A high-efficiency composite drying method for fruit freeze-drying based on graphene coating infrared cooperation

Abstract

The application discloses a kind of based on graphene coating infrared synergistic efficient composite drying method of fruit freeze-drying, the method includes the following steps: S1.fruit is in the pulsed electric field of pulse voltage 35 kV / cm below and is pretreated, and the fruit after pulsed electric field pretreatment is obtained;S2.pretreated fruit is in the electrostatic field of field intensity 30 kV / cm below and is pre-frozen, and the fruit after pre-freezing is obtained;S3.pre-frozen fruit is placed on graphene coating hot plate, and is dried under vacuum condition, and the freeze-dried fruit is obtained;The heating rate of graphene coating hot plate is 2~5℃ / min, heating temperature is 30~50℃, and drying time is 8~12 h.The fresh fruit is sequentially treated by pulsed electric field, electrostatic field assisted directional freezing treatment and graphene coating infrared heating drying process synergy, so that freeze-dried fruit nutrient retention rate is high, rehydration is good, and freeze-drying cycle is shortened by 25~45%, energy consumption is reduced by 25~40%, suitable for efficient high-quality energy-saving drying processing of fresh fruit.

Description

Technical Field

[0001] This invention belongs to the field of food drying technology, specifically relating to a highly efficient composite drying method for fruit freeze-drying based on graphene coating and infrared synergy. Background Technology

[0002] Fresh fruits are rich in vitamins, minerals, dietary fiber, and other nutrients, but their high water content and delicate texture make them prone to spoilage after harvesting. Their shelf life at room temperature is extremely short, severely limiting their storage and transportation range and shelf life. Freeze-drying technology, by freezing the water in fruit into ice and then sublimating the ice directly into water vapor in a vacuum environment, can maximize the preservation of the fruit's original nutrients, color, flavor, and shape, while also achieving excellent rehydration properties. It is currently the preferred technology in the field of fruit processing.

[0003] Chinese invention patent CN118902031A discloses a method for preparing freeze-dried fruit. This method involves evenly placing processed fruit slices on a freezing tray, then placing the tray in a freezer for two-stage freeze-drying. The two stages include a vacuum-cooling stage and a heating stage to obtain freeze-dried fruit slices, thus preserving the color, aroma, taste, shape, and nutritional components of fresh fruit. However, existing technologies directly freeze-dry fruit through vacuum freezing, which makes it difficult to construct directional moisture migration channels, resulting in high resistance to moisture sublimation and quality problems such as incomplete drying, poor rehydration, and nutrient loss. Furthermore, freeze-drying equipment typically uses aluminum alloy heating plates, which are inefficient (usually below 75%), have slow heat conduction, uneven heating, long freeze-drying cycles, and high energy consumption. Chinese invention patent CN120898951A discloses a comprehensive fruit freeze-drying processing method to reduce nutrient loss in fruits. The method involves immersing fresh-cut fruit in a composite color-protecting agent, subjecting the fruit slices containing the composite color-protecting agent to ultrasonic and pulsed electric field treatment, and then magnetic field treatment to obtain coated fruit slices. This technology uses an immersion-type color-protecting treatment, which adds extra moisture to the material and further prolongs the drying time. Moreover, the addition of the color-protecting agent will cause the flavor of the freeze-dried fruit to be affected to a certain extent.

[0004] Therefore, it is necessary to develop a composite drying method using efficient heating freeze-drying technology to address the shortcomings of existing technologies, which has significant practical implications and application value. Summary of the Invention

[0005] To address the problems of low freeze-drying efficiency, high energy consumption, uneven heating, high resistance to moisture migration, and poor product quality in existing fruit freeze-drying technologies, this invention provides a highly efficient composite drying method for fruit freeze-drying based on graphene coating and infrared heating, thereby simultaneously improving fruit freeze-drying efficiency, product quality, and energy-saving effects.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A highly efficient composite drying method for fruit freeze-drying based on graphene coating and infrared synergy includes the following steps: S1. The fruit is pretreated in a pulsed electric field with a pulse voltage of less than 35 kV / cm to obtain the fruit after pulsed electric field pretreatment; S2. The pretreated fruit is pre-frozen in an electrostatic field with an electric field strength of less than 30 kV / cm to obtain pre-frozen fruit; S3. Place the pre-frozen fruit on a graphene-coated heating plate and dry it under vacuum conditions to obtain freeze-dried fruit; the heating rate of the graphene-coated heating plate is 2~5℃ / min, the heating temperature is 30~50℃, and the drying time is 8~12 h.

[0007] This invention combines pulsed electric field, electrostatic field, and graphene-coated heating plate technologies to improve fruit drying efficiency and ensure fruit quality. Pulsed electric field treatment induces uniform electroporation in the fruit cell walls, creating directional water migration channels. The electrostatic field induces directional polarization of water molecule dipoles, forcing water molecules to align in an orderly manner along the electric field direction. Ice crystals grow directionally along this direction, forming regular columnar or sheet-like fine ice crystals. This prevents random large ice crystals from piercing cell walls and damaging tissue morphology, thus preserving the fruit's texture to the maximum extent. Simultaneously, the ordered ice crystals significantly reduce the resistance to subsequent sublimation mass transfer. Combined with the high-efficiency infrared heating characteristics of the graphene coating, this further accelerates the dehydration rate and shortens the freeze-drying cycle. By matching the heating temperature and rate of the graphene-coated infrared heating plate to the sublimation rate of ice, the problem of localized overheating or incomplete drying of the fruit material is avoided. In this solution, the graphene-coated infrared heating plate replaces the traditional aluminum alloy heating plate to provide the heat source for the sublimation and desorption drying stages of fruit freeze-drying. Combined with the synergistic effect of the pulsed electric field and electrostatic field, the freeze-drying cycle of fruit is shortened by 25-45% compared to traditional methods, while simultaneously improving freeze-drying efficiency, product quality, and energy-saving effects.

