A method for the frozen processing of whole mango

Abstract

The application provides a kind of mango whole fruit's frozen processing method, through raw material preparation and insertion stick, liquid phase medium pulse electric field pretreatment, pulsed vacuum impregnation, gradient precooling treatment and variable temperature gradient ultrasonic synergistic freezing shaping are handled to mango whole fruit, can promote the penetration depth and uniformity of antifreeze component, effectively refine ice crystal size, wherein pulse electric field pretreatment is combined with pulsed vacuum impregnation, and antifreeze protective component such as soybean oligopeptide, trehalose and ice structure protein is penetrated to the deep part of fruit core, the gradient precooling temperature is dynamically adjusted according to the sugar content of mango, the ice crystal morphology is regulated in stages by variable temperature ultrasonic freezing, effectively reduces thawing juice loss, maintains the original texture and fruit shape of pulp, improves the frozen quality of mango whole fruit, maintains good freshness, achieves ideal frozen preservation effect.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, and in particular to a method for freezing whole mangoes. Background Technology

[0002] Mangoes are a high-value specialty fruit in my country's tropical and subtropical regions, rich in nutrients and with a unique flavor, leading to a continuous expansion of the planting and processing industry. As frozen food consumption trends towards higher quality and more natural products, frozen whole mangoes, preserving the integrity of the fruit flesh, are gaining increasing market acceptance and show promising prospects for industrial application due to their ability to maintain the texture and flavor of fresh fruit to the greatest extent. Currently, mango freezing processing mainly uses a diced quick-freezing process. Related technologies primarily improve the freezing quality of diced fruit flesh through methods such as osmotic dehydration pretreatment, color protection treatment, and staged cooling freezing, providing basic technological references for mango freezing processing. However, research on whole-fruit morphology mainly focuses on peeling and shaping processes, lacking a systematic design for quality control during the freezing process.

[0003] However, existing whole-fruit freezing processes for mangoes still have significant technical limitations, lacking a comprehensive quality control system tailored to the physical characteristics of whole fruits. In the maceration process, whole mangoes are large, dense, and have long mass transfer pathways. Conventional static maceration or ordinary vacuum maceration only allows antifreeze components to act on the surface of the pulp, making it difficult to evenly diffuse to the core. This results in significant differences in antifreeze effects between the inside and outside of the whole fruit, and the problem of ice crystal damage to the internal tissue cannot be effectively improved. While some strong physical field-enhanced maceration processes can increase the penetration rate, they easily cause damage to the pulp cell structure and degradation of active ingredients, making it difficult to balance penetration depth and quality preservation. In the freezing and shaping stage, existing processes mostly adopt a freezing mode with fixed temperature parameters, without considering the impact of differences in sugar content and physical properties of mangoes from different origins and at different ripeness levels on the freezing point. This results in insufficient process adaptability and significant fluctuations in product quality between batches. Furthermore, conventional freezing processes often only reduce ice crystal formation through rapid cooling in a crude manner, failing to match the dynamic characteristics of ice crystal nucleation, growth, and solidification stages for precise control. The effects of ice crystal refinement and structural protection are limited, ultimately leading to the formation of large ice crystals that pierce cell structures, causing quality problems such as juice loss, fruit collapse, and soft texture after thawing. This makes it difficult to meet the production requirements of high-quality whole-fruit frozen mango products. Summary of the Invention

[0004] In view of this, the present invention proposes a method for freezing whole mangoes to solve the above problems.

[0005] The technical solution of this invention is implemented as follows: A method for freezing whole mangoes, comprising the following steps:

[0006] S1. Raw material preparation and insertion of sticks: Take the whole peeled mango flesh and insert a food-grade popsicle stick along the long axis.

[0007] S2, Liquid medium pulsed electric field pretreatment: The mango pulp after the insertion rod is completely immersed in the conductive medium, and a pulsed electric field is applied in a rotating manner for pretreatment;

[0008] S3, Pulsed Vacuum Impregnation: Mango pulp pretreated with a pulsed electric field is immersed in an impregnation solution containing soybean oligopeptides, trehalose, and ice structural proteins for pulsed vacuum impregnation.

[0009] S4. Gradient precooling treatment: The soaked mango pulp is subjected to gradient precooling treatment at a temperature related to sugar content, wherein the temperature of the gradient precooling treatment is T = -(0.03 × sugar content value + 0.3);

[0010] S5. Variable temperature gradient ultrasound-assisted cryopreservation: The pre-cooled mango pulp is immersed in variable temperature gradient ultrasound-assisted cryopreservation.

[0011] Furthermore, the mango is a fresh mango with a ripeness of eight to nine tenths and a sugar content of 18 to 22° Brix. After being steamed at 95 to 100°C for 10 to 15 seconds, the skin is mechanically rubbed off to obtain intact peeled flesh, while retaining the natural shape of the stem end and the calyx end. The food-grade popsicle stick is inserted to a depth of 2 / 3 to 3 / 4 of the length of the whole fruit.

[0012] Furthermore, the conductive medium in S2 is a 3-5 wt% trehalose solution, the field strength of the pulsed electric field is 1.0-2.5 kV / cm, the pulse width is 80-150 μs, the number of pulses is 8-15, the processing time is 15-40 s, and the temperature of the processing solution is 10-15℃; the rotation speed is 8-10 rpm.

