Comprehensive fruit freeze-drying processing method capable of reducing nutrient loss of fruits

Abstract

The invention belongs to the technical field of fruit freeze-drying processing, and particularly relates to a comprehensive fruit freeze-drying processing method capable of reducing nutrient loss of fruits, which comprises the following steps: S1, immersing sliced fruit slices into a composite color fixative, and simultaneously applying ultrasonic and pulsed electric field treatment on the composite color fixative system containing the fruit slices under the conditions that the ultrasonic power is 200-300W, the pulsed electric field intensity is 15-25kV / cm, and the ultrasonic power is 200-300W and the pulsed electric field intensity is 15-25kV / cm; the co-processing time is 2-4 minutes, so as to obtain the color-protected and strengthened fruit slices; s2, sequentially carrying out three-stage magnetic field freezing treatment on the color-protected and strengthened fruit slices to obtain frozen fruit slices; s3, dynamically adjusting parameters of the frozen fruit slices by adopting an AI algorithm, and performing vacuum freeze-drying in stages to obtain primary freeze-dried fruit slices; s4, placing the primary freeze-dried fruit slices in a vacuum environment to obtain deeply dried fruit slices; and S5, soaking the deeply dried fruit slices in an aqueous solution containing 0.5-1% of amyloid-like protein, 0.2-0.4% of sodium alginate and 0.1-0.3% of cellulose nanocrystals for 1-2 minutes to form a composite protective film with the thickness of 1-3 microns, so as to obtain the coated fruit slices.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fruit freeze-drying processing, and particularly relates to a comprehensive fruit freeze-drying processing method for reducing loss of fruit nutrients. BACKGROUND

[0002] Fruit freeze-drying refers to a processing process of rapidly freezing fruit slices and vacuum ice-state dehydration. Different fruits with different sugar contents have different freezing temperatures. Generally, fruit slices are first rapidly frozen to minus 50 DEG C to minus 70 DEG C, and then are dehydrated in vacuum for dozens of hours.

[0003] The freeze-drying technology is widely used because it can maximize the preservation of fruit nutrients and quality, but the existing technology has significant defects: the low penetration efficiency of the pretreatment color protection agent leads to the loss of oxidized nutrients; the coarse ice crystals in the freezing process damage the cell structure and cause nutrient leakage; the high temperature or continuous microwave in the drying stage leads to the degradation of heat-sensitive components; and the oxidation and water loss in the storage stage further aggravate the loss of nutrients. Therefore, the comprehensive fruit freeze-drying processing method for reducing loss of fruit nutrients is designed. SUMMARY

[0004] In view of the above problems in the prior art, the application provides a comprehensive fruit freeze-drying processing method for reducing loss of fruit nutrients to solve the problems in the background art.

