A kind of processing method of wolfberry dried fruit

Abstract

The invention relates to the technical field of natural material processing, and in particular to a processing method and application of wolfberry dried fruit. The invention adopts a freeze-thaw plus vacuum microwave drying method to replace traditional hot air drying, so that the water content of the prepared wolfberry dried fruit is lower than 13%, the total sugar content is higher than 57%, the color is uniform, and there is no obvious color difference. Compared with hot air drying, on the basis of achieving similar water content, the total sugar content is increased by 41.4%. In addition, by adopting the same polysaccharide extraction method, the yield of wolfberry polysaccharide of the wolfberry dried fruit prepared by the invention is significantly higher than that of the wolfberry dried fruit prepared by hot air drying, so the quality and market value of the product are effectively improved, and the invention can be applied to food processing, especially sweet foods such as chocolate and fructose.

Description

Technical Field

[0001] The invention relates to the technical field of natural material processing, in particular to a method for processing wolfberry dried fruit. Background Art

[0002] Wolfberry (Lycium barbarum) is a traditional Chinese medicinal material and health food, which has attracted widespread attention due to its rich nutritional ingredients. Dried wolfberry not only occupies an important position in Chinese food culture, but is also gradually recognized by the international market. Its main ingredients include polysaccharides, amino acids, vitamins, minerals, etc., and it has multiple health functions such as anti-oxidation, immune regulation, and anti-fatigue.

[0003] At present, the processing of wolfberry dried fruit mainly adopts natural drying, hot air drying, vacuum drying and other methods. Although these traditional methods are simple, they are easy to cause the loss of nutrients in wolfberry during processing, especially heat-sensitive components such as polysaccharides and vitamins. In addition, traditional drying methods are often difficult to effectively control the moisture content of dried fruits, resulting in a high moisture content in the final product, affecting its storage stability and taste.

[0004] In recent years, with the development of food processing technology, many new drying technologies have been gradually applied to the processing of wolfberry dried fruit. For example, microwave drying, freeze drying, spray drying and other technologies can quickly remove moisture at a lower temperature and retain the nutritional components of wolfberry to the maximum extent. However, it still inevitably leads to the loss of water-soluble sugars.

[0005] In summary, the existing wolfberry dried fruit processing methods have certain deficiencies in terms of total sugar content and water content, which affects its nutritional value and market competitiveness. Therefore, the present invention aims to propose a new wolfberry dried fruit processing method to solve the above problems and meet market demand. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a processing method for wolfberry dried fruit, so as to provide a wolfberry dried fruit with high total sugar content and low water content.

[0007] Based on the above purpose, the present invention provides a method for processing wolfberry dried fruit, comprising the following steps:

[0008] (1) Cleaning: Rinse the wolfberries with clean water, air dry them, and set aside;

[0009] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at a temperature of 0±0.5°C for 40-50 min, rinse with water, and finally air dry naturally;

[0010] (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with wolfberries in a refrigerator, gradually cool it to -25±5°C, freeze it at -25±5°C for 2-4h, and finally thaw it naturally;

[0011] (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them in a nitrogen atmosphere at a positive pressure environment, a power of 800-1200 W, and a temperature of 20-30° C. for 50-70 min, then at a negative pressure environment, a power of 400-600 W, and a temperature of 20-30° C. for 100-140 min, then at a positive pressure environment, a power of 800-1200 W, and a temperature of 20-30° C. for 20-40 min, then at a negative pressure environment, a power of 400-600 W, and a temperature of 20-30° C. for 40-80 min, and then perform vacuum microwave drying to obtain dried wolfberries.

[0012] Preferably, the wolfberries in step (1) are wolfberries with impurities removed and petioles of uniform size, mature and plump.

[0013] Preferably, the clean water flushing in step (1) is performed by flushing with clean water 2-4 times, each time for 5-20 seconds.

[0014] Preferably, the mass concentration of the sodium carbonate solution in step (2) is 15-25 g / L.

[0015] Furthermore, the mass concentration of the sodium carbonate solution in step (2) is 20 g / L.

[0016] Preferably, the clean water flushing in step (2) is performed by flushing with clean water 2-4 times, each time for 5-20 seconds.

[0017] Preferably, the gradient cooling in step (3) is: firstly cooling from room temperature to 0°C at a cooling rate of 1°C / min, then cooling from 0°C to -10°C at a cooling rate of 0.5°C / min, and then cooling from -10°C to -25±5°C at a cooling rate of 0.1°C / min.

