Method for producing D-allose 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 system crystal structure and a uniform particle size distribution of crystal particles.

Background Art

[0002] D-allulose is also called D-psicose as an epimer of the 3rd carbon of fructose. D-allulose has a sweetness of 70% compared to sugar (Oshima 2006), but has only 0.3% energy, so it is a functional monosaccharide applicable as a low-calorie sweetener for diet foods (Matsuo et al.2002). In addition, D-allulose has a function of suppressing the absorption of glucose and blood sugar, and can be applied to foods and beverages for diabetics, health foods and beverages, etc. By suppressing the enzyme activity involved in lipid synthesis in the liver, abdominal fat accumulation can be suppressed, so it can be used in various functional foods such as 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 replace sugar, but it belongs to rare sugars, which are monosaccharides that exist very rarely in nature. Therefore, in order to apply it to the food industry, a method for efficiently producing allulose is required. The most efficient method for industrial production of allulose is a method of converting fructose to allulose using D-allulose 3-epimerase. Since the reaction solution containing D-allulose produced by the enzyme reaction is a low-purity product containing about 30% (w / w) of D-allulose solids, in order to produce high-purity D-psicose crystal particles of 98% (w / w) or more, it is required to produce a high-purity allulose-containing mother liquor using chromatography.

[0004] Generally, the crystallization methods of saccharides are roughly classified into two types. One is the concentration crystallization method, and the other is the cooling crystallization method. Both methods utilize the principle of inducing crystal growth within the interval of the metastable zone of the supersaturated state as crystallization methods for saccharides. Usually, the crystallization of saccharides is carried out in the metastable zone, and such a state means the range from the equilibrium concentration of the solution, i.e., the saturation concentration, to the minimum supersaturation at which crystals spontaneously precipitate. Crystallization phenomena such as crystal nucleation do not occur at the concentration in this region, but when new crystals are introduced from the outside, crystal growth occurs and the crystal size increases. That is, when seed crystals are introduced into a solution with a concentration above the saturation concentration to generate crystals, the seed crystals grow in the metastable zone and crystal growth takes place. If the solution for crystallization is overly concentrated or rapidly cooled, it will enter a supersaturated state beyond the metastable zone, and the generation of new crystal nuclei rather than crystal growth will occur, which becomes an inhibitory factor for crystal growth due to the increase in the number of individuals. Therefore, temperature conditions and the initial entering supersaturation concentration are important for crystal growth.

[0005] D-allose shows characteristics with almost no change in crystal formation rate and crystal growth rate even in the supersaturated concentration range, so it can be classified as a saccharide with difficult crystallization conditions for particle size growth. Usually, the crystal grain size is known as an important factor in the saccharide crystallization industry. When the crystals produced in a mass production system are fine crystals, the separation of crystals and mother liquor in the equipment of the crystal centrifuge is not easily carried out due to the viscosity in the supersaturated concentration range, so the purity of the final product decreases due to the influence of the remaining mother liquor. In addition, the remaining mother liquor causes the phenomenon of crystal agglomeration during drying, resulting in a decrease in the packaged quantity of the final product and a decline in marketability. Therefore, these fine crystals are not suitable for mass production methods.

[0006] In connection with a method for producing D-allulose crystals, Korean Patent Registration Publication No. 10-1189640 discloses a method for producing D-psicose crystals, which includes treating a D-psicose solution with a decolorizing agent and an ion exchange resin for purification 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 at 0.01 to 1% (g / g) of the total amount of D-psicose in the concentrated D-psicose solution, and crystallizing D-psicose in a supersaturated state in the metastable zone. Also, Korean Patent Registration Publication No. 10-1749527 discloses a method for producing D-psicose crystals, which includes removing impurities from a D-psicose solution to obtain a purified D-psicose solution, concentrating the purified D-psicose solution to 80 Brix (%) to 85 Brix (%), cooling the concentrated D-psicose solution by 5°C to 20°C per hour to 30°C to 40°C through a heat exchanger, crystallizing the D-psicose solution at 30°C to 40°C to obtain a massecuite, and performing main crystallization at 30°C to 40°C using the seeded massecuite.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been derived under the background of the prior art. The 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 crystal particles. Another object of the present invention is to provide a method for producing D-allulose crystals with improved crystallization yield.