[0013] Furthermore, based on the total mass of the impregnation solution, the impregnation solution in S3 contains 2.0–5.0 wt% soybean oligopeptides, 8–12 wt% trehalose, and 0.005–0.02 wt% ice structural protein, wherein the molecular weight of the soybean oligopeptides is <1000 Da.

[0014] Furthermore, the pulsed vacuum impregnation in S3 includes: during the exhaust phase, the vacuum level is evacuated to -0.065 to -0.075 MPa and maintained for 6 to 8 minutes; during the pulse perfusion phase, the vacuum level fluctuates back and forth at 1.5 cycles per minute within the range of -0.02 to -0.04 MPa and is maintained for 12 to 18 minutes, while simultaneously superimposed with 30 to 40 W, 28 kHz low-frequency ultrasound; during the target balancing phase, the vacuum is released to atmospheric pressure and maintained for 6 to 8 minutes.

[0015] Furthermore, in step S4, the temperature T = -(0.03 × sugar content + 0.3) of the gradient precooling treatment is obtained as follows: the actual freezing point temperature of whole mangoes within the sugar content range of 18 to 22°Brix is ​​measured, and a linear regression is performed with sugar content as the independent variable and freezing point temperature as the dependent variable, with a correlation coefficient R² ≥ 0.95; the gradient precooling treatment ensures that whole mangoes of different sugar content batches reach their respective near-freezing point supercooled state before freezing.

[0016] Furthermore, the cooling rate of the gradient precooling process in S4 is 0.5 to 1.5 °C / min, and the temperature is maintained for 15 to 30 minutes after reaching the target temperature.

[0017] Furthermore, the immersion-type variable temperature gradient ultrasound-assisted cryopreservation in S5 includes: a uniform nucleation stage at -8 to -5°C with ultrasound at 200 to 280 W and 40 kHz until the core temperature reaches -5°C; a controlled growth stage at -23 to -20°C with ultrasound at 60 to 100 W until the core temperature reaches -15°C; and a cryogenic solidification stage at -38 to -35°C with ultrasound turned off until the core temperature is ≤ -18°C.

[0018] Furthermore, the refrigerant in S5 is a 50-55 wt% propylene glycol aqueous solution, the fruit rotates at a uniform speed of 3-5 rpm, and the ultrasonic transducers are arranged on the upper and lower sides of the freezing tank.

[0019] Furthermore, in step S5, dynamic control is implemented using the core temperature as a feedback signal: during the uniform nucleation stage, the temperature of the refrigerant is reduced to -8 to -5°C at a rate of 0.5 to 1.0°C / min, and ultrasound is triggered when the core temperature drops to -3°C; during the controllable growth stage, the cooling rate of the refrigerant is dynamically adjusted according to the core cooling rate: when the core cooling rate is <0.3°C / min, the refrigerant cools at 1.5°C / min; when the core cooling rate is 0.3 to 0.6°C / min, the refrigerant cools at 1.0°C / min; when the core cooling rate is ≥0.6°C / min, the refrigerant cools at 0.5°C / min; during the cryogenic solidification stage, the refrigerant cools to -38 to -35°C at a rate of 2.0°C / min.

[0020] Among them, the uniform nucleation stage uses the core temperature dropping to -3℃ as the ultrasonic trigger threshold and the core temperature reaching -5℃ as the end of the stage. Both are real-time monitoring nodes for core temperature, corresponding to the beginning and end of the ice crystal nucleation window period, respectively.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The mango whole-fruit freezing processing method of this invention forms reversible micropores on the cell membrane of the pulp through pretreatment with a liquid-phase medium pulsed electric field, opening mass transfer channels for the migration of antifreeze components to the deep core of the fruit. Combined with the pressure reciprocating fluctuation of pulsed vacuum impregnation and the low-frequency ultrasonic cavitation effect, the impregnation solution containing soybean oligopeptides, trehalose, and ice structural proteins is uniformly penetrated into the deep layers of the whole fruit, so that the whole fruit obtains a relatively consistent antifreeze protection effect inside and outside. On this basis, by performing linear regression fitting on the actual freezing point temperature of whole mangoes in the sugar content range of 18-22°Brix, a gradient precooling temperature formula related to mango sugar content is obtained: T=-(0.03×sugar content value+0.3) (correlation coefficient R²≥0.95). The precooling target temperature is dynamically adjusted according to the actual sugar content of the raw material, so that whole mangoes of different sugar contents reach their respective near-freezing point supercooled state before freezing, providing uniform thermodynamic initial conditions for subsequent ultrasonic-induced uniform nucleation. Then, by using variable temperature gradient ultrasound-assisted freezing and shaping, a large number of small crystal nuclei are induced to grow synchronously with high-power ultrasound during the nucleation stage, and the growth of ice crystal tips is inhibited with low-power ultrasound during the growth stage. During the cryogenic solidification stage, the ultrasound is turned off to quickly fix the morphology of the fine crystals. This achieves staged control over the entire process of ice crystal nucleation, growth, and solidification, effectively reducing the size of ice crystals and protecting the integrity of cell structure. It alleviates the problems of juice loss, soft texture, and fruit collapse caused by the difficulty of deep penetration of whole fruit and the rough control of ice crystals in the existing process. It provides a feasible technical solution for the industrial production of high-quality whole-fruit frozen mango products. Detailed Implementation

[0023] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0024] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0025] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0026] Example 1

[0027] A method for freezing whole mangoes, comprising the following steps:

[0028] S1. Raw material preparation and stick insertion: Select fresh Tainong No. 1 mangoes from the same origin, at 80% ripeness, with a sugar content of 18°Brix and a single fruit weight of 150-170g. After steaming the skin at 95℃ for 10 seconds, use a brush-type peeling machine to mechanically peel the skin, obtaining whole peeled flesh that retains the natural shape of the stem end and calyx end, without making horizontal cuts; insert a food-grade birch popsicle stick vertically from the center point of the stem end along the long axis of the mango, with the insertion depth being 2 / 3 of the length of the whole fruit.

