A method for improving the drying quality and functional factors of fruits and vegetables by low-temperature freeze-thaw combined with integrated immersion freeze-drying

Abstract

The present invention relates to a method for improving the drying quality and functional factors of fruits and vegetables by low-temperature freeze-thaw combined with integrated immersion freeze-drying, and belongs to the technical field of fruit and vegetable drying processing. The method uses fruits and vegetables with solid content less than 12% as raw materials, adopts a cyclic low-temperature freeze-thaw method to complete the freeze-thaw link of the material in a frozen state, selects small molecule peptides, functional oligosaccharides, and soluble dietary fiber as sugar substitutes to increase the solid content and functional factors, and adopts a fruit and vegetable raw water collection system to recover the water and flavor and pigment substances removed during the vacuum freeze-drying process. At the same time, the loss of nutrients is avoided by atomizing and spraying the impregnation liquid, and the pre-drying, vacuum impregnation, freezing, and post-drying processes are completed in one device. The patented method greatly improves the processing efficiency of dried fruit and vegetable products, reduces the loss of nutrients during the processing process, realizes the comprehensive utilization of fruit and vegetable raw water and flavor pigments, and enriches a variety of nutritional functional factors.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable drying processing, and particularly relates to a method and product for improving the drying quality and functional factors of fruits and vegetables by low-temperature freeze-thaw combined integrated immersion freeze-drying. Background Art

[0002] With the improvement of people's living standards and the enhancement of health awareness, the types and proportion of fruits and vegetables in daily diet are increasing. Fruits and vegetables can not only provide the basic nutrients such as vitamins, minerals, crude fiber, etc. that are necessary for the human body, but also contain rich bioactive substances, which have a positive effect on preventing diseases and promoting health. However, fresh fruits and vegetables have a high water content and are very easy to rot and deteriorate after harvesting, which is not conducive to transportation and storage. They have strong seasonality and regionality. Dehydrated fruits and vegetables are light in weight, small in size, avoid microbial reproduction, have a long shelf life, are easy to store and transport, and can meet the high-efficiency and fast-paced lifestyle of modern people.

[0003] Since fresh fruits and vegetables contain 85-95% water and very little solid content, the output rate after dehydration and drying is very low. In actual production, glucose, sucrose, etc. are often added to increase the output rate of dehydrated fruits and vegetables and improve the color of the products, while fruit and vegetable crisps and dried fruit manufacturers add sugar to improve the taste and texture of the products. Chinese patent CN104026214B discloses a method for preparing a vacuum freeze-dried strawberry product, in which the mass ratio of granulated sugar in the impregnation solution is 25-35%; Chinese patent CN105685355A discloses a processing method for instant freeze-dried sugared strawberries, in which water and granulated sugar are mixed in a ratio of 0.5:1-3:1, and the sugar is dissolved by heating; Chinese patent CN108023940A discloses a processing method for persimmon preserves with a crisp taste, in which the concentration of granulated sugar in the sugar solution is controlled at 18-25%. It can be seen that a large amount of sugar is added in the current production process of dehydrated fruits and vegetables, which increases the sugar intake of people during their diet. However, in modern society, there are health problems such as an increase in the number of people with diabetes and excessive sugar intake in the diet. People advocate reducing sugar intake in the diet, increasing the intake of nutritional functional factors, and reducing the harm of sub-health and chronic diseases caused by poor diet. Therefore, finding nutritious and healthy sugar substitutes will be of great significance to the development of the dehydrated fruit and vegetable industry and people's dietary health.

