A preparation method for anti-caking D-psicose crystals

Abstract

The present invention provides a method for preparing anti-caking D-psicose crystals, comprising the steps of: injecting concentrated D-psicose syrup into a sugar boiling tank and a concentration tank, respectively; further concentrating in the sugar boiling tank to stimulate crystallization and then crystallizing; then equally cross-dividing the slurry obtained in the sugar boiling tank and the D-psicose syrup in the concentration tank into two identical crystallizers, mixing, and cooling and crystallizing to obtain D-psicose crystals. The cross-dividing method reduces the crystal nucleus density, thereby increasing the crystal particles, improving the crystal morphology, reducing crystal collision and nucleation between crystals, and preparing a highly anti-caking D-psicose crystal product. The process does not use any organic solvent, and the obtained D-psicose crystal yield is above 47wt%, of which crystals above 40 mesh account for 80-83.8wt%, the crystal aspect ratio is between 3:1 and 4:1, and the crystal is short rod-shaped, with an angle of repose of about 35°, good fluidity, little crystal fragmentation, and good anti-caking performance.

Description

Technical Field

[0001] The present invention belongs to the field of chemical engineering industrial crystallization technology, and specifically relates to a production method and application of D-psicose crystals, and in particular to a preparation method and application of anti-caking D-psicose crystals. Background Art

[0002] In recent years, the prevalence of chronic diseases such as diabetes, hypertension and obesity has increased rapidly worldwide, posing a serious threat to human health. These diseases are partly caused by excessive dietary energy intake, and the use of low-calorie and functional foods to replace high-energy, high-sugar, and high-fat diets is considered an effective strategy to solve these problems. Therefore, low-calorie functional sugars are increasingly valued in the research and development and production of food and medicine. D-psicose, as a low-calorie sugar substitute, is considered to be the most promising sugar to replace sucrose in the future and has received widespread attention from researchers. The English name of D-psicose is D-psicose, and its molecular formula is C6H 12 O6. It is usually a white crystalline powder with a refreshing sweetness. Its sweetness is 70% of sucrose, and its calorie content is only 0.4 kcal / g. Its sweet taste is similar to that of sucrose, and it can be used as a low-calorie sweetener to replace sucrose in food. In addition, compared with other sugar substitutes, D-psicose has significant physiological functions. It can effectively lower blood sugar and blood lipids, and has a significant antagonistic effect on inflammatory responses. In 2021, my country's National Health Commission has accepted the application of D-psicose as a new food ingredient. In the next few years, D-psicose is expected to be approved for listing, and the market prospects are broad.

[0003] Currently, D-psicose production in my country is primarily concentrated in Shandong and other regions, with the majority of its products destined for export. Since D-psicose is primarily used by food companies for rapid re-dissolution to produce functional sugar syrups, high particle flowability is crucial after unpacking from bulk bags. For substances like D-psicose, which have long rod- or needle-shaped crystals, high water solubility, and strong hygroscopicity, significant clumping can occur during long-distance transportation and storage, seriously impacting the crystals' application in customer production. Agglomeration is the process by which a low-moisture, free-flowing powder transforms into agglomerated solids, leading to loss of functionality and reduced quality. This is a common problem in industries such as food, fertilizer, pharmaceutical, and chemical. For functional sugar crystals, particle size and shape are crucial to product quality. Agglomeration irreversibly damages the size and shape of the crystals, and even after breaking and agglomerating, agglomerated crystals no longer retain the properties of the original crystals. This has a significant negative impact on downstream processes and long-distance trade and transportation of functional sugars. The main cause of agglomeration is that when crystal particles come into contact with each other, the contact points dissolve due to the presence of water. As the temperature and humidity change day and night, this crystal bridge grows, dissolves, and grows, becoming stronger and stronger, thus forming agglomerates. Therefore, it is necessary to optimize from two perspectives: water content and the particles themselves to combat agglomeration. For the particles themselves, agglomeration is usually effectively combated by improving the crystal size and crystal habit. Larger particle size and less fine powder content can reduce the number of contact points of crystals per unit mass, thereby reducing the agglomeration rate. Improving the long crystal habit to short rods or blocks, that is, a morphology closer to a spherical shape, can also effectively promote solid-liquid separation and reduce contact between crystals. These are all effective strategies to combat agglomeration. Regarding moisture content, the focus is on improving back-end crystallization technology. Although some post-processing technologies, such as conveyor line dehumidification and the addition of maturation bins, can reduce the moisture content of crystal products by removing residual moisture before packaging, during long-distance transportation, due to the hygroscopicity of D-psicose crystals and inadequate packaging seals, water vapor can still diffuse into the packaging. Moisture migration caused by alternating daytime and nighttime temperature and humidity can lead to hard agglomerates, which is particularly evident during sea transportation. Therefore, starting from the crystallization process, producing larger crystals, improving product morphology, and reducing the amount of fine powder to reduce contact points between crystals can fundamentally enhance the anti-caking properties of D-psicose crystals.

