Drying method of day lily

Abstract

The invention discloses a drying method of day lily, which adopts a segmented variable-temperature variable-humidity air drying process: in the first stage, drying for 1-2 hours at the temperature of 60-65 DEG C and the relative humidity of 30-40%, and balancing for 25-35 minutes after the drying is finished; in the second stage, drying is carried out for 3-4 hours at the temperature of 50-55 DEG C and the relative humidity of 15%-25%, and balancing is carried out for 55-65 minutes after drying is finished; in the third stage, drying at 45-50 DEG C under the relative humidity of 10-15% until the final water content is less than or equal to 8%; the air flow and the surface of the material form an included angle of 30-45 degrees during the drying period, the air speed is 2.0-2.5 m / s in the initial 0-5 minutes, the air speed is increased to 3.0-3.5 m / s in a stepped manner within 5-10 minutes, and the air speed is reduced to 1.0-1.5 m / s in the remaining drying time. According to the method, the drying efficiency and uniformity of the day lily can be effectively improved, browning and shape damage are reduced, and the high-quality dried product is obtained.

Description

Technical Field

[0001] The present invention relates to the field of food processing. More specifically, the present invention relates to a drying method for daylily flowers. Background Art

[0002] Daylily flowers ( Hemerocallis citrina Baroni ) as an important edible and medicinal cash crop, the quality of its dried products directly affects its commercial value and food safety. Hot air drying is one of the most widely used technologies in the large-scale processing of daylily flowers at present. However, when the traditional hot air drying process is applied to daylily flowers, it faces at least the following problems.

[0003] First of all, the flower bud structure of daylily flowers is delicate, rich in heat-sensitive substances such as polysaccharides, and has a high water content. It is difficult for the traditional constant temperature or simple segmented drying process to balance drying efficiency and quality. In the initial stage of drying, if the temperature is too high or the humidity is too low, the surface moisture of the material evaporates too fast, which easily leads to rapid shrinkage and hardening of the surface layer, forming a dense layer, hindering the outward migration of internal moisture. This not only prolongs the drying time, but also easily causes excessive heating of the internal moisture, resulting in the collapse of the flower bud shape, deepening of the color browning, and even the generation of burnt smell. On the contrary, if the initial temperature is too low and the humidity is too high, the drying efficiency is low, and staying in a temperature and humidity environment suitable for the growth of microorganisms for a long time increases the risk of mildew. Therefore, seeking a temperature and humidity change trajectory that can quickly dehydrate and maximize the protection of the material tissue structure and color is one of the main difficulties.

[0004] Secondly, the air flow organization during the drying process is crucial for drying uniformity and efficiency. In the traditional process, the wind speed usually remains constant or changes simply. When the wind speed is too high, the direction is single (such as vertically downward) and continuously acts on the surface of the material, it will intensify the forced dehydration in local areas, resulting in uneven drying; at the same time, the excessive air flow impact force is easy to damage the delicate flower bud shape. While too low wind speed is not conducive to the efficiency of heat and moisture exchange, affecting the drying rate. How to dynamically adjust the wind speed magnitude and even direction according to the physical state changes of the material (such as the surface hardening degree) at different stages of drying to balance the dehydration efficiency and protect the flower bud shape and promote the internal moisture diffusion is a key challenge.

[0005] Furthermore, the drying methods of static stacking or simple turning easily lead to uneven heating and dehydration within the material layer, between layers, and at different parts of a single flower bud. This not only makes it difficult to judge the drying end point (some areas are over-dried while some areas still contain too much water), but also significantly affects the overall color, rehydration property, and texture uniformity of the product. To achieve uniform heating and air exposure of the material during drying and avoid local overheating or insufficient dehydration, a more effective dynamic processing mechanism is needed.

[0006] Finally, the transitional treatment between drying stages is often overlooked. After completing a relatively intense dehydration stage, there are significant gradients in moisture distribution and temperature between the interior and surface of the material. If directly entering the next drying stage or cooling, due to the sudden change in internal and external stresses, it is extremely easy to cause cracking of the flower bud epidermis, damage to the internal structure (such as forming a hollow), or the product's moisture absorption and rehumidification, which affects the stability of the final moisture content. How to create a suitable temperature and humidity environment during the stage transition to redistribute the internal moisture and temperature of the material to reach a relatively balanced state, so as to buffer the stress and stabilize the structure, is an important link to ensure the integrity and storage stability of the product. Summary of the Invention

[0007] The object of the present invention is to provide a drying method for daylily to solve at least the above problems.