Means for Solving the Problems

[0008] When the inventors of the present invention added seed crystals to a D-allulose-containing mother liquor and induced crystallization while cooling under temperature gradient conditions in the metastable zone at normal pressure, crystals having a long needle-like structure were produced, and the crystals grown during the crystallization process were broken and undifferentiated. As a result, the particle size distribution was non-uniform, and when separating the allulose crystals produced after the crystallization reaction was completed and the remaining mother liquor by a method such as filtration, it was confirmed that the filtration performance was significantly reduced by the fine crystal particles. In order to solve this problem, the inventors of the present invention confirmed that when inducing allulose crystals from a D-allulose-containing mother liquor, using a reduced pressure condition within a predetermined range enables the production of allulose crystals having a cubic crystal system type crystal structure, a large average particle size of the crystal particles, and a uniform particle size distribution, and thus completed the present invention. Further, the inventors of the present invention confirmed that when inducing allulose crystals from a D-allulose-containing mother liquor, when adding distilled water or a mother liquor with a low concentration in a predetermined amount from the time when fine crystals are produced until the crystallization reaction ends in order to suppress the generation of new crystal nuclei, the crystallization yield is significantly increased, and thus completed the present invention.

[0009] As used herein, the term "supersaturated state" refers to an unstable state in which a solute is dissolved in a solvent in an amount exceeding the solvent's dissolution capacity, and means a state in which the solute can precipitate as a solid. Therefore, a supersaturated state is always necessary to separate the solute in the 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" means a state in which the concentration of the solution is in the range from the saturation concentration to the minimum supersaturation concentration at which crystals spontaneously precipitate. At the concentration in this region, crystallization phenomena such as crystal nucleation do not occur. However, since it is a supersaturated concentration, when crystals are introduced from the outside, crystal growth occurs spontaneously and the crystal size increases. That is, in order to produce crystals, when a seed crystal is introduced into a solution having a concentration above the saturation concentration, the seed crystal grows in the metastable zone to form large crystals.

[0011] As used herein, the supersaturated state of the "unstable zone" means a state in which the concentration of the solution is in a range exceeding the minimum supersaturation concentration. At the concentration in this region, spontaneous generation of crystal nuclei occurs.

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

[0013] To solve the above object, the present invention provides a method for producing D-allose crystals, which includes a step of allowing a crystallization reaction to proceed under a temperature gradient in which the temperature of the mother liquor containing D-allose is decreased from an initial temperature T i to a final temperature T f after adding D-allose seed crystals to the mother liquor containing D-allose.

[0014] In the present invention, considering smooth crystallization of D-allulose, the size of D-allulose crystal particles, and the economy of the crystallization reaction, etc., the initial solid content concentration of the D-allulose-containing mother liquor is preferably 70 to 86 Brix, and more preferably 75 to 85 Brix. Further, considering the size of D-allulose crystal particles, the purity of D-allulose crystal particles, and the economy of the crystallization reaction, etc., the initial D-allulose content of the D-allulose-containing mother liquor is preferably 94 to 99% by weight based on the total weight of the saccharides in the mother liquor, and more preferably 95 to 98% by weight. For example, the saccharide composition of the D-allulose-containing mother liquor may be composed of 95 to 98% by weight of allulose, 0.1 to 2% by weight of fructose, 0.5 to 4% by weight of glucose, and the balance of other saccharides based on the total weight of the saccharides in the mother liquor. In the present invention, the D-allulose-containing mother liquor used as a starting material may be produced by various known methods. For example, the D-allulose-containing mother liquor can be produced by reacting fructose syrup with D-allulose 3-epimerase to produce an allulose-containing solution, followed by decolorization, desalting, fractionation by chromatography, and concentration processes.

