Preparation method of D-psicose crystal

Abstract

The present invention provides a method for preparing a D-psicose crystal, the method comprising the steps of adding a D-psicose seed crystal to a mother liquor containing D-psicose, and then performing a crystallization reaction at a temperature gradient in which the temperature of the mother liquor containing D-psicose is reduced from an initial temperature Ti to a final temperature Tf. In the preparation method of the D-psicose crystal, the temperature gradient comprises a temperature condition corresponding to a supersaturated state of a metastable zone, and the crystallization reaction is carried out under a reduced pressure condition of 10-100 mbar (mb). Most of the D-psicose crystal particles prepared by the method disclosed by the invention have a cubic crystal structure, and the particle size distribution of the crystal particles is uniform, so that the D-psicose crystal particles have good flowability. Moreover, when the D-psicose crystal is prepared by the method disclosed by the invention, the crystallization yield can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to a method for preparing D-psicose crystals, and more particularly, to a method for preparing D-psicose crystals having a cubic crystal structure and uniform particle size distribution of crystal particles. Background Art

[0002] D-allulose is the epimer of fructose at carbon 3, and is also called D-psicose. Compared with white sugar, D-allulose has a sweetness of 70% (Oshima, 2006), but the calorie content is only 0.3% of that of white sugar, so it is a functional monosaccharide that can be used as a low-calorie sweetener for diet foods (Matsuo et al., 2002). In addition, D-allulose has the function of inhibiting glucose absorption and blood sugar, so it can be used in foods for diabetic patients, diet foods, etc., and it can inhibit abdominal fat accumulation by inhibiting the activity of enzymes involved in lipid synthesis in the liver, so it can be used in various functional foods such as health foods, etc. (Matsuo et al. 2001; Iida et al. 2008; Hayashi et al. 2010; Hossain et al. 2011).

[0003] Due to the characteristics described above, psicose is a good raw material that can replace white sugar, but since it belongs to rare sugars as a monosaccharide that is extremely rare in nature, a method for effectively producing psicose is needed for application in the food industry. The most effective method for producing psicose for industrialization includes a method for converting fructose into psicose using D-psicose 3-epimerase. Since the reaction liquid containing D-psicose produced by the enzyme reaction is a low-purity product containing about 30% (w / w) of D-psicose solid content, it is necessary to prepare a high-purity mother liquor containing psicose using chromatography to prepare high-purity D-allulose crystal particles of 98% (w / w) or more.

[0004] Generally, the crystallization method of sugar is mainly divided into two kinds, the first kind is the concentration crystallization method, and the second kind is the cooling crystallization method. Both methods are the crystallization methods of sugar, which utilize the principle of inducing the growth of crystals in the metastable zone of supersaturated state. Generally, the crystallization method of sugar is carried out in the metastable zone, and this state means that the concentration of the solution is the equilibrium concentration, that is, the range of the minimum supersaturated concentration from the saturated concentration to the spontaneous precipitation of crystals. Crystallization phenomena such as crystal nucleation will not occur at the concentration in this region, but when new crystals are added from the outside, crystal growth will occur and cause the crystal size to increase. That is, in order to generate crystals, when seed crystals are added to the solution above the saturated concentration, the growth of crystals is achieved due to the growth of seed crystals in the metastable zone. When the solution used for crystallization is over-concentrated or rapidly cooled, it will become supersaturated beyond the metastable zone, resulting in the generation of new crystal nuclei instead of crystal growth. This becomes a factor that inhibits crystal growth due to the increase in quantity. Therefore, temperature conditions and initial supersaturated concentration are important for crystal growth.

[0005] Even within the supersaturated concentration range, D-psicose shows that the crystal formation rate and crystal growth rate are almost unchanged, so it can be classified as a sugar with difficult crystallization conditions for particle size growth. Generally, it is known that the size of the crystal particle size is an important factor in the sugar crystallization industry. When the crystals generated in a large-scale production system are micro-crystals, the separation of the crystals and the mother liquor in the crystal centrifuge equipment is not easy due to the viscosity of the supersaturated concentration range. Therefore, the purity of the final product is reduced due to the influence of the residual mother liquor, and the residual mother liquor has a phenomenon of crystals agglomerating with each other during drying, which leads to a reduction in the packaging volume of the final product or a reduction in commerciality. Therefore, such micro-crystals are not suitable for large-scale production methods.