[0008] Further, in step S1, the pulsed electric field has a pulse voltage of 15~35 kV / cm, a pulse width of 10~50 μs, a pulse frequency of 40~60 Hz, and a processing time of 2~8 min; preferably, the pulsed electric field has a pulse voltage of 25 kV / cm, a pulse width of 20~30 μs, a pulse frequency of 50 Hz, and a processing time of 4 min.

[0009] Further, the electrostatic field described in step S2 has an electric field strength of 10~30 kV / cm and a frequency of 40~60 Hz; preferably, the electrostatic field has an electric field strength of 20 kV / cm and a frequency of 50 Hz.

[0010] Further, the pre-freezing temperature in step S2 is -40~-20℃, and the pre-freezing time is 1~3 h; preferably, the pre-freezing temperature is -30℃, and the pre-freezing time is 2 h.

[0011] Preferably, the pre-freezing causes the free water and bound water in the material to freeze completely in stages.

[0012] Further, the fruit mentioned in step S1 is a pome, drupe, berry, or tropical fruit; preferably, the drupe is selected from one or more of mango, peach, apricot, or cherry; the berry is selected from one or more of honeysuckle berry, blueberry, raspberry, or strawberry.

[0013] Preferably, the fruit mentioned in step S1 is the fleshy part of a fresh fruit after removing the stem, peel, and pit.

[0014] Furthermore, the fruit in step S1 is in the form of slices, strips, or granules; preferably, the fruit is in the form of slices or strips with a thickness of 3-8 mm; preferably, the fruit is in the form of granules with a particle size not exceeding 1 cm.

[0015] Furthermore, the fruit in step S1 needs to be pre-cooled before pulse voltage treatment, and the pre-cooling is carried out in an environment with a temperature of 0~4℃ for 10~20 min; preferably, the pre-cooling is carried out in an environment with a temperature of 4℃ for 20 min.

[0016] Further, the graphene-coated heating plate in step S3 includes a substrate, a graphene coating, and electrodes. The substrate is a glass fiber substrate, and the graphene coating is disposed on the surface of the substrate with a coating thickness of 100~500 μm. The electrodes are fixed to both ends of the substrate and electrically connected to the graphene coating.

[0017] Preferably, the graphene coating in step S3 is prepared on the substrate surface by a spraying process.

[0018] Preferably, the electrode in step S3 is a copper electrode.

[0019] Furthermore, the graphene-coated heating plate described in step S3 has an electrothermal efficiency of not less than 99% and a thermal conductivity of not less than 5000 W / (m·K).

[0020] Further, the pulsed electric field in step S1 includes opposing plates, the distance between the plates is 5~10 cm, and the thickness of the fruit in the pulsed electric field does not exceed 1 / 2 of the distance between the plates; preferably, the distance between the plates is 10 cm, and the thickness of the fruit in the pulsed electric field does not exceed 5 cm of the distance between the plates.

[0021] Preferably, during the pulsed electric field treatment or electrostatic treatment process described in step S1, the fruit pretreatment material is laid flat without stacking, and the electric field or pulsed electric field is evenly distributed in the material.

[0022] Further, the temperature of the pulse voltage in step S1 is 20~25℃; preferably, the temperature of the pulse voltage is 20℃.

[0023] Furthermore, the vacuum condition described in step S3 is to maintain a vacuum level of 10~50 Pa. The vacuum level is always maintained below the triple point pressure of water to accelerate the freeze-drying rate.

[0024] Preferably, the fruit freeze-dried in step S3 is then refrigerated at a temperature of 0-4°C; preferably, the refrigeration also requires vacuum packaging or packaging with inert gas.

[0025] Preferably, the above packaging is a food-grade high-barrier vacuum-sealed packaging. The nitrogen gas introduced during the packaging process ensures that the oxygen content inside the packaging is ≤1%, preventing the freeze-dried fruit product from absorbing moisture, oxidizing and browning, and losing its flavor.

[0026] Compared with the prior art, the present invention has the following technical effects: (1) The present invention combines fresh fruit with pulse electric field treatment, electrostatic field assisted directional freezing treatment and graphene coating infrared heating drying technology in sequence, so that the water content of the freeze-dried fruit does not exceed 3%, the nutrient retention rate is not less than 88%, the anthocyanin retention rate is not less than 90%, the carotenoid retention rate is not less than 88%, and the finished product has good rehydration properties.

[0027] (2) Compared with the prior art, the present invention significantly shortens the freeze-drying time of fruit to 8-12 hours, shortens the freeze-drying cycle by 25-45%, reduces energy consumption by 25-40%, preserves the nutritional components of fruit to the maximum extent, and the moisture content of the finished product does not exceed 3%. It is suitable for efficient, high-quality and energy-saving drying processing of fresh fruit. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the graphene-coated heating plate in this invention; Figure 1 1 is the substrate; 2 is the graphene coating; 3 is the electrode; 4 is the fruit; 5 is the material tray; 6 is the freeze-drying chamber.

[0029] Figure 2 This is a schematic diagram comparing the freeze-drying time of Example 1 and Comparative Examples 1-5 in this invention.

[0030] Figure 3 This is a schematic diagram comparing the energy consumption reduction rate of Example 1 and Comparative Examples 1-5 in this invention.

[0031] Figure 4 This is a schematic diagram comparing the anthocyanin retention rates of Example 1 and Comparative Examples 1-5 in this invention.

[0032] Figure 5 This is a schematic diagram comparing the freeze-drying time of Example 2 and Comparative Examples 6-10 in this invention.

[0033] Figure 6 This is a schematic diagram comparing the energy consumption reduction rate of Example 2 and Comparative Examples 6-10 in this invention.

[0034] Figure 7 This is a schematic diagram comparing the β-carotene retention rates of Example 2 and Comparative Examples 6-10 in this invention. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments so that those skilled in the art can understand it, but the scope of protection of the present invention is not limited to the embodiments described.

