Freeze-drying process and freeze-drying equipment for mixed food

Abstract

The invention provides a freeze-drying process and freeze-drying equipment for mixed food. The freeze-drying process comprises the following steps: step 1, raw material pretreatment: classifying and screening, carrying out personalized treatment, and mixing and blending; step 2, gradient freezing: a rapid precooling stage and a gradient cooling stage; step 3, sectional type vacuum freeze-drying: a low vacuum sublimation stage, a middle vacuum transition stage and a high vacuum drying stage; step 4, microwave-assisted freeze-drying: introducing microwave-assisted heating in the middle and later periods of the sectional type vacuum freeze-drying process; and step 5, packaging and storing: packaging the freeze-dried mixed food, wherein a packaging material has good sealing property and moisture resistance. By combining the sectional type vacuum freeze-drying process with the microwave-assisted freeze-drying technology, the freeze-drying efficiency is improved, the freeze-drying time is shortened, the freeze-drying conditions can be accurately controlled according to the moisture content and drying requirements of materials in different stages, it is ensured that the materials are optimally treated in the whole freeze-drying process, and the freeze-drying efficiency is improved. And the quality and the stability of products are further improved.

Description

Technical Field

[0001] The invention relates to the technical field related to food processing, and in particular to a freeze-drying process for mixed freeze-dried food. Background Art

[0002] Food processing is the process of transforming raw grains, fruits and vegetables, meat, eggs, milk and other agricultural products into foods that can be eaten by people or have specific functions. Through processing methods such as drying, freezing, pickling, canning, etc., the growth and reproduction of microorganisms and the occurrence of chemical reactions can be inhibited. The use of high-temperature sterilization, irradiation and other methods in the processing process can kill harmful microorganisms and ensure food safety. Processed foods are easier to store, transport and eat.

[0003] At present, the common methods for drying mixed foods include natural drying and hot air drying. Although natural drying has low cost, it is greatly affected by the weather, takes a long time to dry, and is easily contaminated by dust, insects, etc., resulting in unstable product quality. Although hot air drying is faster, the temperature is high, which can easily destroy the nutrients and active substances in the mixed food, affecting the quality and taste of the product. In addition, traditional drying methods also have problems such as uneven drying. Summary of the invention

[0004] The object of the present invention is to provide a freeze-drying process for mixed freeze-dried food, so as to solve the common mixed food drying methods proposed in the above-mentioned background technology, which mainly include natural air-drying, hot air drying, etc. Although natural air-drying has low cost, it is greatly affected by the weather, takes a long time to dry, and is easily contaminated by dust, insects, etc., resulting in unstable product quality. Although hot air drying is faster, the temperature is higher, which can easily destroy the nutrients and active substances in the mixed food, affecting the quality and taste of the product. In addition, the traditional drying method also has problems such as uneven drying.

[0005] To achieve the above object, the present invention provides a freeze-drying process for a mixed freeze-dried food, comprising the following steps:

[0006] Step 1: Raw material pretreatment: classification, screening, personalized processing, and mixed blending;

[0007] Step 2, gradient freezing: rapid precooling stage, gradient cooling stage;

[0008] Step 3, segmented vacuum freeze drying: low vacuum sublimation stage, medium vacuum transition stage, high vacuum drying stage;

[0009] Step 4, microwave-assisted freeze-drying: In the middle and late stages of the segmented vacuum freeze-drying process, microwave-assisted heating is introduced;

[0010] Step 5: Packaging and storage: Pack the freeze-dried mixed food. The packaging material should have good sealing and moisture-proof properties.

[0011] Preferably, the classification screening in step 1 is carried out according to different characteristics of the mixed food raw materials, such as texture (soft, hard), moisture content (high moisture, low moisture), and vulnerability of nutrient components (easy to oxidize, heat-sensitive, etc.).

