Method for carrying out vacuum cooling on high-temperature flour product under assistance of magnetic field and application of method

Abstract

The invention discloses a method for magnetic field assisted vacuum cooling of a high-temperature flour product and application thereof, and the method comprises the following steps: the flour product is placed in a magnetic field assisted vacuum cooling environment for cooling treatment, the magnetic field is a static magnetic field, the magnetic field intensity is set to be 0.1-5T, the vacuum degree is set to be 0.1-2kPa, and in the cooling treatment process, the magnetic field intensity is set to be 0.1-5T, and the vacuum degree is set to be 0.1-2kPa; and the center temperature of the flour product is reduced from 50-100 DEG C to 0-30 DEG C. According to the magnetic field assisted vacuum cooling method, the problems of water loss and mass loss in the vacuum cooling process of the high-temperature flour products are solved, the food quality is improved, and the method is easy to operate, low in cost and remarkable in benefit and shows wide application prospects in the field of precooling and preservation of the high-temperature baked or cooked flour products.

Description

Technical Field

[0001] This invention belongs to the field of pre-cooling and preservation technology for high-temperature steamed and baked flour products, specifically relating to a method for magnetic field-assisted vacuum cooling of high-temperature flour products and its application. Background Technology

[0002] Vacuum cooling technology is a widely used rapid cooling technology in the food industry. It creates a low-pressure vacuum environment, causing rapid evaporation of moisture from the surface and interior of food, thus achieving rapid cooling. Compared to traditional cooling methods such as natural cooling, air cooling, and water cooling, vacuum cooling offers rapid cooling, uniform and precisely controllable temperature distribution, reduces microbial growth, ensures food quality, and extends shelf life. However, its core mechanism—rapid evaporation of moisture under low pressure—also directly leads to severe moisture loss and quality degradation during the cooling process, negatively impacting the texture, taste, and nutritional value of the food.

[0003] To address the aforementioned issues, existing technologies often employ "hydration" strategies, such as immersion vacuum cooling, bubbling vacuum cooling, ultrasonic-assisted immersion vacuum cooling, vacuum cooling followed by immersion vacuum cooling, and cooling medium-assisted vacuum cooling (see patent documents CN109393301B, CN118242810A, CN106879713B, CN106942341B). However, these methods involve direct contact processing, requiring spraying or soaking the food. While these methods can alleviate moisture loss to some extent, they are not suitable for flour-based products. Therefore, a non-contact processing method is urgently needed to solve these problems.

[0004] Magnetic field technology, as a green, non-contact, physical, and non-thermal processing technology, has shown potential in the food industry. However, its current application is mainly focused on the freezing process of food. For example, Pan Zhili et al. studied the effect of magnetic field-assisted freezing on the quality of frozen cooked noodles. The magnetic field inhibited the growth of ice crystals inside the frozen cooked noodles and reduced the recrystallization of ice by limiting the migration of bound water, thereby reducing the degree of damage to the noodles and improving the quality of frozen cooked noodles (see: Pan Zhili, Wu Yangyang, Shen Jiajin, et al. Effect of magnetic field-assisted freezing on the quality of frozen cooked noodles [J]. Transactions of the Chinese Society of Agricultural Engineering, 2022(014):038.).

[0005] However, there is a fundamental difference between freezing and vacuum cooling of food: freezing usually occurs in an environment with normal pressure and below -18°C. Under this environment, the water in the food undergoes a phase transition from liquid water to solid ice. The magnetic field mainly acts on the solid ice in this process, and its core mechanism is to control the nucleation and growth of ice crystals. Vacuum cooling, on the other hand, occurs in an environment with negative pressure and above 0°C. The water in the food always exists in liquid form and evaporates rapidly. According to the general understanding in the field, a magnetic field can inhibit the condensation of solid ice during freezing processes that last for more than 24 hours. However, the existing magnetic field strength is difficult to affect the water loss or distribution during the rapid water loss process under the negative pressure of vacuum cooling. Furthermore, during the processing of flour into flour products, the physicochemical properties of its internal nutritional components are altered, significantly changing their interaction with water (strongly bound water, immobile water, and free water). For example, when flour is kneaded, fermented, steamed, or baked into steamed buns or bread, or whipped and baked into cakes, starch granules rapidly gelatinize to form a gel structure, while proteins undergo denaturation and conformational changes, leading to significant alterations in the binding sites and distribution of water molecules. Currently, there is a lack of systematic research and related technical reports on the influence of magnetic fields on the form and distribution of internal liquid water and its interaction with denatured starch and proteins during the vacuum cooling process of high-temperature flour products.