[0004] CN 113412266 A describes a method for crystallizing D-psicose by adding a small amount of ethanol as an organic solvent and recovering the mother liquor. This method shortens the crystallization process and produces D-psicose crystals with a low residual organic solvent content, meeting food safety requirements. However, the resulting D-psicose particle size is not large enough, and the addition of ethanol as an organic solvent can increase costs. The addition of ethanol requires expensive explosion-proof equipment for mother liquor treatment, which increases the cost of D-psicose production and hinders product promotion. CN 109923120 A describes a method for preparing D-psicose crystals using a sugar paste as a seed slurry. This method effectively reduces the number of crystal nuclei and produces large D-psicose particles. However, images of the resulting product show that the aspect ratio is often greater than 4:1, increasing the risk of crystal agglomeration. This work investigates the sugar paste process. Because D-psicose crystals, unlike the blocky crystal habits of fructose and other sugars, have long rod-shaped or even needle-shaped crystals, leaving the sugar paste in the crystals does increase the risk of further elongation, significantly increasing the agglomeration rate. CN 11257263 A proposes a method for preparing D-psicose crystals by evaporation-coupled cooling crystallization. The resulting D-psicose crystals have good morphology and an aspect ratio between 3:1 and 4:1, but the crystals are primarily distributed between 40 and 60 mesh, and the crystal size is not large enough. Furthermore, none of the aforementioned patents investigates the agglomeration of D-psicose crystals. Therefore, using anti-caking performance as the ultimate evaluation metric for the product, finding a method for preparing D-psicose crystals that can significantly increase crystal size, improve crystal morphology, reduce crystal fragmentation, and thereby enhance anti-caking performance, while also being industrializable, remains an unresolved problem in the prior art. Summary of the Invention

[0005] The present invention provides a production method and application of large-particle D-psicose crystals. The D-psicose crystal production method comprises the following steps: forming a slurry containing D-psicose crystals and syrup by stimulating crystallization and performing evaporative dynamic crystallization after evaporation and concentration as a first mixture; forming a high-concentration D-psicose syrup by evaporation and concentration as a second mixture; pumping the two tanks of materials into a cooling crystallizer, mixing, and then cooling and crystallizing. No organic solvent is used in the crystallization process. The obtained psicose crystals have a yield of over 44 wt%, of which crystals with a mesh size of 40 or larger account for over 80 wt%, the crystals have good three-dimensional morphology, an aspect ratio of 3:1 to 4:1 or less, little broken crystals, and good anti-caking performance.

[0006] One objective of the present invention is to provide a method for producing D-psicose crystals. The method comprises injecting concentrated D-psicose syrup into a sugar boiling tank and a concentration tank, respectively. Seed crystals are then added to the sugar boiling tank to stimulate crystallization and undergo dynamic evaporation to achieve crystallization. The D-psicose syrup is then evenly cross-flowed with the D-psicose syrup in the concentration tank and then fed into two identical crystallizers for mixing. The mixture is then cooled and crystallized to obtain D-psicose crystals. The specific steps are as follows:

[0007] (1) The concentrated D-psicose syrup is injected into the sugar boiling tank and the concentration tank respectively;

[0008] (2) The concentrated D-psicose syrup injected into the sugar boiling tank is further concentrated to increase the supersaturation, and seed crystals are added to stimulate crystallization, followed by evaporation crystallization. At the same time, D-psicose syrup raw material liquid is added to form crystals to maintain the dynamic stability of the concentration in the mixed solution;

[0009] (3) The mixed solution obtained in the sugar boiling tank in step (2) and the D-psicose syrup concentrated in the concentration tank in step (1) are equally cross-divided and respectively introduced into two identical crystallizers for mixing, and the mixture is cooled and crystallized to obtain D-psicose crystals.

[0010] In the present invention, the preparation method of the D-psicose syrup concentrated in step (1) comprises: concentrating the D-psicose syrup raw material liquid separated and purified upstream and subjected to triple-effect evaporation into saturated or slightly saturated D-psicose syrup;

[0011] Preferably, the concentration of the D-psicose syrup raw material liquid after triple-effect evaporation is 60-70 wt %;

[0012] Preferably, the temperature of the D-psicose syrup raw material liquid after triple-effect evaporation is 70-90° C.

