Method for preparing D-allulose crystals

Abstract

This invention relates to the field of crystallization and purification, specifically to a method for preparing D-allulose crystals. The method includes: (1) mixing a concentrated D-allulose solution with D-allulose seed crystals to obtain a mixture; (2) subjecting the mixture to pre-crystallization and cooling crystallization under intermittent ultrasonic waves to obtain a slurry; and (3) performing solid-liquid separation on the slurry to obtain D-allulose crystals and a mother liquor. This method can achieve a high crystallization yield in a short time, produces crystallized products with uniform particle size, and operates under mild conditions. The process is simple, requires less equipment, has lower costs, is easily industrialized, avoids the use of organic reagents, and has minimal environmental pollution, thus showing good industrialization prospects.

Description

Technical Field

[0001] This invention relates to the field of crystallization and purification, and specifically to a method for preparing D-allulose crystals. Background Technology

[0002] D-Allulose is a C-3 epimer of D-fructose, with a sweetness equivalent to 70% of sucrose and calories equivalent to 0.3% of sucrose. It can be used as a sucrose substitute in the food and pharmaceutical industries. D-Allulose has the effect of controlling obesity and diabetes, and can significantly inhibit weight gain and abdominal fat accumulation.

[0003] However, D-allulose is highly water-soluble, making crystallization difficult. Spray drying also causes it to deliquesce and result in poor quality. Therefore, developing a suitable crystallization process is crucial for the development of the D-allulose industry.

[0004] Currently, there are generally three approaches to the commonly used aqueous crystallization technology for D-allulose. The first approach involves adjusting the supersaturation of the crystallization solution by changing the relationship between temperature and solubility, as disclosed in TW100110374 and CN201780066740.7. The second approach involves continuously reducing the water content in the crystallization mother liquor through evaporation to increase the crystallization yield, as disclosed in CN201910876767.3. However, this method requires high energy consumption for evaporation and concentration, and the high temperature can easily cause caramelization of the sugar solution, affecting the product color. The third approach involves two-step crystallization: first, crystallization through concentration; then, when the concentration of the concentrated crystallization mother liquor is too high, crystallization is carried out at a lower temperature, as disclosed in CN201911015344.9 and CN201680069967.2. This method combines the advantages of the second and third approaches to some extent, but ultimately cannot avoid the problems of small evaporation area, inefficient heat transfer, and susceptibility to browning.

[0005] Furthermore, current conventional crystallization techniques have several disadvantages. First, the D-allulose concentrate itself contains a small amount of gas, which easily forms microbubbles within the liquid due to temperature changes, affecting microscopic mass transfer. Second, the high viscosity of the liquid causes voids (i.e., microbubbles) to form between the D-allulose crystal particles and the D-allulose concentrate after the seed crystals are added, making it difficult for D-allulose molecules in the liquid to contact the seed crystal particles, thus affecting the crystallization rate. Third, high viscosity reduces the speed of molecular motion at the microscale, also decreasing the crystallization rate of D-allulose. Fourth, conventional stirring creates dead zones in the container, where crystals tend to agglomerate, affecting not only the quality and yield of the crystallized product but also posing a risk of clogging pipelines. In addition, current crystallization methods often use environmentally polluting organic reagents.

[0006] Therefore, the current D-allulose crystallization process still suffers from problems such as low crystallization yield, uneven crystal particles, easy clumping, long processing time, and high production costs, while also causing environmental pollution. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned problems in the prior art and provide a method for D-allulose crystallization. This method has mild operating conditions, can obtain a high crystallization yield in a short time without the use of organic solvents, and produces uniform crystal particles that are not prone to clumping. It is highly efficient and the production process is environmentally friendly.

[0008] To achieve the above objectives, the present invention provides a method for preparing D-allulose crystals, the method comprising:

[0009] (1) Mix D-allulose concentrate with D-allulose seed crystals to obtain a mixture;

[0010] (2) Under the intermittent presence of ultrasound, the mixture is subjected to pre-crystallization and cooling crystallization to obtain a slurry;

[0011] (3) The slurry is subjected to solid-liquid separation to obtain D-aloxose crystals and mother liquor.