[0006] In conclusion, developing a method to effectively address the problem of rapid moisture loss and quality degradation in high-temperature flour products during vacuum cooling is of great significance for improving food quality. Summary of the Invention

[0007] To address the problems of the prior art, this invention discloses a method for magnetic field-assisted vacuum cooling of high-temperature flour products and its application. This invention innovatively proposes combining magnetic field and vacuum cooling to process high-temperature flour products. Research has found that this method can effectively reduce the inherent moisture loss and quality loss during vacuum cooling, thereby improving food quality.

[0008] In a first aspect, the present invention provides a method for magnetic field-assisted vacuum cooling of dough products, the method comprising the following steps: placing the dough products in a magnetic field-assisted vacuum cooling environment for cooling treatment.

[0009] Furthermore, the magnetic field is a static magnetic field with a magnetic field strength of 0.1-5T, specifically such as 0.1, 0.5, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5T, preferably 0.5-1.5T, and more preferably 1T.

[0010] Furthermore, the magnetic field originates from a permanent magnet. In this invention, a permanent magnet is placed inside the vacuum chamber of a vacuum cooling device (specifically, around a container holding food) to form a static magnetic field (constant magnetic field). After the vacuum pump is turned on to evacuate the vacuum, a magnetic field-assisted vacuum cooling environment is created.

[0011] Furthermore, the number of permanent magnets is two. In this invention, the distance between the two permanent magnets is 10 cm.

[0012] Furthermore, the permanent magnet has dimensions of 200×50×15mm.

[0013] Furthermore, during the cooling process, the vacuum level is set to 0.1-2 kPa, specifically such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0 kPa, preferably 0.6-0.8 kPa.

[0014] Preferably, the method includes the following steps: placing the dough product in a magnetic field-assisted vacuum cooling environment for cooling treatment, wherein the magnetic field is a static magnetic field with a magnetic field strength of 0.1-5T and a vacuum degree of 0.1-2kPa.

[0015] Furthermore, during the cooling process, the center temperature of the dough product is reduced to a set temperature.

[0016] Furthermore, the core temperature of the dough product is 50-100℃, specifically such as 50, 55, 60, 65, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100℃, preferably 75-97℃.

[0017] Further, the set temperature is 0-30℃, specifically such as 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30℃, preferably 4-25℃, more preferably 4℃, 10℃ or 25℃.

[0018] Furthermore, the time for the center temperature of the dough product to drop to the set temperature is 1-15 minutes, specifically 1, 2, 3, 3.5, 3.6, 3.8, 4, 4.5, 4.6, 5, 6, 6.2, 6.5, 6.7, 7, 8, 8.5, 8.9, 9, 9.4, 9.5, 10, 10.2, 10.5, 11, 12, 13, 14, 15 minutes, preferably 3-10.5 minutes, more preferably 3.6-10.2 minutes.

[0019] Furthermore, the noodle product is a noodle product that has been heat-processed to reach a cooked state, and the heat processing is selected from one or more of steaming, boiling, baking, frying, deep-frying and baking.

[0020] Furthermore, the dough product is selected from one or more of the following: toast, cake, steamed bun, twisted roll, steamed noodles, cornbread, barbecued pork bun, meat bun, red bean bun, custard bun, sesame seed cake, rice cake, steamed sponge cake, bread, fried dough sticks, fried cake, and twisted dough sticks. In some embodiments of the present invention, the dough product is toast, cake, or steamed bun.