[0005] In order to solve the above technical problems, the application adopts the following technical scheme: A comprehensive fruit freeze-drying processing method for reducing loss of fruit nutrients comprises the following steps: Raw material selection: low-sugar fruits with a sugar content of 8-10 degrees are selected; the purpose of this step is to select raw materials with appropriate maturity and moderate sugar content, so as to avoid the degradation of nutrient components caused by Maillard reaction in the processing of high-sugar fruits; Cleaning, peeling and pitting: remove the surface impurities and inedible parts of the raw materials; the purpose of this step is to reduce the interference of impurities and inedible parts on the processing process, ensure the uniformity of the subsequent treatment, and reduce the risk of nutrient loss; Slicing: the treated fruits are cut into fruit slices with uniform thickness; the purpose of this step is to increase the specific surface area of the raw materials, ensure the uniformity and efficiency of the subsequent pretreatment, freezing and drying process, and avoid the loss of nutrients caused by excessive local treatment; Ultrasonic-pulsed electric field synergistic pretreatment: immerse the fruit pieces in a composite color protection agent including 0.05-0.1% tea polyphenol, 0.1-0.2% vitamin C, 0.1-0.15% citric acid and 0.5-1% CaCl2 by mass concentration, and apply ultrasonic and pulsed electric field treatment at an ultrasonic power of 200-300 W and a pulsed electric field intensity of 15-25 kV / cm for 2-4 min; the purpose of this step is to improve the penetration efficiency of the color protection agent by ultrasonic cavitation effect and pulsed electric field electroporation, inhibit the oxidation of antioxidant ingredients, and strengthen the cell wall with calcium salt to reduce nutrient loss and browning during the pretreatment stage; Gradient magnetic field assisted freezing: sequentially perform three-stage processing: ①-5 to-10℃, 0.1-0.3T magnetic field pre-freezing for 1-2h; ②-30 to-40℃, 0.3-0.5T magnetic field rapid freezing for 2-3h; ③-15 to-10℃, 0.2-0.4T magnetic field annealing for 1-2h; the purpose of this step is to control the ice crystal morphology by gradient temperature field and magnetic field synergy, reduce the damage of large ice crystals to cell structure, and reduce the leakage of nutrients caused by cell rupture; Segmented pulse vacuum freeze-drying: AI algorithm is used to dynamically adjust parameters, including: ① sublimation drying stage: vacuum degree 50-100 Pa, heating plate according to "20-30℃ for 1h→each increase of 5℃ for 30min" step pulse temperature rise, synchronous to "60 Pa for 8min→90 Pa for 4min" periodical adjustment of vacuum degree, control the moisture content to 30-35%; ② desorption drying stage: vacuum degree 20-50 Pa, heating temperature 35-45℃, use "3-5W / g microwave power intermittent irradiation (work 3min stop 1min)" synergistic heating, control the moisture content to 15-20%; the purpose of this step is to avoid the degradation of heat-sensitive nutrients by segmenting pulse regulation and AI dynamic optimization, while efficiently dehydrating to reduce nutrient loss during the drying stage; Nano-adsorption-microwave synergistic drying: under the condition of 0.08-0.09MPa vacuum degree and 30-35℃, use 3A molecular sieve loaded with 5-10% nano-SiO2 for adsorption dehydration, supplemented with 2-3W / g microwave power for 10-15min, control the final moisture content ≤5%; the purpose of this step is to use the high adsorption of nano materials and the synergistic effect of low temperature microwave to deeply dehydrate at low energy consumption, avoiding the destruction of nutrients caused by traditional high temperature drying; Amyloid-like protein coating packaging: immerse the freeze-dried fruit pieces in an aqueous solution containing 0.5-1% amyloid-like protein (ALP), 0.2-0.4% sodium alginate and 0.1-0.3% cellulose nanocrystals for 1-2min to form a composite protective film with a thickness of 1-3μm; the purpose of this step is to block oxygen and moisture by natural polymer composite film, reduce the oxidative degradation of nutrients and the quality deterioration caused by water migration during storage; Inert gas nanometer film packaging: in a nitrogen environment with a purity of 99.9%, an aluminized nanometer SiO2 antibacterial film is used for sealing and packaging; the purpose of this step is to isolate oxygen by inert gas and to strengthen the barrier property and antibacterial property of the nanometer film, so as to inhibit the oxidation reaction and microbial pollution during the storage stage, and to prolong the nutrient retention period. Further, the low-sugar fruits are selected from apples, pears, peaches, strawberries or blueberries. Further, the fruit slice thickness is 2-7mm, wherein the berry fruit slice thickness is 2-4mm, and the drupe and stone fruit slice thickness is 3-7mm. Further, the synergistic pretreatment further comprises a surface dehydration step: 300-500r / min centrifugal treatment for 1-2min to remove excess color protection agent on the surface. Further, the AI algorithm is based on a Bayesian optimization model, and real-time temperature, pressure and infrared thermal imaging data are collected to dynamically adjust the heating rate and vacuum degree parameters. Further, during the formation of the composite protective film, the amyloid-like protein and sodium alginate form a three-dimensional network structure through intermolecular hydrogen bonds, and the cellulose nanocrystals are uniformly dispersed in the network to enhance the mechanical strength of the film. Further, the fruit slice after coating and packaging has a moisture loss rate of ≤5% / 24h at 37℃.

[0006] Further, the oxygen transmission rate of the aluminized nanometer SiO2 antibacterial film is ≤0.01cm³ / (m²·24h·0.1MPa). Further, the regeneration cycle of the nanometer SiO2-loaded 3A molecular sieve is 50-100 batches, and the regeneration conditions are 150-200℃ heating for 2-3h. Further, during the segmented pulse vacuum freeze-drying process, the 0.2-0.4T magnetic field strength is synchronously maintained during the sublimation drying stage.

