A method for preparing high-purity glucomannan

Abstract

The present invention relates to the technical field of glucomannan preparation, and provides a method for preparing high-purity glucomannan, which solves the problems of insufficient purity and large molecular weight distribution of current glucomannan. The technical solution includes: pre-treating fresh konjac tubers and sequentially performing multi-stage concentration extraction with ethanol to obtain crude glucomannan; performing ultrasound-assisted purification with isopropyl alcohol; subjecting the purified product to hydrosolization, flocculation treatment with aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan. The aluminum chloride / chitosan composite flocculant is reacted with aluminum chloride hexahydrate and sodium hydroxide to prepare a polyaluminum chloride stock solution, and chitosan is dissolved in a hydrochloric acid solution to prepare a chitosan stock solution, and then a composite reaction is performed to obtain the glucomannan. The glucomannan prepared by the method has a purity of 95.0-98.2%, a molecular weight polydispersity index PDI of 1.6-2.2, a simple process, low cost, and has broad application prospects in the fields of food, medicine, and chemical industry.

Description

Technical Field

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

[0002] With the rapid development of high-end applications in functional foods, biopharmaceuticals, and novel materials, glucomannan, as a key natural polysaccharide, has demonstrated tremendous application potential and market value in areas such as food additives, drug carriers, biofilm materials, and smart hydrogels. In the functional food sector, glucomannan's excellent thickening, film-forming, and gelling properties make it an ideal raw material for low-calorie foods and dietary fiber supplements. In biopharmaceutical applications, its excellent biocompatibility and biodegradability provide a crucial foundation for controlled-drug delivery systems and tissue engineering scaffolds. However, these high-end applications place extremely stringent demands on the material properties of glucomannan, particularly regarding purity and molecular weight distribution, which directly impact the functional performance and quality stability of the final product. High-purity glucomannan ensures consistent and reliable performance in complex application environments, while a narrow molecular weight distribution is crucial for precise functional control and performance optimization. Meeting these stringent performance requirements will not only significantly enhance the product's market competitiveness and application value, but will also drive related industries towards high-quality, high-value-added development, laying a solid material foundation for the in-depth application of glucomannan in a wider range of fields.

[0003] Although glucomannan has shown good application prospects in many fields, the current preparation technology still has significant deficiencies in meeting the needs of high-end applications, which restricts its promotion in the field of precision applications. Traditional extraction and purification methods often use a single solvent system and conventional separation technology, resulting in the generally low purity of the glucomannan products prepared, making it difficult to effectively remove impurities such as proteins, polyphenols, and inorganic salts. At the same time, the random breakage and polymerization of the molecular chains during the extraction process make the molecular weight distribution of the product present a broad feature. For example, the Chinese patent publication number CN107141368A discloses a method for extracting glucomannan from konjac, but there are problems of insufficient purity and large molecular weight distribution. The prior art lacks a systematic multi-stage purification strategy and accurate molecular weight control means, which makes the prepared glucomannan perform poorly in terms of batch consistency, functional stability, etc. In addition, the traditional method is not refined enough to optimize the extraction conditions, and lacks 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 have seriously affected 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 problems solved

[0005] The purpose of the present invention is to provide a method for preparing high-purity glucomannan to solve the current problems of insufficient purity and large molecular weight distribution of glucomannan.

[0006] (2) Technical solution

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing high-purity glucomannan comprises the following steps:

[0009] S1: Fresh konjac tubers were pretreated and then subjected to multi-level concentration extraction using 60 wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol in sequence to obtain crude glucomannan;

[0010] S2: Ultrasound-assisted purification of crude glucomannan using isopropanol;

[0011] S3: The purified product is subjected to hydrosolization, flocculation treatment with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying treatment to obtain high-purity glucomannan.

[0012] The aluminum chloride / chitosan composite flocculant is obtained by alkalizing 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 dropwise adding the chitosan stock solution to the polyaluminum chloride stock solution for a composite reaction.

[0013] Furthermore, the preparation of the aluminum chloride / chitosan composite flocculant includes: heating an aluminum chloride aqueous solution with a concentration of 0.45 to 0.55 mol / L to 72.0 to 78.0° C., adding a sodium hydroxide aqueous solution with a concentration of 0.45 to 0.55 mol / L at a dropping rate of 25.0 to 35.0 mL / h for an alkalization reaction under a stirring rate of 800 to 1200 rpm, controlling the molar ratio of hydroxide ions to aluminum ions to be 1.8 to 2.2, and carrying out an alkalization reaction for 60 to 90 min. After the reaction is completed, the solution is diluted with deionized water to an aluminum ion concentration of 0.08 to 0.12 mol / L.

