Freeze-drying storage method for almonds based on oriented crystallization in magnetic field and intelligent humidity control

Abstract

The invention relates to the technical field of deep processing and preservation of agricultural products, and discloses a freeze-drying storage method for badam flowers based on magnetic field oriented crystallization and intelligent humidity control, which comprises the following steps: (1) pretreatment: carrying out two-stage ultrasonic cleaning on the badam flowers, and soaking the badam flowers in a composite color protection solution; (2) pre-freezing in a magnetic field: pre-freezing the pretreated almonds in a static magnetic field at the rate of more than or equal to 5 DEG C / min until the central temperature is less than or equal to-25 DEG C; (3) gradient freeze-drying: in the first stage, the vacuum degree is less than or equal to 50Pa, the temperature is raised to-20 DEG C at the speed of 0.5 DEG C / min, and the temperature is maintained for 4-6 hours; in the second stage, the vacuum degree is smaller than or equal to 10 Pa, the temperature is increased to 5 DEG C at the speed of 0.2 DEG C / min, and microwave pulse is applied for 30 seconds every 1.5 hours; and (4) packaging: nitrogen-filled sealing is performed by adopting a five-layer composite film subjected to plasma treatment. Through three technical innovations of field oriented crystallization, microwave-vacuum linkage and bionic packaging, the ice crystal form of the badam flowers is controllable in the freeze-drying process, cell damage can be effectively reduced, the retention rate of flavonoid substances is larger than 90%, and the loss rate of aroma components is smaller than 10%.

Description

Technical Field

[0001] The present invention relates to the technical field of deep processing and preservation of agricultural products, and in particular to a freeze-drying storage method for almond flowers based on magnetic field oriented crystallization and intelligent moisture control. Background Art

[0002] Almond flowers, also known as the flowers of the almond tree, are typically white or pale pink. Rich in flavonoids and volatile aromatic compounds, almond flowers offer the following benefits: 1) Tonifying the Spleen and Lungs: Almond flowers can help alleviate symptoms such as diarrhea caused by spleen deficiency and cough and asthma caused by lung deficiency, and are often used in combination with herbs such as Chinese yam, ginseng, and astragalus. 2) Nourishing the Blood: The flowers contain blood-nourishing ingredients that can improve symptoms such as pale complexion, numbness of the hands and feet, and neurasthenia caused by postpartum weakness or blood deficiency, promoting the recovery of Qi and blood. 3) Dispelling Wind: Almond flowers promote the production of body fluids and moisten dryness, helping to dispel wind and cold, alleviating headaches, numbness of limbs, and other discomforts caused by wind-cold. 4) Calming the Mind: Almond flowers can regulate the mind and alleviate symptoms such as palpitations, insomnia, and restlessness caused by timidity and fear. Therefore, based on the above-mentioned medicinal properties of almond flowers, in order to comprehensively develop the "ecological industrialization and industrial ecology" path of almond flowers, it is necessary to further explore the application value of almond flowers in medicine and health care.

[0003] Almond flowers are a seasonal product of the almond plant, blooming in spring, typically from late March to mid-April. To develop applications in medicine and healthcare, almond flowers require antioxidant drying and storage. However, freshly harvested almond flowers have a high moisture content of 75-85%, making traditional drying methods prone to the following problems: First, hot air drying causes browning of the flowers and loss of over 40% of their aroma components; second, conventional freeze-drying, due to ice crystals damaging cell walls, results in poor rehydration; and third, existing color-protection technologies often use sulfites, posing a food safety risk. Summary of the Invention

[0004] In order to solve the above-mentioned problems in the prior art, the present invention proposes a freeze-drying storage method for almond flowers based on magnetic field oriented crystallization and intelligent humidity control, which is suitable for the industrial production of high value-added flower products.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A freeze-dried storage method for almond flowers based on magnetic field-oriented crystallization and intelligent moisture control comprises the following steps:

[0007] (1) Pretreatment: After the fresh almond flowers were cleaned by two-stage ultrasonic cleaning at 40-60 kHz, they were immersed in a composite color-protecting solution of ascorbic acid, citric acid, tea polyphenols and rosmarinic acid for 8-15 minutes, with a liquid-to-solid ratio of 3:1;

[0008] (2) Magnetic field prefreezing: Place the pretreated almond flowers in a quick freezing device and prefreeze at a rate of ≥5°C / min at -35 to -45°C and a static magnetic field of 0.5-1.0T to a center temperature of ≤-25°C;

[0009] (3) Gradient freeze-drying:

[0010] Stage 1: Vacuum degree ≤ 50Pa, heating at 0.5℃ / min to -20℃ and maintaining for 4-6 hours;

[0011] The second stage: vacuum degree ≤ 10Pa, temperature increased to 5°C at 0.2°C / min, and microwave pulses of 30 seconds (power density 2-5 W / g) were applied every 1.5 hours;

[0012] (4) Packaging: It is made of plasma-treated five-layer composite film (PET / Al / PA / EVOH / CPP), nitrogen-sealed, and has a built-in nano-SiO2-activated carbon-VE composite adsorbent and an intelligent humidity indicator card.