[0012] Preferably, the personalized treatment in step 1 is targeted at different types of raw materials. For example, for easily oxidized raw materials, they are soaked in a solution containing antioxidants (such as tea polyphenols, vitamin C, etc.) for a certain period of time after washing; for high-moisture raw materials (such as green peppers, etc.), appropriate dehydration pretreatment is performed (among which bitter melon needs to be debittered in advance. First, cut the bitter melon in half, remove the white membrane and seeds inside, then add honey and stir, let it stand for 10-15 minutes, then blanch the bitter melon slices in boiling water, then soak them in clean water for 10-20 minutes, finally rinse them and dehydrate them), and the moisture content can be initially reduced to a certain level by mild centrifugation or natural drainage.

[0013] Preferably, in step 1, the processed raw materials are mixed according to a predetermined ratio, and an appropriate amount of stabilizer (such as sodium carboxymethyl cellulose, pectin, etc.) and flavoring agent (according to product requirements) are added and stirred evenly to ensure that the raw materials have good uniformity after mixing.

[0014] Preferably, in the rapid precooling stage in step 2, the mixed raw materials are quickly placed in a freezing device and cooled to -20°C at a relatively fast cooling rate of -10°C / min, so that the surface of the raw materials is quickly frozen to form a thin ice shell, thereby preventing the migration of water inside the raw materials during the subsequent freezing process and causing uneven growth of ice crystals.

[0015] Preferably, the gradient cooling stage in step 2 starts from -20°C, and gradually cools to -40°C with a smaller temperature gradient of -5°C / h, and maintains this temperature for a certain period of time of 2-3 hours, so that the moisture inside the raw material is fully frozen into small and uniform ice crystals. This slow gradient cooling method helps to reduce the damage of ice crystals to the cell structure, thereby better preserving the original shape and nutritional components of the food.

[0016] Preferably, in the step 3, the vacuum pump is started during the low vacuum sublimation stage to reduce the pressure in the freeze-drying chamber to a low level of 100-200 Pa, and the frozen raw materials are heated at the same time, and the heating temperature is controlled between -20°C and -10°C, so that the ice crystals begin to sublime at a relatively low temperature. Maintaining a relatively low temperature and vacuum degree at this stage is conducive to the slow and stable sublimation of ice crystals, avoiding the formation of a hard shell due to excessively high temperature or low vacuum degree causing the surface of the material to dry too quickly, thereby hindering the continued sublimation of internal moisture.

[0017] Preferably, in the medium vacuum transition stage in step 3, when most of the free water in the material has been sublimated, the vacuum degree is further increased to 50-100 Pa, and the heating temperature is increased to -5°C to 5°C. At this stage, the bound water inside the material begins to gradually desorb and sublime. Properly increasing the temperature and vacuum degree can accelerate this process, but care should be taken to control the heating rate to prevent local overheating or deformation of the material due to excessively rapid temperature rise.

[0018] Preferably, after most of the bound water in the material is removed in the high vacuum drying stage in step 3, the high vacuum drying stage is entered, the vacuum degree in the freeze drying chamber is increased to 10-50 Pa, and the heating temperature is increased to 20°C-30°C, and the final drying treatment is performed to remove the remaining trace moisture. The high vacuum environment and high temperature in this stage can ensure that the moisture in the material is completely removed without causing excessive damage to the nutritional components and flavor of the material.

[0019] Preferably, in step 4, microwave-assisted freeze-drying, microwave-assisted heating is introduced in the middle and late stages of the segmented vacuum freeze-drying process. When the moisture content of the material drops to a certain level of 30%-40%, the microwave generator is turned on to intermittently irradiate the material with microwaves at an appropriate power (adjusted according to the nature and amount of the material).

[0020] A freeze-drying device for mixed freeze-dried food, comprising a freeze-drying tank and a drying mechanism, wherein a vacuum pump is installed on one side of the surface of the freeze-drying tank, a refrigeration compressor is installed on the other side of the surface of the freeze-drying tank, a discharge pipe is connected to the bottom of the freeze-drying tank, a tank cover is installed at the bottom of the freeze-drying tank, a drying mechanism is arranged inside the freeze-drying tank, a stirring mechanism is arranged inside the freeze-drying tank, a material feeding hopper is installed on one side of the surface of the tank cover, a pressure display instrument is installed on one side of the surface of the tank cover, and a pressure sensor is installed at the bottom of the tank cover;