[0008] To achieve the object and other advantages of the present invention, there is provided a drying method for daylily, adopting a segmented variable-temperature and variable-humidity hot air drying process, including: The first stage is dried at 60 - 65°C and a relative humidity of 30% - 40% for 1 - 2 hours. After the first stage of drying, it is balanced at 33 - 37°C and a relative humidity of 43% - 47% for 25 - 35 minutes; The second stage is dried at 50 - 55°C and a relative humidity of 15% - 25% for 3 - 4 hours. At the start of the second stage, an atomized mixed solution of vitamin C and chitosan is injected into the hot air system, with an atomization particle size of 5 - 8 μm and an injection rate of 0.5 - 1.0 L / h; the vitamin C solution is precooled to 8 ± 2°C before atomization; after the second stage of drying, it is balanced at 23 - 27°C and a relative humidity of 58% - 62% for 55 - 65 minutes; The third stage is dried at 45 - 50°C and a relative humidity of 10% - 15% until the final moisture content ≤ 8%; where During drying, the air flow forms an angle of 30° - 45° with the material surface through an adjustable deflector. In the initial 0 - 5 minutes, a directional circulating air flow with a wind speed of 2.0 - 2.5 m / s is adopted. Within 5 - 10 minutes, the wind speed is stepped up to 3.0 - 3.5 m / s, and the wind speed is reduced to 1.0 - 1.5 m / s for the remaining drying time; the material is placed on a hollow rotating tray with a rotation speed of 3 - 5 rpm. After the tray rotates forward 85 - 95° each time, it immediately rotates backward 28 - 32°, and repeats until the end of the stage; 10 minutes after the first stage of drying, when rotating backward, the wind speed is instantaneously increased to 1.8 - 2.2 m / s and maintained for 4 - 6 seconds.

[0009] Preferably, the pretreatment of the daylily before the first stage includes: the fresh daylily is first sterilized with steam at 100°C for 90-120s, then immersed in water at 70-75°C for 30-35s, then immersed in cold water at 0-4°C for 60-65s, and finally placed in a mixed solution containing 0.1% (mass percentage) citric acid and 0.05% (mass percentage) calcium chloride at 35-40°C, and simultaneously applied with pulsed ultrasound with a frequency of 40±2kHz, a power density of 80-120W / L, and an operation time of 5s / interval of 2s, for 18-22 minutes.

[0010] Preferably, 2 minutes before the end of ultrasonic treatment, the power density is linearly reduced to 30-40 W / L, and the pulse mode is changed to working for 1 s and resting for 3 s.

[0011] Preferably, after the pulse ultrasonic treatment is completed, the material is taken out of the mixed solution and allowed to stand for draining for 5±0.5 minutes; during the draining period, the ambient temperature is maintained at 35±1°C, the relative humidity is maintained at 50±5%, and the rotating tray is operated at a speed of 2±0.3 rpm.

[0012] Preferably, the second stage atomization injection method is as follows: a) an annular atomizing nozzle is provided in the drying chamber 20-30 cm above the material layer, with the nozzle axis forming an elevation angle of 15°-25° with the horizontal plane; b) 1.5%-2.5% vitamin C solution and 0.05%-0.1% chitosan solution are premixed in a volume ratio of 1:3, and droplets are generated by an ultrasonic atomizer; c) during atomization, the air flow in the drying chamber is controlled to form a vortex flow field with a Reynolds number of 3500-4500 and a vortex period of 8-12 seconds / time; d) when the temperature in the nozzle area is ≥42°C, switch to an intermittent spray mode of working for 2 seconds and resting for 1 second.

[0013] Preferably, after the atomization injection is completed, the -8kV electrostatic field is maintained for 5±0.5 minutes to perform film curing. During the curing stage: the vortex flow field is turned off, and the side wall guide plates are started to form a 0.7-0.9m / s vertical laminar flow; after the curing is completed, the electrostatic field is returned to zero, and the original vortex flow field is restored and operated for 50-70 seconds; the relative humidity in the curing zone is controlled at 35±5%.

[0014] Preferably, the third stage of drying includes: arranging a porous vapor diffusion membrane on the top of the drying chamber, and loading trehalose-silica composite particles with a particle size of 50-80 nm on the surface of the membrane; cyclically performing the drying step and the breathing step, the drying step: drying at 45-50°C and a relative humidity of 10%-15% for 23-27 minutes; the breathing step: passing a saturated wet air pulse of 38-42°C and 0.15-0.25 MPa into the vapor diffusion membrane for a duration of 8-10 seconds, and then passing a dry air pulse of 44-46°C for 2-4 seconds, and the dry air flow rate is 1.1-1.3 times that of the wet air; circulating until the moisture content is ≤8%, and the moisture content decrease rate in the last 5 cycles is ≤0.3% / minute.

[0015] Preferably, in the drying step of each circulation unit in the third stage: when the drying proceeds to the 15±1 minute, the ambient relative humidity is instantaneously increased to 18±2% and maintained for 2±0.3 minutes, and then restored to 10%-15%.