[0014] Furthermore, the preparation method of the polyaluminium chloride stock solution includes: taking aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution with a concentration of 0.45 to 0.55 mol / L; taking sodium hydroxide to prepare an aqueous sodium hydroxide solution with a concentration of 0.45 to 0.55 mol / L for standby use; placing the aluminum chloride aqueous solution in a reaction vessel, heating it to 72.0 to 78.0° C., and slowly dripping the sodium hydroxide aqueous solution into the aluminum chloride aqueous solution at a dripping rate of 25.0 to 35.0 mL / h under a stirring rate of 800 to 1200 rpm to perform an alkalization reaction; during the alkalization reaction, the molar ratio of hydroxide ions to aluminum ions is controlled to be 1.8 to 2.2, and the alkalization reaction time is 60 to 90 minutes; after the alkalization reaction is completed, the resulting solution is cooled to room temperature and then diluted with deionized water to an aluminum ion concentration of 0.08 to 0.12 mol / L to obtain the polyaluminium chloride stock solution.

[0015] Furthermore, the preparation method of the chitosan stock solution includes: taking 0.08 to 0.12 parts of chitosan by weight and adding it to 0.12 to 0.20 parts of a 0.08 to 0.12 mol / L hydrochloric acid aqueous solution, stirring at 200 to 400 rpm at room temperature for 50 to 70 minutes until completely dissolved, and then diluting the volume to 180 to 220 mL with deionized water.

[0016] This invention utilizes an aluminum chloride / chitosan composite flocculant designed to improve the efficiency and selectivity of impurity removal during glucomannan extraction. This composite flocculant combines the strong charge-neutralizing ability of polyaluminum chloride with the macromolecular bridging properties of chitosan, achieving a synergistic structure and function at the molecular level. Polyaluminum chloride is produced through the alkalinization reaction of aluminum chloride hexahydrate and sodium hydroxide, forming a polynuclear hydroxyaluminum complex with a high degree of polymerization and charge density, enabling rapid adsorption of negatively charged impurity molecules in solution. Chitosan, protonated with hydrochloric acid, forms a positively charged polycation. Its long-chain structure captures suspended colloidal impurities through molecular entanglement, hydrogen bonding, and physical encapsulation. During the composite process, some Al⁺ forms weak coordination or electrostatic adsorption with hydroxyl groups and unprotonated amino groups on the chitosan molecular chain, forming an organic-inorganic hybrid flocculation network. Within this structure, chitosan not only improves the flocculant's dispersibility and stability but also enhances its ability to capture macromolecular impurities, while polyaluminum chloride provides rapid charge neutralization and sedimentation. This synergistic mechanism is significantly superior to a single component. When processing complex glucomannan extract systems, it can achieve efficient, gentle and controllable removal of multiple types of impurities, thus providing solid technical support for obtaining high-purity glucomannan.

[0017] Further, the fresh konjac tubers in S1 are pretreated including: peeling, washing, and chopping into small pieces with a side length of 3 to 5 mm, drying at a temperature of 45 to 55° C. for 20 to 28 h, and grinding to a particle size of 80 to 100 meshes after drying;

[0018] The multi-stage concentration extraction in S1 includes: mixing the ground konjac tuber with 60wt% ethanol in 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 minutes, filtering and collecting the filter residue, mixing the filter residue with 70wt% ethanol in a weight ratio of 1:(5.0-6.0) and repeatedly grinding and filtering, mixing the filter residue with 80wt% ethanol in a weight ratio of 1:(5.5-6.0) and repeatedly grinding and filtering, collecting all the filtrates and drying them at 45-55°C for 20-28 hours to obtain crude glucomannan.

[0019] 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), ultrasonically treat it at a frequency of 20-25 kHz and a power of 200-300 W for 8-12 minutes, and dry the product after ultrasonic purification at a temperature of 45-55 ° C for 10-14 hours.