[0021] Furthermore, the shape and volume of the dough product can be adjusted according to actual needs.

[0022] In some embodiments of the present invention, the method includes the following steps: placing a dough product with a center temperature of 75-97°C in a magnetic field-assisted vacuum cooling environment for cooling treatment, wherein the magnetic field is a static magnetic field, the magnetic field strength is set to 0.5-1.5T, the vacuum degree is 0.6-0.8kPa, until the center temperature of the dough product reaches 4-25°C.

[0023] A second aspect of the invention provides the application of the method described in the first aspect of the invention in reducing the quality loss of dough products during the cooling process.

[0024] A third aspect of the invention provides the application of the method described in the first aspect of the invention in increasing the moisture content of flour products during the cooling process.

[0025] Furthermore, the flour product is a short-term storage flour product, and the short-term storage time is 0-12h, specifically 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12h.

[0026] A fourth aspect of the invention provides the application of the method described in the first aspect of the invention in increasing the bound water content of flour products during the cooling process.

[0027] Furthermore, the bound water is strongly bound water and / or water that is not easily flowable, preferably strongly bound water.

[0028] Furthermore, the flour product is a short-term storage flour product, and the short-term storage time is 0-12h, specifically 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12h.

[0029] A fifth aspect of the invention provides the application of the method described in the first aspect of the invention in suppressing the conversion of bound water to free water in dough products during the cooling process.

[0030] Furthermore, the bound water is strongly bound water and / or water that is not easily flowable, preferably strongly bound water.

[0031] Furthermore, the flour product is toast or steamed bun.

[0032] The present invention has the following beneficial effects: (1) This invention is the first to apply magnetic field technology to the unique scenario of vacuum. Specifically, by introducing a strong magnetic field into the vacuum cooling process, which involves a rapid decrease in air pressure, this method not only maintains the inherent rapid cooling characteristics of the vacuum cooling process but also unexpectedly and significantly suppresses the moisture loss and quality loss of the flour products. In contrast, a weak magnetic field is less able to resist the rapid moisture loss and quality loss caused by the low-pressure environment of a vacuum.

[0033] (2) Compared with vacuum cooling, magnetic field-assisted vacuum cooling can reduce the mass loss rate of high-temperature flour products by more than 9%, and increase the proportion of bound water (especially strongly bound water) in high-temperature flour products. The increase rate of strongly bound water content can reach more than 6%, and up to about 20%. This shows that the method of the present invention better maintains the moisture content of flour products. In addition, the magnetic field-assisted vacuum cooling method used in the present invention is beneficial to the moisture retention of flour products during short-term storage (such as 0-12h).

[0034] (3) The magnetic field-assisted vacuum cooling method used in this invention has a faster cooling rate, which is significantly higher than that of natural cooling and forced air cooling. In addition, the cooling time required by the method of this invention is short, there is no need to cut the dough products into small pieces in advance, the operation is simple, and it is particularly suitable for batch cooling of food.

[0035] (4) The magnetic field-assisted vacuum cooling method used in this invention does not require contact to replenish moisture, which can reduce microbial contamination and extend the shelf life of food.

[0036] (5) The magnetic field-assisted vacuum cooling method for high-temperature flour products of the present invention is simple to operate, low in cost, and has significant benefits. It shows broad application prospects in the field of pre-cooling and preservation of high-temperature baked or steamed flour products. Attached Figure Description

[0037] Figure 1The figure shows the effect of different cooling methods on the cooling rate of toast. Different letters in the figure indicate significant differences between groups of different cooling methods. P <0.05) Figure 2 The figure shows the effects of vacuum cooling and magnetic field-assisted vacuum cooling on the cooling characteristics of toast. (A) Cooling rate and mass loss; (B) Moisture content. Different letters in the figure indicate significant differences between groups of different cooling methods. P <0.05).

