Method for producing D-allulose crystals

Abstract

The present invention provides a method for producing D-allose crystals, which includes the step of adding D-allose seed crystals to a D-allose-containing mother liquor and then allowing a crystallization reaction to proceed under a temperature gradient in which the temperature of the D-allose-containing mother liquor is decreased from an initial temperature T i to a final temperature T f . In the method for producing D-allose crystals according to the present invention, the temperature gradient includes temperature conditions corresponding to a supersaturated state in a metastable zone, and the crystallization reaction is carried out under a reduced pressure condition of 10 to 100 millibars (mb). The D-allose crystal particles produced by the method of the present invention mostly have a cubic crystal system type crystal structure, and the particle size distribution of the crystal particles is uniform, so the fluidity is good. Further, when producing D-allose crystals by the method of the present invention, the crystallization yield can be greatly improved.

Description

[Technical Field]

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

[0002] D-allulose, also known as D-psicose, is the epimer of fructose at the third carbon atom. Compared to sugar, D-allulose has 70% the sweetness (Oshima 2006) but only 0.3% of the energy content, making it a functional monosaccharide suitable for use as a low-calorie sweetener in diet foods (Matsuo et al. 2002). Furthermore, D-allulose suppresses glucose absorption and blood glucose levels, making it suitable for use in foods for diabetics and health foods. It also inhibits the activity of enzymes involved in hepatic lipid synthesis, thereby suppressing abdominal fat accumulation. Therefore, it can be used in a variety of functional foods, including health foods (Matsuo et al. 2001; Iida et al. 2008; Hayashi et al. 2010; Hossain et al. 2011).

[0003] Due to the above characteristics, allulose is a good source that can be used as a substitute for sugar. However, because it is a rare sugar, a monosaccharide that is rarely found in nature, an efficient method for producing allulose is required for its application in the food industry. The most efficient method for producing allulose industrially is to convert fructose to allulose using a D-allulose 3-epimerization enzyme. The reaction solution containing D-allulose produced by the enzymatic reaction is a low-purity product containing approximately 30% (w / w) D-allulose solids. Therefore, in order to produce high-purity D-psicose crystalline particles with a purity of 98% (w / w) or more, it is necessary to produce a high-purity allulose-containing mother liquor using chromatography.

[0004] Sugar crystallization methods are generally divided into two categories: concentration crystallization and cooling crystallization. Both methods utilize the principle of inducing crystal growth within the metastable zone, a supersaturated state. Sugar crystallization typically occurs in the metastable zone, which refers to the range of solution concentration from the equilibrium concentration (i.e., saturation) to the minimum supersaturation at which spontaneous crystal precipitation occurs. While crystal nucleation and other crystal formation phenomena do not occur within this concentration range, the addition of new crystals from outside induces crystal growth and increases the crystal size. In other words, when seed crystals are added to a solution above saturation concentration, the seed crystals grow in the metastable zone, resulting in crystal growth. If the crystallization solution is excessively concentrated or cooled rapidly, it will reach a supersaturated state beyond the metastable zone, resulting in the formation of new crystal nuclei rather than crystal growth, which will inhibit crystal growth due to an increase in the number of crystals. Therefore, temperature conditions and the initial supersaturated concentration are important for crystal growth.

[0005] D-allulose exhibits almost no change in crystal formation rate and crystal growth rate even in the supersaturation concentration range, so it can be classified as a sugar that is difficult to crystallize under the conditions for particle size growth. Generally, in the sugar crystallization industry, crystal particle size is known to be an important factor. When the crystals produced in a mass production system are fine crystals, the separation of the crystals and the mother liquor in the crystal centrifuge equipment is difficult due to the viscosity in the supersaturation concentration range. The remaining mother liquor reduces the purity of the final product. Furthermore, the remaining mother liquor causes the crystals to solidify during drying, resulting in a reduced packaging volume and reduced marketability of the final product. Therefore, these fine crystals are not suitable for mass production.