[0004] Vacuum freeze drying is a drying method that maintains the original structure and nutrients of fruits and vegetables to the greatest extent. It is often used as a combined pre-drying technology. After the fruits and vegetables are dried to a certain moisture content, sugar is impregnated into the material by vacuum impregnation, and then other drying methods are used to dry the fruit and vegetable materials to a set moisture content. Chinese patent CN113632826A discloses a method for regulating the texture of freeze-dried fruits and vegetables by freeze-drying with integrated freeze-thaw and ultrasound. The patent includes screening raw materials, cleaning and cutting, blanching and killing, ultrasonic-assisted freeze-thaw, first freeze-drying, vacuum impregnation, and second freeze-drying; Chinese patent CN105685355A discloses a processing method for instant freeze-dried sugared strawberries. The patent includes picking, cleaning, one-time tray loading, quick freezing, freeze drying, sugar solution impregnation, second tray loading, and freeze drying. Both patents have undergone pre-drying, impregnation, and re-drying processes. In this process, vacuum freeze drying equipment, vacuum impregnation equipment, and freezing equipment are required. The materials need to be continuously transferred between the equipment. The process is cumbersome, the cost investment is large, and the operating efficiency is low. At the same time, vacuum impregnation requires the material to be immersed in the impregnation liquid for a certain period of time, and the nutrients in the material will be lost to a certain extent during the impregnation process. Summary of the invention

[0005] Technical issues

[0006] The purpose of the present invention is to: in view of the problems existing in the above-mentioned prior art, a method for improving the drying quality and functional factors of fruits and vegetables by low-temperature freeze-thaw combined with integrated immersion freeze-drying is proposed, small molecule peptides, functional oligosaccharides, and soluble dietary fiber are used as sugar substitutes to increase the solid content of dehydrated fruits and vegetables and increase the nutritional functional factors of the products, while the low-temperature freeze-thaw technology is used to avoid the loss of nutrients caused by cell rupture; a spray immersion vacuum freeze-drying integrated equipment is used to complete the pre-drying, vacuum immersion, freezing, and post-drying processes in one device, which greatly saves production cost investment, significantly improves work efficiency, and improves technical economy. The invention can effectively promote the rapid development of the fruit and vegetable dehydration and drying technology industry, and promote the development of my country's fruit and vegetable leisure food in the direction of efficiency, health, and green.

[0007] Technical Solution

[0008] A method for improving the drying quality and functional factors of fruits and vegetables by low-temperature freeze-thaw combined with integrated immersion freeze-drying, characterized in that:

[0009] (1) Raw material selection: Select fresh, appropriately mature, and solid content less than 12% fruit and vegetable raw materials;

[0010] (2) Cleaning and cutting: Clean the fruits and vegetables and cut them into the required shapes according to the requirements;

[0011] (3) Blanching and freezing: Put the cut vegetables into 95-100°C hot water for blanching for 30-120 seconds and then cool them. Put the cut fruits and cooled vegetables into a -15--10°C freezing device and freeze them for 5-10 hours.

[0012] (4) Low-temperature freeze-thaw cycle: Place the frozen fruits and vegetables in a -5 to 0°C freezer for 20 to 24 hours, then lower the temperature of the freezer to -15 to -10°C and keep it for 4 to 8 hours. Repeat the low-temperature freeze-thaw cycle 5 to 7 times, and finally control the material temperature at -15 to -10°C.

[0013] (5) Vacuum freeze drying: Place the frozen and thawed fruits and vegetables on a material tray and place them in a spray immersion vacuum freeze drying integrated equipment for vacuum freeze drying for 3 to 10 hours until the moisture content is 40 to 60%;

[0014] (6) Vacuum impregnation: Turn on the impregnation liquid spray system in the spray impregnation vacuum freeze-drying integrated equipment, spray for 10 to 40 seconds and pause for 1 to 5 minutes, and spray 3 to 10 times in total;

[0015] (7) Secondary vacuum freeze drying: The fruits and vegetables after vacuum impregnation are further vacuum freeze dried in a spray impregnation vacuum freeze drying integrated equipment until the moisture content is 5-10%.

[0016] The soaking liquid spraying system sprays the soaking liquid, which is composed of 0-5% small molecule peptides, 15-20% functional oligosaccharides, 0-6% soluble dietary fiber, and 75-85% fruit and vegetable raw water.