[0018] Preferably, the microwave vacuum drying step in step (4) is: first, in a negative pressure environment, at a power of 400-600 W, at a temperature of 40-50° C., drying for 40-80 min, then in a negative pressure environment, at a power of 0 W, at a temperature of 40-60° C., for 50-70 min, and then in a negative pressure environment, at a microwave power of 250-350 W, at a temperature of 40-50° C., drying for 420-540 min.

[0019] Preferably, in step (4), the negative pressure is an absolute pressure of 1±0.2 MPa, and the positive pressure is an absolute pressure of 0.05±0.01 MPa.

[0020] Preferably, the water content of the wolfberry dried fruit is less than 13%, and the total sugar content is not less than 56%.

[0021] Furthermore, the present invention also provides an application of wolfberry dried fruit, which can be applied to food processing, especially sweet foods such as chocolate and fructose.

[0022] Beneficial effects of the present invention:

[0023] The present invention adopts a freeze-thaw plus vacuum microwave drying method to replace traditional hot air drying, so that the water content of the prepared wolfberry dried fruit is lower than 13%, the total sugar content is higher than 57%, the color is uniform, and there is no obvious color difference. Compared with hot air drying, on the basis of achieving similar water content, the total sugar content is increased by 41.4%. In addition, by adopting the same polysaccharide extraction method, the yield of wolfberry polysaccharide of the wolfberry dried fruit prepared by the present invention is significantly higher than that of the wolfberry dried fruit prepared by hot air drying, thereby effectively improving the quality and market value of the product.

[0024] The present invention adopts low-temperature dewaxing to treat the cuticle on the surface of wolfberry. Compared with room temperature dewaxing, low-temperature dewaxing helps to increase the total sugar content and rehydration rate of wolfberry dry fruit. This is mainly because at low temperature, the sugar inside the wolfberry is less lost during the dewaxing process, and at low temperature, it is easier to control the erosion rate of the dewaxing agent on the cuticle on the surface of the wolfberry, thereby avoiding excessive erosion leading to a large amount of sugar loss, especially the loss of small molecule sugar.

[0025] The present invention performs freeze-thaw treatment on the dewaxed wolfberry, and the freeze-thaw treatment helps to reduce the water content and improve the drying efficiency and the rehydration rate. This is mainly because the freeze-thaw treatment helps to form ice crystals inside the wolfberry, thereby forming a porous structure. In addition, the present invention further adopts gradient cooling. Under the gradient cooling, the ice crystals are formed more evenly and completely, thereby helping to improve the porous structure. The perfect porous structure helps to improve the removal of water. At the same time, a better framework structure is maintained, so that it has a higher rehydration rate.

[0026] The present invention performs positive pressure-reverse pressure microwave treatment on wolfberries after freeze-thaw treatment. The positive pressure-reverse pressure process is helpful to improve the total sugar content and rehydration rate of wolfberry dried fruit, and significantly reduce the molecular weight of wolfberry polysaccharides. This is mainly because the positive pressure-reverse pressure can avoid the rapid loss of water in the initial stage of the microwave treatment process, thereby taking away small molecular weight sugars, and at the same time, cooperates with the freeze-thaw treatment to construct a porous internal structure, effectively improve the rehydration rate and remove water in the later stage of drying. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0028] In the specific implementation manner of the present invention, wolfberries were purchased from Ningxia Zaokang Wolfberry Co., Ltd. in Zhongning County, Ningxia. They are mature wolfberries picked in early July.

[0029] Embodiment 1:

[0030] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0031] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at 0°C and a mass concentration of 20 g / L for 45 min, remove them and rinse them with clean water three times for 10 s each time to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0032] (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with the wolfberries in a refrigerator, first cool it down from room temperature to 0°C at a rate of 1°C / min, then cool it down from 0°C to -10°C at a rate of 0.5°C / min, then cool it down from -10°C to -25°C at a rate of 0.1°C / min, then freeze it at -25°C for 3 h, and finally thaw it naturally;

[0033] (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them for 60 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C. in a nitrogen atmosphere, then dry them for 120 min at an absolute pressure of 0.05 MPa, a power of 500 W, and a temperature of 25° C., then dry them for 30 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C., and then dry them for 30 min at an absolute pressure of 0.05 MPa. Power 500 W, temperature 25 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 500 W, temperature 45 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 0 W, temperature 50 ℃, time for 60 minutes, then at an absolute pressure of 0.05 MPa, microwave power 300 W, temperature 45 ℃, dry for 480 minutes. After drying, turn off the microwave, turn off the vacuum, obtain wolfberry dried fruit, package and refrigerate at 5 ℃.