[0038] Figure 3 The figure shows the effects of vacuum cooling and magnetic field-assisted vacuum cooling on the moisture distribution of toast during storage. (A) Final cooling temperature: 4℃; (B) Final cooling temperature: 10℃. Different letters in the figure indicate significant differences between groups of different cooling methods. P <0.05).

[0039] Figure 4 The figure shows the effects of vacuum cooling and magnetic field-assisted vacuum cooling on the moisture distribution of cakes during storage. (A) Final cooling temperature: 4℃; (B) Final cooling temperature: 10℃; (C) Final cooling temperature: 25℃. Different letters in the figure indicate significant differences between groups using different cooling methods. P <0.05).

[0040] Figure 5 The figure shows the effects of vacuum cooling and magnetic field-assisted vacuum cooling on the moisture distribution of steamed buns during storage. Different letters in the figure indicate significant differences between groups for different cooling methods. P <0.05). Detailed Implementation

[0041] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0042] The term "flour products" refers to flour products that have been cooked through heat processing (such as steaming, boiling, baking, frying, grilling, etc.). These flour products include, but are not limited to, toast, cakes, steamed buns, twisted rolls, steamed noodles, cornbread, barbecued pork buns, meat buns, red bean buns, custard buns, sesame seed cakes, rice cakes, steamed sponge cakes, bread, fried dough sticks, fried cakes, and twisted dough sticks.

[0043] All publications, patents, and published patent specifications cited in this article are incorporated herein in their entirety through citation.

[0044] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1: The effect of different cooling methods on the cooling rate of toast 1. Different cooling methods for toast Preparation of toast: Mix oat flour, wheat gluten, white sugar, salt, butter, yeast and water to form a dough. Place the dough in a mold and let it ferment for 2 hours until it is nine-tenths full. Place the mold in the oven and bake at 170°C top heat and 180°C bottom heat for 35 minutes. After baking, the center temperature of the toast should be 91°C.

[0046] (1) Natural cooling: Take the baked toast (center temperature of 91℃) out of the oven and let it cool naturally at room temperature (25±3℃) until the center temperature of the toast reaches 25℃.

[0047] (2) Blow-air cooling: Take out the baked toast (center temperature of 91℃) along with the mold immediately and place it in a constant temperature blow-air drying oven with a temperature set at 25℃ and a wind speed of 1m / s for blow-air cooling until the center temperature of the toast reaches 25℃.

[0048] (3) Vacuum cooling: Take out the baked toast (center temperature of 91°C) along with the mold immediately and place it in a vacuum cooling device for vacuum cooling. Set the final pressure to 600 Pa until the center temperature of the toast reaches 25°C.

[0049] (4) Magnetic field-assisted vacuum cooling: The baked toast (center temperature of 91℃) along with the mold is immediately taken out and placed in a magnetic field-assisted vacuum cooling device (two strip permanent magnets are placed parallel to each other on both sides of the container holding the food in the vacuum chamber. The specifications of the strip permanent magnets are 200×50×15mm and the distance between the magnets is fixed at 10cm) for cooling treatment. The magnetic field strength is 1T and the vacuum degree is 0.6kPa until the center temperature of the toast reaches 25℃.

[0050] 2. The effect of different cooling methods on the cooling rate of toast (1) Measurement method The cooling rate was determined by real-time temperature monitoring. The thermocouple probe was inserted into the center of the toast, and the temperature value was recorded every 30 seconds. The cooling time was recorded to calculate the cooling rate.

