only be extended, and the sterilization effect is still difficult to guarantee. If the culture medium is not sealed, the sterilization temperature can reach the boiling point of water, 100°C. However, since the culture medium is in contact with the ambient air, the sterilized culture medium is easily contaminated again.

[0006] 2. High-pressure sterilization involves microwave heating of sealed, bagged culture medium sticks inside a pressure vessel. The sterilization environment pressure is greater than standard atmospheric pressure, and the temperature can reach 120°C. The thermal and non-thermal effects of microwave energy rapidly kill bacteria and microorganisms in the culture medium. After sterilization, the sealed culture medium must be cooled to room temperature and the pressure reduced to ambient pressure before it can be removed. Otherwise, the internal pressure of the sealed culture medium will be greater than the ambient pressure, causing the bag to bulge and break. This method still cannot fundamentally solve the problems of long sterilization time and the complexity, size, and high cost of industrial sterilization equipment. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and sterilization method for continuously and efficiently sterilizing moist and soft solid biological culture media.

[0008] The objective of this invention is achieved through the following technical solution.

[0009] A solid biological culture medium sterilization system includes, in sequence, a spiral feeding device, a microwave sterilization device, a constant pressure transfer chamber, a spiral discharging device, and a cooling discharging device; wherein... The constant pressure transfer chamber is a sealed metal cavity with a dust baffle plate in the upper middle part of the cavity and a constant pressure relief valve at the top of the cavity. One side of the middle part is connected to the discharge end of the microwave sterilization device, and the bottom discharge port is connected to the inlet end of the spiral discharge device. The discharge end of the spiral discharge device is connected to the inlet end of the cooling discharge device located below the spiral discharge device through a drop vertical pipe.

[0010] Furthermore, the dust baffle consists of at least two downwardly inclined baffles arranged in an alternating pattern, with gaps between adjacent baffles.

[0011] Furthermore, the spiral feeding device consists of a feed pipe with an outer closed end and a feed spiral pusher disposed in the feed pipe; the inner cavity of the feed pipe consists of an outer section with a large inner diameter, an inner section with a small inner diameter, and a conical transition section located between the outer section and the inner section, with a matrix feed inlet provided at the top of the outer section, and the front end of the inner section extending into the inner tube of the microwave sterilization device. The microwave sterilization device includes a coaxial outer tube and an inner tube, a waveguide and a magnetron mounted on the outer tube; both ends of the outer tube and the inner tube are sealed, the inner tube is a tube made of a wave-transparent material, and the discharge end of the inner tube is connected to a constant pressure transfer chamber.

[0012] Furthermore, the spiral discharge device consists of a discharge pipe closed at both ends and a discharge spiral pusher installed inside the discharge pipe; the inner cavity of the discharge pipe consists of a large inner diameter section located below the constant pressure transfer chamber, a subsequent conical transition section and a small inner diameter section, with an inlet at the top of the large inner diameter section of the discharge pipe that connects to the discharge port at the bottom of the constant pressure transfer chamber, and a discharge port at the bottom of the small inner diameter section of the discharge pipe that connects to the discharge vertical pipe.

[0013] Furthermore, the cooling discharge device includes a cooling discharge pipe closed at one end, a finished product spiral pusher disposed inside the cooling discharge pipe, and a water-cooling jacket disposed outside the cooling discharge pipe; the top of the closed end of the cooling discharge pipe is provided with an inlet that connects to the discharge vertical pipe, and the unclosed end is the finished product outlet.

[0014] The sterilization method of the solid biological culture substrate sterilization system of the present invention is as follows: The substrate material to be sterilized enters the feed pipe through the substrate inlet and is pushed forward by the feed screw pusher. It is compressed and squeezed through the conical transition section of the feed pipe, forming a dynamic embolism in the inner section with a small inner diameter, thus sealing the inlet of the inner tube of the microwave sterilization device. After being sterilized by microwave heating in the inner tube, the material enters the constant pressure transfer chamber, and then falls into the screw discharge device. The conical transition section of the discharge pipe of the screw discharge device compresses and squeezes the substrate material and forms a dynamic embolism in the small inner diameter section of the discharge pipe. With the help of the constant pressure relief valve, a stable high-pressure, high-temperature sterilization zone is formed in the inner tube and the constant pressure transfer chamber. The sterilized substrate material falls into the cooling discharge device through the discharge vertical pipe. During the process of passing through the cooling discharge pipe, it is forced to be water-cooled to room temperature and sent out from the finished product outlet.

