Crystallization method of psicose

Abstract

The invention relates to the technical field of crystallization, and provides a crystallization method of psicose. The method comprises the following steps: separating a psicose crude product solution by adopting a simulated moving bed method to obtain a psicose purified solution; evaporating the psicose purified liquid to constant weight to obtain a psicose concentrate; mixing the psicose concentrate, water and a psicose seed crystal to obtain a mixture; and cooling and crystallizing the mixture, and carrying out solid-liquid separation to obtain the psicose crystal. The method provided by the invention has the advantages of high crystallization yield, proper crystallization rate, full crystal form, simple preparation process, no use of organic reagents, environmental friendliness, economy, high efficiency, improvement of production efficiency and product quality, and low production cost, and brings innovation and improvement for the production process of psicose.

Description

Technical Field

[0001] The present invention relates to the field of crystallization technology, and in particular to a method for crystallizing psicose. Background Art

[0002] Allulose is a widely used drug and food additive. It usually exists in a crystalline form and is used to prepare products such as medicines, health products and foods. D-allulose, also known as D-glucitol or D-1,3,4,5,6-pentahydroxyhexanone, is a monosaccharide with a sweet taste similar to glucose. Compared with glucose, allulose has a lower calorie content and does not significantly affect blood sugar levels, so it has attracted much attention in the modern food and pharmaceutical industries.

[0003] Psicose is usually produced by bioconversion or chemical synthesis. Bioconversion methods involve the conversion of low-value sugars or sugar alcohols using enzymes or microorganisms. Chemical synthesis methods involve multi-step reactions on suitable substrates to form the Psicose structure. Psicose usually exists in a crystalline form for stable storage and application.

[0004] At present, common allulose crystallization processes include ethanol precipitation and direct cooling crystallization. The ethanol precipitation method requires a large amount of anhydrous ethanol, and explosion-proof equipment is used in the production process, which is costly; while the direct cooling crystallization method requires repeated heating and cooling due to the high saturation concentration, high viscosity and difficulty in crystallization of the allulose solution. The operation is complicated and the yield is low, which is not economical and efficient. Summary of the invention

[0005] In view of this, the present invention provides a method for crystallizing psicose. The method provided by the present invention is simple to operate, has a high yield, a suitable crystallization rate, full crystals with a crystal form, good product stability, high purity, and does not use organic solvents, is environmentally friendly, and is economical and efficient.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for crystallizing psicose, comprising the following steps:

[0008] The crude psicose solution is separated by a simulated moving bed method to obtain a psicose purified liquid; the psicose content in the psicose purified liquid is ≥98wt%;

[0009] evaporating the purified psicose liquid to a constant weight to obtain a psicose concentrate;

[0010] mixing the psicose concentrate, water and psicose seed crystals to obtain a mixture, wherein the mass of the water is 1% to 30% of the mass of the psicose concentrate;

[0011] The mixture is cooled and crystallized, and then solid-liquid separation is performed to obtain the psicose crystals; the starting temperature of the cooling and crystallization is 40-60°C, the end temperature is 25-30°C, and the cooling rate from the starting temperature to the end temperature is 0.5-1°C / h.

[0012] Preferably, the content of psicose in the crude psicose solution is 35-45 wt %.

[0013] Preferably, the method of mixing the psicose concentrate, water and psicose seed crystals is: first mixing the psicose concentrate and water, and then adding the psicose seed crystals.

[0014] Preferably, the mass percentage of the psicose seed crystals in the psicose concentrate is 0.1% to 5%.

[0015] Preferably, the mesh size of the psicose seed crystals is 10 to 50 meshes.

[0016] Preferably, the cooling crystallization is carried out under stirring conditions, and the stirring rate is 10 to 150 rpm.

[0017] Preferably, the cooling crystallization time is 36 to 120 hours.

[0018] Preferably, the cooling crystallization time is 48 hours.

[0019] Preferably, the temperature reduction crystallization is carried out in a rotary evaporator with a temperature control system.

