Method for reducing shrinkage in the vacuum drying process of fresh wolfberry fruit

Abstract

The application discloses a method for reducing shrinkage in a vacuum drying process of fresh wolfberry fruits, comprising the following steps: pretreatment, vacuum drying: the pretreated fresh wolfberry fruits are put into a drying machine for vacuum drying, the vacuum drying is divided into three stages, and specifically as follows: in the first stage, the temperature is not higher than 55 DEG C, the vacuum pressure is not higher than 1200 pa, the cold trap temperature is not lower than -15 DEG C, and the drying time is not less than 10 h; in the second stage, on the basis of the first stage, the temperature is increased by 5 DEG C to 15 DEG C, the vacuum pressure is reduced by 700 pa to 800 pa, the cold trap temperature is increased by 10 DEG C to 20 DEG C, and the drying time is not less than 8 h; in the third stage, on the basis of the second stage, the temperature is increased by 5 DEG C to 10 DEG C, the vacuum pressure is reduced by 50 pa to 150 pa, the cold trap temperature is reduced by 20 DEG C to 25 DEG C, and the drying time is not less than 5 h. The moisture migration speed is comprehensively controlled, the problems of shrinkage and dark color in the vacuum drying process of the fresh wolfberry fruits are reduced, and the qualified rate and appearance of dried fruits are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of agricultural product primary processing, and in particular to a method for reducing shrinkage in the vacuum drying process of fresh wolfberry fruits. BACKGROUND

[0002] Wolfberry has gradually been known by the general consumers due to its high nutritional value and medicinal value. Wolfberry has the characteristics of disordered inflorescence and continuous flowers and fruits, and its harvesting has obvious seasonality and regionalism. Moreover, fresh wolfberry fruits are a kind of high-moisture and high-sugar berries. Before being made into various products, the picked fresh wolfberry fruits need to undergo a dehydration and drying process to be made into dried fruits with low water content, so as to improve the color, appearance and texture of wolfberry, and facilitate the preservation and storage of wolfberry.

[0003] The widely used vacuum pulsating drying technology is a new drying technology. In the drying process, the drying chamber is in an alternating cycle state of vacuum and normal pressure, which not only forms a honeycomb pore structure in the internal organization of the material, but also destroys the balance between the vapor pressure of the material surface layer and the pressure in the drying chamber, and has the advantages of high drying efficiency and good product quality. For example, in the Chinese patent application No. CN201710302966.4, the temperature in the drying chamber is first raised to 65-70℃, and then the temperature is maintained, and the vacuum pulsating drying is performed for 3-4h with a pulsation ratio of (10min-15min):(2min-5min); then the temperature in the drying chamber is lowered to 60-65℃, and then the temperature is maintained, and the vacuum pulsating drying is performed for 2.5-4h with a pulsation ratio of (10min-15min):(2min-5min); then the temperature in the drying chamber is lowered to 55-60℃, and then the temperature is maintained, and the vacuum pulsating drying is performed for 1-2h with a pulsation ratio of (10min-15min):(2min-5min); the vacuum working pressure is less than 8kPa, and finally the dried wolfberry fruits are obtained. Although this vacuum pulsating drying method improves the drying efficiency, the dried wolfberry fruits are severely shrunk, the fruit shape is not well expanded, and the color is also darkened, which seriously affects the appearance of wolfberry. SUMMARY

[0004] Therefore, the present application provides a method for reducing shrinkage in the vacuum drying process of fresh wolfberry fruits and maintaining good color, so as to solve the technical problem that the dried wolfberry fruits are severely shrunk, the fruit shape is not well expanded, and the color is also darkened, which seriously affects the appearance of wolfberry in the prior art.