[0051] (2) Measurement results The cooling rate results of toast treated with four different cooling methods are as follows: Figure 1As shown, vacuum cooling reduced the core temperature from 91℃ to 25℃ in 3.7 minutes, saving approximately 20 times the time compared to natural cooling (80.0 minutes) or forced-air cooling (71.5 minutes). Magnetic field-assisted vacuum cooling, with a cooling time of 3.8 minutes, achieved the same rapid cooling as vacuum cooling. Even at a final cooling temperature of 10℃, vacuum cooling and magnetic field-assisted vacuum cooling took 6.6 minutes and 6.2 minutes respectively, maintaining their advantage of short cooling times. At a final cooling temperature of 4℃, vacuum cooling and magnetic field-assisted vacuum cooling took 9.2 minutes and 8.9 minutes respectively. Although the cooling time increased with lower final temperatures, the advantages of significantly reduced cooling time were still evident. Similarly, the cooling rates of the vacuum cooling group and the magnetic field-assisted vacuum cooling group were 16.30℃ / min and 15.67℃ / min, respectively, which were significantly higher than those of the other groups (P<0.05). Moreover, the cooling rate of the magnetic field-assisted vacuum cooling group was 14.51 times and 12.54 times higher than that of the natural cooling group (1.08℃ / min) and the blower cooling group (1.25℃ / min), respectively. Compared with the traditional cooling method, the cooling efficiency was significantly improved, which shows that vacuum cooling and magnetic field-assisted vacuum cooling have the same fast and efficient cooling efficiency.

[0052] Example 2: The effect of magnetic field-assisted vacuum cooling on the cooling characteristics of toast 1. Toast preparation The toast was processed according to the vacuum cooling and magnetic field-assisted vacuum cooling steps of Example 1, and the final cooling temperature of the toast was set to 25°C, 10°C and 4°C respectively. The remaining steps were the same as in Example 1.

[0053] 2. Measurement Method The cooling rate was determined by real-time temperature monitoring. A thermocouple probe was inserted into the center of the toast, and the temperature value was recorded every 30 seconds. The cooling time was recorded to calculate the cooling rate. The mass loss during the cooling process was calculated by measuring the mass of the toast sample before and after cooling.

[0054] Toasts cooled in vacuum cooling groups (25℃, 10℃, and 4℃) and magnetic field-assisted vacuum cooling groups (4℃) were stored at room temperature (25±3℃) for 12 hours. The moisture content was determined using the constant weight method according to the national standard GB 5009.3—2016. The toasts were dried in a drying oven at 101℃-105℃ until constant weight was achieved. The moisture content was calculated based on the weight difference of the toasts before and after drying.

[0055] 3. Measurement Results The effects of vacuum cooling and magnetic field-assisted vacuum cooling on the cooling characteristics of toast at different temperatures are as follows: Figure 2As shown. At a final cooling temperature of 25℃, the cooling rates of the vacuum cooling group and the magnetic field-assisted vacuum cooling group were 16.30℃ / min and 15.67℃ / min, respectively. At a final cooling temperature of 10℃, the cooling rates of the vacuum cooling group and the magnetic field-assisted vacuum cooling group were 11.42℃ / min and 12.10℃ / min, respectively. At a final cooling temperature of 4℃, the cooling rates of the vacuum cooling group and the magnetic field-assisted vacuum cooling group were 8.78℃ / min and 9.07℃ / min, respectively. Figure 2 A) This indicates that as the final cooling temperature decreases, the cooling time increases and the cooling rate decreases, but magnetic field assistance does not change the advantage of rapid cooling in vacuum.

[0056] It is noteworthy that, at a final cooling temperature of 4°C, compared to the vacuum cooling group (9.44%), the mass loss of toast treated with magnetic field-assisted vacuum cooling (8.59%) was significantly reduced by 9.00% (P<0.05). Figure 2 A) At final cooling temperatures of 10°C and 25°C, the bread treated with magnetic field-assisted vacuum cooling showed slightly lower mass loss compared to the vacuum cooling group; however, the difference was not significant (P>0.05). This indicates that at a final cooling temperature of 4°C, extending the cooling time allows for more time for the magnetic field to work, effectively reducing the mass loss of the bread.

[0057] Before storage, at a final cooling temperature of 4°C, the moisture content of toast treated with magnetic field-assisted vacuum cooling (30.45%) was significantly higher than that treated with vacuum cooling alone (29.45%), with an increase of 3.40% (P<0.05). Figure 2 B). Moreover, after 12 hours of storage and at a final cooling temperature of 4°C, magnetic field-assisted treatment still significantly increased the moisture content of the vacuum-cooled toast, with the increase rate further increasing to 4.91% (P<0.05). These results indicate that although magnetic field assistance can reduce the mass loss caused by vacuum cooling by suppressing moisture loss, it does not diminish the advantages of rapid and efficient vacuum cooling.

