Method for extracting psicose crystals from psicose fermentation liquor

Abstract

The invention belongs to the technical field of psicose preparation, and particularly relates to a method for extracting psicose crystals from psicose fermentation broth, which comprises the following steps of: performing ceramic membrane filtration and nanofiltration on the psicose fermentation broth, concentrating a nanofiltration filtered phase, performing activated carbon decoloration, performing chromatographic desalination decoloration by using a sodium chromatographic column, and performing freeze-drying to obtain the psicose crystals. And collecting the slow component for cation and anion exchange, concentrating the obtained ion exchange liquid, performing chromatographic purification by using a calcium type chromatographic column, collecting the rear-end AD liquid, and evaporating and concentrating the AD liquid. Cooling to room temperature, adding psicose ground powder as a seed crystal, adding ethanol while stirring to separate out crystals to obtain a solid-liquid mixture, and centrifuging the solid-liquid mixture to obtain psicose crystals. By adopting the method disclosed by the invention, the crystalline psicose can be extracted from the psicose fermentation liquor in a high-efficiency and energy-saving manner, and the psicose with better crystal form and higher purity and yield is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of psicose preparation, and particularly relates to a method for extracting psicose crystals from psicose fermentation broth. Background Art

[0002] D-Allulose is a rare six-carbon ketose that exists in nature but in very small amounts. The sweetness of allulose is about 70% of that of sucrose. In addition, the calories of allulose are very low, about 0.4 calories per gram, and it is sometimes called "zero-calorie" sugar. Due to its low calories and small effect on blood sugar, studies have shown that allulose does not significantly increase blood sugar or insulin levels, may help control weight and blood sugar levels, and has certain preventive and therapeutic potential for type 2 diabetes. As an emerging sweetener, allulose is gradually attracting market attention, especially in today's increasingly health-conscious world. Its low calories and small effect on blood sugar make it a potential sucrose substitute.

[0003] The preparation methods of allulose mainly include chemical synthesis and biotransformation. The chemical synthesis of allulose mainly uses glucose as raw material, and is catalyzed by molybdate, and then separated and purified by chromatography, concentrated and crystallized. The chemical synthesis method has the disadvantages of high cost, dangerous operation, difficult process, complex purification, low yield, and easy environmental pollution, so it is not conducive to large-scale industrial production. Therefore, the production of allulose is mainly carried out by biotransformation. The biotransformation method uses glucose or fructose as substrates to produce allulose through enzymatic reaction or microbial fermentation. The conversion rate of this method is relatively high, but the purification is more complicated. For example, in the process of producing allulose by microbial fermentation, in order to improve the conversion rate, salt, alkali, ammonia, etc. are added to control the pH and fermentation rate of the fermentation liquid, which will cause a large amount of salt, pigment and protein impurities to remain in the allulose fermentation liquid. The traditional purification method is plate and frame filtration or centrifuge centrifugation, followed by activated carbon decolorization, ion exchange desalination, chromatographic separation and purification, and then concentration and crystallization. The disadvantages of this purification method are that the degree of automation of plate and frame filtration is low, the labor cost is high, and the filtrate after plate and frame treatment still has a lot of impurities. The resin fails quickly during desalination and separation, resulting in a small number of material passes, and multiple separations are required to meet the standards. In addition, the solubility of allulose in water is extremely high. The ordinary concentration and crystallization process needs to increase the purity to more than 98% to successfully obtain crystalline allulose, and the process is complicated. Even if allulose crystals can be successfully obtained, the yield is not ideal. This is also the difficulty of industrial production of allulose. In view of this, it is still necessary to find a new method for purifying allulose. Summary of the invention

[0004] In order to solve the problems of the prior art, the object of the present invention is to provide a method for extracting psicose crystals from psicose fermentation broth. The method consumes less energy and has a simple and reasonable process. In particular, the desalination process is effectively improved, the labor intensity of workers is reduced, and the processing cost is greatly saved, which is about 15% less than the traditional process.