[0020] Preferably, the solid-liquid separation also obtains a mother liquor; a portion of the mother liquor is mixed with the purified psicose solution, and the psicose content in the obtained mixed solution is controlled to be not less than 98%; and the remaining mother liquor is mixed with the crude psicose solution to be separated.

[0021] The invention provides a method for crystallizing psicose, comprising the following steps: separating a psicose crude solution by a simulated moving bed method to obtain a psicose purified solution; the psicose content in the psicose purified solution is ≥98wt%; evaporating the psicose purified solution to a constant weight to obtain a psicose concentrate; mixing the psicose concentrate, water and psicose seed crystals to obtain a mixture; the mass of the water is 1% to 30% of the mass of the psicose concentrate; cooling and crystallizing the mixture, and then performing solid-liquid separation to obtain the psicose crystals; the starting temperature of the cooling and crystallization is 50 to 55°C, the end temperature is 25 to 30°C, and the cooling rate from the starting temperature to the end temperature is 0.5 to 1°C / h. The present invention adds seed crystals when the solid content is relatively low, and utilizes the low viscosity and excellent mass transfer performance of the sugar solution at this time to facilitate molecular movement and crystal growth, which not only shortens the entire crystallization cycle, but also improves the crystal yield. The present invention adopts a cooling crystallization method, and significantly improves the crystallization yield of allulose by optimizing the cooling rate and the crystallization temperature. By controlling the crystallization conditions during the cooling process, it is also possible to achieve precise control of the crystallization process, so that the product has a more uniform lattice structure, improves product stability, reduces the presence of impurities, and improves product purity. The results of the embodiment show that under optimal conditions, the purity of allulose crystals can reach 99.98%, and the crystallization yield can reach more than 72%, which is significantly improved compared with the traditional process.

[0022] In addition, the crystallization method provided by the present invention is simpler and easier to operate, has a short crystallization cycle, does not require repeated heating and cooling processes, and omits the step of using a large amount of ethanol precipitation in the traditional method, thereby reducing the expensive equipment investment required for explosion-proof production and product collection, effectively reducing production costs, and is also more environmentally friendly, reducing waste generation, and helping to improve the sustainability of the process.

[0023] In addition, the crystallization method of the present invention reduces steps and energy consumption, improves production efficiency, reduces production costs, is suitable for large-scale production, and can be widely used to prepare products of different purities of allulose to meet the needs of different fields.

[0024] Furthermore, the present invention performs cooling crystallization in a rotary evaporator with a temperature control system, which can increase the grain size of the psicose crystals, thereby obtaining large-particle crystals, which helps to improve the quality and performance of the product.

[0025] Furthermore, by optimizing the seed crystal size, the present invention can ensure that the seed crystal is neither too large to cause uneven crystal size nor too small to cause a slow crystallization process, thereby obtaining a more uniform crystal size distribution.

[0026] In summary, the crystallization method provided by the present invention is economical and efficient, the crystallization process is controllable, the crystallization rate is appropriate, the crystals are full and have a crystal form, it is environmentally friendly and sustainable, and has a wide range of applications. It has achieved significant beneficial effects in many aspects, not only improving production efficiency and product quality, but also reducing production costs, bringing innovation and improvement to the production process of allulose. DETAILED DESCRIPTION

[0027] The present invention provides a method for crystallizing psicose, comprising the following steps:

[0028] The crude psicose solution is separated by a simulated moving bed method to obtain a psicose purified liquid; the psicose content in the psicose purified liquid is ≥98wt%;

[0029] evaporating the purified psicose liquid to a constant weight to obtain a psicose concentrate;

[0030] mixing the psicose concentrate, water and psicose seed crystals to obtain a mixture, wherein the mass of the water is 1% to 30% of the mass of the psicose concentrate;

[0031] The mixture is cooled and crystallized, and then solid-liquid separation is performed to obtain the psicose crystals; the starting temperature of the cooling and crystallization is 40-60°C, the end temperature is 25-30°C, and the cooling rate from the starting temperature to the end temperature is 0.5-1°C / h.

