A drying method for daylily

Abstract

The invention discloses a drying method for daylily, which adopts a segmented variable temperature and variable humidity hot air drying process: the first stage is dried at 60-65°C and a relative humidity of 30%-40% for 1-2 hours, and then balanced for 25-35 minutes; the second stage is dried at 50-55°C and a relative humidity of 15%-25% for 3-4 hours, and then balanced for 55-65 minutes; the third stage is dried at 45-50°C and a relative humidity of 10%-15% to a final moisture content of ≤8%; during the drying period, the air flow is at an angle of 30-45° to the surface of the material, the initial 0-5 minute wind speed is 2.0-2.5m / s, the wind speed is stepped up to 3.0-3.5m / s within 5-10 minutes, and the wind speed is reduced to 1.0-1.5m / s during the remaining drying time. The method of the present invention can effectively improve the drying efficiency and uniformity of daylily, reduce browning and morphological damage, and obtain high-quality dried products.

Description

Technical Field

[0001] The present invention relates to the field of food processing, and more particularly to a method for drying daylily. Background Art

[0002] Daylily ( Hemerocallis citrina Baroni As an important edible and medicinal cash crop, the quality of its dried products directly impacts its commercial value and food safety. Hot air drying is currently one of the most widely used technologies for large-scale processing of daylilies. However, traditional hot air drying processes face at least the following challenges when applied to daylilies.

[0003] First of all, the flower buds of daylily are delicate in structure, rich in heat-sensitive substances such as polysaccharides, and have a high moisture content. Traditional constant temperature or simple segmented drying processes make it difficult to strike a balance between drying efficiency and quality. In the early stages of drying, if the temperature is too high or the humidity is too low, the moisture on the surface of the material evaporates too quickly, which can easily cause the surface layer to shrink and harden rapidly, forming a dense layer that hinders the internal moisture from migrating outward. This not only prolongs the drying time, but also easily causes the internal moisture to be overheated, resulting in the collapse of the flower bud shape, a deeper browning of the color, and even a burnt smell. On the contrary, if the initial temperature is too low and the humidity is too high, the drying efficiency is low, and the temperature and humidity environment suitable for microbial growth is kept for a long time, increasing the risk of mildew. Therefore, one of the main difficulties is to find a temperature and humidity change trajectory that can both quickly dehydrate and maximize the protection of the material's organizational structure and color.

[0004] Secondly, the organization of airflow during the drying process is crucial to the uniformity and efficiency of drying. In traditional processes, the wind speed is usually kept constant or changes simply. When the wind speed is too high, the direction is single (such as vertically downward), and it continuously acts on the surface of the material, it will aggravate the forced dehydration of local areas, resulting in uneven drying; at the same time, excessive airflow impact can easily damage the delicate flower buds. Too low a wind speed is not conducive to the efficiency of heat and moisture exchange, affecting the drying rate. How to dynamically adjust the wind speed and even the direction according to the changes in the physical state of the material (such as the degree of surface hardening) at different stages of drying to balance the dehydration efficiency with protecting the flower bud morphology and promoting internal moisture diffusion is a key challenge.

[0005] Furthermore, static stacking or simple turning drying methods can easily lead to uneven heating and dehydration within and between layers, as well as within individual flower buds. This not only makes it difficult to determine the drying endpoint (some areas are over-dried, others still contain too much moisture), but also significantly affects the overall color, rehydration, and texture uniformity of the product. To ensure uniform heating and ventilation of the material during the drying process and avoid localized overheating or insufficient dehydration, a more effective dynamic processing mechanism is needed.

