Litchi freeze-drying process and production system

Abstract

The invention discloses a lychee freeze-drying process. The lychee freeze-drying process comprises the following steps: S1, storing and feeding raw materials; s2, pretreatment: cleaning, peeling and denucleating, disinfecting and protecting color, rinsing and draining; s3, buffering and temporarily storing a semi-finished product; S4, quickly freezing; s5, performing vacuum freeze drying; and S6, packaging. The invention further discloses a freeze-drying system for implementing the lychee freeze-drying process. The freeze-drying system comprises a raw material storage unit, a pretreatment unit, the buffer refrigeration house, a quick-freezing device, a vacuum freeze-drying device, a logistics carrier unit and a control unit. The strict semi-finished product buffer temporary storage link is set, and the disinfection and color protection steps are combined, so that microbial growth, enzymatic browning and juice loss are inhibited to the greatest extent, and the quality of the final lychee freeze-dried product is ensured. By arranging the buffer refrigeration house and the matched control system, pulse type production control based on inventory level is implemented, and the problem of semi-finished product overstock caused by mismatching of productivity of the previous and later procedures is solved.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a lychee freeze-drying process and production system. Background Technology

[0002] Lychees are rich in nutrients, but they are extremely prone to browning and rotting after harvesting, resulting in a very short shelf life. While vacuum freeze-drying technology can preserve the color, aroma, flavor, and nutrients of fruits and vegetables to the greatest extent and is an effective means of producing high-quality dried lychee products, significant problems remain in practical application. In existing technologies, the outer skin of lychees must be removed before freeze-drying, resulting in direct exposure of the pulp, which is highly susceptible to enzymatic browning. Furthermore, the soft texture of the pulp makes it easily damaged and prone to juice leakage during subsequent processing, causing the freeze-dried lychee pulp to shrink and become dull in color. In addition, the long processing cycle of freeze-drying equipment becomes a bottleneck in the production line, while the pre-processing steps are fast. If pre-processing is continuous, a large amount of peeled lychee semi-finished product will accumulate in front of the freeze dryer for a long time, affecting the quality of the final lychee pulp. Summary of the Invention

[0003] The purpose of this invention is to provide a lychee freeze-drying process and production system to solve the problems existing in the prior art.

[0004] To achieve the above objectives, the technical solution of the present invention provides a lychee freeze-drying process comprising the following steps: S1. Raw material storage and feeding; S2. Pre-treatment, specifically including the following steps: S21. Cleaning: Cleaning the lychees; S22. Peeling and pitting: Removing the peel and pit to obtain whole, peel-free lychee pulp; S23. Disinfection and color protection: Disinfecting and protecting the color of the peel-free lychee pulp; S24. Rinsing and draining; S3. Semi-finished product buffer storage: Transferring the peel-free lychee pulp treated in S2 to a buffer cold storage; S4. Quick freezing: Taking the freeze-drying trays out of the buffer cold storage in a "first-in, first-out" order and sending them into a quick-freezing device; S5. Vacuum freeze drying: Placing the quick-frozen lychee pulp in a vacuum freeze-drying device for drying until the moisture content of the lychee pulp drops to 3%-5%; S6. Packaging: Sorting and packaging the freeze-dried finished product in a low-temperature and low-humidity environment.

[0005] Furthermore, in step S1, the raw materials are stored in a raw material cold storage at a temperature of 0-4℃ and a relative humidity of 90-95%; in step S3, the buffer cold storage is at a temperature of 0-4℃ and a relative humidity of 85%-95%, and the time that the peeled lychees stay in it does not exceed 2 hours.

[0006] Furthermore, the specific process of disinfection and color protection in step S23 is as follows: Immerse the peelless lychee pulp in a mixed solution at room temperature containing 50-100ppm stable chlorine dioxide, 0.5%-1% citric acid and 0.2%-0.5% ascorbic acid for 2-3 minutes; the specific process of rinsing and draining in step S24 is to quickly rinse with clean low-temperature water at 0-4℃ to remove residual liquid on the surface, and then drain the water from the surface of the pulp.

[0007] Furthermore, step S4, quick-freezing, involves rapid freezing at -30°C to -35°C, causing the core temperature of the lychee pulp to drop below -18°C within 30 minutes.