[0005] The technical solution of the present application to solve the above technical problem is as follows:

[0006] A method for reducing shrinkage in the vacuum drying process of fresh wolfberry fruits, comprising the following steps:

[0007] S1, pretreatment: the picked fresh wolfberry fruit is subjected to maturity detection, spraying, and air knife draining;

[0008] S2, vacuum drying: the pretreated fresh wolfberry fruit is placed into a drying machine for vacuum drying, which is divided into three stages as follows:

[0009] In the first stage, the temperature is kept not higher than 55℃, the vacuum pressure is kept not higher than 1200pa, the cold trap temperature is kept not lower than -15℃, and the drying time is not less than 10h;

[0010] In the second stage, based on the first stage, the temperature is increased by 5℃-15℃, the vacuum pressure is decreased by 700pa-800pa, the cold trap temperature is increased by 10℃-20℃, and the drying time is not less than 8h;

[0011] In the third stage, based on the second stage, the temperature is increased by 5℃-10℃, the vacuum pressure is decreased by 50pa-150pa, the cold trap temperature is decreased by 20℃-25℃, and the drying time is not less than 5h;

[0012] S3, cooling: the vacuum dried wolfberry dried fruit is cooled to room temperature to obtain the finished wolfberry dried fruit.

[0013] Preferably, in the method for reducing shrinkage in the vacuum drying process of the fresh wolfberry fruit, in the first stage, the temperature gradient is increased, the vacuum pressure gradient is decreased, and the cold trap temperature gradient is increased; in the second stage, the temperature gradient is increased, the vacuum pressure is gently decreased, and the cold trap temperature is gently decreased; and in the third stage, the temperature, vacuum pressure, and cold trap temperature are kept constant.

[0014] Preferably, the method for reducing shrinkage in the vacuum drying process of the fresh wolfberry fruit comprises the following steps:

[0015] The temperature is kept at 45℃-50℃, the vacuum pressure is kept at 1100pa-1200pa, the cold trap temperature is kept at -10℃--15℃, and the drying time is kept for 3h-5h;

[0016] The temperature is kept at 50℃-55℃, the vacuum pressure is kept at 800pa-1000pa, the cold trap temperature is kept at -5℃-5℃, and the drying time is kept for 5h-7h;

[0017] The temperature is kept at 55℃-60℃, the vacuum pressure is kept at 500pa-600pa, the cold trap temperature is kept at 10℃-15℃, and the drying time is kept for 3h-4h;

[0018] The temperature is kept at 60℃-65℃, the vacuum pressure is kept at 400pa-500pa, the cold trap temperature is kept at 5℃-10℃, and the drying time is kept for 2h-3h;

[0019] Maintain a temperature of 65℃~67℃, a vacuum pressure of 350pa-400pa, a cold trap temperature of 0℃~5℃, and dry for 1h~2h;

[0020] Maintain a temperature of 67℃~70℃, a vacuum pressure of 300pa-350pa, a cold trap temperature of -15℃~-20℃, and dry for 5h~6h.

[0021] Preferably, in the above method for reducing shrinkage during the vacuum drying process of fresh wolfberry, the vacuum pressure in step S2 is constant or fluctuates.

[0022] Preferably, in the method for reducing shrinkage during the vacuum drying process of fresh wolfberries, step S1 includes testing the maturity of the harvested fresh wolfberries, selecting those that are orange-red or bright red, with a soluble solids content of not less than 17% and a hardness of not less than 1.4 kg / cm². 2 Fresh goji berries.

[0023] Preferably, in the above method for reducing shrinkage during the vacuum drying process of fresh wolfberry, step S1 involves 4 to 8 spray washing cycles.

[0024] Preferably, in the above-mentioned method for reducing shrinkage during the vacuum drying process of fresh wolfberry, the conveyor belt frequency during the spray washing is 10Hz to 19Hz, the spray water pressure above the conveyor belt is 0.05Mpa to 0.20Mpa, and the spray washing time is 60s to 90s.

[0025] Preferably, in the method for reducing shrinkage during the vacuum drying process of fresh wolfberry, the angle and wind speed of the air knife in step S1 are adjustable.

[0026] Preferably, the air knife draining method described above for reducing shrinkage during the vacuum drying process of fresh wolfberry involves draining through 3 to 6 air curtains.

[0027] Preferably, in the above-mentioned method for reducing shrinkage during vacuum drying of fresh wolfberries, the cooling environment is a clean environment with a temperature of 20℃~30℃ and a humidity of 20%~50%RH.