[0029] S2. Liquid-phase medium pulsed electric field pretreatment: The mango pulp after the insertion of the rod is completely immersed in a batch-type parallel plate pulsed electric field treatment chamber containing a 3wt% trehalose solution. The solution temperature is controlled at 10℃ by an external circulating refrigeration unit. The fruit is rotated uniformly in the treatment solution at a speed of 8rpm. At the same time, a pulsed electric field is applied with a field strength of 1.0kV / cm, a pulse width of 80μs, 8 pulses, and a total treatment time of 15s.

[0030] S3. Pulsed Vacuum Impregnation: The mango pulp pretreated with a pulsed electric field is rapidly transferred to a vacuum impregnation tank and completely immersed in the impregnation solution (the fruit remains stationary during the impregnation process). The impregnation solution formula is: 2.0 wt% soybean oligopeptides (molecular weight < 1000 Da), 8 wt% trehalose, 0.005 wt% ice structural protein, and the remainder is purified water. The pulsed vacuum procedure is executed as follows: During the exhaust phase, the vacuum is evacuated to -0.065 MPa and maintained for 6 minutes; during the pulse infusion phase, the vacuum level fluctuates between -0.02 MPa and -0.04 MPa at 1.5 cycles per minute and is maintained for 12 minutes. Simultaneously, the ultrasonic transducer at the bottom of the tank is activated to apply 30W, 28kHz low-frequency ultrasonic mass transfer assistance; during the targeted equilibrium phase, the vacuum is released to atmospheric pressure and maintained for 6 minutes; after completion, the mango is removed and the surface free liquid is quickly dried with 4℃ low-temperature sterile air.

[0031] S4. Gradient precooling treatment: Place the soaked mangoes in a programmable cold air precooling device. Substitute the measured sugar content into the formula T=-(0.03×sugar content value+0.3) to calculate the target precooling temperature as -0.84℃. The actual controlled temperature is -0.8℃. After cooling to the target temperature at a rate of 0.5℃ / min, maintain it for 15 minutes until the temperature difference between the inside and outside of the whole fruit is ≤0.2℃, achieving a uniform supercooling state.

[0032] In this embodiment, the formula T = -(0.03 × sugar content + 0.3) was obtained by measuring the freezing point of whole mangoes with a sugar content of 18–22°Brix and fitting the results with linear regression, with a correlation coefficient R² ≥ 0.95. Taking the Tainong No. 1 mango with a sugar content of 18°Brix as an example, the target pre-cooling temperature was calculated to be -0.84℃, and the actual controlled temperature was -0.8℃. This ensured that the fruit pulp reached a near-freezing-point supercooled state before freezing, providing uniform thermodynamic initial conditions for subsequent ultrasonic-induced uniform nucleation.

[0033] S5. Variable Temperature Gradient Ultrasonic Co-operative Freezing and Shaping: Pre-cooled mangoes are rapidly immersed in an immersion ultrasonic freezing tank. The refrigerant is a 55wt% propylene glycol aqueous solution (freezing point approximately -38℃). The fruit is connected to a rotating support via ice rods and rotates at a uniform speed of 3 rpm. Ultrasonic transducers are symmetrically arranged on the upper and lower sides of the freezing tank. The core temperature is monitored in real time using a sheathed thermocouple inserted into the core as a feedback signal, and the following dynamic control is implemented:

[0034] Uniform nucleation stage: The temperature of the coolant is reduced from the initial temperature to -8℃ at a rate of 0.5℃ / min. When the core temperature drops to -3℃, ultrasound is triggered with a power of 200W and a frequency of 40kHz. This stage ends when the core temperature reaches -5℃.

[0035] Controlled growth stage: The refrigerant temperature drops rapidly to -23℃, and the cooling rate is dynamically adjusted according to the core cooling rate: when the core cooling rate is <0.3℃ / min, the refrigerant cools at 1.5℃ / min; when the core cooling rate is 0.3~0.6℃ / min, the refrigerant cools at 1.0℃ / min; when the core cooling rate is ≥0.6℃ / min, the refrigerant cools at 0.5℃ / min. The ultrasonic power is adjusted to 60W and the frequency remains unchanged until the core temperature reaches -15℃.

[0036] Cryogenic curing stage: The refrigerant is cooled to -38℃ at a rate of 2.0℃ / min, the ultrasonic treatment is turned off, and freezing continues until the core temperature is ≤-18℃; after removal, it is immediately packaged and transferred to -18℃ cold chain storage.