[0008] Furthermore, step S5, vacuum freeze drying, includes the following steps: S51. Sublimation drying stage: the heating plate temperature is controlled between -10°C and 0°C, the vacuum degree is maintained at 80-100 Pa, and the duration is 6-8 hours; S52. Desorption transition stage: the heating plate temperature is gradually increased from 0°C to 40-50°C, and the vacuum degree is stabilized at 50-70 Pa, and the duration is 3-4 hours; S53. Final desorption stage: the heating plate temperature is increased to 55-70°C, the vacuum degree is maintained at 50-60 Pa, and the duration is 2-3 hours, until the product moisture content drops to 3%-5%.

[0009] This invention also discloses a freeze-drying system for implementing the above-mentioned lychee freeze-drying process, comprising a raw material storage unit, a pre-treatment unit, a buffer cold storage, a quick-freezing device, a vacuum freeze-drying device, a logistics carrier unit, and a control unit; the raw material storage unit is a raw material cold storage; the pre-treatment unit includes a washing device, a peeling and pitting device, a disinfection and color-protecting soaking tank, a rinsing tank, and a draining device; the logistics carrier unit includes a pallet rack and freeze-drying trays, and the pallet rack is equipped with RFID tags. The control unit includes an equipment control subunit, an inventory monitoring subunit, and a control subunit.

[0010] Furthermore, the equipment control subunit communicates with the equipment controllers of the raw material storage unit, pretreatment unit, buffer cold storage, quick-freezing device, and vacuum freeze-drying device through an industrial network to achieve control of individual equipment; the inventory monitoring subunit is an RFID reader installed at the entrance and exit of the buffer cold storage; the control subunit controls the working status of each device according to a preset algorithm based on the data from the control subunit and the inventory monitoring subunit.

[0011] This invention, by establishing a strict buffer storage stage for semi-finished products (0-4℃, humidity 5%-95%, residence time <2 hours) and combining it with disinfection and color-protection steps, maximizes the inhibition of microbial growth, enzymatic browning, and juice loss, thus ensuring the quality of the final freeze-dried lychee product. By setting up a buffer cold storage and a corresponding control system, and implementing "pulse-type" production control based on inventory levels, the pre-processing unit can operate efficiently and in batches, while the post-processing units (quick-freezing and freeze-drying) can operate continuously and stably. This effectively solves the problem of semi-finished product backlog caused by mismatched production capacity between upstream and downstream processes, avoids quality degradation due to excessive waiting time, and significantly improves the equipment utilization and production efficiency of the entire system. Attached Figure Description

[0012] Figure 1 This is a flowchart of the lychee freeze-drying process of the present invention.

[0013] Figure 2 This is a schematic diagram of the lychee freeze-drying production system of the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] As attached Figure 1 As shown, this invention discloses a lychee freeze-drying process, including the following steps: S1. Raw material storage and feeding: Fresh, unshelled lychees that have passed inspection are stored in a raw material cold storage at a temperature of 0-4℃ and a relative humidity of 90-95% for short-term storage; According to production instructions, raw materials are taken from the raw material cold storage in batches and fed into the pre-processing process.

[0016] S2. Pre-treatment, specifically including the following steps: S21. Washing: Clean the lychees; S22. Peeling and pitting: Remove the peel and pit using commercially available equipment to obtain whole, peel-free lychee pulp; S23. Disinfection and color protection: Immerse the peel-free lychee pulp in a mixed solution at room temperature containing 50-100ppm stable chlorine dioxide, 0.5%-1% citric acid, and 0.2%-0.5% ascorbic acid for 2-3 minutes; S24. Rinsing and draining: Quickly rinse with clean, low-temperature water at 0-4℃ to remove surface residue, and then drain the surface moisture of the pulp.

[0017] S3. Buffer storage of semi-finished products: The peeled lychee pulp after S2 treatment is laid in a single layer in a freeze-drying tray and quickly transferred to a buffer cold storage; the environmental parameters of the buffer cold storage are strictly controlled as follows: temperature 0-4℃, relative humidity 85%-95%, and the time that the peeled lychees stay in it does not exceed 2 hours. S4. Quick-freezing: Take the freeze-drying trays out of the buffer cold storage in the order of "first in first out" and put them into the quick-freezing device. They are quickly frozen at -30℃ to -35℃, so that the temperature of the center of the lychee pulp drops to below -18℃ within 30 minutes.

