Preparation method of high-purity glucomannan

Abstract

The invention relates to the technical field of glucomannan preparation, provides a preparation method of high-purity glucomannan, and solves the problems of insufficient purity and large molecular weight distribution of existing glucomannan. According to the technical scheme, the method comprises the following steps: pretreating fresh konjak tubers, and sequentially performing multi-stage concentration extraction by using ethanol to obtain crude glucomannan; carrying out ultrasonic-assisted purification by using isopropanol; the purified product is subjected to hydrosolation, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation and drying treatment, and high-purity glucomannan is obtained. Wherein the aluminum chloride / chitosan composite flocculant is obtained by carrying out alkalization reaction on aluminum chloride hexahydrate and sodium hydroxide to prepare a polyaluminum chloride stock solution, dissolving chitosan in a hydrochloric acid solution to prepare a chitosan stock solution and then carrying out composite reaction. The purity of the glucomannan prepared by the method reaches 95.0-98.2%, the molecular weight polydispersity index PDI is 1.6-2.2, the process is simple, the cost is low, and the glucomannan has wide application prospects in the fields of food, medicine, chemical engineering and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of glucomannan preparation, and particularly relates to a method for preparing high-purity glucomannan. Background Art

[0002] With the rapid development of high-end application fields such as functional foods, biopharmaceuticals, and new materials, glucomannan, as an important natural polysaccharide material, shows great application potential and market value in fields such as food additives, drug carriers, biomembrane materials, and intelligent hydrogels. In the field of functional foods, the excellent thickening, film-forming, and gelling properties of glucomannan make it an ideal raw material for low-calorie foods and dietary fiber supplements. In biomedical applications, its good biocompatibility and degradability provide an important basis for drug controlled-release systems and tissue engineering scaffold materials. However, these high-end applications pose extremely strict requirements on the material properties of glucomannan. In particular, the control precision of purity and molecular weight distribution directly affects the functional performance and quality stability of the final product. High-purity glucomannan can ensure the performance consistency and reliability of products in complex application environments, while narrow molecular weight distribution is a key factor for achieving precise functional regulation and performance optimization. Meeting these strict performance requirements can not only significantly enhance the market competitiveness and application value of products, but also promote the development of related industries towards high quality and high added value, laying a solid material foundation for the in-depth application of glucomannan in a wider range of fields.

[0003] Although glucomannan shows good application prospects in multiple fields, the current preparation technologies still have significant deficiencies in meeting the requirements of high-end applications, restricting its promotion in precision application fields. Traditional extraction and purification methods often use a single solvent system and conventional separation technologies, resulting in generally low purity of the prepared glucomannan products, making it difficult to effectively remove impurities such as proteins, polyphenols, and inorganic salts. At the same time, the random breakage and polymerization of molecular chains during the extraction process make the molecular weight distribution of the products show a broad characteristic. For example, Chinese Patent No. CN107141368A discloses a method for extracting glucomannan from konjac, but there are problems of insufficient purity and large molecular weight distribution. The existing technologies lack systematic multi-stage purification strategies and precise molecular weight control means, resulting in poor performance of the prepared glucomannan in terms of batch-to-batch consistency and functional stability. In addition, the optimization of extraction conditions by traditional methods is not fine enough, lacking in-depth research on key links such as solvent selection, reaction parameter control, and separation and purification process design, further exacerbating the instability of product quality. These technical limitations seriously affect the industrial development of glucomannan in high-value-added application fields, and there is an urgent need to develop new preparation technologies with high purity and narrow molecular weight distribution characteristics. Summary of the Invention

[0004] (1) Technical problem to be solved The object of the present invention is to provide a method for preparing high-purity glucomannan to solve the problems of insufficient purity and large molecular weight distribution of glucomannan at present.

[0005] (2) Technical solution To achieve the above object, the present invention provides the following technical solution: A method for preparing high-purity glucomannan, comprising the following steps: S1: After pretreating fresh konjac tubers, perform multi-stage concentration extraction with 60 wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol in sequence to obtain crude glucomannan; S2: Ultrasonically assist in purifying the crude glucomannan with isopropanol; S3: Subject the purified product to solubilization with water, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan.

[0006] The aluminum chloride / chitosan composite flocculant is obtained by subjecting aluminum chloride hexahydrate and sodium hydroxide to an alkalization reaction to prepare a polyaluminum chloride stock solution, dissolving chitosan in a hydrochloric acid solution to prepare a chitosan stock solution, and then dropping the chitosan stock solution into the polyaluminum chloride stock solution for a composite reaction.

[0007] Further, the preparation of the aluminum chloride / chitosan composite flocculant includes: heating an aqueous aluminum chloride solution with a concentration of 0.45 - 0.55 mol / L to 72.0 - 78.0 °C, and dropping an aqueous sodium hydroxide solution with a concentration of 0.45 - 0.55 mol / L into it at a dropping rate of 25.0 - 35.0 mL / h under a stirring rate of 800 - 1200 rpm for an alkalization reaction, controlling the molar ratio of hydroxide ions to aluminum ions to be 1.8 - 2.2, with an alkalization reaction time of 60 - 90 min, and after the reaction, diluting with deionized water to an aluminum ion concentration of 0.08 - 0.12 mol / L.

[0008] Further, the preparation method of the polyaluminum chloride stock solution includes: taking aluminum trichloride hexahydrate and preparing an aluminum trichloride aqueous solution with a concentration of 0.45 - 0.55 mol / L; separately taking sodium hydroxide and preparing a sodium hydroxide aqueous solution with a concentration of 0.45 - 0.55 mol / L for standby; placing the aluminum trichloride aqueous solution in a reaction vessel, heating it to 72.0 - 78.0 °C, and slowly dropping the sodium hydroxide aqueous solution into the aluminum trichloride aqueous solution at a dropping rate of 25.0 - 35.0 mL / h under the condition that the stirring rate is 800 - 1200 rpm for alkalization reaction; during the alkalization reaction process, the molar ratio of hydroxide ions to aluminum ions is controlled to be 1.8 - 2.2, and the alkalization reaction time is 60 - 90 min; after the alkalization reaction ends, cooling the obtained solution to room temperature, and then diluting it with deionized water to an aluminum ion concentration of 0.08 - 0.12 mol / L to obtain the polyaluminum chloride stock solution.

[0009] Further, the preparation method of the chitosan stock solution includes: taking 0.08 - 0.12 parts by weight of chitosan and adding it to 0.12 - 0.20 parts of a hydrochloric acid aqueous solution with a concentration of 0.08 - 0.12 mol / L, stirring at 200 - 400 rpm at room temperature for 50 - 70 min until completely dissolved, and then diluting and fixing the volume to 180 - 220 mL with deionized water.

