A method for recovering D-psicose crystals from syrup

Abstract

The invention discloses a method for recovering D-psicose crystals from syrup, belongs to the technical field of D-psicose crystallization, and optimizes the crystallization process parameters of D-psicose by using SAS company's JMP software for experimental design (design of experiment, DOE), deeply analyzes the influence of crystallization process parameters on crystallization yield, and establishes a crystallization yield prediction model, thereby accurately controlling the crystallization process. The crystallization yield of D-psicose according to the present invention is increased from 81%% to 91.36% (the highest crystallization rate published by existing data); and the obtained D-psicose crystals are uniform in size, smooth in surface, and have a relatively regular long rod shape with high quality; at the same time, the method also establishes a prediction model for crystallization rate, which can provide guidance for crystallization parameter control in subsequent large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of D-psicose crystals, and particularly relates to a method for recovering D-psicose crystals from syrup. Background Art

[0002] Rare sugar D-psicose (D-psicose; D-ribose-2-hexone sugar; CAS: 551-68-8; molecular formula: C6H 12 D-psicose (D-psicose, molecular weight: 180.156) is a new sweetener with great potential. It has the characteristics of low calories and high sweetness. Its taste is very similar to sucrose, with a sweetness of about 70% of sucrose, but only 0.3% of the calories of sucrose. It hardly participates in the metabolic cycle of the human body and is not easily absorbed and utilized by intestinal microorganisms. D-psicose is a C-3 phase difference isomer of D-fructose, but compared with ketose such as D-fructose, D-tagatose, and D-sorbose, D-psicose has better gel properties, antioxidant properties, foaming properties, and emulsification stability, and is more helpful in improving the color, flavor, and taste of the product. In 2011, the U.S. Food and Drug Administration (FDA) determined that D-psicose is a generally recognized as safe food (GRAS) and can be used as a component of food or food additives. It is safe for humans to consume 31 to 33 g (based on average body weight) of D-psicose per day.

[0003] Since D-psicose is less in nature, it is difficult to meet market demand. For a long time, many scientific research teams at home and abroad have been committed to finding a method for large-scale production of D-psicose. At present, the method for producing D-psicose is mainly a bioenzymatic method, that is, D-fructose is converted into D-psicose by D-tagatose 3-epimerase or D-psicose 3-epimerase to obtain a mixed sugar solution of D-psicose and D-fructose, and then decolorized, filtered, ion exchanged, and chromatographically separated to obtain D-psicose syrup. However, the storage and transportation of D-psicose syrup are extremely inconvenient, and it is easy to precipitate at low temperature, which seriously affects product quality and application.

[0004] Crystallization is an important means of separating solid products from solutions and a key technology for achieving high-end and high-value products. Li Can used natural cooling to slowly precipitate D-psicose, thereby obtaining D-psicose crystals. Guo Yuanheng et al. used ethanol as the crystallization system, adopted a constant temperature crystallization method, and optimized the density of the D-psicose solution, the amount of ethanol added, the crystallization time and the crystallization temperature, and the crystallization yield could reach 71.58%. However, natural cooling precipitation and constant temperature crystallization lack control over crystal nucleation and growth, which is not conducive to the quality stability of the crystallized product. Zhang Mingzhan et al. of Bailong Chuangyuan used fructose syrup as raw material, added D-psicose diastereomerase to react, obtained a mixed sugar solution containing D-psicose, fructose and glucose, and then crystallized at a cooling rate of 0.1℃ / h in the range of 30-40℃. This method is time-consuming, has a low yield, and the crystallized product is a mixture, and subsequent separation is cumbersome. CN106852145B, CJ CheilJedang Co., Ltd. rapidly cools the concentrated D-psicose solution to 40°C, adds an appropriate amount of seed crystals, and then cools the solution to 10°C at a cooling rate of 1°C / h, maintains the temperature at 10°C for 30h, obtains a sugar paste containing D-psicose crystals, and finally obtains D-psicose crystals by centrifugation. Although the crystallization yield of this method can reach 81%, there are still some defects. This method uses pure water for crystallization. In the pure water system, psicose and water have a strong interaction, high solubility, high solution viscosity, and low mass transfer efficiency, resulting in slow crystal growth, and easy nucleation to produce fine crystals, and the crystallization yield cannot be improved. In other words, this method can only improve the particle size and yield of drug crystals by repeatedly heating and cooling for 5-10 times. Due to the lack of optimization of the crystallization process and the lack of understanding of the correlation between process parameters and crystallization yield, the further improvement of D-psicose crystallization yield is limited. Summary of the invention

[0005] In order to overcome the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for recovering D-psicose crystals from syrup, which can solve the technical problem of low yield of D-psicose crystals in the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention discloses a method for recovering D-psicose crystals from syrup, comprising the following steps:

[0008] 1) concentrating the psicose solution to obtain a syrup;

[0009] 2) Add 20% of the volume of syrup into the seeding device, and add ethanol in proportion;

[0010] 3) Raise the temperature to the initial crystallization temperature of 60°C, keep warm for 30 minutes, add seed crystals, stir slowly to make the seed crystals evenly dispersed in the syrup, balance for 30 minutes, and then cool to the crystallization termination temperature of 20°C;

[0011] 4) vacuum filtering to obtain crystals, drying, and obtaining D-psicose crystals.