[0028] The technical solution adopted in this application can achieve the following beneficial effects:

[0029] The harvested fresh goji berries are tested for maturity, sprayed and washed, and air-dried. Then they are placed in a dryer for vacuum drying, which is carried out in three stages. Different drying temperatures and vacuum pressure cold trap temperatures are used to dry the fresh goji berries in stages. The moisture migration rate is comprehensively controlled to reduce the shrinkage and dark color of fresh goji berries during vacuum pulsation processing, thereby improving the qualified rate and appearance of dried fruit. Attached Figure Description

[0030] Figure 1This is a graph showing the change in heating temperature with drying time during the vacuum drying process of this invention.

[0031] Figure 2 This is a graph showing the change in vacuum pressure with drying time during the vacuum drying process of this invention.

[0032] Figure 3 This is a graph showing the change in cold trap temperature with drying time during the vacuum drying process of this invention. Detailed Implementation

[0033] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0034] It should be noted that when a device is considered to be "connected" to another device, it can be directly connected to the other device or there may be an intervening device present. The terms "inside," "top," "upper," "lower," "above," "below," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] In a preferred embodiment, a method for reducing shrinkage during the vacuum drying process of fresh wolfberries includes:

[0037] S1. Pre-treatment: The ripeness of the harvested fresh goji berries is tested, they are sprayed and washed, and then air-dried.

[0038] S2. Vacuum Drying: The pre-treated fresh goji berries are placed in a dryer for vacuum drying. The vacuum drying process consists of three stages, as detailed below:

[0039] In the first stage, the temperature is kept not higher than 55℃, the vacuum pressure is not higher than 1200pa, the cold trap temperature is not lower than -10℃, and the drying time is not less than 10h.

[0040] Preferably, in the first stage, the temperature gradient increases, the vacuum pressure decreases gradually, and the cold trap temperature increases gradually. Initially, the temperature is maintained at 45℃~50℃, the vacuum pressure at 1100pa-1200pa, and the cold trap temperature at -10℃~-15℃ for 3h~5h. Then, the temperature is increased to 50℃~55℃, the vacuum pressure decreases to 800pa-1000pa, and the cold trap temperature rises to -5℃~5℃, continuing drying for 5h~7h. Maintaining a relatively low temperature during this stage is beneficial for shaping the dried fruit and prevents crusting, color deterioration, and other problems.

[0041] In the second stage, based on the first stage, the temperature is increased by 5℃ to 15℃, the vacuum pressure is reduced by 700pa to 800pa, the cold trap temperature is increased by 10℃ to 20℃, and the drying time is not less than 8 hours.

[0042] Preferably, in the second stage, the temperature gradient increases, the vacuum pressure gradient decreases, and the cold trap temperature gradient increases. In this stage, the temperature is first maintained at 55℃~60℃, the vacuum pressure at 500pa-600pa, and the cold trap temperature at 10℃~15℃ for 3h~4h; then the temperature is maintained at 60℃~65℃, the vacuum pressure at 400pa-500pa, and the cold trap temperature at 5℃~10℃ for 2h~3h; finally, the temperature is maintained at 65℃~67℃, the vacuum pressure at 350pa-400pa, and the cold trap temperature at 0℃~5℃ for 1h~2h.

[0043] In the third stage, the temperature is increased by 5℃ to 10℃, the vacuum pressure is reduced by 50pa to 150pa, the cold trap temperature is reduced by 20℃ to 25℃, and the drying time is not less than 5 hours, based on the second stage.

[0044] Preferably, the temperature is maintained at 67℃~70℃, the vacuum pressure is 300pa-350pa, the cold trap temperature is -15℃~-20℃, and the drying time is 5h~6h.

[0045] S3. Cooling: Cool the vacuum-dried goji berries to room temperature to obtain the finished goji berry product.

[0046] In a preferred embodiment, the vacuum pressure is constant or fluctuates. When the vacuum pressure fluctuates, the drying chamber is in an alternating state of vacuum and atmospheric pressure during the drying process. This not only allows the internal tissue of the goji berries to form a honeycomb-like porous structure, but also disrupts the balance between the vapor pressure on the surface of the goji berries and the pressure inside the drying chamber, resulting in advantages such as high drying efficiency and good product quality.

[0047] Furthermore, the maturity test includes testing the maturity of the harvested fresh goji berries, selecting those that are orange-red or bright red, with a soluble solids content of not less than 17% and a hardness of not less than 1.4 kg / cm². 2Fresh goji berries. For firmness testing, 10-15 mature berries were randomly selected from each plot at harvest time. Soluble solids were measured using a digital saccharimeter, and firmness was determined using a GY-3 fruit firmness tester. The average value was then taken.