[0012] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0013] 1. The method of this invention can achieve a high crystallization yield in a relatively short time. Furthermore, the obtained crystal particles are less prone to clumping, have uniform particle size, and possess high quality.

[0014] 2. The method of the present invention has mild operating conditions, simple process flow, commonly used and widely available equipment, low production cost, can be produced without the use of organic solvents, is environmentally friendly, and is easy to scale up industrially. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] In a first aspect, the present invention provides a method for preparing D-allulose crystals, the method comprising:

[0017] (1) Mix D-allulose concentrate with D-allulose seed crystals to obtain a mixture;

[0018] (2) Under the intermittent presence of ultrasound, the mixture is subjected to pre-crystallization and cooling crystallization to obtain a slurry;

[0019] (3) The slurry is subjected to solid-liquid separation to obtain D-aloxose crystals and mother liquor.

[0020] According to the present invention, a preferred method for obtaining D-allulose concentrate includes: purifying a D-allulose solution to be purified to obtain a purified D-allulose solution; concentrating the purified D-allulose solution to obtain a D-allulose concentrate; wherein the purity of the purified D-allulose solution is not less than 98.5% by weight (e.g., 98.5% by weight, 98.7% by weight, or 99% by weight).

[0021] The D-allulose solution to be purified can be any one or a mixture of two or three of the following materials: naturally extracted, enzymatically synthesized, or chemically synthesized. For example, the D-allulose solution to be purified can be obtained by converting fructose through the catalytic conversion of D-allulose 3-epimerase.

[0022] The purification method is not particularly limited and can be any conventional choice in the art, as long as the purity of the purified D-allulose solution is not less than 98.5% by weight. For example, the purification method can employ ion exchange chromatography or simulated moving bed separation technology.

[0023] According to the present invention, the concentration of the D-allulose concentrate is not particularly limited and can be selected within a wide range. However, in order to further ensure a high crystallization yield in a shorter time and to make the crystal particles more uniform, the concentration of the D-allulose concentrate is preferably 830-930 g / L (for example, 830 g / L, 850 g / L, 870 g / L, 890 g / L, 900 g / L, 930 g / L), more preferably 850-900 g / L, and even more preferably 880 g / L.

[0024] It is understandable that "purity" and "concentration" are different concepts. In actual production, solutions containing D-allulose often contain other sugars or alcohols (dry matter) in addition to D-allulose. Purity refers to the ratio of the weight of D-allulose to the total weight of dry matter in the solution; while concentration refers to the ratio of the sum of the weights of all sugars and alcohols to the total weight of the solution.

[0025] The concentration equipment is not subject to any particular restrictions, but in order to facilitate operation during industrial scale-up and lower the threshold for process technology scale-up, single-effect, double-effect, triple-effect, and quadruple-effect concentration equipment can be used.

[0026] According to the present invention, in order to avoid the caramelization reaction caused by excessively high local temperature during the concentration process of D-allulose, which would lead to browning of the concentrate and result in the final D-allulose crystals being yellow, it is preferable that the temperature during the concentration process be controlled not higher than 50°C (for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C).

[0027] According to the present invention, the concentration method is not particularly limited and can be any conventional choice in the art. Preferably, the concentration method is vacuum concentration. It is understood that in vacuum concentration, the lower the concentration pressure, the better, but taking into account cost and ease of operation, the concentration pressure is based on the principle of achieving rapid concentration of the purified D-allulose solution at a lower temperature.

[0028] According to the present invention, the amount of D-allulose seed crystals can be selected within a wide range. However, in order to further ensure a high crystallization yield in a shorter time and to make the crystal particles more uniform, preferably, the amount of D-allulose seed crystals is 1-50g (e.g., 1g, 5g, 10g, 20g, 30g, 40g, 50g) relative to 1L of D-allulose concentrate, more preferably 10-30g, and even more preferably 20g.