[0036] It should be noted that the pulsed electric field processing device used in the following embodiments is a conventional commercial device. The graphene-coated heating plate adopts a structure of glass fiber substrate, graphene coating and copper electrode. The thickness of the graphene coating is 100~500 μm, preferably 300 μm, with an electrothermal conversion efficiency of not less than 99% and a thermal conductivity of not less than 5000 W / (m·K); preferably, the electrothermal conversion efficiency is 99% and the thermal conductivity is 5000 W / (m·K). The aluminum alloy heating plate adopts a conventional commercial freeze-drying-specific aluminum alloy heating plate with an electrothermal conversion efficiency of not more than 75% and a thermal conductivity of not more than 600 W / (m·K). Preferably, the aluminum alloy is 6063 aluminum alloy, with an electrothermal conversion efficiency of 75% and a thermal conductivity of 600 W / (m·K). Figure 1 As shown, it is set in the freeze-drying chamber 6, which includes a substrate 1, a graphene coating 2 and an electrode 3. The substrate 1 is a glass fiber substrate, the graphene coating 2 is set on the surface of the substrate 1, and the coating thickness is 300 μm. The material plate 5 is used to place the fruit 4. The electrode 3 is fixed at both ends of the substrate 1 and electrically connected to the graphene coating 2.

[0037] All fruits used are selected as fresh fruits that are free from rot, bruising, and pesticide residues. The process parameters in each step can be adjusted appropriately according to the type and size of the fruit.

[0038] Design a comparative experiment of single-factor optimization and collaborative optimization to verify the interaction between electric field and graphene heating parameters: 1. Single-factor optimization experiment of electric field (using aluminum alloy heating plate, commercial conventional heating parameters): With the freeze-drying vacuum degree fixed at 30 Pa and the pre-freezing parameters at -30℃ / 2h, the effects of pulse electric field strength (10~40 kV / cm), pulse frequency (30~60 Hz), pulse treatment time (1~4 min), and electrostatic field strength (10~30 kV / cm) on freeze-drying time, energy consumption, and nutrient retention rate were investigated. The optimal parameters for single pulse electric field treatment were determined as follows: for honeysuckle fruit, the pulse electric field strength was 20 kV / cm, the pulse frequency was 50 Hz, and the treatment time was 2 min; for mango, the pulse voltage was 15 kV / cm, the pulse frequency was 40 Hz, the treatment time was 3 min, and the electrostatic field strength was 20 kV / cm.

[0039] 2. Single-factor optimization experiment of graphene coating infrared heating (without electric field treatment): With the freeze-drying vacuum degree fixed at 30 Pa and the pre-freezing parameters at -30℃ / 2h, the effects of heating temperature (25~50℃), heating rate (1~5℃ / min), and material spacing (5~20 cm) on the core indicators were investigated. The optimal parameters for heating the graphene coating alone were determined as follows: for honeysuckle fruit, the optimal parameters were heating temperature at 40℃, heating rate at 2℃ / min, and material spacing at 10 cm; for mango, the optimal parameters were heating temperature at 45℃, heating rate at 3℃ / min, and material spacing at 10 cm.

[0040] 3. Further investigation was conducted into the effects of pulsed electric field and electrostatic field on ultrasonic treatment, graphene coating and aluminum alloy heating plate on freeze drying. See the results of Examples 1-2, Comparative Examples 1-10 and Test Example 1 for details.

[0041] Example 1: Preparation of freeze-dried honeysuckle fruit This embodiment provides a highly efficient composite drying method for honeysuckle fruit freeze-drying based on graphene coating and infrared synergy, including the following steps: S1. Pre-treat honeysuckle berries in a pulsed electric field to obtain honeysuckle berries pre-treated with a pulsed electric field; S2. Pre-freeze the pretreated honeysuckle berries under an electrostatic field to obtain pre-frozen honeysuckle berries; S3. Place the pre-frozen honeysuckle berries on a graphene-coated heating plate and dry them under vacuum to obtain freeze-dried honeysuckle berries.

[0042] The specific steps are as follows: (1) Select fresh honeysuckle berries with a diameter of about 1 cm, remove the fruit stems and impurities, rinse them with clean water, drain the surface water, and obtain honeysuckle berry pre-treated material without cutting. Place the honeysuckle berry pre-treated material in a low temperature environment of 4℃ for 20 min.

[0043] (2) Spread the pre-cooled honeysuckle berry pre-treatment material from step (1) between the plates of the pulse electric field treatment device. The plate spacing is 10 cm and the thickness of the honeysuckle berry pre-treatment material layer is 5 mm (not exceeding 1 / 2 of the plate spacing). Set the pulse electric field parameters: pulse voltage is 25 kV / cm, pulse width is 30 μs, pulse frequency is 50 Hz, and the treatment is carried out at room temperature (20℃) for 4 min.

[0044] (3) Place the pretreated honeysuckle berries processed in step (2) into the material tray of the freeze dryer, spread them evenly with a thickness of 10 mm, and send them into the pre-freezing chamber of the freeze dryer equipped with an electrostatic field assisted freezing module. Start the electrostatic field system (field strength 20 kV / cm, frequency 50 Hz) and simultaneously gradient-cool down for pre-freezing. The pre-freezing temperature is -30℃ and the pre-freezing time is 2 h to completely freeze the moisture in the material.

[0045] (4) Send the pre-frozen material tray from step (3) into the drying chamber, start the vacuum pump, and maintain the vacuum in the drying chamber at 30 Pa; start the graphene-coated infrared heating plate, control the heating temperature at 45℃, and the heating rate at 3℃ / min until the temperature of the honeysuckle fruit rises to 30℃ and remains stable; the sublimation drying stage lasts for 6 hours, the desorption drying stage lasts for 4 hours, and the total freeze-drying time is 10 hours.

[0046] (5) Take out the freeze-dried honeysuckle fruit from step (4), cool it to 25°C in a clean environment, sieve to remove the broken pieces, vacuum pack it and fill it with nitrogen (oxygen content ≤1%), and store it in an environment of 0°C.