[0005] In order to achieve the above object, the present invention provides a method for extracting psicose crystals from a psicose fermentation broth, comprising the following steps:

[0006] S1, filtering the fermented liquid after fermentation through a ceramic membrane to obtain a clear phase and a concentrated phase, and filtering the clear phase through a nanofiltration membrane to obtain a nanofiltration clear phase;

[0007] S2, vacuum concentrating the nanofiltration clear phase to a concentration of 40-60% to obtain a concentrated solution;

[0008] S3, the concentrated solution is preliminarily decolorized with activated carbon, and after the preliminary decolorization, chromatographic desalting and re-decolorization are performed to remove the fast component and collect the slow component;

[0009] S4, subjecting the slow component liquid to ion exchange by firstly passing through a cation exchange resin and then passing through an anion exchange resin to obtain an ion exchange liquid, and controlling the conductivity of the ion exchange liquid to be ≤20 μs / cm;

[0010] S5, concentrating the ion exchange liquid to obtain a concentrated liquid with a concentration of 50%-60%;

[0011] S6, chromatographically purify the concentrated solution, remove the front BD solution, and collect the rear AD solution;

[0012] S7, evaporating the AD liquid to a concentration of 20%-30%, and continuing steam heating until the discharge concentration increases to 80%-88% to obtain a concentrated liquid;

[0013] S8, cooling the concentrated solution obtained in S7 to room temperature, adding seed crystals, and adding ethanol in an amount of 30%-80% by mass of the sugar paste while stirring. After the addition is completed, the crystals are grown for 8-20 hours to obtain a solid-liquid mixture; adding the solid-liquid mixture into a centrifuge for solid-liquid separation, and the separated liquid is a psicose mother liquor. The psicose mother liquor is distilled to recover ethanol and then added to the concentrated solution in S7; and the separated solid portion is heated and dried to obtain solid crystalline psicose.

[0014] In the above method for extracting psicose crystals from psicose fermentation broth, the pressure of the nanofiltration membrane in step S1 is no more than 30 bar.

[0015] In the above method for extracting psicose crystals from psicose fermentation broth, the concentration of the nanofiltration clear phase in step S1 is 13-18% and the purity is 85-89%.

[0016] In the above method for extracting psicose crystals from psicose fermentation broth, in step S2, the nanofiltration clear phase is vacuum concentrated at 50° C.-70° C. to a concentration of 40-60% to obtain a concentrated solution.

[0017] In the above method for extracting psicose crystals from psicose fermentation broth, the activated carbon is preliminarily decolorized in step S3, and the amount of activated carbon added is 0.3-0.8% of the mass of the concentrated liquid.

[0018] In the above method for extracting psicose crystals from psicose fermentation broth, the amount of activated carbon added is 0.5% of the mass of the concentrated liquid.

[0019] In the above method for extracting psicose crystals from psicose fermentation broth, sodium-type chromatographic resin is selected as the filling material for chromatographic desalting in step S3.

[0020] In the above method for extracting psicose crystals from psicose fermentation broth, in step S6, chromatographic purification is performed and calcium-type chromatographic resin is selected as the filling material.

[0021] In the above method for extracting psicose crystals from psicose fermentation broth, the purity of psicose in the AD liquid in step S6 is greater than 95%.

[0022] In the above method for extracting psicose crystals from psicose fermentation broth, the temperature for centrifuging the solid-liquid mixture in step S8 is 20-30°C.

[0023] The beneficial effects of the technical solution of the present invention are:

[0024] 1. The method of extracting psicose crystals from psicose fermentation broth of the present invention can obtain psicose crystals with better crystal form and a purity of up to 99.8%. Compared with the traditional process (the yield of the traditional process is difficult to reach 60%), the yield of the method of the present invention can reach more than 70%, and can reach up to 79%, which is significantly improved.

[0025] 2. In the crystallization stage, the present invention cooperates with adding seed crystals and dripping poor ethanol solvent to obtain D-psicose crystals with better crystal yield and higher purity.