[0006] Regarding a method for preparing D-psicose crystals, Korean Patent Gazette No. 10-1189640 discloses a method for preparing D-allulose crystals, the method comprising the steps of: purifying a D-allulose solution by treating it with a decolorizing agent and an ion exchange resin to obtain a purified D-allulose solution, and concentrating the purified D-allulose solution; and adding D-allulose seed crystals in an amount of 0.01% (g / g) to 1% (g / g) of the total amount of D-allulose in the concentrated D-allulose solution to the concentrated D-allulose solution and crystallizing D-allulose in a supersaturated state in a metastable zone. Also, Korean Patent Gazette No. 10-1749527 discloses a method for preparing D-allulose crystals, the method comprising the steps of obtaining a purified D-allulose solution by removing impurities from a D-allulose solution; concentrating the purified D-allulose solution to 80 to 85 Brix; cooling the concentrated D-allulose solution to 30 to 40° C. at a rate of 5 to 20° C. per hour through a heat exchanger; obtaining a massecuite by crystallizing the D-allulose solution at 30 to 40° C. within a range of 30 to 40° C.; and subjecting the massecuite crystallized using seed crystals to main crystallization at a temperature of 30 to 40° C. Summary of the invention

[0007] Technical issues

[0008] The present invention is proposed under the existing technical background, and an object of the present invention is to provide a method for preparing D-psicose crystals having a cubic crystal structure and uniform particle size distribution of crystal particles. In addition, another object of the present invention is to provide a method for preparing D-psicose crystals with improved crystallization yield.

[0009] Technical Solution

[0010] When seed crystals are added to a mother liquor containing D-psicose and crystallization is induced while cooling under normal pressure under a temperature gradient condition in a metastable zone, the inventors of the present invention have confirmed that crystals having a long needle-like structure are generated, and the grown crystals are broken into fine powders during the crystallization process, thereby causing uneven particle size distribution, and when the crystallization reaction is completed, when the generated psicose crystals are separated from the remaining mother liquor by filtration or the like, the filtration performance is significantly reduced due to the fine crystal particles. In order to solve the above problems, the inventors of the present invention have confirmed that when psicose crystals are induced from a mother liquor containing D-psicose using a predetermined range of reduced pressure conditions, psicose crystals having a cubic crystal structure, a large average particle size of crystal particles, and a uniform particle size distribution can be prepared, thereby completing the present invention. Furthermore, the inventors of the present invention confirmed that when inducing D-psicose crystals from a mother liquor containing D-psicose, in order to suppress the generation of new crystal nuclei, when a prescribed amount of distilled water or a low-concentration mother liquor is added from the time point of microcrystal formation until the completion of the crystallization reaction, the crystallization yield is significantly increased, thereby completing the present invention.

[0011] The term "supersaturated state" used in this specification refers to an unstable state in which a solute is dissolved above the solubility of a solvent, and refers to a state in which a solute can be precipitated in a solid form. Therefore, a supersaturated state is necessary to separate the solute in a solution by crystallization. Generally, the supersaturated state of a solution may be affected by external conditions, impurities, temperature, concentration, pH, etc.

[0012] The term "supersaturated state of the metastable zone" used in this specification refers to a state in which the concentration of the solution is in a range from the saturated concentration to the minimum supersaturated concentration at which crystals are spontaneously precipitated. Crystallization phenomena such as crystal nucleation do not occur at the concentration in this region, but since it is a supersaturated concentration, when crystals are added from the outside, crystal growth occurs spontaneously, resulting in an increase in crystal size. That is, in order to generate crystals, when seed crystals are added to a solution above the saturated concentration, large crystals are formed due to the growth of the seed crystals in the metastable zone.

[0013] The supersaturated state of the term "unstable zone" used in this specification refers to a state in which the concentration of the solution is in a range greater than the minimum supersaturated concentration. Spontaneous crystal nucleation occurs at the concentration in this region.

[0014] In the present specification, Brix, which is a unit of solid concentration of the mother solution containing D-psicose, may be used interchangeably with weight percentage.

[0015] In order to solve the above object, the present invention provides a method for preparing D-psicose crystals, comprising adding D-psicose seed crystals to a mother liquor containing D-psicose, and then raising the temperature of the mother liquor containing D-psicose from an initial temperature T i Reduce to the final temperature T f The crystallization reaction is carried out under a temperature gradient.