[0016] The present invention has at least the following beneficial effects: 1. Through the segmented temperature and humidity variation process, the high-temperature and medium-humidity environment in the first stage is combined with the stepped wind speed change: the initial directional airflow accelerates the surface dehydration, the stepped speed increase strengthens the heat transfer, and the later speed reduction avoids damage, effectively suppressing the internal moisture migration blocked caused by surface hardening; the specific temperature and humidity balance treatment between stages, such as the medium-temperature and medium-humidity balance after the first stage, alleviates the sudden change of internal stress of the material and reduces the risk of epidermal cracking. The medium-temperature and low-humidity in the second stage are combined with the constant-speed airflow, and the pre-cooled and atomized vitamin C is atomized at the start, synergistically inhibiting browning and improving the nutrient retention rate. The low-temperature and low-humidity drying in the third stage ensures that the final moisture content meets the standard. The airflow at an angle of 30°-45° throughout the process reduces local overheating, and the positive and reverse rotation of the rotating tray alternately cooperate with the instantaneous wind speed increase during the specific stage reverse to significantly improve the heating uniformity of the material, avoiding stacking adhesion and morphological collapse, and finally realizing efficient and low-loss drying.

[0017] 2. Through the instantaneous steam sterilization combined with the alternating immersion of high and low water temperatures, it effectively kills microorganisms and fixes the flower bud morphology, reducing the risk of subsequent drying deformation. The pulsed ultrasonic wave is treated in a warm solution containing citric acid and calcium chloride, and the cavitation effect is used to strengthen the solution penetration and promote the combination of calcium ions and pectin, significantly improving the mechanical strength of the flower buds; the intermittent working mode avoids local overheating damage, provides structural integrity guarantee for subsequent drying, and at the same time shortens the pretreatment time.

[0018] 3. Gradually reduce the power density and adjust the pulse mode at the end of the ultrasonic treatment to achieve a smooth attenuation of energy input, avoiding the solution turbulence impact on the material caused by suddenly stopping the ultrasonic wave. The linear power reduction combined with the extended intermittent time reduces the mechanical damage of the cavitation bubble collapse to the surface layer of the flower buds, protects the formed strengthened structure, and ensures the transition stability from the pretreatment stage to the drying stage.

[0019] 4. The water drainage stage is carried out in a specific temperature and humidity environment of 35±1°C and a relative humidity of 50±5%, combined with a low-speed rotating tray of 2±0.3 rpm, promoting the uniform evaporation of surface moisture rather than dripping, and avoiding uneven drying caused by local water accumulation. The static water drainage and low-speed rotation cooperate to form a uniform thin layer of the residual color protection liquid citric acid and the hardening agent calcium chloride on the surface of the flower buds, providing consistent initial conditions for subsequent drying, and reducing color difference and structural deformation.

[0020] 5. The annular atomizing nozzle sprays directionally at an elevation angle of 15°-25°, combined with a vortex flow field, enabling the atomized mixture of vitamin C + chitosan to form micron-sized droplets that are evenly suspended in the drying chamber, enhancing the contact efficiency with the material. In the intermittent spraying mode, the nozzle operates for 2 s and pauses for 1 s when the temperature is ≥42°C, preventing the sudden drop in hot air temperature caused by local low-temperature solution and avoiding dew condensation or humidity fluctuations. The vortex cycle design of 8–12 seconds per time ensures the dynamic coverage of droplets on the material surface, forming a continuous antioxidant protective film.

[0021] 6. After atomization, apply an electrostatic field of -8 kV. Under a vertical laminar flow of 0.7–0.9 m / s and a specific humidity of 35±5%, drive the negatively charged chitosan-vitamin C droplets to be directionally adsorbed onto the surface of the flower buds, promoting the densification of the film formation. After the electrostatic field is turned off, restore the short-term vortex flow field to redistribute the droplets that have not been fully adsorbed, avoiding local accumulation. This combined operation enhances the uniformity and adhesion of the antioxidant film, reducing the risk of film layer shedding during drying.

[0022] 7. In the third stage, alternate cycles of drying steps and breathing steps are adopted: saturated humid air pulses at 38–42°C briefly soften the surface layer, promoting the outward diffusion of internal moisture; dry air pulses at 44–46°C quickly remove the vaporized moisture. The porous membrane loaded with trehalose-silica composite particles regulates the steam diffusion rate, avoiding local over-drying. The design of cycling to the final moisture content and the last 5 cycles ≤0.3% per minute ensures the full migration of the core moisture of the material, preventing moisture absorption after the drying end point and enhancing the storage stability.