[0007] Compared with the prior art, the present application has the following beneficial effects: Through the whole-chain technology synergy of "ultrasonic-pulse electric field pretreatment → gradient magnetic field freezing → AI dynamic freeze-drying → nanometer adsorption drying", the efficient retention of key nutrients in fruits is realized. Among them, the synergistic effect of ultrasonic and pulse electric field makes the penetration efficiency of color protection agent increase by 30-50%, the gradient magnetic field freezing reduces the cell rupture caused by the refinement of ice crystals, and the low-temperature nanometer adsorption drying avoids the degradation of heat-sensitive components, which fundamentally solves the three problems of oxidation loss, cell damage and thermal degradation in the traditional freeze-drying process.

[0008] The method is designed with different parameters for different types of fruits, suitable for various low-sugar fruits such as pome fruits (apple, pear), stone fruits (peach), and berries (strawberry, blueberry). By adjusting the slice thickness (berries 2-4mm, pome / stone fruits 3-7mm), color protection agent concentration, magnetic field strength, and other key parameters, the optimal processing effect can be achieved for fruits with different structures and compositions. Experimental verification shows that all types of fruits processed by this method maintain a stable high nutrient retention rate, solving the limitations of existing technologies that are not suitable for specific fruits. The innovative integration of ultrasonic-pulsed electric field synergy, gradient magnetic field regulation, AI dynamic optimization, nanomaterial adsorption, and natural polymer coating five cutting-edge technologies, builds a full-process nutrient protection system of "pre-treatment color protection enhancement - cell freezing protection - drying precise temperature control - storage barrier protection". Compared with existing technologies, it breaks through the limitations of traditional freeze-drying which only focuses on single link optimization: through the AI Bayesian optimization model to real-time control freeze-drying parameters, avoid local overheating; using amyloid-like protein composite film and nano-antibacterial film double barrier, the 24h water loss rate is controlled at 2.1-2.8% in 37℃ environment, far lower than the traditional method of 8.5-9.2%, achieving double control of nutrient loss in processing and storage stage. The combination of gradient magnetic field freezing and segmented pulse freeze-drying technology maximizes the retention of fruit cell structure integrity, with a rehydration rate of over 90%, color L value of 47.2-48.9, close to fresh fruit state, without wrinkles, hardening and other quality deterioration phenomena. The formation of amyloid-like protein composite protective film not only enhances the mechanical strength of the product, but also gives it good moisture resistance and antioxidant properties, solving the problem of traditional freeze-dried products prone to moisture absorption and flavor loss. The use of AI dynamic control technology achieves precise matching of freeze-drying parameters, reducing sublimation drying time by 15-20%; the high adsorption performance of nano-SiO2 molecular sieve reduces drying energy consumption by 10-15% compared to traditional hot air drying, and the molecular sieve can be regenerated and reused after 50-100 batches, reducing production costs. At the same time, the standardization design of the whole process parameters ensures the stability of the product quality, with a difference in nutrient retention rate between batches of ≤2%, meeting the quality control requirements of large-scale industrial production. Through the double protection of "amyloid-like protein coating packaging + inert gas nano-membrane packaging", the product oxygen transmission rate is ≤0.01cm³ / (m²・24h・0.1MPa), with a shelf life of more than 12 months at room temperature, significantly better than the traditional packaging shelf life of 6 months. The vitamin oxidation loss rate is controlled within 5% during storage, solving the industry's difficult problem of continuous nutrient loss of freeze-dried products during storage, and expanding the market circulation range of the products. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1A flow chart of a comprehensive fruit freeze-drying processing method for reducing nutrient loss of fruits; DETAILED DESCRIPTION In order to enable those skilled in the art to better understand the present application, the technical solutions of the present application are further described below in conjunction with the drawings and examples.

[0010] The core idea of the present application is to design targeted technical solutions for the key links of nutrient loss in the fruit freeze-drying process (oxidative degradation, cell structure damage, loss of heat-sensitive ingredients, storage oxidation, etc.), to realize the whole-process nutrient retention closed loop of "pre-treatment color protection strengthening-freezing cell damage control-precise drying temperature control-storage barrier protection", and to improve the process stability and efficiency through AI dynamic regulation, nanomaterial application and other technologies.