[0016] In the present invention, considering the smooth crystallization of D-psicose, the size of D-psicose crystal particles, the economic efficiency of the crystal reaction, etc., the initial solid concentration of the mother liquor containing D-psicose is preferably 70 to 86 Brix, and more preferably 75 to 85 Brix. In addition, considering the size of D-psicose crystal particles, the purity of D-psicose crystal particles, the economic efficiency of the crystal reaction, etc., based on the total weight of the sugars in the mother liquor, the initial D-psicose content of the mother liquor containing D-psicose is preferably 94 to 99 weight percent, and more preferably 95 to 98 weight percent. For example, based on the total weight of the sugars in the mother liquor, the sugar composition of the mother liquor containing D-psicose can be composed of 95 to 98 weight percent of psicose, 0.1 to 2 weight percent of fructose, 0.5 to 4 weight percent of glucose, and the remainder of other sugars. In the present invention, the mother liquor containing D-psicose used as a starting material can be prepared by various known methods. For example, the mother liquor containing D-psicose can be prepared by reacting fructose syrup with D-psicose 3-epimerase to prepare a solution containing D-psicose, and then undergoing decolorization, desalting, fractionation by chromatography, and concentration processes.

[0017] In the present invention, the D-psicose seed crystals are microcrystals composed of high-purity D-psicose, and the D-psicose purity of the D-psicose seed crystals is preferably 99-100% (w / w), and more preferably 99.5-100% (w / w). In addition, the average particle size of the D-psicose seed crystals is not too limited, and can be selected from 50-300 μm, preferably 100-250 μm. The amount of the D-psicose seed crystals added is not too limited. Considering the size of the D-psicose crystal particles, the economic efficiency of the crystal reaction, etc., it is preferably 0.1-5.0% (w / w), and more preferably 0.2-3.0% (w / w), relative to the total weight of the solid matter of the mother liquor containing D-psicose.

[0018] In the present invention, considering the smooth crystallization of D-psicose, the size of D-psicose crystal particles, the economic efficiency of the crystallization reaction, etc., the initial temperature T for the crystallization reaction is iIt is preferably selected from 30 to 55°C, and more preferably selected from 35 to 52°C. When the initial temperature T i When the initial temperature is lower than 30°C, there may be a risk of solidification during the crystallization reaction, resulting in a decrease in crystallinity (or crystallization yield), which may cause difficulties in industrial application. i When the temperature is higher than 55°C, the solid concentration of the mother liquor containing D-psicose corresponding to the supersaturated state is too high, which may cause the stirring process to be unsmooth. In the present invention, the final temperature T for the crystallization reaction is f Can be selected from the initial temperature T i The temperature is preferably selected from the initial temperature T i In particular, when the crystallization reaction is carried out under reduced pressure conditions close to a vacuum state of 10 to 100 mbar (mb), even if the final temperature T f Selected from the initial temperature T i By lowering the temperature by 1 to 5°C, crystal particles having a cubic structure and uniform particle size distribution can be obtained. In the present invention, in order to induce the crystallization reaction, the temperature of the mother solution containing D-psicose is lowered from the initial temperature T i Reduce to the final temperature T f The temperature gradient includes a temperature condition corresponding to at least a supersaturated state of a metastable zone, and preferably consists of a temperature condition that maintains a supersaturated state of a metastable zone during the crystallization reaction.

[0019] In the present invention, the crystallization reaction time is not particularly limited. Considering the size of the D-psicose crystal particles, the economic efficiency of the crystallization reaction, etc., it is preferably selected from 35 to 100 hours, and more preferably selected from 40 to 80 hours.

[0020] In the present invention, the crystallization reaction is carried out under a reduced pressure of 10 to 100 millibars (mb), preferably 30 to 80 millibars (mb). When the crystallization reaction is carried out under a reduced pressure close to a vacuum state, the generated crystal particles mainly have a cubic crystal structure, and the particle size distribution of the crystal particles is uniform, so when the generated crystals and the mother liquor are separated after the crystallization reaction is completed, the filtration is smooth, and the fluidity of the obtained crystal particles is improved.