[0015] The beneficial effects of this invention are as follows: 1. Microwave sterilization devices utilize the thermal and non-thermal effects of microwave energy to continuously sterilize loose, solid biological culture media, resulting in rapid, efficient, and thorough sterilization. Microwaves heat the entire substrate without core-surface temperature difference, eliminating the need for a heat transfer medium, leading to rapid heating, high thermal efficiency, and energy savings and environmental friendliness.

[0016] 2. Connect one side of the constant pressure transfer chamber to the discharge end of the microwave sterilization device. The solid substrate is pushed out from the discharge end of the microwave sterilization device and falls naturally. During the fall, the material is dispersed and turned over, which is more conducive to the even sterilization of the substrate and improves the sterilization effect. A dust baffle is installed in the upper middle part of the constant pressure transfer chamber to prevent dust from rising and clogging the constant pressure relief valve, ensuring the stable operation of the constant pressure transfer chamber and reducing maintenance costs.

[0017] 3. The horizontal movement of the soft solid substrate is powered by multiple sets of helical push rods, while the vertical movement relies on its own gravity. It is simple, safe, controllable, and reliable.

[0018] 4. The change in the inner diameter of the feed pipe of the screw feeding device and the discharge pipe of the screw discharging device can form a dynamic embolism of the matrix in the small inner diameter section, thereby forming a stable high temperature and high pressure zone in the inner tube of the microwave sterilization device and the constant pressure transfer chamber, achieving efficient microwave high temperature and high pressure sterilization. 5. The substrate, sterilized by high temperature and high pressure, is rapidly cooled to near room temperature by water cooling and then sent to a sterile workshop for packaging or into film bags to make mushroom sticks. This realizes the sterilization of the loose solid substrate first, and then packaging or making mushroom sticks. It changes the traditional method of first packaging the solid substrate in a sealed and compacted state and then heating it for sterilization. This method is not only highly efficient and thorough in sterilization, but also does not require the bags for sterile packaging of the culture substrate to be heat-resistant, wave-transparent, or made of certain materials, which greatly reduces production costs.

[0019] 6. The sterilization system of the present invention is simple and reliable, can realize continuous production line production, reduce the labor intensity of workers, and save investment costs.

[0020] 7. The equipment has good versatility and can also be used for high-temperature heating of solid materials rich in moisture. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the sterilization system of the present invention. Detailed Implementation

[0022] The invention will now be further described in conjunction with the accompanying drawings.

[0023] like Figure 1 As shown, the solid biological culture medium sterilization system of the present invention includes a spiral feeding device 1, a microwave sterilization device 2, a constant pressure transfer chamber 3, a spiral discharging device 4, and a cooling discharging device 5 arranged in sequence.

[0024] The constant pressure transfer chamber 3 is a sealed metal cavity. A dust baffle 12 is installed in the upper middle part of the cavity, and a constant pressure relief valve 13 is installed at the top of the cavity. One side of the middle section is connected to the discharge end of the microwave sterilization device 2, and the bottom discharge port is connected to the inlet end of the spiral discharge device 4. The discharge end of the spiral discharge device 4 is connected to the inlet end of the cooling discharge device 5 located below the spiral discharge device via a drop vertical pipe 15. The dust baffle 12 consists of at least two downward-sloping baffles arranged in an alternating pattern. In this embodiment, two baffles are provided, with a gap a between them. This ensures that the constant pressure relief valve maintains constant pressure throughout the cavity and prevents dust from rising and material from accumulating too high and clogging the constant pressure relief valve.

[0025] The spiral feeding device 1 consists of a feed pipe 6 with its outer end closed and a feed spiral pusher 7 disposed in the feed pipe. The inner cavity of the feed pipe consists of an outer section with a large inner diameter, an inner section with a small inner diameter, and a conical transition section located between the outer and inner sections. A substrate inlet 21 is provided at the top of the outer section, and the front end of the inner section extends into the inner tube 11 of the microwave sterilization device 2. The central shaft of the feed spiral pusher 7 passes through the closed end of the feed pipe and is connected to a motor. The rotation of the motor drives the feed spiral pusher to rotate, thereby pushing the substrate entering the feed pipe towards the inner tube. As the substrate moves through the conical transition section of the feed pipe, it is continuously compressed and squeezed, forming a dynamic plug resistance in the inner section with a small inner diameter of the feed pipe, and creating a pressure isolation between the inner tube and the feed pipe.