[0037] Example 2

[0038] A method for freezing whole mangoes, comprising the following steps:

[0039] S1. Raw material preparation and stick insertion: Select fresh Golden Mangoes from the same origin, 90% ripe, with a sugar content of 22°Brix and a single fruit weight of 190-210g. After steaming at 100℃ for 15s, peel them mechanically using a brush-type peeling machine to obtain whole peeled flesh that retains the natural shape of the stem end and calyx end, without making horizontal cuts; insert a food-grade birch popsicle stick vertically from the center point of the stem end along the long axis of the mango, with the insertion depth being 3 / 4 of the length of the whole fruit.

[0040] S2. Liquid-phase medium pulsed electric field pretreatment: The mango pulp after the insertion of the rod is completely immersed in a batch-type parallel plate pulsed electric field treatment chamber containing a 5wt% trehalose solution. The solution temperature is controlled at 15℃ by an external circulating refrigeration unit. The fruit is rotated uniformly in the treatment solution at a speed of 10rpm. At the same time, a pulsed electric field is applied with a field strength of 2.5kV / cm, a pulse width of 150μs, 15 pulses, and a total treatment time of 40s.

[0041] S3. Pulsed Vacuum Impregnation: The mango pulp pretreated with a pulsed electric field is rapidly transferred to a vacuum impregnation tank and completely immersed in the impregnation solution (the fruit remains stationary during the impregnation process). The impregnation solution formula is: 5.0 wt% soybean oligopeptides (molecular weight < 1000 Da), 12 wt% trehalose, 0.02 wt% ice structural protein, and the remainder is purified water. The pulsed vacuum procedure is executed as follows: During the exhaust phase, the vacuum is evacuated to -0.075 MPa and maintained for 8 minutes; during the pulse infusion phase, the vacuum level fluctuates between -0.02 MPa and -0.04 MPa at 1.5 cycles per minute and is maintained for 18 minutes. Simultaneously, the ultrasonic transducer at the bottom of the tank is activated to apply 40W, 28kHz low-frequency ultrasonic mass transfer assistance; during the targeted equilibrium phase, the vacuum is released to atmospheric pressure and maintained for 8 minutes; after completion, the mango is removed and the surface free liquid is quickly dried with 4℃ low-temperature sterile air.

[0042] S4. Gradient precooling treatment: Place the soaked mangoes in a programmable cold air precooling device. Substitute the measured sugar content into the formula T=-(0.03×sugar content value+0.3) to calculate the target precooling temperature as -0.96℃. The actual controlled temperature is -1.0℃. After cooling to the target temperature at a rate of 1.5℃ / min, maintain it for 30 minutes until the temperature difference between the inside and outside of the whole fruit is ≤0.2℃, achieving a uniform supercooling state.

[0043] In this embodiment, the formula T = -(0.03 × sugar content + 0.3) was obtained by measuring the freezing point of whole mangoes with a sugar content in the range of 18–22°Brix and fitting the results with linear regression, with a correlation coefficient R² ≥ 0.95. Taking the Jin Huang mango with a sugar content of 22°Brix in this embodiment as an example, the target pre-cooling temperature was calculated to be -0.96℃, and the actual controlled temperature was -1.0℃, so that the pulp reached a near-freezing point supercooled state before freezing, providing uniform thermodynamic initial conditions for subsequent ultrasonic-induced uniform nucleation.

[0044] S5. Variable Temperature Gradient Ultrasonic Co-operative Freezing and Shaping: Pre-cooled mangoes are rapidly immersed in an immersion ultrasonic freezing tank. The refrigerant is a 50wt% propylene glycol aqueous solution (freezing point approximately -33℃). The fruit is connected to a rotating support via ice rods and rotates at a uniform speed of 5 rpm. Ultrasonic transducers are symmetrically arranged on the upper and lower sides of the freezing tank. The core temperature is monitored in real time using a sheathed thermocouple inserted into the core as a feedback signal, and the following dynamic control is implemented:

[0045] Uniform nucleation stage: The temperature of the coolant is reduced from the initial temperature to -5℃ at a rate of 1.0℃ / min. When the core temperature drops to -3℃, ultrasound is triggered with a power of 280W and a frequency of 40kHz. This stage ends when the core temperature reaches -5℃.

[0046] Controlled growth stage: The refrigerant temperature drops rapidly to -20℃, and the cooling rate is dynamically adjusted according to the fruit core cooling rate: when the fruit core cooling rate is <0.3℃ / min, the refrigerant cools at 1.5℃ / min; when the fruit core cooling rate is 0.3~0.6℃ / min, the refrigerant cools at 1.0℃ / min; when the fruit core cooling rate is ≥0.6℃ / min, the refrigerant cools at 0.5℃ / min. The ultrasonic power is adjusted to 100W and the frequency remains unchanged until the fruit core temperature reaches -15℃.

[0047] Cryogenic curing stage: The refrigerant is cooled to -35°C at a rate of 2.0°C / min, the ultrasonic treatment is turned off, and freezing continues until the core temperature is ≤-18°C; after removal, it is immediately packaged and transferred to -18°C cold chain storage.

[0048] Example 3

[0049] A method for freezing whole mangoes, comprising the following steps:

[0050] S1. Raw material preparation and stick insertion: Select fresh Guifei mangoes from the same origin, 85% ripe, with a sugar content of 20°Brix and a single fruit weight of 170-190g. After scalding the skin with 98℃ steam for 12s, use a brush-type peeling machine to mechanically peel the skin, obtaining whole peeled flesh that retains the natural shape of the stem end and calyx end, without making horizontal cuts; insert a food-grade birch popsicle stick vertically from the center point of the stem end along the long axis of the mango, with the insertion depth being 7 / 10 of the whole fruit length.