[0006] Finally, the transition process between drying stages is often overlooked. After a relatively intense dehydration phase, a significant gradient in moisture distribution and temperature exists between the material's interior and surface. Directly proceeding to the next drying stage or cooling can easily lead to cracking of the buds' epidermis, damage to the internal structure (such as hollowing), or moisture resorption, affecting the stability of the final moisture content. Creating the appropriate temperature and humidity environment during stage transitions to redistribute moisture and temperature within the material and achieve a relative equilibrium to buffer stress and stabilize the structure is crucial for ensuring product integrity and storage stability. Summary of the Invention

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

[0008] In order to achieve the purpose and other advantages of the present invention, a method for drying daylily is provided, which adopts a staged temperature-variable humidity-variable hot air drying process, comprising:

[0009] The first stage is drying at 60-65℃ and relative humidity of 30%-40% for 1-2 hours. After the first stage of drying, it is balanced at 33-37℃ and relative humidity of 43%-47% for 25-35 minutes;

[0010] The second stage is dried at 50-55°C and a relative humidity of 15%-25% for 3-4 hours. At the beginning of the second stage, a mixed solution of atomized vitamin C and chitosan is injected into the hot air system with an atomized particle size of 5-8 μm and an injection rate of 0.5-1.0 L / h. The vitamin C solution is pre-cooled to 8±2°C before atomization. After the second stage of drying, the mixture is equilibrated at 23-27°C and a relative humidity of 58%-62% for 55-65 minutes.

[0011] The third stage is drying at 45-50℃ and relative humidity 10%-15% to a final moisture content of ≤8%;

[0012] During the drying process, the airflow is adjusted to form an angle of 30°-45° with the material surface through the adjustable guide plate. A directional circulating airflow with a wind speed of 2.0-2.5m / s is used in the initial 0-5 minutes. The wind speed is increased step by step to 3.0-3.5m / s within 5-10 minutes, and the wind speed is reduced to 1.0-1.5m / s for the remaining drying time. The material is placed on a hollow rotating tray with a speed of 3-5rpm. After each forward rotation of 85-95°, the tray is immediately reversed by 28-32°, and this is repeated until the end of the stage. After 10 minutes of drying in the first stage, the wind speed is instantly increased to 1.8-2.2m / s during the reverse rotation and maintained for 4-6 seconds.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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%.

[0018] 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.

[0019] Preferably, in the drying step of each cycle unit in the third stage: when the drying reaches the 15±1 minute, the relative humidity of the environment is instantaneously increased to 18±2% and maintained for 2±0.3 minutes, and then restored to 10%-15%.

[0020] The present invention has at least the following beneficial effects:

[0021] 1. Through a staged variable temperature and humidity process, the first stage combines a high-temperature, medium-humidity environment with a stepped wind speed change: initial directional airflow accelerates surface dehydration, a stepped increase in speed enhances heat transfer, and a subsequent decrease in speed prevents damage, effectively inhibiting the internal moisture migration caused by surface hardening. Specific temperature and humidity balance treatments between stages, such as the medium-temperature, medium-humidity balance after the first stage, alleviate sudden stress changes within the material and reduce the risk of surface cracking. The second stage combines medium-temperature, low-humidity with constant airflow, combined with pre-cooled, atomized vitamin C injected at the start, to synergistically inhibit browning and improve nutrient retention. The third stage, low-temperature, low-humidity drying, ensures that the final moisture content meets the standard. Airflow at an angle of 30°-45° throughout the process reduces local overheating. The alternating forward and reverse rotation of the rotating tray, combined with the instantaneous increase in wind speed during the reversal at specific stages, significantly improves heating uniformity of the material, preventing accumulation, adhesion, and morphological collapse, ultimately achieving efficient, low-loss drying.

[0022] 2. Instant steam sterilization combined with alternating high and low water temperature immersion effectively kills microorganisms and stabilizes the bud morphology, reducing the risk of deformation during subsequent drying. Pulsed ultrasonic treatment in a warm solution containing citric acid and calcium chloride utilizes the cavitation effect to enhance solution penetration, promote the binding of calcium ions with pectin, and significantly improve the mechanical strength of the buds. The intermittent working mode avoids localized overheating damage, ensuring structural integrity for subsequent drying, while also shortening pretreatment time.