[0026] 3. The chromatographic desalting and decolorizing treatment adopted in the present invention can effectively improve the traditional complicated process and effectively reduce the labor intensity; the processing cost can be saved by about 15% compared with the traditional process, which greatly reduces the production cost.

[0027] 4. The present invention utilizes the principle that pigments and inorganic salt ions are desorbed faster in sodium-type chromatographic resins, while psicose is desorbed slower in sodium-type chromatographic resins during chromatographic desalting and decolorization. The present invention uses sodium-type chromatographic resins as fillers to separate pigments and anions and cations from psicose, thereby achieving the purpose of desalting and decolorization.

[0028] 5. The present invention uses calcium-type chromatographic resin for chromatographic purification because calcium ions can form coordination bonds with the groups of the psicose molecule and have a strong affinity, while other substances have a weak affinity for calcium-type ion chromatographic resin. The use of calcium-type chromatographic resin can separate psicose from other miscellaneous sugars to achieve the purpose of purification.

[0029] 6. In terms of the crystallization of allulose, the traditional process requires a purity of about 98% for successful crystallization. The crystallization method of the present invention reduces the stringent requirements on the purity of the crystallized sugar paste, and it can be successfully crystallized when the purity reaches 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments and test examples. However, it should be understood by those skilled in the art that the embodiments are only used to illustrate the technical solution of the present invention and should not be regarded as limiting the scope of protection of the present invention. Based on the following embodiments, all other implementation schemes obtained by ordinary technicians in the field without making creative work, such as modification, deformation or simple replacement, should belong to the scope of protection of the present invention.

[0032] The manufacturers of the main reagents and instruments involved in the preparation process of the present invention are as follows:

[0033] SSMB chromatography system: Shanghai Zhaoguang Chromatography Separation Technology Co., Ltd.; sodium type chromatography resin: DuPont, USA; anion and cation exchange resin: Zhejiang Zhengguang Industrial Co., Ltd.; calcium type chromatography resin: DuPont, USA.

[0034] Example 1: The present invention provides a method for extracting psicose crystals from psicose fermentation broth, comprising the following steps:

[0035] 1) Filtration: The fermented liquid with bacteria after fermentation is filtered through a ceramic membrane, and the clear phase is collected. The bacteria in the concentrated phase are inactivated and discharged at high temperature; the ceramic membrane clear phase is further filtered through nanofiltration to obtain a nanofiltration clear phase, and the pressure of the nanofiltration membrane is no more than 30 bar.

[0036] 2) Concentration: the nanofiltration clear phase in step 1 is concentrated in vacuo at 50-70° C. to a concentration of 40-60%.

[0037] 3) Decolorization: the concentrated solution is initially decolorized by adding activated carbon, the addition ratio is 0.3-0.8% of the mass of the concentrated solution.

[0038] 4) Chromatographic desalting and decolorization, the concentrate is separated into two components by chromatography, using the SSMB system. Since our feed solution contains a large amount of sodium ions, we choose sodium-type chromatographic resin as the filling material to separate the two components. Since pigments and inorganic salt ions are easier to desorb in sodium-type chromatographic resins, i.e., they run faster, while allulose is slower to desorb in sodium-type chromatographic resins, i.e., it runs slower. By using this principle, we can separate pigments and anions and cations from allulose, and achieve the purpose of desalting and decolorization.

[0039] This scheme measured the concentration, transmittance, pH and conductivity of different liquids before and after chromatographic desalting and decolorization. The specific data are shown in Table 1. Considering that the comparison of transmittance and conductivity is meaningful only at the same concentration, the pre-chromatographic stock solution was diluted to make it consistent with the concentration of the slow component liquid after chromatographic separation so as to compare the transmittance and conductivity.