[0034] Embodiment 2:

[0035] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0036] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at 0°C and a mass concentration of 15 g / L for 50 min, remove them and rinse them with clean water three times for 10 s each time to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0037] (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with the wolfberries in a refrigerator, first cool it down from room temperature to 0°C at a rate of 1°C / min, then cool it down from 0°C to -10°C at a rate of 0.5°C / min, then cool it down from -10°C to -20°C at a rate of 0.1°C / min, then freeze it at -20°C for 4 h, and finally thaw it naturally;

[0038] (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them for 70 min at an absolute pressure of 1 MPa, a power of 800 W, and a temperature of 30°C in a nitrogen atmosphere, then dry them for 140 min at an absolute pressure of 0.05 MPa, a power of 400 W, and a temperature of 30°C, then dry them for 40 min at an absolute pressure of 1 MPa, a power of 800 W, and a temperature of 30°C, and then dry them for 40 min at an absolute pressure of 0.05 MPa, a power of 100 W, and a temperature of 30°C. The dried fruits were dried at a power of 600 W and a temperature of 30°C for 80 min, then dried at an absolute pressure of 0.05 MPa, a power of 500 W and a temperature of 45°C for 60 min, then dried at an absolute pressure of 0.05 MPa, a power of 0 W and a temperature of 50°C for 60 min, then dried at an absolute pressure of 0.05 MPa, a microwave power of 300 W and a temperature of 45°C for 480 min. After drying, the microwave and the vacuum were turned off to obtain the dried wolfberry fruit, which was packaged and refrigerated at 5°C.

[0039] Embodiment 3:

[0040] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0041] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at 0°C and a mass concentration of 30 g / L for 30 min, remove them and rinse them with clean water for 3 times, each time for 10 s to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0042] (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with the wolfberries in a refrigerator, first cool it down from room temperature to 0°C at a rate of 1°C / min, then cool it down from 0°C to -10°C at a rate of 0.5°C / min, then cool it down from -10°C to -30°C at a rate of 0.1°C / min, then freeze it at -30°C for 2 h, and finally thaw it naturally;

[0043] (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them for 50 min at an absolute pressure of 1 MPa, a power of 1200 W, and a temperature of 20° C. in a nitrogen atmosphere, then dry them for 100 min at an absolute pressure of 0.05 MPa, a power of 600 W, and a temperature of 20° C., then dry them for 20 min at an absolute pressure of 1 MPa, a power of 1200 W, and a temperature of 20° C., and then dry them for 20 min at an absolute pressure of 0.05 MPa. The mixture was dried at a power of 600 W and a temperature of 20°C for 40 min, then dried at an absolute pressure of 0.05 MPa, a power of 500 W and a temperature of 45°C for 60 min, then dried at an absolute pressure of 0.05 MPa, a power of 0 W and a temperature of 50°C for 60 min, then dried at an absolute pressure of 0.05 MPa, a microwave power of 300 W and a temperature of 45°C for 480 min. After drying, the microwave and the vacuum were turned off to obtain the dried wolfberry fruit, which was packaged and refrigerated at 5°C.

[0044] Comparative Example 1:

[0045] The difference between Comparative Example 1 and Example 1 is that the temperature of the dewaxing treatment in Comparative Example 1 is room temperature, and the specific steps are as follows:

[0046] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0047] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at room temperature with a mass concentration of 20 g / L for 45 min, remove them and rinse them with clean water for 3 times, each time for 10 s to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0048] (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with the wolfberries in a refrigerator, first cool it down from room temperature to 0°C at a rate of 1-2°C / min, then cool it down from 0°C to -10°C at a rate of 0.5°C / min, then cool it down from -10°C to -25°C at a rate of 0.1°C / min, then freeze it at -25°C for 3 h, and finally thaw it naturally;

[0049] (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them for 60 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C. in a nitrogen atmosphere, then dry them for 120 min at an absolute pressure of 0.05 MPa, a power of 500 W, and a temperature of 25° C., then dry them for 30 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C., and then dry them for 30 min at an absolute pressure of 0.05 MPa. Power 500 W, temperature 25 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 500 W, temperature 45 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 0 W, temperature 50 ℃, time for 60 minutes, then at an absolute pressure of 0.05 MPa, microwave power 300 W, temperature 45 ℃, dry for 480 minutes. After drying, turn off the microwave, turn off the vacuum, obtain wolfberry dried fruit, package and refrigerate at 5 ℃.