[0032] The present invention adopts a simulated moving bed method to separate a crude psicose solution to obtain a purified psicose solution; the psicose content in the purified psicose solution is ≥98wt%. In the present invention, the components in the crude psicose solution include psicose and fructose, the psicose content in the crude psicose solution is preferably 35-45%, more preferably 40wt%, and the solvent of the crude psicose solution is water.

[0033] In a specific embodiment of the present invention, the crude psicose solution is preferably introduced into a simulated moving bed device, and then the psicose is separated by controlling the operating conditions to collect the psicose component with a purity of more than 98%, thereby obtaining the psicose purified solution.

[0034] The present invention has no special requirements for the specific operating methods and conditions of the simulated moving bed method, and those familiar to those skilled in the art can be adopted. In a specific embodiment of the present invention, it is preferred to first perform a single column experiment on the crude allulose solution, draw a single column separation curve, set the initial parameters of the simulated moving bed according to the separation curve data, and then pump the sample into the simulated moving bed device, operate the parameters, change the material inlet and outlet positions, simulate the relative movement of the resin and the mobile phase, collect the fast components and the slow components, detect and optimize the parameters, and continuously cycle to finally obtain a qualified purified solution.

[0035] After obtaining the purified psicose liquid, the present invention evaporates the purified psicose liquid to constant weight to obtain a psicose concentrate. In the present invention, the evaporation is preferably rotary evaporation, and the temperature of the rotary evaporation is preferably 60° C. The present invention rotary evaporates the purified psicose liquid to constant weight (i.e., evaporates to dryness, and the remainder is the psicose concentrate), which can ensure the accuracy of the subsequent water addition. If the rotary evaporation is not performed to constant weight, the subsequent water addition will cause errors.

[0036] After obtaining the psicose concentrate, the present invention mixes the psicose concentrate, water and psicose seed crystals to obtain a mixture. In the present invention, the method of mixing the psicose concentrate, water and psicose seed crystals is: firstly mix the psicose concentrate and water, and then add the psicose seed crystals. In the present invention, the mass of the water is 1% to 30% of the mass of the psicose concentrate, preferably 5% to 15%, which is equivalent to adding 10 to 300 g (i.e., 10 to 300 mL), preferably 50 to 150 g, of water to 1 kg of psicose concentrate. In the present invention, when too little water is added to the psicose concentrate, the fluidity of the crystallization solution is poor, and when too much water is added, part of the seed crystals will dissolve when the seed crystals are added thereto, and the yield will be reduced.

[0037] In the present invention, the mass percentage of the psicose seed crystals in the psicose concentrate is 0.1% to 10%, preferably 0.5% to 2%. In a specific embodiment of the present invention, the mass percentage of the psicose seed crystals in the psicose concentrate is 0.5% to 2%, which is the best. When the amount of seed crystals added is less than 0.5%, the total crystallization time will be extended; when the amount of seed crystals added is higher than 2%, the crystallization rate will be accelerated, but the crystal form may be smaller.

[0038] In the present invention, the mesh size of the psicose seed crystals is preferably 10 to 50 meshes, more preferably 20 to 40 meshes; the present invention controls the size of the psicose seed crystals within the above range, which can ensure a faster crystallization process and obtain crystals of uniform size; if the size of the psicose seed crystals is too large, the number of seed crystals is insufficient, which easily leads to crystallization from spontaneously formed nuclei, resulting in a large final crystal size distribution range and uneven crystal size; if the size of the psicose seed crystals is too small, it is easy to cause a slow crystallization process.

[0039] After obtaining the mixture, the present invention cools and crystallizes the mixture, and then performs solid-liquid separation to obtain psicose crystals. In the present invention, the starting temperature of the cooling crystallization is 40-60°C, preferably 40°C, 50°C or 60°C; the terminal temperature of the cooling crystallization is 25-30°C, preferably 30°C, and the cooling rate from the starting temperature to the terminal temperature is 0.5-1°C / h, preferably 1°C / h. In the present invention, a starting temperature that is too high or too low will affect the overall crystallization rate, resulting in a prolonged crystallization time; a cooling rate higher than 1°C / h will result in an accelerated crystallization rate, uneven crystal size, and low psicose yield and purity; a cooling rate lower than 0.5°C / h will result in a slow crystallization rate.