[0011] Specifically, by selecting low-sugar fruits with a sugar content of 8-10 degrees, the probability of Maillard reaction occurring during processing is reduced from the source, and the degradation of nutrients caused by the reaction of sugars and amino acids is reduced. Removing impurities and inedible parts avoids contamination and interference, uniform slicing increases the specific surface area, ensuring uniformity in subsequent processing, and preventing excessive processing in some areas that can lead to nutrient loss. Using ultrasonic cavitation effect and pulsed electric field electroporation, the penetration efficiency of the composite color protection agent (tea polyphenol, vitamin C, etc. antioxidant components, CaCl2 strengthening agent) into the cells is improved; antioxidant components directly inhibit the activity of polyphenol oxidase and free radical oxidation reaction, and calcium salt enhances the stability of cell wall structure, blocking the oxidation of nutrients and the leakage channel of cell rupture from the pre-treatment stage. Through the synergistic effect of three-stage gradient temperature field and magnetic field, the ice crystal nucleation and growth process is regulated, forming a fine and uniform ice crystal structure, avoiding the mechanical damage of coarse ice crystals to the cell structure in traditional freezing, and reducing the leakage of nutrients such as vitamins and polyphenols caused by cell rupture. AI algorithm is used to dynamically control the parameters of sublimation drying and analytical drying, and the temperature is increased in steps and the vacuum degree is periodically adjusted to avoid continuous high temperature; intermittent microwave irradiation in the analytical drying stage not only efficiently removes bound water, but also reduces the degradation of heat-sensitive nutrients (such as vitamins A and C) caused by local overheating; a magnetic field is applied simultaneously in the sublimation stage to further stabilize the cell structure and reduce the risk of nutrient loss. With the high specific surface area adsorption performance of nano-SiO2 loaded molecular sieves, combined with low temperature and microwave assistance at 30-35°C, deep dehydration is achieved at low energy consumption with a water content of ≤5%, avoiding the thermal damage of nutrients caused by traditional high-temperature drying, while the nano-materials enhance the dehydration efficiency and reduce the processing time. By forming a three-dimensional network composite film with amyloid-like proteins and sodium alginate, and enhancing the film strength with cellulose nanocrystals, a physical barrier of 1-3 μm is formed on the surface of the fruit slices, blocking the migration of oxygen and water, and reducing the oxidative degradation of nutrients and the quality deterioration caused by water changes during storage. High-purity nitrogen environment isolates oxygen, and the aluminum-coated nano-SiO2 antibacterial film has excellent oxygen barrier property with a permeability of ≤0.01 cm³ / (m²・24h・0.1MPa) and antibacterial performance, which synergistically inhibits oxidation and microbial contamination during storage, prolonging the nutrient retention period.

[0012] In summary, this method achieves precise control of fruit nutrient loss through the synergistic effect of various technologies in four dimensions: nutrient oxidation inhibition, cell structure protection, thermal damage avoidance, and storage environment control, significantly improving the retention rate of key nutrients such as vitamins and polyphenols.

[0013] Example 1: Red Fuji apple (pome fruit) Raw material processing: Select red Fuji apples with a sugar content of 10 degrees, wash, peel, core, and cut into 5 mm thick slices.

[0014] Pre-treatment: 250W ultrasound + 20kV / cm pulsed electric field treatment for 3min in the composite color protection agent (0.08% tea polyphenol + 0.15% vitamin C + 0.12% citric acid + 0.8% CaCl2), and centrifugal dehydration at 300r / min for 1.5min.

[0015] Gradient freezing: pre-freezing at -8℃, 0.2T for 1.5h→ freezing at -35℃, 0.4T for 2.5h→ annealing at -12℃, 0.3T for 1.5h.

[0016] Sectional freeze-drying: AI dynamic adjustment, sublimation drying (vacuum degree 70Pa, 25℃→30℃→35℃ stepwise temperature rise, vacuum pulse) to 32% water content; analytical drying (35Pa, 40℃, 3W / g microwave intermittent irradiation) to 18% water content.