[0048] Furthermore, in the method for reducing shrinkage during the vacuum drying process of fresh goji berries described above, step S1 involves 4 to 8 spray washing cycles. During the spray washing, the conveyor belt frequency is 10Hz to 19Hz, the water pressure sprayed above the conveyor belt is 0.05MPa to 0.20MPa, and the spray washing time is 60s to 90s. For example, during spray washing, the conveyor belt frequency can be adjusted to 16Hz to ensure that each fresh goji berry is sprayed with clean water, ensuring a more thorough cleaning. The water pressure is 0.15MPa to reduce the damage to the fresh goji berries caused by water pressure during spraying, preventing damage during washing. The spray washing time is 80s to ensure the fresh goji berries are thoroughly cleaned.

[0049] Furthermore, the angle and wind speed of the air knife are adjustable, and the optimal angle and wind speed can be selected according to the actual situation.

[0050] Furthermore, the air knife drying process involves 3 to 6 air curtains. These air curtains are spaced apart sequentially along the conveying direction of the goji berries, and the arrangement of 3 to 6 air curtains satisfies both the requirements for drying efficiency and maximizes moisture removal.

[0051] Furthermore, in the above-mentioned method for reducing shrinkage during the vacuum drying process of fresh wolfberries, the cooling environment is a clean environment with a temperature of 20℃~30℃ and a humidity of 20%~50%RH.

[0052] Specifically, the sample should be orange-red in color, with a soluble solids content of not less than 17% and a hardness of not less than 1.4 kg / cm². 2For qualified fresh goji berries, the firmness is determined by randomly selecting 10-15 mature berries from each plot at harvest time. The soluble solids content is measured using a digital saccharimeter, and the firmness is determined using a GY-3 fruit firmness tester. The average value is then taken. The selected qualified fresh goji berries are placed on a stainless steel conveyor belt with a mesh (the mesh size ensures no leakage). The conveyor belt carries the fresh goji berries into a spray washing area, where they undergo 4-8 spray washes with clean, purified water. The conveyor belt then carries them to a draining area, where they pass through 3-6 air knives to quickly remove residual water droplets from the surface of the fresh goji berries. The angle and speed of the air knives are adjustable for optimal selection. The drained fresh goji berries are then automatically loaded onto trays, with each tray containing 2-3.8 kg of fresh berries. The bottom of the trays is lined with a lint-free, food-grade white cloth, and the fresh berries are spread evenly, with a thickness of no more than 2 cm, which is more conducive to drying effect and efficiency. Load the material trays into the material cart, ensuring the trays are perpendicular to the ground. The cart frame is adjustable to raise and lower, allowing for adjustment of the distance between the trays and the heating plates to ensure efficient heat transfer. The loaded carts are then systematically placed into the dryer, which is divided into a drying chamber and a cooling chamber. The cooling chamber contains at least one cold trap, the temperature of which can be adjusted as needed. Observation ports are located on the sides of the material area and cold trap area in the drying chamber, providing clear visibility of the changes in the fresh fruit during the drying process and the effect of water vapor condensation. Process adjustments can be made in real time based on the changes in the fresh fruit. Vacuum drying is performed inside the dryer, and the drying process is divided into three stages. In the first stage, the temperature is maintained at no higher than 55℃, the vacuum pressure at no higher than 1200 Pa, the cold trap temperature at no lower than -10℃, and the drying time is no less than 10 hours. In the second stage, based on the first stage, the temperature is increased by 5℃ to 15℃, the vacuum pressure is decreased by 600 Pa to 700 Pa, the cold trap temperature is increased by 10℃ to 20℃, and the drying time is no less than 8 hours. In the third stage, based on the second stage, the temperature is increased by 5℃ to 10℃, the vacuum pressure is decreased by 50 Pa to 150 Pa, the cold trap temperature is decreased by 20℃ to 25℃, and the drying time is no less than 5 hours. The vacuum level inside the dryer is controlled by a cold trap. The lower temperature control of the cold trap maintains the vacuum level, achieving a lower ultimate vacuum. This allows for rapid transfer and condensation of evaporated moisture, avoiding heat evaporation, shortening the drying time, and resulting in goji berries with good plumpness and color.For example, initially, the temperature of the plates in the drying chamber is raised to 45℃~50℃ and held, while the vacuum pressure is maintained at 1100pa-1200pa, and the cold trap temperature is controlled at -10℃~-15℃, for vacuum drying for 3h~5h; further, the temperature of the plates in the drying chamber is raised to 50℃~55℃ and held, while the vacuum pressure is maintained at 800pa-1000pa, and the cold trap temperature is controlled at -5℃~5℃, for vacuum drying for 5h~7h; further, the temperature of the plates in the drying chamber is raised to 55℃~60℃ and held, while the vacuum pressure is maintained at 500pa-600pa, and the cold trap temperature is controlled at 105℃~15℃, for vacuum drying for 3h. ~4h; Further, raise the plate temperature in the drying chamber to 60℃~65℃ and maintain it at that temperature, keep the vacuum pressure at 400pa~500pa, control the cold trap temperature at 5℃~10℃, and vacuum dry for 2h~3h; Further, lower the plate temperature in the drying chamber to 65℃~67℃ and maintain it at that temperature, keep the vacuum pressure at 350pa~400pa, control the cold trap temperature at 0℃~5℃, and vacuum dry for 1h~2h; Further, raise the plate temperature in the drying chamber to 67℃~70℃ and maintain it at that temperature, keep the vacuum pressure at 300pa~350pa, control the cold trap temperature at -10℃~-20℃, and vacuum dry for 5h~6h.