[0047] Comparative Example 1: Preparation of freeze-dried honeysuckle fruit This comparative example provides a method for freeze-drying honeysuckle fruit. The preparation method is the same as in Example 1, except that pulsed electric field and electrostatic field treatments are not performed, and a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. The specific preparation steps are as follows: (1) Select fresh honeysuckle berries, remove the fruit stems and impurities, rinse them with clean water, drain the surface water, and freeze-dry the whole fruit without cutting them to obtain honeysuckle berry pre-treated material; place the honeysuckle berry pre-treated material in a low temperature environment of 4℃ for 20 min to pre-cool it. (2) The pre-cooled honeysuckle berries from step (1) are directly fed into the subsequent pre-freezing process; (3) Place the pretreated honeysuckle fruit material from step (2) into the freeze dryer material tray, spread it evenly with a thickness of 10 mm, send it into the pre-freezing chamber, control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 h, so that the water in the honeysuckle fruit is completely frozen into ice. (4) Send the pre-frozen material tray from step (3) into the drying chamber, start the vacuum pump, and maintain the vacuum in the drying chamber at 30 Pa; start the commercial aluminum alloy heating plate of the same size, control the heating temperature at 45℃, and the heating rate at 3℃ / min until the temperature of the honeysuckle fruit rises to 30℃ and remains stable; the sublimation drying stage lasts for 9.5 h, the desorption drying stage lasts for 5.5 h, and the total freeze-drying time is 15 h; (5) Take out the freeze-dried honeysuckle fruit from step (4), cool it to 20°C in a clean environment, sieve to remove the broken pieces, vacuum pack it and fill it with nitrogen (oxygen content not higher than 1%), and store it in an environment of 0°C.

[0048] Comparative Example 2: Preparation of freeze-dried honeysuckle fruit This comparative example provides a method for freeze-drying honeysuckle berries. The preparation method is the same as in Example 1, except that ultrasound is used instead of pulsed electric field and electrostatic field treatment, and a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. The specific preparation steps are as follows: (1) Select fresh honeysuckle berries, remove the fruit stems and impurities, rinse them with clean water, drain the surface water, and freeze-dry the whole fruit without cutting them to obtain honeysuckle berry pre-treated material; place the honeysuckle berry pre-treated material in a low temperature environment of 4℃ for 20 min to pre-cool it. (2) Place the pre-cooled honeysuckle berries from step (1) into an ultrasonic treatment device, add an appropriate amount of water (enough to cover the surface of the honeysuckle berries), set the ultrasonic parameters: power 200 W, frequency 40 kHz, and treat for 10 min at room temperature (20℃). After treatment, drain the surface moisture. (3) Place the pretreated honeysuckle fruit material after ultrasonic treatment in step (2) into the material tray of the freeze dryer, spread it with a thickness of 10mm, send it into the pre-freezing chamber, control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 hours, so that the water in the honeysuckle fruit is completely frozen into ice. (4) Start the vacuum pump to maintain the vacuum in the drying chamber at 30 Pa; start the commercial aluminum alloy heating plate, control the heating temperature at 45℃ and the heating rate at 3℃ / min until the temperature of the honeysuckle fruit rises to 30℃ and remains stable; the sublimation drying stage lasts for 8 h, the desorption drying stage lasts for 5.5 h, and the total freeze-drying time is 13.5 h. (5) Take out the freeze-dried honeysuckle fruit from step (4), cool it to 25°C in a clean environment, sieve to remove the broken pieces, vacuum pack it and fill it with nitrogen (oxygen content not higher than 1%), and store it in an environment of 0°C.

[0049] Comparative Example 3: Preparation of freeze-dried honeysuckle fruit This comparative example provides a method for freeze-drying honeysuckle fruit. The preparation method is the same as in Example 1, except that a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. The specific preparation steps are as follows: (1) Select fresh honeysuckle berries, remove the fruit stems and impurities, rinse them with clean water, drain the surface water, and freeze-dry the whole fruit without cutting them to obtain honeysuckle berry pre-treated material; place the honeysuckle berry pre-treated material in a low temperature environment of 4℃ for 20 minutes. (2) Spread the pre-cooled honeysuckle berries from step (1) between the plates of the pulse electric field treatment device. The plate spacing is 10 cm and the thickness of the honeysuckle berries pre-treatment layer is 10 mm. Set the pulse electric field parameters: pulse voltage is 25 kV / cm, pulse width is 30 μs, pulse frequency is 50 Hz, and the treatment is carried out at room temperature (20℃) for 5 min. (3) Place the pretreated honeysuckle fruit material treated by pulse electric field in step (2) into the material tray of the freeze dryer, spread it with a thickness of 10 mm, and send it into the pre-freezing chamber of the freeze dryer equipped with an electrostatic field assisted freezing module. Start the electrostatic field system (field strength 20 kV / cm, frequency 50 Hz), control the pre-freezing temperature to -30℃, the gradient cooling rate to 8℃ / h, and the pre-freezing time to 3 h, so that the water in the honeysuckle fruit is completely frozen into ice. (4) Start the vacuum pump to maintain the vacuum in the drying chamber at 30 Pa; start the commercial aluminum alloy heating plate, control the heating temperature at 45℃ and the heating rate at 3℃ / min until the temperature of the honeysuckle fruit rises to 30℃ and remains stable; the sublimation drying stage lasts for 7 h, the desorption drying stage lasts for 4.8 h, and the total freeze-drying time is 11.8 h. (5) Take out the freeze-dried honeysuckle fruit from step (4), cool it to 25°C in a clean environment, sieve to remove the broken pieces, vacuum pack it and fill it with nitrogen (oxygen content not higher than 1%), and store it in an environment of 0°C.