[0013] Preferably, the concentration of the D-psicose syrup formed by the concentration in step (1) is 84-86 wt%;

[0014] Preferably, the temperature of the D-psicose syrup formed by the concentration in step (1) is 48-50°C.

[0015] In the present invention, in step (2), the sugar boiling tank continues to concentrate until the state of the concentration tank remains unchanged during the evaporation dynamic crystallization process.

[0016] Preferably, the concentration of the concentrated solution obtained by continuing to concentrate in step (2) is 85-87wt%;

[0017] Preferably, the temperature for stimulating crystallization in step (2) is 48-50°C;

[0018] Preferably, the average particle size of the seed crystals in step (2) is 150-325 mesh, preferably 150-200 mesh;

[0019] Preferably, the amount of seed crystals added in step (2) is 0.01-1 wt % of the dry matter content in the concentrated solution obtained by further concentration, preferably 0.05-0.1 wt %;

[0020] Preferably, the D-psicose syrup raw material liquid in step (2) is added by feeding;

[0021] Preferably, the concentration of the D-psicose syrup raw material liquid in step (2) is 60-70 wt%;

[0022] Preferably, the temperature of the D-psicose syrup raw material liquid in step (2) is 70-90° C.;

[0023] Preferably, the evaporation crystallization in step (2) is carried out under vacuum conditions with a vacuum degree of 5-100 mbar, preferably 10-40 mbar;

[0024] Preferably, the evaporation crystallization in step (2) is carried out under stirring conditions, and the stirring power is 0.2-0.3kW / m 3 .

[0025] In the present invention, the cross-flow in step (3) can be carried out by first unloading the sugar boiling tank or first unloading the concentration tank;

[0026] Preferably, the temperature of the cross-flow in step (3) is 48-50° C., and the time of the cross-flow is 1-2 h.

[0027] Preferably, in step (3), the volumes of the sugar boiling tank, the concentration tank and the crystallizer are the same;

[0028] Preferably, the cooling crystallization in step (3) is carried out in four steps: the first step is to cool the temperature from 48-50°C to 40-42°C at a cooling rate of 0.2-0.25°C / h; the second step is to cool the temperature from 40-42°C to 35-37°C at a cooling rate of 0.25-0.33°C / h; the third step is to maintain the temperature at 35-37°C for 4 hours; the fourth step is to cool the temperature from 35-37°C to 27-29°C at a cooling rate of 0.33-0.4°C / h, and stop the cooling crystallization;

[0029] Preferably, the cooling crystallization in step (3) is carried out under stirring conditions with a stirring power of 0.1-0.2 kW / m 3 , horizontal stirring is adopted for stirring.

[0030] In the present invention, the step (3) further comprises sequentially performing solid-liquid separation and drying on the mixture obtained after the cooling crystallization;

[0031] Preferably, the solid-liquid separation method is centrifugation;

[0032] Preferably, the drying method is normal pressure drying, the drying temperature is 25-55° C., and the drying time is 6-48 hours.

[0033] A second object of the present invention is to provide a preparation method as described in the first object to prepare D-psicose crystals.

[0034] The D-psicose crystals prepared by the method of the present invention are short rod-shaped crystals with regular shapes and an aspect ratio of 3:1 to 4:1. The mass of crystal particles larger than 40 mesh accounts for 80-83.8wt%, and the crystals have the characteristics of high purity, good fluidity, large crystal particle size and uniform shape.

[0035] A third object of the present invention is to provide a use of the D-psicose crystals as described in the second object in products for human and / or animal consumption, such as food products, beverages, pharmaceutical products, nutritional products, sports products, or cosmetics.

[0036] The technical features and beneficial effects of the present invention are as follows:

[0037] 1. The present invention proposes, for the first time, a cross-flow method to reduce the initial crystal nucleus density during cooling crystallization to produce large-particle D-psicose crystals. Cross-flow simply combines two of the parallel "sugar boiling-cooling crystallization" production lines currently used in most sugar factories into a single set of production equipment. This process modification can be completed by connecting the existing sugar boiling tanks and crystallization tanks through the conveying pipelines. This eliminates the need for equipment upgrades or additional seed tank processing capacity to achieve crystal nucleus density control, making it easy to scale up production.

[0038] 2. The present invention reduces the inter-batch difference in the number of crystals produced during each whole-pot sugar boiling by two times through a cross-diversion method, thereby increasing the repeatability of D-psicose crystal production.