[0020] Furthermore, the flocculation treatment in step S3 includes: preparing the purified glucomannan into a hydrosol with a mass concentration of 0.8-1.2%, adding an aluminum chloride / chitosan composite flocculant to the hydrosol in an amount of 1-2% of the sol volume, stirring at a temperature of 35-45°C for 15-30 minutes, and then performing two centrifugal separations in sequence at a centrifugal speed of 3500-4500 rpm and a centrifugal time of 18-22 minutes.

[0021] Furthermore, the ethanol precipitation in S3 includes: adding 3 to 4 times the volume of 90 wt% ethanol to the clarified liquid obtained by centrifugation, mixing thoroughly, and standing for 1.5 to 2.5 hours to precipitate glucomannan precipitate, then filtering under reduced pressure to collect the precipitate, drying the collected precipitate at a temperature of 45 to 55° C. and a vacuum degree of -0.08 to -0.1 MPa for 20 to 28 hours, grinding after drying, and passing through a 60-mesh sieve.

[0022] Furthermore, the purity of the high-purity glucomannan is 95.0-98.2%, and the molecular weight polydispersity index (PDI) is 1.6-2.2.

[0023] The present invention aims to address the key technical issues of insufficient purity and excessive molecular weight distribution, which are common in existing glucomannan preparation processes. By addressing the core bottlenecks of traditional processes, such as low impurity removal efficiency, poor target component separation selectivity, and easily damaged molecular chain structures, a highly efficient purification system has been constructed, centered around multi-stage ethanol extraction, isopropyl alcohol ultrasound-assisted purification, and aluminum chloride / chitosan composite flocculation. By introducing a gradient of ethanol concentrations during the initial extraction phase, impurities of varying polarity are gradually removed, laying the foundation for subsequent purification. During the intermediate processing step, ultrasound in an isopropyl alcohol system enhances the disaggregation of macromolecular clusters and the desorption of impurities, maintaining the integrity of the polysaccharide backbone structure under mild conditions. In the key separation step, a composite flocculant is used instead of a traditional single inorganic flocculant, leveraging the charge neutralization ability of polyaluminum chloride and the capture effect of chitosan's long-chain structure to achieve synergistic removal of both macromolecular colloidal impurities and small charged impurities, effectively improving flocculation efficiency and selectivity and significantly improving the problem of impurity residues in the product. Ultimately, ethanol precipitation and a multi-stage drying process further converged the molecular weight distribution and reduced polydispersity, resulting in a glucomannan product with uniform structure, enhanced purity, and stable performance. The invention aims to overcome the technical limitations of traditional methods in high-purity preparation and molecular weight control by constructing an extraction and purification system that integrates multiple mechanisms, balances structural protection, and achieves efficient separation. This system provides a more stable and reliable raw material foundation for the subsequent application of glucomannan in food, pharmaceuticals, and high-end functional materials.

[0024] (3) Beneficial technical effects

[0025] 1. The aluminum chloride / chitosan composite flocculation system constructed in the present invention significantly improves the impurity removal efficiency, structural integrity and purification selectivity during the glucomannan extraction process through the synergistic effect of electrical neutralization and molecular bridging, which is superior to a single flocculant system.

[0026] 2. The present invention effectively improves the purity and structural homogeneity of glucomannan through the synergistic combination of multi-stage ethanol extraction, isopropanol ultrasonic purification, and aluminum chloride / chitosan composite flocculation, significantly optimizing separation efficiency and product performance, making it suitable for high-standard food and biomaterial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the XRD phase analysis diagram of glucomannan prepared in Example 1 of the present invention.

[0028] Figure 2 This is the FTIR infrared Fourier spectrum of the glucomannan prepared in Example 1 of the present invention.

[0029] Figure 3 This is the FTIR infrared Fourier spectrum of the aluminum chloride / chitosan composite flocculant prepared in Example 1 of the present invention.

[0030] Figure 4 This is a physical picture of the fresh konjac prepared in Example 1 of the present invention.

[0031] Figure 5 This is a physical picture of the dried konjac pieces prepared in Example 1 of the present invention.

[0032] Figure 6 This is a physical picture of the high-purity glucomannan prepared in Example 1 of the present invention.

[0033] Figure 7 The figure is a comparison chart of the purity of each sample of the embodiment of the present invention and the comparative example.

[0034] Figure 8 The figure is a comparison chart of the molecular weight distribution of each sample of the embodiment of the present invention and the comparative example.