[0023] 8. Instantaneously increase the humidity to 18±2% and maintain it for 2±0.3 minutes in the middle of the drying step to simulate the "conditioning effect": the surface layer moderately absorbs moisture and softens, relieving the internal tension gradient formed by continuous dehydration and reducing the generation of microcracks; then restore the low-humidity environment to continue dehydration, avoiding the efficiency decline caused by long-term high humidity. This fine-tuning strategy further optimizes the drying uniformity and improves the rehydration of the product.

[0024] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Detailed Description of the Invention

[0025] The following further elaborates on the present invention with reference to embodiments, enabling those skilled in the art to implement it according to the description in the specification.

[0026] It should be noted that the experimental methods described in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0027] According to an embodiment of the present invention, the implementation steps of a drying method for daylily are as follows: First-stage drying: The daylily flowers pretreated by steam sterilization are evenly spread on the hollow rotating tray. Set the temperature in the drying chamber to 63°C and the relative humidity to 35%. Adjust the hot air direction through the adjustable deflector to make the air flow form an angle of 38° with the material surface to avoid vertical impact. In the initial 5 minutes, use a directional circulating air flow of 2.2 m / s to gently start the dehydration process; then, stepwise increase the wind speed to 3.2 m / s within the next 5 minutes to strengthen the internal heat transfer; after that, maintain a low-speed air flow of 1.2 m / s throughout the process. The tray rotates at a constant speed of 4 rpm. After every 90° forward rotation, the drive motor immediately reverses by 32°. This cyclic action breaks the fixed orientation of the material. Especially when the drying reaches 10 minutes, the wind speed suddenly rises to 2.0 m / s and lasts for 5 seconds at each reverse moment, using the air flow shear force to disperse the possibly adhered petals. After continuous drying for 1 hour and 45 minutes, transfer to the equilibration stage: turn off the heating, adjust the environment to a temperature of 35°C and a relative humidity of 45%, and let it stand for 30 minutes to make the internal moisture gradient of the flower buds tend to be gentle. Second-stage drying: After equilibration, raise the temperature to 53°C and reduce the relative humidity to 20%. Start the atomization system at the beginning of the stage: The mixed solution of vitamin C and chitosan pre-cooled to 8°C is atomized by an ultrasonic atomizer to generate 6 μm-sized droplets, which are injected into the drying chamber from the annular nozzle at a flow rate of 0.8 L / h. The nozzle elevation angle is 22° to ensure uniform diffusion of the droplets. Maintain the air flow direction at an angle of 38°, and continue the variable-speed wind mode of the first stage (skip the initial speed-up section and directly maintain 1.2 m / s). The tray continues to alternate between 90° forward rotation and 32° reverse rotation to prevent the material layers from being pressed and overlapped. Stop the machine after drying for 3 hours and 30 minutes and enter the secondary equilibration: lower the temperature to 25°C, raise the relative humidity to 60%, and process for 60 minutes to eliminate the internal thermal stress. Third-stage drying: Set the temperature to 48°C and the relative humidity to 12%. Retain the low-speed air flow of 1.2 m / s at an angle of 38°. Adjust the rotation rate of the tray to 3 rpm and maintain the forward and reverse rotation alternation mode until the end. Monitor the moisture content in real time during the drying process and terminate the program when it drops to 8%. The continuous low-speed oblique air flow in this stage avoids physical impact on the fragile flower buds, and the rotating tray ensures that each side of each flower bud evenly contacts the hot air, completely eliminating the drying dead corners.

[0028] The traditional hot air drying of daylily flowers adopts a three-stage constant temperature process: drying at 65°C for 2 hours in the first stage, drying at 55°C for 4 hours in the second stage, and drying to the end at 45°C in the third stage. The wind speed is fixed at 2.0 m / s for the vertical downward air flow throughout the process. The material is laid flat on the static tray, and the temperature is directly reduced and switched between stages. This method causes the surface layer of the flower buds to quickly harden, hinders the internal moisture migration, and often results in hollow or browning in the middle after drying; the vertical air flow continuously impacts the top of the flower buds, causing the petals to adhere or be flattened; the sudden temperature change during stage conversion causes an internal and external contraction stress difference, and the flower buds frequently crack; the static tray makes the lower-layer materials pressed and adhered, and the moisture content difference exceeds 5%.