[0039] 3. The present invention designs different cooling rates within different temperature ranges based on the molecular thermodynamics and crystal growth kinetics parameters of D-psicose. In the higher temperature range (45-50°C), D-psicose nucleation is significantly inhibited, resulting in a faster growth rate. Therefore, at a reasonable cooling rate, secondary nucleation does not occur. Below 40°C, although D-psicose's secondary nucleation ability is enhanced, making nucleation more likely at the same supersaturation, the early crystals have already grown significantly, leaving more crystal faces to absorb the supersaturation, allowing for a gradually increased cooling rate. By rationally designing a cooling curve, secondary nucleation during crystallization can be avoided without the need for rewarming, resulting in the production of large-particle D-psicose crystals with minimal crystal fragmentation.

[0040] 4. The present invention measured the effect of D-psicose crystal morphology on the agglomeration rate, clarifying that low aspect ratio crystal habits and large crystals are the primary means of enhancing the anti-caking properties of D-psicose crystals. Following crystallization according to the preparation method of the present invention, more than 80% by weight of the resulting D-psicose crystals can have a crystal size of 40 mesh or larger, exhibit short rod-shaped crystal habits, and have an aspect ratio between 3:1 and 4:1. The crystals exhibit good fluidity and anti-caking properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 : Optical microscope image of D-psicose crystals obtained in Example 1;

[0042] Figure 2 : Optical microscope image of D-psicose crystals obtained in Example 2;

[0043] Figure 3 : Optical microscope image of D-psicose crystals obtained in Example 3;

[0044] Figure 4 : Optical microscope image of D-psicose crystals obtained in Comparative Example 1;

[0045] Figure 5 : Optical microscope image of D-psicose crystals obtained in Comparative Example 2;

[0046] Figure 6 : Optical microscope image of D-psicose crystals obtained in Comparative Example 3;

[0047] Figure 7 : Optical microscope image of D-psicose crystals obtained in Comparative Example 4;

[0048] Figure 8 : X-ray diffraction (XRD) characterization of the D-psicose aggregate crystals in Example 1 and comparison with the diffraction peaks recorded by the Cambridge Crystallographic Data Center (CCDC);

[0049] Figure 9 : Illustration of the D-psicose angle of repose test method;

[0050] Figure 10 : Schematic diagram of the cross-flow step during the crystallization of D-psicose;

[0051] Figure 11 : Variation of viscosity of D-psicose saturated solution with temperature at different temperatures. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are only provided to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0053] To enable those skilled in the art to more clearly understand the technical solutions of this application, the technical solutions of this application are described in detail below with reference to specific examples. If specific experimental conditions are not specified in the examples, conventional conditions or those recommended by the reagent company are generally followed. The allulose solution used in the following examples was purchased from Shandong Fuyang Biotechnology Co., Ltd. All other reagents and consumables used were commercially available unless otherwise specified. Example 1:

[0054] (1) The 70°C, 60 wt% D-psicose solution separated and purified upstream was evaporated and concentrated to form a 48°C, 84 wt% D-psicose syrup, which was then injected into a sugar boiling tank and a concentration tank of equal volume, respectively;

[0055] (2) The D-psicose syrup injected into the sugar boiling tank was further concentrated at 48°C to obtain 85 wt% D-psicose syrup, and 0.1 wt% 150-200 mesh seed crystals were added to stimulate crystallization, and then evaporation crystallization was carried out. The vacuum degree was 20 mbar and the stirring power was 0.2 kW / m 3 , the same 70°C as the upstream separation and purification liquid used in step (1) was added, and 60 wt% of allulose syrup was used to replenish the latent heat lost by water evaporation to maintain the dynamic stability of the concentration in the mixed solution. The solid mass of the obtained slurry accounted for 14 wt%; at this time, the temperature of the concentration tank obtained in step (1) was maintained, and the state remained unchanged;

[0056] (3) The mixed solution obtained in the sugar boiling tank in step (2) and the concentrated D-psicose syrup in the concentration tank in step (1) were equally cross-divided and respectively entered into two identical crystallizers for mixing for 1 hour, during which the temperature was maintained at 48°C, and then the temperature was lowered and crystallized. The cooling rate was: within 48-40°C, the temperature was lowered by 0.2°C per hour; within 40-35°C, the temperature was lowered by 0.33°C per hour; at 35°C, the temperature was maintained unchanged for 4 hours; within 35-27°C, the temperature was lowered by 0.4°C per hour; and the temperature was stopped at 27°C. The stirring power was maintained at 0.1kW / m during the whole process. 3 . D-psicose crystals were obtained.