[0017] The spray impregnation vacuum freeze drying integrated equipment comprises a freeze drying chamber (1), a cold trap chamber A (2) and a cold trap chamber B (3), a vacuum unit, a refrigeration unit A (4) and a refrigeration unit B (5), a heater (6), an impregnation liquid spray system, and a raw water collection system. The bottom end of the freeze drying chamber (1) is connected to the impregnation liquid spray system. The freeze drying chamber (1) is connected to the cold trap chamber A (2) and the cold trap chamber B (3) through a butterfly valve A (7) and a butterfly valve B (8). The other ends of the cold trap chamber A (2) and the cold trap chamber B (3) are connected through butterfly valves C (7) and B (8). (9) and butterfly valve D (10) are connected to a vacuum unit, the vacuum unit is composed of two Roots pumps (11) connected in series and two water ring pumps (12) connected in parallel, the cold trap chamber A (2) and the cold trap chamber B (3) are connected to the refrigeration unit A (4) and the refrigeration unit B (5) respectively, and the bottom ends are connected to two raw water collection systems respectively, the heater (6) is connected to the heating partition (13) in the freeze-drying chamber (1), and is connected to the heating coil A (14) and the heating coil B (15) in the cold trap chamber A (2) and the cold trap chamber B (3) respectively.

[0018] The impregnation liquid spray system comprises a U-shaped impregnation liquid delivery pipe (16), a nozzle delivery pipe (17), an atomizing nozzle (18), an impregnation liquid tank (19), an external delivery pipeline (20), a high-pressure pump (21), and a flow regulating valve (22). The U-shaped impregnation liquid delivery pipe (16) is arranged on both sides of the inner wall of the tank body of the freeze-drying bin (1), one end of the U-shaped impregnation liquid delivery pipe is connected to the nozzle delivery pipe (17), the nozzle delivery pipe (17) is arranged between the heating baffle (13) and the material tray (23), and a certain number of atomizing nozzles (18) are arranged on the nozzle delivery pipe (17). The bottom end of the U-shaped impregnation liquid delivery pipe (16) is connected to the impregnation liquid tank (19) through the external delivery pipeline (20), and a high-pressure pump (21) and a flow regulating valve (22) are arranged in the middle.

[0019] The two raw water collection systems are respectively composed of a raw water collection box A (24) and a raw water collection box B (25), a vacuum diaphragm valve A (26) and a vacuum diaphragm valve B (27), a pressure relief valve A (28) and a pressure relief valve B (29), and a drain valve A (30) and a drain valve B (31). The raw water collection box A (24) and the raw water collection box B (25) are respectively connected to the cold trap chamber A (2) and the cold trap chamber B (3), and a vacuum diaphragm valve A (26) and a vacuum diaphragm valve B (27) are respectively arranged in the middle. The upper end of the raw water collection box is provided with a pressure relief valve A (28) and a pressure relief valve B (29), and the lower end is provided with a drain valve A (30) and a drain valve B (31).

[0020] The spray-impregnation vacuum freeze-drying integrated drying steps are:

[0021] The frozen fruit and vegetable materials are evenly spread on the material plate (23), placed in the freeze-drying chamber, and the refrigeration unit A (4) and the butterfly valve A (7), the vacuum unit and the butterfly valve C (9) are turned on, and the butterfly valve B (8) and the butterfly valve D (10) are closed to carry out the first vacuum freeze-drying. During the vacuum freeze-drying process, the ice in the material is directly sublimated into water vapor, which is brought into the cold trap chamber A (2) under the action of the vacuum unit. Under the action of the refrigeration unit A (4), the water vapor is quickly frozen into ice and covers the inside of the cold trap chamber A (2). When the water vapor is condensed to a certain degree, the refrigeration unit A (4), the butterfly valve A (7) and the butterfly valve C (9) are turned off, and the refrigeration unit B (5), the butterfly valve B (8) and the butterfly valve D (10) are turned on. The water vapor condenses into ice in the cold trap B (3) through the butterfly valve B (8), and at the same time, the heating coil A (14) in the cold trap A (2) is opened, and the heat source delivered by the heater (6) melts the frozen ice in the cold trap A (2) into water, and the drain valve A (30) is closed, and the vacuum diaphragm valve A (26) and the pressure relief valve A (28) are opened, and the raw water removed from the material in the cold trap A (2) is transported to the raw water collection tank A (24). When the raw water in the raw water collection tank A (24) reaches a certain height, the vacuum diaphragm valve A (26) is closed, and the raw water in the material is discharged through the drain valve A (30). Through the above steps, the cold trap A (2) and the cold trap B (3) are opened cyclically to collect the raw water of the material.