[0018] S5. Vacuum freeze-drying: The quick-frozen lychee pulp is placed in a vacuum freeze-drying apparatus and dried under a vacuum of 50-100 Pa, with the temperature of the heating plates controlled in stages, until the moisture content of the lychee pulp drops to 3%-5%. The specific process includes the following steps: S51. Sublimation Drying Stage: The heating plate temperature is controlled between -10°C and 0°C, and the vacuum degree is maintained at 80-100Pa for 6-8 hours. The low-temperature slow sublimation in this stage aims to ensure that the ice crystals sublimate smoothly, forming a stable porous skeleton to support the product shape and is key to preventing the pulp from collapsing.

[0019] S52. Desorption Transition Stage: The temperature of the heating plate is gradually increased from 0°C to 40-50°C, and the vacuum level is stabilized at 50-70 Pa for 3-4 hours. At this point, most of the free water has been removed, and moderate heating begins the desorption of some bound water.

[0020] S53. Final Desorption Stage: Raise the heating plate temperature to 55-70°C, maintain the vacuum at 50-60 Pa, and continue for 2-3 hours until the product moisture content drops to 3%-5%. This stage thoroughly removes strongly bound water while ensuring the product does not char.

[0021] By employing the segmented drying process described above, and through the coordinated control of "low-temperature shape preservation in the early stage and efficient dehydration in the later stage," the problem of lychee pulp shrinkage and deformation caused by excessively rapid temperature rise in the early stage in traditional freeze-drying processes is effectively solved. The final product has a full shape and good rehydration properties.

[0022] S6. Packaging: Sorting and packaging the freeze-dried products in a low-temperature and low-humidity environment.

[0023] As attached Figure 2 As shown, the present invention also discloses a lychee freeze-drying production system for implementing the above-mentioned process, including a raw material storage unit, a pre-processing unit, the buffer cold storage, a quick-freezing device, a vacuum freeze-drying device, a logistics carrier unit, and a control unit.

[0024] The raw material storage unit is a cold storage warehouse with temperature and humidity control, used to store lychees in their shells.

[0025] The pretreatment unit includes a cleaning device, a peeling and pitting device, a disinfection and color-protecting soaking tank, a rinsing tank, and a draining device.

[0026] The buffer cold storage is equipped with a humidification system to ensure that the internal environment is constant at 0-4℃ and humidity at 85%-95%.

[0027] The quick-freezing device is used to quick-freeze the semi-finished lychee pulp in the buffer cold storage.

[0028] The vacuum freeze-drying device is used to freeze-dry the quick-frozen semi-finished product.

[0029] The aforementioned raw material storage unit, pretreatment unit, buffer cold storage, quick-freezing device, and vacuum freeze-drying device are all commercially available lychee pulp.

[0030] The logistics carrier unit adopts a standardized pallet rack as the logistics carrier; the pallet rack can carry a preset number of freeze-drying trays, and its structural dimensions are matched with the feeding system of the buffer cold storage location, quick-freezing device and vacuum freeze-drying device; each pallet rack is fixed with an industrial-grade RFID electronic tag with a unique ID.

[0031] The control unit includes an equipment control subunit, an inventory monitoring subunit, and a control subunit.

[0032] The equipment control subunit communicates with the equipment controllers of the raw material storage unit, pretreatment unit, buffer cold storage, quick-freezing device, and vacuum freeze-drying device via an industrial network to achieve start-up and shutdown, speed adjustment, and setting and closed-loop control of process parameters (such as temperature and time) for individual equipment. Specifically, commercially available fieldbus technology is used for implementation.

[0033] The inventory monitoring subunit is an RFID reader installed at the entrance and exit of the buffer cold storage. It automatically identifies pallets entering and leaving the storage, and calculates and monitors the number of pallets (i.e., inventory level) in real time. The RFID reader is for commercially available lychee pulp.

[0034] The control subunit controls the operating status of each device according to a preset algorithm based on data from the control subunit and the inventory monitoring subunit. The control subunit is a host computer, which can be a PC or other industrial control host computer. Its specific control flow is as follows: Step 1: Preset the lower and upper limits of inventory levels (L and H), and set the standard operating cycle time for each process in the system database, especially the key cycles of the post-processing unit, such as the quick-freezing cycle (T_quick-freeze) and the vacuum freeze-drying cycle (T_freeze-dry).

[0035] Step 2: Obtain the current inventory quantity N in real time, the current operating status (running or stopped) of the pre-processing unit, and the real-time operating status and running time of the post-processing unit (quick freezer, freeze dryer).