[0050] Comparative Example 4: Preparation of freeze-dried honeysuckle fruit This comparative example provides a method for freeze-drying honeysuckle fruit. The preparation method is the same as in Example 1, except that a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. Other steps remain unchanged. The specific preparation steps are as follows: (1) Select fresh honeysuckle berries, remove the fruit stems and impurities, rinse them with clean water, drain the surface water, and freeze-dry the whole fruit without cutting them to obtain honeysuckle berry pre-treated material; place the honeysuckle berry pre-treated material in a low temperature environment of 4℃ for 20 min to pre-cool it. (2) Without electric field, ultrasound or any other pretreatment, the pre-cooled honeysuckle berries (1) are directly sent to the subsequent pre-freezing process. (3) Place the pretreated honeysuckle fruit material from step (2) into the freeze dryer material tray, spread it evenly with a thickness of 10 mm, send it into the pre-freezing chamber, control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 h, so that the water in the honeysuckle fruit is completely frozen into ice. (4) Start the vacuum pump to maintain the vacuum in the drying chamber at 30 Pa; start the graphene-coated infrared heating plate (with the same parameters as the heating plate in Example 1), control the heating temperature at 45°C and the heating rate at 3°C / min until the temperature of the honeysuckle fruit rises to 30°C and remains stable; the sublimation drying stage lasts for 7 h, the desorption drying stage lasts for 4.5 h, and the total freeze-drying time is 11.5 h; (5) Take out the freeze-dried honeysuckle fruit from step (4), cool it to 25°C in a clean environment, sieve to remove the broken pieces, vacuum pack it and fill it with nitrogen (oxygen content not higher than 1%), and store it in an environment of 0°C.

[0051] Comparative Example 5: Preparation of freeze-dried honeysuckle fruit This comparative example provides a freeze-drying method for honeysuckle berries. The preparation method is the same as in Example 1, except that the pretreatment is performed using ultrasound instead of pulsed electric field and electrostatic field treatment. Other steps remain unchanged. The specific preparation steps are as follows: (1) Select fresh honeysuckle berries, remove the fruit stems and impurities, rinse them with clean water, drain the surface water, and freeze-dry the whole fruit without cutting them to obtain honeysuckle berry pre-treated material; place the honeysuckle berry pre-treated material in a low temperature environment of 4℃ for 20 min to pre-cool it. (2) Place the pre-cooled honeysuckle berries from step (1) into an ultrasonic treatment device, add an appropriate amount of water (enough to cover the surface of the honeysuckle berries), set the ultrasonic parameters: power 200 W, frequency 40 kHz, and treat for 10 min at room temperature (20℃). After treatment, drain the surface moisture. (3) Place the pretreated honeysuckle fruit material after ultrasonic treatment in step (2) into the material tray of the freeze dryer, spread it with a thickness of 10mm, send it into the pre-freezing chamber, control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 hours, so that the water in the honeysuckle fruit is completely frozen into ice. (4) Start the vacuum pump to maintain the vacuum in the drying chamber at 30 Pa; start the graphene-coated heating plate (with the same parameters as the heating plate in Example 1), control the heating temperature at 45°C and the heating rate at 3°C / min until the temperature of the honeysuckle fruit rises to 30°C and remains stable; the sublimation drying stage lasts for 6.8 h, the desorption drying stage lasts for 4.2 h, and the total freeze-drying time is 11 h; (5) Take out the freeze-dried honeysuckle fruit from (4), cool it to 20°C in a clean environment, sieve to remove the broken pieces, vacuum pack it and fill it with nitrogen (oxygen content not higher than 1%), and store it in an environment of 0°C.

[0052] Example 2 Preparation of freeze-dried mango cubes This embodiment provides a highly efficient composite drying method for mango freeze-drying based on graphene coating and infrared synergy, including the following steps: S1. Pre-treat the mango in a pulsed electric field to obtain the mango after pulsed electric field pretreatment; S2. Pre-freeze the pre-treated mangoes under an electrostatic field to obtain pre-frozen mangoes; S3. Place the pre-frozen mango on a graphene-coated heating plate and dry it under vacuum to obtain freeze-dried mango.

[0053] The specific steps are as follows: (1) Select fresh mangoes, peel and pit them, and cut them into 5 mm × 5 mm × 5 mm cubes to obtain mango pretreatment material; place the mango pretreatment material in a low temperature environment of 4℃ for 20 min to pre-cool. (2) Spread the pre-cooled mango pretreatment material from step (1) between the plates of the pulse electric field treatment device. The plate spacing is 8 mm and the thickness of the mango pretreatment material layer is 4 mm. Set the pulse electric field parameters: pulse voltage is 20 kV / cm, pulse width is 20 μs, pulse frequency is 50 Hz, and the treatment is carried out at room temperature (20℃) for 4 min. (3) Place the pre-treated mango material after step (2) into the material tray of the freeze dryer, spread it evenly with a thickness of 10 mm, and send it into the pre-freezing chamber of the freeze dryer equipped with an electrostatic field assisted freezing module. Start the electrostatic field system (field strength 20 kV / cm, frequency 50 Hz), pre-freezing temperature -30℃, pre-freezing time 2 h, so that the free water and bound water in the material are completely frozen step by step.

[0054] (4) Send the material tray that has been pre-frozen in step (3) into the drying chamber, start the vacuum pump, and maintain the vacuum degree in the drying chamber at 20 Pa; start the graphene-coated infrared heating plate, control the heating temperature at 50℃, and the heating rate at 4℃ / min until the temperature of the mango pieces rises to 32℃ and remains stable; the sublimation drying stage lasts for 5 hours, the desorption drying stage lasts for 3 hours, and the total freeze-drying time is 8 hours. (5) Take out the freeze-dried mango pieces from step (4), cool them to 25°C in a clean environment, sieve to remove fragments and impurities, vacuum pack them and fill them with nitrogen (oxygen content not higher than 1%), and store them in an environment at 0°C.