[0040] Table 1 Parameters of different liquids before and after chromatography

[0041] concentration% Transmittance% pH Conductivity μs / cm Pre-chromatographic stock solution 50-60 0.1-0.5 5.0-6.0 4000-4500 Pre-chromatographic stock solution dilution 23-24 5-7 5.0-6.0 7000-8000 Chromatographic separation of fast fraction liquid 1-3 3.0-7.0 5.0-6.5 9800-1200 Slow component liquid after chromatographic separation 23-24 50-65 4.5-5.5 350-570

[0042] It can be seen that when the two components are separated, the fast component liquid is composed of fast-running pigments and anions and cations, and contains almost no sugar; the slow component liquid contains a small amount of salt and pigment, allulose solution, which is lighter in color and has lower conductivity.

[0043] 5) ion exchange, the chromatographic desalting slow component liquid obtained in step 4 is first passed through a cation exchange column and then an anion exchange column to further remove metal ions and other impurity ions, and the conductivity of the ion exchange liquid is controlled to be ≤20μs / cm;

[0044] In this step, the cation exchange column is selected first and then the anion exchange column, and the anion exchange liquid is finally collected, and the pH value is between 4-9. After concentration, it can directly meet the pH requirement of the chromatographic feed. If the anion exchange column is used first and then the cation exchange column, the pH value of the finally obtained cation exchange liquid is lower than 4, there is a risk of corrosion to the equipment during concentration, and the pH requirement of the chromatographic feed is not met.

[0045] 6) Concentrating: concentrating the ion exchange solution in step 5 to a concentration of about 50%-60%.

[0046] 7) Chromatographic purification: chromatographic two-component purification is performed. This chromatography also uses the SSMB system. At this time, the purpose of the chromatography is different from the previous one. After chromatographic desalting and decolorization, the feed liquid is particularly clean after further ionization and concentration treatment, but allulose is still mixed with miscellaneous sugars. This chromatographic operation is to remove the miscellaneous sugars and improve the purity of allulose. This chromatography uses a calcium-type chromatographic resin. The calcium-type chromatographic resin is selected for chromatographic purification because calcium ions can form coordination bonds with the groups of the allulose molecules and have a strong affinity, while other substances have a weak affinity for calcium-type ion chromatographic resins. The calcium-type chromatographic resin can separate allulose from other miscellaneous sugars to achieve the purpose of purification. After two-component separation, the front-end miscellaneous sugars (BD liquid) are removed, so that the purity of allulose in the AD liquid can be increased from 85-90% to more than 95%.

[0047] 8) Evaporation and purification of AD liquid to a concentration of about 20-30%. After continued addition of steam for heating, the discharge concentration continues to increase to 80-88%.

[0048] 9) Crystallization: The concentrated solution is cooled to room temperature, a small amount of seed crystals is added, and 30%-80% of the weight of the sugar paste ethanol is added dropwise while stirring. After the addition is completed, continue to grow the crystals for about 8-20 hours.

[0049] Psicose is very soluble in water, but almost insoluble in ethanol. Based on this solubility difference and solvation, we introduced the principle of precipitation by adding a poor solvent, that is, adding a poor ethanol solvent to a psicose aqueous solution close to saturation reduces the solubility of psicose in the ethanol solvent, resulting in a decrease in the solubility of psicose in the ethanol aqueous solution. This is because the interaction between the psicose molecules and the ethanol molecules is weak, and the psicose molecules cannot be effectively stabilized in the ethanol aqueous solution. When the solubility of psicose is reduced to a certain extent, psicose will precipitate from the ethanol aqueous solution. In addition, in order to better control the crystal form, we also introduced seed crystals. In this step, the addition of seed crystals and the dropwise addition of a poor ethanol solvent cooperate with each other to obtain psicose crystals with a better crystal form yield and higher purity.

[0050] 10) centrifugation, adding the solid-liquid mixture in step 9 into a centrifuge for solid-liquid centrifugation, and the separated liquid portion is the psicose mother liquor. After the psicose mother liquor is distilled to recover ethanol, it is added to step 6 for mixing; considering that ethanol is volatile, in order to improve the recovery rate of ethanol, the speed and temperature are controlled during centrifugation to keep the temperature as low as possible. However, the centrifugal speed cannot be lower than 20 Hz. If the speed is too low, more ethanol will remain in the solid product, and if the speed is too high, it is not conducive to the recovery of ethanol.