[0021] Preferably, the method for preparing D-psicose crystals of the present invention may further include adjusting the concentration of the mother liquor containing D-psicose by adding a diluent solution to the mother liquor containing D-psicose during the crystallization reaction. Furthermore, the addition of the diluent solution may be performed by adding water alone, or by adding a diluent mother liquor having a lower solid concentration than the mother liquor containing D-psicose alone, or by alternately adding water and a solution containing D-psicose. The solid concentration of the diluent mother liquor containing D-psicose used as the diluent solution is preferably 10 to 45 degrees Brix to prevent the concentration of the mother liquor containing D-psicose undergoing a crystallization reaction from changing rapidly when the diluent solution is added. Furthermore, the saccharide composition of the solution containing D-psicose alternately added with water is preferably the same as the saccharide composition of the mother liquor containing D-psicose. Furthermore, the solid concentration of the D-psicose-containing solution added alternately with water is preferably 55 to 80 degrees Brix to prevent the concentration of the D-psicose-containing mother liquor undergoing a crystallization reaction from changing rapidly when the D-psicose-containing solution is added. In the present invention, the concentration of the D-psicose-containing mother liquor is adjusted by adding a diluent solution during the crystallization reaction in order to suppress the generation of new microcrystals or remove the already formed microcrystals during the crystallization reaction. During the crystallization reaction, when the D-psicose-containing mother liquor is in an oversaturated state in an unstable zone due to various factors such as reaction temperature, reaction pressure, and precipitation of crystals, D-psicose microcrystals such as crystal nuclei are formed, and the microcrystals have a negative impact on the structure of the crystal particles, the size of the crystal particles, the particle size distribution of the crystal particles, and the like. In the present invention, during the crystallization reaction, from the time point when new microcrystals are generated until the crystallization reaction is completed, a dilution solution is added to the mother liquor containing D-psicose more than once, preferably several times (e.g., 2 to 4 times), so that the time when the mother liquor containing D-psicose is in the supersaturated state in the unstable zone can be minimized and most of the time it is in the supersaturated state in the metastable zone, and new microcrystals formed due to various factors can be suppressed or the formed microcrystals can be removed. In the present invention, during the crystallization reaction, the time point when new microcrystals are generated depends on various factors such as the conditions of the mother liquor containing D-psicose, the temperature gradient conditions, the stirring conditions, the pressure conditions, etc., and is usually a time point of about 20 to 24 hours from the time point when D-psicose seed crystals are added to the mother liquor containing D-psicose and the crystallization reaction is carried out under the temperature gradient. In addition, in the present invention, the dilution solution is added during the crystallization reaction, so that the structure of the crystal particles and the particle size distribution of the crystal particles can be controlled, and the precipitation rate of the crystal particles can be significantly increased.In the method for preparing D-psicose crystals of the present invention, the total amount of the diluent solution added is not particularly limited. Taking into account the effective adjustment of the concentration of the mother liquor containing D-psicose, the smooth inhibition and removal of microcrystal formation, etc., the total amount of the diluent solution added is preferably 1 to 10% (w / w), and more preferably 2 to 8% (w / w), relative to the total weight of the mother liquor containing D-psicose.

[0022] Preferably, the method for preparing D-psicose crystals of the present invention may further include the following steps: after the crystallization reaction is completed, the mother liquor is washed, dehydrated and dried to obtain D-psicose crystal particles. The process of dehydrating the mother liquor with a washing agent can be achieved by various well-known methods such as centrifugation, vacuum filtration using filter paper or filter cloth, etc. In addition, the drying process can be achieved by various well-known methods such as hot air drying, spray drying, fluidized bed drying, etc.

[0023] Most of the D-psicose crystal particles prepared by the method for preparing D-psicose crystals of the present invention have a cubic crystal structure and show a relatively uniform particle size distribution, and therefore have excellent fluidity. In addition, the average particle size of the D-psicose crystal particles prepared by the method for preparing D-psicose crystals of the present invention is 200 to 500 μm, preferably 220 to 460 μm. In addition, the D-psicose purity of the D-psicose crystal particles prepared by the method for preparing D-psicose crystals of the present invention is 98.5% (w / w) or more (e.g., 98.5 to 100%), preferably 99% (w / w) or more (e.g., 99 to 99.9%).

[0024] Effects of the Invention

[0025] Most of the D-psicose crystal particles prepared by the method of the present invention have a cubic crystal structure, and the particle size distribution of the crystal particles is uniform, so they have good fluidity. In addition, when D-psicose crystals are prepared by the method of the present invention, the crystallization yield can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The saturation curve and supersaturation curve of D-psicose crystals are shown.