[0050] Comparative Example 2:

[0051] The difference between Comparative Example 2 and Example 1 is that no freeze-thaw treatment is performed, and the specific steps are as follows:

[0052] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0053] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at 0°C and a mass concentration of 20 g / L for 45 min, remove them and rinse them with clean water three times for 10 s each time to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0054] (3) Drying: Spread the dewaxed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them for 60 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C. in a nitrogen atmosphere, then dry them for 120 min at an absolute pressure of 0.05 MPa, a power of 500 W, and a temperature of 25° C., then dry them for 30 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C., and then dry them for 30 min at an absolute pressure of 0.05 MPa. Power 500 W, temperature 25 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 500 W, temperature 45 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 0 W, temperature 50 ℃, time for 60 minutes, then at an absolute pressure of 0.05 MPa, microwave power 300 W, temperature 45 ℃, dry for 480 minutes. After drying, turn off the microwave, turn off the vacuum, obtain wolfberry dried fruit, package and refrigerate at 5 ℃.

[0055] Comparative Example 3:

[0056] The difference between Comparative Example 3 and Example 1 is that the freeze-thaw treatment does not use gradient freezing, but directly cools from room temperature to -25°C at a cooling rate of 1°C / min, and then freezes at -25°C for 3h. The specific steps are as follows:

[0057] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0058] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at 0°C and a mass concentration of 20 g / L for 45 min, remove them and rinse them with clean water three times for 10 s each time to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0059] (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with the wolfberries in a refrigerator, first cool it down from room temperature to -25°C at a rate of 1°C / min, then freeze it at -25°C for 3 h, and finally thaw it naturally;

[0060] (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them for 60 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C. in a nitrogen atmosphere, then dry them for 120 min at an absolute pressure of 0.05 MPa, a power of 500 W, and a temperature of 25° C., then dry them for 30 min at an absolute pressure of 1 MPa, a power of 1000 W, and a temperature of 25° C., and then dry them for 30 min at an absolute pressure of 0.05 MPa. Power 500 W, temperature 25 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 500 W, temperature 45 ℃, dry for 60 minutes, then at an absolute pressure of 0.05 MPa, power 0 W, temperature 50 ℃, time for 60 minutes, then at an absolute pressure of 0.05 MPa, microwave power 300 W, temperature 45 ℃, dry for 480 minutes. After drying, turn off the microwave, turn off the vacuum, obtain wolfberry dried fruit, package and refrigerate at 5 ℃.

[0061] Comparative Example 4:

[0062] The difference between Comparative Example 4 and Example 1 is that there is no positive pressure-negative pressure conversion during the drying process, and the drying is always carried out at an absolute pressure of 0.05 MPa. The specific steps are as follows:

[0063] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0064] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at 0°C and a mass concentration of 20 g / L for 45 min, remove them and rinse them with clean water three times for 10 s each time to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0065] (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with the wolfberries in a refrigerator, first cool it down from room temperature to 0°C at a rate of 1°C / min, then cool it down from 0°C to -10°C at a rate of 0.5°C / min, then cool it down from -10°C to -25°C at a rate of 0.1°C / min, then freeze it at -25°C for 3 h, and finally thaw it naturally;

[0066] (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them for 60 min at an absolute pressure of 0.05 MPa, a power of 1000 W, and a temperature of 25°C in a nitrogen atmosphere, then dry them for 120 min at an absolute pressure of 0.05 MPa, a power of 500 W, and a temperature of 25°C, then dry them for 30 min at an absolute pressure of 0.05 MPa, a power of 1000 W, and a temperature of 25°C, and then dry them for 30 min at an absolute pressure of 0.05 MPa. pa, power 500 W, temperature 25 ℃, dry for 60 min, then at absolute pressure 0.05 MPa, power 500 W, temperature 45 ℃, dry for 60 min, then at absolute pressure 0.05 MPa, power 0 W, temperature 50 ℃, time is 60 min, then at absolute pressure 0.05 MPa, microwave power 300 W, temperature 45 ℃, dry for 480 min. After drying, turn off the microwave, turn off the vacuum, get wolfberry dried fruit, package and refrigerate at 5 ℃.