[0023] 3. At the end of the ultrasonic treatment, gradually reduce the power density and adjust the pulse mode to achieve a smooth attenuation of energy input and avoid the turbulent impact of the solution on the material caused by the sudden cessation of ultrasound. Linear power reduction combined with extended intervals reduces mechanical damage to the bud surface caused by the collapse of cavitation bubbles, protects the existing reinforced structure, and ensures the transition stability from the pretreatment stage to the drying stage.

[0024] 4. The drainage stage is carried out at a specific temperature and humidity of 35±1°C and 50±5% relative humidity. The tray rotates at a low speed of 2±0.3rpm to promote uniform evaporation of surface moisture rather than dripping, thus avoiding uneven drying caused by localized water accumulation. The static drainage and low-speed rotation work together to form a uniform thin layer of residual color-protecting solution citric acid and hardening agent calcium chloride on the surface of the buds, providing consistent initial conditions for subsequent drying and reducing color variations and structural deformation.

[0025] 5. The annular atomizing nozzle sprays at a directional angle of 15°-25°, combined with a vortex flow field, to form uniformly suspended micron-sized droplets of the vitamin C and chitosan atomized mixture within the drying chamber, enhancing contact efficiency with the material. The intermittent spray mode, operating for 2 seconds and resting for 1 second at temperatures ≥42°C, prevents sudden drops in the hot air temperature caused by localized low temperatures, condensation, and humidity fluctuations. The vortex cycle of 8–12 seconds ensures that the droplets dynamically cover the material surface, forming a continuous antioxidant protective film.

[0026] 6. After atomization, an -8kV electrostatic field is applied. Under a vertical laminar flow of 0.7–0.9 m / s and a specific humidity of 35±5%, negatively charged chitosan-vitamin C droplets are directed to the bud surface, promoting film formation and densification. After the electrostatic field is turned off, a short vortex flow field is restored, redistributing incompletely adsorbed droplets and preventing localized accumulation. This combined operation enhances the uniformity and adhesion of the antioxidant film, reducing the risk of film shedding during drying.

[0027] 7. The third stage alternates between drying and breathing steps: 38–42°C saturated moist air pulses briefly soften the surface, promoting internal moisture diffusion; 44–46°C dry air pulses rapidly remove vaporized moisture. A porous membrane loaded with trehalose-silica composite particles regulates the vapor diffusion rate to prevent localized overdrying. Cycling to the final moisture content, with a final five cycles of ≤0.3% / minute, ensures sufficient moisture migration from the core of the material, preventing moisture resorption after the drying endpoint and improving storage stability.

[0028] 8. During the drying step, the humidity is instantaneously raised to 18±2% and maintained for 2±0.3 minutes to simulate a "slow rehydration effect": the surface absorbs moisture moderately, softening it and alleviating the internal tension gradients caused by continued dehydration, thus reducing the formation of microcracks. Dehydration is then resumed at a low humidity level to avoid the efficiency drop caused by prolonged high humidity. This fine-tuning strategy further optimizes drying uniformity and improves product rehydration.

[0029] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0031] It should be noted that the experimental methods described in the following examples, unless otherwise specified, are conventional methods, and the reagents and materials, unless otherwise specified, can be obtained from commercial channels.

[0032] According to one embodiment of the present invention, a method for drying daylily comprises the following steps:

[0033] In the first drying stage, steam-sterilized daylilies are evenly spread onto a hollow rotating tray. The drying chamber temperature is set at 63°C and the relative humidity at 35%. Adjustable deflectors adjust the direction of the hot air, creating a 38° angle between the airflow and the surface of the material to avoid vertical impact. Directed, circulating air at 2.2 m / s is used for the initial five minutes to gently initiate the dehydration process. The air speed is then gradually increased to 3.2 m / s over the next five minutes to enhance internal heat transfer. A low air speed of 1.2 m / s is then maintained throughout the drying process. The tray rotates at a constant speed of 4 rpm. After every 90° of forward rotation, the motor immediately reverses 32°, creating a cyclical motion that breaks the material's fixed orientation. Specifically, at the 10-minute mark, each reverse rotation triggers a sudden increase in air speed to 2.0 m / s for five seconds, using shear force to dislodge any petals that may be clinging. After drying for 1 hour and 45 minutes, the drying chamber enters the equilibrium stage: heating is turned off, the ambient temperature is adjusted to 35°C, and the relative humidity is 45%. The chamber is left to rest for 30 minutes to allow the moisture gradient within the buds to level out.

