Membrane filtration method of polydextrose and application of membrane filtration method

Abstract

The invention relates to a membrane filtration method of polydextrose and application thereof, and the membrane filtration method of polydextrose comprises the following steps: taking a feed liquid containing a polydextrose crude product, carrying out ultrafiltration by using an ultrafiltration device, with the molecular weight cut-off of an ultrafiltration membrane being 1000-1200, the ultrafiltration pressure being 0.15-0.25 MPa and the temperature being 33-37 DEG C, and collecting a permeate. The preparation process and impurities of the crude polydextrose product are deeply analyzed, a targeted membrane filtration method is further designed, various impurities can be efficiently separated by controlling the whole filtration process, and the method has important significance on efficient and low-cost preparation of refined polydextrose.

Description

Technical Field

[0001] The invention belongs to the field of biotechnology and relates to a polydextrose membrane filtration method and application thereof. Background Art

[0002] Dietary fiber refers to the sum of edible plant ingredients, carbohydrates and similar substances that cannot be digested and absorbed by the human small intestine, but can be partially or completely fermented in the human large intestine, including polysaccharides, oligosaccharides, lignin and related plant substances. For a long time, dietary fiber has been considered as waste because it can neither provide nutrition to the human body nor be digested and utilized by the human body, and can only be excreted as fecal residue. However, in recent years, medical scientists have found that as people's diets become more and more refined, dietary fiber is decreasing, and more and more diseases are caused. After in-depth research, nutritionists finally called dietary fiber and the traditional six nutrients - protein, fat, carbohydrates, vitamins, minerals, and water - the "seventh nutrient."

[0003] Polydexose is a water-soluble dietary fiber, which can be regarded as a banner of food ingredients. It adapts to the development trend of the food industry and the ever-changing market demand. With the continuous improvement of people's living standards, people's dietary characteristics are concentrated on high fat, high calories and high sugar. High-sugar diet brings many hidden diseases to people and has adverse effects on physical health. With the continuous improvement of people's health awareness, they gradually realize the harm of excessive intake of sugar, and sugar-reducing diet has become a trend worldwide. As a soluble dietary fiber, polydexose has great development potential in sugar reduction. Its low calorie characteristics and non-insulin dependence make its development opportunities in sugar reduction consumption worthy of exploration.

[0004] Polydextrose is a polymer of glucose with irregular cross-linking. It has a variety of glycosidic bonds, mainly 1,6-bonds, and also contains some sorbitol end groups and citrate bonds. Its branching degree is higher than other carbohydrates. This compact and complex structure can effectively prevent hydrolysis by digestive enzymes. The average molecular weight of polydextrose is greater than 3200, and the average degree of polymerization is greater than 20. Due to different degrees of polymerization, the molecular weight ranges from 162 to 18000. Generally speaking, polydextrose is formed by intermolecular dehydration polymerization of D-glucose monomers under the catalysis of organic acids (such as fumaric acid, citric acid, etc.). During polymerization, about 10% by weight of sorbitol is usually added to allow sorbitol molecules to penetrate into the polymer chain to reduce the viscosity of the polymer, and also help improve the taste and color. The average molecular weight of the polymer depends on the reaction time, polymerization temperature and vacuum degree. The purpose of using high vacuum degree is to allow the water molecules generated by polymerization to quickly leave the reaction system. The polymerization reaction is carried out in a molten state. The product after polymerization is acidic because it contains organic acids and glucose monomolecular dehydration products, but neutral products are more suitable for use in various food products, so they usually need to be neutralized. In addition, in the traditional polymerization process, due to the excessively high local temperature, high molecular weight products (molecular weight>22000) will be produced, and the glucose molecules will be carbonized and discolored. Therefore, the neutralized solution should be filtered to remove the high molecular weight components insoluble in methanol and an oxidant should be added to remove the caramel color of the product.