[0055] Comparative Example 6: Preparation of freeze-dried mango chunks This comparative example provides a freeze-drying method for mango chunks, which is similar to Example 2, except that pulsed electric field and electrostatic field treatments are not performed, and a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. The specific preparation steps are as follows: (1) Select fresh mangoes, peel and pit them, and cut them into 5 mm × 5 mm × 5 mm cubes to obtain mango pretreatment material; place the mango pretreatment material in a low temperature environment of 4℃ for 20 min to pre-cool. (2) Without pulsed electric field, ultrasound or any other pretreatment, the mango pre-treated material after pre-cooling in step (1) is directly sent to the subsequent pre-freezing process; (3) Place the mango pretreatment material from step (2) into the freeze dryer material tray, spread it evenly with a thickness of 10 mm, send it into the pre-freezing chamber, control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 h, so that the water in the mango is completely frozen into ice. (4) Send the pre-frozen material tray from step (2) into the drying chamber, start the vacuum pump, and maintain the vacuum in the drying chamber at 20 Pa; start the commercial aluminum alloy heating plate, control the heating temperature at 50℃, and the heating rate at 4℃ / min until the temperature of the mango pieces rises to 32℃ and remains stable; the sublimation drying stage lasts for 8.5 h, the desorption drying stage lasts for 4.8 h, and the total freeze-drying time is 13.3 h; (5) Take out the freeze-dried mango pieces from step (4), cool them to 23°C in a clean environment, sieve to remove fragments and impurities, vacuum pack them and fill them with nitrogen (oxygen content not higher than 1%), and store them in an environment at 0°C.

[0056] Comparative Example 7: Preparation of freeze-dried mango chunks This comparative example provides a method for freeze-drying mangoes. The preparation method is the same as in Example 2, except that ultrasound is used instead of pulsed electric field and electrostatic field treatment, and a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. The specific preparation steps are as follows: (1) Select fresh mangoes, peel and pit them, and cut them into 5 mm × 5 mm × 5 mm cubes to obtain mango pretreatment material; place the mango pretreatment material in a low temperature environment of 4℃ for 20 min to pre-cool. (2) Place the pre-cooled mango pre-treated material from step (1) into an ultrasonic treatment device, add an appropriate amount of water (enough to cover the surface of the mango pieces), set the ultrasonic parameters: power 200 W, frequency 40 kHz, and treat for 10 min at room temperature (20℃). After treatment, drain the surface moisture. (3) Place the mango pre-treated material after ultrasonic treatment in step (2) into the material tray of the freeze dryer, spread it with a thickness of 10mm, send it into the pre-freezing chamber, control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 hours, so that the water in the mango is completely frozen into ice. (4) Start the vacuum pump to maintain the vacuum in the drying chamber at 30 Pa; start the commercial aluminum alloy heating plate, control the heating temperature at 50℃ and the heating rate at 4℃ / min until the temperature of the mango pieces rises to 32℃ and remains stable; the sublimation drying stage lasts for 7 h, the desorption drying stage lasts for 4.8 h, and the total freeze-drying time is 11.8 h. (5) Take out the freeze-dried mango pieces from step (4), cool them to 25°C in a clean environment, sieve to remove fragments and impurities, vacuum pack them and fill them with nitrogen (oxygen content not higher than 1%), and store them in an environment at 0°C.

[0057] Comparative Example 8: Preparation of freeze-dried mango chunks This comparative example provides a method for freeze-drying mangoes. The preparation method is the same as in Example 2, except that a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. The specific preparation steps are as follows: (1) Select fresh mangoes, peel and pit them, and cut them into 5 mm × 5 mm × 5 mm cubes to obtain mango pretreatment material; place the mango pretreatment material in a low temperature environment of 4℃ for 20 min to pre-cool. (2) Spread the pre-cooled mango pretreatment material from step (1) between the plates of the pulse electric field treatment device. The plate spacing is 10 cm and the thickness of the mango pretreatment material layer is 10 mm. Set the pulse electric field parameters: pulse voltage is 20 kV / cm, pulse width is 20 μs, pulse frequency is 50 Hz, and treat at room temperature (20℃) for 4 min (consistent with the pulse electric field parameters in Example 2). (3) Place the mango pre-treated material after pulse electric field treatment in step (2) into the material tray of the freeze dryer, spread it with a thickness of 10 mm, and send it into the pre-freezing chamber of the freeze dryer equipped with electrostatic field assisted freezing module. Start the electrostatic field system (field strength 20 kV / cm, frequency 50 Hz), control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 h, so that the water in the mango is completely frozen into ice. (4) Start the vacuum pump to maintain the vacuum in the drying chamber at 20 Pa; start the commercial aluminum alloy heating plate, control the heating temperature at 50℃ and the heating rate at 4℃ / min until the temperature of the mango pieces rises to 32℃ and remains stable; the sublimation drying stage lasts for 6.2 h, the desorption drying stage lasts for 4 h, and the total freeze-drying time is 10.2 h. (5) Take out the freeze-dried mango pieces from step (4), cool them to 25°C in a clean environment, sieve to remove fragments and impurities, vacuum pack them and fill them with nitrogen (oxygen content not higher than 1%), and store them in an environment at 0°C.

[0058] Comparative Example 9: Preparation of freeze-dried mango chunks This comparative example provides a method for freeze-drying mangoes. The preparation method is the same as in Example 2, except that a commercial aluminum alloy heating plate is used instead of a graphene-coated infrared heating plate. Other steps remain unchanged. The specific preparation steps are as follows: (1) Select fresh mangoes, peel and pit them, and cut them into 5 mm × 5 mm × 5 mm cubes to obtain mango pretreatment material; place the mango pretreatment material in a low temperature environment of 3℃ for 12 min to pre-cool. (2) Without pulsed electric field, ultrasound or any other pretreatment, the mango pre-treated material after pre-cooling in step (1) is directly sent to the subsequent pre-freezing process; (3) Place the mango pretreatment material from step (2) into the freeze dryer material tray, spread it evenly with a thickness of 8 mm, send it into the pre-freezing chamber, control the pre-freezing temperature to -30℃, and the pre-freezing time to 2 h, so that the water in the mango is completely frozen into ice. (4) Start the vacuum pump to maintain the vacuum in the drying chamber at 20 Pa; start the graphene-coated heating plate (with the same parameters as the heating plate in Example 2), control the heating temperature at 50°C and the heating rate at 4°C / min until the temperature of the mango pieces rises to 32°C and remains stable; the sublimation drying stage lasts for 5.8 h, the desorption drying stage lasts for 3.5 h, and the total freeze-drying time is 9.3 h; (5) Take out the freeze-dried mango pieces from step (4), cool them to 25°C in a clean environment, sieve to remove fragments and impurities, vacuum pack them and fill them with nitrogen (oxygen content not higher than 1%), and store them in an environment at 0°C.