[0017] Nanodrying: 0.085MPa, 32℃, 3A molecular sieve loaded with 8% nano-SiO2, 2.5W / g microwave drying for 12min, final water content 4.5%.

[0018] Coating packaging: dipping in 0.8%ALP + 0.3% sodium alginate + 0.2% cellulose nanocrystal solution for 1.5min to form a 2μm film.

[0019] Packaging: 99.9% nitrogen environment, sealed with aluminum-coated nano-SiO2 film.

[0020] Example 2: Dangshan pear (drupes) Raw material treatment: Dangshan pears with a sugar content of 8 degrees were washed, peeled, cored, and cut into 3mm thick slices.

[0021] Pre-treatment: 200W ultrasound + 15kV / cm pulsed electric field treatment for 2min in the composite color protection agent (0.05% tea polyphenol + 0.2% vitamin C + 0.1% citric acid + 0.5% CaCl2), and centrifugal dehydration at 500r / min for 1min.

[0022] Gradient freezing: pre-freezing at -5℃, 0.1T for 1h→ freezing at -30℃, 0.3T for 2h→ annealing at -15℃, 0.2T for 1h.

[0023] Sectional freeze-drying: sublimation drying (50Pa, 20℃→25℃ stepwise temperature rise) to 30% water content; analytical drying (20Pa, 35℃, 5W / g microwave intermittent) to 15% water content.

[0024] Nanodrying: 0.08MPa, 30℃, 3A molecular sieve loaded with 5% nano-SiO2, 2W / g microwave drying for 10min, final water content 3.8%.

[0025] Coating encapsulation: dipping in 0.5% ALP + 0.2% sodium alginate + 0.1% cellulose nanocrystal solution for 1 min, forming 1 μm film.

[0026] Packaging: same as Example 1.

[0027] Example 3: Jintong No. 5 yellow peach (drupes) Raw material treatment: yellow peach with 8 degrees of sugar, washed, peeled, pitted, and cut into 7 mm thick slices.

[0028] Pretreatment: 300 W ultrasonic + 25 kV / cm pulsed electric field treatment for 4 min in the composite color protection agent (0.1% tea polyphenol + 0.15% vitamin C + 0.15% citric acid + 1% CaCl2), centrifugal dehydration for 2 min at 400 r / min.

[0029] Gradient freezing: pre-freezing at -10℃, 0.3T for 2h→ freezing at -40℃, 0.5T for 3h→ annealing at -10℃, 0.4T for 2h.

[0030] Sectional freeze-drying: sublimation drying (100 Pa, 30℃→35℃ stepwise temperature rise) to 35% moisture content; analytical drying (50 Pa, 45℃, 4W / g microwave intermittence) to 20% moisture content.

[0031] Nanodrying: 0.09 MPa, 35℃, 3W / g microwave drying for 15 min with 10% nano-SiO2 loaded 3A molecular sieve, final moisture content 4.8%.

[0032] Coating encapsulation: dipping in 1% ALP + 0.4% sodium alginate + 0.3% cellulose nanocrystal solution for 2 min, forming 3 μm film.

[0033] Packaging: same as Example 1.

[0034] Example 4: strawberry (berry) Raw material treatment: strawberry with 9 degrees of sugar, washed, calyx removed, and cut into 3 mm thick slices.

[0035] Pretreatment: 280 W ultrasonic + 22 kV / cm pulsed electric field treatment for 3.5 min in the composite color protection agent (0.07% tea polyphenol + 0.18% vitamin C + 0.13% citric acid + 0.7% CaCl2), centrifugal dehydration for 1.5 min at 350 r / min.

[0036] Gradient freezing: pre-freezing at -7℃, 0.25T for 1.8h→ freezing at -38℃, 0.45T for 2.8h→ annealing at -13℃, 0.35T for 1.8h.

[0037] Sublimation drying (80 Pa, 28 °C→33 °C stepwise heating) to 33% moisture content; desorption drying (40 Pa, 42 °C, 3.5 W / g microwave intermittently) to 17% moisture content.

[0038] Nano-drying: 0.088 MPa, 33 °C, 3A molecular sieves loaded with 7% nano-SiO2, 2.8 W / g microwave drying for 13 min, final moisture content 4.2%.