[0005] Refined polydextrose is obtained by refining ordinary polydextrose, such as CN102199227A discloses the use of a simulated moving bed chromatography separation system for refining. Refined polydextrose has better taste, better fluidity and better solubility than ordinary polydextrose, and is suitable for high-end food manufacturing, especially widely used in beverage production. At present, most polydextrose products on the Chinese market are ordinary polydextrose, and the scale is small, which makes it difficult to meet the growing market demand.

[0006] In summary, how to improve the production process and technical level of refined polydextrose and reduce production costs is still one of the urgent issues to be solved in the field of polydextrose development. Summary of the invention

[0007] In view of the deficiencies of the prior art and actual needs, the present invention provides a membrane filtration method for polydextrose and its application, in order to achieve efficient and low-cost preparation of refined polydextrose.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a membrane filtration method for polydextrose, which comprises: taking a feed liquid containing a crude polydextrose, and ultrafiltration the feed liquid using an ultrafiltration device, wherein the retention molecular weight of the ultrafiltration membrane is 1000 to 1200 Daltons (for example, it may be 1100, etc.), the ultrafiltration pressure is 0.15 to 0.25 MPa (for example, it may be 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23 or 0.24 MPa, etc.), the temperature is 33 to 37°C (for example, it may be 34, 35 or 36°C, etc.), and the permeate is collected.

[0010] In the present invention, the preparation process and impurities of crude polydextrose are deeply analyzed, and a targeted membrane filtration method is further designed. By controlling the overall filtration process, various impurities can be efficiently separated, which is of great significance for the preparation of refined polydextrose.

[0011] In the present invention, compared with traditional chromatographic purification, the polydextrose solution is purified and concentrated by optimizing the membrane separation process conditions, reducing the water consumption and energy consumption in the process, and creating better economy.

[0012] Preferably, the ultrafiltration membrane is made of polytetrafluoroethylene.

[0013] In the present invention, an ultrafiltration membrane made of polytetrafluoroethylene is used to simultaneously achieve the purification and concentration of polydextrose, thereby reducing the energy consumption in the subsequent production process and improving the product quality of the polydextrose product.

[0014] Preferably, the flow rate of the feed liquid in the ultrafiltration is 40 to 50 L / (m 2 h), for example, 41, 42, 43, 44, 45, 46, 47, 48 or 49 L / (m 2 h) etc.

[0015] In the present invention, the specific pressure and flow rate are designed and controlled for the ultrafiltration process of the crude polydextrose, and they cooperate with each other to further improve the ultrafiltration efficiency.

[0016] Preferably, the concentration of the crude polydextrose in the feed solution is 45% to 50%, for example, 46%, 47%, 48% or 49%.

[0017] The invention designs and controls the concentration of a specific feed solution for the ultrafiltration process of a crude polydextrose product, which is helpful to improve the ultrafiltration efficiency.

[0018] Preferably, the polydextrose membrane filtration method further comprises the step of cleaning the ultrafiltration membrane.

[0019] Preferably, the step of cleaning the ultrafiltration membrane comprises: using water for forward flushing and reverse flushing, using an alkaline solution to repeatedly perform forward flushing and reverse flushing, using an ethanol solution to repeatedly perform forward flushing and reverse flushing, and then cleaning with water.

[0020] During the membrane filtration process, the high cost of membrane consumables leads to an increase in the overall cost. To address this problem, the present application designs a new membrane assembly cleaning method, which uses a hybrid method for cleaning, so that the membrane reuse rate reaches more than 98%, reducing the cost of equipment use.

[0021] Preferably, the pressure of the forward flushing and the reverse flushing are independently 0.08 to 0.12 MPa (for example, 0.09, 0.10 or 0.11 MPa, etc.), and the speed is independently 60 to 80 L / (m 2 h), for example, 62, 64, 66, 68, 70, 72, 74, 76 or 78L (m 2 h) etc.

[0022] Preferably, the pH of the alkaline solution is 11-12.

[0023] Preferably, the alkaline solution includes sodium hydroxide solution and ammonia solution.

[0024] Preferably, the ethanol content in the ethanol solution is 95% to 98% (mass percentage).