[0051] S2. Liquid-phase medium pulsed electric field pretreatment: The mango pulp after the insertion of the rod is completely immersed in a batch-type parallel plate pulsed electric field treatment chamber containing a 4wt% trehalose solution. The solution temperature is controlled at 12℃ by an external circulating refrigeration unit. The fruit is rotated uniformly in the treatment solution at a speed of 9rpm. At the same time, a pulsed electric field is applied with a field strength of 1.8kV / cm, a pulse width of 120μs, 12 pulses, and a total treatment time of 25s.

[0052] S3. Pulsed Vacuum Impregnation: The mango pulp pretreated with a pulsed electric field is quickly transferred to a vacuum impregnation tank and completely immersed in the impregnation solution (the fruit remains stationary during the impregnation process). The impregnation solution formula is: 3.5wt% soybean oligopeptides (molecular weight <1000Da), 10wt% trehalose, 0.012wt% ice structural protein, and the remainder is purified water. The pulsed vacuum procedure is executed as follows: During the exhaust phase, the vacuum is evacuated to -0.07MPa and maintained for 7 minutes; during the pulse infusion phase, the vacuum level fluctuates between -0.02MPa and -0.04MPa at 1.5 cycles per minute and is maintained for 15 minutes. Simultaneously, the ultrasonic transducer at the bottom of the tank is activated to apply 35W, 28kHz low-frequency ultrasonic mass transfer assistance; during the targeted equilibrium phase, the vacuum is released to atmospheric pressure and maintained for 7 minutes; after completion, the mango is removed and the surface free liquid is quickly dried with 4℃ low-temperature sterile air.

[0053] S4. Gradient precooling treatment: Place the soaked mangoes in a programmable cold air precooling device. Substitute the measured sugar content into the formula T=-(0.03×sugar content value+0.3) to calculate the target precooling temperature as -0.9℃. Cool the mangoes to the target temperature at a rate of 1.0℃ / min and maintain it for 20 minutes until the temperature difference between the inside and outside of the whole fruit is ≤0.2℃, thus achieving a uniform supercooling state.

[0054] In this embodiment, the formula T = -(0.03 × sugar content + 0.3) was obtained by measuring the freezing point of whole mangoes with a sugar content in the range of 18–22°Brix and fitting the results with linear regression, with a correlation coefficient R² ≥ 0.95. Taking the Guifei mango with a sugar content of 20°Brix in this embodiment as an example, the target pre-cooling temperature was calculated to be -0.9℃ by substituting the formula, so that the pulp reaches a near-freezing point supercooled state before freezing, providing uniform thermodynamic initial conditions for subsequent ultrasonic-induced uniform nucleation.

[0055] S5. Variable Temperature Gradient Ultrasonic Co-operative Freezing and Shaping: Pre-cooled mangoes are rapidly immersed in an immersion ultrasonic freezing tank. The refrigerant is a 52wt% propylene glycol aqueous solution (freezing point approximately -35 to -36℃). The fruit is connected to a rotating support via ice rods and rotates at a uniform speed of 4 rpm. Ultrasonic transducers are symmetrically arranged on the upper and lower sides of the freezing tank. The core temperature is monitored in real time using a sheathed thermocouple inserted into the core as a feedback signal, and the following dynamic control is implemented:

[0056] Uniform nucleation stage: The temperature of the coolant is reduced from the initial temperature to -6℃ at a rate of 0.8℃ / min. When the core temperature drops to -3℃, ultrasound is triggered with a power of 240W and a frequency of 40kHz. This stage ends when the core temperature reaches -5℃.

[0057] Controlled growth stage: The refrigerant temperature drops rapidly to -22℃, and the cooling rate is dynamically adjusted according to the fruit core cooling rate: when the fruit core cooling rate is <0.3℃ / min, the refrigerant cools at 1.5℃ / min; when the fruit core cooling rate is 0.3~0.6℃ / min, the refrigerant cools at 1.0℃ / min; when the fruit core cooling rate is ≥0.6℃ / min, the refrigerant cools at 0.5℃ / min. The ultrasonic power is adjusted to 80W and the frequency remains unchanged until the fruit core temperature reaches -15℃.

[0058] Cryogenic curing stage: The refrigerant is cooled to -36℃ at a rate of 2.0℃ / min, the ultrasonic treatment is turned off, and freezing continues until the core temperature is ≤-18℃; after removal, it is immediately packaged and transferred to -18℃ cold chain storage.

[0059] Example 4

[0060] Based on Example 3, this embodiment adjusts the total processing time of the S2 pulse electric field to 15s and the number of pulses to 8, and the S5 variable temperature gradient ultrasound-assisted cryo-settling to be the same as in Example 3.