[0022] The impregnation liquid is placed in an impregnation liquid tank (19). When the first vacuum freeze drying is completed, the high-pressure pump (21) of the impregnation liquid spray system is turned on, and the impregnation liquid is transported to the U-shaped impregnation liquid transport pipe (16) through the external transport pipe (20). The impregnation liquid is then transported to the atomizing nozzle (18) through the nozzle transport pipe (17). The atomizing nozzle (18) atomizes the impregnation liquid into small droplets and sprays them onto the surface of the material. Then, the pressure relief valve C (32) is slowly opened. The impregnation liquid is impregnated into the material under the action of positive and negative pressures inside and outside the cell. The atomizing nozzle (18) is continuously opened to spray the impregnation liquid according to the impregnation speed of the impregnation liquid. The flow rate of the impregnation liquid is regulated by the flow regulating valve (22).

[0023] After the vacuum impregnation is completed, the impregnated material is frozen to -15 to -10°C by the refrigeration unit A (4) or the refrigeration unit B (5), and then the vacuum unit is turned on to carry out a second vacuum freeze drying. After the drying is completed, the pressure relief valve C (32) is opened to take out the product.

[0024] The product obtained by the method of low-temperature freeze-thaw combined with integrated immersion freeze-drying to improve the drying quality and functional factors of fruits and vegetables.

[0025] Beneficial Effects

[0026] 1. The present invention introduces low-temperature cycle freeze-thaw technology, which not only improves the late freeze-drying rate but also avoids the loss of nutrients caused by freeze-thaw. Due to the problems of high energy consumption and long time in vacuum freeze-drying technology, the traditional process promotes the destruction of cell structure through repeated freeze-thaw, and forms a water migration channel inside the cells of fruits and vegetables, which can accelerate the late freeze-drying rate and reduce production costs. However, during the traditional freeze-thaw process, due to the destruction of the cell structure, the cell contents will be lost, and the shape and structure of fruits and vegetables will also change to a certain extent. The present invention adopts reverse thinking to innovatively propose high-temperature freezing and low-temperature freeze-thaw technology. During the high-temperature freezing process of fruits and vegetables, larger ice crystals will be generated to destroy the cell structure. At the same time, high and low temperature conversion freeze-thaw is performed while ensuring that the cells are in a frozen state, further destroying the cell structure, constructing a water migration channel during the freeze-drying process, and improving the freeze-drying rate. The introduction of this technology not only ensures the formation of the fruit and vegetable drying migration channel, but also avoids the loss of nutrients inside the cells during this process.

[0027] 2. The present invention uses nutritional functional ingredients as sugar substitutes to increase the solid content of dried fruit and vegetable products and enrich nutritional functional factors. Since fruits and vegetables with a solid content of less than 12% have poor crispness and low output after vacuum freeze-drying, they cannot meet the goals of consumers and business operators, and traditional sugar impregnation will bring consumers the adverse effects of excess sugar. The present invention adds small molecular weight and highly functional substances such as small molecule peptides, functional oligosaccharides, and soluble dietary fiber cones to fruit and vegetable materials. Combined with the moisture migration channel constructed by the above-mentioned low-temperature cycle freeze-thaw technology, these functional factors can easily enter the fruit and vegetable materials, which can improve the quality and output of dried fruit and vegetable products, and give the dried fruit and vegetable products stronger functional effects.

[0028] 3. The spray impregnation vacuum freeze drying integrated equipment designed by the present invention can realize the precise control of the concentration of the impregnation liquid by atomizing spray impregnation, and avoid the loss of nutrients in fruits and vegetables. Traditional vacuum impregnation requires that the material be placed in the impregnation liquid to achieve the effect of impregnation. During the impregnation process, the contents of the fruit and vegetable materials will be dissolved, resulting in the loss of nutrients. A U-shaped impregnation liquid delivery pipe is provided in the freeze drying chamber of the equipment designed by the present invention, one end of which is connected to the nozzle delivery pipe, and a certain number of atomizing nozzles are provided on the nozzle delivery pipe, and the other end is connected to the external delivery pipeline, and is connected to the impregnation liquid tank through the external delivery pipeline. This design realizes that the work of the vacuum freeze drying equipment, vacuum impregnation equipment and freezing equipment is completed by one device, avoiding the transfer of materials between multiple devices, saving labor input and equipment cost investment, and improving production efficiency. At the same time, the impregnation liquid is sprayed on the surface of the material during the spray impregnation process, and is quickly impregnated into the material under the action of positive and negative pressure inside and outside the cell, avoiding the change of the concentration of the impregnation liquid when a large amount of materials are impregnated in the traditional vacuum impregnation, which is difficult to achieve precise control, and retains a large amount of nutrients in the material.