[0025] Preferably, the working mode of the ultrafiltration includes cyclic ultrafiltration and cross-flow filtration.

[0026] It can be understood that the number of forward flushing and reverse flushing can be adjusted according to actual conditions, for example, using water for forward flushing and reverse flushing 2 to 4 times, using alkaline solution to repeat forward flushing and reverse flushing 1 to 3 times, using ethanol solution to repeat forward flushing and reverse flushing, flushing 1 to 3 times, and then using water to wash 2 to 2 times.

[0027] Preferably, the elution volume of the ultrafiltration is 200-210 L / m 2 , for example, it can be 202, 204, 206 or 208 L / m 2 wait.

[0028] In the present invention, the specific elution volume is designed and controlled for the ultrafiltration process of the crude polydextrose, which can effectively coordinate the recovery rate and the process time and improve the production capacity.

[0029] The present invention also includes pre-treatment of the feed liquid, including removal of impurities by high-speed centrifugation, microfiltration, value adjustment, heat treatment or flocculant method.

[0030] As a preferred technical solution, the membrane filtration method of polydextrose is:

[0031] Take a feed liquid containing crude polydextrose, and adjust the concentration of crude polydextrose in water to 45% to 50% to obtain a feed liquid, and use a polytetrafluoroethylene membrane ultrafiltration device to ultrafilter the feed liquid, the ultrafiltration membrane has a molecular weight cutoff of 1000 to 1200, and the flow rate of the feed liquid is 40 to 50 L / (m 2 h), the ultrafiltration pressure is 0.15-0.25 MPa, the temperature is 33-37°C, and the permeate is collected;

[0032] The ultrafiltration membrane is forwardly flushed and reversely flushed with water, repeatedly forwardly flushed and reversely flushed with an alkaline solution with a pH of 11 to 12, repeatedly forwardly flushed and reversely flushed with an ethanol solution, and then washed with water.

[0033] The present invention designs the conditions of each step of ultrafiltration, which are coordinated as a whole. The membrane flux of ultrafiltration can be maintained at a relatively high level. The attenuation amplitude of the membrane flux before and after ultrafiltration is relatively small, which effectively slows down the influence of concentration polarization on the ultrafiltration process, so that the separation efficiency and the processing capacity of the equipment can be further improved by more than 30%, and the yield of the obtained product can be further improved to 90%; low-pressure and high-speed forward washing can utilize the shear force caused by the high-speed flow of the medium on the membrane surface to remove the pollutants on the membrane surface, and backwashing can reversely press the cleaning medium through the membrane to remove the pollutants in the membrane pores. At the same time, repeated cleaning with distilled water, alkaline solution and ethanol can better remove acidic polysaccharides and other fat-soluble impurities. The recovery rate of the membrane pure water flux after mixed cleaning reaches more than 98%, which reduces the consumable material cost of membrane filtration.

[0034] In a second aspect, the present invention provides use of the polydextrose membrane filtration method described in the first aspect in preparing purified polydextrose.

[0035] In a third aspect, the present invention provides a method for preparing refined polydextrose, the method for preparing refined polydextrose comprising:

[0036] The feed liquid containing the crude polydextrose is taken, decolorized and coarsely filtered, and then membrane filtered using the polydextrose membrane filtration method described in the first aspect to obtain refined polydextrose.

[0037] Preferably, the decolorization method includes temperature-increasing decolorization; the temperature-increasing decolorization includes: adding activated carbon and performing heating treatment.

[0038] Preferably, the amount of activated carbon added is 0.3% to 0.8% (mass percentage), for example, it can be 0.4%, 0.5%, 0.6% or 0.7%, etc., the heating treatment temperature is 40 to 60°C, for example, it can be 45, 50 or 55°C, etc., and the time is 20 to 40 minutes, for example, it can be 25, 30 or 35 minutes, etc.

[0039] Preferably, the coarse filtration treatment method includes plate and frame filtration.