[0029] According to the present invention, preferably, the total time for the pre-crystallization and cooling crystallization is 80-100 hours (for example, it can be 80 hours, 85 hours, 90 hours, 95 hours, or 100 hours).

[0030] According to the present invention, preferably, in step (2), the method of providing ultrasound is as follows: ultrasound is provided for 10-60 seconds every 10-120 seconds, and this is continued for 1-10 minutes. Then, the ultrasound is turned off and maintained for 1-3 hours. The operation of ultrasound and turning off ultrasound is repeated until the pre-crystallization and cooling crystallization are completed. More preferably, the method of providing ultrasound is as follows: ultrasound is provided for 10-30 seconds every 10-30 seconds, and this is continued for 3-7 minutes. Then, the ultrasound is turned off and maintained for 1.5-2.5 hours. The operation of ultrasound and turning off ultrasound is repeated until the pre-crystallization and cooling crystallization are completed. For example, ultrasound can be provided for 20 seconds every 20 seconds, and this is continued for 5 minutes. Then, the ultrasound is turned off and maintained for 2 hours. Then, the operation of ultrasound and turning off ultrasound is repeated until the pre-crystallization and cooling crystallization are completed. The inventors of the present invention have found in their research that the method of providing ultrasound as described above can promote the movement and collision of molecules in the mixture, accelerate molecular mixing at the microscale, promote mass transfer, accelerate crystallization, and also quickly remove bubbles in the liquid, eliminate cavities on the surface of the seed crystals, promote the vibration of crystal particles without dead angles, avoid agglomeration, and further make the crystal particles more uniform. Using the ultrasonic method described above results in lower energy consumption and avoids continuous ultrasonic action, leading to higher energy in the mixture.

[0031] It is understandable that an ultrasonic probe can be inserted below the surface of the mixture to provide ultrasonic waves.

[0032] According to the present invention, in order to further ensure a high crystallization yield in a shorter time and to make the crystal particles more uniform, the ultrasonic power is preferably 100-1000 W / m. 3 Mixture (e.g., 100W / m) 3 Mixed material, 200W / m 3 Mixed material, 300W / m 3 Mixed material, 400W / m 3 Mixed material, 500W / m 3 Mixed material, 600W / m 3 Mixed material, 700W / m 3 Mixed material, 800W / m 3 Mixed material, 900W / m 3 Mixed material, 1000W / m 3 (mixture), more preferably 300-500 W / m 3 The mixture, preferably 400W / m 3 Mixture.

[0033] According to the present invention, in order to further ensure a high crystallization yield in a shorter time and to make the crystal particles more uniform, the pre-crystallization conditions preferably include: a temperature of 45-55°C (e.g., 45°C, 47°C, 49°C, 50°C, 52°C, 53°C, 55°C), a time of 20-40 h (e.g., 20 h, 25 h, 30 h, 35 h, 40 h), and a stirring rate of 50-150 rpm (e.g., 50 rpm, 70 rpm, 90 rpm, 100 rpm, 120 rpm, 135 rpm, 150 rpm). More preferably, the stirring rate of the pre-crystallization is 90-120 rpm.

[0034] According to the present invention, in order to further ensure a high crystallization yield in a shorter time and to make the crystal particles more uniform, the preferred conditions for the cooling crystallization include: cooling at a cooling rate of 0.8-1.5℃ / h (e.g., 0.8℃ / h, 1℃ / h, 1.2℃ / h, 1.3℃ / h, 1.5℃ / h), cooling to 22-28℃ (e.g., 22℃, 24℃, 25℃, 26℃, 28℃) and maintaining the temperature at 22-28℃, with a stirring rate of 50-150 rpm (e.g., 50 rpm, 70 rpm, 90 rpm, 100 rpm, 120 rpm, 135 rpm, 150 rpm). Cooling crystallization is generally completed in 40-70 hours. Stirring is performed during the cooling process and during the process of the temperature reaching and maintaining the target temperature. It is understood that cooling can bring the mixture to a supersaturated state, thereby promoting crystallization. The inventors of this invention discovered during their research that by employing the conditions described above, particularly the cooling rate, drastic changes in conditions can be avoided, thus promoting crystallization while preventing any impact on the purity and uniformity of the crystal particles. More preferably, the stirring rate during the cooling crystallization is 90-120 rpm.