[0012] Preferably, in step 1), the psicose solution with a purity of 99% is concentrated to a Brix degree of 80%.

[0013] Preferably, in step 2), the mass ratio of the added syrup to ethanol, i.e., the syrup-to-ethanol ratio (w / w) is: 1:3, 1:2, 1:1, 2:1, 3:1;

[0014] More preferably, the mass ratio of the added syrup to the ethanol is 2:1.

[0015] Preferably, in step 3), the mass of the seed crystals added is 10% of the mass of the syrup.

[0016] Preferably, in step 3), the stirring speed is 300 rpm.

[0017] Preferably, in step 3), the cooling rate is 1.5°C / h.

[0018] Preferably, the crystallization yield prediction model equation of D-psicose crystals is as follows:

[0019] Y=-0.0000011a 2 +0.018b 2 -0.00063ab+0.0051ac+1.56bc+0.00016A+0.035B-0.33C+0.84

[0020] Wherein, Y represents the crystallization yield of D-psicose, A: stirring speed, B: cooling rate, C: seed addition amount, a: stirring speed -190, b: cooling rate -0.95, c: seed addition amount -0.049;

[0021] This prediction model can be used to measure the effect of parameter changes during the crystallization process on the crystallization yield.

[0022] The present invention also discloses D-psicose crystals prepared by the method for recovering D-psicose crystals from syrup, characterized in that the D-psicose crystals are uniform in size, smooth in surface, and in a regular long rod shape with a size of 400 μm*100 μm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Compared with the closest prior art (CJ), the present invention has two very critical differences: first, different solvents are used. The present invention adopts organic solvent ethanol, while CJ uses pure water; second, the crystallization temperature range is different. The present method achieves crystallization by cooling from 60 degrees to 20 degrees, while CJ can only achieve crystallization in a lower temperature range. In terms of the effects, firstly, in terms of the crystallization process: the introduction of solvent ethanol avoids repeated heating and cooling, and the energy consumption is greatly reduced compared with the pure water system; the crystallization time is greatly shortened, and under the optimal conditions, the entire crystallization process can be completed in only 26.6 hours, while the entire crystallization process of CJ takes 80-120 hours; secondly, the solubility of the product is greatly reduced, and the product yield is improved. The yield of a single crystallization can reach up to 91.3%, which is significantly higher than the 81% crystallization yield after multiple heating and cooling of the CJ method; in addition, the viscosity of the ethanol system is reduced, the mass transfer efficiency is increased, and the solid content of the solution is reduced, making the crystallization system easier to stir and mix, and the requirements for crystallization equipment are lower, and it is easier to industrialize; in addition, the pure water system is difficult to separate water during the filtration process, the wet product has a high water content, and the drying time is long. The ethanol water system product has a low moisture content after filtration, and due to the presence of ethanol, the filtration and drying time is greatly shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The polarizing microscope photograph of D-psicose crystals prepared by the method of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0027] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0029] The present invention discloses a method for recovering D-psicose crystals from syrup. By using SAS company's JMP software for design of experiment (DOE), the crystallization process parameters of D-psicose are optimized, the influence of the crystallization process parameters on the crystallization yield is deeply analyzed, and a crystallization yield prediction model is established, so as to accurately control the crystallization process. The prediction model can provide guidance for the control of crystallization parameters in subsequent large-scale production. The crystallization yield of D-psicose is increased from 81% to 91.36% (the highest crystallization rate published by existing data so far); and the obtained D-psicose crystals are uniform in size, smooth in surface, and have a relatively regular long rod shape with high quality; at the same time, the method also establishes a prediction model for the crystallization rate, which can provide guidance for the control of crystallization parameters in subsequent large-scale production.