[0010] The present invention adopts the design of an aluminum chloride / chitosan composite flocculant, aiming to improve the removal efficiency and selectivity of impurities during the extraction process of glucomannan. This composite flocculant combines the strong charge neutralization ability of polyaluminum chloride and the macromolecular bridging characteristics of chitosan, achieving complementary synergy in structure and function at the molecular level. Polyaluminum chloride is generated through the alkalization reaction of aluminum trichloride hexahydrate and sodium hydroxide, forming a polynuclear hydroxyaluminum complex with high polymerization degree and charge density, which can rapidly adsorb negatively charged impurity molecules in the solution. After protonation treatment with hydrochloric acid, chitosan forms a positively charged polycation, and its long-chain structure can capture suspended colloidal impurities through molecular entanglement, hydrogen bonding, and physical coating. During the compounding process of the two, some Al³⁺ forms weak coordination or electrostatic adsorption with the hydroxyl groups and unprotonated amino groups on the chitosan molecular chain, constructing an organic-inorganic hybrid flocculation network. In this structure, chitosan not only improves the dispersibility and stability of the flocculant but also enhances the capture ability for macromolecular impurities, while polyaluminum chloride is responsible for rapid electro-neutralization and sedimentation. This synergistic mechanism is significantly superior to single components. When dealing with a complex glucomannan extraction liquid system, it can achieve efficient, mild, and controllable removal of various impurities, thus providing a solid technical support for obtaining high-purity glucomannan.

[0011] Furthermore, the pretreatment of fresh konjac tubers in S1 includes: peeling, washing, and then cutting into small pieces with a side length of 3 - 5 mm, drying at a temperature of 45 - 55 °C for 20 - 28 h, and grinding to a particle size of 80 - 100 mesh after drying; The multi - stage concentration extraction in S1 includes: mixing the ground konjac tubers with 60 wt% ethanol at a weight ratio of 1:(5.0 - 6.0), performing high - speed homogenization grinding at a rotation speed of 6000 - 8000 rpm for 3 - 5 min, then filtering to collect the filter residue. Mix the filter residue with 70 wt% ethanol at a weight ratio of 1:(5.0 - 6.0) and repeat the grinding and filtering. Mix the filter residue with 80 wt% ethanol at a weight ratio of 1:(5.5 - 6.0) and repeat the grinding and filtering. Collect all the filtrates and dry at a temperature of 45 - 55 °C for 20 - 28 h to obtain crude glucomannan.

[0012] Furthermore, the ultrasonic - assisted purification in step S2 is to mix the crude glucomannan with 80 wt% isopropanol at a solid - liquid weight ratio of 1:(10 - 15), perform ultrasonic treatment at a frequency of 20 - 25 kHz and a power of 200 - 300 W for 8 - 12 min, and dry the product after ultrasonic purification at a temperature of 45 - 55 °C for 10 - 14 h.

[0013] Furthermore, the flocculation treatment in step S3 includes: preparing the purified glucomannan into a hydrogel with a mass concentration of 0.8 - 1.2%, adding an aluminum chloride / chitosan composite flocculant to the hydrogel, with the addition amount being 1 - 2% of the volume of the sol, stirring at a temperature of 35 - 45 °C for 15 - 30 min, and then performing two - stage centrifugal separation successively, with the centrifugal rotation speed being 3500 - 4500 rpm and the centrifugal time being 18 - 22 min.

[0014] Furthermore, the ethanol precipitation in S3 includes: adding 3 - 4 times the volume of 90 wt% ethanol to the clarified liquid obtained by centrifugal separation, fully mixing and then standing for 1.5 - 2.5 h to precipitate glucomannan, then performing vacuum filtration to collect the precipitate, drying the collected precipitate at a temperature of 45 - 55 °C and a vacuum degree of - 0.08 - - 0.1 MPa for 20 - 28 h, and grinding and sieving through a 60 - mesh sieve after drying.

[0015] Furthermore, the purity of the high - purity glucomannan is 95.0 - 98.2%, and the polydispersity index PDI of the molecular weight is 1.6 - 2.2.

[0016] The present invention aims to solve the key technical problems of insufficient purity and excessive molecular weight distribution range commonly existing in the existing glucomannan preparation process. Aiming at the core bottlenecks such as low impurity removal efficiency, poor separation selectivity of target components and easy damage of molecular chain structure in traditional processes, an efficient purification system with multi-stage ethanol extraction, isopropanol ultrasonic-assisted purification and aluminum chloride / chitosan composite flocculation as the core is constructed. By introducing gradient ethanol concentrations at the beginning of extraction, impurities of different polarities are gradually stripped off, laying the foundation for subsequent purification; in the intermediate processing link, the depolymerization and impurity desorption of macromolecular clusters are enhanced by ultrasonic action under isopropanol system, and the integrity of the main chain structure of polysaccharides is maintained under mild conditions; in the key separation step, a composite flocculant is used to replace the traditional single inorganic flocculant, giving full play to the charge neutralization ability of polyaluminum chloride and the capture effect of the long chain structure of chitosan, realizing the synergistic removal of macromolecular colloidal impurities and small molecular charged impurities, effectively improving the flocculation efficiency and selectivity, and significantly improving the problem of impurity residues in the product. Finally, the molecular weight distribution was further converged and the polydispersity was reduced through ethanol precipitation and multi-stage drying processes, and a glucomannan product with uniform structure, improved purity and stable performance was obtained. The purpose of the invention is to break through the technical limitations of traditional methods in high-purity preparation and molecular weight control by constructing a set of extraction and purification systems that combine multi-mechanism synergy, structural protection and separation efficiency, and provide a more stable and reliable raw material basis for the subsequent application of glucomannan in food, medicine and high-end functional materials.

[0017] (3) Beneficial technical effects 1. The aluminum chloride / chitosan composite flocculation system constructed by the present invention significantly improves the impurity removal efficiency, structural integrity and purification selectivity in the glucomannan extraction process through the synergistic effect of electrical neutralization and molecular bridging, which is superior to a single flocculant system.

[0018] 2. The present invention effectively improves the purity and structural uniformity of glucomannan through the synergistic combination of multi-stage ethanol extraction, isopropanol ultrasonic purification and aluminum chloride / chitosan composite flocculation, significantly optimizes separation efficiency and product performance, and is suitable for high-standard food and biomaterial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the XRD phase analysis diagram of glucomannan prepared in Example 1 of the present invention.