[0026] The microwave sterilization device 2 includes a coaxial outer tube 8 and an inner tube 11, a waveguide 9 and a magnetron 10 mounted on the outer tube; both ends of the outer and inner tubes are sealed, and the inner tube is made of a microwave-transparent material. The outlet end of the inner tube is connected to the constant pressure transfer chamber 3. A microwave-transparent insulating material can be filled between the outer and inner tubes. The outer tube 8 is a sealed metal tube, with one end connected to the constant pressure transfer chamber and the other end sealed to the outer wall of the feed pipe to prevent microwave leakage. The inner cavity size of the outer tube meets the conditions for microwave standing wave formation, and the outer tube sidewalls have staggered openings through which the waveguide 9 is installed. The magnetron 10 is installed at the outer end of the waveguide located on the outside of the outer tube. The inner tube 11 is made of a microwave-transparent material. A section of the feed pipe with a small inner diameter extends into the feed end of the inner tube, and the outlet end of the inner tube is securely connected to the constant pressure transfer chamber 3. During the process of the substrate moving through the inner tube into the constant pressure transfer chamber, it is heated to a high temperature under high pressure by multiple sets of magnetrons mounted on the outer tube.

[0027] The spiral discharge device 4 consists of a discharge pipe 14 closed at both ends and a discharge spiral pusher 16 disposed inside the discharge pipe. The inner cavity of the discharge pipe consists of a large inner diameter section located below the constant pressure transfer chamber 3, a subsequent conical transition section, and a small inner diameter section. The top of the large inner diameter section of the discharge pipe has an inlet connected to the discharge port at the bottom of the constant pressure transfer chamber, and the bottom of the small inner diameter section of the discharge pipe has a discharge port connected to the discharge vertical pipe 15. The central axis of the discharge spiral pusher 16 passes through the closed end on the discharge port side of the discharge pipe and is connected to a motor. The rotation of the motor drives the discharge spiral pusher to rotate, thereby pushing the substrate entering the discharge pipe toward the discharge vertical pipe 15. As the substrate moves through the conical transition section of the discharge pipe, it is continuously compressed and squeezed, forming a dynamic blockage in the small inner diameter section of the discharge pipe, and creating a pressure isolation between the discharge vertical pipe 15 and the discharge pipe 14.

[0028] The cooling discharge device 5 includes a cooling discharge pipe 17 closed at one end, a finished product spiral pusher 19 disposed inside the cooling discharge pipe, and a water-cooling jacket 20 disposed on the outer wall of the cooling discharge pipe. The closed end of the cooling discharge pipe has an inlet connected to the discharge vertical pipe 15, and the unclosed end is the finished product outlet 18. The central shaft of the finished product spiral pusher 19 passes through the closed end of the cooling discharge pipe and is connected to a motor. The rotation of the motor drives the finished product spiral pusher to rotate, pushing the sterilized substrate inside the cooling discharge pipe towards the finished product outlet 18. The substrate sterilized by high temperature and high pressure is cooled to near room temperature by the water-cooling jacket on the outer wall of the cooling discharge pipe (maintaining the temperature of the finished sterilized substrate above room temperature, ensuring positive pressure within the entire sterilization device cavity, and preventing ambient air from contaminating the substrate).