[0027] Figure 2 This is an image of D-psicose crystals obtained in Preparation Example 6 of the present invention taken through a microscope.

[0028] Figure 3 This is an image of D-psicose crystals obtained in Preparation Example 13 of the present invention taken through a microscope. DETAILED DESCRIPTION

[0029] Hereinafter, the present invention will be specifically described by the following examples. However, the following examples are only used to clearly illustrate the technical features of the present invention and do not limit the protection scope of the present invention.

[0030] Example 1: Preparation of a mother solution containing D-psicose

[0031] A psicose epimerase variant derived from Flavonifractor plautii is added to a solution containing fructose and reacted, and then the supernatant is recovered by centrifugation. Regarding the process of converting fructose into psicose using a psicose epimerase variant, the present invention refers to Korean Patent Publication No. 10-2021-0132405 and Korean Patent Publication No. 10-2254411. Then, the supernatant is decolorized by treating it with activated carbon, and it is desalted by an ion exchange resin column to obtain a purified solution containing low-purity psicose. Then, the solution containing low-purity psicose is concentrated to a solid concentration of about 50 degrees Brix, and the concentrated solution containing low-purity psicose is chromatographically separated by a calcium-substituted ion exchange resin (MUK 555) to obtain a solution containing high-purity D-psicose. Then, the high-purity D-psicose-containing solution was concentrated to prepare mother solutions containing high-purity D-psicose with various solid concentrations. The solid concentration of the mother solution containing D-psicose was 70 to 84 degrees Brix, and the sugar composition was 95.6% (w / w) of psicose, 1.0% (w / w) of fructose, 1.9% (w / w) of glucose, and 1.5% (w / w) of other sugars based on the total weight of the solids.

[0032] Example 2: Preparation of D-psicose seed crystals

[0033] D-psicose seed crystals were prepared using a mother liquor containing D-psicose having a solid concentration of 84 degrees Brix. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring and temperature control system, and the temperature of the mother liquor was adjusted to 40°C, and then more than 95% of a reagent-grade psicose granular product was added thereto in an amount of about 3 weight percent relative to the solid content of the mother liquor, and the reagent-grade psicose granular product was uniformly dispersed by stirring at a speed of about 100 rpm. Then, the stirring speed was reset to about 1.0 to 1.5 rpm, and a crystallization reaction was performed under a temperature gradient condition in which the temperature of the mother liquor was slowly cooled from 40°C to 10°C in about 70 hours. Then, the solution subjected to the crystallization reaction was washed and dehydrated by centrifugation, and dried at a temperature of about 50°C for 6 hours to obtain D-psicose seed crystals. The average crystal particle size of the obtained D-psicose seed crystals was about 150 μm, and the content of psicose in the carbohydrate composition was 99.9 weight percent.

[0034] Example 3: Determination of saturation concentration and supersaturation concentration of D-psicose crystals

[0035] Under a specific temperature condition selected from 30 to 80° C., a small amount of the D-psicose seed crystals obtained in Example 2 were added to distilled water for dissolution, and the concentration at which no more dissolution occurred was defined as the saturation concentration at the temperature. In addition, high-purity D-psicose solutions having solid concentrations of 83 Brix, 89 Brix, and 92 Brix were prepared using the D-psicose seed crystals obtained in Example 2, and then slowly cooled and the temperature at the time when crystal particles began to form was measured, and the concentration of each sample was defined as the supersaturation concentration at the temperature. Figure 1 The saturation curve and supersaturation curve of D-psicose crystals are shown.

[0036] Example 4: Crystallization experiment of mother liquor containing D-psicose under normal pressure and temperature gradient in metastable zone