[0059] Comparative Example 10: Preparation of freeze-dried mango chunks This comparative example provides a method for freeze-drying mangoes. The preparation method is the same as in Example 2, except that the pretreatment is performed using ultrasound instead of pulsed electric field and electrostatic field treatment. Other steps remain unchanged. The specific preparation steps are as follows: (1) Select fresh mangoes, peel and pit them, and cut them into 5 mm × 5 mm × 5 mm cubes to obtain mango pretreatment material; place the mango pretreatment material in a low temperature environment of 4℃ for 20 min to pre-cool. (2) Place the pre-cooled mango pre-treated material from step (1) into an ultrasonic treatment device, add an appropriate amount of water (enough to cover the surface of the mango pieces), set the ultrasonic parameters: power 200 W, frequency 40 kHz, and treat for 10 min at room temperature (20℃). After treatment, drain the surface moisture. (3) Place the mango pre-treated material after ultrasonic treatment in step (2) into the material tray of the freeze dryer, spread it evenly with a thickness of 10 mm, and send it into the pre-freezing chamber. The pre-freezing temperature is -30℃ and the pre-freezing time is 2 h, so that the free water and bound water in the material are completely frozen step by step.

[0060] (4) Send the pre-frozen material tray from step (3) into the drying chamber, start the vacuum pump, and maintain the vacuum in the drying chamber at 20 Pa; start the graphene-coated heating plate (with parameters consistent with the heating plate in Example 2), control the heating temperature at 50°C, and the heating rate at 4°C / min until the temperature of the mango pieces rises to 32°C and remains stable; the sublimation drying stage lasts for 5.5 h, the desorption drying stage lasts for 3.3 h, and the total freeze-drying time is 8.8 h; (5) Take out the freeze-dried mango pieces from step (4), cool them to 25°C in a clean environment, sieve to remove fragments and impurities, vacuum pack them and fill them with nitrogen (oxygen content not higher than 1%), and store them in an environment at 0°C.

[0061] Test Example 1 1. Testing Method Sensory evaluation was performed on the freeze-dried fruits prepared in Examples 1-2 and Comparative Examples 1-10 to characterize their color, flavor, and aroma. Specific evaluations were conducted according to the sensory evaluation standards in Table 1. Anthocyanin retention rate, water content, rehydration properties, and energy consumption were measured. The anthocyanin retention rate was determined according to T / ZNZ 320-2025 Determination of Total Anthocyanin Content in Plant-Derived Edible Agricultural Products (Spectrophotometric Method). Water content was determined according to GB 5009.3-2016 National Food Safety Standard for Determination of Moisture in Food. The rehydration property was determined by placing 2 g of dried berry sample in 40 g of distilled water at 50°C for 50 min. After rehydration, the surface moisture was removed using filter paper, and the sample was weighed. The rehydration ratio was obtained by dividing the rehydrated mass by the unrehydrated mass. Energy consumption was measured using an electricity meter and expressed in kJ / kg.

[0062] Table 1 Sensory Evaluation Criteria for Freeze-Dried Fruits

[0063] 2. Test Results (1) Combining sensory evaluation results and Figures 2-4It can be seen that the freeze-dried honeysuckle berries prepared in Example 1 have a deep blue and bright color, retain the inherent flavor and aroma of fresh honeysuckle berries, an anthocyanin retention rate of 92.86%, a water content of 2.5%, and good rehydration properties. Soaking in warm water for 3 minutes is sufficient to restore them to a form close to that of fresh honeysuckle berries. The freeze-drying cycle is shortened by 33% compared to the traditional method, and energy consumption is reduced by 38.63%. The freeze-dried honeysuckle berries prepared in Comparative Example 1 have a dull color, an anthocyanin retention rate of 75.15%, a water content of 4.2%, poor rehydration properties (still unable to fully rehydrate after soaking in warm water for 5 minutes), high energy consumption, and a freeze-drying cycle that is 50% longer than that of Example 1. The freeze-dried honeysuckle berries prepared in Comparative Example 2 have a slightly dull color, an anthocyanin retention rate of 79.61%, a water content of 3.8%, and moderate rehydration properties (rehydrates after soaking in warm water for 4 minutes). Energy consumption is reduced by 4.66%, and the freeze-drying cycle is 35% longer than that of Example 1. Comparative Example 3: The freeze-dried honeysuckle berries prepared had a acceptable color, an anthocyanin retention rate of 83.37%, a water content of 3.2%, and good rehydration properties (rehydration after soaking in warm water for 3.5 min). Energy consumption was reduced by 10.98%, and the freeze-drying cycle was extended by 18% compared to Example 1. Comparative Example 4: The freeze-dried honeysuckle berries prepared had a deep blue color, an anthocyanin retention rate of 86.91%, a water content of 3.0%, and good rehydration properties (rehydration after soaking in warm water for 3.2 min). Energy consumption was reduced by 31.71%, and the freeze-drying cycle was extended by 15% compared to Example 1. Comparative Example 5: The freeze-dried honeysuckle berries prepared had a deep blue color, an anthocyanin retention rate of 87.82%, a water content of 2.8%, and good rehydration properties (rehydration after soaking in warm water for 3.1 min). Energy consumption was reduced by 34.15%, and the freeze-drying cycle was extended by 10% compared to Example 1.