[0020] Figure 2 This is the FTIR infrared Fourier spectrum of the glucomannan prepared in Example 1 of the present invention.

[0021] Figure 3 This is the FTIR infrared Fourier spectrum of the aluminum chloride / chitosan composite flocculant prepared in Example 1 of the present invention.

[0022] Figure 4 This is a physical picture of the fresh konjac prepared in Example 1 of the present invention.

[0023] Figure 5 This is a physical picture of the dried small pieces of konjac prepared in Example 1 of the present invention.

[0024] Figure 6 This is a physical picture of the high-purity glucomannan prepared in Example 1 of the present invention.

[0025] Figure 7 This is a comparison chart of the purity of each sample in the examples and comparative examples of the present invention.

[0026] Figure 8 This is a comparison chart of the molecular weight distribution of each sample in the examples and comparative examples of the present invention.

[0027] Figure 9 This is a comparison chart of the rheological properties of each sample in the examples and comparative examples of the present invention.

[0028] Figure 10 This is a comparison chart of the dissolution properties of each sample in the examples and comparative examples of the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0030] Example 1 A method for preparing high-purity glucomannan includes the following steps: S1: After pretreating the fresh konjac tuber, perform multi-stage concentration extraction with 60 wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol in sequence to obtain crude glucomannan; the pretreatment of the fresh konjac tuber includes: peeling, washing, and then chopping into small pieces with a side length of 3 mm, drying at a temperature of 45°C for 20 h, and grinding to a particle size of 80 meshes after drying; the multi-stage concentration extraction includes: mixing the ground konjac tuber with 60 wt% ethanol at a weight ratio of 1:5.0, performing high-speed homogenization grinding at a rotation speed of 6000 rpm for 3 min and then filtering to collect the filter residue, mixing the filter residue with 70 wt% ethanol at a weight ratio of 1:5.0 and repeating the grinding and filtering, mixing the filter residue with 80 wt% ethanol at a weight ratio of 1:5.5 and repeating the grinding and filtering, and collecting all the filtrates and drying at a temperature of 45°C for 20 h to obtain crude glucomannan.

[0031] S2: Perform ultrasonic-assisted purification on the crude glucomannan with isopropanol; the ultrasonic-assisted purification is to mix the crude glucomannan with 80 wt% isopropanol at a solid-liquid weight ratio of 1:10, perform ultrasonic treatment at a frequency of 20 kHz and a power of 200 W for 8 min, and dry the product after ultrasonic purification at a temperature of 45°C for 10 h.

[0032] S3: Subject the purified product to solubilization with water, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan. The flocculation treatment includes: form a hydrocolloid of the purified glucomannan with a mass concentration of 0.8%, add the aluminum chloride / chitosan composite flocculant to the hydrocolloid, with the addition amount being 1% of the volume of the sol, stir at a temperature of 35°C for 15 min, then perform two centrifugal separations in sequence, with the centrifugal speed being 3500 rpm and the centrifugal time being 18 min. The ethanol precipitation includes: add 3 times the volume of 90 wt% ethanol to the clarified liquid obtained by centrifugal separation, fully mix and then let stand for 1.5 h to precipitate the glucomannan, then perform vacuum filtration to collect the precipitate, and dry the collected precipitate at a temperature of 45°C and a vacuum degree of -0.08 MPa for 20 h, and after drying, grind and pass through a 60-mesh sieve.

[0033] The aluminum chloride / chitosan composite flocculant is obtained by subjecting aluminum trichloride hexahydrate and sodium hydroxide to an alkalization reaction to prepare a polyaluminum chloride stock solution, dissolving chitosan in a hydrochloric acid solution to prepare a chitosan stock solution, and then dropping the chitosan stock solution into the polyaluminum chloride stock solution for a composite reaction.

[0034] The preparation of the aluminum chloride / chitosan composite flocculant in this example includes: heating an aqueous aluminum trichloride solution with a concentration of 0.48 mol / L to 73.8°C, and under the condition of a stirring rate of 920 rpm, dropping an aqueous sodium hydroxide solution with a concentration of 0.48 mol / L at a dropping rate of 28.0 mL / h for an alkalization reaction, controlling the molar ratio of hydroxide ions to aluminum ions to be 1.9, with the alkalization reaction time being 69 min, and after the reaction ends, diluting with deionized water to an aluminum ion concentration of 0.09 mol / L.

[0035] The preparation method of the polyaluminum chloride stock solution in this example includes: take aluminum trichloride hexahydrate and prepare an aqueous aluminum trichloride solution with a concentration of 0.48 mol / L; take another portion of sodium hydroxide and prepare an aqueous sodium hydroxide solution with a concentration of 0.48 mol / L for standby; place the aqueous aluminum trichloride solution in a reaction vessel, heat to 73.8°C, and under the condition of a stirring rate of 920 rpm, slowly drop the aqueous sodium hydroxide solution into the aqueous aluminum trichloride solution at a dropping rate of 28.0 mL / h for an alkalization reaction; during the alkalization reaction, control the molar ratio of hydroxide ions to aluminum ions to be 1.9, and the alkalization reaction time to be 69 min; after the alkalization reaction ends, cool the obtained solution to room temperature, and then dilute with deionized water to an aluminum ion concentration of 0.09 mol / L to obtain the polyaluminum chloride stock solution.

[0036] The preparation method of the chitosan stock solution of this embodiment includes: adding 0.09 parts of chitosan by weight to 0.14 parts of 0.09 mol / L hydrochloric acid aqueous solution, stirring at 260 rpm at room temperature for 56 min until completely dissolved, and then diluting with deionized water to 192 mL.

[0037] The purity of the high-purity glucomannan in this example is 95.0%, and the molecular weight polydispersity index PDI is 1.6.

[0038] Based on the above analysis results, the present invention successfully prepared a high-purity glucomannan product and verified its structural characteristics and process effectiveness through a variety of characterization methods. Figure 1 XRD phase analysis confirmed the crystal structure characteristics of the final product. Figure 2 The FTIR infrared spectrum of the product fully confirmed that the prepared product has typical glucomannan molecular structure characteristics through key absorption bands such as the OH group broad peak at 3432cm⁻¹, the alkyl vibration band in the range of 2850-2925cm⁻¹, the CO stretching vibration at 1640.23cm⁻¹, and the COC characteristic peak at 1158cm⁻¹. Figure 3 The FTIR spectrum of aluminum chloride / chitosan composite flocculant shows that Al 13 The simultaneous presence of the central Al-O bond vibration peak, the Al-OH2 bending vibration peaks at 980 cm⁻¹ and 1160 cm⁻¹, and the characteristic absorption peaks of chitosan such as 1645 cm⁻¹ amide band I, 1533 cm⁻¹ amide band II, and 1330 cm⁻¹ amide band III, indicates that the composite flocculant was successfully formed and maintained the structural characteristics of the two components; Figures 4 to 6 The actual picture clearly shows the complete preparation process from fresh konjac raw material to drying to the final high-purity glucomannan product, in which the final product is in the form of white powder with uniform and fine particles, proving the feasibility of the process route of the present invention and the excellent quality of the product, and providing a solid experimental basis for the industrial application of the preparation method.