[0035] Figure 9 4 is a comparison chart of the rheological properties of the samples of the embodiments of the present invention and the comparative examples.

[0036] Figure 10 The figure is a comparison chart of the solubility performance of each sample of the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions and advantages of the embodiments of the present invention more clear, 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.

[0038] Example 1

[0039] A method for preparing high-purity glucomannan comprises the following steps:

[0040] S1: After pretreating fresh konjac tubers, multi-stage concentration extraction is performed with 60wt% ethanol, 70wt% ethanol, and 80wt% ethanol in sequence to obtain crude glucomannan; the pretreatment of fresh konjac tubers includes: peeling, washing, and chopping into small pieces with a side length of 3mm, drying at a temperature of 45°C for 20h, and grinding to a particle size of 80 mesh after drying; the multi-stage concentration extraction includes: mixing the ground konjac tubers with 60wt% ethanol in a weight ratio of 1:5.0, performing high-speed homogenization grinding at a speed of 6000rpm for 3min, and then filtering and collecting the filter residue, mixing the filter residue with 70wt% ethanol in a weight ratio of 1:5.0, repeatedly grinding and filtering, mixing the filter residue with 80wt% ethanol in a weight ratio of 1:5.5, repeatedly grinding and filtering, collecting all the filtrates and drying at 45°C for 20h to obtain crude glucomannan.

[0041] S2: The crude glucomannan was subjected to ultrasonic-assisted purification using isopropanol. Ultrasonic-assisted purification involved mixing the crude glucomannan with 80 wt% isopropanol at a solid-liquid weight ratio of 1:10, ultrasonically treating it at a frequency of 20 kHz and a power of 200 W for 8 minutes. The ultrasonically purified product was dried at 45°C for 10 hours.

[0042] S3: The purified product is subjected to hydrosolization, flocculation with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying to obtain high-purity glucomannan. The flocculation treatment includes preparing the purified glucomannan into a 0.8% aqueous sol, adding an aluminum chloride / chitosan composite flocculant at 1% of the sol volume, stirring at 35°C for 15 minutes, and then centrifuging twice at 3500 rpm for 18 minutes. The ethanol precipitation includes adding three volumes of 90 wt% ethanol to the clarified liquid obtained by centrifugation, mixing thoroughly, and then allowing the liquid to stand for 1.5 hours to precipitate the glucomannan. The precipitate is then collected by vacuum filtration and dried at 45°C under a vacuum of -0.08 MPa for 20 hours. After drying, the precipitate is ground and passed through a 60-mesh sieve.

[0043] 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 dropwise adding the chitosan stock solution into the polyaluminum chloride stock solution to carry out a composite reaction.

[0044] The preparation of the aluminum chloride / chitosan composite flocculant of this embodiment includes: heating an aluminum chloride aqueous solution with a concentration of 0.48 mol / L to 73.8° C., adding a sodium hydroxide aqueous solution with a concentration of 0.48 mol / L at a dropping rate of 28.0 mL / h under a stirring rate of 920 rpm to perform an alkalization reaction, wherein 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, the solution is diluted with deionized water to an aluminum ion concentration of 0.09 mol / L.

[0045] The preparation method of the polyaluminium chloride stock solution of the present embodiment includes: taking aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution with a concentration of 0.48 mol / L; taking sodium hydroxide to prepare a sodium hydroxide aqueous solution with a concentration of 0.48 mol / L for standby use; placing the aluminum chloride aqueous solution in a reaction vessel, heating it to 73.8° C., and slowly dripping the sodium hydroxide aqueous solution into the aluminum chloride aqueous solution at a dripping rate of 28.0 mL / h under a stirring rate of 920 rpm to perform 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, the resulting solution is cooled to room temperature and then diluted with deionized water to an aluminum ion concentration of 0.09 mol / L to obtain a polyaluminium chloride stock solution.

[0046] The preparation method of the chitosan stock solution of this embodiment includes: taking 0.09 parts of chitosan by weight and adding it to 0.14 parts of a 0.09 mol / L hydrochloric acid aqueous solution, stirring at 260 rpm at room temperature for 56 minutes until it is completely dissolved, and then diluting the volume to 192 mL with deionized water.

[0047] The purity of the high-purity glucomannan in this example is 95.0%, and the molecular weight polydispersity index PDI is 1.6.