[0006] Korean Patent Publication No. 10-1189640 discloses a method for producing D-allulose crystals, which includes the steps of treating and purifying a D-psicose solution with a decolorizing agent and an ion exchange resin to obtain a purified D-psicose solution, concentrating the purified D-psicose solution, and adding D-psicose seed crystals to the concentrated D-psicose solution in an amount of 0.01 to 1% (g / g) of the total amount of D-psicose in the concentrated D-psicose solution to crystallize D-psicose in a supersaturated state in the metastable zone. Korean Patent Publication No. 10-1749527 discloses a method for producing D-psicose crystals, including the steps of removing impurities from a D-psicose solution to obtain a purified D-psicose solution, concentrating the purified D-psicose solution to 80 to 85 Brix (%), cooling the concentrated D-psicose solution to 30 to 40°C at a rate of 5 to 20°C per hour using a heat exchanger, crystallizing the D-psicose solution at 30 to 40°C within a range of 30 to 40°C to obtain massecuite, and performing the main crystallization at 30 to 40°C using the seed crystallized massecuite. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention was developed under the background of the prior art, and an object of the present invention is to provide a method for producing allulose crystals having a cubic crystal structure and a uniform particle size distribution of the crystal particles. Another object of the present invention is to provide a method for producing D-allulose crystals with an improved crystallization yield. [Means for solving the problem]

[0008] The inventors of the present invention have confirmed that when seed crystals are added to a D-allulose-containing mother liquor and crystallization is induced by cooling under a temperature gradient in the metastable zone at atmospheric pressure, crystals with a long needle-like structure are produced, and the crystals grown during the crystallization process are broken and undifferentiated, resulting in non-uniform particle size distribution. Furthermore, when the allulose crystals produced after the crystallization reaction is completed are separated from the remaining mother liquor by filtration or other methods, the filtration performance is significantly reduced due to the fine crystal particles. To solve this problem, the inventors of the present invention have confirmed that when allulose crystals are induced from a D-allulose-containing mother liquor under reduced pressure conditions within a certain range, it is possible to produce allulose crystals with a cubic crystal structure, a large average crystal particle size, and a uniform particle size distribution, and have completed the present invention. Furthermore, the inventors of the present invention have confirmed that when allulose crystals are induced from a D-allulose-containing mother liquor, the crystallization yield increases significantly when a predetermined amount of distilled water or a low-concentration mother liquor is added from the time when fine crystals are generated until the end of the crystallization reaction in order to suppress the generation of new crystal nuclei, and thus completed the present invention.

[0009] The term "supersaturated state" as used herein refers to an unstable state in which a solute is dissolved in a solvent in excess of its dissolving capacity, and the solute may precipitate as a solid. Therefore, a supersaturated state is necessary to separate a solute in a solution by crystallization. Generally, the supersaturated state of a solution can be affected by external conditions, impurities, temperature, concentration, pH, etc.

[0010] As used herein, the term "supersaturated state in the metastable zone" refers to a state in which the concentration of a solution is in the range from the saturated concentration to the minimum supersaturated concentration at which spontaneous crystal precipitation occurs. At concentrations in this range, crystallization phenomena such as crystal nucleation do not occur, but because the concentration is supersaturated, spontaneous crystal growth occurs when crystals are added from the outside, increasing the crystal size. That is, when seed crystals are added to a solution whose concentration is above the saturated concentration to generate crystals, the seed crystals grow in the metastable zone to form large crystals.

[0011] As used herein, the term "unstable zone" supersaturation refers to a solution concentration range above the minimum supersaturation concentration where spontaneous crystal nucleation occurs.

[0012] In this specification, Brix, which is a concentration unit of the solid content of the D-allulose-containing mother liquor, may be used interchangeably with weight %.

[0013] In order to achieve the above object, the present invention provides a method for preparing a D-allulose-containing mother liquor by adding D-allulose seeds to the D-allulose-containing mother liquor and then adjusting the temperature of the D-allulose-containing mother liquor to a first temperature T i to the final temperature T f The present invention provides a method for producing D-allulose crystals, comprising the step of proceeding with a crystallization reaction under a temperature gradient that decreases from 0.01 to 0.01.