[0039] Example 2 A method for preparing high-purity glucomannan comprises the following steps: S1: Pretreat fresh konjac tubers and then perform multi-stage concentration extraction with 60 wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol in sequence to obtain crude glucomannan. The pretreatment of fresh konjac tubers includes: peeling, washing, cutting into small pieces with a side length of 4 mm, drying at 48 °C for 22 h, and grinding to a particle size of 86 mesh after drying. The multi-stage concentration extraction includes: mixing the ground konjac tubers with 60 wt% ethanol at a weight ratio of 1:5.3, performing high-speed homogenization and grinding at 6600 rpm for 4 min, then filtering to collect the filter residue, mixing the filter residue with 70 wt% ethanol at a weight ratio of 1:5.3 and repeating the grinding and filtering, mixing the filter residue with 80 wt% ethanol at a weight ratio of 1:5.7 and repeating the grinding and filtering, and collecting all the filtrates and drying at 48 °C for 22 h to obtain crude glucomannan.

[0040] S2: Ultrasound-assisted purification of the crude glucomannan with isopropanol. The ultrasound-assisted purification is to mix the crude glucomannan with 80 wt% isopropanol at a solid-liquid weight ratio of 1:12, perform ultrasonic treatment at a frequency of 22 kHz and a power of 230 W for 9 min, and dry the product after ultrasonic purification at 48 °C for 11 h.

[0041] S3: Subject the purified product to solubilization, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan. The flocculation treatment includes: preparing a hydrocolloid with a mass concentration of 0.9% from the purified glucomannan, adding an aluminum chloride / chitosan composite flocculant to the hydrocolloid, with the addition amount being 1.3% of the volume of the sol, stirring at 38 °C for 20 min, and then performing two centrifugal separations in sequence, with a centrifugal speed of 3800 rpm and a centrifugal time of 19 min. The ethanol precipitation includes: adding 3.3 times the volume of 90 wt% ethanol to the clarified liquid obtained by centrifugal separation, fully mixing, standing for 1.8 h to precipitate the glucomannan, then performing vacuum filtration to collect the precipitate, and drying the collected precipitate at 48 °C and a vacuum degree of -0.09 MPa for 22 h, and grinding and passing through a 60-mesh sieve after drying.

[0042] The aluminum chloride / chitosan composite flocculant is prepared by alkalizing aluminum chloride hexahydrate with sodium hydroxide to prepare a polyaluminum chloride stock solution, dissolving chitosan in a hydrochloric acid solution to prepare a chitosan stock solution, and then dropping the chitosan stock solution into the polyaluminum chloride stock solution for a composite reaction.

[0043] The preparation of the aluminum chloride / chitosan composite flocculant in this example includes: heating an aluminum trichloride aqueous solution with a concentration of 0.45 mol / L to 72.0 °C, and under the condition of a stirring rate of 800 rpm, dropping an aqueous sodium hydroxide solution with a concentration of 0.45 mol / L at a dropping rate of 25.0 mL / h for the alkalization reaction. The molar ratio of hydroxide ions to aluminum ions is controlled to be 1.8, the alkalization reaction time is 60 min, and after the reaction is completed, it is diluted with deionized water to an aluminum ion concentration of 0.08 mol / L.

[0044] The preparation method of the polyaluminum chloride stock solution in this example includes: taking aluminum trichloride hexahydrate and preparing an aluminum trichloride aqueous solution with a concentration of 0.45 mol / L; separately taking sodium hydroxide and preparing an aqueous sodium hydroxide solution with a concentration of 0.45 mol / L for standby; placing the aluminum trichloride aqueous solution in a reaction vessel, heating it to 72.0 °C, and under the condition of a stirring rate of 800 rpm, slowly dropping the aqueous sodium hydroxide solution into the aluminum trichloride aqueous solution at a dropping rate of 25.0 mL / h for the alkalization reaction; during the alkalization reaction, the molar ratio of hydroxide ions to aluminum ions is controlled to be 1.8, and the alkalization reaction time is 60 min; after the alkalization reaction is completed, the obtained solution is cooled to room temperature, and then diluted with deionized water to an aluminum ion concentration of 0.08 mol / L to obtain a polyaluminum chloride stock solution.

[0045] The preparation method of the chitosan stock solution in this example includes: taking 0.08 parts by weight of chitosan and adding it to 0.12 parts of a hydrochloric acid aqueous solution with a concentration of 0.08 mol / L, stirring at 200 rpm at room temperature for 50 min until completely dissolved, and then diluting and fixing the volume to 180 mL with deionized water.

[0046] The preparation of the aluminum chloride / chitosan composite flocculant in this example includes: heating an aluminum trichloride aqueous solution with a concentration of 0.48 mol / L to 73.8 °C, and under the condition of a stirring rate of 920 rpm, dropping an aqueous sodium hydroxide solution with a concentration of 0.48 mol / L at a dropping rate of 28.0 mL / h for the alkalization reaction. The molar ratio of hydroxide ions to aluminum ions is controlled to be 1.9, the alkalization reaction time is 69 min, and after the reaction is completed, it is diluted with deionized water to an aluminum ion concentration of 0.09 mol / L.

[0047] The preparation method of the polyaluminum chloride stock solution in this example includes: taking aluminum trichloride hexahydrate and preparing an aluminum trichloride aqueous solution with a concentration of 0.48 mol / L; separately taking sodium hydroxide and preparing a sodium hydroxide aqueous solution with a concentration of 0.48 mol / L for standby; placing the aluminum trichloride aqueous solution in a reaction vessel, heating it to 73.8 °C, and slowly dropping the sodium hydroxide aqueous solution into the aluminum trichloride aqueous solution at a dropping rate of 28.0 mL / h under the condition of a stirring rate of 920 rpm to carry out an alkalization reaction; during the alkalization reaction, the molar ratio of hydroxide ions to aluminum ions is controlled to be 1.9, and the alkalization reaction time is 69 min; after the alkalization reaction is completed, cooling the obtained solution to room temperature, and then diluting it with deionized water to an aluminum ion concentration of 0.09 mol / L to obtain the polyaluminum chloride stock solution The preparation method of the chitosan stock solution in this example includes: taking 0.09 parts by weight of chitosan and adding it to 0.14 parts of a hydrochloric acid aqueous solution with a concentration of 0.09 mol / L, stirring at 260 rpm at room temperature for 56 min until completely dissolved, and then diluting and fixing the volume to 192 mL with deionized water.