[0051] 11) Drying: The solid portion separated in step 10 is heated and dried to obtain solid crystalline psicose, which is then packaged to form a finished product.

[0052] Example 2: In order to verify the effects of concentrate concentration, seed crystals, ethanol addition amount and crystal growing time on the yield and purity of psicose during the crystallization process, the present invention set up the following comparative experiments to analyze the effects of concentrate concentration, seed crystals, ethanol addition amount and crystal growing time on the yield and purity of psicose, as shown in Table 2 below.

[0053] Table 2 Yield and purity of psicose obtained under different experimental conditions

[0054]

[0055]

[0056] Note: In experiment 4, ethanol was not added. After adding the seed crystals, the mixture was stirred and crystallized directly, and crystals were precipitated normally. However, the obtained solid-liquid mixture was extremely viscous, and solid-liquid separation could not be performed, and the solid product could not be collected.

[0057] It can be seen from Table 2 that at the same concentration, with the gradual increase in the amount of ethanol added, the yield and purity of psicose show an upward trend. This is because psicose is almost insoluble in ethanol. With the increase of the ethanol content in the solvent, the amount of psicose precipitated will increase, while other miscellaneous sugars have not reached saturation, so the yield and purity of psicose show an upward trend; the use of seed crystals and the use of no seed crystals have a greater impact on the yield and purity of psicose. Although crystals can be precipitated without using seed crystals, the precipitation rate is difficult to control, impurities are easily wrapped on the psicose molecules, and the particle sizes are different, which is prone to explosion.

[0058] By cooperating with each other by adding seed crystals and dropping poor ethanol solvent, D-psicose crystals with better crystal form, higher yield and higher purity are obtained.

[0059] Example 3: In order to verify the effects of different rotation speeds, different centrifugation times and different centrifugation temperatures on the yield of allulose during the centrifugation stage, the present invention centrifuged the solid-liquid mixture obtained after the same batch of crystal growth at different rotation speeds, centrifugation times and centrifugation temperatures. The results are shown in Table 3 below.

[0060] Table 3 Effect of different centrifugation conditions on the yield of psicose

[0061] Group <![CDATA[Rotational speed H Z > Time min Temperature ℃ Allulose yield % Experiment 1 25 90 30-40 72 Experiment 2 25 90 20-30 78 Experiment 3 35 60 30-40 75 Experiment 4 35 60 20-30 79

[0062] It can be seen from Table 3 that controlling the temperature at 20-30°C is more conducive to improving the yield of psicose.

[0063] The present invention exemplifies the method of the present invention by extracting psicose from two different batches of psicose fermentation broths according to the method of the present invention, as shown in detail as follows.

[0064] Example 4: This example provides a method for extracting psicose crystals from psicose fermentation broth, comprising the following steps:

[0065] S1. A batch of allulose fermentation broth was selected, and the purity was measured to be 87%. The fermentation broth was filtered through a ceramic membrane to collect the clear phase, and the concentrated phase was inactivated and discharged by high-temperature treatment; then the clear phase was filtered through a nanofiltration membrane to remove bacteria and solid impurities, and the pressure of the nanofiltration membrane was controlled to be no more than 30 bar to obtain 200L of nanofiltration clear phase liquid, with a measured concentration of about 13%, a conductivity of about 8500μs / cm, and a transmittance of about 1.1%.

[0066] S2. At 60°C, the nanofiltration clear phase liquid is concentrated by a double-effect evaporator to obtain a concentrated liquid with a concentration of 50%;

[0067] S3, adding activated carbon with a mass of 5‰ of the concentrated solution to the concentrated solution for decolorization to obtain a decolorized solution, and measuring the light transmittance of the decolorized solution to be 20%;