[0021] The drying mechanism comprises a mounting groove, a temperature sensor, a temperature display, a storage battery, a heat insulation board, a heating wire and a heat conducting plate. The inner wall of the freeze drying tank is provided with a mounting groove, the bottom of the tank cover is provided with a temperature sensor, one side of the surface of the tank cover is provided with a temperature display, one side of the surface of the tank cover is provided with a storage battery, a heat insulation board is provided inside the mounting groove, a heating wire is provided inside the mounting groove, and a heat conducting plate is provided inside the mounting groove;

[0022] The temperature sensor is electrically connected to the temperature display, the battery is electrically connected to the heating wire, the heat insulation board is in contact with the inner wall of the freeze-drying tank inside the installation groove, the heat insulation board is a glass fiber board, the heating wire is installed between the heat insulation board and the heat conducting board, and the heat conducting board is made of aluminum alloy;

[0023] Preferably, the stirring mechanism comprises a support frame, a driving motor, a supporting rod, a stirring blade and a scraper, the inner bottom surface of the freeze-drying tank is fixedly connected to the support frame, a driving motor is installed on one side of the surface of the tank cover, the output end of the driving motor is connected to the supporting rod, the surface of the supporting rod is installed with a stirring blade, and the surface of the supporting rod is installed with a scraper;

[0024] The support rod is arranged inside the freeze-drying tank, one end of the support rod is embedded in the support frame, four groups of stirring blades are arranged, the stirring blades are distributed at equal intervals, and one end of the scraper is in contact with the heat conduction plate.

[0025] Compared with the prior art, the beneficial effects of the present invention are: the freeze-drying process of the mixed freeze-dried food includes the following effects:

[0026] 1. Through raw material pretreatment, raw materials with different characteristics are classified and optimized, which improves the uniformity of mixed food raw materials and lays the foundation for subsequent uniform freeze-drying, thereby significantly improving the overall quality and taste of the product.

[0027] 2. Gradient freezing can make the water in the mixed food ingredients form small and uniform ice crystals, reducing the damage of ice crystals to the cell structure and retaining the original shape, nutrients and flavor of the food to the greatest extent.

[0028] 3. The segmented vacuum freeze-drying process combined with microwave-assisted freeze-drying technology not only improves the freeze-drying efficiency, shortens the freeze-drying time, and reduces energy consumption, but also can accurately control the freeze-drying conditions according to the moisture content and drying requirements of the material at different stages, ensuring that the material is best treated throughout the freeze-drying process, further improving the quality and stability of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a side view schematic diagram of the overall structure of the present invention;

[0030] Figure 2 It is a schematic cross-sectional view of the overall structure of the present invention;

[0031] Figure 3 Schematic diagram of the drying mechanism structure of the present invention

[0032] Figure 4 This is a schematic diagram of the stirring mechanism structure of the present invention;

[0033] Figure 5 It is a schematic diagram of the structure of the tank cover and the pressure sensor cooperating with each other in the present invention.

[0034] In the figure: 1. freeze drying tank; 2. vacuum pump; 3. refrigeration compressor; 4. discharge pipe; 5. tank cover; 6. drying mechanism; 601. mounting slot; 602. temperature sensor; 603. temperature display; 604. battery; 605. heat insulation board; 606. heating wire; 607. heat conducting plate; 7. stirring mechanism; 701. support frame; 702. driving motor; 703. support rod; 704. stirring blade; 705. scraper; 8. feeding hopper; 9. pressure display; 10. pressure sensor. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the implementation regulations described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The present invention provides a freeze-drying process for a mixed freeze-dried food, comprising the following steps:

[0037] Step 1: Raw material pretreatment: classification, screening, personalized processing, and mixed blending;

[0038] Step 2, gradient freezing: rapid precooling stage, gradient cooling stage;

[0039] Step 3, segmented vacuum freeze drying: low vacuum sublimation stage, medium vacuum transition stage, high vacuum drying stage;

[0040] Step 4, microwave-assisted freeze-drying: In the middle and late stages of the segmented vacuum freeze-drying process, microwave-assisted heating is introduced;

[0041] Step 5: Packaging and storage: Pack the freeze-dried mixed food. The packaging material should have good sealing and moisture-proof properties.