[0014] In the present invention, the initial solids concentration of the D-allulose-containing mother liquor is preferably 70 to 86 Brix (Brix), more preferably 75 to 85 Brix (Brix), when considering smooth crystallization of D-allulose, the size of the D-allulose crystalline particles, and the economic efficiency of the crystallization reaction. Furthermore, the initial D-allulose content of the D-allulose-containing mother liquor is preferably 94 to 99 wt %, more preferably 95 to 98 wt %, based on the total weight of the sugars in the mother liquor, when considering the size of the D-allulose crystalline particles, the purity of the D-allulose crystalline particles, and the economic efficiency of the crystallization reaction. For example, the sugar composition of the D-allulose-containing mother liquor may be 95 to 98 wt % allulose, 0.1 to 2 wt % fructose, 0.5 to 4 wt % glucose, and the remainder being other sugars, based on the total weight of the sugars in the mother liquor. The D-allulose-containing mother liquor used as a starting material in the present invention may be prepared by various known methods. For example, the D-allulose-containing mother liquor may be prepared by reacting fructose syrup with D-allulose 3-epimerase to prepare an allulose-containing solution, followed by decolorization, desalting, chromatographic fractionation, and concentration.

[0015] In the present invention, the D-allulose seed crystals are fine crystals composed of high-purity D-allulose, and the purity of the D-allulose seed crystals is preferably 99-100% (w / w), more preferably 99.5-100% (w / w). The average particle size of the D-allulose seed crystals is not significantly limited and may be selected from 50-300 μm, preferably 100-250 μm. The amount of the D-allulose seed crystals added is not significantly limited, and considering the size of the D-allulose crystal particles and the economic efficiency of the crystallization reaction, it is preferably 0.1-5.0% (w / w), more preferably 0.2-3.0% (w / w), based on the total weight of the solids in the D-allulose-containing mother liquor.

[0016] In the present invention, the initial temperature T iWhen taking into consideration the smooth crystallization of D-allulose, the size of D-allulose crystal particles, the economic efficiency of the crystallization reaction, etc., the initial temperature T is preferably selected from the range of 30 to 55°C, and more preferably from 35 to 52°C. i If the initial temperature T is less than 30°C, a solidification phenomenon may occur during the crystallization reaction, which may result in a low crystallinity (or crystallization yield), making it difficult to apply industrially. i If the final temperature T for the crystallization reaction is higher than 55°C, the solid concentration of the D-allulose-containing mother liquor, which corresponds to a supersaturated state, is too high, and processes such as stirring may not be smooth. f is the initial temperature T i The initial temperature T i It is preferable to select a temperature 1 to 10°C lower than the final temperature T f is the initial temperature T i Even if the temperature is selected to be 1 to 5°C lower than the initial temperature T i to the final temperature T f The temperature gradient that decreases includes at least a temperature condition corresponding to a supersaturated state in the metastable zone, and preferably is configured as a temperature condition that maintains the supersaturated state in the metastable zone during the crystallization reaction.

[0017] In the present invention, the crystallization reaction time is not significantly limited, and when taking into consideration the size of D-allulose crystal particles, the economic efficiency of the crystallization reaction, etc., it is preferably selected to be 35 to 100 hours, more preferably 40 to 80 hours.

[0018] In the present invention, the crystallization reaction is carried out under reduced pressure conditions of 10 to 100 mbar (mb), preferably 30 to 80 mbar (mb). When the crystallization reaction is carried out under reduced pressure conditions close to a vacuum, the resulting crystal particles have a predominantly cubic structure, resulting in a uniform particle size distribution. This allows for smooth filtration and improved flowability of the resulting crystal particles when separating the resulting crystals from the mother liquor after the crystallization reaction is completed.