[0034] Second Drying Stage: After equilibration, the temperature was raised to 53°C, and the relative humidity was reduced to 20%. At the start of this stage, the atomization system was activated: a pre-cooled vitamin C and chitosan mixture was passed through an ultrasonic atomizer to generate 6 μm droplets. This was injected into the drying chamber at a flow rate of 0.8 L / h through a circular nozzle, with the nozzle angled at 22° to ensure uniform droplet distribution. The airflow was maintained at a 38° angle, continuing the variable speed airflow pattern of the first stage (skipping the initial speed increase and maintaining it at 1.2 m / s). The trays continuously rotated in alternating 90° forward and 32° reverse directions to prevent material stacking. After 3 hours and 30 minutes of drying, the machine was shut down for the second equilibration stage: the temperature was lowered to 25°C, the relative humidity was increased to 60%, and the drying process lasted 60 minutes to eliminate internal thermal stresses.

[0035] The third drying stage: Set the temperature to 48°C and the relative humidity to 12%. Maintain a low-speed airflow of 1.2 m / s at a 38° angle, adjust the tray rotation rate to 3 rpm, and maintain a forward-reverse alternating pattern until the drying finishes. Monitor the moisture content in real time during the drying process, terminating the process when it drops to 8%. The continuous low-speed, oblique airflow during this stage prevents physical impact on the delicate buds, and the rotating tray ensures that all sides of each bud are evenly exposed to the hot air, completely eliminating any drying dead spots.

[0036] Traditional hot air drying of daylilies uses a three-stage constant temperature process: the first stage is 65°C for 2 hours, the second stage is 55°C for 4 hours, and the third stage is 45°C until the end. The wind speed is fixed at 2.0 m / s throughout the process, with vertical downward airflow. The material is spread flat on a static tray, and the temperature is directly lowered between stages. This method causes the surface of the buds to harden rapidly, hindering internal moisture migration. After drying, the center often becomes hollow or brown. The vertical airflow continuously impacts the top of the buds, causing the petals to stick or flatten. The sudden temperature change during the stage transition triggers a difference in internal and external shrinkage stress, causing the buds to frequently crack. The static tray causes the lower layer of material to adhere under pressure, resulting in a moisture content difference of over 5%.

[0037] Compared with traditional processes, the solution of the present invention solves industry pain points through three core improvements: 38° inclined airflow replaces vertical air supply, reducing the physical damage rate of petals to below 5%; temperature and humidity balance treatment between the two stages (35℃ / 45% humidity and 25℃ / 60% humidity) buffers shrinkage stress, and the bud cracking rate drops by 90%; the rotating tray is combined with asymmetric forward and reverse movements (90°+32°) and the instantaneous wind speed increase during reversal, so that the moisture content difference between material layers is controlled within 1.5%, eliminating the need for manual sorting.

[0038] According to another embodiment of the present invention, the pretreatment steps of the present invention are as follows:

[0039] Steam sterilization: Freshly harvested daylilies are placed on a conveyor belt and treated with 100°C saturated steam for 105 seconds. The high-temperature steam penetrates the gaps between the flower buds and completely kills the microorganisms lurking on the surface and in the folds.

[0040] Hot and cold alternating shaping: After sterilization, the material is immediately transferred to a 72℃ hot water tank for immersion for 32 seconds. The hot water causes the petal cuticle to slightly stretch. Then the mesh belt is lifted and transferred to a 2℃ ice water tank. The cold shock treatment for 65 seconds causes the stretched cuticle to instantly shrink and shape.