[0042] Furthermore, the classification and screening in step 1 is carried out according to different characteristics of the mixed food raw materials, such as texture (soft, hard), moisture content (high moisture, low moisture), and vulnerability of nutrient components (easy to oxidize, heat-sensitive, etc.).

[0043] Furthermore, the personalized treatment in step 1 is targeted at different types of raw materials. For example, for easily oxidized raw materials, they are soaked in a solution containing antioxidants (such as tea polyphenols, vitamin C, etc.) for a certain period of time after washing; for high-moisture raw materials (such as green peppers, etc.), appropriate dehydration pretreatment is carried out (among which bitter melon needs to be debittered in advance. First, cut the bitter melon in half, remove the white membrane and seeds inside, then add honey and stir, let it stand for 10-15 minutes, then blanch the bitter melon slices in boiling water, then soak them in clean water for 10-20 minutes, finally rinse them and dehydrate them), and the moisture content can be initially reduced to a certain level by mild centrifugation or natural drainage.

[0044] Furthermore, bitter melon needs to be added to the raw material processing. The bitter melon needs to be debittered in advance. First, cut the bitter melon in half, remove the white membrane and seeds inside, then add salt and stir. After standing for 10-15 minutes, wash it clean, blanch the bitter melon slices in boiling water, then soak them in clean water for 10-20 minutes, and finally rinse them clean.

[0045] Furthermore, in step 1, the processed raw materials are mixed according to a predetermined ratio, and appropriate amounts of stabilizers (such as sodium carboxymethyl cellulose, pectin, etc.) and flavoring agents (according to product requirements) are added and stirred evenly to ensure that the raw materials have good uniformity after mixing.

[0046] Furthermore, in the rapid precooling stage in step 2, the mixed raw materials are quickly placed in a freezing device and cooled to -20°C at a relatively fast cooling rate of -10°C / min, so that the surface of the raw materials is quickly frozen to form a thin ice shell, thereby preventing the migration of water inside the raw materials during the subsequent freezing process and causing uneven growth of ice crystals.

[0047] Furthermore, in step 2, the gradient cooling stage starts from -20°C and gradually cools to -40°C at a smaller temperature gradient of -5°C / h, and maintains this temperature for a certain period of time of 2-3 hours, so that the moisture inside the raw material is fully frozen into small and uniform ice crystals. This slow gradient cooling method helps to reduce the damage of ice crystals to the cell structure, thereby better preserving the original shape and nutritional components of the food.

[0048] Furthermore, in step 3, the vacuum pump is started during the low vacuum sublimation stage to reduce the pressure in the freeze-drying chamber to a low level of 100-200 Pa. At the same time, the frozen raw materials are heated, and the heating temperature is controlled between -20°C and -10°C, so that the ice crystals begin to sublime at a relatively low temperature. Maintaining a relatively low temperature and vacuum degree in this stage is conducive to the slow and stable sublimation of ice crystals, avoiding the formation of a hard shell due to excessively high temperature or too low vacuum degree causing the surface of the material to dry out too quickly, thereby hindering the continued sublimation of internal moisture.

[0049] Furthermore, in the medium vacuum transition stage in step 3, when most of the free water in the material has been sublimated, the vacuum degree is further increased to 50-100 Pa, and the heating temperature is increased to -5°C to 5°C. At this stage, the bound water inside the material begins to gradually desorb and sublime. Properly increasing the temperature and vacuum degree can speed up this process, but care must be taken to control the heating rate to prevent local overheating or deformation of the material due to excessively rapid temperature rise.

[0050] Furthermore, after most of the bound water in the material is removed in the high vacuum drying stage in step 3, the high vacuum drying stage is entered, the vacuum degree in the freeze-drying chamber is increased to 10-50Pa, and the heating temperature is increased to 20℃-30℃ for the final drying process to remove the remaining trace moisture. The high vacuum environment and high temperature in this stage can ensure that the moisture in the material is completely removed without causing excessive damage to the nutritional components and flavor of the material.