[0036] Step 3: Time-based forecasting and assessment. The system predicts material demand over a future period based on the current status of the post-processing equipment and the standard operating cycle. For example, if the system detects that a batch in the freeze dryer has been running for 10 hours (its standard cycle T_freeze drying is 12 hours), it predicts that the equipment will finish the current batch in about 2 hours and will need to be fed with new materials. Under this prediction, even if the current inventory N is higher than the lower limit threshold L, to prevent the post-processing equipment from running idle while waiting for materials, the system will maintain the pre-processing unit in a low-speed operating state or trigger a small production pulse in advance to ensure seamless subsequent material feeding.

[0037] The system executes the following basic logic to ensure that inventory remains stable within a reasonable range [L, H]: Condition A: If the preprocessing unit is in running state and N≥H, then issue a stop command to the preprocessing unit.

[0038] Condition B: If the preprocessing unit is in a stopped state and N≤L, then issue a start command to the preprocessing unit.

[0039] Condition C: If neither of the above two conditions applies, then the current state of the pre-processing unit remains unchanged. This basic logic ensures a safety baseline of no inventory overflow and no material shortage.

[0040] Step 4: The system executes steps two through four in a set cycle (e.g., every minute) to achieve continuous monitoring and dynamic optimization scheduling of the entire production process.

[0041] Example 1 Raw material storage: Select "Feizixiao" lychees, about 80% ripe, free from pests, diseases, and mechanical damage. After inspection, the lychees are immediately sent to a raw material cold storage at a temperature of 2±0.5℃ and a humidity of 93±2%.

[0042] Pre-treatment: The existing washing equipment, peeling and pitting equipment, disinfection and color protection soaking tank, rinsing tank and draining equipment are used to clean the whole fruit of lychee, peel and pit, disinfect and color the pulp, rinse and drain.

[0043] The disinfectant and color-protecting solution formula is as follows: at room temperature, the stable concentration of chlorine dioxide is 80 ppm, the concentration of citric acid is 0.8%, and the concentration of ascorbic acid is 0.3%. Soaking time is 2.5 minutes. After soaking, rinse quickly with 3°C cold water and drain.

[0044] Semi-finished product buffer storage: Processed lychee pulp is laid in a single layer on trays (approximately 1 kg per tray), with 20 trays stacked on a standardized pallet rack. The pallet racks are transported to the buffer cold storage via AGV. Upon entry, an RFID reader at the entrance automatically identifies and records the information. The buffer cold storage environment is maintained by an automatic control system: temperature (2±0.5)℃, humidity (90±3)%. The system automatically records the entry time of each pallet rack, ensuring that any batch of semi-finished products remains in the storage for no more than 2 hours.

[0045] A strict matching relationship is established between the loading capacity of the pallet rack and the single-batch processing capacity of the post-processing equipment. This can be a one-to-one matching or a many-to-one matching. A one-to-one matching means that the capacity of a standard pallet rack is equal to the single-batch loading volume of an independent station in a quick-freezing or vacuum freeze-drying unit. For example, each compartment of a multi-compartment freeze dryer can hold exactly one pallet rack. A many-to-one matching means that the sum of the capacities of multiple (e.g., 2 or 3) standard pallet racks is equal to the single-batch loading volume of the entire quick-freezing or vacuum freeze-drying unit. This allows for material scheduling on a "whole rack" basis, enabling the post-processing equipment to feed at the optimal capacity and maximizing equipment utilization.

[0046] Quick-freezing and freeze-drying: The control system follows the "first-in, first-out" principle, scheduling AGVs to transport pallet racks from the buffer cold storage to the -33℃ quick-freezing device, where the core temperature of the lychee pulp reaches below -20℃ within 25 minutes.

[0047] The product is then placed in a vacuum freeze-drying apparatus. The temperature of the heating plate in the vacuum freeze-drying apparatus is controlled between -10°C and 0°C, and the vacuum degree is maintained at 80 Pa for 6 hours. After that, the temperature of the heating plate is gradually increased from 0°C to 50°C, and the vacuum degree is stabilized at 70 Pa for 3 hours. Then, the temperature of the heating plate is increased to 60°C, and the vacuum degree is maintained at 60 Pa for 2 hours, until the moisture content of the product drops to 3%-5%.

[0048] After discharge, the material is quickly inspected and packaged in a low-temperature and low-humidity workshop (temperature 18℃, humidity 25%).