[0058] Example 3: Effect of magnetic field-assisted vacuum cooling on moisture distribution during the storage period of toast 1. Toast preparation Toasts (provided in Example 2) with vacuum cooling groups and magnetic field-assisted vacuum cooling groups with final cooling temperatures of 25°C, 10°C, and 4°C were stored at room temperature (25±3°C) for 12 hours.

[0059] 2. Measurement Method The moisture distribution of the toast was determined. The parameters of the low-field NMR spectrometer were set as follows: Carr-Purcell-Meiboom-Gill pulse sequence, operating temperature 32℃, main frequency 21MHz, sampling frequency 200kHz, RF delay 0.05ms, digital gain 3, analog gain 20dB, 90° pulse width 5.4μs, 180° pulse width 9.44μs, echo time 0.2ms, and number of echoes 8000.

[0060] 3. Measurement Results The effects of vacuum cooling and magnetic field-assisted vacuum cooling on the moisture distribution of toast under different storage times are as follows: Figure 3 As shown, the largest proportion of water in toast is weakly bound water, followed by strongly bound water and free water. At 0 hours of storage and a final cooling temperature of 4°C, toast treated with magnetic field-assisted vacuum cooling (17.56%) had a significantly higher proportion of strongly bound water (6.75%) than toast cooled under vacuum (16.45%) (P<0.05). Figure 3 A). At 0 h of storage and a final cooling temperature of 10 °C, the amount of strongly bound water in toast treated with magnetic field-assisted vacuum cooling significantly increased by 6.52% compared to that treated with vacuum cooling (P<0.05). Figure 3 B). This proves that magnetic field conditions affect the redistribution of moisture and enhance the degree of proton fixation, thereby increasing the content of bound water. It further illustrates that magnetic field assistance at pre-cooling final temperatures of 4℃ and 10℃ is beneficial to the water retention of strongly bound water in toast.

[0061] After 12 hours of storage, magnetic field-assisted vacuum cooling significantly increased the bound water content and reduced the free water content in the toast. With prolonged storage, the strongly bound water content of the toast decreased, primarily due to the conversion of strongly bound water into weakly bound water and free water during storage. At 12 hours of storage and a final cooling temperature of 4°C, the strongly bound water content in toast treated with magnetic field-assisted vacuum cooling (15.02%) was significantly increased by 10.28% compared to toast cooled under vacuum (13.62%) (P<0.05). Figure 3 A); After 12 hours of storage and at a final cooling temperature of 10°C, the amount of strongly bound water in toast treated with magnetic field-assisted vacuum cooling significantly increased by 7.56% compared to that treated with vacuum cooling (P<0.05). Figure 3 B). This indicates that magnetic field-assisted vacuum cooling can increase the content of strongly bound water in toast, and this effect is applicable to applications with a final cooling temperature of 4°C and 10°C.

[0062] Example 4: Effect of magnetic field-assisted vacuum cooling on moisture distribution during cake storage 1. Cake preparation and cooling Preparation of buckwheat cake: Whisk egg whites containing sugar until stiff peaks form, then mix with buckwheat flour, vegetable oil, and milk, stirring in a Z-shaped motion until a smooth batter is formed. Pour the batter into a mold, preheat the oven to 165℃ (325°F), and bake for 20 minutes, until the center temperature of the buckwheat cake reaches 87℃.

[0063] (1) Vacuum cooling: The baked buckwheat cake (center temperature of 87℃) along with the mold was immediately taken out and placed in a vacuum cooling device for vacuum cooling. The final pressure was set to 600pa, so that the center temperature of the buckwheat cake reached 25℃, 10℃ and 4℃ respectively, and the cooling time was 3.7min, 7.0min and 10.2min respectively.