[0029] 4. The spray impregnation vacuum freeze drying integrated equipment designed by the present invention is equipped with a fruit and vegetable raw water recovery system, which can realize the recycling of raw water and reduce the loss rate of flavor pigment substances. Fresh fruits and vegetables contain 80-90% of water. During the drying process, these water will be sublimated into water vapor and condensed into ice in the cold trap. The traditional process directly melts the ice through the cold trap and discards it, resulting in a lot of waste; at the same time, during the drying process, the volatile flavor substances and pigment substances of fruits and vegetables will be lost with the migration of water. The equipment designed by the present invention is connected to the cold trap with a raw water collection box. Through the conversion between the two cold traps, the raw water is collected on the basis of ensuring continuous freeze drying. The raw water of fruits and vegetables is added when preparing the impregnation liquid, and the volatile flavor substances and pigment substances lost in the freeze drying process are given to the fruits and vegetables again, and the secondary utilization of the raw water of fruits and vegetables is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the structure of the spray impregnation vacuum freeze drying integrated equipment;

[0031] Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure of the freeze-drying chamber;

[0032] In the figure: 1-freeze drying chamber, 2-cold trap chamber A, 3-cold trap chamber B, 4-refrigeration unit A, 5-refrigeration unit B, 6-heater, 7-butterfly valve A, 8-butterfly valve B, 9-butterfly valve C, 10-butterfly valve D, 11-Roots pump, 12-water ring pump, 13-heating baffle, 14-heating coil A, 15-heating coil B, 16-U-type impregnation liquid delivery pipe, 17-nozzle delivery pipe, 18-atomizing nozzle, 19-impregnation liquid tank, 20-external delivery pipeline, 21-high pressure pump, 22-flow regulating valve, 23-material tray, 24-raw water collection box A, 25-raw water collection box B, 26-vacuum diaphragm valve A, 27-vacuum diaphragm valve B, 28-pressure relief valve A, 29-pressure relief valve B, 30-drain valve A, 31-drain valve B, 32-pressure relief valve C. DETAILED DESCRIPTION

[0033] (1) Spray impregnation vacuum freeze drying integrated equipment

[0034] The spray impregnation vacuum freeze drying integrated equipment of the present invention is as follows Figure 1 and Figure 2As shown, it includes a freeze-drying bin 1, a cold trap bin A2 and a cold trap bin B3, a vacuum unit, a refrigeration unit A4 and a refrigeration unit B5, a heater 6, an impregnation liquid spray system, and a raw water collection system. The U-shaped impregnation liquid delivery pipe 16, the nozzle delivery pipe 17, and the atomizing nozzle 18 of the impregnation liquid spray system are located inside the freeze-drying bin 1. The lower end of the U-shaped impregnation liquid delivery pipe 16 extends from the bottom end of the freeze-drying bin 1 and is connected to the impregnation liquid tank through an external delivery pipe 20. The U-shaped impregnation liquid delivery pipe 16 is arranged on both sides of the inner wall of the tank body of the freeze-drying bin 1, and the nozzle delivery pipe 17 is arranged between the heating partition 15 and the material tray 23, and one end is connected to the U-shaped impregnation liquid delivery pipe 16. A certain number of atomizing nozzles 18 are arranged on the nozzle delivery pipe 17 to ensure that the impregnation liquid mist sprayed by the nozzle is evenly sprayed on the surface of the material.