[0053] After drying, the drying trays are removed from the drying chamber and placed in a clean environment with a temperature of 20℃~30℃ and a humidity of 20%~50%RH for cooling until the dried fruit cools to room temperature. When the moisture content of the dried goji berries is 10%~13.5%, the drying is complete, and the finished dried goji berry product is obtained.

[0054] This vacuum drying method, verified through multiple sets of experiments from different perspectives, yielded the optimal process parameters. The initial temperature is low, followed by a slow increase, while the vacuum pressure in the chamber decreases gradually and the cold trap temperature is moderate. This ensures that the thermal stress and shrinkage of the fresh fruit are reduced before it solidifies, that moisture migrates smoothly, that wrinkling is significantly reduced, and that good color is maintained, resulting in a significant improvement in appearance.

[0055] It is worth noting that the process temperature, process time, and process pressure mentioned in the above embodiments are all temperatures, times, or pressures used in the experiment. Any reasonable adjustments made by those skilled in the art based on the process temperature, process time, and process pressure provided by this invention, within the error range, should be included within the protection scope of this invention.

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below.

[0057] Comparative example:

[0058] Raw material maturity testing: The maturity of fresh goji berries about to be harvested was tested. 500g samples of bright red goji berries were randomly selected from the field. From these samples, 15 ripe berries were randomly selected, and the average firmness was measured using a GY-3 fruit firmness tester to be 1.5 kg / cm². 2， The average soluble solids content, measured using a digital saccharimeter, was 17.8%.

[0059] Spray washing: Fresh goji berries are evenly spread in a single layer on the conveyor chain. The conveyor belt frequency is 15Hz, the water pressure sprayed above the conveyor belt is 0.05Mpa, and the spray washing time is 70 seconds. Clean purified water is used for 4 spray washings to obtain clean fresh goji berries. Air knife draining: The water droplets remaining on the surface of the fruit are quickly removed by 4 air curtains.

[0060] Loading: Control the amount of fresh fruit to 3kg / tray, and line the bottom of the tray with a lint-free food-grade white cloth. The thickness of the fresh fruit should be less than 2cm and the fruit should be spread evenly. Loading: Load the trays into the drying machine, with the trays perpendicular to the ground. Feeding: The loaded trays are fed into the drying machine in an orderly manner. Adjust the height of the racks to ensure that all trays are evenly spread on the heating plate.