[0019] The method for producing D-allulose crystals according to the present invention may preferably further comprise the step of adjusting the concentration of the D-allulose-containing mother liquor by adding a diluent to the D-allulose-containing mother liquor during the crystallization reaction. The diluent may be added by adding water alone, by adding a diluted mother liquor having a lower solids concentration than the D-allulose-containing mother liquor alone, or by alternately adding water and the D-allulose-containing solution. The solids concentration of the D-allulose-containing diluted mother liquor used as the diluent is preferably 10 to 45 Brix to prevent a sudden change in the concentration of the D-allulose-containing mother liquor undergoing crystallization at the time of adding the diluent. The sugar composition of the D-allulose-containing solution added alternately with water is preferably the same as that of the D-allulose-containing mother liquor. In addition, the solids concentration of the D-allulose-containing solution added alternately with water is preferably 55 to 80 Brix to prevent a sudden change in the concentration of the D-allulose-containing mother liquor undergoing crystallization at the time of addition. In the present invention, the reason for adjusting the concentration of the D-allulose-containing mother liquor by adding a dilution solution during the crystallization reaction is to prevent the formation of new fine crystals during the crystallization reaction or to remove the fine crystals that have already formed. During the crystallization reaction, if the D-allulose-containing mother liquor is in a supersaturated state in the unstable region due to various factors such as reaction temperature, reaction pressure, and crystal precipitation, D-allulose fine crystals such as crystal nuclei are formed, and these fine crystals have a negative impact on the structure, size, and size distribution of the crystal particles. In the present invention, by adding a dilution solution to the D-allulose-containing mother liquor at least once, preferably multiple times (e.g., 2 to 4 times), from the time when new fine crystals are generated during the crystallization reaction until the end of the crystallization reaction, the time when the D-allulose-containing mother liquor is in a supersaturated state in the unstable region is minimized, and the D-allulose-containing mother liquor spends most of its time in a supersaturated state in the metastable region, thereby suppressing the generation of new fine crystals due to various factors or removing the formed fine crystals.In the present invention, the time point at which new fine crystals are formed during the crystallization reaction is determined by various factors such as the D-allulose-containing mother liquor conditions, temperature gradient conditions, stirring conditions, and pressure conditions. Generally, it is about 20 to 24 hours after adding D-allulose seed crystals to the D-allulose-containing mother liquor and carrying out the crystallization reaction under a temperature gradient. Furthermore, in the present invention, adding a diluent solution during the crystallization reaction can control the structure and size distribution of the crystal particles, thereby significantly increasing the precipitation rate of the crystal particles. The total amount of diluent solution added in the method for producing D-allulose crystals according to the present invention is not significantly limited. Considering efficient concentration control of the D-allulose-containing mother liquor and smooth inhibition or removal of fine crystal formation, the total amount of diluent solution added is preferably 1 to 10% (w / w), more preferably 2 to 8% (w / w), of the total weight of the D-allulose-containing mother liquor.

[0020] The method for producing D-allulose crystals according to the present invention may preferably further comprise the step of washing and dehydrating the mother liquor after the crystallization reaction is completed, and then drying to obtain D-allulose crystalline particles. The washing and dehydrating process of the mother liquor may be carried out by various known methods such as centrifugation, vacuum filtration using filter paper or filter cloth, etc. The drying process may be carried out by various known methods such as hot air drying, spray drying, fluidized bed drying, etc.

[0021] The D-allulose crystalline particles produced by the method for producing D-allulose crystals according to the present invention have a mostly cubic crystalline structure and a relatively uniform particle size distribution, resulting in excellent flowability. The average particle size of the D-allulose crystalline particles produced by the method for producing D-allulose crystals according to the present invention is 200-500 μm, preferably 220-460 μm. The D-allulose crystalline particles produced by the method for producing D-allulose crystals according to the present invention have a D-allulose purity of 98.5% (w / w) or more (e.g., 98.5-100%), preferably 99% (w / w) or more (e.g., 99-99.9%). [Effects of the Invention]

[0022] The D-allulose crystalline particles produced by the method of the present invention have a mostly cubic crystalline structure and a uniform particle size distribution, resulting in good flowability. Furthermore, when producing D-allulose crystals by the method of the present invention, the crystallization yield can be significantly improved. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 shows the saturation curve and supersaturation curve of D-allulose crystals. [Figure 2] FIG. 2 is a micrograph of the D-allulose crystals obtained in Production Example 6 of the present invention. [Figure 3] FIG. 3 is a micrograph of the D-allulose crystals obtained in Production Example 13 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will now be described in detail with reference to the following examples, which are merely intended to clearly illustrate the technical features of the present invention and are not intended to limit the scope of the present invention.

[0025] Example 1: Preparation of D-allulose-containing mother liquor An allulose epimerization enzyme mutant derived from Flavonifractor plautii was added to a fructose-containing solution, reacted, and then centrifuged to collect the supernatant. Regarding the process of converting fructose to allulose using an allulose epimerization enzyme mutant, the present invention refers to Korean Patent Publication No. 10-2021-0132405 and Korean Patent Registration No. 10-2254411. The supernatant was then treated with activated carbon to decolorize it, and passed through an ion exchange resin column for desalting, yielding a purified, low-purity allulose-containing solution. The low-purity allulose-containing solution was then concentrated to a solids concentration of approximately 50 Brix. The low-purity allulose-containing concentrate was then passed through a calcium-substituted ion exchange resin (MUK 555) for chromatographic separation, yielding a high-purity D-allulose-containing solution. The high-purity D-allulose-containing solution was then concentrated to prepare high-purity D-allulose-containing mother liquors with various solid concentrations. The solid concentrations of the D-allulose-containing mother liquors were 70 to 84 Brix, and the sugar composition, based on the total weight of the solids, was 95.6% (w / w) allulose, 1.0% (w / w) fructose, 1.9% (w / w) glucose, and 1.5% (w / w) others.