[0029] Compared with traditional processes, the solution of the present invention addresses the industry pain points through three core improvements: 38° inclined airflow replaces vertical air supply, reducing the physical damage rate of flower buds to less than 5%; the temperature and humidity balance treatment between two stages (35°C / 45% humidity and 25°C / 60% humidity) buffers the shrinkage stress, and the flower bud cracking rate drops by 90%; the rotating tray cooperates with the asymmetric forward and reverse movements (90° + 32°) and the instantaneous wind speed increase during reverse rotation, controlling the moisture content difference between material layers within 1.5%, eliminating the need for manual sorting. According to another embodiment of the present invention, the pretreatment steps of the present invention are as follows: Steam sterilization: Freshly harvested daylilies are laid on a conveyor mesh belt, and saturated steam at 100°C is introduced for 105 seconds. The high-temperature steam penetrates the gaps between the flower buds, thoroughly killing the microorganisms latent on the surface and in the folds. Thermal and cold alternating shaping: After sterilization, the material is immediately transferred to a 72°C hot water tank and immersed for 32 seconds. The hot water slightly relaxes the cutin layer of the flower petals; then the mesh belt is lifted and transferred to a 2°C ice water tank, and a 65-second cold shock treatment causes the relaxed cutin layer to instantaneously contract and shape. Pulsed ultrasonic enhancement: The flower buds are moved into a 38°C mixed solution tank (containing 0.1% citric acid and 0.05% calcium chloride), and a 40kHz ultrasonic generator is started. A pulsed working mode is adopted: ultrasonic waves are emitted for 5 seconds (power density 100W / L) and then intermittent for 2 seconds, and the treatment continues for 20 minutes. The ultrasonic cavitation effect promotes the combination of calcium ions and pectin, forming a strengthened grid on the surface layer of the flower buds; citric acid simultaneously penetrates and inhibits the activity of polyphenol oxidase. Final power gradient change: Two minutes before the end of the treatment, the ultrasonic power density linearly decreases to 35W / L, and at the same time, it switches to the mode of emitting for 1 second / intermittent for 3 seconds, gradually weakening the cavitation intensity to avoid structural impact. Traditional daylily pretreatment processes usually only use single hot water blanching or short-time steam sterilization. For example, a common method is to soak in 85°C hot water for 2 minutes. This operation cannot completely inactivate heat-resistant bacteria, and the mildew rate is high after drying; the continuous action of high temperature causes the softening of the flower bud tissue, and the morphological collapse rate exceeds 25% during subsequent drying; moreover, there is a lack of hardening treatment, and the flower petals are brittle and cracked after drying, with a transportation loss of more than 30%. Even more, the traditional process completely ignores the strengthening of the micro-structure, and the cell walls of the flower buds are easily broken during drying, resulting in the loss of nutrients. Compared with traditional single hot blanching, the solution of the present invention: The sterilization efficiency of 100°C steam is more than 3 times higher than that of 85°C hot water, and the subsequent drying mildew rate approaches zero; the instantaneous thermal and cold alternation of 72°C hot water and 2°C ice water causes a "shape memory" effect on the cutin layer of the flower petals, and the morphological integrity rate after drying exceeds 95%; the pulsed ultrasonic waves act directionally in an environment of calcium ions and citric acid, constructing a strengthened framework inside the flower buds, and the transportation breakage rate is reduced to less than 8%.

[0030] According to another embodiment of the present invention, the operation at the end of the pretreatment of the present invention is as follows: In a mixed solution containing 0.1% citric acid and 0.05% calcium chloride at 38°C, the material is treated with ultrasonic waves at 40 kHz for 18 minutes (working for 5 seconds / interval for 2 seconds, power density 100 W / L). When entering the last 2 minutes, start the power gradient program: Power linear attenuation: The ultrasonic power density decreases uniformly from 100 W / L, decreasing by 32.5 W / L per minute, and reaching 35 W / L at the end. Pulse mode switching: Synchronously adjust the working cycle to emit for 1 second and then interval for 3 seconds, extending the buffer time. For example, when processing to the 18th minute, the power drops to 67.5 W / L, and to 35 W / L at the 19th minute. At the same time, a gentle pulse of 1 second working / 3 seconds interval is maintained throughout the process.

[0031] In traditional ultrasonic pretreatment, the ultrasonic generator is directly turned off at the end of the treatment, resulting in the instantaneous collapse of cavitation bubbles in the solution. For example, in an existing technology, after continuously applying ultrasonic waves with a fixed power in a color protection solution at 40°C for 20 minutes and then suddenly stopping, the high-pressure shock wave generated by the collapsing bubbles causes the surface cells of the flower buds to rupture. Microscopic observation shows obvious tearing holes. These damaged parts become the starting points of browning during subsequent drying, and the spot rate of the finished product exceeds 15%. Moreover, the sudden stop easily causes turbulence, resulting in an increase in the mechanical damage rate of the flower buds by 12%. Compared with the traditional sudden stop method, the solution of the present invention: the linear decrease in power gradually reduces the number of cavitation bubbles, avoiding the shock wave generated by collective collapse; the working / interval ratio is adjusted from 5:2 to 1:3, greatly reducing the energy input per unit time and allowing the solution flow field to transition smoothly. The microscopic structure of the flower buds shows that the integrity of the cell wall after the end treatment is improved by more than 90% compared with the traditional process, and the surface of the dried finished product is smooth and without broken spots.