[0048] The purity of the high-purity glucomannan in this example is 96.0%, and the polydispersity index PDI of the molecular weight is 1.8.

[0049] Example 3 A preparation method of high-purity glucomannan includes the following steps: S1: After pretreating fresh konjac tubers, performing multi-stage concentration extraction with 60 wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol in sequence to obtain crude glucomannan; the pretreatment of fresh konjac tubers includes: peeling, washing, and then cutting them into small pieces with a side length of 4 mm, drying at a temperature of 51 °C for 25 h, and grinding to a particle size of 92 mesh after drying; the multi-stage concentration extraction includes: mixing the ground konjac tubers with 60 wt% ethanol at a weight ratio of 1:5.6, performing high-speed homogenization grinding at a rotation speed of 7200 rpm for 4 min and then filtering to collect the filter residue, mixing the filter residue with 70 wt% ethanol at a weight ratio of 1:5.6 and repeating the grinding and filtering, mixing the filter residue with 80 wt% ethanol at a weight ratio of 1:5.8 and repeating the grinding and filtering, and collecting all the filtrates and drying them at a temperature of 51 °C for 25 h to obtain crude glucomannan.

[0050] S2: Performing ultrasonic-assisted purification of the crude glucomannan with isopropanol; the ultrasonic-assisted purification is to mix the crude glucomannan with 80 wt% isopropanol at a solid-liquid weight ratio of 1:13, perform ultrasonic treatment at a frequency of 23 kHz and a power of 260 W for 10 min, and drying the product after ultrasonic purification at a temperature of 51 °C for 12 h.

[0051] S3: The purified product is subjected to solubilization in water, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan. The flocculation treatment includes: preparing a hydrocolloid of the purified glucomannan with a mass concentration of 1.0%, adding the aluminum chloride / chitosan composite flocculant to the hydrocolloid, with the addition amount being 1.6% of the volume of the sol, stirring at a temperature of 41°C for 24 min, and then performing two centrifugal separations in sequence, with the centrifugal speed being 4100 rpm and the centrifugal time being 20 min. The ethanol precipitation includes: adding 4 times the volume of 90 wt% ethanol to the clarified liquid obtained by centrifugal separation, fully mixing and then standing for 2.1 h to precipitate the glucomannan, then performing vacuum filtration to collect the precipitate, and drying the collected precipitate at a temperature of 51°C and a vacuum degree of -0.09 MPa for 25 h. After drying, it is ground and passed through a 60-mesh sieve.

[0052] The aluminum chloride / chitosan composite flocculant is prepared by subjecting aluminum chloride hexahydrate and sodium hydroxide to an alkalization reaction to prepare a polyaluminum chloride stock solution, dissolving chitosan in a hydrochloric acid solution to prepare a chitosan stock solution, and then dropping the chitosan stock solution into the polyaluminum chloride stock solution for a composite reaction.

[0053] The preparation of the polyaluminum chloride stock solution in this example includes: heating an aqueous solution of aluminum chloride with a concentration of 0.55 mol / L to 78.0°C, and dropping an aqueous solution of sodium hydroxide with a concentration of 0.55 mol / L into it at a dropping rate of 35.0 mL / h under a stirring rate of 1200 rpm for an alkalization reaction, controlling the molar ratio of hydroxide ions to aluminum ions to be 2.2, with the alkalization reaction time being 90 min. After the reaction, it is diluted with deionized water to an aluminum ion concentration of 0.12 mol / L.

[0054] The preparation method of the polyaluminum chloride stock solution in this example includes: taking aluminum chloride hexahydrate and preparing an aqueous solution of aluminum chloride with a concentration of 0.55 mol / L; taking another portion of sodium hydroxide and preparing an aqueous solution of sodium hydroxide with a concentration of 0.55 mol / L for standby; placing the aqueous solution of aluminum chloride in a reaction vessel, heating it to 78.0°C, and slowly dropping the aqueous solution of sodium hydroxide into the aqueous solution of aluminum chloride at a dropping rate of 35.0 mL / h under a stirring rate of 1200 rpm for an alkalization reaction; during the alkalization reaction, controlling the molar ratio of hydroxide ions to aluminum ions to be 2.2, and the alkalization reaction time being 90 min; after the alkalization reaction, cooling the obtained solution to room temperature, and then diluting it with deionized water to an aluminum ion concentration of 0.12 mol / L to obtain the polyaluminum chloride stock solution.

[0055] The preparation method of the chitosan stock solution in this example includes: taking 0.12 parts by weight of chitosan and adding it to 0.20 parts of a hydrochloric acid aqueous solution with a concentration of 0.12 mol / L, stirring at 400 rpm for 70 min at room temperature until completely dissolved, and then diluting and making up the volume to 220 mL with deionized water.

[0056] The purity of the high-purity glucomannan in this example is 98.2%, and the polydispersity index PDI of the molecular weight is 2.2.

[0057] Example 4 A preparation method of high-purity glucomannan includes the following steps: S1: After pre-treating fresh konjac tubers, perform multi-stage concentration extraction successively with 60wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol to obtain crude glucomannan; the pre-treatment of fresh konjac tubers includes: peeling, washing and then chopping into small pieces with a side length of 5 mm, drying at a temperature of 55°C for 28 h, and grinding to a particle size of 100 mesh after drying; the multi-stage concentration extraction includes: mixing the ground konjac tubers with 60wt% ethanol at a weight ratio of 1:6.0, performing high-speed homogenization and grinding at a rotation speed of 8000 rpm for 5 min and then filtering to collect the filter residue, mixing the filter residue with 70wt% ethanol at a weight ratio of 1:6.0 and repeating the grinding and filtering, mixing the filter residue with 80wt% ethanol at a weight ratio of 1:6.0 and repeating the grinding and filtering, collecting all the filtrates and drying at a temperature of 55°C for 28 h to obtain crude glucomannan.

[0058] S2: Ultrasonically assist in purifying the crude glucomannan with isopropanol; the ultrasonic-assisted purification is to mix the crude glucomannan with 80wt% isopropanol at a solid-liquid weight ratio of 1:15, perform ultrasonic treatment at a frequency of 25 kHz and a power of 300 W for 12 min, and dry the product after ultrasonic purification at a temperature of 55°C for 14 h.