[0015] In the present invention, the D-allulose seed crystal is a fine crystal composed of high-purity D-allulose. The purity of D-allulose in the D-allulose seed crystal is preferably 99 to 100% (w / w), and more preferably 99.5 to 100% (w / w). Also, the size of the average particles of the D-allulose seed crystal is not greatly restricted and may be selected from 50 to 300 μm, and is preferably 100 to 250 μm. The addition amount of the D-allulose seed crystal is not greatly restricted. Considering the size of D-allulose crystal particles, the economy of the crystallization reaction, etc., it is preferably 0.1 to 5.0% (w / w) relative to the total weight of the solid content of the D-allulose-containing mother liquor, and more preferably 0.2 to 3.0% (w / w).

[0016] In the present invention, the initial temperature T for the crystallization reaction iis preferably selected at 30 to 55°C, more preferably at 35 to 52°C, when considering the smooth crystallization of D-allose, the size of D-allose crystal particles, the economy of the crystallization reaction, etc. The initial temperature T i If it is less than 30°C, there is a risk of solidification during the progress of the crystallization reaction, which may result in a low degree of crystallization (or crystallization yield) and difficulty in industrial application. Also, the initial temperature T i If it exceeds 55°C, the solid content concentration of the D-allose-containing mother liquor corresponding to the supersaturated state is too high, and the processes such as stirring may not be smooth. In the present invention, the final temperature T f for the crystallization reaction may be selected at a temperature 1 to 15°C lower than the initial temperature T i , and it is preferably selected at a temperature 1 to 10°C lower than the initial temperature T i . In particular, as described later, when the crystallization reaction is carried out under reduced pressure conditions close to a vacuum state of 10 to 100 millibars (mb), even if the final temperature T f is selected at a temperature 1 to 5°C lower than the initial temperature T i , crystal particles mainly having a cubic crystal system type structure and having a uniform particle size distribution can be obtained. In the present invention, in order to induce the crystallization reaction, the temperature gradient for reducing the temperature of the D-allose-containing mother liquor from the initial temperature T i to the final temperature T f includes at least the temperature conditions corresponding to the supersaturated state in the metastable zone, and preferably, it is composed of the temperature conditions maintained in the supersaturated state in the metastable zone during the progress of the crystallization reaction.

[0017] In the present invention, the crystallization reaction time is not greatly restricted, and when considering the size of D-allose crystal particles, the economy of the crystallization reaction, etc., it is preferably selected at 35 to 100 hours (hr), more preferably at 40 to 80 hours (hr).

[0018] In the present invention, the crystallization reaction is carried out under reduced pressure conditions of 10 to 100 millibars (mb), preferably 30 to 80 millibars (mb). When the crystallization reaction is carried out under reduced pressure conditions close to a vacuum state, the generated crystal particles mainly have a cubic crystal system type structure, the particle size distribution of the crystal particles becomes uniform, and after the crystallization reaction is completed, when separating the generated crystals from the mother liquor, filtration is smooth and the flowability of the obtained crystal particles is improved.