[0068] S4. The decolorizing liquid is subjected to chromatographic separation of two components using the SSMB system. Since the decolorizing liquid contains a large amount of sodium ions, a sodium-type chromatographic resin is selected as the filling material for separation of the two components, and the fast component liquid is discharged and the slow component liquid is collected. Since pigments and inorganic salt ions are easier to desorb in the sodium-type chromatographic resin, that is, they run faster, and allulose is slower to desorb in the sodium-type chromatographic resin, that is, it runs slower, this principle can be used to separate pigments and anions and cations from allulose, thereby achieving the purpose of desalting and decolorizing. Impurities such as anions and cations, pigments, etc. will be intercepted into the fast component liquid and discharged to the sewage station for treatment. The collected slow component liquid detection data are as follows: concentration 23%, conductivity 450μs / cm, transmittance 56%, purity 90%.

[0069] S5, exchanging the collected slow component liquid with cations and anions, controlling the conductivity of the exchange liquid to below 20 μs / cm, and concentrating it to a concentration of 50%;

[0070] S6, chromatographically purifying the concentrate of S5 again, specifically using calcium-type chromatographic resin as the filling material; the purpose of chromatography in this step is different from that in S4. Although the feed liquid of S4 is particularly clean after chromatographic desalting and decolorization and further ionization and concentration, miscellaneous sugars are still mixed in the psicose. The purpose of adding chromatographic operation in this step is to remove the miscellaneous sugars and improve the purity of psicose. The purity of the purified feed liquid is measured to be 95.5%;

[0071] S7, evaporating and concentrating the purified liquid to a concentration of 84%, and cooling to room temperature;

[0072] S8. Add 1% of the mass of the massecuite D-psicose powder to the cooled concentrated solution as a seed crystal, then slowly dropwise add 30% ethanol, centrifuge, and obtain crystalline D-psicose. The purity of the D-psicose is measured to be 99.477%. The dry matter yield of the fermentation broth to chromatographic purification is 75%, and the dry matter yield of the crystallization is 72%.

[0073] Example 5: This example provides a method for extracting psicose crystals from psicose fermentation broth, comprising the following steps:

[0074] S1. A batch of allulose fermentation broth was selected, and the purity was measured to be 85%. The fermentation broth was filtered through a ceramic membrane to collect the clear phase, and the concentrated phase was inactivated and discharged by high-temperature treatment; then the clear phase was filtered through a nanofiltration membrane to remove bacteria and solid impurities, and the pressure of the nanofiltration membrane was controlled to be no more than 30 bar to obtain 200L of nanofiltration clear phase liquid, with a measured concentration of about 13%, a conductivity of about 9100 μs / cm, and a transmittance of about 0.8%.

[0075] S2. At 60°C, the nanofiltration clear phase liquid is concentrated by a double-effect evaporator to obtain a concentrated liquid with a concentration of 50%;

[0076] S3, adding activated carbon with a mass of 5‰ of the concentrated solution to the concentrated solution for decolorization to obtain a decolorized solution, and measuring the light transmittance of the decolorized solution to be 20%;

[0077] S4. The decolorizing liquid is subjected to chromatographic separation of two components using the SSMB system. Since the decolorizing liquid contains a large amount of sodium ions, a sodium-type chromatographic resin is selected as the filling material for two-component separation, and the fast component liquid is discharged and the slow component liquid is collected. Since pigments and inorganic salt ions are easier to desorb in the sodium-type chromatographic resin, that is, they run faster, and allulose is slower to desorb in the sodium-type chromatographic resin, that is, it runs slower, this principle can be used to separate pigments and anions and cations from allulose, thereby achieving the purpose of desalting and decolorizing. Impurities such as anions and cations, pigments, etc. will be intercepted into the fast component liquid and discharged to the sewage station for treatment. The collected slow component liquid detection data are as follows: concentration 24%, conductivity 550μs / cm, transmittance 47%, purity 89%.