[0035] According to the present invention, preferably, the solid-liquid separation is selected from at least one of centrifugal separation and filtration separation. It is understood that the solid-liquid separation may also be a combination of centrifugal separation and filtration separation.

[0036] According to the present invention, after solid-liquid separation, the D-allulose crystals can be dried. The drying method can be a conventional choice in the art, preferably at least one of fluidized bed drying and vacuum drying.

[0037] According to the present invention, in order to further improve the crystallization yield, preferably, a portion of the mother liquor is taken and returned to be mixed with the purified D-allulose solution and concentrated together; wherein, the amount of the portion of mother liquor is such that after it is returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight; for example, if the purity of the purified D-allulose solution is 99.0% by weight, then the amount of mother liquor returned to be mixed with the purified D-allulose solution is such that the purity of the mixed material is not less than 98.5% by weight.

[0038] According to the present invention, the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0039] According to a particularly preferred embodiment of the present invention, D-allulose crystallization is carried out according to the following method:

[0040] (1) The D-allulose solution to be purified is purified to obtain a purified D-allulose solution with a purity of not less than 98.5% by weight.

[0041] Take the purified D-allulose solution as described above and concentrate it under reduced pressure at a temperature not exceeding 50°C until the concentration is 870-890 g / L, to obtain a concentrated D-allulose solution.

[0042] Take the D-allulose solution concentrate as described above and mix it with D-allulose seed crystals (the amount of D-allulose seed crystals is 18-22g relative to 1L of D-allulose solution concentrate), and stir it to make the D-allulose seed crystals more evenly dispersed to obtain a mixture.

[0043] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 380-420W / m. 3 Mix the materials and set the ultrasonic treatment to be performed every 18-22 seconds for 18-22 seconds. Continue this for 4-6 minutes, then turn off the ultrasonic treatment and maintain it for 1.8-2.2 hours. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0044] The pre-crystallization conditions include: a temperature of 49-51℃, a time of 40-42 hours, and a stirring rate of 95-105 rpm. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 0.9-1.1℃ / h to 24-26℃ and maintaining that temperature, with a stirring rate of 95-105 rpm during the cooling crystallization process. The cooling crystallization time is 40-42 hours, after which a slurry is obtained.

[0045] (3) The slurry is centrifuged in a centrifuge to obtain D-allulose crystals and mother liquor. The D-allulose crystals are then vacuum dried in a vacuum drying oven and weighed.

[0046] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0047] The present invention will be described in detail below through embodiments. In the following embodiments and test examples,

[0048] The ultrasonic circulating extractor, model GCXZ-2B, was purchased from Beijing Hongxianglong Biotechnology Co., Ltd.

[0049] The vacuum drying oven, model DZF-6050, was purchased from Shanghai Bozheng Industrial Co., Ltd.

[0050] The centrifugal filter, model SSC300, was purchased from Yongle Machinery Equipment Manufacturing Co., Ltd.

[0051] Allulose standard was purchased from Shanghai Lizhi Biotechnology Co., Ltd.

[0052] Example 1

[0053] This invention provides a method for illustrating the crystallization of D-allulose.

[0054] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0055] Take the purified D-allulose solution as described above and concentrate it under reduced pressure at 50°C to a concentration of 880 g / L to obtain a concentrated D-allulose solution.