[0059] S3: Subject the purified product to solubilization, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan. The flocculation treatment includes: preparing the purified glucomannan into a hydrocolloid with a mass concentration of 1.2%, adding an aluminum chloride / chitosan composite flocculant to the hydrocolloid, with the addition amount being 2% of the volume of the sol, stirring at a temperature of 45°C for 30 min, and then performing two centrifugal separations successively, with a centrifugal rotation speed of 4500 rpm and a centrifugal time of 22 min. The ethanol precipitation includes: adding 4 times the volume of 90wt% ethanol to the clarified liquid obtained by centrifugal separation, fully mixing and then standing for 2.5 h to precipitate the glucomannan, and then performing vacuum filtration to collect the precipitate, drying the collected precipitate at a temperature of 55°C and a vacuum degree of -0.1 MPa for 28 h, and grinding and sieving through a 60-mesh sieve after drying.

[0060] The aluminum chloride / chitosan composite flocculant is prepared by subjecting aluminum trichloride hexahydrate to an alkalization reaction with sodium hydroxide to prepare a polyaluminum chloride stock solution, dissolving chitosan in a hydrochloric acid solution to prepare a chitosan stock solution, and then dropping the chitosan stock solution into the polyaluminum chloride stock solution for a composite reaction.

[0061] The preparation of the aluminum chloride / chitosan composite flocculant in this example includes: heating an aqueous aluminum chloride solution with a concentration of 0.51 mol / L to 75.6 °C, and dropping an aqueous sodium hydroxide solution with a concentration of 0.51 mol / L into it at a dropping rate of 31.0 mL / h under a stirring rate of 1040 rpm for an alkalization reaction. The molar ratio of hydroxide ions to aluminum ions is controlled to be 2.0, and the alkalization reaction time is 78 min. After the reaction, it is diluted with deionized water to an aluminum ion concentration of 0.10 mol / L.

[0062] The preparation method of the polyaluminum chloride stock solution in this example includes: taking aluminum trichloride hexahydrate and preparing an aqueous aluminum chloride solution with a concentration of 0.51 mol / L; taking another portion of sodium hydroxide and preparing an aqueous sodium hydroxide solution with a concentration of 0.51 mol / L for standby; placing the aqueous aluminum chloride solution in a reaction vessel, heating it to 75.6 °C, and slowly dropping the aqueous sodium hydroxide solution into the aqueous aluminum chloride solution at a dropping rate of 31.0 mL / h under a stirring rate of 1040 rpm for an alkalization reaction; during the alkalization reaction, the molar ratio of hydroxide ions to aluminum ions is controlled to be 2.0, and the alkalization reaction time is 78 min; after the alkalization reaction ends, the obtained solution is cooled to room temperature and then diluted with deionized water to an aluminum ion concentration of 0.10 mol / L to obtain the polyaluminum chloride stock solution.

[0063] The preparation method of the chitosan stock solution in this example includes: taking 0.10 parts by weight of chitosan and adding it to 0.17 parts of a hydrochloric acid aqueous solution with a concentration of 0.10 mol / L, stirring at 320 rpm at room temperature for 62 min until completely dissolved, and then diluting and making up the volume to 204 mL with deionized water.

[0064] The purity of the high-purity glucomannan in this example is 97.0%, and the polydispersity index PDI of the molecular weight is 2.0.

[0065] Comparative Example 1 It is basically the same as Example 1, except that in step S1, only ethanol with a single concentration of 70 wt% is used for extraction instead of using ethanol with concentrations of 60 wt%, 70 wt%, and 80 wt% for multi-stage concentration extraction in sequence.

[0066] Comparative Example 2 It is basically the same as Example 1, except that ethanol is used instead of isopropanol for ultrasonic-assisted purification in step S2, and other ultrasonic conditions remain unchanged.

[0067] Comparative Example 3 It is basically the same as Example 1, except that only polyaluminum chloride is used as the flocculant in step S3, and the aluminum chloride / chitosan composite flocculant is not used.

[0068] Comparative Example 4 It is basically the same as Example 1, except that only chitosan is used as the flocculant in step S3, and the aluminum chloride / chitosan composite flocculant is not used.

[0069] Comparative Example 5 It is basically the same as Example 1, except that the concentration of the aluminum trichloride aqueous solution is 0.3 mol / L in the preparation process of the aluminum chloride / chitosan composite flocculant.

[0070] Comparative Example 6 It is basically the same as Example 1, except that the alkalization reaction temperature is 60°C in the preparation process of the aluminum chloride / chitosan composite flocculant.

[0071] Comparative Example 7 It is basically the same as Example 1, except that the molar ratio of hydroxide ions to aluminum ions is 1.5 in the preparation process of the aluminum chloride / chitosan composite flocculant.

[0072] Comparative Example 8 It is basically the same as Example 1, except that sulfuric acid solution is used instead of hydrochloric acid solution to dissolve chitosan in the preparation process of the chitosan stock solution.

[0073] Comparative Example 9 It is basically the same as Example 1, except that the high-speed homogenization grinding speed is 4000 rpm in the multi-stage concentration extraction process.

[0074] Comparative Example 10 It is basically the same as Example 1, except that the ultrasonic frequency is 15 kHz in the ultrasonic-assisted purification process.

[0075] Comparative Example 11 It is basically the same as Example 1, except that the addition amount of the aluminum chloride / chitosan composite flocculant is 0.5% of the sol volume in the flocculation treatment process.

[0076] Comparative Example 12 It is basically the same as Example 1, except that the polyaluminum chloride stock solution is added dropwise to the chitosan stock solution in the preparation process of the aluminum chloride / chitosan composite flocculant, rather than the chitosan stock solution being added dropwise to the polyaluminum chloride stock solution.

[0077] Performance test: Purity determination experiment: The purity of the prepared glucomannan sample was analyzed by high performance liquid chromatography (HPLC). The tested object was the glucomannan product prepared in each example. An amino column was used as the stationary phase, an acetonitrile-water system was used as the mobile phase, and a differential refractive index detector was used for detection. The mass fraction of glucomannan in the sample was calculated by comparing with the standard product and integrating the peak area.

[0078] Molecular weight and its distribution determination experiment: The weight-average molecular weight, number-average molecular weight and polydispersity index PDI of glucomannan were determined by gel permeation chromatography (GPC). The tested object was the glucomannan sample prepared under different process conditions. TSK-GEL series chromatographic columns were used, 0.1M NaNO3 solution was used as the mobile phase, and a differential refractive index detector was used for detection. A standard curve was established with dextran standard. The experimental method referred to ASTM D3593-80 standard.