[0040] In the present invention, the cooling crystallization is preferably carried out under stirring conditions, and the stirring rate is preferably 10 to 150 rpm, more preferably 50 to 100 rpm; the present invention controls the stirring rate within the above range, which can obtain a higher crystallization yield in a shorter time, and make the crystal particles more uniform and less likely to form agglomerates. When the stirring rate is too fast or too slow, it will lead to uneven crystal size, affecting the overall crystallization rate.

[0041] In the present invention, the cooling crystallization time is preferably 36 to 120 hours, more preferably 36 to 72 hours, and further preferably 48 hours. Too low or too high a crystallization time will result in a low crystallization yield.

[0042] In the present invention, the temperature reduction crystallization is preferably carried out in a rotary evaporator with a temperature control system.

[0043] After solid-liquid separation, the present invention preferably dries the obtained psicose crystals. The present invention has no special requirements for the drying conditions, and those known to those skilled in the art can be used. In the present invention, the purity of the psicose crystals is 99.8% (w / w) or more.

[0044] In the present invention, the solid-liquid separation also obtains a mother liquor; the present invention preferably mixes part of the mother liquor with the purified psicose solution, controls the psicose content in the obtained mixed solution to be not less than 98%, and then performs subsequent evaporation, water addition, seed addition, cooling and crystallization on the obtained mixed solution; mixes the remaining part of the mother liquor with the crude psicose solution to be separated, and continues the simulated moving bed separation process.

[0045] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] Example 1

[0047] (1) The crude psicose solution to be purified (wherein the psicose content was 40 wt%) was treated using simulated moving bed separation technology to obtain a purified psicose solution with a purity of 98.3%.

[0048] (2) The purified psicose solution was concentrated by a rotary evaporation concentration device at 60° C. until a stable psicose concentrate was obtained.

[0049] (3) 92.5 g of the above-mentioned psicose concentrate was added with 8 ml of water, and the mixture was thoroughly mixed. Then, 1.0175 g of psicose seed crystals (the mass of the psicose seed crystals was 1.1% of the psicose concentrate, and the mesh size of the psicose seed crystals was 35-40 meshes) were added, and the mixture was stirred to ensure that the psicose seed crystals were evenly dispersed to obtain a mixture.

[0050] (4) The mixture was placed in a rotary evaporator with a temperature control system for cooling crystallization. The initial temperature of the cooling crystallization was 60°C, and the temperature was reduced from 60°C to 30°C at a rate of 1°C / h. The temperature was maintained at 30°C for crystallization for 72 hours. During the 72-hour cooling crystallization process, the stirring rate was 100 rpm to obtain a slurry.

[0051] (5) The slurry was subjected to solid-liquid separation to obtain psicose crystals and mother liquor. The psicose crystals were oven dried and weighed. After the crystallization was completed, the psicose crystals were subjected to purity detection and yield calculation. The results showed that the yield was 50.8% and the purity was 99.95%. The color of the obtained crystals was not very white, with obvious crystal form, and the crystal size was 25 to 30 meshes.

[0052] Part of the mother liquor is mixed with the purified psicose solution to ensure that the purity of the mixed material is not less than 98wt%, and then concentrated and secondary crystallized. The remaining mother liquor is returned to the crude psicose solution to be purified to continue the separation and purification process.

[0053] Example 2

[0054] (1) The crude psicose solution to be purified (wherein the psicose content was 40 wt%) was treated using simulated moving bed separation technology to obtain a purified psicose solution with a purity of 98.5%.

[0055] (2) The purified psicose solution was concentrated by a rotary evaporation concentration device at 60° C. until a stable psicose concentrate was obtained.

[0056] (3) 128.6 g of the above-mentioned psicose concentrate was added with 10 ml of water, and the mixture was thoroughly mixed. Then, 1.286 g of psicose seed crystals (the mass of the psicose seed crystals was 1% of the psicose concentrate, and the mesh size of the psicose seed crystals was 35-40 meshes) were added, and the mixture was stirred to ensure that the psicose seed crystals were evenly dispersed to obtain a mixture.