[0032] According to another embodiment of the present invention, the draining operation of the present invention is as follows: The material after the ultrasonic strengthening is taken out of the mixed solution tank as a whole and transferred to a dedicated draining chamber. The temperature in the chamber is constantly maintained at 35°C and the relative humidity is 50%. The material is laid flat on a hollow rotating tray, and the tray rotates continuously and slowly at a rate of 2 revolutions per minute. The flower buds continuously change the contact sites as the tray moves, and the residual liquid on the surface evaporates evenly under the temperature-controlled environment. Stop immediately when it reaches 5 minutes exactly. At this time, a very thin and uniform liquid film is formed on the surface of the flower buds without dripping phenomenon.

[0033] The traditional water-draining process is to place the pre-treated daylily flowers in a room-temperature environment and let them drain naturally for 10 - 15 minutes. For example, the ultrasonically treated flower buds are directly spread on a stainless-steel wire rack, with the ambient temperature fluctuating between 25 - 30°C and the relative humidity reaching 40 - 70% depending on the weather. This operation causes three major problems: First, the citric acid-calcium chloride solution remaining on the surface of the flower buds aggregates downward due to gravity, forming a liquid accumulation area at the bottom. After drying, this area hardens excessively, while the top shrinks due to rapid water loss, and the color difference rate of the same batch of materials exceeds 35%; Second, when standing for water-draining, the liquid accumulated at the contact area between the flower buds and the wire rack cannot evaporate, becoming a breeding point for microorganisms; Third, out-of-control temperature and humidity cause the components of the color-protecting solution to crystallize and precipitate, forming white mottles on the surface of the flower buds. Compared with the traditional natural water-draining, the solution of the present invention is as follows: The ambient temperature of 35°C is higher than the freezing point of the solution, preventing the crystallization and precipitation of calcium chloride; The relative humidity of 50% ensures a moderate evaporation rate, avoiding premature local drying; The low-speed rotation of 2 revolutions per minute makes each side of the flower buds alternately exposed to the air flow, completely eliminating the dead corners of liquid accumulation. The actual measurement after drying shows that the color uniformity of the flower buds is improved to more than 95%, there are no crystalline white spots on the surface, and there is no hidden danger of mildew at the bottom layer.

[0034] According to another embodiment of the present invention, the atomizing injection operation of the present invention is as follows: Install a ring-shaped atomizing nozzle 25 cm above the material layer in the drying chamber, with the axis of the nozzle at a 20° elevation angle to the horizontal plane. Mix a 2.0% vitamin C solution and a 0.08% chitosan solution in a volume ratio of 1:3, generate 6-μm particle-size droplets through an ultrasonic atomizer, and spray at a flow rate of 0.7 L / h. At the same time, control the air flow in the drying chamber to form a vortex flow field with a Reynolds number of 4000 and a vortex period of 1 second per 10 seconds. When the infrared sensor detects that the temperature in the nozzle area reaches 42°C, automatically switch to an intermittent mode of spraying for 2 seconds and pausing for 1 second.

[0035] The traditional drying process directly sprays the vitamin C solution in the second stage, using a vertically downward spraying method. This method has obvious defects: The droplets quickly settle due to gravity, resulting in excessive adsorption on the upper-layer materials and caking, and insufficient coverage on the lower layer; When the cold solution (8°C) contacts the hot air, the temperature near the nozzle drops suddenly, generating condensed water and locally diluting and invalidating the mixed solution; Static spraying makes almost no additives adhere to the leeward side of the materials, and the browning inhibition rate is less than 50%. Compared with the traditional vertical spraying, the 20° elevation angle design makes the droplets spread along the tangential direction; The layout of the ring-shaped nozzles combined with the vortex air flow extends the suspension time of the droplets by 3 times, and the coverage rate of each side of the materials exceeds 95%; The intermittent spraying mode completely eliminates the condensed water, and the temperature fluctuation in the nozzle area is controlled within ±1°C. The detection after drying shows that the integrity of the antioxidant film on the surface of the flower buds reaches 98%, and there are no caking or local failure phenomena. According to another embodiment of the present invention, the film curing operation of the present invention is as follows: Immediately start an electrostatic field of -8 kV after the atomization injection is completed, synchronously close the vortex flow field, and switch the sidewall deflector to form a vertical laminar flow of 0.8 m / s and maintain it for 5 minutes. The relative humidity in the curing area is strictly controlled at 35%. At this time, the negatively charged chitosan-vitamin C droplets are directionally adsorbed onto the surface of the flower buds under the drive of the electrostatic field to form a dense coating layer. After the electrostatic field is turned off, the voltage is returned to zero, and the original vortex flow field is restored to operate for 60 seconds to evenly redistribute the droplets that have not been fully adsorbed for the second time.