[0037] D-psicose crystals were prepared using mother liquors containing D-psicose having various solid concentrations. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring and temperature control system, and the temperature of the mother liquor was adjusted to a specific temperature, and then the D-psicose seed crystals obtained in Example 2 were added thereto in a specified amount relative to the solid content of the mother liquor, and the D-psicose seed crystals were uniformly dispersed by stirring at a speed of about 100 rpm. Then, the stirring speed was reset to about 1.0 to 1.5 rpm, and the mother liquor was cooled for a specified time under normal pressure or maintained at a cooled temperature for a specified time, thereby performing a crystallization reaction under a temperature gradient condition corresponding to the metastable zone. Then, the solution subjected to the crystallization reaction was washed and dehydrated by centrifugation, and dried at a temperature of about 50° C. for 6 hours to obtain D-psicose crystals. The following Tables 1 and 2 show the crystallization reaction conditions used in Example 4 and the analysis results of the obtained D-psicose crystals. Figure 2 The image of the D-psicose crystals obtained in Preparation Example 6 of the present invention was taken through a microscope. Figure 2 As shown in the figure, when seed crystals are added to the mother liquor containing D-psicose, and the mother liquor is cooled and crystallized at a temperature gradient condition of the metastable zone under normal pressure, crystals with a long needle structure are generated, and the grown crystals are broken into micro powders during the crystallization process, resulting in an uneven particle size distribution. In Preparation Example 6, when the solution after the crystallization reaction is filtered by centrifugation or the like, a dense film is formed on the filter cloth due to the micronized crystal particles, and the filtration performance is significantly reduced. In addition, the D-psicose crystal particles prepared in Preparation Example 6 contain a large number of microcrystalline particles, and the particle size distribution is uneven, resulting in poor fluidity even after drying.

[0038] Table 1

[0039]

[0040] Table 2

[0041]

[0042]

[0043] Example 5: Preliminary experiment for setting pressure conditions during crystallization of a mother solution containing D-psicose under a temperature gradient in the metastable zone

[0044] A mother liquor containing D-psicose having a solid concentration of 81 degrees Brix was placed in a crystallizer equipped with a stirring, temperature regulator and pressure regulating system, and the temperature of the mother liquor was adjusted to 45° C. Then, the D-psicose seed crystals obtained in Example 2 were added thereto in an amount of 0.5 weight percent relative to the solid content of the mother liquor, and the D-psicose seed crystals were uniformly dispersed by stirring at a speed of about 100 rpm. Then, the stirring speed was reset to about 1.0 to 1.5 rpm, and crystal formation in the mother liquor containing D-psicose was observed while the internal pressure of the crystallizer was gradually reduced from 250 mbar (mb) to 50 mbar (mb). Under the near-vacuum condition where the internal pressure of the crystallizer was less than 100 mbar (mb), the growth of D-psicose crystals began and a whitening phenomenon occurred.

[0045] Example 6: Crystallization experiment of mother liquor containing D-psicose under reduced pressure and temperature gradient in metastable zone

[0046] D-psicose crystals were prepared using mother liquors containing D-psicose having various solid concentrations. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring, temperature regulation, and pressure regulation system, and the temperature of the mother liquor was adjusted to a specific temperature, and then the D-psicose seed crystals obtained in Example 2 were added thereto in a specified amount relative to the solids of the mother liquor, and the D-psicose seed crystals were uniformly dispersed by stirring at a speed of about 100 rpm. Then, the stirring speed was reset to about 1.0 to 1.5 rpm, and the decompression conditions were adjusted to within a specified range, while the mother liquor was cooled for a specified time or maintained at a cooled temperature for a specified time, thereby performing a crystallization reaction under a temperature gradient condition corresponding to the metastable zone. Then, the solution subjected to the crystallization reaction was washed and dehydrated by centrifugation, and dried at a temperature of about 50° C. for 6 hours to obtain D-psicose crystals. Tables 3 and 4 below show the crystallization reaction conditions used in Example 6 and the analysis results of the obtained D-psicose crystals.

[0047] Table 3

[0048]

[0049] Table 4

[0050]

[0051] Example 7: Crystallization experiment based on mother liquor containing D-psicose under reduced pressure, temperature gradient in metastable zone and addition of dilute solution