[0019] The method for producing D-allose crystals according to the present invention may preferably further include a step of adding a dilution solution to the D-allose-containing mother liquor to adjust the concentration of the D-allose-containing mother liquor while the crystallization reaction is in progress. Further, the addition of the dilution solution may be carried out by adding water alone, adding a dilution mother liquor having a lower solid content concentration than the D-allose-containing mother liquor alone, or by alternately introducing water and a D-allose-containing solution. The solid content concentration of the D-allose-containing dilution mother liquor used as the dilution solution is preferably 10 to 45 Brix in order to suppress a rapid change in the concentration of the D-allose-containing mother liquor in which the crystallization reaction is in progress at the time of adding the dilution solution. Further, the saccharide composition of the D-allose-containing solution alternately introduced with the water is preferably the same as the saccharide composition of the D-allose-containing mother liquor. Further, the solid content concentration of the D-allose-containing solution alternately introduced with the water is preferably 55 to 80 Brix in order to suppress a rapid change in the concentration of the D-allose-containing mother liquor in which the crystallization reaction is in progress at the time of addition. In the present invention, the reason for adding a dilution solution to adjust the concentration of the D-allose-containing mother liquor while the crystallization reaction is in progress is to suppress the generation of new fine crystals or to remove the formed fine crystals during the crystallization reaction process. If the D-allose-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 during the crystallization reaction process, D-allose fine crystals such as crystal nuclei are formed, and the fine crystals have a negative impact on the structure of crystal particles, the size of crystal particles, the particle size distribution of crystal particles, etc. In the present invention, from the time when new fine crystals are generated until the crystallization reaction ends while the crystallization reaction is in progress, the dilution solution is added to the D-allose-containing mother liquor one or more times, preferably a plurality of times (for example, 2 to 4 times), so as to minimize the time during which the D-allose-containing mother liquor is in a supersaturated state in the unstable region, make the majority of the time in a supersaturated state in the metastable region, and suppress the generation of new fine crystals due to various factors or remove the formed fine crystals.In the present invention, the point in time when new fine crystals are generated during the progress of the crystallization reaction is determined by various factors such as the conditions of the mother liquor containing D-allose, the temperature gradient conditions, the stirring conditions, the pressure conditions, etc. Generally, it is the time when about 20 to 24 hours have elapsed since adding D-allose seed crystals to the mother liquor containing D-allose and proceeding with the crystallization reaction under a temperature gradient. Further, in the present invention, by adding a dilution solution during the progress of the crystallization reaction, 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 producing D-allose crystals according to the present invention, the total addition amount of the dilution solution is not greatly restricted. Considering efficient concentration adjustment of the mother liquor containing D-allose, smooth suppression or removal of the generation of fine crystals, etc., it is preferably 1 to 10% (w / w), more preferably 2 to 8% (w / w) relative to the total weight of the mother liquor containing D-allose.

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

[0021] The D-allose crystal particles produced by the method for producing D-allose crystals according to the present invention mostly have a cubic crystal system type crystal structure and exhibit a relatively uniform particle size distribution, so they have excellent fluidity. Further, the average particle size of the D-allose crystal particles produced by the method for producing D-allose crystals according to the present invention is 200 to 500 μm, preferably 220 to 460 μm. Also, the D-allose crystal particles produced by the method for producing D-allose crystals according to the present invention have a D-allose purity of 98.5% (w / w) or more (for example, 98.5 to 100%), preferably 99% (w / w) or more (for example, 99 to 99.9%).

Effects of the Invention

[0022] The D-allulose crystal particles produced by the method of the present invention mostly have a cubic crystal structure, and since the particle size distribution of the crystal particles is uniform, they have good fluidity. Further, when producing D-allulose crystals by the method of the present invention, the crystallization yield can be greatly improved.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0024] Hereinafter, the present invention will be specifically described by the following examples. However, the following examples are only for clearly exemplifying the technical features of the present invention and do not limit the protection scope of the present invention.