[0064] (2) Magnetic field-assisted vacuum cooling: The baked buckwheat cake (center temperature of 87℃) along with the mold was immediately taken out and placed in a magnetic field-assisted vacuum cooling device (two strip permanent magnets are placed parallel to each other on both sides of the container holding the food in the vacuum chamber. The specifications of the strip permanent magnets are 200×50×15mm and the distance between the magnets is fixed at 10cm) for cooling treatment. The magnetic field strength is 1T and the vacuum degree is 0.7kPa. The center temperature of the buckwheat cake reached 25℃, 10℃ and 4℃ respectively, and the cooling time was 3.6min, 6.7min and 10.2min respectively.

[0065] 2. Measurement Method The moisture distribution of buckwheat cake was determined. The parameters of the low-field nuclear magnetic resonance spectrometer were set as follows: Carr-Purcell-Meiboom-Gill pulse sequence, operating temperature 32℃, main frequency 21MHz, sampling frequency 200kHz, RF delay 0.05ms, digital gain 3, analog gain 20dB, 90° pulse width 5.4μs, 180° pulse width 9.44μs, echo time 0.2ms, and number of echoes 8000.

[0066] 3. Measurement Results The effects of vacuum cooling and magnetic field-assisted vacuum cooling on the moisture distribution of buckwheat cake under different storage times are as follows: Figure 4 As shown in the figure, at storage times of 0 h and final cooling temperatures of 4℃, 10℃, and 25℃, the strongly bound water in the buckwheat cakes of the magnetic field-assisted vacuum cooling group increased significantly by 18.59%, 14.65%, and 10.22% respectively compared to the vacuum cooling group (P<0.05). At storage times of 12 h and final cooling temperatures of 4℃, 10℃, and 25℃, the free water in the buckwheat cakes also increased. Furthermore, the strongly bound water in the cakes treated with magnetic field-assisted vacuum cooling still increased by 13.80%, 6.67%, and 6.40% respectively compared to the vacuum cooling group (P<0.05). This indicates that magnetic field assistance effectively increases the fixation of bound water molecules in the buckwheat cakes, which is beneficial to the cakes' water retention performance, and the effect is more significant at lower final pre-cooling temperatures.

[0067] Example 5: Effect of magnetic field-assisted vacuum cooling on moisture distribution of steamed buns during storage 1. Preparation and cooling of steamed buns Preparation of steamed buns: Steamed buns are made using a two-stage fermentation method. Wheat flour, yeast, and water are mixed, stirred, and kneaded into a dough. The dough is then fermented at 37°C for 1 hour. Once the dough has doubled in size, it is manually kneaded 10 times to release the air. The dough is then divided and placed in a steamer. A second fermentation is carried out without turning on the heat for 20 minutes. After that, the dough is steamed over medium-high heat for 12 minutes. After turning off the heat, the steamed buns are left to rest in the steamer for 5 minutes to reach equilibrium. At this point, the center temperature of the steamed buns is 82°C.

[0068] (1) Vacuum cooling: The steamed buns (with a center temperature of 82°C) are immediately taken out and placed in a vacuum cooling device for vacuum cooling. The final pressure is set to 600 Pa until the center temperature of the buns reaches 25°C. The process takes 3.3 minutes, which is 16 times longer than the natural cooling process which takes 55.7 minutes.

[0069] (2) Magnetic field-assisted vacuum cooling: The steamed buns (with a center temperature of 82℃) were immediately taken out and placed in a magnetic field-assisted vacuum cooling device (two bar permanent magnets were placed parallel to each other on both sides of the container holding the food in the vacuum chamber. The specifications of the bar permanent magnets were 200×50×15mm and the distance between the magnets was fixed at 10cm) for cooling treatment. The magnetic field strength was 1T and the vacuum degree was 0.6kPa until the center temperature of the buns reached 25℃, which took 3.8min.