[0035] In order to realize the collection of raw water in the case of continuous freeze drying, the equipment is provided with two sets of refrigeration systems and raw water collection systems, which are respectively connected to the freeze drying chamber 1 through butterfly valve A7 and butterfly valve B8. The switching of butterfly valve A7 and butterfly valve B8 enables one set of refrigeration systems and raw water collection systems to perform freeze drying refrigeration and raw water vapor condensation, and the other set to melt raw water ice and collect raw water through the heat source of heater 6. The other ends of the two sets of refrigeration systems are connected to the same vacuum unit, and the vacuum degree of the two sets of refrigeration systems is changed by switching butterfly valve C9 and butterfly valve D10.

[0036] (II) Embodiment

[0037] Example 1

[0038] Fresh strawberries were selected as raw materials, the stems were removed and washed with clean water, the surface water was drained, the strawberries were cut into 5 cm thick slices, evenly spread on the material tray 23, and placed in a -15°C freezer for 6 hours, the temperature of the freezer was raised to -2°C and kept for 22 hours, and then the temperature of the freezer was lowered to -15°C and kept for 6 hours, and the low-temperature freeze-thaw cycle was repeated 5 times, and finally the material temperature was controlled at -15°C; the frozen and thawed strawberry slices were placed on the material tray 23, and placed in a spray impregnation vacuum freeze drying machine. In the integrated equipment, the refrigeration unit A4 and the butterfly valve A7, the vacuum unit and the butterfly valve C9 are turned on, the butterfly valve B8 and the butterfly valve D10 are closed, and the vacuum freeze-drying is carried out for 4 hours until the moisture content is 50%. At the same time, the original water vapor sublimated from the strawberry slices condenses into ice in the cold trap A2; the refrigeration unit A4, the butterfly valve A7 and the butterfly valve C9 are turned off, the heating coil A14 in the cold trap A2 is turned on, and the heat source delivered by the heater 6 melts the frozen ice in the cold trap A2 into water, and the vacuum diaphragm valve A26 and the pressure relief valve are turned on. Valve A28 is used to transport the melted strawberry slice raw water to the raw water collection box A24, and the water release valve A30 is opened to collect the water; the collected raw water is used to prepare the impregnation solution, and the impregnation solution is 2% small molecule peptide, 15% functional oligosaccharide, 3% soluble dietary fiber, and 80% strawberry slice raw water. The impregnation solution is loaded into the impregnation liquid tank 19, and the high-pressure pump 21 and the flow regulating valve 22 are turned on. The impregnation liquid is transported to the U-shaped impregnation liquid delivery pipe 16 through the external delivery pipe 20, and then transported to the nozzle delivery pipe The delivery pipe 17 sprays the impregnation liquid onto the surface of the strawberry slices with a moisture content of 50% through the atomizing nozzle, and the pressure relief valve C32 is slowly opened. The impregnation liquid is impregnated into the strawberry slices under the action of positive and negative pressures inside and outside the cells. The cyclic spraying and opening of the pressure relief valve C32 allow the impregnation liquid to be completely immersed in the strawberry slice tissue, and the impregnation liquid spray system is closed; at this time, the refrigeration unit B5, the butterfly valve B8 and the butterfly valve D10 are opened to freeze the impregnated strawberry slices to -15°C and then vacuum freeze-dry them to obtain a dried strawberry slice product.

[0039] Example 2

[0040] Fresh carrots were selected as raw materials, the surface of the carrots was cleaned with clean water, the carrot heads and the surface fibrous roots were cut off, the carrots were peeled and cut into strips with a thickness of 0.3 cm and a length of 4 cm, and the strips were spread on the material tray 23, and placed in a -12°C freezing device for freezing for 8 hours, the freezing device temperature was raised to -0°C and maintained for 20 hours, and then the freezing device temperature was lowered to -12°C and maintained for 8 hours, and the low-temperature freezing and thawing was repeated 7 times, and finally the material temperature was controlled at -12°C; the frozen and thawed carrot strips were placed on the material tray 23, placed in the spray impregnation vacuum freeze-drying integrated equipment, and the vacuum unit and The first refrigeration unit is used for vacuum freeze drying for 8 hours until the moisture content is 40%. The first refrigeration unit is turned off, and the raw water collection system and the heating coil connected to the first cold trap are turned on to melt the raw water of the carrot strips and collect it. The impregnation liquid is prepared with a ratio of 5% small molecule peptides, 20% functional oligosaccharides, and 85% raw water of the carrot strips, and is placed in the impregnation liquid tank 19. The impregnation liquid spray system and the pressure relief valve are opened in a cycle to spray the impregnation liquid into the carrot strip tissue. Then the second refrigeration unit is turned on to complete the later vacuum freeze drying of the carrot strips to obtain a dried carrot strip product.