[0026] Example 2: Preparation of D-allulose seed crystals D-allulose seed crystals were prepared using a D-allulose-containing mother liquor with a solids concentration of 84 Brix. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring and temperature control system, and the temperature was adjusted to 40°C. Then, approximately 3% by weight of reagent-grade allulose particle product (>95%) was added to the mother liquor solids. The mixture was stirred at approximately 100 rpm to uniformly disperse the reagent-grade allulose particle product. The stirring speed was then reset to approximately 1.0-1.5 rpm, and the mother liquor was slowly cooled from 40°C to 10°C over approximately 70 hours under temperature gradient conditions. The solution after the crystallization reaction was then centrifuged, washed with water, dehydrated, and dried at approximately 50°C for 6 hours to obtain D-allulose seed crystals. The obtained D-allulose seed crystals had an average crystal particle size of approximately 150 μm, and the sugar composition contained 99.9% by weight of allulose.

[0027] Example 3: Measurement of saturation and supersaturation concentrations of D-allulose crystals The D-allulose seed crystals obtained in Example 2 were added in small amounts to distilled water and dissolved at a specific temperature selected from 30 to 80°C, and the concentration at which no further dissolution occurred was defined as the saturation concentration at that temperature. High-purity D-allulose solutions with solid concentrations of 83 Brix, 89 Brix, and 92 Brix were prepared using the D-allulose seed crystals obtained in Example 2, respectively, and then gradually cooled to measure the temperature at which crystal particles began to form. The concentration of each sample was defined as the supersaturation concentration at that temperature. Figure 1 shows the saturation and supersaturation curves of D-allulose crystals.

[0028] Example 4: Crystallization experiment of D-allulose-containing mother liquor under normal pressure conditions and temperature gradient in the metastable region Allulose crystals were prepared using D-allulose-containing mother liquors with 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. The D-allulose seed crystals obtained in Example 2 were then added in a predetermined amount relative to the solid content of the mother liquor. The mixture was stirred at approximately 100 rpm to uniformly disperse the D-allulose seed crystals. The stirring speed was then reset to approximately 1.0-1.5 rpm, and the mother liquor was cooled or maintained at the cooled temperature for a predetermined period under atmospheric pressure, allowing the crystallization reaction to proceed under a temperature gradient corresponding to the metastable region. The solution after the crystallization reaction was then centrifuged, washed with water, dehydrated, and dried at approximately 50°C for 6 hours to obtain D-allulose crystals. Tables 1 and 2 below show the crystallization reaction conditions used in Example 4 and the analytical results of the resulting D-allulose crystals. Figure 2 is a micrograph of D-allulose crystals obtained in Preparation Example 6 of the present invention. As shown in Figure 2, when seed crystals were added to an allulose-containing mother liquor and crystallization was induced by cooling under a temperature gradient in the metastable zone at atmospheric pressure, crystals with long needle-like structures were produced. The crystals grown during the crystallization process were broken and undifferentiated, resulting in a non-uniform particle size distribution. When the solution after the crystallization reaction in Preparation Example 6 was filtered by centrifugation, the undifferentiated crystal particles formed a fine membrane on the filter cloth, significantly reducing filtration performance. In addition, the D-allulose crystal particles prepared in Preparation Example 6 contained many fine crystal particles and had a non-uniform particle size distribution, resulting in poor flowability even after drying.

[0029] [Table 1]

[0030] [Table 2]

[0031] Example 5: Preliminary experiment to determine pressure conditions during crystallization of D-allulose-containing mother liquor by temperature gradient in the metastable region A D-allulose-containing mother liquor with a solids concentration of 81 Brix was placed in a crystallizer equipped with a stirring, temperature control, and pressure control system, and the temperature of the mother liquor was adjusted to 45°C. The D-allulose seed crystals obtained in Example 2 were then added in an amount of 0.5 wt% based on the solids content of the mother liquor. The mixture was stirred at approximately 100 rpm to uniformly disperse the D-allulose seed crystals. The stirring speed was then reset to approximately 1.0-1.5 rpm, and the internal pressure of the crystallizer was gradually reduced from 250 mbar to 50 mbar. Crystal growth within the allulose-containing mother liquor was observed when the internal pressure of the crystallizer was below 100 mbar, a near-vacuum condition. D-allulose crystal growth began, and whitening was observed.