[0056] Take 20L of the D-allulose solution concentrate as described above and mix it with 400g of D-allulose seed crystals (i.e., the amount of D-allulose seed crystals used is 20g relative to 1L of D-allulose solution concentrate), and stir it to make the D-allulose seed crystals more evenly dispersed to obtain a mixture.

[0057] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 400W / m. 3Mix the materials and set the ultrasonic treatment to 20 seconds every 20 seconds. Continue this for 5 minutes, then turn off the ultrasonic treatment and maintain it for 2 hours. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0058] The pre-crystallization conditions include: a temperature of 50°C, a time of 40 hours, and a stirring rate of 100 rpm. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 1°C / hour to 25°C and maintaining that temperature, with a stirring rate of 100 rpm during the cooling crystallization process. The cooling crystallization time is 40 hours, after which a slurry is obtained.

[0059] (3) The slurry is centrifuged in a centrifuge to obtain D-allulose crystals and mother liquor. The D-allulose crystals are then vacuum dried in a vacuum drying oven and weighed.

[0060] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0061] Example 2

[0062] This invention provides a method for illustrating the crystallization of D-allulose.

[0063] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0064] Take the purified D-allulose solution as described above and concentrate it under reduced pressure at 45°C to a concentration of 850 g / L to obtain a concentrated D-allulose solution.

[0065] Take 20L of the D-allulose solution concentrate as described above and mix it with 200g of D-allulose seed crystals (i.e., the amount of D-allulose seed crystals used is 10g relative to 1L of D-allulose solution concentrate), and stir it to make the D-allulose seed crystals more evenly dispersed to obtain a mixture.

[0066] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 300W / m. 3 Mix the materials and set the ultrasonic treatment to 10 seconds every 10 seconds. Continue this for 7 minutes, then turn off the ultrasonic treatment and maintain it for 1.5 hours. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0067] The pre-crystallization conditions include: a temperature of 45℃, a time of 30 hours, and a stirring rate of 90 rpm. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 0.8℃ / h to 28℃ and maintaining that temperature, with a stirring rate of 90 rpm during the cooling crystallization process. The cooling crystallization time is 65 hours, after which a slurry is obtained.

[0068] (3) The slurry is centrifuged in a centrifuge to obtain D-allulose crystals and mother liquor. The D-allulose crystals are then vacuum dried in a vacuum drying oven and weighed.

[0069] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0070] Example 3

[0071] This invention provides a method for illustrating the crystallization of D-allulose.

[0072] (1) The D-allulose solution to be purified was purified by a simulated moving bed separation technique to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0073] Take the purified D-allulose solution as described above and concentrate it under reduced pressure at 40°C to a concentration of 900 g / L to obtain a concentrated D-allulose solution.

[0074] Take 20L of the D-allulose solution concentrate as described above and mix it with 600g of D-allulose seed crystals (i.e., the amount of D-allulose seed crystals used is 30g relative to 1L of D-allulose solution concentrate), and stir it to make the D-allulose seed crystals more evenly dispersed to obtain a mixture.

[0075] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 500W / m. 3 Mix the materials and set the ultrasonic treatment to 30 seconds every 30 seconds. Continue this for 3 minutes, then turn off the ultrasonic treatment and maintain it for 2.5 hours. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0076] The pre-crystallization conditions include: a temperature of 55℃, a time of 20 hours, and a stirring rate of 120 rpm. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 1.5℃ / h to 22℃ and maintaining that temperature, with a stirring rate of 120 rpm during the cooling crystallization process. The cooling crystallization time is 70 hours, after which a slurry is obtained.

[0077] (3) The slurry is centrifuged in a centrifuge to obtain D-allulose crystals and mother liquor. The D-allulose crystals are then vacuum dried in a vacuum drying oven and weighed.

[0078] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0079] Example 4

[0080] This invention provides a method for illustrating the crystallization of D-allulose.

[0081] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0082] Take the purified D-allulose solution as described above and concentrate it under reduced pressure at 35°C to a concentration of 830 g / L to obtain a concentrated D-allulose solution.