[0025] Example 1: Preparation of D-allulose-containing mother liquor After adding an allulose epimerase variant derived from Flavonifractor plautii to a fructose-containing solution and reacting it, centrifugation was performed to recover the supernatant. In relation to the step of converting fructose to allulose using the allulose epimerase variant, the present invention refers to Korean Patent Publication No. 10-2021-0132405 and Korean Registered Patent Publication No. 10-2254411. Thereafter, the supernatant was treated with activated carbon for decolorization, passed through an ion exchange resin column for desalting, and a purified low-purity allulose-containing solution was obtained. Thereafter, the low-purity allulose-containing solution was concentrated to a solid content concentration of about 50 Brix, and the low-purity allulose-containing concentrated solution was passed through an ion exchange resin (MUK 555) substituted with a calcium group to perform chromatographic separation, and a high-purity D-allulose-containing solution was obtained. Thereafter, the high-purity D-allulose-containing solution was concentrated to prepare high-purity D-allulose-containing mother liquors with various solid content concentrations. The solid content concentration of the D-allulose-containing mother liquor is 70 to 84 Brix, and the sugar composition is 95.6% (w / w) allulose, 1.0% (w / w) fructose, 1.9% (w / w) glucose, and 1.5% (w / w) others based on the total weight of the solid content.

[0026] Example 2: Production of D-allulose seed crystal D-allose seed crystals were produced using a D-allose-containing mother liquor with a solid content concentration of 84 Brix. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring and temperature control system. After adjusting the temperature of the mother liquor to 40°C, a reagent-grade allose particle product with a purity of over 95% was added in an amount of about 3% by weight relative to the solid content of the mother liquor, and the mixture was stirred at a speed of about 100 rpm to uniformly disperse the reagent-grade allose particle product. Thereafter, the stirring speed was reset to about 1.0 - 1.5 rpm, and the crystallization reaction was allowed to proceed under a temperature gradient condition where the temperature of the mother liquor was slowly cooled from 40°C to 10°C over about 70 hours. Thereafter, the solution in which the crystallization reaction had proceeded was washed with water and dehydrated using centrifugation, and dried at about 50°C for 6 hours to obtain D-allose seed crystals. The obtained D-allose seed crystals had an average crystal particle size of about 150 μm, and the sugar composition had an allose content of 99.9% by weight.

[0027] Example 3: Measurement of the saturation concentration and supersaturation concentration of D-allose crystals The D-allose seed crystals obtained in Example 2 were added little by little to distilled water and dissolved under specific temperature conditions selected from 30 to 80°C, and the concentration at which no further dissolution occurred was defined as the saturation concentration at the corresponding temperature. Also, using the D-allose seed crystals obtained in Example 2, high-purity D-allose solutions with solid content concentrations of 83 Brix, 89 Brix, and 92 Brix, respectively, were prepared. Then, while gradually cooling, the temperature at which crystal particles began to form was measured, and the concentration of each sample was defined as the supersaturation concentration at the corresponding temperature. Figure 1 shows the saturation curve and supersaturation curve of D-allose crystals.

[0028] Example 4: Crystallization experiment of D-allose-containing mother liquor under normal pressure conditions and temperature gradient in the metastable region D-allulose crystals were produced 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 after adjusting the temperature of the mother liquor to a specific temperature, the D-allulose seed crystals obtained in Example 2 were added in a predetermined amount relative to the solids content of the mother liquor, and stirred at a speed of about 100 rpm to uniformly disperse the D-allulose seed crystals. Thereafter, the stirring speed was reset to about 1.0 - 1.5 rpm, and the mother liquor was cooled over a predetermined time or maintained at the cooled temperature for a predetermined time under atmospheric pressure conditions, and the crystallization reaction proceeded under temperature gradient conditions corresponding to the metastable zone. Thereafter, the solution in which the crystallization reaction had proceeded was washed with water and dehydrated using centrifugation, and dried at about 50 °C for 6 hours to obtain D-allulose crystals. The crystallization reaction conditions used in Example 4 and the analysis results of the obtained D-allulose crystals are shown in Tables 1 and 2 below. Figure 2 is a photograph of the D-allulose crystals obtained in Production Example 6 of the present invention taken with a microscope. As shown in Figure 2, when seed crystals were added to the allulose-containing mother liquor and crystallization was induced while cooling under the temperature gradient conditions of the metastable zone at atmospheric pressure, crystals having a long needle-like structure were generated, and the crystals grown during the crystallization process were broken and undifferentiated, whereby the particle size distribution was non-uniform. When the solution in which the crystallization reaction was completed in Production Example 6 was filtered by centrifugation or the like, a fine-mesh membrane was formed on the filter cloth by the undifferentiated crystal particles, and the filtration performance was significantly reduced. Further, the D-allulose crystal particles produced in Production Example 6 had a large number of fine crystal particles and a non-uniform particle size distribution, and thus had poor flowability even after drying.