[0057] (4) The mixture was placed in a rotary evaporator with a temperature control system for cooling crystallization. The initial temperature of the cooling crystallization was 40°C, and the temperature was reduced from 40°C to 25°C at a rate of 1°C / h. The temperature was maintained at 25°C for crystallization for 72 hours. During the 72-hour cooling crystallization process, the stirring rate was 100 rpm to obtain a slurry.

[0058] (5) The slurry was subjected to solid-liquid separation to obtain psicose crystals and mother liquor. The psicose crystals were oven dried and weighed. After the crystallization was completed, the psicose crystals were subjected to purity detection and yield calculation. The results showed that the yield was 38.9% and the purity was 99.89%. The color of the obtained crystals was not very white, with obvious crystal form, and the crystal size was 30 to 35 mesh.

[0059] Part of the mother liquor is mixed with the purified psicose solution to ensure that the purity of the mixed material is not less than 98wt%, and then concentrated and secondary crystallized. The remaining mother liquor is returned to the crude psicose solution to be purified to continue the separation and purification process.

[0060] Example 3

[0061] (1) The crude psicose solution to be purified (wherein the psicose content was 40 wt%) was treated using simulated moving bed separation technology to obtain a purified psicose solution with a purity of 98.8%.

[0062] (2) The purified psicose solution was concentrated by a rotary evaporation concentration device at 60° C. until a stable psicose concentrate was obtained.

[0063] (3) 106 g of the above-mentioned psicose concentrate was added with 16 ml of water, and the mixture was thoroughly mixed. Then, 10.6 g of psicose seed crystals (the mass of the psicose seed crystals was 10% of the psicose concentrate, and the mesh size of the psicose seed crystals was 35-40 meshes) were added, and the mixture was stirred to ensure that the psicose seed crystals were evenly dispersed to obtain a mixture.

[0064] (4) The mixture was placed in a rotary evaporator with a temperature control system for cooling crystallization. The initial temperature of the cooling crystallization was 50°C, and the temperature was reduced from 50°C to 30°C at a rate of 1°C / h. The temperature was maintained at 30°C for crystallization for 120 hours. During the 120-hour cooling crystallization process, the stirring rate was 100 rpm to obtain a slurry.

[0065] (5) The slurry was subjected to solid-liquid separation to obtain psicose crystals and mother liquor. The psicose crystals were oven dried and weighed. After the crystallization was completed, the psicose crystals were subjected to purity detection and yield calculation. The results showed that the yield was 32% and the purity was 99.95%. The color of the obtained crystals was not very white, with obvious crystal form, and the crystal size was 30-35 mesh.

[0066] Part of the mother liquor is mixed with the purified psicose solution to ensure that the purity of the mixed material is not less than 98wt%, and then concentrated and secondary crystallized. The remaining mother liquor is returned to the crude psicose solution to be purified to continue the separation and purification process.

[0067] Example 4

[0068] (1) The crude psicose solution to be purified (wherein the psicose content was 40 wt%) was treated using simulated moving bed separation technology to obtain a purified psicose solution with a purity of 98.5%.

[0069] (2) The purified psicose solution was concentrated by a rotary evaporation concentration device at 60° C. until a stable psicose concentrate was obtained.

[0070] (3) 117.6 g of the above-mentioned psicose concentrate was added with 12 ml of water, and the mixture was thoroughly mixed. Then, 11.76 g of psicose seed crystals (the mass of the psicose seed crystals was 10% of the psicose concentrate, and the mesh size of the psicose seed crystals was 35-40 meshes) were added, and the mixture was stirred to ensure that the psicose seed crystals were evenly dispersed to obtain a mixture.

[0071] (4) The mixture was placed in a rotary evaporator with a temperature control system for cooling crystallization. The initial temperature of the cooling crystallization was 50°C, and the temperature was reduced from 50°C to 30°C at a rate of 1°C / h. The temperature was maintained at 30°C for crystallization for 64 hours. During the 64-hour cooling crystallization process, the stirring rate was 100 rpm to obtain a slurry.