[0061] Example 5

[0062] This embodiment is based on embodiment 3, except that the ultrasonic power in the controllable growth stage of S5 is adjusted to 60W, and the other parameters and steps are the same as in embodiment 3.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 3 is that the S2 liquid-phase medium pulsed electric field pretreatment step is omitted, and the mango is directly subjected to S3 pulsed vacuum impregnation after peeling and inserting the rod. The remaining steps and parameters are the same as in Example 3.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 3 is that S3 uses ordinary constant pressure vacuum impregnation, the vacuum degree is kept constant at -0.07MPa, the total impregnation time is 29 minutes, no pulse pressure fluctuation is performed, and low frequency ultrasound is not superimposed. The remaining steps and parameters are the same as in Example 3.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 3 is that the impregnation solution in S3 is replaced with a single-component impregnation solution: trehalose 10wt%, the remainder is purified water, and no soybean oligopeptides and ice structural proteins are added. The remaining steps and parameters are the same as in Example 3.

[0069] Comparative Example 4

[0070] The difference between this comparative example and Example 3 is that S4 uses a fixed temperature precooling, with the precooling temperature uniformly set to -5℃, and is not dynamically adjusted through the sugar content correlation formula. The remaining steps and parameters are the same as in Example 3.

[0071] Comparative Example 5

[0072] The difference between this comparative example and Example 3 is that S5 uses constant power ultrasonic freezing throughout the process, the refrigerant temperature is kept constant at -25℃, the ultrasonic power is kept constant at 150W, the core temperature is not used as a feedback signal, dynamic control is not implemented, and the temperature and ultrasonic power are not adjusted in stages. The freezing is carried out until the core temperature is ≤-18℃. The remaining steps and parameters are the same as in Example 3.

[0073] Comparative Example 6

[0074] This comparative example is a conventional immersion quick-freezing control group. The whole mangoes after peeling and inserting the sticks were directly placed in a -36°C, 52wt% propylene glycol refrigerant for freezing. There was no pulsed electric field pretreatment, no vacuum impregnation, no gradient precooling, and no ultrasonic assistance. The mangoes were frozen until the core temperature was ≤-18°C. The other conditions were the same as in Example 3.

[0075] The frozen whole mangoes obtained in Examples 1-5 and Comparative Examples 1-6 were stored at -18℃ for 90 days, then thawed naturally in a 4℃ refrigerator for 12 hours, followed by quality index testing. All testing methods referenced general standards in the quick-frozen fruit and vegetable industry.

[0076] Fruit core penetration uniformity: Fruit pulp samples were taken from 2 mm below the surface and from the core. The soluble solids content was measured using a handheld refractometer. The penetration uniformity was expressed as the ratio of the core solids content to the surface solids content. The closer the ratio is to 1, the more uniform the penetration.

[0077] Thawing juice loss rate: Refer to the method for determining the juice loss rate of quick-frozen fruits and vegetables in SB / T 10379-2012. Weigh the total mass of the sample before thawing and the mass of the sample after draining the surface free liquid. Juice loss rate = (mass before thawing - mass after draining) / mass before thawing × 100%.

[0078] Fruit pulp firmness retention rate: A texture analyzer was used for puncture testing. The probe was a P / 5 cylindrical probe, the testing speed was 1.0 mm / s, and the puncture distance was 10 mm. Firmness retention rate = average firmness of thawed fruit pulp / average firmness of fresh fruit pulp × 100%.

[0079] Average equivalent diameter of ice crystals: Fruit pulp tissue from the middle part between the core and the surface of the fruit was taken, fixed with glutaraldehyde at low temperature, freeze-dried, and the ice crystal pores in the cross section were observed with a scanning electron microscope. The equivalent diameter of no less than 200 pores was counted by image analysis software, and the average value was taken.

[0080] Fruit shape integrity rate: 30 thawed samples were randomly selected, and the percentage of samples with no fruit collapse and no skin damage was counted.

[0081] The measurement results are shown in the table below:

[0082] Example 1 0.87 7.9 76.2 32.4 94 Example 2 0.93 6.2 78.5 27.8 93 Example 3 0.92 6.4 82.1 27.8 95 Example 4 0.85 8.5 74.0 35.0 91 Example 5 0.91 7.6 77.4 33.2 93 Comparative Example 1 0.65 12.3 62.4 47.2 81 Comparative Example 2 0.72 10.8 67.3 42.5 85 Comparative Example 3 0.78 11.8 64.5 44.6 83 Comparative Example 4 0.91 9.5 72.6 38.3 88 Comparative Example 5 0.92 11.2 63.8 51.7 82 Comparative Example 6 — 18.7 51.2 76.4 68

[0083] The results above show that the whole mango freezing processing method provided by the present invention has a positive effect on improving the quality of whole fruit freezing. Under the conditions of the example, after storage at -18℃ for 90 days, the juice loss rate of whole mango can be controlled within the range of 6.2% to 7.9%, the pulp firmness retention rate can reach 76.2% to 82.1%, the average equivalent diameter of ice crystals can be controlled within 27.8 to 32.4 μm, and the fruit shape integrity rate can reach 93% to 95%. To a certain extent, it alleviates the problems of juice loss, soft texture, and fruit shape collapse after freezing whole mango.

