A method for preparing a d-allulose crystal

Abstract

The application provides a preparation method of D-psicose crystal, and particularly relates to a preparation method of D-psicose large-particle-size crystal through cooling and coupling with solvent analysis, and the method comprises the following steps: adding D-psicose seed crystal into a D-psicose saturated solution with a temperature of 50-60 DEG C, cooling and crystallizing through staged temperature reduction to 20-30 DEG C, and adding ethanol when the temperature is reduced to 35-30 DEG C to obtain D-psicose crystal. By controlling the particle number, particle size of the added seed crystal, the addition amount and addition rate of ethanol within the optimal range, the crystal can grow in a good form quickly in the subsequent cooling and coupling with solvent analysis crystallization process. The D-psicose crystal has a high uniformity in particle size, and more than 88wt% of the D-psicose crystal is between 40-60 meshes, the one-way yield of the product reaches more than 60%, the method has strong operability, low energy consumption and high economic benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of crystallization technology in chemical engineering industry, and particularly relates to a preparation method of D-psicose crystal, and especially to a preparation method of large-size D-psicose crystal by coupling cooling and solventing-out. BACKGROUND

[0002] D-psicose is a C-3 epimer of D-fructose, which is naturally present in a small amount of food such as figs and brown sugar. At present, D-psicose is mainly synthesized by biological transformation. D-psicose is white powder or crystal in macroscopic morphology, and has a relative sweetness of about 70% of sucrose and an energy deposition efficiency of about 0.3% of sucrose in the body. In the food field, compared with sugar alcohols such as erythritol and xylitol, the human body has better tolerance to D-psicose. D-psicose can produce Maillard reaction in food protein, and the reaction intensity is even greater than that of fructose and glucose. In the field of baking and candy, D-psicose has the performance of improving color, flavor and water retention, and can reduce the freezing point, so it becomes an excellent choice for reducing sugar and heat in desserts such as ice cream. It also does not crystallize in high-solid foods and has high application value in chocolate production. In the medical field, in addition to the typical role of sugar substitutes such as reducing blood sugar, D-psicose combined with radiation therapy has been proven to be effective against cancer, and the antioxidant properties of D-psicose also have obvious therapeutic effects on inflammation. In the field of pesticides, studies have shown that D-psicose can play a role in regulating plant growth and resisting pests and diseases, and can be used to develop environmentally friendly biological pesticides.

[0003] CN 109748940 A proposes a method for D-psicose evaporation cooling coupled crystallization from ethanol-water solution. The method can improve the single-pass crystallization rate by continuously evaporating and concentrating in the ethanol-water system and cooling crystallization. However, the use of a large amount of ethanol can affect the flavor of the product and reduce the marketability of the sugar crystal product, and the use of a large amount of ethanol at high temperature can have a high-temperature explosion hazard. CN 108290917 A proposes a method for obtaining high-yield and high-purity D-psicose by multiple concentration and cooling and impurity separation by chromatography. However, the operation is complex and the cycle is long. CN 112574263 A proposes a method for preparing D-psicose crystal by evaporation cooling coupled crystallization. The process is relatively simple and the crystallization cycle is short, but effective control strategies for obtaining large-size crystals have not been realized.

[0004] Therefore, it is still a technical problem that cannot be solved by the prior art to find a preparation method of D-psicose crystal product that can increase the particle size of the crystal, improve the single-pass yield of crystallization, reduce the amount of organic solvent used, and is expected to be industrialized. SUMMARY

[0005] The present application provides a method of adding crystal seeds to a D-psicose saturated solution first, and then cooling crystallization, and injecting a small amount of ethanol into the system at a low temperature stage of the cooling process to achieve cooling coupled with solvent-analytical crystallization. The product prepared by the method has uniform particle size distribution, smooth surface, good morphology, good flowability, and more than 88.5 wt% of the crystal size is in the range of 40-60 mesh, and the single-pass yield of the product is more than 60%, which has high economic benefits.