[0051] Furthermore, in step 4, microwave-assisted freeze-drying, microwave-assisted heating is introduced in the middle and late stages of the segmented vacuum freeze-drying process. When the moisture content of the material drops to a certain level of 30%-40%, the microwave generator is turned on to intermittently irradiate the material with microwaves at an appropriate power (adjusted according to the nature and amount of the material). Microwaves can penetrate the interior of the material, causing the water molecules inside the material to vibrate and rub violently, thereby generating heat and accelerating the evaporation and sublimation of water. At the same time, microwave heating is selective and can act preferentially on water, reducing the impact on other nutrients. By reasonably controlling the power and irradiation time of the microwave, the freeze-drying efficiency can be significantly improved and the freeze-drying time can be shortened without increasing the overall temperature of the material.

[0052] Example 1: Preparation of freeze-dried food mixed with fruit and yogurt

[0053] 1. Raw material preparation

[0054] Fruits: Choose fresh strawberries, blueberries, mangoes and bananas. Wash the strawberries and blueberries and remove the stems; peel and core the mangoes and cut them into small pieces; peel the bananas and cut them into thin slices.

[0055] Yogurt: Choose high-quality plain yogurt.

[0056] 2. Preprocessing

[0057] Fruit treatment: Soak strawberries and blueberries in an antioxidant solution containing 0.1% vitamin C and 0.05% tea polyphenols for 15 minutes, then remove and drain.

[0058] The mango chunks and banana slices were subjected to mild centrifugal dehydration to reduce their moisture content by about 10%.

[0059] Mixing and preparation: Mix the processed fruit and yogurt in a ratio of 3:2, add 0.2% sodium carboxymethyl cellulose as a stabilizer and an appropriate amount of honey as a flavoring agent, and stir evenly.

[0060] 3. Gradient Freezing

[0061] Rapid pre-cooling stage: quickly put the mixed raw materials into the freezing equipment and cool them down to -20℃ at a cooling rate of -10℃ / min.

[0062] Gradient cooling stage: starting from -20℃, gradually cool down to -40℃ with a temperature gradient of -5℃ / h and maintain for 3 hours.

[0063] 4. Segmented vacuum freeze drying and microwave assisted

[0064] Low vacuum sublimation stage: Start the vacuum pump to reduce the pressure in the freeze-drying chamber to 150Pa, and heat the raw materials at the same time, control the temperature at -15℃, and maintain it for 8 hours. During this period, turn the materials every 2 hours to ensure uniform sublimation.

[0065] Medium vacuum transition stage: When most of the free water in the material has been sublimated, the vacuum degree is increased to 80Pa, and the heating temperature is increased to 0℃ and maintained for 6 hours.

[0066] High vacuum drying stage: After most of the bound water in the material is removed, the vacuum degree is increased to 30Pa, and the heating temperature is increased to 25°C for the final drying process until the moisture content of the material drops below 5%.

[0067] Microwave assistance: When the moisture content of the material drops to 35%, turn on the microwave generator and irradiate the material with intermittent microwaves at a power of 500W. Each irradiation time is 30 seconds, the interval time is 2 minutes, and a total of 5-6 irradiations are performed.

[0068] 5. Packaging: The freeze-dried fruit and yogurt mixed food is vacuum packed in an aluminum foil composite bag to prevent the product from moisture and oxidation.

[0069] Example 2: Preparation of freeze-dried food mixed with vegetables and meat

[0070] 1. Raw material preparation

[0071] Vegetables: Choose green peppers, okra and bitter melon.

[0072] Meat: Choose lean beef, cut into thin slices, and marinate with appropriate amount of salt, pepper and light soy sauce for 30 minutes.

[0073] 2. Preprocessing

[0074] Vegetable processing: Blanch small pieces of green pepper and okra segments in boiling water for 2 minutes, remove them and quickly cool them with cold water, then soak them in a color preservative solution containing 0.2% vitamin E and 0.1% citric acid for 10 minutes, and drain the water.

[0075] Bitter melon needs to be debittered in advance. First, cut the bitter melon in half, remove the white membrane and seeds inside, then add honey and stir. After letting it stand for 10-15 minutes, blanch the bitter melon slices in boiling water, then soak them in clean water for 10-20 minutes, finally rinse them and dehydrate them.