Claims

1. A method for improving the drying quality and functional factors of fruits and vegetables by low-temperature freeze-thaw combined with integrated immersion freeze-drying, characterized in that: (1) Raw material selection: Select fresh, appropriately mature, and solid content less than 12% fruit and vegetable raw materials; (2) Cleaning and cutting: Clean the fruits and vegetables and cut them into the required shapes according to the requirements; (3) Blanching and freezing: Put the cut vegetables into 95-100°C hot water for blanching for 30-120 seconds and then cool them. Put the cut fruits and cooled vegetables into a -15--10°C freezing device and freeze them for 5-10 hours. (4) Low-temperature freeze-thaw cycle: Place the frozen fruits and vegetables in a -5 to 0°C freezer for 20 to 24 hours, then lower the temperature of the freezer to -15 to -10°C and keep it for 4 to 8 hours. Repeat the low-temperature freeze-thaw cycle 5 to 7 times, and finally control the material temperature at -15 to -10°C. (5) Vacuum freeze drying: Place the frozen and thawed fruits and vegetables on a material tray and place them in a spray immersion vacuum freeze drying integrated equipment for vacuum freeze drying for 3 to 10 hours until the moisture content is 40 to 60%; (6) Vacuum impregnation: Turn on the impregnation liquid spray system in the spray impregnation vacuum freeze-drying integrated equipment, spray for 10 to 40 seconds and pause for 1 to 5 minutes, and spray 3 to 10 times in total; (7) Secondary vacuum freeze drying: The fruits and vegetables after vacuum impregnation are further vacuum freeze dried in a spray impregnation vacuum freeze drying integrated device until the moisture content is 5-10%; The impregnation liquid spraying system sprays the impregnation liquid, which is composed of 0-5% small molecule peptides, 15-20% functional oligosaccharides, 0-6% soluble dietary fiber, and 75-85% fruit and vegetable raw water; the soluble dietary fiber does not include functional oligosaccharides; The spray impregnation vacuum freeze drying integrated equipment comprises a freeze drying chamber (1), a cold trap chamber A (2) and a cold trap chamber B (3), a vacuum unit, a refrigeration unit A (4) and a refrigeration unit B (5), a heater (6), an impregnation liquid spray system, and a raw water collection system. The bottom end of the freeze drying chamber (1) is connected to the impregnation liquid spray system. The freeze drying chamber (1) is connected to the cold trap chamber A (2) and the cold trap chamber B (3) through a butterfly valve A (7) and a butterfly valve B (8). The other ends of the cold trap chamber A (2) and the cold trap chamber B (3) are connected through butterfly valves C (7) and B (8). (9) and butterfly valve D (10) are connected to a vacuum unit, the vacuum unit is composed of two Roots pumps (11) connected in series and two water ring pumps (12) connected in parallel, the cold trap chamber A (2) and the cold trap chamber B (3) are connected to the refrigeration unit A (4) and the refrigeration unit B (5) respectively, and the bottom ends are connected to two raw water collection systems respectively, the heater (6) is connected to the heating partition (13) in the freeze-drying chamber (1), and is connected to the heating coil A (14) and the heating coil B (15) in the cold trap chamber A (2) and the cold trap chamber B (3) respectively; The impregnation liquid spray system is composed of a U-shaped impregnation liquid delivery pipe (16), a nozzle delivery pipe (17), an atomizing nozzle (18), an impregnation liquid tank (19), an external delivery pipeline (20), a high-pressure pump (21), and a flow regulating valve (22). The U-shaped impregnation liquid delivery pipe (16) is arranged on both sides of the inner wall of the tank body of the freeze-drying bin (1), one end of the U-shaped impregnation liquid delivery pipe is connected to the nozzle delivery pipe (17), the nozzle delivery pipe (17) is arranged between the heating baffle (13) and the material tray (23), and a certain number of atomizing nozzles (18) are arranged on it. The bottom end of the U-shaped impregnation liquid delivery pipe (16) is connected to the impregnation liquid tank (19) through the external delivery pipeline (20), and a high-pressure pump (21) and a flow regulating valve (22) are arranged in the middle. The two raw water collection systems are respectively composed of a raw water collection box A (24) and a raw water collection box B (25), a vacuum diaphragm valve A (26) and a vacuum diaphragm valve B (27), a pressure relief valve A (28) and a pressure relief valve B (29), and a drain valve A (30) and a drain valve B (31). The raw water collection box A (24) and the raw water collection box B (25) are respectively connected to the cold trap chamber A (2) and the cold trap chamber B (3), and a vacuum diaphragm valve A (26) and a vacuum diaphragm valve B (27) are respectively arranged in the middle. The upper end of the raw water collection box is provided with a pressure relief valve A (28) and a pressure relief valve B (29), and the lower end is provided with a drain valve A (30) and a drain valve B (31).