[0006] One of the purposes of the present application is to provide a preparation method of D-psicose crystals, which comprises the following steps:

[0007] Step (1): D-psicose crystal seeds are added to a D-psicose saturated solution at a temperature of 50-60 ℃, and the solution is cooled in three steps: the first step is to cool from 50-60 ℃ to 45-55 ℃ at a cooling rate of 0.2-0.3 ℃ / h, the second step is to cool from 45-55 ℃ to 40-50 ℃ at a cooling rate of 0.3-0.4 ℃ / h, and the third step is to cool from 40-50 ℃ to 20-30 ℃ at a cooling rate of 0.4-0.6 ℃ / h;

[0008] Step (2): When the temperature of the system in step (1) is reduced to 35-30 ℃, ethanol is added to perform cooling coupled with solvent-analytical crystallization;

[0009] Step (3): The solid-liquid mixture obtained in step (2) is centrifuged and dried to obtain D-psicose crystals.

[0010] The concentration of the D-psicose saturated solution in step (1) is 85-88 wt%;

[0011] The particle size of the D-psicose crystal seeds in step (1) is 100-200 mesh;

[0012] The addition amount of the D-psicose crystal seeds in step (1) is 1-5 wt% of the addition amount of D-psicose in the D-psicose supersaturated solution;

[0013] The D-psicose saturated solution in step (1) is a solution obtained by catalytic conversion of a fructose solution into D-psicose by D-psicose 3-epimerase, separation and purification, and evaporation and concentration treatment;

[0014] The total addition amount of ethanol in step (2) is 10-30% of the amount of pure water solvent;

[0015] The addition rate of ethanol in step (2) is 1-3 % / h of the amount of the original D-psicose saturated solution;

[0016] The preparation method in the step (3) further comprises sequentially performing solid-liquid separation, washing and drying on the obtained mixed solution after cooling crystallization.

[0017] The solid-liquid separation in the step (3) is centrifugation.

[0018] The drying in the step (3) is performed at a temperature of 50 ℃ for 12 h.

[0019] The D-allulose crystal prepared by the method has a regular shape, and more than 88.5 wt% of the average crystal has a size of 40-60 mesh, and has the characteristics of short rod shape, good fluidity, large crystal particle size and uniform shape.

[0020] The D-allulose crystal prepared by the method is applied to the fields of food and biological pesticides, and is preferably used as a food additive or for preparing a pesticide for resisting pests and diseases.

[0021] The technical features and beneficial effects of the present application are as follows:

[0022] 1. The present application uses a cooling coupled solvent-out crystallization technology to prepare D-allulose crystals, and a small amount of ethanol is added at the low-temperature stage of the cooling process to avoid burst nucleation at the low-temperature stage and promote the growth of crystals at the low-temperature stage, so that the crystal form is highly uniform, and large-particle-size crystal products can be effectively obtained.

[0023] 2. The present application selects to add an organic solvent to reduce the viscosity of the system, which reduces the operation difficulty, reduces the equipment loss, and the process is simple and easy to operate; in addition, the ethanol is added at the low-temperature stage and the amount of ethanol used is small, which reduces the danger of high-temperature explosion of ethanol and improves the safety of the process production.

[0024] 3. According to the growth and nucleation characteristics of D-allulose, the present application sets a stepwise cooling curve, and designs different cooling rates at different temperature intervals, which can uniformly consume the supersaturation generated by the system, avoids burst after adding ethanol, promotes the growth of crystals, lengthens the cooling interval, and significantly improves the single-pass yield of crystallization.