[0040] Preferably, the membrane filtration treatment further includes concentration treatment, drying treatment and pulverization treatment.

[0041] Preferably, the concentration treatment method comprises falling film triple-effect evaporation concentration.

[0042] Preferably, the drying method comprises vacuum drying.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects:

[0044] In the present invention, the preparation process and impurities of the crude polydextrose are deeply analyzed, and a targeted membrane filtration method is further designed. By controlling the overall filtration process, various impurities can be effectively separated, the filtration efficiency can be improved, and the product yield can be increased to 90%. At the same time, a membrane cleaning method is designed, and the reuse rate of the membrane reaches more than 98%, which reduces the use cost of the equipment and is of great significance for the preparation of refined polydextrose. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the process flow for refining polydextrose. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0047] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased through regular channels.

[0048] During the preparation of crude polydextrose, sugars are prone to various reactions (such as hydrolysis, dehydration, decomposition and polymerization) under acidic and high temperature conditions, among which colored impurities mainly include dehydrated sugars, methyl furfural, furan compounds, melanin-like pigments produced by Maillard reaction, etc. These pigments are ionized in the solution and have negative charges, and can be purified by activated carbon treatment, membrane filtration, ion chromatography, solvent extraction and other methods. The present invention is committed to the efficient and low-cost preparation of refined polydextrose, the development of a new membrane filtration process, the effective separation of various impurities, and the further design of the overall process of dissolution, decolorization, coarse filtration, membrane filtration, concentration, drying and the like (an exemplary process flow chart is shown in FIG. Figure 1 As shown), efficient and low-cost preparation of refined polydextrose is achieved.

[0049] The crude polydextrose to be purified in the specific embodiment is purchased, and its preparation method includes adding glucose monomer, organic acid and sugar alcohol into a reaction container, and reacting at 180° C. and vacuum degree of 10 mmHg to obtain the crude polydextrose.

[0050] The test methods mainly include the following:

[0051] ① Reducing sugar content detection: 3,5-dinitrosalicylic acid (DNS) method to determine reducing sugar content

[0052] Under alkaline conditions, 3,5-dinitrosalicylic acid is reduced to a brown-red amino compound after being heated with reducing sugar. Within a certain range, the amount of reducing sugar is proportional to the color intensity of the reaction solution. The sugar content in the sample can be determined by colorimetry.

[0053] ② High performance liquid chromatography: Use gel chromatography column, chromatography 802 column is used to separate molecular weight within 10 4 The following substances, and the separation range of chromatographic column 804 is 180~6.7×10 5 Therefore, 802.5 was selected to measure the size of the main peak molecular weight of polydextrose and the overall distribution of the molecular weight of polydextrose, and triple-distilled water was selected as the mobile phase.

[0054] ③ Phenol-sulfuric acid method to measure total sugar content

[0055] Principle: Polysaccharides or oligosaccharides are hydrolyzed into monosaccharides by concentrated sulfuric acid at a suitable high temperature, and then rapidly dehydrated to form furfural derivatives. The derivatives react with phenol under strong acid conditions to form orange-yellow compounds. At a wavelength of 490nm and within a certain concentration range, the absorbance value is linearly related to the sugar concentration. By measuring the absorbance, the total sugar content is calculated according to the standard curve.

[0056] ④ Determination of decolorization rate and total sugar loss rate: The refined polydextrose solution was scanned within the visible light range, with distilled water as a blank. The results showed that there was no maximum absorption wavelength. According to the principle of complementary colors, it can be known that the solution mainly absorbs blue light. Therefore, 420nm was selected as the detection wavelength to measure the absorbance of the polydextrose solution before and after decolorization. The absorbance value of the refined polydextrose solution at this wavelength showed a good linear relationship with its color value.

[0057] ⑤ Refined polydextrose infrared (IR analysis): Weigh 1 mg of dried refined polydextrose sample and grind it evenly with 150 mg of dried KBr powder in an agate mortar. Press it into uniform and transparent thin slices and perform conventional IR analysis (Fourier transform infrared spectrometer, VECTOR 22). The spectrum measurement range is 4000-500 cm -1 , Scan times: 32, beam resolution 4cm -1 .