[0039] Coating packaging: dipping in 0.7% ALP + 0.35% sodium alginate + 0.25% cellulose nanocrystal solution for 1.8 min, forming a 2.5 μm film.

[0040] Packaging: same as Example 1.

[0041] Example 5: Blueberry (berry) Raw material treatment: blueberry with 10 degrees of sugar, washed and cut into 2 mm thick slices (with peel retained).

[0042] Pretreatment: composite color protection agent (0.06% tea polyphenol + 0.12% vitamin C + 0.11% citric acid + 0.6% CaCl2), 220 W ultrasonic + 18 kV / cm pulsed electric field treatment for 2.5 min, 450 r / min centrifugal dehydration for 1.2 min.

[0043] Gradient freezing: -6 °C, 0.15 T pre-freezing for 1.2 h→-32 °C, 0.35 T freezing for 2.2 h→-14 °C, 0.25 T annealing for 1.2 h.

[0044] Sublimation drying (60 Pa, 22 °C→27 °C stepwise heating) to 31% moisture content; desorption drying (30 Pa, 38 °C, 4.5 W / g microwave intermittently) to 16% moisture content.

[0045] Nano-drying: 0.082 MPa, 31 °C, 3A molecular sieves loaded with 6% nano-SiO2, 2.2 W / g microwave drying for 11 min, final moisture content 3.9%.

[0046] Coating packaging: dipping in 0.6% ALP + 0.25% sodium alginate + 0.15% cellulose nanocrystal solution for 1.2 min, forming a 1.5 μm film.

[0047] Packaging: same as Example 1.

[0048] Comparative Example The corresponding fruits were treated by a conventional method: conventional color protection (without ultrasonic-pulsed electric field)→-30 °C freezing for 1 h→ freeze-drying to 37% moisture content→ microwave vacuum drying to 10%→ hot air drying to ≤5%; without gradient freezing, nano-drying, coating packaging and nano-membrane packaging.

[0049] Comparison of experimental data (detection results of each fruit freeze-dried product) Examples 1-5 cover pome fruits (apple, pear), stone fruits (yellow peach), berries (strawberry, blueberry), and the nutrient retention rates of all fruits are significantly higher than traditional methods (increased by 23.0-43.0%), proving that the method is suitable for a variety of fruits. Comparing the same type of fruit examples with traditional methods, ultrasonic-pulsed electric field pretreatment improves the penetration efficiency of color protection agent and reduces oxidative loss; gradient magnetic field freezing reduces cell damage by refining ice crystals (such as apple vitamin C retention rate increased by 12.7% due to gradient freezing); nano-adsorption-microwave drying is efficient at low temperature, avoiding the nutrient degradation caused by high temperature hot air (such as strawberry anthocyanin retention rate increased by 18.5% due to nano drying). The amyloid-like protein coating and nano-membrane packaging synergize to control the moisture loss rate at 37°C to 2.1-2.8%, which is much lower than the 8.5-9.2% of traditional methods, reducing nutrient oxidation during the storage phase.

[0050] The above is only an embodiment of the present application, and the circuit and electronic components and modules involved are prior art. Those skilled in the art can implement it without further description. The content protected by this application does not involve the improvement of software and methods. The specific structure and characteristics of the scheme known to the public are not described in detail here. Those skilled in the art know all the ordinary technical knowledge in the field of the application before the filing date or the priority date, can obtain all the prior art in this field, and have the ability to apply conventional experimental means before that date. Those skilled in the art can improve and implement the present scheme based on their own ability under the guidance of this application. Some typical known structures or known methods should not be an obstacle for those skilled in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should be considered as the protection scope of the present application. These will not affect the effectiveness and practicality of the present application.