[0052] D-psicose crystals were prepared using mother liquors containing D-psicose having various solid concentrations. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring, temperature regulation, and pressure regulation system, and the temperature of the mother liquor was adjusted to a specific temperature, and then the D-psicose seed crystals obtained in Example 2 were added thereto in a prescribed amount relative to the solid content of the mother liquor, and the D-psicose seed crystals were uniformly dispersed by stirring at a speed of about 100 rpm. Then, the stirring speed was reset to about 1.0 to 1.5 rpm, and the decompression conditions were adjusted to within a prescribed range, while the mother liquor was cooled for a prescribed time or maintained at a cooled temperature for a prescribed time, thereby performing a crystallization reaction under a temperature gradient condition corresponding to the metastable zone. Furthermore, during the crystallization reaction, from the time point when microcrystals are generated (when the crystallization reaction time is about 24 hours) until the crystallization reaction is completed, distilled water alone, a diluted mother liquor containing D-psicose having a solid content of 35 Brix alone, or a combination of distilled water and a mother liquor containing D-psicose having a solid content of 70 Brix are added as diluent solutions twice at a prescribed time interval to adjust the concentration of the mother liquor and inhibit new crystal nucleation. The total amount of the diluent solution added is 5% (w / w) relative to the total weight of the mother liquor containing D-psicose used for the crystallization reaction. Then, the solution undergoing the crystallization reaction is washed and dehydrated by centrifugation, and dried at a temperature of about 50° C. for 6 hours to obtain D-psicose crystals. Table 5 below shows the crystallization reaction conditions used in Example 7 and the analysis results of the obtained D-psicose crystals. Figure 3 The image of the D-psicose crystals obtained in Preparation Example 13 of the present invention was taken through a microscope. Figure 3 As shown in the figure, when seed crystals are added to a mother liquor containing D-psicose, and crystallization is induced while cooling under reduced pressure at a temperature gradient condition of a metastable zone, and a diluent solution is added during the crystallization reaction to adjust the concentration of the mother liquor and inhibit the generation of new microcrystals, crystals having a cubic crystal structure are generated, and the phenomenon of crystals growing during the crystallization process being broken is minimized, so that the particle size distribution is uniform. In Preparation Example 13, when the solution after the crystallization reaction is completed is filtered by centrifugation or the like, there is almost no reduction in filtration performance. In addition, the average particle size of the D-psicose crystal particles prepared in Preparation Example 13 is within an appropriate range, and the particle size distribution is uniform, so that it has good fluidity even after drying.

[0053] Table 5

[0054]

[0055]

[0056] As described above, the present invention is described by the embodiments, but the present invention is not necessarily limited thereto, and various modifications can be made without departing from the scope and idea of ​​the present invention. Therefore, the protection scope of the present invention should be interpreted as including all embodiments belonging to the scope of the patent application attached to the present invention.

Claims

1. A method for preparing D-psicose crystals, characterized in that: include: D-psicose seed crystals are added to the mother solution containing D-psicose, and then the temperature of the mother solution containing D-psicose is increased from the initial temperature T i Reduce to the final temperature T f The crystallization reaction is carried out under a temperature gradient of The temperature gradient includes temperature conditions corresponding to a supersaturated state in the metastable zone, The crystallization reaction is carried out under reduced pressure of 10 to 100 mbar.

2. The method for preparing D-psicose crystals according to claim 1, characterized in that: The method further includes adjusting the concentration of the mother liquor containing D-psicose by adding a diluent solution to the mother liquor containing D-psicose during the crystallization reaction.

3. The method for preparing D-psicose crystals according to claim 1, characterized in that: The initial solid concentration of the mother liquor containing D-psicose is 70 to 86 degrees Brix, and the initial D-psicose content of the mother liquor containing D-psicose is 94 to 99 weight percent based on the total weight of sugars in the mother liquor.

4. The method for preparing D-psicose crystals according to claim 1, characterized in that: The amount of the D-psicose seed crystals added is 0.1 to 5.0% (w / w) relative to the total weight of the solid content of the mother liquor containing D-psicose.

5. The method for preparing D-psicose crystals according to claim 1, characterized in that: The initial temperature T i Selected from 30~55℃, the final temperature T f Selected from the initial temperature T i Lower the temperature by 1 to 15°C.

6. The method for preparing D-psicose crystals according to claim 1, characterized in that: The crystallization reaction time is selected from 35 to 100 hours.

7. The method for preparing D-psicose crystals according to claim 2, characterized in that: The addition of the dilution solution is performed by adding water alone, or adding a dilution mother solution having a lower solid concentration than the mother solution containing D-psicose alone, or alternately adding water and a solution containing D-psicose.

8. The method for preparing D-psicose crystals according to claim 2, characterized in that: The addition of the diluent solution is performed multiple times starting from the point in time when microcrystals are formed until the crystallization reaction is completed.

9. The method for preparing D-psicose crystals according to claim 2, characterized in that: The total amount of the dilution solution added is 1 to 10% (w / w) relative to the total weight of the mother solution containing D-psicose.

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