[0070] 2. Measurement Method The moisture distribution of steamed buns was determined using the following parameters of a low-field nuclear magnetic resonance spectrometer: Carr-Purcell-Meiboom-Gill pulse sequence, operating temperature 32℃, main frequency 21MHz, sampling frequency 200kHz, RF delay 0.05ms, digital gain 3, analog gain 20dB, 90° pulse width 5.4μs, 180° pulse width 9.44μs, echo time 0.2ms, and echo count 8000.

[0071] 3. Measurement Results The effects of vacuum cooling and magnetic field-assisted vacuum cooling on the moisture distribution of steamed buns during storage at different storage times are as follows: Figure 5As shown in the figure, A21 represents the proportion of strongly bound water tightly bound to macromolecules, A22 represents the proportion of poorly flowing water (weakly bound water), and A23 represents the proportion of free water. At 0 h of storage, the strongly bound water content in steamed buns treated with magnetic field-assisted vacuum cooling (19.62%) increased by 20.07% compared to those treated with vacuum cooling (16.34%) (P<0.05). With prolonged storage, the effect of magnetic field assistance in increasing the proportion of strongly bound water increased. At 6 h of storage, the strongly bound water content in the magnetic field-assisted vacuum cooling group increased by 11.57% compared to the vacuum cooling group (P<0.05), and at 12 h of storage, the strongly bound water content in the magnetic field-assisted vacuum cooling group increased by 19.76% compared to the vacuum cooling group (P<0.05). This indicates that magnetic field assistance inhibits the conversion of strongly bound water to free water in steamed buns, which is beneficial for maintaining the moisture content of the steamed buns during storage.

[0072] 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, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0073] The foregoing embodiments and methods described in this invention may vary based on the capabilities, experience, and preferences of those skilled in the art.

[0074] Listing the steps of the method in a certain order in this invention does not constitute any restriction on the order of the method steps.

Claims

1. A method for magnetic field-assisted vacuum cooling of surface products, characterized in that, The method includes the following steps: placing the dough product in a magnetic field-assisted vacuum cooling environment for cooling treatment, wherein the magnetic field is a static magnetic field, the magnetic field strength is set to 0.1-5T, and the vacuum degree is 0.1-2kPa; During the cooling process, the center temperature of the dough product is reduced to a set temperature; the center temperature of the dough product is 50-100℃, and the set temperature is 0-30℃.

2. The method according to claim 1, characterized in that, The magnetic field strength is 0.5-1.5T, preferably 1T; Preferably, the vacuum degree is 0.6-0.8 kPa.

3. The method according to claim 1, characterized in that, The core temperature of the dough product is 75-97℃; Preferably, the set temperature is 4-25℃.

4. The method according to claim 1, characterized in that, The time for the center temperature of the dough product to drop to the set temperature is 1-15 minutes, preferably 3-10.5 minutes.

5. The method according to claim 1, characterized in that, The magnetic field originates from a permanent magnet.

6. The method according to claim 5, characterized in that, The number of permanent magnets is two, and / or the size of the permanent magnets is 200×50×15 mm.

7. The method according to claim 1, characterized in that, The noodle product is a noodle product that has been heat-processed to reach a cooked state, and the heat processing is selected from one or more of steaming, boiling, baking, frying, deep-frying and baking. Preferably, the flour product is selected from one or more of the following: toast, cake, steamed bun, twisted roll, steamed noodles, cornbread, barbecued pork bun, meat bun, red bean bun, custard bun, sesame seed cake, rice cake, steamed sponge cake, bread, fried dough sticks, fried cake, and twisted dough sticks.

8. The method according to any one of claims 1-7, characterized in that, The method includes the following steps: placing the dough product with a center temperature of 75-97℃ in a magnetic field-assisted vacuum cooling environment for cooling treatment, wherein the magnetic field is a static magnetic field, the magnetic field strength is set to 0.5-1.5T, the vacuum degree is 0.6-0.8kPa, until the center temperature of the dough product reaches 4-25℃.

9. The application of the method as described in any one of claims 1-8 in reducing the quality loss of dough products during the cooling process.

10. The application of the method as described in any one of claims 1-8 in increasing the moisture content or bound water content of flour products during the cooling process.

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