[0076] Mixing and blending: Mix the processed vegetables with the marinated beef in a ratio of 4:3, add 0.1% pectin as a stabilizer and an appropriate amount of cumin powder as a seasoning, and stir well.

[0077] 3. Gradient Freezing

[0078] Rapid pre-cooling stage: quickly put the mixed raw materials into the freezing equipment and cool them down to -20℃ at a cooling rate of -8℃ / min.

[0079] Gradient cooling stage: starting from -20℃, gradually cool down to -35℃ at a temperature gradient of -4℃ / h and maintain for 2.5 hours.

[0080] 4. Segmented vacuum freeze drying and microwave assisted

[0081] Low vacuum sublimation stage: Start the vacuum pump to reduce the pressure in the freeze-drying chamber to 180Pa, and at the same time heat the raw materials and control the temperature at -18°C for 10 hours.

[0082] Medium vacuum transition stage: When most of the free water in the material has been sublimated, the vacuum degree is increased to 60Pa, and the heating temperature is increased to -3°C and maintained for 8 hours.

[0083] High vacuum drying stage: After most of the bound water in the material is removed, the vacuum degree is increased to 20Pa and the heating temperature is increased to 28°C for the final drying process until the moisture content of the material drops below 6%.

[0084] -Microwave assisted: When the moisture content of the material drops to 30%, turn on the microwave generator and irradiate the material with intermittent microwaves at a power of 600W. Each irradiation time is 20 seconds, the interval time is 1.5 minutes, and a total of 4-5 irradiations are performed.

[0085] 5. Packaging: The freeze-dried vegetable and meat mixed food is vacuum packed in PET / PE composite bags to ensure the shelf life and quality of the product.

[0086] Furthermore, it includes a freeze drying tank 1 and a drying mechanism 6, characterized in that: a vacuum pump 2 is installed on one side of the surface of the freeze drying tank 1, a refrigeration compressor 3 is installed on the other side of the surface of the freeze drying tank 1, a discharge pipe 4 is connected to the bottom of the freeze drying tank 1, a tank cover 5 is installed at the bottom of the freeze drying tank 1, a drying mechanism 6 is arranged inside the freeze drying tank 1, a stirring mechanism 7 is arranged inside the freeze drying tank 1, a hopper 8 is installed on one side of the surface of the tank cover 5, a pressure display instrument 9 is installed on one side of the surface of the tank cover 5, and a pressure sensor 10 is installed at the bottom of the tank cover 5;

[0087] The drying mechanism 6 includes a mounting groove 601, a temperature sensor 602, a temperature display 603, a battery 604, a heat insulation board 605, a heating wire 606 and a heat conducting plate 607. The inner wall of the freeze drying tank 1 is provided with a mounting groove 601, a temperature sensor 602 is installed at the bottom of the tank cover 5, a temperature display 603 is installed on one side of the surface of the tank cover 5, a battery 604 is installed on one side of the surface of the tank cover 5, a heat insulation board 605 is installed inside the mounting groove 601, a heating wire 606 is installed inside the mounting groove 601, and a heat conducting plate 607 is installed inside the mounting groove 601;

[0088] The temperature sensor 602 is electrically connected to the temperature display 603, the storage battery 604 is electrically connected to the heating wire 606, the heat insulation board 605 is in contact with the inner wall of the freeze drying tank 1 inside the installation groove 601, the heat insulation board 605 is a glass fiber board, the heating wire 606 is installed between the heat insulation board 605 and the heat conducting board 607, and the heat conducting board 607 is made of aluminum alloy;

[0089] Furthermore, the stirring mechanism 7 includes a support frame 701, a drive motor 702, a support rod 703, a stirring blade 704 and a scraper 705. The inner bottom surface of the freeze-drying tank 1 is fixedly connected to the support frame 701, and the drive motor 702 is installed on one side of the surface of the tank cover 5. The output end of the drive motor 702 is connected to the support rod 703, and the surface of the support rod 703 is installed with a stirring blade 704, and the surface of the support rod 703 is installed with a scraper 705;

[0090] The support rod 703 is arranged inside the freeze drying tank 1, and one end of the support rod 703 is embedded in the support frame 701. Four groups of stirring blades 704 are arranged, and the stirring blades 704 are distributed at equal intervals. One end of the scraper 705 is in contact with the heat conduction plate 607.