[0084] Compared with Comparative Example 1, the Example Group introduced a liquid-phase medium pulsed electric field pretreatment before impregnation. By applying a pulsed electric field of 1.0 to 2.5 kV / cm to treat the whole mango fruit, reversible nanoscale micropores may be formed on the cell membrane of the pulp. This opens a mass transfer channel for the migration of antifreeze components in the impregnation solution to the deeper core of the fruit. Combined with the pulsed vacuum impregnation process, antifreeze protective components such as soybean oligopeptides, trehalose, and ice structural proteins are delivered to the deep layers of the whole fruit, constructing a more consistent antifreeze protection system inside and outside the pulp cells. This reduces the degree of ice crystal damage at the cellular level. Among them, soybean oligopeptides have a small molecular weight and may be more likely to penetrate into the intercellular space along the electroporation channel to exert an antifreeze protection effect. Trehalose helps maintain the integrity of the cell membrane structure, and ice structural proteins may further refine the ice crystal size by inhibiting ice crystal growth. The synergistic effect of the three helps to improve the frozen quality of the whole mango fruit.

[0085] Compared with Comparative Example 2, the pulsed vacuum impregnation superimposed with low-frequency ultrasound-assisted mass transfer method was used. The sponge effect generated by the periodic reciprocating fluctuation of vacuum pressure and the cavitation effect of low-frequency ultrasound synergistically enhanced the convective mass transfer of the impregnation liquid in the pores of mango tissue. Under similar impregnation time, the penetration depth and uniformity were better than those of ordinary constant pressure vacuum impregnation. At the same time, the mild action conditions of low-frequency ultrasound caused relatively little damage to the fruit pulp cell structure, which is conducive to maintaining the integrity of the fruit pulp tissue while improving the penetration efficiency. This lays the foundation for the antifreeze components to fully exert their protective effect during the subsequent freezing process.

[0086] Compared with Comparative Example 3, Example 3 used a single-component impregnation solution (10wt% trehalose only), without the addition of soybean oligopeptides and ice structural proteins. Example 3 used a ternary compound impregnation solution of soybean oligopeptides, trehalose, and ice structural proteins. The steric hindrance effect of soybean oligopeptides inhibits the aggregation and growth of ice crystal particles, trehalose maintains the integrity of cell membrane structure, and ice structural proteins precisely fill ice crystal lattice defects. These three components form a layered mechanism combining basic protection and targeted crystal control. Comparative results showed that Example 3 had better core penetration uniformity and pulp firmness retention rate than Comparative Example 3, and lower juice loss rate and ice crystal size. This indicates that the addition of soybean oligopeptides and ice structural proteins, along with trehalose, created a synergistic effect. The combination of these three components provides better antifreeze protection in terms of deep penetration and ice crystal refinement of the whole fruit than trehalose alone, which is beneficial for further improving the frozen quality of whole mangoes.

[0087] Compared with Comparative Example 4, the example group established a gradient precooling temperature formula related to mango sugar content. The target precooling temperature was dynamically adjusted according to the actual sugar content of each batch of mangoes, so that different raw materials reached a relatively consistent near-freezing supercooled thermodynamic state before freezing. This provided relatively uniform initial conditions for subsequent ultrasonic-induced uniform nucleation, which is conducive to reducing quality fluctuations caused by differences in raw material properties between batches and improving the industrial adaptability of the process and product stability.

[0088] Compared with Comparative Example 5, in the cryogenic shaping stage, different temperature and ultrasonic power parameters were matched according to the ice crystal kinetic characteristics of different freezing stages. In the nucleation stage, the use of higher power ultrasound may help induce the synchronous generation of a large number of small crystal nuclei. In the growth stage, the use of lower power ultrasound may help inhibit the growth of ice crystal tips and avoid secondary nucleation. In the cryogenic solidification stage, turning off ultrasound may help to quickly fix the already formed fine crystal morphology. Through staged regulation, the nucleation, growth and solidification process of ice crystals can be controlled to a certain extent, which is conducive to reducing the size of ice crystals and alleviating the damage of freezing to the cell structure of mango pulp.

[0089] Compared with Comparative Example 6, the Example Group was a conventional quick-freezing control group, which was directly quick-frozen with refrigerant without pulsed electric field pretreatment, vacuum impregnation, gradient precooling and ultrasonic-assisted freezing. In the example group, reversible micropores were formed on the cell membrane of the fruit pulp through pretreatment with a pulsed electric field in a liquid medium. This opened mass transfer channels for the migration of antifreeze components to the deep core of the fruit. Combined with the pressure reciprocating fluctuations of pulsed vacuum impregnation and the low-frequency ultrasonic cavitation effect, the antifreeze protective components were delivered to the deep layers of the whole fruit. A gradient precooling temperature formula related to the sugar content of the mango was established so that different raw materials reached a relatively consistent near-freezing thermodynamic state before freezing. Then, through variable temperature gradient ultrasound-assisted freezing and shaping, a large number of small crystal nuclei were induced to be generated synchronously by high-power ultrasound during the nucleation stage, the growth of ice crystal tips was inhibited by low-power ultrasound during the growth stage, and the formed fine crystal morphology was quickly fixed by turning off ultrasound during the cryogenic solidification stage. Through the functional complementarity and progressive enhancement of each link in the whole process, the overall effect that is difficult to achieve by a single link or simple combination can be achieved in terms of deep penetration of the whole fruit, precise control of ice crystals at multiple stages, and protection of the cell structure system. This helps to reduce the loss of thawed juice, maintain the original texture and shape of the fruit pulp, and improve the frozen quality of the whole mango.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for freezing whole mangoes, characterized in that: Includes the following steps: S1. Raw material preparation and insertion of sticks: Take the whole peeled mango flesh and insert a food-grade popsicle stick along the long axis. S2, Liquid medium pulsed electric field pretreatment: The mango pulp after the insertion rod is completely immersed in the conductive medium, and a pulsed electric field is applied in a rotating manner for pretreatment; S3, Pulsed Vacuum Impregnation: Mango pulp pretreated with a pulsed electric field is immersed in an impregnation solution containing soybean oligopeptides, trehalose, and ice structural proteins for pulsed vacuum impregnation. S4. Gradient precooling treatment: The soaked mango pulp is subjected to gradient precooling treatment at a temperature related to sugar content, wherein the temperature of the gradient precooling treatment is T = -(0.03 × sugar content value + 0.3); S5. Variable temperature gradient ultrasound-assisted cryopreservation: The pre-cooled mango pulp is immersed in variable temperature gradient ultrasound-assisted cryopreservation.