[0025] 4. According to the preparation method of the present application, the D-allulose crystal obtained after crystallization has good morphology and highly uniform particle size, and more than 88.5 wt% of the crystal size is 40-60 mesh, has good fluidity and is not easy to agglomerate. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 : Optical microscope picture of D-allulose crystal before adding ethanol in Example 1;

[0027] Figure 2 : Optical microscope picture of D-allulose crystal after crystallization in Example 1;

[0028] Figure 3 Optical microscope picture of D-psicose crystal before adding ethanol in Example 2;

[0029] Figure 4 Optical microscope picture of D-psicose crystal after crystallization in Example 2;

[0030] Figure 5 Optical microscope picture of D-psicose crystal before adding ethanol in Example 3;

[0031] Figure 6 Optical microscope picture of D-psicose crystal after crystallization in Example 3;

[0032] Figure 7 Optical microscope picture of D-psicose crystal after crystallization in Comparative Example 1;

[0033] Figure 8 Optical microscope picture of D-psicose crystal after crystallization in Comparative Example 2;

[0034] Figure 9 Optical microscope picture of D-psicose crystal after crystallization in Comparative Example 3. DETAILED DESCRIPTION

[0035] Example

[0036] (1) 5 wt% 120-140 mesh seed crystals were added to a 55 °C crystallizer containing a saturated solution of D-psicose at 85-88 wt%.

[0037] (2) Temperature was decreased for crystallization, at the interval of 55-50 °C, 0.25 °C per hour, at the interval of 50-45 °C, 0.33 °C per hour, at the interval of 45-25 °C, 0.5 °C per hour, until 25 °C was reached and crystallization was stopped.

[0038] (3) Temperature was decreased for crystallization coupled with solvent addition, at the interval of 30-25 °C, 1 % / h of the original D-psicose saturated solution was added to the crystallizer until crystallization was stopped.

[0039] (4) Product handling: centrifugation at 1000 rpm, 2000 rpm, 3000 rpm for 5 min each, and drying at 50 °C for 12 h.

[0040] Optical microscope pictures of D-psicose crystal before adding ethanol and D-psicose product after crystallization are shown in Figure 1 , Figure 2The D-psicose crystal has a smooth surface, a good appearance, a highly uniform particle size, and a crystal size of 40-60 mesh of 86 wt% or more. The product has good fluidity and is not easy to agglomerate. The one-pass yield of the D-psicose crystallization is 58 wt%, and the crystal size distribution is shown in the following table (Table 2).

[0041] Table 1. Crystal size distribution of Example 1

[0042] Particle size Product (wt %) 40 mesh and above 1.8 40-60 mesh 88.5 60 mesh and below 9.7 Example

[0043] (1) 3 wt% of 150-200 mesh seed crystals were added to a 60 °C crystallizer containing a saturated solution of D-psicose at 85-88 wt%.

[0044] (2) Temperature reduction and crystallization: the temperature was reduced by 0.25 °C per hour in the range of 60-55 °C, by 0.33 °C per hour in the range of 55-50 °C, and by 0.5 °C per hour in the range of 50-30 °C, and the crystallization was stopped at 30 °C.

[0045] (3) Temperature reduction and crystallization coupled with solvent elution: 3% of the original D-psicose saturated solution was added to the crystallizer per hour in the low-temperature range of 35-30 °C until the crystallization was stopped.

[0046] (4) Product processing: centrifugation at 1000 rpm, 2000 rpm, and 3000 rpm for 5 min each, and drying at 50 °C for 12 h.

[0047] The optical microscope images of the D-psicose crystals before the addition of ethanol and the D-psicose product after the crystallization are shown in Figure 3 , Figure 4 The D-psicose crystal has a smooth surface, a good appearance, a highly uniform particle size, and a crystal size of 40-60 mesh of 86 wt% or more. The product has good fluidity and is not easy to agglomerate. The one-pass yield of the D-psicose crystallization is 58 wt%, and the crystal size distribution is shown in the following table (Table 2).

[0048] Table 2. Crystal size distribution of Example 2

[0049] Particle size Product (wt %) 40 mesh and above 3.6 40-60 mesh 86.0 60 mesh and below 10.4 Example

[0050] (1) 5 wt% of 120-140 mesh seed crystals were added to a 50 °C crystallizer containing a saturated solution of D-psicose at 85-88 wt%.