[0041] Pulsed Ultrasound Enhancement: Place the flower buds in a 38°C mixed solution tank (containing 0.1% citric acid and 0.05% calcium chloride). Activate a 40kHz ultrasonic generator. Use pulsed ultrasound (power density 100W / L) for 5 seconds, followed by a 2-second pause, for 20 minutes. The ultrasonic cavitation effect promotes the binding of calcium ions with pectin, forming a reinforced lattice on the flower bud surface. Simultaneous penetration of citric acid inhibits polyphenol oxidase activity.

[0042] Final power gradient: 2 minutes before the end of treatment, the ultrasonic power density is linearly reduced to 35W / L, and at the same time, it is switched to the emission 1 second / interval 3 seconds mode to gradually weaken the cavitation intensity to avoid structural impact.

[0043] Traditional pretreatment of daylilies typically involves only a single blanching or short-term steam sterilization. For example, a common method involves soaking in 85°C hot water for two minutes, which fails to completely inactivate heat-resistant bacteria and results in a high rate of mold growth after drying. The continuous high temperature softens the bud tissue, leading to over 25% morphological collapse during subsequent drying. The lack of hardening treatment also results in brittle petals after drying, resulting in over 30% shipping losses. Furthermore, traditional processes completely ignore microstructural strengthening, causing the bud cell walls to rupture during drying, leading to nutrient loss.

[0044] Compared with traditional single blanching, the solution of the present invention has the following advantages: 100℃ steam has a sterilization efficiency more than three times that of 85℃ hot water, and the subsequent drying mildew rate is close to zero; the instantaneous hot and cold alternation of 72℃ hot water and 2℃ ice water makes the petal cuticle produce a "shape memory" effect, and the morphological integrity rate after drying exceeds 95%; pulsed ultrasonic waves act in a direction in a calcium ion and citric acid environment to build a reinforced skeleton inside the flower buds, reducing the transportation damage rate to below 8%.

[0045] According to another embodiment of the present invention, the pretreatment end stage of the present invention is performed as follows:

[0046] The material was treated with 40kHz ultrasound for 18 minutes (5 seconds on / 2 seconds off, power density 100W / L) in a mixed solution of 0.1% citric acid and 0.05% calcium chloride at 38°C. The power ramp program was started during the last 2 minutes:

[0047] Power linear attenuation: Ultrasonic power density decreases uniformly from 100W / L, decreasing by 32.5W / L per minute, reaching 35W / L at the end;

[0048] Pulse mode switching: Synchronously adjust the working cycle to transmit for 1 second and then pause for 3 seconds to extend the buffer time.

[0049] For example, the power dropped to 67.5W / L at the 18th minute and to 35W / L at the 19th minute, while maintaining a soothing pulse of 1 second working / 3 seconds rest throughout the process.

[0050] Traditional ultrasonic pretreatment simply shuts off the ultrasonic generator at the end of treatment, causing cavitation bubbles in the solution to collapse instantly. For example, a certain existing technique applies a fixed-power ultrasonic wave to a 40°C color-protecting solution for 20 minutes before suddenly stopping. The high-pressure shockwave generated by the collapsed bubbles ruptures the surface cells of the flower buds, revealing visible tears under microscopic observation. These damaged areas become the starting points of browning during subsequent drying, resulting in a spotting rate exceeding 15% in the finished product. Furthermore, the turbulence caused by the sudden stop can cause the flower buds to collide with each other, increasing the mechanical damage rate by 12%.

[0051] Compared to traditional abrupt stop methods, the present invention's solution achieves this by linearly decreasing power to gradually reduce the number of cavitation bubbles, thus avoiding the shock waves caused by their collective collapse. The duty cycle ratio is adjusted from 5:2 to 1:3, significantly reducing energy input per unit time and ensuring a smooth transition in the solution flow field. Flower bud microstructure analysis reveals that the cell wall integrity after the final treatment is over 90% higher than that of traditional processes, resulting in a smooth, spotless surface finish without cracks or spots.