[0013] Preferably, in step (1), the composite color-protecting solution is composed of: 0.5-1.5% ascorbic acid, 0.1-0.3% citric acid, 0.02-0.08% tea polyphenols, 0.01-0.03% rosmarinic acid, and the remainder is water.

[0014] Preferably, in step (1), the pH value of the composite color-protecting liquid is 3.5-4.0, and the entire soaking process is carried out in a low-temperature environment of 4-8°C.

[0015] Preferably, in step (2), the static magnetic field is generated by a permanent magnet array, the direction of the magnetic field is adjustable, and the magnetic field intensity gradient is 0.1 T / cm.

[0016] Preferably, in step (2), the almond flowers are dispersed into petal shapes and spread flat on a freeze-drying plate, and the direction of the static magnetic field is controlled to form an angle of 30-60° with the plane of the petals.

[0017] Preferably, in step (3), the microwave pulse is dynamically associated with the vacuum degree, and the microwave is automatically triggered when the vacuum degree is greater than 15 Pa, and the power density satisfies the formula: P = 5×(20-Pa) / 15W / g, where Pa is the current vacuum degree value.

[0018] Preferably, in step (3), the freeze-drying process is monitored in real time using infrared thermal imaging, and when the regional temperature difference is greater than 1.5°C, the temperature distribution of the heating plate is automatically adjusted to control the sublimation interface movement rate to be ≤0.2 mm / min.

[0019] Preferably, in step (4), the nano-SiO2-activated carbon-VE composite adsorbent is composed of the following: amino-modified nano-SiO2 (particle size 50 nm), silver-loaded activated carbon (silver content 0.5 wt%) and vitamin E microcapsules, and the mass ratio of the three is 4:1:0.3.

[0020] Preferably, in step (4), the plasma treatment parameters are: argon pressure 10 Pa, radio frequency power 100-150 W, treatment time 30-60 seconds, and the surface roughness of the film after treatment is Ra=1.2-1.8 μm.

[0021] Preferably, in step (4), the moisture content of the sealed and packaged final product is ≤3%, the rehydration ratio is ≥6.0 g / g, the anthocyanin retention rate is ≥97%, and the total number of microorganisms is ≤10 CFU / g.

[0022] Preferably, the quick-freezing equipment uses a multi-zone independent temperature-controlled radiation heating plate with a temperature control accuracy of ±0.3°C.

[0023] Preferably, the quick-freezing equipment uses an integrated microwave emission array, 2.45 GHz, with an adjustable power density of 0-10 W / g.

[0024] Preferably, the quick freezing equipment adopts a three-stage gradient cold trap system, and the temperatures are set to -55°C, -65°C, and -75°C respectively.

[0025] Preferably, the cold trap in the three-stage gradient cold trap system adopts a spiral guide plate design, with an ice capture efficiency of ≥98% and energy consumption reduced by 30%.

[0026] The present invention adopts the above technical solution, which has the following technical effects compared with the prior art:

[0027] The freeze-drying storage method of almond flowers based on magnetic field oriented crystallization and intelligent moisture control provided by the present invention realizes the controllable morphology of almond flower ice crystals during the freeze-drying process through the triple technological innovation of magnetic field oriented crystallization, microwave-vacuum linkage, and bionic packaging, and the directional arrangement of ice crystals reduces cell damage (the rehydration ratio is increased by more than 50%). The active ingredients of almond flowers freeze-dried and stored using this method are highly retained, with a flavonoid retention rate of >90% and an aroma component loss rate of <10%. In addition, a five-layer composite film treated with plasma is used for sealing packaging, and the oxygen permeability is <1cc / m 2 day, humidity response accuracy ±3%RH, good storage effect. DETAILED DESCRIPTION

[0028] The present invention will be described in detail and specifically below through specific examples to provide a better understanding of the present invention, but the following examples do not limit the scope of the present invention.