[0049] The buffer cold storage has a maximum capacity of 20 pallet racks. The lower inventory threshold L = 6 racks (30% of total capacity) is set in the control unit. The upper inventory threshold H = 16 racks (80% of total capacity). Initially, the buffer cold storage inventory is 0. When the control system detects that the current inventory N ≤ L(6), it immediately starts the pre-processing unit to produce at maximum capacity until the inventory reaches 16 racks, at which point it automatically stops. The downstream quick-freezing and freeze-drying equipment runs continuously for 24 hours, sequentially taking materials from the buffer cold storage outlet to consume the inventory. When the inventory reaches 6 racks, the control system triggers the pre-processing unit again to replenish production. This cycle repeats, forming a stable "pulse-like" production rhythm.

[0050] It should be noted that, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "joining," "fixing," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

Claims

1. A lychee freeze-drying process, characterized in that, Includes the following steps: S1. Raw material storage and feeding; S2. Pre-treatment, specifically including the following steps: S21. Washing: Cleaning the lychees; S22. Peeling and pitting: Removing the peel and pit to obtain whole, peel-free lychee pulp; S23. Disinfection and color protection: Disinfecting and protecting the color of the peel-free lychee pulp; S24. Rinsing and draining; S3. Temporary storage of semi-finished products: Transfer the peeled lychee pulp after S2 treatment to a buffer cold storage; S4. Quick-freezing: Take the freeze-drying trays out of the buffer cold storage in the order of "first in first out" and send them into the quick-freezing device; S5. Vacuum freeze-drying: Place the quick-frozen lychee pulp in a vacuum freeze-drying device for drying until the moisture content of the lychee pulp drops to 3%-5%; S6. Packaging: Sorting and packaging the freeze-dried products in a low-temperature and low-humidity environment.

2. The freeze-drying process according to claim 1, characterized in that, In step S1, the raw materials are stored in a raw material cold storage at a temperature of 0-4℃ and a relative humidity of 90-95%; in step S3, the buffer cold storage is at a temperature of 0-4℃ and a relative humidity of 85%-95%, and the peeled lychees stay in it for no more than 2 hours.

3. The freeze-drying process according to claim 1, characterized in that, The specific process for disinfection and color protection in step S23 is as follows: Immerse the peeled lychee pulp in a mixed solution at room temperature containing 50-100ppm stable chlorine dioxide, 0.5%-1% citric acid and 0.2%-0.5% ascorbic acid for 2-3 minutes; The specific process for rinsing and draining in step S24 is to quickly rinse with clean, low-temperature water at 0-4℃ to remove residual liquid on the surface, and then drain the water from the surface of the pulp.

4. The freeze-drying process according to claim 1, characterized in that, Step S4, quick freezing, involves rapidly freezing the lychee pulp at -30°C to -35°C, causing the core temperature to drop below -18°C within 30 minutes.

5. The freeze-drying process according to claim 1, characterized in that, Step S5, vacuum freeze drying, includes the following steps: S51. Sublimation drying stage: The temperature of the heating plate is controlled between -10°C and 0°C, the vacuum degree is maintained at 80-100 Pa, and the duration is 6-8 hours; S52. Analysis transition stage: The temperature of the heating plate is raised from 0°C to 40-50°C at a gradual rate, and the vacuum degree is stabilized at 50-70 Pa for 3-4 hours. S53. Final analysis stage: Raise the temperature of the heating plate to 55-70°C, maintain the vacuum at 50-60 Pa for 2-3 hours until the product moisture content drops to 3%-5%.

6. A freeze-drying system for implementing the freeze-drying process of litchi according to any one of claims 1-5, characterized in that, The system includes a raw material storage unit, a pre-processing unit, a buffer cold storage, a quick-freezing device, a vacuum freeze-drying device, a logistics carrier unit, and a control unit. The raw material storage unit is a raw material cold storage facility. The pre-processing unit includes a washing device, a peeling and pitting device, a disinfection and color-protecting soaking tank, a rinsing tank, and a draining device. The logistics carrier unit includes pallet racks and freeze-drying trays, with the pallet racks equipped with RFID tags. The control unit includes an equipment control subunit, an inventory monitoring subunit, and a control subunit.

7. The freeze-drying system according to claim 6, characterized in that, The equipment control subunit communicates with the equipment controllers of the raw material storage unit, pre-processing unit, buffer cold storage, quick-freezing device, and vacuum freeze-drying device through an industrial network to control individual equipment; the inventory monitoring subunit is an RFID reader installed at the entrance and exit of the buffer cold storage. The control subunit controls the working status of each device according to a preset algorithm based on data from the control subunit and the inventory monitoring subunit.

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