[0051] (2) Cooling crystallization, cooling at the rate of 0.25 °C / h in the range of 50-45 °C, 0.33 °C / h in the range of 45-40 °C, and 0.5 °C / h in the range of 40-20 °C, and stopping the crystallization at 20 °C;

[0052] (3) Cooling and coupling with solvent elution crystallization, adding ethanol to the crystallizer at the rate of 1 % / h of the saturated liquid solvent amount of D-psicose in the low temperature range of 30-20 °C until the crystallization is stopped.

[0053] (4) Product processing: centrifugation at the speed of 1000 rpm, 2000 rpm, and 3000 rpm for 5 min each, and drying at 50 °C for 12 h.

[0054] The optical microscope pictures of D-psicose crystals before adding ethanol and D-psicose product after crystallization are shown in Figure 5 , Figure 6 The D-psicose crystals have smooth surface, good appearance, highly uniform particle size, and 85 wt% or more of the crystal size is in the range of 40-60 mesh, without broken crystals, and good fluidity and not easy to agglomerate. The one-pass yield of D-psicose crystallization is 55 wt%, and the crystal size distribution is shown in the following table (Table 3).

[0055] Table 3. Crystal size distribution of Example 3

[0056] Particle size Product (wt %) 40 mesh and above 0.5 40-60 mesh 85.0 60 mesh and below 9.0

[0057] The D-psicose crystals are prepared according to the method of Example 1, except that no ethanol is added during the cooling crystallization, and other steps and operations are the same as those of Example 1.

[0058] The optical microscope pictures of D-psicose product after crystallization are shown in Figure 7 , and a large number of broken crystals and serious crystal agglomeration occur during the crystallization process. Most of the crystals have small particle size, and the particle size distribution is not uniform. The particle size distribution is shown in the following table (Table 4), and 60.7 wt% of the product is in the size range of 40-60 mesh. The one-pass yield of D-psicose crystallization is 40 wt%, and there is less large particle product.

[0059] Table 4. Crystal size distribution of Comparative Example 1

[0060] Particle size Product (wt %) 40 mesh and above 0.3 40-60 mesh 60.7 60 mesh and below 39.0

[0061] The D-psicose crystals are prepared according to the method of Example 2, except that 1 wt% of 250-300 mesh seed crystals are directly added in step (1), and other steps and operations are the same as those of Example 2.

[0062] The optical microscope pictures of D-psicose crystal product after crystallization end are shown in Figure 8 Although the mass fraction of the seed crystal used is small, the number of particles is large because the mesh number is extremely small. During the cooling process, the particles are limited by the growth space and the change of surface free energy, resulting in a large number of agglomeration of the final crystals, leading to crystal agglomeration. The particle size distribution is shown in the following table (Table 5), 50.6 wt% product is in 40-60 mesh, and the D-psicose crystal yield is 56 wt%.

[0063] Table 5. Crystal particle size distribution of Comparative Example 2

[0064] Particle size Product (wt %) 40 mesh and above 0.5 40-60 mesh 50.6 60 mesh and below 48.9

[0065] D-psicose crystals were prepared according to the method of Example 3, except that the cooling rate was 0.5°C per hour at a uniform rate, and other steps and operations were the same as those of Example 3.

[0066] The optical microscope pictures of D-psicose crystal product before adding ethanol and after crystallization end are shown in Figure 9 The crystal particle size is not uniform, there are more fine crystals, the crystals are easy to agglomerate, and the crystals are long rod-shaped, and the product has poor flowability. The particle size distribution is shown in the following table (Table 6), 69 wt% product is in 40-60 mesh, and the D-psicose crystal yield is 45 wt%.