[0083] Take 20L of the D-allulose solution concentrate as described above and mix it with 20g of D-allulose seed crystals (i.e., the amount of D-allulose seed crystals used is 1g relative to 1L of D-allulose solution concentrate), and stir it to make the D-allulose seed crystals more evenly dispersed to obtain a mixture.

[0084] (2) An ultrasonic circulating extractor is used. The ultrasonic probe is inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 100W / m. 3 Mix the materials and set the ultrasonic treatment to 10 seconds every 10 seconds. Continue this for 1 minute, then turn off the ultrasonic treatment and maintain it for 1 hour. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0085] The pre-crystallization conditions include: a temperature of 50℃, a time of 20 hours, and a stirring rate of 50 rpm. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 1.5℃ / h to 22℃ and maintaining that temperature, with a stirring rate of 50 rpm during the cooling crystallization process. The cooling crystallization time is 70 hours, after which a slurry is obtained.

[0086] (3) The slurry is centrifuged in a centrifuge to obtain D-allulose crystals and mother liquor. The D-allulose crystals are then vacuum dried in a vacuum drying oven and weighed.

[0087] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0088] Example 5

[0089] This invention provides a method for illustrating the crystallization of D-allulose.

[0090] (1) The D-allulose solution to be purified was purified by continuous ion exchange chromatography to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0091] Take the purified D-allulose solution as described above and concentrate it under reduced pressure at 35°C to a concentration of 930 g / L to obtain a concentrated D-allulose solution.

[0092] Take 20L of the D-allulose solution concentrate as described above and mix it with 1000g of D-allulose seed crystals (i.e., the amount of D-allulose seed crystals used is 50g relative to 1L of D-allulose solution concentrate), and stir it to make the D-allulose seed crystals more evenly dispersed to obtain a mixture.

[0093] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 1000W / m. 3 Mix the materials and set the ultrasonic treatment to 60 seconds every 120 seconds. Continue this for 10 minutes, then turn off the ultrasonic treatment and maintain it for 3 hours. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0094] The pre-crystallization conditions include: a temperature of 55℃, a time of 20 hours, and a stirring rate of 150 rpm. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 1.5℃ / h to 22℃ and maintaining that temperature, with a stirring rate of 150 rpm during the cooling crystallization process. The cooling crystallization time is 70 hours, after which a slurry is obtained.

[0095] (3) The slurry is centrifuged in a centrifuge to obtain D-allulose crystals and mother liquor. The D-allulose crystals are then vacuum dried in a vacuum drying oven and weighed.

[0096] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0097] Example 6

[0098] D-allulose crystallization was performed according to the method in Example 1, except that during the 80 hours of pre-crystallization and cooling crystallization, ultrasound was performed for 20 seconds every 20 seconds, i.e., the ultrasound was not turned off.

[0099] Comparative Example 1

[0100] D-allulose crystallization was carried out according to the method of Example 1, except that ultrasound was not provided during pre-crystallization and cooling crystallization.

[0101] Comparative Example 2

[0102] Take 20L of the purified D-allulose solution obtained in Example 1, and crystallize D-allulose according to the method of CN201780066740.7. Record the time required to obtain the same weight of D-allulose crystals as obtained in Example 1, which is 130h.

[0103] Test case

[0104] The purity, crystallinity, and particle uniformity of the D-allulose crystals obtained in Examples 1-6 and Comparative Examples 1-2 were tested, and the presence of agglomeration was observed. The results are shown in Table 1. The obtained crystals refer to the D-allulose crystals obtained after solid-liquid separation of the slurry and drying, i.e., before the mother liquor was returned.