[0057] After the crystallization, the obtained slurry was subjected to solid-liquid separation treatment with a centrifugal speed of 1000 rpm, 2000 rpm for 1 min each, and 3000 rpm for 5 min, and dried at 50°C for 9 h to obtain D-psicose crystal products.

[0058] The optical microscope picture of the crystals obtained at the end of the crystallization of Psicose is shown in Figure 1The window showed low levels of broken crystals, large crystal size, and aspect ratios ranging from 3:1 to 4:1. The yield of D-psicose crystals was 48.8 wt%, with 83.8 wt% of the resulting crystal product containing larger particles larger than 40 mesh. Example 2:

[0059] (1) The 90°C, 70 wt% D-psicose solution separated and purified upstream was evaporated and concentrated to form a 50°C, 86 wt% D-psicose syrup, which was then injected into a sugar boiling tank and a concentration tank of equal volume, respectively;

[0060] (2) The D-psicose syrup injected into the sugar boiling tank was further concentrated at 50°C to obtain 87 wt% D-psicose syrup, and 0.05 wt% 150-200 mesh seed crystals were added to stimulate crystallization, and then evaporation crystallization was carried out. The vacuum degree was 10 mbar and the stirring power was 0.3 kW / m 3 , the same 90°C as the upstream separation and purification liquid used in step (1) was added, and 70 wt% of allulose syrup was used to replenish the latent heat lost by water evaporation to maintain the dynamic stability of the concentration in the mixed solution. The solid mass of the obtained slurry accounted for 20 wt%; at this time, the temperature of the concentration tank obtained in step (1) was maintained, and the state remained unchanged;

[0061] (3) The mixed solution obtained in the sugar boiling tank in step (2) and the concentrated D-psicose syrup in the concentration tank in step (1) were equally cross-divided and then sent to two identical crystallizers for mixing for 2 hours, during which the temperature was maintained at 50°C, and then the temperature was lowered and crystallized. The cooling rate was: within 50-42°C, the temperature was lowered by 0.25°C per hour; within 42-37°C, the temperature was lowered by 0.33°C per hour; at 37°C, the temperature was maintained unchanged for 4 hours; within 37-29°C, the temperature was lowered by 0.4°C per hour; and the temperature was stopped at 27°C. The stirring power was maintained at 0.2kW / m during the whole process. 3 . D-psicose crystals were obtained.

[0062] After the crystallization, the obtained slurry was subjected to solid-liquid separation treatment with a centrifugal speed of 1000 rpm, 2000 rpm for 1 min each, and 3000 rpm for 5 min, and dried at 50°C for 9 h to obtain D-psicose crystal products.

[0063] The optical microscope picture of the crystals obtained at the end of the crystallization of Psicose is shown in Figure 2 The window showed low levels of broken crystals, large crystal size, and an aspect ratio between 3:1 and 4:1. The yield of D-psicose crystals was 50.3 wt%, with 81 wt% of the resulting crystal product consisting of larger particles larger than 40 mesh. Example 3:

[0064] (1) The 80°C, 65 wt% D-psicose solution separated and purified upstream was evaporated and concentrated to form a 49°C, 85 wt% D-psicose syrup, which was then injected into a sugar boiling tank and a concentration tank of equal volume, respectively;

[0065] (2) The D-psicose syrup injected into the sugar boiling tank was further concentrated at 49°C to obtain 86 wt% D-psicose syrup, and 0.08 wt% 150-200 mesh seed crystals were added to stimulate crystallization, and then evaporation crystallization was carried out. The vacuum degree was 15 mbar and the stirring power was 0.25 kW / m 3 , the same 80°C as the upstream separation and purification liquid used in step (1) was added, and 65 wt% of allulose syrup was used to replenish the latent heat lost by water evaporation to maintain the dynamic stability of the concentration in the mixed solution. The solid mass of the obtained slurry accounted for 16 wt%; at this time, the temperature of the concentration tank obtained in step (1) was maintained, and the state remained unchanged;

[0066] (3) The mixed solution obtained in the sugar boiling tank in step (2) and the concentrated D-psicose syrup formed in the concentration tank in step (1) were equally cross-divided and respectively entered into two identical crystallizers for mixing for 1 hour, during which the temperature was maintained at 49°C, and then the temperature was lowered and crystallized. The cooling rate was: within 49-41°C, the temperature was lowered by 0.3°C per hour; within 41-36°C, the temperature was lowered by 0.3°C per hour; at 36°C, the temperature was maintained unchanged for 4 hours; within 36-28°C, the temperature was lowered by 0.35°C per hour; and the temperature was stopped at 28°C. The stirring power was maintained at 0.16kW / m during the whole process. 3 . D-psicose crystals were obtained.