Claims

1. A comprehensive fruit freeze-drying processing method that reduces nutrient loss in fruits, characterized in that: Includes the following steps; S1. Immerse the sliced ​​fruit pieces in a composite color-protecting agent, and simultaneously apply ultrasonic and pulsed electric field treatment to the composite color-protecting agent system containing the fruit pieces. The composite color-protecting agent includes 0.05-0.1% tea polyphenols, 0.1-0.2% vitamin C, 0.1-0.15% citric acid and 0.5-1% CaCl2 by mass concentration. The ultrasonic power is 200-300W, the pulsed electric field intensity is 15-25kV / cm, and the synergistic treatment time is 2-4min, to obtain fruit pieces with enhanced color protection. S2. The color-protected and enhanced fruit slices are subjected to a three-stage magnetic field freezing treatment to obtain frozen fruit slices; S3. The parameters of the frozen fruit slices are dynamically adjusted using an AI algorithm, and the primary freeze-dried fruit slices are obtained by vacuum freeze-drying in stages. S4. The primary freeze-dried fruit slices are placed in a vacuum environment and dehydrated by adsorption using 3A molecular sieve loaded with 5-10% nano SiO2. They are then treated with microwave power of 2-3W / g for 10-15 minutes, with the vacuum degree controlled at 0.08-0.09MPa and the temperature at 30-35℃, until the moisture content of the fruit slices is ≤5%, thus obtaining deeply dried fruit slices. S5. Immerse the deep-dried fruit slices in an aqueous solution containing 0.5-1% amyloid protein (ALP), 0.2-0.4% sodium alginate, and 0.1-0.3% cellulose nanocrystals for 1-2 minutes to form a composite protective film with a thickness of 1-3 μm, thus obtaining coated fruit slices.

2. The comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 1, characterized in that: The process also includes placing the coated fruit slices obtained in step S5 into a nitrogen replacement packaging machine, and sealing them in a nitrogen environment with a purity of ≥99.9% using an aluminum-plated nano-SiO2 antibacterial film with a thickness of 20-30μm to obtain the finished freeze-dried fruit.

3. The comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 1, characterized in that: The fruit slices that have been enhanced with color protection are subjected to a three-stage magnetic field freezing treatment to obtain frozen fruit slices, including: The color-protecting and strengthening fruit slices were laid flat on a freezing tray and subjected to three stages of treatment: the first stage was pre-freezing at -5 to -10℃ and a magnetic field of 0.1 to 0.3T for 1 to 2 hours; The second stage involves rapid freezing for 2-3 hours at -30 to -40°C and a magnetic field of 0.3-0.5T. In the third stage, the sample was annealed at -15 to -10℃ and in a magnetic field of 0.2 to 0.4T for 1 to 2 hours to obtain the frozen sample.

4. The comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 1, characterized in that: The process of dynamically adjusting parameters using an AI algorithm to freeze-dry the frozen fruit slices in stages to obtain primary freeze-dried fruit slices includes: Sublimation drying stage: Control the vacuum degree to 50-100Pa, and increase the temperature of the heating plate in a stepwise manner: "hold at 20-30℃ for 1 hour → hold for 30 minutes every 5℃ increase", while simultaneously adjusting the vacuum degree in a cycle of "hold at 60Pa for 8 minutes → hold at 90Pa for 4 minutes" until the moisture content of the fruit slices is 30-35%; Analysis and drying stage: control the vacuum degree to 20-50Pa, the heating temperature to 35-45℃, and use "3-5W / g microwave intermittent irradiation, working for 3 minutes and stopping for 1 minute" for coordinated heating until the fruit slice moisture content is 15-20%, and obtain the primary freeze-dried fruit slices.

5. The comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 1, characterized in that: The fruit is selected from at least one of apples, pears, peaches, strawberries, or blueberries.

6. The comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 1, characterized in that: The thickness of the fruit slices is 2-7 mm, of which the thickness of berry fruit slices is 2-4 mm, and the thickness of pome and drupe fruit slices is 3-7 mm.

7. The comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 1, characterized in that: The AI ​​algorithm is based on a Bayesian optimization model and collects real-time data on fruit slice temperature, freeze-drying chamber pressure, and infrared thermal imaging, with a temperature control accuracy of ±1℃.

8. The comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 1, characterized in that: The mass ratio of the 3A molecular sieve loaded with nano-SiO2 to the primary freeze-dried fruit slices is 2-3:1, and the molecular sieve is evenly spread 5-10 mm below the fruit slices.

9. A comprehensive fruit freeze-drying processing method for reducing nutrient loss in fruits as described in claim 4, characterized in that: The sublimation drying stage is maintained with a magnetic field strength of 0.2-0.4T throughout, and the magnetic field is perpendicular to the heating direction.

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