[0029] The sterilization method of the sterilization system of the present invention is as follows: The matrix material to be sterilized is fed into the feed pipe 6 through the matrix inlet 21. The feed screw pusher 7 pushes the matrix material forward. The matrix material is compressed and squeezed through the conical transition section of the feed pipe, forming a dynamic embolism in the inner section with a small inner diameter. The inlet of the inner pipe 11 of the microwave sterilization device is sealed, forming a pressure isolation between the inner pipe and the feed pipe. The pressure in the inner pipe and the constant pressure transfer chamber 3 is greater than the ambient pressure, forming a stable high-pressure sterilization zone. The matrix material is pushed into the inner pipe and moves towards the constant pressure transfer chamber. The microwaves emitted by the magnetron 10 pass through the waveguide 9 and the inner pipe made of the wave-transparent material to heat the matrix material. The matrix material is repeatedly heated by the heating sections formed by multiple sets of magnetrons during its movement. The material contains a large amount of water. Water molecules are polar molecules. Under microwave irradiation, water molecules rub and collide at high speed at the same frequency as the microwave, causing the temperature to rise rapidly. Because the inner tube and the constant pressure transfer chamber maintain high pressure, the heating temperature can rise to more than 100°C, achieving rapid sterilization of bacteria and microorganisms in the matrix under high temperature and high pressure. The sterilized matrix material enters the constant pressure transfer chamber 3 and slides down to the bottom of the chamber under gravity, entering the discharge pipe 14 of the spiral discharge device 4. The conical transition section of the discharge pipe 14 compresses and squeezes the matrix material and forms a dynamic plug in the small inner diameter section of the discharge pipe. With the action of the constant pressure relief valve 13, the high pressure and high temperature in the inner tube 11 and the constant pressure transfer chamber 3 are maintained. The inner diameter of the inner tube is much larger than the inner diameter of the feed pipe. After the matrix material enters the inner tube, due to the increase in inner diameter and microwave heating, the matrix material returns to a loose state. The discharge screw pusher 16 rotates, pushing the sterilized matrix material in the discharge pipe towards the drop vertical pipe 15. The matrix material falls naturally into the cooling discharge device 5 through the drop vertical pipe 15. The finished product screw pusher 19 pushes the sterilized matrix material towards the finished product outlet. During the process of passing through the cooling discharge pipe 17, the sterilized matrix material is forcibly cooled by the cold water flowing in the water-cooling jacket 20, reducing its temperature and controlling the discharge temperature of the matrix material to be higher than the external ambient temperature (maintaining positive pressure in the equipment cavity). The matrix material then enters the aseptic packaging environment, where it is quickly packaged in aseptic packaging bags and the sterilized matrix material delivered from the finished product outlet 18 is sealed. Thus, the rapid, automated sterilization and packaging operation of the matrix material is realized.

[0030] Application Examples Prepare a substrate for the mycelium culture of edible fungi in PE bags to be sterilized. The substrate formula is 77% broadleaf tree wood chips, 20% wheat bran, 1% sucrose, 1% gypsum powder, and 1% lime, with a moisture content of about 65%.

[0031] The sterilization temperature is set to ≥ 120℃, the sterilization pressure to ≥ 0.3MPa, the magnetron microwave frequency to 2450MHz, the total microwave heating power to 24KW, and the constant pressure relief valve pressure to be set to 0.3MPa~0.35MPa. The inner tube of the microwave heating device has an inner diameter of 100mm and a length of 1300mm, and is divided into 6 heating sections.

[0032] The matrix material is continuously added to the feed pipe 6. The feed screw pusher 7 rotates, pushing the matrix material towards the inner pipe 11. After entering the inner pipe 11, the matrix material is heated and sterilized by microwaves during its forward movement. The movement speed of the matrix material in the inner pipe is controlled at approximately 100 mm / s. The pressure in the inner pipe 11 and the constant pressure transfer chamber 3 is maintained at 0.3 MPa to 0.35 MPa, forming a stable high-pressure sterilization zone, with the heating temperature rising to above 120°C. The matrix material enters the constant pressure transfer chamber 3 through the inner pipe and naturally slides down to the bottom of the constant pressure transfer chamber under gravity, then enters the discharge pipe 14. The discharge screw pusher 16 rotates, pushing the matrix material towards the discharge vertical pipe 15, then entering the discharge vertical pipe 15, where it automatically falls under gravity into the cooling discharge pipe 17. The finished product spiral pusher 19 rotates, pushing the matrix material towards the finished product outlet 18. During this movement, the matrix material is rapidly cooled by water, lowering its temperature. The outlet temperature of the matrix material is controlled to be ≥35℃, ensuring that the inner cavity of the cooling outlet pipe 17 maintains positive pressure relative to the environment. The cooled matrix material is then quickly packaged in aseptic PE bags and sealed. Based on 3 tons of matrix material, the entire production process takes only 8 hours.