[0067] After the crystallization, the obtained slurry was subjected to solid-liquid separation treatment with a centrifugal speed of 1000 rpm, 2000 rpm for 1 min each, and 3000 rpm for 5 min, and dried at 50°C for 9 h to obtain D-psicose crystal products.

[0068] The optical microscope picture of the crystals obtained at the end of the crystallization of Psicose is shown in Figure 3 The window showed low levels of broken crystals, large crystal size, and aspect ratios ranging from 3:1 to 4:1. The yield of D-psicose crystals was 47.3 wt%, with 80.1 wt% of the resulting crystal product consisting of larger particles larger than 40 mesh.

[0069] The above embodiments are preferred implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

[0070] Comparative Example 1:

[0071] D-psicose crystals were prepared according to the method of Example 1. The difference from Example 1 was that the cross-diversion step and the preparation of the second mixture were omitted, and the first mixture was directly subjected to cooling crystallization. The other steps and operations were the same as in Example 1.

[0072] The optical microscope picture of the crystals obtained at the end of the crystallization of Psicose is shown in Figure 4 The yield of D-psicose crystals was 49.1wt%. The crystals were still relatively uniform, but the particle size was small, and there were many broken crystals in the window. The mass of the larger crystals above 40 mesh in the obtained crystal product accounted for 46.4wt%.

[0073] Comparative Example 2:

[0074] D-psicose crystals were prepared according to the method of Example 2. The difference from Example 2 was that the temperature of step (2) stimulating crystallization and step (3) evaporation dynamic crystallization was 60°C, the concentration was 89 wt%, and the cooling rate was: within the range of 60-40°C, the temperature was lowered by 0.25°C per hour; within the range of 40-35°C, the temperature was lowered by 0.33°C per hour; at 35°C, the temperature was maintained unchanged for 4 hours; within the range of 35-27°C, the temperature was lowered by 0.33°C per hour; cooling and crystallization were stopped at 27°C. The stirring power was maintained at 0.2 kW / m during the whole process. 3 The other steps and operations are the same as those in Example 2.

[0075] The optical microscope picture of the crystals obtained at the end of D-psicose crystallization is shown in Figure 5 The yield of D-psicose crystals was detected to be 58.3wt%, the product contained many broken crystals, the window was blurred, the aspect ratio of the crystals was about 4:1, and the mass of larger particles larger than 40 mesh in the obtained crystal product accounted for 72.4wt%.

[0076] Comparative Example 3:

[0077] D-psicose crystals were prepared according to the method of Example 3. The difference from Example 3 was that the stirring power of evaporation dynamic crystallization and cooling crystallization was increased to 1 kW / m 3 , other steps and operations are the same as those in Example 3.

[0078] After the crystallization was completed, the yield of D-psicose crystals was detected to be 48.7 wt %. The optical microscope photo of the crystals obtained at the end of the crystallization was as follows: Figure 6 As shown, the product has many broken crystals, small particle size, and crystal aspect ratio above 4:1. The proportion of larger particle crystals above 40 mesh in the obtained crystal product is 59.7wt%.

[0079] Comparative Example 4:

[0080] D-psicose crystals were prepared according to the process parameters of Example 1. The difference from Example 1 was that a sugar paste retention process was adopted. After the crystallization of Example 1 was completed, 30 wt% of D-psicose syrup was retained as a seed slurry, which was mixed with the second mixture and then cooled and crystallized to obtain a crystal product.

[0081] After the crystallization was completed, the yield of D-psicose crystals was detected to be 52.3 wt %. The optical microscope photo of the crystals obtained at the end of the crystallization was as follows: Figure 7 As shown, the obtained product has many broken crystals, the crystals are obviously elongated, and the aspect ratio is above 5:1. The larger particle crystals above 40 mesh account for 72.4wt% of the obtained crystal product.