[0048] 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 various 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 3432 cm⁻¹, the alkyl vibration band in the range of 2850-2925 cm⁻¹, the CO stretching vibration at 1640.23 cm⁻¹, and the COC characteristic peak at 1158 cm⁻¹. Figure 3 The FTIR spectrum of aluminum chloride / chitosan composite flocculant showed that the 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 chitosan absorption peaks of 1645 cm⁻¹ amide band I, 1533 cm⁻¹ amide band II, and 1330 cm⁻¹ amide band III indicated that the composite flocculant was successfully formed and maintained the structural characteristics of the two components. Figures 4 to 6The actual picture clearly shows the complete preparation process from fresh konjac raw material to drying treatment 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.

[0049] Example 2

[0050] A method for preparing high-purity glucomannan comprises the following steps:

[0051] S1: After pretreating fresh konjac tubers, multi-stage concentration extraction is performed 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 chopping into small pieces with a side length of 4 mm, drying at a temperature of 48°C for 22 hours, 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 in a weight ratio of 1:5.3, performing high-speed homogenization grinding at a speed of 6600 rpm for 4 minutes, and then filtering and collecting the filter residue, mixing the filter residue with 70 wt% ethanol in a weight ratio of 1:5.3, repeatedly grinding and filtering, mixing the filter residue with 80 wt% ethanol in a weight ratio of 1:5.7, repeatedly grinding and filtering, collecting all the filtrates and drying at 48°C for 22 hours to obtain crude glucomannan.

[0052] S2: The crude glucomannan was subjected to ultrasonic-assisted purification using isopropanol. Ultrasonic-assisted purification involved mixing the crude glucomannan with 80 wt% isopropanol at a solid-to-liquid weight ratio of 1:12, ultrasonically treating the mixture at a frequency of 22 kHz and a power of 230 W for 9 minutes. The ultrasonically purified product was then dried at 48°C for 11 hours.

[0053] S3: The purified product was subjected to hydrosolization, flocculation with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying to obtain high-purity glucomannan. The flocculation treatment included preparing the purified glucomannan into a 0.9% aqueous sol, adding an aluminum chloride / chitosan composite flocculant at 1.3% of the sol volume, stirring at 38°C for 20 minutes, and then centrifuging twice at 3800 rpm for 19 minutes. The ethanol precipitation involved adding 3.3 volumes of 90 wt% ethanol to the clarified liquid obtained by centrifugation. The mixture was thoroughly mixed and allowed to stand for 1.8 hours to precipitate the glucomannan. The precipitate was then collected by vacuum filtration and dried at 48°C under a vacuum of -0.09 MPa for 22 hours. After drying, the precipitate was ground and passed through a 60-mesh sieve.

[0054] 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 dropwise adding the chitosan stock solution into the polyaluminum chloride stock solution to carry out a composite reaction.

[0055] The preparation of the aluminum chloride / chitosan composite flocculant of this embodiment includes: heating a 0.45 mol / L aluminum chloride aqueous solution to 72.0° C., adding a 0.45 mol / L sodium hydroxide aqueous solution at a rate of 25.0 mL / h under a stirring rate of 800 rpm to perform an alkalization reaction, wherein 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, the solution is diluted with deionized water to an aluminum ion concentration of 0.08 mol / L.

[0056] The preparation method of the polyaluminium chloride stock solution of the present embodiment includes: taking aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution with a concentration of 0.45 mol / L; taking sodium hydroxide to prepare a sodium hydroxide aqueous solution with a concentration of 0.45 mol / L for standby use; placing the aluminum chloride aqueous solution in a reaction vessel, heating it to 72.0° C., and slowly dripping the sodium hydroxide aqueous solution into the aluminum chloride aqueous solution at a dripping rate of 25.0 mL / h under a stirring rate of 800 rpm to perform an 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 resulting 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 polyaluminium chloride stock solution.

[0057] The chitosan stock solution of this embodiment was prepared by adding 0.08 parts by weight of chitosan to 0.12 parts of a 0.08 mol / L hydrochloric acid aqueous solution, stirring at 200 rpm for 50 min at room temperature until completely dissolved, and then diluting the solution to 180 mL with deionized water.