[0052] According to another embodiment of the present invention, the draining operation of the present invention is as follows:

[0053] After ultrasonic strengthening, the entire material is removed from the mixed solution tank and transferred to a dedicated drainage chamber. The chamber maintains a constant temperature of 35°C and a relative humidity of 50%. The material is spread flat on a hollow rotating tray, which rotates slowly and continuously at a rate of 2 revolutions per minute. The flower buds continuously change contact points with the tray's movement, and any residual liquid on the surface evaporates evenly under the temperature-controlled environment. The treatment is stopped immediately after 5 minutes, at which point a very thin and uniform liquid film forms on the surface of the flower buds, eliminating any dripping.

[0054] The traditional draining process involves leaving the pre-treated daylily flowers to drain naturally at room temperature for 10-15 minutes. For example, the flower buds after ultrasonic treatment are directly placed on a stainless steel mesh rack. The ambient temperature fluctuates between 25-30°C, and the relative humidity varies with the weather, reaching 40-70%. This operation leads to three major problems: First, the citric acid-calcium chloride solution remaining on the surface of the flower buds accumulates 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, resulting in a color difference rate of over 35% for the same batch of material. Second, during static draining, the liquid accumulated where the flower buds contact the mesh rack cannot evaporate, becoming a breeding ground for microorganisms. Third, uncontrolled temperature and humidity cause the color-protecting liquid components to crystallize and precipitate, forming white spots on the surface of the flower buds.

[0055] Compared to traditional natural drainage, this solution utilizes: a 35°C ambient temperature, above the freezing point of the solution, to prevent calcium chloride crystallization; a 50% relative humidity to ensure a moderate evaporation rate, preventing premature localized drying; and a low-speed rotation of 2 rpm to alternately expose each side of the bud to airflow, completely eliminating dead spots where liquid accumulates. Post-drying measurements show that the buds' color uniformity has increased to over 95%, with no surface white spots and no underlying mold risk.

[0056] According to another embodiment of the present invention, the atomization injection operation is as follows: an annular atomizing nozzle is installed 25 cm above the material layer in the drying chamber, with the nozzle axis at a 20° elevation angle to the horizontal plane. A 2.0% vitamin C solution and a 0.08% chitosan solution are mixed in a volume ratio of 1:3, and an ultrasonic atomizer is used to produce 6μm droplets, which are sprayed at a flow rate of 0.7 L / h. Simultaneously, the airflow in the drying chamber is controlled to form a vortex flow field with a Reynolds number of 4000 and a vortex cycle of 10 seconds per cycle. When the infrared sensor detects that the temperature in the nozzle area reaches 42°C, it automatically switches to an intermittent mode with a spraying time of 2 seconds and a rest time of 1 second.

[0057] The traditional drying process directly sprays the vitamin C solution in the second stage, using a vertical downward spray pattern. This method has significant drawbacks: droplets settle rapidly due to gravity, resulting in excessive adsorption of the upper material, leading to agglomeration and insufficient coverage of the lower layer. When the cold solution (8°C) comes into contact with hot air, the temperature near the nozzle drops sharply, producing condensation, which ineffectively dilutes the mixture. Furthermore, static spraying results in virtually no additive adhering to the leeward side of the material, resulting in less than 50% browning inhibition.

[0058] Compared to traditional vertical spraying, the 20° elevation design allows droplets to diffuse tangentially. The annular nozzle layout, combined with vortex airflow, extends droplet suspension time by three times, achieving over 95% coverage on all surfaces. The intermittent spray mode completely eliminates condensation, keeping temperature fluctuations in the nozzle area within ±1°C. Post-drying testing revealed that the antioxidant film on the bud surface remained 98% intact, with no signs of clumping or localized failure.

[0059] According to another embodiment of the present invention, the membrane curing process is as follows: immediately after the atomization injection is completed, a -8kV electrostatic field is activated, the vortex flow field is simultaneously deactivated, and the sidewall guide plates are switched to form a 0.8 m / s vertical laminar flow, which is maintained for 5 minutes. The relative humidity in the curing zone is strictly controlled at 35%. At this point, the negatively charged chitosan-vitamin C droplets, driven by the electrostatic field, are directed to adsorb onto the flower bud surface, forming a dense coating. After the electrostatic field is deactivated, the voltage is returned to zero, and the original vortex flow field is restored and operated for 60 seconds to allow for a secondary, even distribution of any droplets that were not fully adsorbed.