[0072] (5) The slurry was subjected to solid-liquid separation to obtain psicose crystals and mother liquor. The psicose crystals were oven dried and weighed. After the crystallization was completed, the psicose crystals were subjected to purity detection and yield calculation. The results showed that the yield was 44.22% and the purity was 99.96%. The color of the obtained crystals was not very white, with obvious crystal form, and the crystal size was 25 to 30 meshes.

[0073] Part of the mother liquor is mixed with the purified psicose solution to ensure that the purity of the mixed material is not less than 98wt%, and then concentrated and secondary crystallized. The remaining mother liquor is returned to the crude psicose solution to be purified to continue the separation and purification process.

[0074] Example 5

[0075] (1) The crude psicose solution to be purified (wherein the psicose content was 40 wt%) was treated using simulated moving bed separation technology to obtain a purified psicose solution with a purity of 99.6%.

[0076] (2) The purified psicose solution was concentrated by a rotary evaporation concentration device at 60° C. until a stable psicose concentrate was obtained.

[0077] (3) 222.8 g of the above-mentioned psicose concentrate was added with 35 ml of water, and the mixture was thoroughly mixed. Then, 2.228 g of psicose seed crystals (the mass of the psicose seed crystals was 1% of the psicose concentrate, and the mesh size of the psicose seed crystals was 35-40 meshes) were added, and the mixture was stirred to ensure that the psicose seed crystals were evenly dispersed to obtain a mixture.

[0078] (4) The mixture was placed in a rotary evaporator with a temperature control system for cooling crystallization. The initial temperature of the cooling crystallization was 50°C, and the temperature was reduced from 50°C to 30°C at a rate of 1°C / h. The temperature was maintained at 30°C for crystallization for 72 hours. During the 72-hour cooling crystallization process, the stirring rate was 100 rpm to obtain a slurry.

[0079] (5) The slurry was subjected to solid-liquid separation to obtain psicose crystals and mother liquor. The psicose crystals were oven dried and weighed. After the crystallization was completed, the psicose crystals were subjected to purity detection and yield calculation. The results showed that the yield was 38% and the purity was 99.9%. The color of the obtained crystals was not very white, and they had obvious crystal forms. The crystal size was 25 to 35 meshes.

[0080] Part of the mother liquor is mixed with the purified psicose solution to ensure that the purity of the mixed material is not less than 98wt%, and then concentrated and secondary crystallized. The remaining mother liquor is returned to the crude psicose solution to be purified to continue the separation and purification process.

[0081] Example 6

[0082] (1) The crude psicose solution to be purified (wherein the psicose content was 40 wt%) was treated using simulated moving bed separation technology to obtain a purified psicose solution with a purity of 98.6%.

[0083] (2) The purified psicose solution was concentrated by a rotary evaporation concentration device at 60° C. until a stable psicose concentrate was obtained.

[0084] (3) 557 g of the above-mentioned psicose concentrate was added with 45 ml of water, and the mixture was thoroughly mixed. Then, 2.785 g of psicose seed crystals (the mass of the psicose seed crystals was 0.5% of the psicose concentrate, and the mesh size of the psicose seed crystals was 35-40 meshes) were added, and the mixture was stirred to ensure that the psicose seed crystals were evenly dispersed to obtain a mixture.

[0085] (4) The mixture was placed in a rotary evaporator with a temperature control system for cooling crystallization. The initial temperature of the cooling crystallization was 50°C, and the temperature was reduced from 50°C to 30°C at a rate of 0.5°C / h. The temperature was maintained at 30°C for crystallization for 72 hours. During the 72-hour cooling crystallization process, the stirring rate was 100 rpm to obtain a slurry.

[0086] (5) The slurry was subjected to solid-liquid separation to obtain psicose crystals and mother liquor. The psicose crystals were oven dried and weighed. After the crystallization was completed, the psicose crystals were subjected to purity detection and yield calculation. The results showed that the yield was 65% and the purity was 99.93%. The color of the obtained crystals was not very white, and there was an obvious crystal form. The crystal size was 25 to 30 meshes.