[0032] Example 6: Crystallization experiment of D-allulose-containing mother liquor under reduced pressure conditions and a temperature gradient in the metastable region Allulose crystals were prepared using D-allulose-containing mother liquors with various solid concentrations. Specifically, the mother liquor was placed in a crystallizer equipped with agitation, temperature control, and pressure control systems, and the temperature of the mother liquor was adjusted to a specific temperature. The D-allulose seed crystals obtained in Example 2 were then added in a predetermined amount relative to the solid content of the mother liquor. The mixture was stirred at approximately 100 rpm to uniformly disperse the D-allulose seed crystals. The stirring speed was then reset to approximately 1.0-1.5 rpm, and the mother liquor was cooled or maintained at the cooled temperature for a predetermined period while adjusting the vacuum pressure within a predetermined range. Crystallization was then carried out under temperature gradient conditions corresponding to the metastable region. The solution after the crystallization reaction was then washed and dehydrated using centrifugation, followed by drying at approximately 50°C for 6 hours to obtain D-allulose crystals. The crystallization conditions used in Example 6 and the analytical results of the resulting D-allulose crystals are shown in Tables 3 and 4 below.

[0033] [Table 3]

[0034] [Table 4]

[0035] Example 7: Crystallization experiment of D-allulose-containing mother liquor under reduced pressure conditions, a temperature gradient in the metastable region, and the addition of a dilution solution Allulose crystals were prepared using D-allulose-containing mother liquors with various solid concentrations. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring, temperature control, and pressure control system, and the temperature of the mother liquor was adjusted to a specific temperature. The D-allulose seed crystals obtained in Example 2 were then added in a predetermined amount relative to the solid content of the mother liquor, and the mixture was stirred at about 100 rpm to uniformly disperse the D-allulose seed crystals. The stirring speed was then reset to about 1.0-1.5 rpm, and the mother liquor was cooled for a predetermined time or maintained at the cooled temperature for a predetermined time while adjusting the vacuum pressure within a predetermined range, and the crystallization reaction was carried out under temperature gradient conditions corresponding to the metastable region. In addition, from the point at which fine crystals were formed during the crystallization reaction (approximately 24 hours into the crystallization reaction) until the end of the crystallization reaction, distilled water alone, a D-allulose-containing diluted mother liquor with a solids content of 35 Brix alone, or a combination of distilled water and a D-allulose-containing mother liquor with a solids content of 70 Brix were added twice at regular intervals to adjust the concentration of the mother liquor and suppress the formation of new crystal nuclei. The total amount of the dilution solution added was 5% (w / w) of the total weight of the D-allulose-containing mother liquor used in the crystallization reaction. The solution after the crystallization reaction was then washed and dehydrated using centrifugation and dried at approximately 50°C for 6 hours to obtain D-allulose crystals. Table 5 below shows the crystallization reaction conditions used in Example 7 and the analytical results of the resulting D-allulose crystals. Figure 3 is a microscopic photograph of the D-allulose crystals obtained in Preparation Example 13 of the present invention. As shown in Figure 3, seed crystals were added to an allulose-containing mother liquor, and crystallization was induced by cooling it under reduced pressure under a temperature gradient in the metastable zone. While the crystallization reaction was proceeding, a diluent was added to adjust the concentration of the mother liquor to suppress the formation of new fine crystals. Crystals with a cubic structure were formed, the phenomenon of breakage of the grown crystals during the crystallization process was minimized, and the particle size distribution was uniform. When the solution after the crystallization reaction in Preparation Example 13 was filtered by centrifugation, there was almost no deterioration in filtration performance.Furthermore, the D-allulose crystalline particles produced in Production Example 13 had an average particle size within the appropriate range and a uniform particle size distribution, and therefore had good flowability even after drying.