[0036] After spraying with traditional antioxidants, drying continues directly, and the droplets adhere only by natural sedimentation. This method causes three major problems: The film formed by chitosan on the surface of the material is loose, and the shedding rate exceeds 35% under the scouring of the drying air flow; The uneven distribution of droplets results in weak coverage on the sides and bottom of the flower buds, and the browning inhibition rate is less than 60%; The locally accumulated mixed liquid generates adhesion after heating, damaging the petal morphology. Compared with traditional natural sedimentation, the forced adsorption by the electrostatic field increases the film formation rate to 95%; The vertical laminar flow avoids the displacement of the film layer caused by air flow disturbance; The secondary vortex distribution completely eliminates the coverage dead angle. The detection after drying shows that the integrity of the film layer exceeds 98%, and there is no shedding phenomenon in the air flow scouring experiment. According to another embodiment of the present invention, the operation of the third stage of the present invention is as follows: Install a porous steam diffusion membrane (loaded with trehalose-silica composite particles) on the top of the drying chamber, and alternately execute the drying step and the breathing step. Drying step: Dehydrate at 48°C and a relative humidity of 12% for 25 minutes; Breathing step: Pulse-feed saturated humid air at 40°C and 0.2 MPa into the steam diffusion membrane for 10 seconds to moderately moisten and soften the surface layer of the flower buds, and then feed dry air at 45°C for 3 seconds (the flow rate is 1.2 times that of the humid air) to quickly remove the moisture. Cycle until the moisture content ≤ 8%, and terminate when the moisture content decrease rate ≤ 0.3% / minute in the last 5 cycles.

[0037] Traditional daylily final drying uses constant temperature dehydration at 45°C until the end. This method has fundamental defects: The surface layer of the material quickly hardens to form a dense layer, and the internal moisture migration is blocked, resulting in an excessive moisture content in the core area (>12%); In the later stage of drying, the treatment time is extended to meet the standard, causing the surface layer to become overly brittle and dry, and the petal fracture rate reaches 25% after rehydration; The moisture content detection is lagging, and it is difficult to accurately determine the actual drying end point. Compared with traditional constant temperature drying, the humid air pulse in the breathing step briefly opens the capillary channels on the surface layer, and the internal moisture diffusion efficiency is increased by 40%; The dry air pulse accurately removes the released moisture to avoid repeated moisture absorption; The trehalose-silica composite particles regulate the release rate of the membrane pores to prevent local over-drying. The cycle termination condition ensures the full migration of the core moisture, and the rehydration integrity rate of the dried product reaches 98%. According to another embodiment of the present invention, a dynamic humidity adjustment link is added in the third-stage drying step of the present invention: when the drying proceeds to the 15th minute, the ambient relative humidity is instantaneously increased to 18% and maintained for 2 minutes, and then restored to 12% to continue dehydration. For example, in a drying environment of 48°C, the humidity jump is achieved by injecting a controllable steam flow into the chamber, and the temperature fluctuation is maintained at ≤1°C during this period. This operation makes the surface layer of the flower bud absorb moisture and soften briefly, and the internal stress gradient is gently released.

[0038] During the final drying process of traditional daylilies, a constant low humidity (12%) is maintained throughout, resulting in continuous unidirectional dehydration of the material. In this mode, the internal moisture gradient stress of the flower buds cannot be released. Microscopic observation shows that when the moisture content is dried to about 10%, there are 15 microcracks per square centimeter on average on the surface layer of the petals. During subsequent storage, the cracks expand, causing the fragmentation rate to exceed 18%, and the integrity of the petals is lost after rehydration. Compared with traditional constant-humidity drying, instantaneous humidity adjustment reopens the surface capillaries, reducing the resistance to the outward migration of internal moisture by 40%; the short 2-minute treatment avoids the back-infiltration of deep moisture, and the dehydration efficiency is not affected. Microscopic detection confirms that the number of microcracks is reduced to less than 2 per square centimeter, and the fragmentation rate is controlled within 3% after three months of storage. The equipment quantity and processing scale described here are used to simplify the description of the present invention. The application, modification, and variation of a drying method for a kind of daylily of the present invention are obvious to those skilled in the art.