[0058] The preparation of the aluminum chloride / chitosan composite flocculant of this embodiment includes: heating an aluminum chloride aqueous solution with a concentration of 0.48 mol / L to 73.8° C., adding a sodium hydroxide aqueous solution with a concentration of 0.48 mol / L at a dropping rate of 28.0 mL / h under a stirring rate of 920 rpm to perform an alkalization reaction, wherein 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, the solution is diluted with deionized water to an aluminum ion concentration of 0.09 mol / L.

[0059] The preparation method of the polyaluminium chloride stock solution of the present embodiment includes: taking aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution with a concentration of 0.48 mol / L; taking sodium hydroxide to prepare a sodium hydroxide aqueous solution with a concentration of 0.48 mol / L for standby use; placing the aluminum chloride aqueous solution in a reaction vessel, heating it to 73.8° C., and slowly dripping the sodium hydroxide aqueous solution into the aluminum chloride aqueous solution at a dripping rate of 28.0 mL / h under a stirring rate of 920 rpm to perform 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 minutes; after the alkalization reaction is completed, the resulting solution is cooled to room temperature and then diluted with deionized water to an aluminum ion concentration of 0.09 mol / L to obtain the polyaluminium chloride stock solution.

[0060] The preparation method of the chitosan stock solution of this embodiment includes: taking 0.09 parts of chitosan by weight and adding it to 0.14 parts of a 0.09 mol / L hydrochloric acid aqueous solution, stirring at 260 rpm at room temperature for 56 minutes until it is completely dissolved, and then diluting the volume to 192 mL with deionized water.

[0061] The purity of the high-purity glucomannan in this example is 96.0%, and the molecular weight polydispersity index PDI is 1.8.

[0062] Example 3

[0063] A method for preparing high-purity glucomannan comprises the following steps:

[0064] S1: After pretreating fresh konjac tubers, multi-stage concentration extraction is performed 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 chopping into small pieces with a side length of 4 mm, drying at a temperature of 51°C for 25 hours, 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 in a weight ratio of 1:5.6, performing high-speed homogenization grinding at a speed of 7200 rpm for 4 minutes, and then filtering and collecting the filter residue, mixing the filter residue with 70 wt% ethanol in a weight ratio of 1:5.6, repeatedly grinding and filtering, mixing the filter residue with 80 wt% ethanol in a weight ratio of 1:5.8, repeatedly grinding and filtering, collecting all the filtrates and drying at 51°C for 25 hours to obtain crude glucomannan.

[0065] S2: The crude glucomannan was subjected to ultrasonic-assisted purification using isopropanol. Ultrasonic-assisted purification involved mixing the crude glucomannan with 80 wt% isopropanol at a solid-to-liquid weight ratio of 1:13, ultrasonically treating it at a frequency of 23 kHz and a power of 260 W for 10 min. The ultrasonically purified product was dried at 51°C for 12 h.

[0066] S3: The purified product was subjected to hydrosolization, flocculation with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying to obtain high-purity glucomannan. The flocculation treatment included preparing the purified glucomannan into a 1.0% aqueous sol, adding an aluminum chloride / chitosan composite flocculant at 1.6% of the sol volume, stirring at 41°C for 24 minutes, and then centrifuging twice at 4100 rpm for 20 minutes. The ethanol precipitation involved adding four volumes of 90 wt% ethanol to the clarified liquid obtained by centrifugation. The mixture was thoroughly mixed and allowed to stand for 2.1 hours to precipitate the glucomannan. The precipitate was then collected by vacuum filtration and dried at 51°C under a vacuum of -0.09 MPa for 25 hours. After drying, the precipitate was ground and passed through a 60-mesh sieve.

[0067] 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 dropwise adding the chitosan stock solution into the polyaluminum chloride stock solution to carry out a composite reaction.

[0068] The preparation of the aluminum chloride / chitosan composite flocculant of this embodiment includes: heating an aluminum chloride aqueous solution with a concentration of 0.55 mol / L to 78.0° C., adding a sodium hydroxide aqueous solution with a concentration of 0.55 mol / L at a dropping rate of 35.0 mL / h under a stirring rate of 1200 rpm to perform an alkalization reaction, wherein the molar ratio of hydroxide ions to aluminum ions is controlled to be 2.2, the alkalization reaction time is 90 min, and after the reaction is completed, the solution is diluted with deionized water to an aluminum ion concentration of 0.12 mol / L.