[0061] Vacuum drying: Initially, raise the plate temperature in the drying chamber to 65℃ and maintain it at that temperature, while keeping the vacuum pressure at 800 Pa and the cold trap temperature at -20℃, and vacuum dry for 4 hours; then further lower the plate temperature in the drying chamber to 60℃ and maintain it at that temperature, while keeping the vacuum pressure at 800 Pa and the cold trap temperature at -10℃, and vacuum dry for 4 hours; finally, lower the plate temperature in the drying chamber to 55℃ and maintain it at that temperature, while keeping the vacuum pressure at 800 Pa and the cold trap temperature at -40℃, and vacuum dry for 2 hours.

[0062] After drying, the drying trays were removed from the drying chamber and placed in a clean environment at 25℃ and 40% RH for cooling until the dried fruit reached room temperature, yielding the finished product of dried goji berries. The target moisture content of the dried goji berries was 10%–13.5%. The finished product of dried goji berries was tested, and the results are shown in Table 1.

[0063] Table 1 Comparative example: Vacuum drying process parameters and test data of dried wolfberries.

[0064]

[0065] As can be seen from the table above, when the vacuum pressure of the drying oven is kept constant and the temperature gradient of the heating plates changes, the dried goji berries shrink severely, darken in color, and fail to meet the quality standards.

[0066] It is worth noting that, through color value detection using the Lab color analyzer, a positive value of 'a' represents red and a negative value represents green. The higher the 'a' value, the brighter the color of the goji berries, and vice versa. This is the core parameter for judging color.

[0067] Experiment 1 explores the effect of vacuum degree on the shrinkage rate of dried fruit:

[0068] Other processes are the same as in the comparative example. Please refer to Table 2 for the vacuum drying process parameters. After drying, the drying trays were removed from the drying chamber and placed in a clean environment at 25℃ and 40% RH for cooling until the dried fruit reached room temperature. The finished product of dried goji berries was then tested, and the results are shown in Table 2.

[0069] Table 2. Vacuum drying process parameters and test data of dried wolfberries in Experiment Example 1

[0070]

[0071] As shown in Table 2, when other conditions remain unchanged, the vacuum pressure of the chamber is varied in a gradient to explore the effect of different vacuum pressures on the shrinkage rate of dried goji berries. The data shows that although the shrinkage rate of dried goji berries is reduced, the effect is not obvious and the color is dark, resulting in unqualified appearance.

[0072] Experiment Example 2 explores the effect of drying time on the shrinkage rate of dried wolfberry fruit:

[0073] Other processes are the same as in the comparative example; please refer to Table 3 for the vacuum drying process parameters. The finished dried goji berries were tested, and the results are shown in Table 3.

[0074] Table 3. Vacuum drying process parameters and test data of dried wolfberries in Experiment Example 2

[0075]

[0076] The above experiments show that when other conditions remain unchanged, adjusting the drying time reduces the shrinkage rate, but there is still obvious shrinkage and the dried fruit becomes darker in color.

[0077] Experiment Example 3 explores the effect of cold trap temperature on the shrinkage rate of dried wolfberry:

[0078] Other processes are the same as in the comparative example; please refer to Table 4 for the vacuum drying process parameters. The finished dried goji berries were tested, and the results are shown in Table 4.

[0079] Table 4. Vacuum drying process parameters and test data of dried wolfberries in Experiment Example 2

[0080]

[0081] The table above shows that when other conditions remain unchanged, adjusting the temperature of the cold trap significantly reduces the shrinkage rate of dried goji berries, but some shrinkage and darkening of color still occur. This may be due to the high temperature of the plate layer, which causes the moisture to migrate too quickly during the drying process of goji berries. The temperature can be appropriately lowered for further experiments.

[0082] Experiment Example 4: Exploring the effect of heating temperature on the shrinkage rate of dried wolfberry fruit:

[0083] Other processes are the same as in the comparative example; please refer to Table 4 for the vacuum drying process parameters. The finished dried goji berries were tested, and the results are shown in Table 5.

[0084] Table 5. Experiment 4: Vacuum drying process parameters and test data of dried wolfberries.

[0085]

[0086] As can be seen from Table 5, the shrinkage rate of dried wolfberries dried by the vacuum drying process parameters in Experiment Example 4 was 42% to 43%. Among them, the shrinkage rate of dried fruits under the temperature parameters of Scheme 11 was the best, at only 42.3%. The fruit shape was relaxed, the shrinkage phenomenon was greatly improved, and the color was bright red, which was of qualified quality.