[0058] ⑥ Determination of digestibility of refined polydextrose: The digestibility of refined polydextrose is determined by enzymatic hydrolysis. Weigh 100 mg of polydextrose sample, add 15 mL of phosphate buffer with a pH of 6.9, then add 1 mL of α-amylase and 0.5 mL of glucoamylase, hydrolyze at 37°C, take samples at regular intervals and inactivate them in a boiling water bath, and then determine the glucose content by DNS method.

[0059] The calculation method of membrane reuse rate includes:

[0060] At the same temperature and operating pressure, the ratio of the membrane flux of pure water after ultrafiltration to the membrane flux before ultrafiltration is the membrane reuse rate.

[0061] Example 1

[0062] The present embodiment provides a polydextrose membrane filtration purification method.

[0063] Take the feed liquid containing crude polydextrose, control the feed liquid concentration to 45%, take the feed liquid and use ultrafiltration device for ultrafiltration, the ultrafiltration membrane material is polytetrafluoroethylene (PTFE), the ultrafiltration membrane has a molecular weight cutoff of 1000 Daltons, the working pressure is 0.2MPa, and the feed liquid flow rate is 45L / (m 2 h), temperature is 35°C, elution volume is 205 L / m 2 The working mode is cyclic ultrafiltration. During the ultrafiltration process, the retentate is circulated into the raw liquid and the permeate is collected.

[0064] The membrane components were cleaned by mixing method, and the membrane components were cleaned by low pressure and high speed (0.10MPa, 70L / (m 2 h)) Rinse the components in the forward direction and reverse direction twice, then repeat the above steps with a pH 12 NaOH solution, repeat the forward and reverse flushing with a 96% ethanol solution once, and finally clean the components with distilled water to remove any remaining reagents.

[0065] Example 2

[0066] The present embodiment provides a polydextrose membrane filtration purification method.

[0067] The feed liquid containing crude polydextrose was taken, and the concentration of the feed liquid was controlled to be 45%. The feed liquid was ultrafiltered using a hollow fiber membrane ultrafiltration device. The ultrafiltration membrane material was polytetrafluoroethylene (PTFE), the ultrafiltration membrane had a molecular weight cutoff of 1000 Daltons, the working pressure was 0.15 MPa, and the flow rate was 40 L / (m 2 h), temperature is 33°C, elution volume is 200 L / m 2 The working mode is cyclic ultrafiltration. During the ultrafiltration process, the retentate is circulated into the raw liquid and the permeate is collected.

[0068] The membrane components were cleaned by mixing method, and the membrane components were cleaned by low-pressure and high-speed (0.08MPa, 80L / (m 2 h)) Rinse once in the forward direction and once in the reverse direction, then repeat the above steps with a pH 11 NaOH solution, repeat the forward and reverse flushing with a 95% ethanol solution, and finally clean the remaining reagents on the components with distilled water.

[0069] Example 3

[0070] The present embodiment provides a polydextrose membrane filtration purification method.

[0071] Take the feed liquid containing crude polydextrose, control the feed liquid concentration to 50%, and use the hollow fiber membrane ultrafiltration device for ultrafiltration. The ultrafiltration membrane material is polytetrafluoroethylene (PTFE), the ultrafiltration membrane has a molecular weight cutoff of 1200 Daltons, the working pressure is 0.25 MPa, and the flow rate is 50 L / m 2 , temperature is 37℃, elution volume is 210L / m 2 The working mode is cyclic ultrafiltration. During the ultrafiltration process, the retentate is circulated into the raw liquid and the permeate is collected.

[0072] The membrane components were cleaned by mixing method, and the membrane components were cleaned by low-pressure and high-speed (0.12MPa, 60L / (m 2 h)) Rinse forward and reverse three times, then repeat the above operation with NaOH solution with a pH of 12, repeat the forward and reverse flushing with 98% ethanol solution for three times, and finally clean the remaining reagents on the components with distilled water.