[0069] The preparation method of the polyaluminium chloride stock solution of the present embodiment includes: taking aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution with a concentration of 0.55 mol / L; taking sodium hydroxide to prepare a sodium hydroxide aqueous solution with a concentration of 0.55 mol / L for standby use; placing the aluminum chloride aqueous solution in a reaction vessel, heating it to 78.0° C., and slowly dripping the sodium hydroxide aqueous solution into the aluminum chloride aqueous solution at a dripping rate of 35.0 mL / h under a stirring rate of 1200 rpm to perform an alkalization reaction; during the alkalization reaction, the molar ratio of hydroxide ions to aluminum ions is controlled to be 2.2, and the alkalization reaction time is 90 min; after the alkalization reaction is completed, the resulting solution is cooled to room temperature and then diluted with deionized water to an aluminum ion concentration of 0.12 mol / L to obtain a polyaluminium chloride stock solution.

[0070] The chitosan stock solution of this embodiment was prepared by adding 0.12 parts by weight of chitosan to 0.20 parts of a 0.12 mol / L hydrochloric acid aqueous solution, stirring at 400 rpm for 70 min at room temperature until completely dissolved, and then diluting the solution to 220 mL with deionized water.

[0071] The purity of the high-purity glucomannan in this example is 98.2%, and the molecular weight polydispersity index PDI is 2.2.

[0072] Example 4

[0073] A method for preparing high-purity glucomannan comprises the following steps:

[0074] S1: After pretreating fresh konjac tubers, multi-stage concentration extraction is performed 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 chopping into small pieces with a side length of 5 mm, drying at a temperature of 55°C for 28 hours, and grinding to a particle size of 100 mesh after drying; the multi-stage concentration extraction includes: mixing the ground konjac tubers with 60 wt% ethanol in a weight ratio of 1:6.0, performing high-speed homogenization grinding at a speed of 8000 rpm for 5 minutes, and then filtering and collecting the filter residue, mixing the filter residue with 70 wt% ethanol in a weight ratio of 1:6.0, repeatedly grinding and filtering, mixing the filter residue with 80 wt% ethanol in a weight ratio of 1:6.0, repeatedly grinding and filtering, collecting all the filtrates and drying at 55°C for 28 hours to obtain crude glucomannan.

[0075] S2: The crude glucomannan was subjected to ultrasonic-assisted purification using isopropanol. Ultrasonic-assisted purification involved mixing the crude glucomannan with 80 wt% isopropanol at a solid-liquid weight ratio of 1:15, ultrasonically treating it at a frequency of 25 kHz and a power of 300 W for 12 minutes. The ultrasonically purified product was dried at 55°C for 14 hours.

[0076] S3: The purified product was subjected to hydrosolization, flocculation with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying to obtain high-purity glucomannan. The flocculation treatment included preparing the purified glucomannan into a 1.2% aqueous sol, adding an aluminum chloride / chitosan composite flocculant at 2% of the sol volume, stirring at 45°C for 30 minutes, and then centrifuging twice at 4500 rpm for 22 minutes. The ethanol precipitation involved adding four volumes of 90 wt% ethanol to the clarified liquid obtained by centrifugation. The mixture was thoroughly mixed and allowed to stand for 2.5 hours to precipitate the glucomannan. The precipitate was then collected by vacuum filtration and dried at 55°C under a vacuum of -0.1 MPa for 28 hours. After drying, the precipitate was ground and passed through a 60-mesh sieve.

[0077] 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 dropwise adding the chitosan stock solution into the polyaluminum chloride stock solution to carry out a composite reaction.

[0078] The preparation of the aluminum chloride / chitosan composite flocculant of this embodiment includes: heating an aluminum chloride aqueous solution with a concentration of 0.51 mol / L to 75.6° C., adding a sodium hydroxide aqueous solution with a concentration of 0.51 mol / L at a dropping rate of 31.0 mL / h under a stirring rate of 1040 rpm to perform an alkalization reaction, wherein the molar ratio of hydroxide ions to aluminum ions is controlled to be 2.0, the alkalization reaction time is 78 min, and after the reaction is completed, the solution is diluted with deionized water to an aluminum ion concentration of 0.10 mol / L.