[0082] Crystal form refers to the arrangement of crystal molecules in a crystal and is an important physical and chemical property of the crystal. For polymorphic substances, certain physical and chemical properties (such as melting point, solubility, and stability) may vary due to different crystal forms. Moreover, under different conditions, different crystal forms may transform into each other, resulting in a crystal transformation phenomenon. In order to verify whether the prepared D-psicose crystals have different crystal forms compared with commercial D-psicose crystals, the D-psicose agglomerated crystals in Example 1 were characterized by X-ray diffraction (XRD) and compared with the diffraction peaks recorded by the Cambridge Crystallographic Data Center (CCDC). The diffraction peak positions are shown in Figure 2. Figure 8 As shown in Figure 1, according to the provisions of P372 of the 2015 edition of the Chinese Pharmacopoeia, if two crystalline samples are judged to have the same crystal form, the error range of their diffraction peak positions should be within ±0.2°. Figure 8 It can be seen that the prepared D-psicose crystals have the same diffraction angle as the CCDC standard spectrum peak. Therefore, it can be considered that the D-psicose crystals in this patent are consistent with the crystal form of the currently reported D-psicose products, and no crystal transformation phenomenon occurs during the crystallization process.

[0083] In addition, the repose angle and anti-caking performance of different embodiments and comparative examples were tested to evaluate the quality of their crystal particles. The repose angle test method is based on the repose angle measurement method provided by patent CN113412266A, such as Figure 9 shown.

[0084] The agglomeration rate is determined as follows: 5 g of a crystal sample is accurately weighed using an analytical balance and spread flat on a glass dish. The sample and glass dish are weighed as a whole on an electronic balance. Gently shake the glass dish to ensure that the sample is evenly distributed and in a continuous contact state without overlapping. The sample is then placed in a constant temperature and humidity chamber set to 25°C and a humidity of approximately 60%-30%. The chamber is cycled once every 6 hours and repeated 5 times. After the cycle is completed, the agglomerated crystals are picked out and weighed. The weighed mass is then divided by the initial crystal mass to obtain the agglomeration rate. The following table (Table 1) shows the angle of repose and agglomeration rate of different embodiments and comparative examples.

[0085] Table 1. Dissolution rates and angles of repose of the crystalline products obtained in different examples and comparative examples.

[0086] name Angle of repose / ° Agglomeration rate Example 1 32.4 17.4 Example 2 31.0 19.3 Example 3 35.2 21.6 Comparative Example 1 43.5 36.4 Comparative Example 2 48.7 40.1 Comparative Example 3 40.9 39.3 Comparative Example 4 49.4 45.4

[0087] By comparing Example 1 with Comparative Example 1, it can be seen that the cross-flow operation is very important for reducing the amount of broken crystals and improving the particle size distribution of crystal products. The cross-flow process diagram is shown in FIG. Figure 10 When cross-flow is eliminated and direct cooling crystallization is performed, the number of crystal nuclei participating in the cooling crystallization process in the cooling crystallizer is excessive. Although supersaturation can be consumed more quickly, the excessive number of crystal nuclei hinders crystal growth and increases the probability of collision, resulting in smaller crystal size and more broken crystals. The particles have poor fluidity and are more prone to agglomeration.

[0088] By comparing Example 2 and Comparative Example 2, it can be seen that when the cooling range is too wide, although the single-pass yield of D-psicose crystallization can be increased, it can be seen from the change of the viscosity of the saturated solution of D-psicose at different temperatures with temperature ( Figure 11 The higher the temperature of a saturated D-psicose solution, the higher its viscosity, hindering mass transfer. Furthermore, a key characteristic of sugar crystallization is that solutes in the solution accumulate as the temperature decreases, leading to a gradual increase in supersaturation. Therefore, a high initial concentration results in a high supersaturation at the end of the cooling process, leading to explosive nucleation and a blurred crystal window, significantly widening the particle size distribution. These ultrafine crystals adhere to the surface of the crystal product, making it rough and reducing its fluidity. The adhesion of these ultrafine crystals also increases the contact points between crystals, significantly reducing the crystal's anti-agglomeration properties.

[0089] By comparing Example 3 and Comparative Example 3, it can be seen that when the stirring rate is too fast, although it will promote mass transfer, the nucleation promotion is more obvious at high rotation speed, and too many crystal nuclei will cause the particle size distribution to be low. In addition, excessive shear force will break a considerable part of the crystals, resulting in more broken crystals, thereby making the particle size distribution out of control, worsening the three-dimensional morphology of the crystals, reducing fluidity, and increasing the risk of agglomeration of subsequent products.

[0090] A comparison of Example 1 and Comparative Example 4 shows that when the sugar paste retention process, commonly used in sugar crystallization, is used as the seed crystal slurry production process, the retained crystals further elongate without significantly increasing their lateral width. This indicates that the seed crystals lack effective crystal faces, and the solute consumed by crystal growth is far less than the increase in supersaturation caused by cooling, resulting in explosive nucleation and a high degree of broken crystals. Although the product obtained from the previous batch can be further grown to produce large particles, the excessive length of the large particles also increases the agglomeration rate.