2. The method for freezing whole mangoes as described in claim 1, characterized in that, The mangoes are fresh mangoes that are 80-90% ripe and have a sugar content of 18-22°Brix. They are scalded with steam at 95-100℃ for 10-15 seconds and then mechanically rubbed to remove the skin, resulting in whole peeled fruit flesh, while retaining the natural shape of the stem end and calyx end. The food-grade popsicle sticks are inserted to a depth of 2 / 3 to 3 / 4 of the length of the whole fruit.

3. The method for freezing whole mangoes as described in claim 1, characterized in that, The conductive medium in S2 is a 3-5 wt% trehalose solution, the field strength of the pulsed electric field is 1.0-2.5 kV / cm, the pulse width is 80-150 μs, the number of pulses is 8-15, the processing time is 15-40 s, and the temperature of the processing solution is 10-15℃; the rotation speed is 8-10 rpm.

4. The method for freezing whole mangoes as described in claim 1, characterized in that, Based on the total mass of the impregnation solution, the impregnation solution in S3 contains 2.0-5.0 wt% soybean oligopeptides, 8-12 wt% trehalose, and 0.005-0.02 wt% ice structural protein, wherein the molecular weight of the soybean oligopeptides is <1000 Da.

5. A method for freezing whole mangoes as described in claim 4, characterized in that, The pulsed vacuum impregnation in S3 includes: during the exhaust phase, the vacuum level is evacuated to -0.065 to -0.075 MPa and maintained for 6 to 8 minutes; during the pulse perfusion phase, the vacuum level fluctuates at 1.5 cycles per minute within the range of -0.02 to -0.04 MPa and is maintained for 12 to 18 minutes, while simultaneously superimposed with 30 to 40 W, 28 kHz low-frequency ultrasound; during the target balancing phase, the vacuum is released to normal pressure and maintained for 6 to 8 minutes.

6. The method for freezing whole mangoes as described in claim 1, characterized in that, In step S4, the temperature T = -(0.03 × sugar content + 0.3) of the gradient precooling treatment is obtained as follows: the actual freezing point temperature of whole mangoes in the sugar content range of 18 to 22°Brix is ​​measured, and linear regression fitting is performed with sugar content as the independent variable and freezing point temperature as the dependent variable, with a correlation coefficient R² ≥ 0.95; the gradient precooling treatment enables whole mangoes of different sugar content batches to reach their respective near-freezing point supercooled state before freezing.

7. The method for freezing whole mangoes as described in claim 1, characterized in that, The cooling rate of the gradient precooling process in S4 is 0.5 to 1.5 °C / min, and the temperature is maintained for 15 to 30 minutes after the target temperature is reached.

8. A method for freezing whole mangoes as described in claim 1, characterized in that, Immersion freezing is performed using a refrigerant. The immersion variable temperature gradient ultrasonic-assisted freezing and shaping in S5 includes: a uniform nucleation stage at -8 to -5℃ with ultrasonic waves of 200 to 280 W and 40 kHz, until the core temperature reaches -5℃; a controlled growth stage at -23 to -20℃ with ultrasonic waves of 60 to 100 W, until the core temperature reaches -15℃; and a cryogenic solidification stage at -38 to -35℃ with ultrasonic waves turned off until the core temperature is ≤ -18℃.

9. A method for freezing whole mangoes as described in claim 8, characterized in that, The refrigerant in S5 is a 50-55 wt% propylene glycol aqueous solution. The fruit rotates at a uniform speed of 3-5 rpm, and ultrasonic transducers are arranged on the upper and lower sides of the freezing tank.

10. A method for freezing whole mangoes as described in claim 9, characterized in that, In step S5, dynamic control is implemented using the core temperature as a feedback signal: during the uniform nucleation stage, the temperature of the refrigerant is reduced to -8 to -5℃ at a rate of 0.5 to 1.0℃ / min, and ultrasound is triggered when the core temperature drops to -3℃; during the controllable growth stage, the cooling rate of the refrigerant is dynamically adjusted according to the core cooling rate: when the core cooling rate is <0.3℃ / min, the refrigerant cools at 1.5℃ / min; when the core cooling rate is 0.3 to 0.6℃ / min, the refrigerant cools at 1.0℃ / min; when the core cooling rate is ≥0.6℃ / min, the refrigerant cools at 0.5℃ / min; during the cryogenic solidification stage, the refrigerant cools to -38 to -35℃ at a rate of 2.0℃ / min.