2. The method according to claim 1, characterized in that: The spray-impregnation vacuum freeze-drying integrated drying steps are: The frozen fruit and vegetable materials are evenly spread on the material plate (23), placed in the freeze-drying chamber, and the refrigeration unit A (4) and the butterfly valve A (7), the vacuum unit and the butterfly valve C (9) are turned on, and the butterfly valve B (8) and the butterfly valve D (10) are closed to carry out the first vacuum freeze-drying. During the vacuum freeze-drying process, the ice in the material is directly sublimated into water vapor, which is brought into the cold trap chamber A (2) under the action of the vacuum unit. Under the action of the refrigeration unit A (4), the water vapor is quickly frozen into ice and covers the inside of the cold trap chamber A (2). When the water vapor is condensed to a certain degree, the refrigeration unit A (4), the butterfly valve A (7) and the butterfly valve C (9) are turned off, and the refrigeration unit B (5), the butterfly valve B (8) and the butterfly valve D (10) are turned on. , the water vapor condenses into ice in the cold trap bin B (3) through the butterfly valve B (8), and at the same time, the heating coil A (14) in the cold trap bin A (2) is opened, and the heat source delivered by the heater (6) melts the frozen ice in the cold trap bin A (2) into water, and the drain valve A (30) is closed, and the vacuum diaphragm valve A (26) and the pressure relief valve A (28) are opened, and the raw water removed from the material in the cold trap bin A (2) is transported to the raw water collection tank A (24). When the raw water in the raw water collection tank A (24) reaches a certain height, the vacuum diaphragm valve A (26) is closed, and the raw water in the material is discharged through the drain valve A (30). Through the above steps, the cold trap bin A (2) and the cold trap bin B (3) are opened cyclically to collect the raw water of the material; The impregnation liquid is placed in an impregnation liquid tank (19). After the first vacuum freeze drying is completed, the high-pressure pump (21) of the impregnation liquid spray system is turned on, and the impregnation liquid is transported to the U-shaped impregnation liquid transport pipe (16) through the external transport pipe (20). The impregnation liquid is then transported to the atomizing nozzle (18) through the nozzle transport pipe (17). The atomizing nozzle (18) atomizes the impregnation liquid into small droplets and sprays them onto the surface of the material. Then, the pressure relief valve C (32) is slowly opened. The impregnation liquid is impregnated into the material under the action of positive and negative pressures inside and outside the cell. The atomizing nozzle (18) is continuously opened to spray the impregnation liquid according to the impregnation speed of the impregnation liquid. The flow rate of the impregnation liquid is regulated by the flow regulating valve (22); After the vacuum impregnation is completed, the impregnated material is frozen to -15 to -10°C by the refrigeration unit A (4) or the refrigeration unit B (5), and then the vacuum unit is turned on to carry out a second vacuum freeze drying. After the drying is completed, the pressure relief valve C (32) is opened to take out the product.

3. The product obtained by the method of improving the drying quality and functional factors of fruits and vegetables by low-temperature freeze-thaw combined with integrated immersion freeze-drying as described in claim 1 or 2.

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