[0029]

Table 1

[0030]

Table 2

[0031] Example 5: Preliminary experiment for setting pressure conditions in the crystallization process by the temperature gradient in the metastable zone of the D-allulose-containing mother liquor A crystallizer equipped with a stirring, temperature control, and pressure control system was charged with a mother liquor containing D-allose with a solid content concentration of 81 Brix. After adjusting the temperature of the mother liquor to 45°C, the D-allose seed crystals obtained in Example 2 were added thereto in an amount of 0.5% by weight based on the solid content of the mother liquor, and the mixture was stirred at a speed of about 100 rpm to uniformly disperse the D-allose seed crystals. Thereafter, the stirring speed was reset to about 1.0 - 1.5 rpm, and the formation of crystals in the allose-containing mother liquor was observed while gradually reducing the internal pressure of the crystallizer from 250 millibars (mb) to 50 millibars (mb). The growth of D-allose crystals began under conditions where the internal pressure of the crystallizer was close to a vacuum of 100 millibars (mb) or less, and a whitening phenomenon was shown.

[0032] Example 6: Crystallization experiment of D-allose-containing mother liquor under reduced pressure conditions and temperature gradient in the metastable region Allose crystals were produced using mother liquors containing D-allose with various solid content concentrations. Specifically, a 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. Thereafter, the D-allose seed crystals obtained in Example 2 were added thereto in a predetermined amount based on the solid content of the mother liquor, and the mixture was stirred at a speed of about 100 rpm to uniformly disperse the D-allose seed crystals. Thereafter, the stirring speed was reset to about 1.0 - 1.5 rpm, and while adjusting the reduced pressure conditions within a predetermined range, the mother liquor was cooled over a predetermined time or maintained at a temperature cooled for a predetermined time, and the crystallization reaction proceeded under temperature gradient conditions corresponding to the metastable region. Thereafter, the solution in which the crystallization reaction had proceeded was washed with water and dehydrated using centrifugation, and dried at about 50°C for 6 hours to obtain D-allose crystals. Table 3 and Table 4 below show the crystallization reaction conditions used in Example 6 and the analysis results of the obtained D-allose crystals.

[0033] [Table 3]

[0034] [Table 4]