[0079] Rheological property test experiment: A rotary rheometer was used to measure the viscosity, shear thinning behavior and gel strength of glucomannan aqueous solution. The tested object was glucomannan aqueous solutions with different concentrations (0.5%, 1.0%, 1.5%). Steady shear tests were carried out at 25 °C, and the shear rate range was 0.1 - 100 s⁻¹. At the same time, dynamic oscillation tests were carried out to measure the storage modulus G' and loss modulus G''. The experimental method referred to ISO 3219-1993.

[0080] Dissolution property test experiment: The solubility and dissolution rate of glucomannan in different solvents were determined. The tested object was the glucomannan product prepared in each example. Dissolution tests were carried out in deionized water, 0.1M NaOH solution and 0.1M HCl solution respectively, stirred at a constant temperature of 25 °C, and the time required for complete dissolution and the maximum solubility were recorded.

[0081] The properties of glucomannan in Examples 1 - 4 and Comparative Examples 1 - 12 are summarized in Table 1. From the performance analysis of the comparative examples, it can be seen that deviations in different process parameters have a significant impact on the preparation performance of glucomannan. Using single - concentration ethanol extraction instead of multi - concentration extraction results in insufficient extraction, a significant decrease in purity, and a corresponding reduction in molecular weight. This is because multi - concentration extraction can more effectively remove impurities with different polarities and improve the extraction efficiency. When using ethanol instead of isopropanol for ultrasonic purification, since the dissolution selectivity of ethanol is not as good as that of isopropanol, the purity increases but is still lower than the optimal level, indicating that isopropanol has an advantage in removing specific impurities. When using single polyaluminum chloride or chitosan as flocculants respectively, the purity decreases to varying degrees, demonstrating the importance of the synergistic effect of the composite flocculant in improving the purification effect, as a single component cannot achieve comprehensive removal of different types of impurities. Deviations in the preparation parameters of the flocculant, such as too low concentration of aluminum trichloride, insufficient alkalization temperature, and too small molar ratio of hydroxide to aluminum ion, all lead to a decrease in the activity of the flocculant and a significant drop in purity, indicating that precise control of the flocculant preparation conditions is crucial for maintaining its flocculation performance. When using sulfuric acid instead of hydrochloric acid to dissolve chitosan, since the protonation ability of sulfuric acid is similar, the purity remains at a relatively high level, close to the standard process effect, indicating that the type of strong acid has a limited impact on the protonation effect of chitosan. Using a lower grinding speed results in incomplete crushing of konjac tubers and incomplete release of active ingredients, with both purity and molecular weight decreasing. Using a lower ultrasonic frequency weakens the ultrasonic - assisted purification effect and slightly reduces the product purity. Insufficient dosage of the flocculant leads to incomplete flocculation, poor impurity removal effect, and a significant decrease in purity. Changing the feeding order of the composite reaction disrupts the optimal formation conditions of the composite flocculant, affects the construction of the flocculation network structure, and significantly reduces the purity, indicating the key role of the correct composite reaction process in forming an efficient flocculant structure.

[0082] From Figures 7 - 10 the experimental results, it can be seen that the examples of the present invention are significantly superior to the comparative examples in terms of various performance indicators, and Example 3 exhibits the best comprehensive performance. Figure 7 It shows that the purities of Examples 1 - 4 reach 95.0%, 96.0%, 98.2%, and 97.0% respectively, which are significantly higher than the range of 87.9% - 93.8% of the comparative examples, indicating that the multi - concentration extraction, isopropanol ultrasonic purification, and composite flocculant treatment processes of the present invention can effectively improve the product purity. Figure 8 It indicates that the weight - average molecular weight of the examples is in the range of 8.64 - 12.32×10 5 g / mol, and the PDI value is 1.6 - 2.2, while the weight - average molecular weight of the comparative examples is only 7.85 - 8.71×10 5g / mol, and the PDI values are all 1.6, indicating that the process of the present invention can not only obtain products with higher molecular weight, but also effectively control the molecular weight distribution through the regulation of process parameters. Figure 9 The rheological property test results show that the viscosity of the 1.0% solution of the examples is 2.15 - 2.95 Pa·s, and the storage modulus is 85.2 - 118.3 Pa, both of which are higher than 1.89 - 2.18 Pa·s and 76.4 - 85.9 Pa of the comparative examples, proving that the glucomannan prepared by the present invention has more excellent thickening and gelling properties. Figure 10 The dissolution property data show that the dissolution time of the examples in water is 9.8 - 12.3 min, and the maximum solubility is 28.5 - 32.6 g / L, while the dissolution time of the comparative examples is 12.5 - 14.6 min, and the maximum solubility is 26.5 - 28.3 g / L, indicating that the products prepared by the process of the present invention have a faster dissolution rate and higher solubility, which is attributed to the high product purity, good integrity of the molecular chain structure and reasonable molecular weight distribution, comprehensively verifying the superiority of the technical solution of the present invention and the rationality of the selection of process parameters.

[0083] Table 1 Performance aggregation of glucomannan in Examples 1 - 4 and Comparative Examples 1 - 12 Sample number Purity (%) <![CDATA[Weight-average molecular weight (×10 5 g / mol)]]> <![CDATA[Number average molecular weight (×10 5 g / mol)]]> PDI Viscosity of 1.0% solution (Pa·s) Storage modulus G' (Pa) Dissolution time in water (min) Maximum solubility (g / L) Example 1 95.0 8.64 5.40 1.6 2.15 85.2 12.3 28.5 Example 2 96.0 10.08 5.60 1.8 2.48 96.8 11.8 29.2 Example 3 98.2 12.32 5.60 2.2 2.95 118.3 9.8 32.6 Example 4 97.0 11.20 5.60 2.0 2.72 108.5 10.5 31.8 Comparative Example 1 92.3 7.85 4.90 1.6 1.89 76.4 14.2 26.8 Comparative Example 2 93.2 8.42 5.26 1.6 2.08 82.1 13.8 27.9 Comparative Example 3 91.8 8.58 5.36 1.6 2.12 83.7 12.8 28.1 Comparative Example 4 90.5 8.71 5.44 1.6 2.18 85.9 12.6 28.3 Comparative Example 5 88.7 8.45 5.28 1.6 2.05 81.3 13.5 27.6 Comparative Example 6 89.2 8.52 5.33 1.6 2.09 82.8 13.1 27.9 Comparative Example 7 87.9 8.38 5.24 1.6 2.02 80.5 13.8 27.3 Comparative Example 8 93.8 8.61 5.38 1.6 2.13 84.2 12.5 28.2 Comparative Example 9 91.5 8.28 5.18 1.6 1.95 78.9 14.6 26.5 Comparative Example 10 92.8 8.55 5.34 1.6 2.11 83.4 13.2 27.8 Comparative Example 11 90.2 8.48 5.30 1.6 2.07 81.9 13.6 27.4 Comparative Example 12 89.6 8.41 5.26 1.6 2.04 80.8 14.1 27.1 Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above examples, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention by using the content of the specification and drawings of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for preparing high-purity glucomannan, characterized in that, It includes the following steps: S1: Pretreat the fresh konjac tubers and then perform multi-stage concentration extraction with 60 wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol in sequence to obtain crude glucomannan; S2: Ultrasonically assist in purifying the crude glucomannan with isopropanol; S3: Subject the purified product to solubilization, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan. The aluminum chloride / chitosan composite flocculant is prepared by subjecting aluminum trichloride hexahydrate and sodium hydroxide to an alkalization reaction to prepare a polyaluminum chloride stock solution, dissolving chitosan in a hydrochloric acid solution to prepare a chitosan stock solution, and then dropping the chitosan stock solution into the polyaluminum chloride stock solution for a composite reaction.