[0067] Comparative Example 5:

[0068] Comparative Example 5 adopts traditional hot air drying, and the specific steps are as follows:

[0069] (1) Cleaning: Select mature and plump wolfberries of uniform size, remove impurities and petioles, rinse with clean water three times for 20 seconds each time to remove dirt attached to the surface of the wolfberries, air dry naturally, and finally refrigerate at 5°C for later use;

[0070] (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at room temperature with a mass concentration of 20 g / L for 45 min, remove them and rinse them with clean water for 3 times, each time for 10 s to wash away the dewaxing solution remaining on the surface of the wolfberries, and finally air dry them naturally;

[0071] (3) Drying: Spread the dewaxed wolfberries on a tray, place the tray with the wolfberries in a hot air dryer with a wind speed of 2 m / s, first dry at 40°C for 3 h, then dry at 50°C for 6 h; then dry at 60°C for 20 h. After drying, the wolfberry dried fruit is obtained, which is packaged and refrigerated at 5°C.

[0072] Performance Test:

[0073] Moisture content: The moisture content of the wolfberry dried fruit prepared in the embodiment and the comparative example was measured by the direct drying method described in the national standard (GB 5009.3-2016). Three samples were taken from each group for measurement, and the average value was taken. The results are shown in Table 1.

[0074] Total sugar content: The total sugar content of the wolfberry dried fruit prepared in the embodiment and the comparative example was measured using the Chinese agricultural industry standard (NY / T 2332-2013). Three samples were taken from each group for measurement, and the average value was taken. The results are shown in Table 1.

[0075] Rehydration rate: Take the wolfberry dried fruits prepared in the embodiment and the comparative example, add them into water at 60°C and 100°C and soak them for 30 minutes respectively, calculate the rehydration rate, repeat 3 times, take the average value, and the results are shown in Table 1;

[0076] Extraction of Lycium barbarum polysaccharide: Take the dried Lycium barbarum prepared in the embodiment and comparative example, crush it, add distilled water (solid-liquid ratio 1:20, w / v), and extract at 70° C. for 2 h. After extraction, filter with gauze, centrifuge (7000rpm, 15min), filter with suction, concentrate the extract to 1 / 4 of the original volume with a rotary evaporator, add 4 times the volume of anhydrous ethanol, stand at 4°C for 12h to precipitate polysaccharides, and freeze-dry the precipitate to obtain a crude extract of wolfberry polysaccharide. Add 1 / 3 volume of Sevage reagent (chloroform: n-butanol is 4:1) to the crude extract of wolfberry polysaccharide, stir magnetically for 30min, centrifuge (6000rpm, 8min), pass the supernatant through 0.88μm, 0.45μm filter membranes, put into a dialysis bag and dialyze for 3 days, changing water every 6h. The dialyzed solution is subjected to rotary evaporation, alcohol precipitation, and freeze-drying to obtain wolfberry polysaccharide. The phenol-sulfuric acid method is used to determine the yield of wolfberry polysaccharide, and the gel permeation chromatography method is used to determine the molecular weight of wolfberry polysaccharide. The results are shown in Table 2.

[0077] Table 1 Properties of wolfberry dried fruit

[0078]

[0079] Data Analysis:

[0080] It can be seen from the data of Example 1 and Comparative Example 1 in Table 1 that the low-temperature dewaxing treatment adopted by the present invention helps to increase the total sugar content and rehydration rate in the wolfberry dried fruit, and improves the uniformity of the appearance color and reduces the color difference.

[0081] It can be seen from the data of Example 1 and Comparative Examples 2-3 in Table 1 that the freeze-thaw treatment adopted in the present invention helps to reduce the water content of wolfberry dried fruit and improve the rehydration rate, among which the adoption of the gradient cooling process can further reduce the water content of wolfberry dried fruit and improve the rehydration rate, and most importantly, the adoption of the gradient cooling process increases the total sugar content.

[0082] It can be seen from the data of Example 1 and Comparative Example 4 in Table 1 that the positive pressure-negative pressure conversion adopted in the microwave drying of the present invention effectively improves the rehydration rate and the total sugar content.

[0083] It can be seen from the data of Example 1 and Comparative Example 5 in Table 1 that, compared with traditional hot air drying, the wolfberry dried fruit prepared by the present invention has a significantly increased total sugar content of 41.4%, and the rehydration rate and appearance color are improved.