[0091] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the implementation rules without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A freeze-drying process for mixed freeze-dried food, characterized in that The steps include: Step 1: Raw material pretreatment: classification, screening, personalized processing, and mixed blending; Step 2, gradient freezing: rapid precooling stage, gradient cooling stage; Step 3, segmented vacuum freeze drying: low vacuum sublimation stage, medium vacuum transition stage, high vacuum drying stage; Step 4, microwave-assisted freeze-drying: In the middle and late stages of the segmented vacuum freeze-drying process, microwave-assisted heating is introduced; Step 5, packaging and storage: Packaging the freeze-dried mixed food, the packaging material should have good sealing and moisture-proof properties; The classification screening in step 1 is carried out according to different characteristics of the mixed food raw materials, such as texture (soft, hard), moisture content (high moisture, low moisture), and vulnerability of nutrient components (easy to oxidize, heat-sensitive, etc.). The personalized treatment in step 1 is targeted at different types of raw materials. For example, for easily oxidized raw materials, they are soaked in a solution containing antioxidants (such as tea polyphenols, vitamin C, etc.) for a certain period of time after washing; for high-moisture raw materials (such as green peppers, etc.), appropriate dehydration pretreatment is performed (among which bitter melon needs to be debittered in advance. First, cut the bitter melon in half, remove the white membrane and seeds inside, then add honey and stir, let it stand for 10-15 minutes, then blanch the bitter melon slices in boiling water, then soak them in clean water for 10-20 minutes, finally rinse them and dehydrate them), and the moisture content can be initially reduced to a certain level by mild centrifugation or natural drainage.

2. The freeze-drying process of a mixed freeze-dried food according to claim 1, characterized in that: In the step 1, the processed raw materials are mixed according to a predetermined ratio, and an appropriate amount of stabilizer (such as sodium carboxymethyl cellulose, pectin, etc.) and flavoring agent (according to product requirements) are added and stirred evenly to ensure that the raw materials have good uniformity after mixing.

3. The freeze-drying process of a mixed freeze-dried food according to claim 1, characterized in that: In the rapid precooling stage in step 2, the mixed raw materials are quickly placed in a freezing device and cooled to -20°C at a relatively fast cooling rate of -10°C / min, so that the surface of the raw materials is quickly frozen to form a thin ice shell to prevent the internal moisture of the raw materials from migrating during the subsequent freezing process and causing uneven growth of ice crystals.

4. The freeze-drying process of a mixed freeze-dried food according to claim 1, characterized in that: In step 2, the gradient cooling stage starts from -20°C and gradually cools to -40°C at a smaller temperature gradient of -5°C / h, and maintains this temperature for a certain period of time of 2-3 hours, so that the moisture inside the raw material is fully frozen into small and uniform ice crystals. This slow gradient cooling method helps to reduce the damage of ice crystals to the cell structure, thereby better preserving the original shape and nutritional components of the food.

5. The freeze-drying process of a mixed freeze-dried food according to claim 1, characterized in that: In the low vacuum sublimation stage in step 3, the vacuum pump is started to reduce the pressure in the freeze-drying chamber to a low level of 100-200Pa, and the frozen raw materials are heated at the same time. The heating temperature is controlled between -20°C and -10°C, so that the ice crystals begin to sublime at a relatively low temperature. Maintaining a relatively low temperature and vacuum degree in this stage is conducive to the slow and stable sublimation of ice crystals, avoiding the formation of a hard shell due to excessively high temperature or low vacuum degree causing the surface of the material to dry too quickly, thereby hindering the continued sublimation of internal moisture.