[0060] Traditional antioxidant spraying is followed by direct drying, allowing droplets to settle naturally. This method leads to three major problems: chitosan forms a loose film on the surface, resulting in over 35% shedding under dry airflow; uneven droplet distribution results in weak coverage on the sides and bottom of the buds, resulting in less than 60% browning inhibition; and locally accumulated mixed solution adheres when heated, disrupting the petal shape.

[0061] Compared to traditional natural settling, electrostatic field-forced adsorption increases film formation efficiency to 95%. Vertical laminar flow prevents airflow disturbances that could cause film displacement. Secondary vortex distribution completely eliminates dead corners. Post-drying testing shows film integrity exceeding 98%, with no shedding observed in airflow scouring tests.

[0062] According to another embodiment of the present invention, the third stage operates as follows: a porous vapor diffusion membrane (loaded with trehalose-silica composite particles) is installed on the top of the drying chamber, and alternating drying and breathing steps are performed. The drying step involves dehydration at 48°C and 12% relative humidity for 25 minutes. The breathing step involves pulsed flow of saturated moist air at 40°C and 0.2 MPa through the vapor diffusion membrane for 10 seconds, allowing the flower buds to absorb moisture and soften. Subsequently, 45°C dry air (at a flow rate 1.2 times that of moist air) is passed through the membrane for 3 seconds to rapidly remove moisture. This cycle continues until the moisture content is ≤8%, and the rate of moisture reduction during the final five cycles is ≤0.3% / minute.

[0063] Traditionally, daylily final drying uses a constant temperature of 45°C for continuous dehydration until the end point. This method has fundamental flaws: the surface of the material quickly hardens to form a dense layer, which hinders internal moisture migration and causes the moisture content in the core area to exceed the standard (>12%); in the later stage of drying, the processing time is extended to meet the standard, causing the surface to become overly dry and brittle, and the petal breakage rate reaches 25% after rehydration; moisture content detection is delayed, making it difficult to accurately determine the actual drying end point.

[0064] Compared to traditional constant-temperature drying, the breath-step's moist air pulses briefly open surface capillary channels, increasing internal moisture diffusion efficiency by 40%. Dry air pulses precisely remove and release moisture, preventing repeated moisture absorption. Trehalose-silica composite particles regulate the release rate through the membrane pores, preventing localized overdrying. The cycle termination conditions ensure sufficient core moisture migration, resulting in a 98% rehydration rate for the product after drying.

[0065] According to another embodiment of the present invention, a dynamic humidity control step is added to the third drying step: At the 15th minute of drying, the relative humidity is instantly raised to 18% and maintained for 2 minutes, then returned to 12% to continue dehydration. For example, in a 48°C drying environment, the humidity jump is achieved by injecting a controlled stream of steam into the chamber, while maintaining a temperature fluctuation of ≤1°C. This operation temporarily absorbs moisture and softens the surface of the flower buds, gradually releasing internal stress gradients.

[0066] Traditional daylily drying maintains a constant low humidity (12%) throughout the final drying process, resulting in continuous, one-way dehydration of the material. This mode prevents the release of internal moisture gradient stress within the buds. Microscopic observation of the petals after drying to a moisture content of around 10% reveals an average of 15 microcracks per square centimeter. Subsequent crack expansion during storage leads to a breakage rate exceeding 18%, and the petals lose their integrity upon rehydration.

[0067] Compared to traditional constant humidity drying, instantaneous humidity control reopens surface capillaries, reducing resistance to outward moisture migration by 40%. A short 2-minute treatment prevents deep moisture from seeping back into the soil, without compromising dehydration efficiency. Microscopic examinations confirmed that the number of microcracks was reduced to less than 2 per square centimeter, and the breakage rate was kept below 3% after three months of storage.