[0039] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A drying method for daylily, characterized in that, Adopt a segmented variable-temperature and variable-humidity hot air drying process, including: In the first stage, dry for 1 - 2 hours at 60 - 65°C and a relative humidity of 30% - 40%. After the first stage of drying, balance for 25 - 35 minutes at 33 - 37°C and a relative humidity of 43% - 47%. In the second stage, dry for 3 - 4 hours at 50 - 55°C and a relative humidity of 15% - 25%. At the start of the second stage, inject an atomized mixed solution of vitamin C and chitosan into the hot air system. The atomization particle size is 5 - 8μm, and the injection rate is 0.5 - 1.0L / h; the vitamin C solution is pre-cooled to 8 ± 2°C before atomization. After the second stage of drying, balance for 55 - 65 minutes at 23 - 27°C and a relative humidity of 58% - 62%. In the third stage, dry at 45 - 50°C and a relative humidity of 10% - 15% until the final water content ≤ 8%; where During drying, use a baffle to make the airflow form an angle of 30° - 45° with the surface of the material. In the initial 0 - 5 minutes, use a directional circulating airflow with a wind speed of 2.0 - 2.5m / s. Within 5 - 10 minutes, stepwise increase the wind speed to 3.0 - 3.5m / s, and then reduce the wind speed to 1.0 - 1.5m / s for the remaining drying time; the material is placed on a hollow rotating tray with a rotation speed of 3 - 5rpm. After the tray rotates forward 85 - 95° each time, it immediately rotates backward 28 - 32°, and repeat until the end of the stage; 10 minutes after the first stage of drying, when rotating backward, the wind speed is instantaneously increased to 1.8 - 2.2m / s and maintained for 4 - 6 seconds.

2. The method according to claim 1, characterized in that The pretreatment of daylily before the first stage includes: First, sterilize fresh daylily with 100°C steam for 90 - 120s, then immerse it in 70 - 75°C water for 30 - 35s, then immerse it in 0 - 4°C cold water for 60 - 65s, and finally place it in a mixed solution containing 0.1% citric acid and 0.05% calcium chloride at 35 - 40°C, and simultaneously apply pulsed ultrasonic waves with a frequency of 40 ± 2kHz, a power density of 80 - 120W / L, and a working mode of 5s / interval 2s for 18 - 22 minutes.

3. The method according to claim 2, wherein 2 minutes before the end of the ultrasonic treatment, linearly reduce the power density to 30 - 40W / L, and change the pulse mode to work 1s / interval 3s.

4. The method according to claim 2, wherein After the pulsed ultrasonic treatment, take out the material from the mixed solution and let it stand for water drainage for 5 ± 0.5 minutes; during water drainage, keep the ambient temperature at 35 ± 1°C and the relative humidity at 50 ± 5%, and the rotating tray runs at a rotation speed of 2 ± 0.3rpm.

5. The method according to claim 1, characterized in that, The atomized injection method in the second stage is: a) Set an annular atomizing nozzle 20 - 30cm above the material layer in the drying chamber, and the axis of the nozzle forms an elevation angle of 15° - 25° with the horizontal plane; b) Premix a 1.5% - 2.5% vitamin C solution and a 0.05% - 0.1% chitosan solution in a volume ratio of 1:3, and generate droplets through an ultrasonic atomizer; c) During atomization, control the airflow in the drying chamber to form a vortex flow field with a Reynolds number of 3500 - 4500, and the vortex period is 8 - 12 seconds / time; d) When the temperature in the nozzle area ≥ 42°C, switch to an intermittent injection mode of working 2s / rest 1s.

6. The method according to claim 5, characterized in that After the atomization injection is completed, maintain an electrostatic field of -8 kV for 5 ± 0.5 minutes for film curing. Curing stage: Turn off the vortex flow field and start the side wall guide plates to form a vertical laminar flow of 0.7 - 0.9 m / s; After curing, the electrostatic field returns to zero and the original vortex flow field runs for 50 - 70 seconds; The relative humidity in the curing area is controlled at 35 ± 5%.

7. The method according to claim 1, wherein The third-stage drying includes: arranging a porous steam diffusion membrane at the top of the drying chamber, and loading trehalose-silica composite particles with a particle size of 50 - 80 nm on the membrane surface; Repeatedly execute the drying step and the breathing step. Drying step: Dry at 45 - 50 °C and a relative humidity of 10% - 15% for 23 - 27 minutes; Breathing step: Pass a saturated humid air pulse at 38 - 42 °C and 0.15 - 0.25 MPa to the steam diffusion membrane for 8 - 10 s, and then pass a dry air pulse at 44 - 46 °C for 2 - 4 s. The dry air flow rate is 1.1 - 1.3 times that of the humid air; Repeat until the moisture content ≤ 8%, and the moisture content reduction rate in the last 5 cycles ≤ 0.3% / minute.

8. The method according to claim 7, wherein In the drying step of each cycle unit in the third stage: When the drying proceeds to 15 ± 1 minute, instantaneously increase the ambient relative humidity to 18 ± 2% and maintain it for 2 ± 0.3 minutes, and then return to 10% - 15%.