[0087] Experiment Example 5: Verification Experiment

[0088] The main process conditions are the same as in Experimental Example 4. Based on Experimental Example 4, the three stages of vacuum drying are carried out in a gradient to verify the effectiveness of this scheme. The process parameters and test results are shown in Table 6.

[0089] Table 6. Experiment 4: Vacuum Drying Process Parameters and Dried Goji Berry Fruit Detection Data

[0090]

[0091] As can be seen from the table above, when the vacuum drying process of this application is used to dry fresh wolfberries in a gradient manner, the shrinkage rate of dried wolfberries can be reduced to 42%, the fruit shape is flat and the color is bright red, and the moisture content also meets the target value of 10% to 13.5%.

[0092] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for reducing shrinkage during the vacuum drying process of fresh wolfberries, characterized in that, Includes the following steps: S1. Pre-treatment: The ripeness of the harvested fresh goji berries is tested, they are sprayed and washed, and then air-dried. S2. Vacuum Drying: The pre-treated fresh goji berries are placed in a dryer for vacuum drying. The vacuum drying process consists of three stages, as detailed below: In the first stage, maintain the temperature at 45℃~50℃, the vacuum pressure at 1100pa-1200pa, the cold trap temperature at -10℃~-15℃, and dry for 3h~5h; then maintain the temperature at 50℃~55℃, the vacuum pressure at 800pa-1000pa, the cold trap temperature at -5℃~5℃, and dry for 5h~7h. In the second stage, maintain the temperature at 55℃~60℃, the vacuum pressure at 500pa-600pa, and the cold trap temperature at 10℃~15℃ for 3h~4h; maintain the temperature at 60℃~65℃, the vacuum pressure at 400pa-500pa, and the cold trap temperature at 5℃~10℃ for 2h~3h; maintain the temperature at 65℃~67℃, the vacuum pressure at 350pa-400pa, and the cold trap temperature at 0℃~5℃ for 1h~2h. The third stage involves maintaining a temperature of 67℃~70℃, a vacuum pressure of 300pa-350pa, a cold trap temperature of -15℃~-20℃, and drying for 5h~6h. S3. Cooling: Cool the vacuum-dried goji berries to room temperature to obtain the finished goji berry product; In step S2, in the first stage, the temperature gradient increases, the vacuum pressure gradient decreases, and the cold trap temperature gradient increases; in the second stage, the temperature gradient increases, the vacuum pressure decreases gradually, and the cold trap temperature decreases gradually; in the third stage, the temperature, vacuum pressure, and cold trap temperature remain constant.

2. The method for reducing shrinkage during the vacuum drying process of fresh wolfberry according to claim 1, characterized in that, In step S2, the vacuum pressure is constant or fluctuates.

3. The method for reducing shrinkage during the vacuum drying process of fresh wolfberry according to claim 1, characterized in that, In step S1, the maturity detection includes testing the maturity of the harvested fresh goji berries, selecting those that are orange-red or bright red, with a soluble solids content of not less than 17% and a hardness of not less than 1.4 kg / cm². 2 Fresh goji berries.

4. The method for reducing shrinkage during the vacuum drying process of fresh wolfberry according to claim 1, characterized in that, In step S1, the spray washing consists of 4 to 8 spray cleaning cycles.

5. The method for reducing shrinkage during the vacuum drying process of fresh wolfberry fruit according to claim 4, characterized in that, The frequency of the conveyor belt in the spray washing process is 10Hz to 19Hz, the water pressure sprayed above the conveyor belt is 0.05Mpa to 0.20Mpa, and the spray washing time is 60s to 90s.

6. The method for reducing shrinkage during the vacuum drying process of fresh wolfberry according to claim 1, characterized in that, In step S1, the angle and wind speed of the air knife are adjustable.

7. The method for reducing shrinkage during the vacuum drying process of fresh wolfberry according to claim 6, characterized in that, The air knife drying process involves 3 to 6 air curtains.

8. The method for reducing shrinkage during the vacuum drying process of fresh wolfberry fruit according to claim 1, characterized in that, The cooling environment is a clean environment with a temperature of 20℃~30℃ and a humidity of 20%~50%RH.

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