[0030] 1. Determination of the solubility of D-psicose in water or ethanol

[0031] The solubility of D-psicose in water or ethanol was measured by a dynamic method. The specific method is as follows: accurately weigh 20g of pure water (or ethanol) and place it in a 100mL jacketed crystallization kettle, and connect a uniform speed program-controlled thermostatic bath, an electric stirrer, etc. Turn on the uniform speed program-controlled thermostatic bath, turn on the stirring, and after the system reaches the preset temperature, start adding 1.5g of D-psicose to the system, irradiate the crystallization kettle with a low-power beam, and when the solution in the crystallization kettle is observed to be close to saturation at this temperature, add an appropriate amount of solute (i.e., D-psicose). When insoluble matter is observed in the crystallization kettle at this temperature and it is still not dissolved within 30 minutes, the dissolution end point is reached, and the mass of D-psicose added is recorded, and the temperature is raised again to measure the solubility at the next temperature point. The solubility of all temperature points is determined according to this method.

[0032] The results show that the solubility of D-psicose in water (g / g water) increases with the increase of temperature. When the temperature is 50℃, 60℃, and 70℃, the solubility of D-psicose in water is 5.06g / g, 7.39g / g, and 9.49g / g, respectively. Therefore, due to the high solubility of D-psicose in water, the viscosity is too high during the cooling process of the crystallization system, which is prone to nucleation and is not conducive to the formation of crystals. However, the solubility of D-psicose in ethanol is extremely low. At 20℃, the solubility is less than 0.076g / g, and at 60℃, the solubility is less than 0.19g / g. The lower the solubility, the more conducive it is to the precipitation of crystals. Therefore, ethanol was selected as the crystallization solvent of D-psicose.

[0033] 2. Determination of initial crystallization conditions

[0034] 1) Determination of the ratio of syrup to ethanol (syrup to alcohol ratio)

[0035] The crystallization conditions were controlled as follows: initial temperature 60°C, end temperature 20°C, cooling rate 1°C / h, seed addition amount 5% (w / w) of the syrup mass, and stirring speed 200rpm; and crystallization experiments were carried out with slurry-alcohol ratios (w / w) of 1:3, 1:2, 1:1, 2:1, and 3:1, and the crystallization yield was calculated to investigate the effect of the slurry-alcohol ratio on the crystallization yield.

[0036] The results showed that as the slurry to alcohol ratio (w / w) gradually increased, the crystallization yield increased first and then decreased. When the slurry to alcohol ratio was 2:1, the crystallization yield was the highest. Therefore, a slurry to alcohol ratio of 2:1 was used in subsequent experiments.

[0037] 2) Determination of the termination temperature

[0038] The crystallization conditions were controlled as follows: initial crystallization temperature of 60°C, cooling rate of 1°C / h, seed addition amount of 5% of the syrup mass, stirring speed of 200rpm, slurry-alcohol ratio (w / w) of 2:1; crystallization experiments were carried out with termination temperatures of 10°C, 20°C, and 30°C, and the crystallization yield was calculated to investigate the effect of crystallization termination temperature on the crystallization yield.

[0039] The results showed that when the end temperature was 30℃, the crystallization yield was the lowest, and when the end temperature was 10℃ and 20℃, the crystallization yield was slightly higher than 30℃, but there was no significant difference between 10℃ and 20℃ (p<0.05). Considering that the lower the crystallization termination temperature, the greater the energy consumption, 20℃ was finally selected as the crystallization termination temperature.

[0040] 3. Fractional Factorial Experiment

[0041] The effects of the crystallization process parameters: stirring speed (A), cooling rate (B), and seed addition amount (C) on the crystallization yield (Y) were studied. Based on the previous experimental results, the initial conditions for crystallization were determined as follows: initial temperature of 60°C, slurry-to-alcohol ratio of 2:1, and termination temperature of 20°C. A three-factor, three-level fractional factorial experiment was designed using JMP software (version 10.0, SAS Institute, Inc.), as shown in Table 1:

[0042] Table 1. Levels of partial factorial experiment

[0043]

[0044] The experiment used crystallization yield as the response value, set one center point, and the design type was L9 Taguchi. Each experiment was repeated twice. The specific experimental design and results are shown in Table 2:

[0045] Table 2 Experimental design and results

[0046]

[0047] After the experiment, the least squares regression model was used to analyze the experimental data and establish a prediction model for crystallization yield.

[0048] The prediction model equation is:

[0049] Y=-0.0000011a 2 +0.018b 2 -0.00063ab+0.0051ac+1.56bc+0.00016A+0.035B-0.33C+0.84

[0050] Wherein, Y represents the D-psicose crystallization yield, A: stirring speed, B: cooling rate, C: seed crystal addition amount, a: stirring speed -190, b: cooling rate -0.95, c: seed crystal addition amount -0.049.

[0051] The significance of the influence of parameters on crystallization yield was investigated by t-test. The results showed that the quadratic effects of stirring speed and cooling rate and the quadratic effects of cooling rate and seed addition amount had significant effects on crystallization yield, while the main effects of cooling rate, stirring speed, seed addition amount and other factors had no significant effects on crystallization yield. Therefore, in the subsequent industrial crystallization process, special attention should be paid to the quadratic effects between parameters.