[0073] Example 4

[0074] The difference between this embodiment and embodiment 1 is that the concentration of the feed liquid is 35%.

[0075] Example 5

[0076] The difference between this embodiment and embodiment 1 is that the concentration of the feed liquid is 60%.

[0077] Example 6

[0078] The only difference between this embodiment and embodiment 1 is that the cleaning method of the membrane assembly is: isobaric hydraulic flushing method, which specifically involves closing the ultrafiltrate outlet valve and fully opening the concentrated water outlet valve. At this time, the pressures on both sides of the membrane gradually become equal, and the dirt adhering to the membrane surface is loosened due to the pressure difference, so that the surface is flushed by the increased flow rate.

[0079] Comparative Example 1

[0080] The only difference between this comparative example and Example 1 is that the molecular weight cut-off of the ultrafiltration membrane is 800 Daltons.

[0081] Comparative Example 2

[0082] The only difference between this comparative example and Example 1 is that the molecular weight cut-off of the ultrafiltration membrane is 1400 Daltons.

[0083] Comparative Example 3

[0084] The only difference between this comparative example and Example 1 is that the ultrafiltration pressure is 0.1 MPa.

[0085] Comparative Example 4

[0086] The only difference between this comparative example and Example 1 is that the ultrafiltration pressure is 0.3 MPa.

[0087] Comparative Example 5

[0088] The only difference between this comparative example and Example 1 is that the ultrafiltration temperature is 25°C.

[0089] Comparative Example 6

[0090] The only difference between this comparative example and Example 1 is that the ultrafiltration temperature is 40°C.

[0091] Test Case

[0092] Further overall polydextrose purification process (refer to Figure 1 Process), take the crude polydextrose, mix it with activated carbon in water to obtain a feed liquid, the activated carbon addition amount is 0.5%, 50°C, and decolorization is 30 minutes. Plate and frame filtration is adopted for coarse filtration, and the obtained clear liquid is subjected to membrane filtration, falling film triple-effect evaporation concentration, vacuum drying, and crushing to obtain the product, wherein the membrane filtration adopts the membrane filtration method of polydextrose in each embodiment and comparative example respectively to obtain multiple groups of products.

[0093] The results of the analysis of the prepared products are shown in Table 1.

[0094] Table 1

[0095]

[0096] The results of Examples 1-3 show that when the same output is achieved, the consumed raw materials, time, energy consumption, and water consumption are not much different, and the obtained products all meet the standards.

[0097] Compared with Examples 1-3, when the feed concentration is too low, the processing rate is low in Examples 4-5, which reduces the equipment utilization rate. When the feed concentration is too high, the viscosity of the feed increases significantly, and the membrane quickly becomes clogged when the water permeability rate remains unchanged.

[0098] Compared with Examples 1-3, the reuse rate of the membrane in Example 6 is only about 90%, which is lower than that in Examples 1-3.

[0099] Compared with Example 1-3, when the molecular weight cutoff of the ultrafiltration membrane is too small, part of the polydextrose will be retained, resulting in a decrease in yield. When the molecular weight cutoff of the ultrafiltration membrane is too large, part of the impurities will pass through, resulting in a decrease in product quality.

[0100] Compared with Examples 1-3, when the ultrafiltration pressure is too low, the water flux is too low in Comparative Example 3-4, which reduces the equipment utilization rate. When the operating pressure is too high, although the water flux increases, the membrane will quickly become clogged and the membrane assembly will also be damaged.

[0101] Compared with Examples 1-3, when the temperature is too low, the viscosity of the feed liquid increases, resulting in a low processing speed and reduced equipment utilization. When the temperature is too high, the gaps in the membrane will become larger, causing some impurities to pass through, resulting in a decrease in product quality.