[0091] The present invention discloses and proposes a method for preparing and applying anti-caking D-psicose crystals. Those skilled in the art can implement the method by appropriately modifying certain aspects of the method by drawing upon the present disclosure. The method of the present invention has been described through preferred embodiments. Those skilled in the art will readily be able to modify, alter, and combine the methods and products described herein without departing from the content, spirit, and scope of the present invention to implement the technology of the present invention. It should be noted that all similar substitutions and modifications readily apparent to those skilled in the art are considered encompassed by the spirit, scope, and content of the present invention.

Claims

1. A method for preparing anti-caking D-psicose crystals, characterized in that: The preparation method comprises: (1) injecting the concentrated D-psicose syrup into a sugar boiling tank and a concentration tank respectively; (2) The concentrated D-psicose syrup injected into the sugar boiling tank is further concentrated to increase supersaturation, and seed crystals are added to stimulate crystallization, followed by evaporation crystallization. At the same time, D-psicose syrup raw material liquid is added to form crystals, maintaining the dynamic stability of the concentration in the mixed solution; (3) the mixed solution obtained in the sugar boiling tank in step (2) and the D-psicose syrup concentrated in the concentration tank in step (1) are equally cross-divided and respectively introduced into two identical crystallizers for mixing, and the mixture is cooled and crystallized to obtain D-psicose crystals; The method for preparing the D-psicose syrup formed by concentration in step (1) comprises: concentrating a D-psicose syrup raw material liquid separated and purified upstream and subjected to triple-effect evaporation into a saturated or slightly saturated D-psicose syrup; The concentration of the D-psicose syrup raw material liquid after triple-effect evaporation is 60-70 wt %; The temperature of the D-psicose syrup raw material liquid after triple-effect evaporation is 70-90° C. The concentration of the D-psicose syrup formed by the concentration in step (1) is 84-86 wt %; The temperature of the D-psicose syrup formed by the concentration in step (1) is 48-50° C. The temperature for stimulating crystallization in step (2) is 48-50°C; The average particle size of the seed crystals in step (2) is 150-325 mesh; The evaporation crystallization in step (2) is carried out under stirring conditions with a stirring power of 0.2-0.3 kW / m 3 ; The cross-flow temperature in step (3) is 48-50° C., and the cross-flow time is 1-2 h. The cooling crystallization in step (3) is carried out in four steps: the first step is to reduce the temperature from 48-50°C to 40-42°C at a cooling rate of 0.2-0.25°C / h; the second step is to reduce the temperature from 40-42°C to 35-37°C at a cooling rate of 0.25-0.33°C / h; the third step is to maintain the temperature at 35-37°C for 4h; the fourth step is to reduce the temperature from 35-37°C to 27-29°C at a cooling rate of 0.33-0.4°C / h, and stop the cooling crystallization.

2. The preparation method according to claim 1, characterized in that The concentration of the concentrated solution obtained by continuing to concentrate in step (2) is 85-87wt%.

3. The preparation method according to claim 1, characterized in that The average particle size of the seed crystals in step (2) is 150-200 mesh.

4. The preparation method according to claim 1, characterized in that The amount of the seed crystals added in step (2) is 0.01-1 wt % of the dry matter content in the concentrated solution obtained by further concentration.

5. The preparation method according to claim 4, characterized in that The amount of the seed crystals added in step (2) is 0.05-0.1 wt % of the dry matter content in the concentrated solution obtained by continued concentration.

6. The preparation method according to claim 1, characterized in that The D-psicose syrup raw material liquid in step (2) is added by feeding.

7. The preparation method according to claim 1, characterized in that The evaporation crystallization in step (2) is carried out under vacuum conditions with a vacuum degree of 5-100 mbar.

8. The preparation method according to claim 7, characterized in that The vacuum degree is 10-20 mbar.

9. The preparation method according to claim 1, characterized in that The volumes of the sugar boiling tank, concentration tank and crystallizer in step (3) are the same.

10. The preparation method according to claim 1, characterized in that The cooling crystallization in step (3) is carried out under stirring conditions with a stirring power of 0.1-0.2 kW / m 3 , horizontal stirring is adopted for stirring.

11. The preparation method according to claim 1, characterized in that The step (3) further comprises sequentially performing solid-liquid separation and drying on the mixture obtained after the cooling crystallization.

12. The preparation method according to claim 11, characterized in that The solid-liquid separation method is centrifugation.

13. The preparation method according to claim 11, characterized in that The drying method is normal pressure drying, the drying temperature is 25-55° C., and the drying time is 6-48 hours.

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