[0035] Example 7: Crystallization experiment by decompression conditions of D-allulose-containing mother liquor, temperature gradient in the metastable region, and addition of dilution solution D - allulose crystals were produced using mother liquors with various solid - content concentrations. Specifically, the mother liquor was placed in a crystallizer equipped with a stirring, temperature - regulating, and pressure - regulating system. After adjusting the temperature of the mother liquor to a specific temperature, the D - allulose seed crystals obtained in Example 2 were added in a predetermined amount relative to the solid content of the mother liquor, and then stirred at a speed of about 100 rpm to uniformly disperse the D - allulose seed crystals. Thereafter, the stirring speed was reset to about 1.0 - 1.5 rpm, and the mother liquor was cooled over a predetermined time while adjusting the vacuum condition within a predetermined range, or maintained at the temperature cooled for a predetermined time, and the crystallization reaction proceeded under the temperature - gradient condition corresponding to the metastable region. Also, from the point when fine crystals were generated during the progress of the crystallization reaction (when the crystallization reaction time was about 24 hr) until the end of the crystallization reaction, a dilution solution was added twice at regular intervals, either distilled water alone, a D - allulose - containing diluted mother liquor with a solid - content of 35 Brix alone, or a combination of distilled water and a D - allulose - containing mother liquor with a solid - content of 70 Brix, to adjust the concentration of the mother liquor and suppress the generation of new crystal nuclei. The total addition amount of the dilution solution was 5% (w / w) relative to the total weight of the D - allulose - containing mother liquor used for the crystallization reaction. Thereafter, the solution in which the crystallization reaction had proceeded was washed with water and dehydrated using centrifugation, and dried at about 50°C for 6 hr to obtain D - allulose crystals. Table 5 below shows the crystallization reaction conditions used in Example 7 and the analysis results of the obtained D - allulose crystals. Figure 3 is a photograph taken with a microscope of the D - allulose crystals obtained in Production Example 13 of the present invention. As shown in Figure 3, when seed crystals were added to the allulose - containing mother liquor and crystallization was induced while cooling under the temperature - gradient condition of the metastable zone under vacuum conditions, and a dilution solution was added during the progress of the crystallization reaction to adjust the concentration of the mother liquor and suppress the generation of new fine crystals, crystals having a cubic crystal - system structure were generated, the phenomenon of the crystals grown during the crystallization process being broken was minimized, and the particle - size distribution was uniform. When the solution in which the crystallization reaction was completed in Production Example 13 was filtered by centrifugation or the like, almost no deterioration in filtration performance occurred.In addition, the D-allose crystal particles produced in Production Example 13 had an average particle size within an appropriate range and a uniform particle size distribution, so they had good flowability even after drying.

[0036]

Table 5

[0037] As described above, the present invention has been described by the above embodiments, but the present invention is not necessarily limited only here, and it goes without saying that various modifications can be made within the scope not deviating from the scope and spirit of the present invention. Therefore, the protection scope of the present invention should be analyzed to include all embodiments belonging to the scope of the claims attached to the present invention.

Claims

1. After adding D-allulose seed crystals to the D-allulose-containing mother liquor, the temperature of the D-allulose-containing mother liquor is changed from the initial temperature T ｉ to the final temperature T ｆ and the crystallization reaction is allowed to proceed under a temperature gradient that decreases to. This is a method comprising the step of 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). A method for producing D-allose crystals, characterized in that.

2. The method for producing D-allose crystals according to claim 1, further comprising a step of adding a dilution solution to the D-allose-containing mother liquor during the progress of the crystallization reaction to adjust the concentration of the D-allose-containing mother liquor.

3. The method for producing D-allose crystals according to claim 1, characterized in that the initial solid content concentration of the D-allose-containing mother liquor is 70 to 86 Brix, and the initial D-allose content of the D-allose-containing mother liquor is 94 to 99% by weight based on the total weight of the saccharides in the mother liquor.

4. The method for producing D-allose crystals according to claim 1, characterized in that the addition amount of the D-allose seed crystals is 0.1 to 5.0% (w / w) compared to the total weight of the solid content of the D-allose-containing mother liquor.

5. The initial temperature T ｉ is selected at 30 to 55°C, and the final temperature T ｆ is selected at a temperature 1 to 15°C lower than the initial temperature T ｉ The method for producing D-allose crystals according to claim 1, characterized in that

6. The method for producing D-allose crystals according to claim 1, characterized in that the crystallization reaction time is selected from 35 to 100 hr.

7. The method for producing D-allose crystals according to claim 2, characterized in that the addition of the dilution solution is carried out by adding water alone, adding a dilution mother liquor having a lower solid content concentration than the D-allose-containing mother liquor alone, or alternately introducing water and the D-allose-containing solution.

8. The method for producing D-allose crystals according to claim 2, characterized in that the addition of the dilution solution is carried out in multiple times from the time when fine crystals are formed until the crystallization reaction is completed.

9. The method for producing D-allose crystals according to claim 2, characterized in that the total addition amount of the dilution solution is 1 to 10% (w / w) compared to the total weight of the D-allose-containing mother liquor.

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