2. The preparation method of a high-purity glucomannan as claimed in claim 1, wherein, The preparation of the aluminum chloride / chitosan composite flocculant includes: heating an aluminum chloride aqueous solution with a concentration of 0.45 - 0.55 mol / L to 72.0 - 78.0 °C, and under the condition of a stirring rate of 800 - 1200 rpm, dropping an aqueous sodium hydroxide solution with a concentration of 0.45 - 0.55 mol / L into it at a dropping rate of 25.0 - 35.0 mL / h for an alkalization reaction. The molar ratio of hydroxide ions to aluminum ions is controlled to be 1.8 - 2.2, the alkalization reaction time is 60 - 90 min, and after the reaction, it is diluted with deionized water to an aluminum ion concentration of 0.08 - 0.12 mol / L.

3. The preparation method of a high-purity glucomannan according to claim 1, wherein, The preparation method of the polyaluminum chloride stock solution includes: taking aluminum trichloride hexahydrate and preparing an aluminum chloride aqueous solution with a concentration of 0.45 - 0.55 mol / L; taking another portion of sodium hydroxide and preparing an aqueous sodium hydroxide solution with a concentration of 0.45 - 0.55 mol / L for standby; placing the aluminum chloride aqueous solution in a reaction vessel, heating it to 72.0 - 78.0 °C, and under the condition of a stirring rate of 800 - 1200 rpm, slowly dropping the aqueous sodium hydroxide solution into the aluminum chloride aqueous solution at a dropping rate of 25.0 - 35.0 mL / h for an alkalization reaction; during the alkalization reaction, the molar ratio of hydroxide ions to aluminum ions is controlled to be 1.8 - 2.2, and the alkalization reaction time is 60 - 90 min; after the alkalization reaction, cool the obtained solution to room temperature and then dilute it with deionized water to an aluminum ion concentration of 0.08 - 0.12 mol / L to obtain the polyaluminum chloride stock solution.

4. The preparation method of a high-purity glucomannan according to claim 1, characterized in that, The preparation method of the chitosan stock solution includes: taking 0.08 - 0.12 parts by weight of chitosan and adding it to 0.12 - 0.20 parts of a hydrochloric acid aqueous solution with a concentration of 0.08 - 0.12 mol / L, stirring at 200 - 400 rpm at room temperature for 50 - 70 min until completely dissolved, and then diluting and making up the volume to 180 - 220 mL with deionized water.

5. The preparation method of a high-purity glucomannan according to claim 1, characterized in that, The pretreatment of the fresh konjac tubers in S1 includes: peeling, washing, and then cutting them into small pieces with a side length of 3 - 5 mm, drying at a temperature of 45 - 55 °C for 20 - 28 h, and grinding to a particle size of 80 - 100 mesh after drying; The multi-stage concentration extraction in S1 includes: mixing the ground konjac tuber with 60 wt% ethanol at a weight ratio of 1:(5.0 - 6.0), performing high-speed homogenization grinding at a rotation speed of 6000 - 8000 rpm for 3 - 5 min, then filtering to collect the filter residue. Mix the filter residue with 70 wt% ethanol at a weight ratio of 1:(5.0 - 6.0) and repeat the grinding and filtering. Mix the filter residue with 80 wt% ethanol at a weight ratio of 1:(5.5 - 6.0) and repeat the grinding and filtering. Collect all the filtrates and dry them at 45 - 55 °C for 20 - 28 h to obtain crude glucomannan.

6. The preparation method of a high-purity glucomannan according to claim 1, characterized in that, The ultrasonic-assisted purification in step S2 is to mix the crude glucomannan with 80 wt% isopropanol at a solid-liquid weight ratio of 1:(10 - 15), perform ultrasonic treatment at a frequency of 20 - 25 kHz and a power of 200 - 300 W for 8 - 12 min. The product after ultrasonic purification is dried at a temperature of 45 - 55 °C for 10 - 14 h.

7. The method for preparing high-purity glucomannan according to claim 1, characterized in that, The flocculation treatment in step S3 includes: preparing the purified glucomannan into a hydrogel with a mass concentration of 0.8 - 1.2%, adding an aluminum chloride / chitosan composite flocculant to the hydrogel, with the addition amount being 1 - 2% of the volume of the sol, stirring at a temperature of 35 - 45 °C for 15 - 30 min, and then performing two centrifugal separations in sequence, with the centrifugal rotation speed being 3500 - 4500 rpm and the centrifugal time being 18 - 22 min.

8. The method for preparing high-purity glucomannan according to claim 1, characterized in that, The ethanol precipitation in S3 includes: adding 3 - 4 times the volume of 90 wt% ethanol to the clarified liquid obtained by centrifugal separation, fully mixing and then standing for 1.5 - 2.5 h to precipitate the glucomannan precipitate, then performing vacuum filtration to collect the precipitate, drying the collected precipitate at a temperature of 45 - 55 °C and a vacuum degree of -0.08 - -0.1 MPa for 20 - 28 h, and grinding and sieving through a 60-mesh sieve after drying.

9. The method for preparing high-purity glucomannan according to claim 1, characterized in that, The purity of the high-purity glucomannan is 95.0 - 98.2%, and the polydispersity index PDI of the molecular weight is 1.6 - 2.2.

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