[0029] Example 1 (Basic Implementation)

[0030] A freeze-dried storage method for almond flowers comprises the following steps:

[0031] (1) Pretreatment

[0032] Take 2 kg of fresh almond flowers and place them in a 40 kHz ultrasonic cleaner for 3 minutes, then switch to 60 kHz for 2 minutes;

[0033] Soak in 4°C color-protecting solution (1% ascorbic acid + 0.2% citric acid + 0.05% tea polyphenols + 0.02% rosmarinic acid, pH 3.8) for 12 minutes, with a liquid-to-solid ratio of 3:1;

[0034] (2) Magnetic field pre-freezing

[0035] Spread the flowers flat on a pre-frozen tray, place them in a -40°C quick freezer, apply a 0.6T static magnetic field (at a 45° angle to the petal plane), and cool them down at a rate of 6°C / min to a core temperature of -28°C.

[0036] (3) Gradient freeze-drying

[0037] Primary sublimation: vacuum degree 40Pa, heating at 0.5℃ / min to -20℃, maintain for 5 hours;

[0038] Desorption drying: vacuum degree 8 Pa, heating at 0.2°C / min to 5°C, microwave application for 30 seconds every 1.5 hours (power density 3 W / g);

[0039] (4) Packaging

[0040] The freeze-dried product was placed in a composite film bag treated with argon plasma (150 W, 45 seconds) and filled with 99.9% nitrogen;

[0041] Add composite adsorbent (4g nano-SiO2: 1g silver-loaded activated carbon: 0.3g VE), seal and store in a dark environment at 12°C.

[0042] Example 2 (Magnetic Field Optimization)

[0043] A freeze-dried storage method for almond flowers comprises the following steps:

[0044] (1) Pretreatment

[0045] Take 2 kg of fresh almond flowers and place them in a 40 kHz ultrasonic cleaner for 3 minutes, then switch to 60 kHz for 2 minutes;

[0046] Soak in 4°C color-protecting solution (1% ascorbic acid + 0.2% citric acid + 0.05% tea polyphenols + 0.02% rosmarinic acid, pH 3.8) for 12 minutes, with a liquid-to-solid ratio of 3:1;

[0047] (2) Magnetic field pre-freezing

[0048] Spread the flowers flat on a pre-frozen tray, place them in a -40°C quick freezer, apply a 1T static magnetic field (at a 30° angle to the petal plane), and cool them down at a rate of 6°C / min to a central temperature of -28°C.

[0049] (3) Gradient freeze-drying

[0050] Primary sublimation: vacuum degree 40Pa, heating at 0.5℃ / min to -20℃, maintain for 5 hours;

[0051] Desorption drying: vacuum degree 8 Pa, heating at 0.2°C / min to 5°C, microwave application for 30 seconds every 1.5 hours (power density 3 W / g);

[0052] (4) Packaging

[0053] The freeze-dried product was placed in a composite film bag treated with argon plasma (150 W, 45 seconds) and filled with 99.9% nitrogen;

[0054] Add composite adsorbent (4g nano-SiO2: 1g silver-loaded activated carbon: 0.3g VE), seal and store in a dark environment at 12°C.

[0055] Effect: Ice crystals were oriented (SEM showed an aspect ratio of 5.5:1), and the rehydration time was shortened to 40 seconds (70 seconds for control example 1).

[0056] Comparative Example 1 (conventional freeze-drying)

[0057] Different from the embodiment, step (1) magnetic field pre-freezing and step (2) microwave assistance are eliminated, and step (3) is directly freeze-dried at -50°C for 18 hours. The rest is the same as embodiment 1.

[0058] Results: The rehydration ratio was 4.1 g / g and the benzaldehyde retention rate was 68%.

[0059] Comparative Example 2 (traditional packaging)

[0060] Different from the embodiment, an ordinary aluminum foil bag (not plasma treated) is used in step (4), and no composite adsorbent is added. Other steps are the same as in embodiment 1.

[0061] Results: After 6 months, the total microbial count reached 250 CFU / g and the loss of volatile substances was 42%.

[0062] The freeze-dried almond flower products treated in the above examples and comparative examples were subjected to rehydration tests, benzaldehyde retention rate, package oxygen transmission rate, and activity retention rate tests. The test results are shown in Table 1 below.