[0033] 5% of the sealed, sterilized substrate material was randomly selected and placed in a 35℃ incubator for 72 hours. The test results showed no bacterial or microbial growth, meeting the sterilization requirements of the culture medium.

Claims

1. A solid biological culture medium sterilization system, characterized in that, The system includes, in sequence, a spiral feeding device (1), a microwave sterilization device (2), a constant pressure transfer chamber (3), a spiral discharging device (4), and a cooling discharging device (5); wherein... The constant pressure transfer chamber (3) is a sealed metal cavity. A dust baffle (12) is installed in the upper middle part of the cavity. A constant pressure relief valve (13) is installed at the top of the cavity. One side of the middle part is connected to the discharge end of the microwave sterilization device (2). The bottom discharge port is connected to the feed end of the spiral discharge device (4). The discharge end of the spiral discharge device (4) is connected to the feed end of the cooling discharge device (5) located below the spiral discharge device through the drop vertical pipe (15).

2. The solid biological culture medium sterilization system as described in claim 1, characterized in that, The dust baffle (12) consists of at least two downward-sloping baffles arranged in an alternating pattern, with gaps between adjacent baffles.

3. The solid biological culture medium sterilization system as described in claim 1, characterized in that, The spiral feeding device (1) consists of a feed pipe (6) with its outer end closed and a feed spiral pusher (7) set in the feed pipe; the inner cavity of the feed pipe consists of an outer section with a large inner diameter, an inner section with a small inner diameter, and a conical transition section located between the outer section and the inner section. A matrix feed inlet (21) is set at the top of the outer section, and the front end of the inner section extends into the inner tube (11) of the microwave sterilization device (2). The microwave sterilization device (2) includes a coaxial outer tube (8) and inner tube (11), a waveguide (9) and a magnetron (10) set on the outer tube; the two ends of the outer tube and the inner tube are closed, the inner tube is a tube made of wave-transparent material, and the discharge end of the inner tube is connected to the constant pressure transfer chamber (3).

4. The solid biological culture medium sterilization system as described in claim 1, characterized in that, The spiral discharge device (4) consists of a discharge pipe (14) closed at both ends and a discharge spiral push rod (16) set inside the discharge pipe; the inner cavity of the discharge pipe consists of a large inner diameter section located below the constant pressure transfer chamber (3), a subsequent conical transition section and a small inner diameter section. The top of the large inner diameter section of the discharge pipe is opened to connect to the discharge port at the bottom of the constant pressure transfer chamber, and the bottom of the small inner diameter section of the discharge pipe is opened to connect to the discharge vertical pipe (15).

5. The solid biological culture medium sterilization system as described in claim 1, characterized in that, The cooling discharge device (5) includes a cooling discharge pipe (17) with one end closed, a finished product spiral pusher (19) set inside the cooling discharge pipe, and a water cooling jacket (20) set outside the cooling discharge pipe; the top of the closed end of the cooling discharge pipe is opened to connect to the dropping vertical pipe (15), and the unclosed end is the finished product outlet (18).

6. A sterilization method for a solid biological culture medium sterilization system as described in any one of claims 1 to 5, characterized in that the method... The process is as follows: The substrate material to be sterilized enters the feed pipe (6) through the substrate inlet (21) and is pushed forward by the feed screw pusher (7). It is compressed and squeezed through the conical transition section of the feed pipe and forms a dynamic thrust in the inner section with a small inner diameter, sealing the inlet of the inner tube (11) of the microwave sterilization device. After the material enters the inner tube and is sterilized by microwave heating, it enters the constant pressure transfer chamber (3) and then falls into the screw discharge device (4). The conical transition section of the discharge pipe (14) of the screw discharge device compresses and squeezes the substrate material and forms a dynamic thrust in the inner section with a small inner diameter. With the help of the constant pressure relief valve (13), a stable high-pressure high-temperature sterilization area is formed in the inner tube (11) and the constant pressure transfer chamber (3) to sterilize the material. After sterilization, the material falls into the cooling discharge device (5) through the drop vertical pipe (15) and is forced to be water-cooled to room temperature during the process of passing through the cooling discharge pipe (17) and sent out from the finished product outlet (18).

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