[0067] Table 6. Crystal particle size distribution of Comparative Example 3

[0068] Particle size Product (wt %) 40 mesh and above 4.5 40-60 mesh 69 60 mesh and below 26.5

[0069] From the comparison between Example 1 and Comparative Example 1, it can be seen that when the temperature is lowered for crystallization in a pure water system without adding ethanol, a large number of fine crystals will appear, the product particle size is small and shows a bimodal distribution, which is due to low temperature and accumulation of supersaturation. The decrease in temperature leads to slow mass transfer, and the accumulation of supersaturation further increases the viscosity to hinder mass transfer, which is a vicious cycle that often leads to explosive nucleation, which is not conducive to the growth of subsequent crystals and is prone to a large number of agglomeration of fine crystals.

[0070] From the comparison between Example 2 and Comparative Example 2, it can be seen that when the mesh number of the added seed crystal exceeds the limited range of the present application, the product particle size is small, because the product particle size is proportional to the mesh number of the seed crystal to some extent. The smaller the seed crystal particle size, the more the number of particles, and at the end of crystallization, the particle size of the product is generally small, and the proportion of large particle crystals is significantly reduced.

[0071] It can be known by comparing example 3 and comparative example 3 that when the cooling rate is uniform and fast throughout the whole process, a large number of fine crystals appear from the high-temperature section, because the growth of the crystals cannot consume the supersaturation generated by the fast cooling in time, so that burst nucleation caused by supersaturation accumulation occurs, causing the particle size distribution to be wide, and the aspect ratio of the crystals to be too large; and the addition of ethanol starts when the burst trend appears, so that the amount of ethanol added exceeds 30%, reducing the safety of the process and failing to meet the requirements of the application field on the production process.

[0072] The present application discloses and proposes a preparation method of D-allulose large particle size crystal by cooling coupling dissolution. Those skilled in the art can realize it by changing the cooling interval, cooling rate, seed crystal addition amount, stirring rate and other links by referring to the content of the present application. The method of the present application has been described by the preferred embodiment, and the related technical personnel can obviously make changes or appropriate changes and combinations to the method and product described in the present application without departing from the content, spirit and scope of the present application, to realize the present application technology. It is particularly important to point out that all similar substitutions and changes are obvious to those skilled in the art, and they are considered to be included in the spirit, scope and content of the present application.

Claims

1. A method for preparing D-psicose crystals, characterized in that: The preparation method comprises the following steps: adding D-psicose seed crystals to a saturated D-psicose solution at 50-60°C, and cooling the solution in three steps: a first step of cooling from 50-60°C to 45-55°C at a cooling rate of 0.2-0.3°C / h, a second step of cooling from 45-55°C to 40-50°C at a cooling rate of 0.3-0.4°C / h, and a third step of cooling from 40-50°C to 20-30°C at a cooling rate of 0.4-0.6°C / h. ethanol is added when the temperature drops to 35-30°C to obtain D-psicose crystals; The particle size of the D-psicose seed crystals is 100-200 meshes.

2. The preparation method according to claim 1, characterized in that The concentration of the D-psicose saturated solution is 85-88 wt %.

3. The preparation method according to claim 1, characterized in that The amount of the D-psicose seed crystals added is 1-5 wt % of the amount of D-psicose added in the saturated D-psicose solution.

4. The preparation method according to claim 1, characterized in that The D-psicose saturated solution is a solution obtained by separating, purifying, and evaporating and concentrating a fructose solution into D-psicose by D-psicose 3-epimerase to obtain a mixed solution of fructose and D-psicose.

5. The preparation method according to claim 1, characterized in that The amount of ethanol added is 10-30% of the amount of solvent added to the D-psicose saturated solution.

6. The preparation method according to claim 1, characterized in that The addition rate of ethanol is 1-3% / h of the amount of solvent added to the D-psicose saturated solution.

7. The preparation method according to claim 1, characterized in that The preparation method further comprises sequentially performing solid-liquid separation, washing, and drying on the mixed solution obtained by cooling and crystallizing.

8. The preparation method according to claim 7, characterized in that The solid-liquid separation method is centrifugation.

9. The preparation method according to claim 7, characterized in that The drying temperature is 50° C. and the drying time is 12 h.

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