[0063] Table 1 Test results of freeze-dried almond flower products

[0064]

[0065] Comparing the test results in Table 1 above, it can be seen that the present invention forms fine ice crystals (average particle size ≤50μm as shown by electron microscopy) through rapid pre-freezing, reducing cell structural damage and achieving effective control of ice crystal morphology. It also uses ascorbic acid, tea polyphenols, and vitamin E to form a redox potential gradient protection, forming a synergistic antioxidant system. Furthermore, pressure pulse technology is used in gradient freeze-drying to accelerate water migration through intermittent vacuum adjustment, shortening the freeze-drying time by more than 20%. The experimental data in Table 1 above confirm that key indicators (rehydration, aroma retention, and microbial control) have all undergone breakthrough improvements, and have high industrial application value.

[0066] While the specific embodiments of the present invention have been described in detail above, these are merely exemplary and the present invention is not limited thereto. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, any equivalent changes and modifications made without departing from the spirit and scope of the present invention are intended to be encompassed within the scope of the present invention.

Claims

1. A freeze-dried storage method for almond flowers based on magnetic field oriented crystallization and intelligent humidity control, characterized in that: The steps include: (1) Pretreatment: After the fresh almond flowers were cleaned by two-stage ultrasonic cleaning at 40-60 kHz, they were immersed in a composite color-protecting solution of ascorbic acid, citric acid, tea polyphenols and rosmarinic acid for 8-15 minutes, with a liquid-to-solid ratio of 3:1; (2) Magnetic field prefreezing: Place the pretreated almond flowers in a quick freezing device and prefreeze at a rate of ≥5°C / min at -35 to -45°C and a static magnetic field of 0.5-1.0T to a center temperature of ≤-25°C; (3) Gradient freeze-drying: Stage 1: Vacuum degree ≤ 50Pa, heating at 0.5℃ / min to -20℃ and maintaining for 4-6 hours; The second stage: vacuum degree ≤ 10Pa, temperature increased to 5°C at 0.2°C / min, and microwave pulses of 30 seconds (power density 2-5 W / g) were applied every 1.5 hours; (4) Packaging: It is made of plasma-treated five-layer composite film (PET / Al / PA / EVOH / CPP), nitrogen-sealed, and has a built-in nano-SiO2-activated carbon-VE composite adsorbent and an intelligent humidity indicator card.

2. The freeze-drying storage method according to claim 1, characterized in that In step (1), the composite color-protecting liquid is composed of the following: 0.5-1.5% ascorbic acid, 0.1-0.3% citric acid, 0.02-0.08% tea polyphenols, 0.01-0.03% rosmarinic acid, and the remainder is water.

3. The freeze-drying storage method according to claim 1, wherein In step (1), the pH value of the composite color-protecting liquid is 3.5-4.0, and the soaking is carried out in a low-temperature environment of 4-8°C.

4. The freeze-drying storage method according to claim 1, characterized in that In step (2), the static magnetic field is generated by a permanent magnet array, the direction of the magnetic field is adjustable, and the magnetic field intensity gradient is 0.1 T / cm.

5. The freeze-drying storage method according to claim 1, characterized in that In step (2), the almond flowers are dispersed into petal shapes and spread flat on a freeze-drying plate, and the direction of the static magnetic field is controlled to form an angle of 30-60° with the plane of the petals.

6. The freeze-drying storage method according to claim 1, characterized in that In step (3), the microwave pulse is dynamically associated with the vacuum degree, and the microwave is automatically triggered when the vacuum degree is greater than 15 Pa, and the power density satisfies the formula: P = 5×(20-Pa) / 15W / g, where Pa is the current vacuum degree value.

7. The freeze-drying storage method according to claim 1, characterized in that: In step (3), the freeze-drying process is monitored in real time using infrared thermal imaging. When the regional temperature difference is greater than 1.5°C, the temperature distribution of the heating plate is automatically adjusted to control the sublimation interface movement rate to be ≤0.2 mm / min.

8. The freeze-drying storage method according to claim 1, characterized in that In step (4), the nano-SiO2-activated carbon-VE composite adsorbent is composed of the following: amino-modified nano-SiO2 (particle size 50nm), silver-loaded activated carbon (silver content 0.5wt%) and vitamin E microcapsules, and the mass ratio of the three is 4:1:0.

3.

9. The freeze-drying storage method according to claim 1, characterized in that: In step (4), the plasma treatment parameters are: argon pressure 10 Pa, radio frequency power 100-150 W, treatment time 30-60 seconds, and the surface roughness of the film after treatment is Ra=1.2-1.8 μm.

10. The freeze-drying storage method according to claim 1, characterized in that: In step (4), the moisture content of the sealed packaged final product is ≤3%, the rehydration ratio is ≥6.0 g / g, the anthocyanin retention rate is ≥97%, and the total number of microorganisms is ≤10 CFU / g.

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