[0102] In summary, the present invention conducts an in-depth analysis of the preparation process and impurities of the crude polydextrose, and further designs a targeted membrane filtration method. By controlling the overall filtration process, various impurities can be effectively separated, the filtration efficiency can be improved, and the product yield can be increased to 90%. At the same time, a membrane cleaning method is designed, and the reuse rate of the membrane reaches more than 98%, which reduces the use cost of the equipment, which is of great significance for the preparation of refined polydextrose.

[0103] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A membrane filtration method for polydextrose, characterized in that: The membrane filtration method of polydextrose comprises: Take the feed liquid containing the crude polydextrose and use an ultrafiltration device for ultrafiltration. The ultrafiltration membrane has a molecular weight cutoff of 1000-1200, an ultrafiltration pressure of 0.15-0.25 MPa, and a temperature of 33-37° C. to collect the permeate.

2. The polydextrose membrane filtration method according to claim 1, characterized in that: The material of the ultrafiltration membrane is polytetrafluoroethylene; Preferably, the flow rate of the feed liquid in the ultrafiltration is 40 to 50 L / (m 2 h).

3. The polydextrose membrane filtration method according to claim 1 or 2, characterized in that: The concentration of the crude polydextrose in the feed solution is 45% to 50%.

4. The polydextrose membrane filtration method according to any one of claims 1 to 3, characterized in that: The polydextrose membrane filtration method further comprises the step of cleaning the ultrafiltration membrane; Preferably, the step of cleaning the ultrafiltration membrane comprises: using water for forward flushing and reverse flushing, using an alkaline solution to repeatedly perform forward flushing and reverse flushing, using an ethanol solution to repeatedly perform forward flushing and reverse flushing, and then cleaning with water.

5. The polydextrose membrane filtration method according to claim 4, characterized in that: The pressure of the forward flushing and the reverse flushing are independently 0.08-0.12 MPa, and the speed is independently 60-80 L / (m 2 h); Preferably, the pH of the alkaline solution is 11 to 12; Preferably, the alkaline solution comprises sodium hydroxide solution or ammonia solution; Preferably, the ethanol content in the ethanol solution is 95% to 98%.

6. The polydextrose membrane filtration method according to any one of claims 1 to 5, characterized in that: The working modes of the ultrafiltration include circulating ultrafiltration and cross-flow filtration.

7. The polydextrose membrane filtration method according to any one of claims 1 to 6, characterized in that: The membrane filtration method of polydextrose comprises: Take a feed liquid containing crude polydextrose, and adjust the concentration of crude polydextrose in water to 45% to 50% to obtain a feed liquid, and use an ultrafiltration device to perform ultrafiltration, the ultrafiltration membrane has a molecular weight cutoff of 1000 to 1200, and the flow rate of the feed liquid is 40 to 50 L / (m 2 h), the ultrafiltration pressure is 0.15-0.25 MPa, the temperature is 33-37°C, and the permeate is collected; The ultrafiltration membrane is forwardly flushed and reversely flushed with water, repeatedly forwardly flushed and reversely flushed with an alkaline solution with a pH of 11 to 12, repeatedly forwardly flushed and reversely flushed with an ethanol solution, and then washed with water.

8. Use of the polydextrose membrane filtration method according to any one of claims 1 to 7 in the preparation of purified polydextrose.

9. A method for preparing refined polydextrose, characterized in that: The method for preparing refined polydextrose comprises: The crude polydextrose is dissolved in water to obtain a liquid, the liquid is decolorized and coarsely filtered, and then the polydextrose membrane filtration method according to any one of claims 1 to 7 is used to obtain a refined polydextrose.

10. The method for preparing purified polydextrose according to claim 9, characterized in that: The decolorization method includes a temperature-raising decolorization process; the temperature-raising decolorization process includes: adding activated carbon and performing a heating process; Preferably, the coarse filtration treatment method comprises plate and frame filtration; Preferably, the membrane filtration treatment further includes concentration treatment, drying treatment and pulverization treatment; Preferably, the concentration treatment method includes falling film triple-effect evaporation concentration; Preferably, the drying method comprises vacuum drying.

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