[0105] The purity was determined as follows: A D-allulose standard solution (10.0 mg / mL) was prepared using D-allulose standards and subsequently diluted to concentrations of 10.0 mg / mL, 8.0 mg / mL, 6.0 mg / mL, 4.0 mg / mL, 2.0 mg / mL, 1.0 mg / mL, 0.5 mg / mL, and 0.25 mg / mL. The peak area of ​​the D-allulose standard solution was determined using high-performance liquid chromatography (HPLC). A standard curve was plotted with the peak area (average of three parallel samples) on the ordinate and the solution concentration on the abscissa. The D-allulose crystals in Examples 1-6 and Comparative Examples 1-2 were then quantitatively analyzed based on the standard curve. The chromatographic conditions were as follows: The Agilent 1260 series high-performance liquid chromatography system included a G 1311C quaternary pump, a G 1316A column oven, a G 1329B autosampler, and a G 1236A differential detector. The column was a Waters Sugar-PakI (10 μm, 6.5 mm × 300 mm); the column temperature was 80 °C, the RID detection temperature was 55 °C, the mobile phase was water, and the flow rate was 0.4 mL / min. All samples were filtered through a 0.45 μm microfiltration membrane before injection.

[0106] The method for calculating the primary crystallization rate is as follows: Crystallization yield = (mass of D-allulose crystals) / (volume of D-allulose concentrate * concentration) * 100%.

[0107] The method for detecting particle uniformity is as follows: using 40-mesh and 60-mesh sieves, determine the proportion of the weight of D-allulose with a particle size in the range of 40-60 mesh to the total mass of D-allulose crystals. The higher the proportion, the better the uniformity.

[0108] Table 1

[0109]

[0110] As can be seen from the results in Table 1, Examples 1-6 using the technical solution of the present invention exhibit higher primary crystallization rates and purity, and the obtained crystal particle size distribution is more uniform, avoiding agglomeration and clumping in the crystals. Examples 1-3 show even better results. In contrast, Comparative Examples 1-2 show uneven crystallization rates, with uneven crystal particle size distribution and obvious agglomeration and clumping. Furthermore, the results from Examples 1, 6, and Comparative Example 1 demonstrate that the technical solution of the present invention can achieve a higher crystallization rate in a shorter time, thus significantly reducing time and improving efficiency.

[0111] Furthermore, the technical solution of this invention can achieve a high crystallization rate without the use of organic reagents, the production process is relatively safe, and it avoids pollution and residues from organic reagents, making it environmentally friendly. Moreover, the process is simple, the operating conditions are mild, the equipment requirements are low, the cost is low, it is easy to industrialize, and it has good prospects for industrialization.

[0112] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing D-allulose crystals, characterized in that, The method includes: (1) The D-allulose solution to be purified is purified to obtain a purified D-allulose solution with a purity of not less than 98.5% by weight; Take the purified D-allulose solution as described above, and concentrate it under reduced pressure at a temperature not exceeding 50°C until the concentration is 870-890 g / L to obtain a concentrated D-allulose solution. Take the D-allulose solution concentrate as described above and mix it with D-allulose seed crystals. The amount of D-allulose seed crystals used is 18-22g relative to 1L of D-allulose solution concentrate. Stir the mixture to make the D-allulose seed crystals more evenly dispersed, and obtain a mixture. (2) An ultrasonic circulating extractor is used. The ultrasonic probe is inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 380-420W / m. 3 Mix the materials and set the ultrasonic treatment to be performed every 18-22 seconds for 18-22 seconds. Continue this for 4-6 minutes, then turn off the ultrasonic treatment and maintain it for 1.8-2.2 hours. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed. The pre-crystallization conditions include: a temperature of 49-51℃, a time of 40-42h, and a stirring rate of 95-105rpm. After pre-crystallization, cooling crystallization is carried out, and the cooling crystallization conditions include: cooling at a rate of 0.9-1.1℃ / h to 24-26℃ and maintaining the temperature at 24-26℃, with a stirring rate of 95-105rpm during the cooling crystallization process; the cooling crystallization time is 40-42h, and after completion, a slurry is obtained. (3) The slurry is centrifuged in a centrifuge to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried in a vacuum drying oven and weighed; A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

Images