[0068] The number of equipment and processing scales described herein are intended to simplify the description of the present invention. Applications, modifications, and variations of the method for drying daylilies of the present invention will be readily apparent to those skilled in the art.

[0069] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for drying daylily, characterized in that: The process of segmented variable temperature and humidity hot air drying is adopted, including: The first stage is drying at 60-65℃ and relative humidity of 30%-40% for 1-2 hours. After the first stage of drying, it is balanced at 33-37℃ and 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 beginning of the second stage, a mixed solution of atomized vitamin C and chitosan is injected into the hot air system with an atomized particle size of 5-8 μm and an injection rate of 0.5-1.0 L / h. The vitamin C solution is pre-cooled to 8±2°C before atomization. After the second stage of drying, the mixture is equilibrated at 23-27°C and a relative humidity of 58%-62% for 55-65 minutes. The third stage is drying at 45-50℃ and relative humidity 10%-15% to a final moisture content of ≤8%; During the drying process, the airflow is directed at a 30-45° angle to the material surface through the guide plate. A directional circulating airflow with a wind speed of 2.0-2.5 m / s is used in the initial 0-5 minutes. The wind speed is increased stepwise to 3.0-3.5 m / s within 5-10 minutes, 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 speed of 3-5 rpm. The tray is immediately reversed 28-32° after each 85-95° forward rotation, and this process is repeated until the end of the stage. After 10 minutes of drying in the first stage, the wind speed is instantly increased to 1.8-2.2 m / s during the reverse rotation and maintained for 4-6 seconds. The pretreatment of daylily before the first stage includes: fresh daylily is first sterilized by steam at 100℃ for 90-120s, then immersed in water at 70-75℃ for 30-35s, then immersed in cold water at 0-4℃ for 60-65s, and finally placed in a mixed solution of 0.1% citric acid and 0.05% calcium chloride at 35-40℃, and simultaneously applied with pulsed ultrasound with a frequency of 40±2kHz, a power density of 80-120W / L, and an operating time of 5s / interval of 2s for 18-22 minutes.

2. The method according to claim 1, wherein Two minutes before the end of ultrasonic treatment, the power density was linearly reduced to 30-40 W / L, and the pulse mode was changed to 1 s working / 3 s resting.

3. The method according to claim 1, wherein After the pulse ultrasonic treatment, the material was taken out of the mixed solution and allowed to stand for 5±0.5 minutes to drain. During the draining period, the ambient temperature was maintained at 35±1°C, the relative humidity was maintained at 50±5%, and the rotating tray was operated at 2±0.3 rpm.

4. The method according to claim 1, wherein The second stage of atomization injection is as follows: a) An annular atomizing nozzle is installed 20-30 cm above the material layer in the drying chamber, with the nozzle axis at an elevation angle of 15°-25° to 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 passed through an ultrasonic atomizer to produce droplets; c) During atomization, the airflow 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 per time; d) When the temperature in the nozzle area is ≥42°C, switch to an intermittent spray mode of 2 seconds on and 1 second off.

5. The method according to claim 4, wherein 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 for 50-70 seconds; the relative humidity in the curing area is controlled at 35±5%.

6. The method according to claim 1, wherein 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 50-80nm on the membrane surface; cyclically performing the drying step and the breathing step, drying step: drying at 45-50℃ and relative humidity of 10%-15% for 23-27 minutes; breathing step: passing a saturated wet air pulse at 38-42℃ and 0.15-0.25MPa into the vapor diffusion membrane for 8-10s, followed by a dry air pulse at 44-46℃ for 2-4s, with the dry air flow rate being 1.1-1.3 times that of the wet air; circulate until the moisture content is ≤8%, and the moisture content decrease rate in the last 5 cycles is ≤0.3% / minute.

7. The method according to claim 6, wherein In the drying step of each cycle unit in the third stage: when the drying reaches the 15±1 minute, the relative humidity of the environment is instantly increased to 18±2% and maintained for 2±0.3 minutes, and then restored to 10%-15%.