6. The freeze-drying process of a mixed freeze-dried food according to claim 1, characterized in that: In the medium vacuum transition stage in step 3, when most of the free water in the material has been sublimated, the vacuum degree is further increased to 50-100 Pa, and the heating temperature is increased to -5°C to 5°C. At this stage, the bound water inside the material begins to gradually desorb and sublime. Properly increasing the temperature and vacuum degree can accelerate this process, but care should be taken to control the heating rate to prevent local overheating or deformation of the material due to excessively rapid temperature rise.

7. The freeze-drying process of a mixed freeze-dried food according to claim 1, characterized in that: After most of the bound water in the material is removed in the high vacuum drying stage in step 3, the high vacuum drying stage is entered, the vacuum degree in the freeze drying chamber is increased to 10-50Pa, and the heating temperature is increased to 20℃-30℃ for the final drying process to remove the remaining trace moisture. The high vacuum environment and high temperature in this stage can ensure that the moisture in the material is completely removed without causing excessive damage to the nutritional components and flavor of the material.

8. The freeze-drying process of a mixed freeze-dried food according to claim 1, characterized in that: In the step 4, microwave-assisted freeze-drying, microwave-assisted heating is introduced in the middle and late stages of the segmented vacuum freeze-drying process. When the moisture content of the material drops to a certain level of 30%-40%, the microwave generator is turned on to intermittently irradiate the material with microwaves at an appropriate power (adjusted according to the nature and amount of the material).

9. A freeze-drying device for mixed food A freeze-drying process for mixed freeze-dried food as described in claims 1 to 8, characterized in that: The freeze-drying tank (1) comprises a freeze-drying tank (1) and a drying mechanism (6), and is characterized in that: a vacuum pump (2) is installed on one side of the surface of the freeze-drying tank (1), a refrigeration compressor (3) is installed on the other side of the surface of the freeze-drying tank (1), a discharge pipe (4) is connected to the bottom of the freeze-drying tank (1), a tank cover (5) is installed at the bottom of the freeze-drying tank (1), a drying mechanism (6) is arranged inside the freeze-drying tank (1), a stirring mechanism (7) is arranged inside the freeze-drying tank (1), a material feeding hopper (8) is installed on one side of the surface of the tank cover (5), a pressure display instrument (9) is installed on one side of the surface of the tank cover (5), and a pressure sensor (10) is installed at the bottom of the tank cover (5); The drying mechanism (6) comprises a mounting groove (601), a temperature sensor (602), a temperature display (603), a storage battery (604), a heat insulation board (605), a heating wire (606) and a heat conducting plate (607); the inner wall of the freeze drying tank (1) is provided with a mounting groove (601); the bottom of the tank cover (5) is provided with a temperature sensor (602); one side of the surface of the tank cover (5) is provided with a temperature display (603); one side of the surface of the tank cover (5) is provided with a storage battery (604); the inside of the mounting groove (601) is provided with a heat insulation board (605); the inside of the mounting groove (601) is provided with a heating wire (606); and the inside of the mounting groove (601) is provided with a heat conducting plate (607); The temperature sensor (602) is electrically connected to the temperature display (603), the storage battery (604) is electrically connected to the heating wire (606), the heat insulation board (605) is in contact with the inner wall of the freeze-drying tank (1) inside the installation groove (601), the heat insulation board (605) is a glass fiber board, the heating wire (606) is installed between the heat insulation board (605) and the heat conducting board (607), and the heat conducting board (607) is an aluminum alloy material.

10. The freeze-drying equipment for mixed freeze-dried food according to claim 9, characterized in that: The stirring mechanism (7) comprises a support frame (701), a driving motor (702), a supporting rod (703), a stirring blade (704) and a scraper (705); the inner bottom surface of the freeze-drying tank (1) is fixedly connected to the support frame (701); a driving motor (702) is installed on one side of the surface of the tank cover (5); the output end of the driving motor (702) is connected to the supporting rod (703); the surface of the supporting rod (703) is installed with a stirring blade (704); and the surface of the supporting rod (703) is installed with a scraper (705); The support rod (703) is arranged inside the freeze-drying tank (1), one end of the support rod (703) is embedded in the support frame (701), four groups of stirring blades (704) are arranged, and the stirring blades (704) are distributed at equal intervals. One end of the scraper (705) is in contact with the heat conduction plate (607).

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