[0036] [Table 5]

[0037] Although the present invention has been described with reference to the above examples, it is to be understood that the present invention is not limited thereto and that various modifications can be made without departing from the scope and spirit of the present invention. Therefore, the scope of protection of the present invention should be interpreted as including all embodiments falling within the scope of the appended claims. Furthermore, the present invention includes the following aspects. [Aspect 1] After adding D-allulose seeds to the D-allulose-containing mother liquor, the temperature of the D-allulose-containing mother liquor is initially set to T i to the final temperature T f 1. A method comprising the step of: conducting a crystallization reaction under a temperature gradient that decreases from The temperature gradient includes a temperature condition corresponding to a supersaturated state in a metastable zone, A method for producing D-allulose crystals, wherein the crystallization reaction is carried out under reduced pressure conditions of 10 to 100 millibars (mb). [Aspect 2] The method for producing D-allulose crystals according to aspect 1, further comprising the step of adjusting the concentration of the D-allulose-containing mother liquor by adding a diluent solution to the D-allulose-containing mother liquor during the crystallization reaction. [Aspect 3] A method for producing D-allulose crystals according to aspect 1, characterized in that the initial solid concentration of the D-allulose-containing mother liquor is 70 to 86 Brix, and the initial D-allulose content of the D-allulose-containing mother liquor is 94 to 99 wt % based on the total weight of sugars in the mother liquor. [Aspect 4] A method for producing D-allulose crystals according to aspect 1, wherein the amount of D-allulose seed crystals added is 0.1 to 5.0% (w / w) based on the total weight of the solids in the D-allulose-containing mother liquor. [Aspect 5] The initial temperature T i is selected between 30 and 55°C, and the final temperature T f is the initial temperature T i 2. The method for producing crystals of D-allulose according to claim 1, wherein the temperature is selected to be 1 to 15°C lower than the temperature at which the allulose crystals are formed. [Aspect 6] 2. The method for producing D-allulose crystals according to claim 1, wherein the crystallization reaction time is selected to be 35 to 100 hours. [Aspect 7] The method for producing D-allulose crystals according to aspect 2, wherein the dilution solution is added by adding water alone, by adding a dilution mother liquor having a lower solids concentration than the D-allulose-containing mother liquor alone, or by adding water and the D-allulose-containing solution alternately. [Aspect 8] A method for producing D-allulose crystals according to aspect 2, characterized in that the dilution solution is added multiple times from the time when fine crystals are produced until the end of the crystallization reaction. [Aspect 9] A method for producing D-allulose crystals according to aspect 2, wherein the total amount of the diluted solution added is 1 to 10% (w / w) based on the total weight of the D-allulose-containing mother liquor.

Claims

1. After adding the D-allulose seed crystals to the D-allulose-containing mother liquor, the temperature of the D-allulose-containing mother liquor is initially set to T ｉ to the final temperature T ｆ A method for producing D-allulose crystals, comprising: carrying out a crystallization reaction under a temperature gradient that decreases from the initial temperature T i is selected from the range of 35° C. to 52° C., and the final temperature T f is selected from the range of 1° C. to 10° C. lower than the initial temperature T i ; The temperature gradient satisfies the temperature condition corresponding to the supersaturated state of the metastable zone, The crystallization reaction is carried out under reduced pressure conditions of 30 to 80 millibars (mb), The method further comprises the step of adjusting the concentration of the D-allose-containing mother liquor by adding a diluent solution to the D-allose-containing mother liquor during the crystallization reaction. A method for producing D-allulose crystals.

2. 2. The method for producing D-allulose crystals according to claim 1, wherein the initial solid concentration of the D-allulose-containing mother liquor is 70 to 86 Brix, and the initial D-allulose content of the D-allulose-containing mother liquor is 94 to 99 wt% based on the total weight of sugars in the mother liquor.

3. The method for producing D-allulose crystals according to claim 1, wherein the amount of D-allulose seed crystals added is 0.1 to 5.0% (w / w) based on the total weight of the solids in the D-allulose-containing mother liquor.

4. The method for producing D-allulose crystals according to claim 1, wherein the dilution solution is added by adding water alone, adding a dilution mother liquor having a lower solids concentration than the D-allulose-containing mother liquor alone, or adding water and the D-allulose-containing solution alternately.

5. The method for producing D-allulose crystals according to claim 1, wherein the dilution solution is added multiple times from the time when fine crystals are produced until the crystallization reaction is completed.

6. The method for producing D-allulose crystals according to claim 1, wherein the total amount of the dilution solution added is 1 to 10% (w / w) based on the total weight of the D-allulose-containing mother liquor.

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