[0064] (2) Combining sensory evaluation results and Figures 5-7As can be seen, the freeze-dried mango cubes prepared in Example 2 are golden in color, crisp in texture, retain the sweet flavor of mango, have a β-carotene retention rate of 88.92%, a water content of 2.8%, and no clumping. The freeze-drying cycle is shortened by 39.26% and energy consumption is reduced by 37.24% compared to the traditional method. The freeze-dried mango cubes prepared in Comparative Example 6 are darker in color, have a β-carotene retention rate of 73.71%, a water content of 4.5%, poor rehydration (cannot be fully rehydrated even after soaking in warm water for 5.5 min), no significant reduction in energy consumption, and a freeze-drying cycle that is 66.25% longer than that of Example 2. The freeze-dried mango cubes prepared in Comparative Example 7 are slightly yellow in color, have a β-carotene retention rate of 77.58%, a water content of 4.0%, moderate rehydration (rehydrates after soaking in warm water for 4.5 min), a 6.25% reduction in energy consumption, and a 47.5% longer freeze-drying cycle than that of Example 2. Comparative Example 8: The freeze-dried mango pieces prepared in this example are a light golden-yellow color, with a β-carotene retention rate of 81.29%, a water content of 3.3%, and good rehydration properties (rehydration after soaking in warm water for 3.8 min). Energy consumption was reduced by 14.58%, and the freeze-drying cycle was extended by 4.0% compared to Example 2. Comparative Example 9: The freeze-dried mango pieces prepared in this example are golden-yellow color, with a β-carotene retention rate of 82.63%, a water content of 3.1%, and good rehydration properties (rehydration after soaking in warm water for 3.5 min). Energy consumption was reduced by 29.41%, and the freeze-drying cycle was extended by 16.25% compared to Example 2. Comparative Example 10: The freeze-dried mango pieces prepared in this example are golden-yellow color, with a β-carotene retention rate of 84.23%, a water content of 2.9%, no clumping, and good rehydration properties (rehydration after soaking in warm water for 3.2 min). Energy consumption was reduced by 32.35%, and the freeze-drying cycle was extended by 10% compared to Example 2.

[0065] Conclusion: Based on the above test results, it can be seen that the present invention significantly shortens the freeze-drying time of fruit compared with the prior art, reducing the freeze-drying time to 8-12 hours, shortening the freeze-drying cycle by 25-45%, reducing energy consumption by 25-40%, preserving the nutritional components of the fruit to the maximum extent, and ensuring that the moisture content of the finished product does not exceed 3%. It is suitable for efficient, high-quality and energy-saving drying processing of fresh fruit.

Claims

1. A highly efficient composite drying method for fruit freeze-drying based on graphene coating and infrared synergy, characterized in that, Includes the following steps: S1. The fruit is pretreated in a pulsed electric field with a pulse voltage of less than 35 kV / cm to obtain the fruit after pulsed electric field pretreatment; S2. The pretreated fruit is pre-frozen in an electrostatic field with an electric field strength of less than 30 kV / cm to obtain pre-frozen fruit; S3. Place the pre-frozen fruit on a graphene-coated heating plate and dry it under vacuum conditions to obtain freeze-dried fruit; the heating rate of the graphene-coated heating plate is 2~5℃ / min, the heating temperature is 30~50℃, and the drying time is 8~12 h.

2. The efficient composite drying method for fruit freeze-drying according to claim 1, characterized in that, The pulsed electric field in step S1 has a pulse voltage of 15~35 kV / cm, a pulse width of 10~50 μs, a pulse frequency of 40~60 Hz, and a processing time of 2~8 min; preferably, the pulsed electric field has a pulse voltage of 25 kV / cm, a pulse width of 20~30 μs, a pulse frequency of 50 Hz, and a processing time of 4 min.

3. The efficient composite drying method for fruit freeze-drying according to claim 1, characterized in that, The electrostatic field described in step S2 has an electric field strength of 10~30 kV / cm and a frequency of 40~60 Hz; preferably, the electrostatic field has an electric field strength of 20 kV / cm and a frequency of 50 Hz.

4. The efficient composite drying method for freeze-drying fruit according to claim 1, characterized in that, The pre-freezing temperature in step S2 is -40 to -20°C, and the pre-freezing time is 1 to 3 hours; preferably, the pre-freezing temperature is -30°C, and the pre-freezing time is 2 hours.

5. The efficient composite drying method for fruit freeze-drying according to claim 1, characterized in that, The fruit mentioned in step S1 is a pome, drupe, berry, or tropical fruit; preferably, the drupe is selected from one or more of mango, peach, apricot, or cherry; the berry is selected from one or more of honeysuckle berry, blueberry, raspberry, or strawberry.

6. The efficient composite drying method for fruit freeze-drying according to claim 5, characterized in that, The fruit in step S1 is in the form of slices, strips, or granules; preferably, the fruit is in the form of slices or strips with a thickness of 3-8 mm; preferably, the fruit is in the form of granules with a particle size not exceeding 1 cm.

7. The efficient composite drying method for freeze-drying fruit according to claim 1, characterized in that, The fruit described in step S1 needs to be pre-cooled before pulse voltage treatment. The pre-cooling is performed in an environment with a temperature of 0~4℃ for 10~20 minutes; preferably, the pre-cooling is performed in an environment with a temperature of 4℃ for 20 minutes.

8. The efficient composite drying method for freeze-drying fruit according to claim 1, characterized in that, The graphene-coated heating plate in step S3 includes a substrate, a graphene coating, and electrodes. The substrate is a glass fiber substrate, and the graphene coating is disposed on the surface of the substrate with a coating thickness of 100~500 μm. The electrodes are fixed to both ends of the substrate and electrically connected to the graphene coating.

9. The efficient composite drying method for fruit freeze-drying according to claim 1, characterized in that, The graphene-coated heating plate described in step S3 has an electrothermal efficiency of not less than 99% and a thermal conductivity of not less than 5000 W / (m·K).

10. The efficient composite drying method for freeze-drying fruit according to claim 1, characterized in that, The pulsed electric field in step S1 includes opposing plates, the distance between the plates is 5-10 cm, and the thickness of the fruit in the pulsed electric field does not exceed 1 / 2 of the distance between the plates; preferably, the distance between the plates is 10 cm, and the thickness of the fruit in the pulsed electric field does not exceed 5 cm of the distance between the plates.

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