[0087] Part of the mother liquor is mixed with the purified psicose solution to ensure that the purity of the mixed material is not less than 98wt%, and then concentrated and secondary crystallized. The remaining mother liquor is returned to the crude psicose solution to be purified to continue the separation and purification process.

[0088] Example 7

[0089] (1) The crude psicose solution to be purified (wherein the psicose content was 40 wt%) was treated using simulated moving bed separation technology to obtain a purified psicose solution with a purity of 98.5%.

[0090] (2) The purified psicose solution was concentrated by a rotary evaporation concentration device at 60° C. until a stable psicose concentrate was obtained.

[0091] (3) 310 g of the above-mentioned psicose concentrate was added with 25 ml of water, and the mixture was thoroughly mixed. Then, 3.1 g of psicose seed crystals (the mass of the psicose seed crystals was 1% of the psicose concentrate, and the mesh size of the psicose seed crystals was 35-40 meshes) were added, and the mixture was stirred to ensure that the psicose seed crystals were evenly dispersed to obtain a mixture.

[0092] (4) The mixture was placed in a rotary evaporator with a temperature control system for cooling crystallization. The initial temperature of the cooling crystallization was 50°C, and the temperature was reduced from 50°C to 30°C at a rate of 1°C / h. The temperature was maintained at 30°C for crystallization for 72 hours. During the 72-hour cooling crystallization process, the stirring rate was 100 rpm to obtain a slurry.

[0093] (5) The slurry was subjected to solid-liquid separation to obtain psicose crystals and mother liquor. The psicose crystals were oven dried and weighed. After the crystallization was completed, the psicose crystals were subjected to purity detection and yield calculation. The results showed that the yield was 72% and the purity was 99.98%. The color of the obtained crystals was not very white, and they had obvious crystal forms. The crystal size was 25 to 30 meshes.

[0094] Part of the mother liquor is mixed with the purified psicose solution to ensure that the purity of the mixed material is not less than 98wt%, and then concentrated and secondary crystallized. The remaining mother liquor is returned to the crude psicose solution to be purified to continue the separation and purification process.

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for crystallizing psicose, characterized in that: The following steps are involved: The crude psicose solution is separated by a simulated moving bed method to obtain a purified psicose solution; The content of psicose in the purified psicose solution is ≥98 wt %; evaporating the purified psicose liquid to a constant weight to obtain a psicose concentrate; mixing the psicose concentrate, water and psicose seed crystals to obtain a mixture, wherein the mass of the water is 1% to 30% of the mass of the psicose concentrate; The mixture is cooled and crystallized, and then solid-liquid separation is performed to obtain the psicose crystals; the starting temperature of the cooling and crystallization is 40-60°C, the end temperature is 25-30°C, and the cooling rate from the starting temperature to the end temperature is 0.5-1°C / h.

2. The crystallization method according to claim 1, characterized in that The content of psicose in the crude psicose solution is 35-45 wt %.

3. The crystallization method according to claim 1, characterized in that The method of mixing the psicose concentrate, water and psicose seed crystals is: firstly mixing the psicose concentrate and water, and then adding the psicose seed crystals.

4. The crystallization method according to claim 1, characterized in that The mass percentage of the psicose seed crystals in the psicose concentrate is 0.1% to 10%.

5. The crystallization method according to claim 1, characterized in that The mesh size of the allulose seed crystals is 10 to 50 meshes.

6. The crystallization method according to claim 1, characterized in that The cooling crystallization is carried out under stirring conditions, and the stirring rate is 10 to 150 rpm.

7. The crystallization method according to claim 1, characterized in that The time of the cooling crystallization is 36 to 120 hours.

8. The crystallization method according to claim 7, characterized in that The time for the cooling crystallization is 48h.

9. The crystallization method according to claim 1 or 6 or 7 or 8, characterized in that The cooling crystallization is carried out in a rotary evaporator with a temperature control system.

10. The crystallization method according to claim 1, characterized in that The solid-liquid separation also obtains a mother liquor; a portion of the mother liquor is mixed with the purified psicose solution, and the psicose content in the obtained mixed solution is controlled to be not less than 98%; and the remaining mother liquor is mixed with the crude psicose solution to be separated.