[0078] S5, exchanging the collected slow component liquid with cations and anions, controlling the conductivity of the exchange liquid to below 20 μs / cm, and concentrating it to a concentration of 50%;

[0079] S6, chromatographically purifying the concentrate of S5 again, specifically using calcium-type chromatographic resin as the filling material; the purpose of chromatography in this step is different from that in S4. Although the feed liquid of S4 is particularly clean after chromatographic desalting and decolorization and further ionization and concentration, miscellaneous sugars are still mixed in the psicose. The purpose of adding chromatographic operation in this step is to remove the miscellaneous sugars and improve the purity of psicose. The purity of the purified feed liquid is measured to be 95.5%;

[0080] S7, evaporating and concentrating the purified liquid to a concentration of 84%, and cooling to room temperature;

[0081] S8. Add 1% of the mass of the massecuite D-psicose powder to the cooled concentrated solution as a seed crystal, then slowly dropwise add 50% ethanol, centrifuge, and obtain crystalline D-psicose. The purity of the D-psicose is measured to be 99.411%. The dry matter yield of the fermentation broth to chromatographic purification is 68%, and the dry matter yield of the crystallization is 78%.

[0082] The above is a detailed introduction to a method for extracting psicose crystals from psicose fermentation broth provided by the present invention. The same or similar parts between the various embodiments of the specification can be referred to each other. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for extracting psicose crystals from a psicose fermentation broth, characterized in that: The following steps are involved: S1, filtering the fermented liquid after fermentation through a ceramic membrane to obtain a clear phase and a concentrated phase, and filtering the clear phase through a nanofiltration membrane to obtain a nanofiltration clear phase; S2, vacuum concentrating the nanofiltration clear phase to a concentration of 40-60% to obtain a concentrated solution; S3, the concentrated solution is preliminarily decolorized with activated carbon, and after the preliminary decolorization, chromatographic desalting and re-decolorization are performed to remove the fast component and collect the slow component; S4, subjecting the slow component liquid to ion exchange by firstly passing through a cation exchange resin and then passing through an anion exchange resin to obtain an ion exchange liquid, and controlling the conductivity of the ion exchange liquid to be ≤20 μs / cm; S5, concentrating the ion exchange liquid to obtain a concentrated liquid with a concentration of 50%-60%; S6, chromatographically purify the concentrated solution, remove the front BD solution, and collect the rear AD solution; S7, evaporating the AD liquid to a concentration of 20%-30%, and continuing steam heating until the discharge concentration increases to 80%-88% to obtain a concentrated liquid; S8, cooling the concentrated solution obtained in S7 to room temperature, adding ground allulose powder as a seed crystal, adding ethanol with a mass ratio of 30% to 80% of the mass of the sugar paste while stirring, and growing the crystals for 8 to 20 hours after the addition is completed to obtain a solid-liquid mixture; the amount of the seed crystal is 1% of the mass of the sugar paste; S9, adding the solid-liquid mixture into a centrifuge for solid-liquid separation, the separated liquid is a psicose mother liquor, and the psicose mother liquor is distilled to recover ethanol and then added to the concentrated liquid in S7; S10, heating and drying the solid portion separated in S9 to obtain solid crystalline picose.

2. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: The pressure of the nanofiltration membrane in step S1 is not greater than 30 bar.

3. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: The concentration of the nanofiltration clear phase in step S1 is 13-18%, and the purity is 85-89%.

4. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: In step S2, the nanofiltration clear phase is vacuum concentrated at 50° C.-70° C. to a concentration of 40-60% to obtain a concentrated solution.

5. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: In step S3, the activated carbon is preliminarily decolorized, and the amount of activated carbon added is 0.3-0.8% of the mass of the concentrated liquid.

6. The method for extracting psicose crystals from psicose fermentation broth according to claim 5, wherein: The amount of activated carbon added is 0.5% of the concentrate mass.

7. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: In step S3, sodium type chromatographic resin is selected as the filling material for chromatographic desalting.

8. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: In step S6, chromatographic purification is performed and calcium-type chromatographic resin is selected as the filling material.

9. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: The purity of psicose in the AD solution in step S6 is greater than 95%.

10. The method for extracting psicose crystals from psicose fermentation broth according to claim 1, wherein: The temperature at which the solid-liquid mixture is centrifuged in step S9 is 20-30°C.

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