[0052] The optimal conditions for D-psicose crystallization obtained by using the above prediction equation are: starting temperature 60°C, ending temperature 20°C, slurry alcohol ratio 2:1, stirring speed 300rpm, cooling rate 1.5°C / h, and seed addition amount 10%. Under these conditions, the theoretical value of crystallization yield is 92.85%. After experimental verification: the actual crystallization yield under these conditions is 91.36%, which is not significantly different from the predicted value (p<0.05), indicating that the model prediction is relatively accurate and can be used to predict the effect of parameter changes on crystallization yield during the crystallization process.

[0053] Finally, polarizing microscope was used to observe the D-psicose crystals obtained under the optimal conditions. Figure 1 As shown, D-psicose crystals are uniform in size, smooth in surface, and regular in shape of long rods, with a size of about 400 μm*100 μm. This indicates that high-quality crystal products can be obtained under the optimal crystallization process conditions.

[0054] At the same time, compared with the closest prior art (CN106852145B) mentioned in the background technology, the crystallization rate of the present invention is significantly improved, which is 81%, while the present invention can reach 91.36%. A careful comparison of the process differences is reflected in: first, the prior art chooses to crystallize in the temperature range of 30°C to 40°C, which prolongs the crystallization time and reduces the production efficiency, while the present application selects a starting temperature of 60°C and an end temperature of 20°C for crystallization operation; second, CJ does not use an organic solvent, does not introduce ethanol, and chooses to remove impurities from the D-psicose solution to obtain a purified D-psicose solution; concentrates the purified D-psicose solution; cools the concentrated D-psicose solution to 30°C to 40°C through a heat exchanger, pre-crystallizes the D-psicose solution at 30°C to 40°C to obtain a sugar paste, and uses the pre-crystallized sugar paste for crystallization. Although the method disclosed in the reference document avoids the use of organic solvents, the concentration and viscosity of the sugar paste are extremely high at 30°C to 40°C. The increase in viscosity will hinder the generation of eddies, and the supply of solutes can only be carried out in a diffusion manner. The angular parts of the crystals are more likely to accept solutes and grow faster, while the center of the crystals grow slowly. Crystallization in this temperature range is more likely to form skeletal crystals, which affects the crystal form. It is generally believed by those skilled in the art that repeated temperature-changing crystallization of sugar products in water is beneficial to the improvement of the crystal morphology and increase of the particle size of the product; however, in fact, after the wet product of allulose produced in a pure water system is filtered, it is very easy for the crystal product to dissolve and recrystallize during drying, resulting in product agglomeration and poor product quality. After the present invention introduces ethanol, it not only increases the product yield, but also improves the product morphology. The allulose product produced by the present invention is a monodisperse, uniform, and regular prismatic product, and the product still maintains a monodisperse regular crystal form after drying. The product particle size of the present invention is significantly improved compared with the CJ method, and the fluidity and bulk density are significantly increased, and no agglomeration occurs during drying and storage. Therefore, from the perspective of actual industrial production, this application effectively guarantees the yield while ensuring the quality of the product, and is more suitable for industrial promotion and application.

[0055] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for recovering D-psicose crystals from syrup, characterized in that: The following steps are involved: 1) Concentrating the allulose solution to obtain syrup; 2) Add 20% of the volume of syrup into the seeding device, and add ethanol, the mass ratio of the added syrup to ethanol is 2:1; 3) Raise the temperature to the initial crystallization temperature of 60°C, keep warm for 30 minutes, add seed crystals, stir slowly to make the seed crystals evenly dispersed in the syrup, balance for 30 minutes, and then cool down to the crystallization termination temperature of 20°C; The mass of the seed crystals added was 10% of the mass of the syrup, the stirring speed was 300 rpm, and the cooling rate was 1.5 °C / h; 4) The crystals are obtained by vacuum filtration and dried to obtain D-psicose crystals.

2. The method for recovering D-psicose crystals from syrup according to claim 1, characterized in that: In step 1), the allulose solution with a purity of 99% is concentrated to a Brix degree of 80%.

3. The method for recovering D-psicose crystals from syrup according to claim 1, characterized in that: The crystallization yield prediction model equation of D-psicose crystallization is as follows: Y=-0.0000011a 2 +0.018b 2 -0.00063ab+0.0051ac+1.56bc+0.00016A+0.035B-0.33C+0.84 Wherein, Y represents the crystallization yield of D-psicose, A: stirring speed, B: cooling rate, C: seed addition amount, a: stirring speed -190, b: cooling rate -0.95, c: seed addition amount -0.049; This prediction model can be used to measure the effect of parameter changes during the crystallization process on the crystallization yield.

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