[0084] Table 2 Properties of Lycium barbarum polysaccharides

[0085]

[0086] Data Analysis:

[0087] It can be seen from Example 1 and Comparative Example 1 that the low-temperature dewaxing treatment adopted by the present invention is helpful to improve the yield of wolfberry polysaccharides and significantly reduce the molecular weight of the polysaccharides.

[0088] It can be seen from Example 1 and Comparative Examples 2-3 that the freeze-thaw treatment adopted in the present invention is helpful to improve the yield of Lycium barbarum polysaccharides, wherein the gradient cooling process has a significant effect on the molecular weight of Lycium barbarum polysaccharides.

[0089] It can be seen from Example 1 and Comparative Example 4 that the positive pressure-negative pressure conversion used in the microwave drying of the present invention is helpful to improve the yield of Lycium barbarum polysaccharides, and most importantly, significantly reduce the molecular weight of Lycium barbarum polysaccharides.

[0090] It can be seen from Example 1 and Comparative Example 5 that the present invention significantly improves the yield of Lycium barbarum polysaccharides compared with traditional hot air drying.

[0091] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A method for processing wolfberry dried fruit, characterized in that: The following steps are involved: (1) Cleaning: Rinse the wolfberries with clean water, air dry naturally, and set aside; (2) Dewaxing: Soak the washed wolfberries in a sodium carbonate solution at a temperature of 0±0.5°C for 30-50 min, rinse with water, and finally air dry naturally; (3) Freeze-thaw: Spread the dewaxed wolfberries on a tray, place the tray with wolfberries in a refrigerator, gradually cool it to -25±5°C, freeze it at -25±5°C for 2-4h, and finally thaw it naturally; (4) Drying: Spread the frozen and thawed wolfberries on a tray, place the tray containing the wolfberries in a microwave dryer, and dry them in a nitrogen atmosphere at a positive pressure environment, a power of 800-1200 W, and a temperature of 20-30° C. for 50-70 min, then at a negative pressure environment, a power of 400-600 W, and a temperature of 20-30° C. for 100-140 min, then at a positive pressure environment, a power of 800-1200 W, and a temperature of 20-30° C. for 20-40 min, then at a negative pressure environment, a power of 400-600 W, and a temperature of 20-30° C. for 40-80 min, and then perform vacuum microwave drying to obtain dried wolfberries.

2. The method for processing wolfberry dried fruit according to claim 1, characterized in that: In the step (1), the wolfberries are those with impurities removed and petioles of uniform size, mature and plump.

3. The method for processing wolfberry dried fruit according to claim 1, characterized in that: The clean water flushing in step (1) is performed by flushing with clean water 2-4 times, each time for 5-20 seconds.

4. The method for processing wolfberry dried fruit according to claim 1, characterized in that: The mass concentration of the sodium carbonate solution in step (2) is 15-25 g / L.

5. The method for processing wolfberry dried fruit according to claim 1, characterized in that: The clean water flushing in step (2) is performed by flushing with clean water 2-4 times, each time for 5-20 seconds.

6. The method for processing wolfberry dried fruit according to claim 1, characterized in that: The gradient cooling in step (3) is: firstly, cooling from room temperature to 0°C at a cooling rate of 1°C / min, then cooling from 0°C to -10°C at a cooling rate of 0.5°C / min, and then cooling from -10°C to -25±5°C at a cooling rate of 0.1°C / min.

7. The method for processing wolfberry dried fruit according to claim 1, characterized in that: The vacuum microwave drying step in step (4) is as follows: first, in a negative pressure environment, at a power of 400-600 W, at a temperature of 40-50° C., drying for 40-80 min; then, in a negative pressure environment, at a power of 0 W, at a temperature of 40-60° C., for 50-70 min; and then, in a negative pressure environment, at a microwave power of 250-350 W, at a temperature of 40-50° C., drying for 420-540 min.

8. The method for processing wolfberry dried fruit according to claim 1, characterized in that: In the step (4), the positive pressure is an absolute pressure of 1±0.2 MPa, and the negative pressure is an absolute pressure of 0.05±0.01 MPa.

9. The method for processing wolfberry dried fruit according to claim 1, characterized in that: The water content of the wolfberry dried fruit is lower than 13%, and the total sugar content is not lower than 56%.

10. An application of wolfberry dried fruit according to claims 1-9, characterized in that: Used in food processing.

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