[0079] The preparation method of the polyaluminium chloride stock solution of the present embodiment includes: taking aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution with a concentration of 0.51 mol / L; taking sodium hydroxide to prepare a sodium hydroxide aqueous solution with a concentration of 0.51 mol / L for standby use; placing the aluminum chloride aqueous solution in a reaction vessel, heating it to 75.6° C., and slowly dripping the sodium hydroxide aqueous solution into the aluminum chloride aqueous solution at a dripping rate of 31.0 mL / h under a stirring rate of 1040 rpm to perform 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 is completed, the resulting solution is cooled to room temperature and then diluted with deionized water to an aluminum ion concentration of 0.10 mol / L to obtain a polyaluminium chloride stock solution.

[0080] The preparation method of the chitosan stock solution of this embodiment includes: taking 0.10 parts of chitosan by weight and adding it to 0.17 parts of 0.10 mol / L hydrochloric acid aqueous solution, stirring at 320 rpm at room temperature for 62 minutes until it is completely dissolved, and then diluting it with deionized water to 204 mL.

[0081] The purity of the high-purity glucomannan in this example is 97.0%, and the molecular weight polydispersity index PDI is 2.0.

[0082] Comparative Example 1

[0083] The method is basically the same as Example 1, except that in step S1, only a single concentration of 70 wt % ethanol is used for extraction, instead of using 60 wt % ethanol, 70 wt % ethanol, and 80 wt % ethanol in sequence for multi-level extraction.

[0084] Comparative Example 2

[0085] The method is basically the same as Example 1, except that ethanol is used instead of isopropanol for ultrasound-assisted purification in step S2, and other ultrasound conditions remain unchanged.

[0086] Comparative Example 3

[0087] The process is basically the same as Example 1, except that in step S3, only polyaluminium chloride is used as a flocculant instead of aluminium chloride / chitosan composite flocculant.

[0088] Comparative Example 4

[0089] The process is basically the same as Example 1, except that in step S3, only chitosan is used as a flocculant instead of aluminum chloride / chitosan composite flocculant.

[0090] Comparative Example 5

[0091] The method is basically the same as Example 1, except that the concentration of the aluminum chloride aqueous solution during the preparation of the aluminum chloride / chitosan composite flocculant is 0.3 mol / L.

[0092] Comparative Example 6

[0093] The method is basically the same as Example 1, except that the alkalization reaction temperature during the preparation of the aluminum chloride / chitosan composite flocculant is 60°C.

[0094] Comparative Example 7

[0095] The method is basically the same as Example 1, except that the molar ratio of hydroxide ions to aluminum ions during the preparation of the aluminum chloride / chitosan composite flocculant is 1.5.

[0096] Comparative Example 8

[0097] The method is basically the same as Example 1, except that sulfuric acid solution is used instead of hydrochloric acid solution to dissolve chitosan during the preparation of chitosan stock solution.

[0098] Comparative Example 9

[0099] The method is basically the same as Example 1, except that the high-speed homogenizing and grinding speed during the multi-stage concentration extraction process is 4000 rpm.

[0100] Comparative Example 10

[0101] The method is basically the same as Example 1, except that the ultrasonic frequency during the ultrasonic-assisted purification process is 15 kHz.

[0102] Comparative Example 11

[0103] The method is basically the same as Example 1, except that the amount of aluminum chloride / chitosan composite flocculant added during the flocculation treatment is 0.5% of the sol volume.

[0104] Comparative Example 12

[0105] The method is basically the same as Example 1, except that during the preparation of the aluminum chloride / chitosan composite flocculant, the polyaluminum chloride stock solution is added dropwise to the chitosan stock solution, rather than the chitosan stock solution being added dropwise to the polyaluminum chloride stock solution.

[0106] Performance testing:

[0107] Purity Assay: High-performance liquid chromatography (HPLC) was used to analyze the purity of the prepared glucomannan samples. The glucomannan products prepared in each example were tested using an amino column as the stationary phase, an acetonitrile-water system as the mobile phase, and a differential refractive index detector. The mass fraction of glucomannan in the samples was calculated by comparing with a standard and integrating the peak area.

[0108] Molecular Weight and Distribution Determination: Gel permeation chromatography (GPC) was used to determine the weight-average molecular weight, number-average molecular weight, and polydispersity index (PDI) of glucomannan. Glucomannan samples prepared under different process conditions were tested using a TSK-GEL series column, a 0.1 M NaNO3 solution as the mobile phase, and a differential refractive index detector. A calibration curve was established using glucan standards. The experimental method was based on ASTM D3593-80.

[0109] Rheological properties testing: A rotational rheometer was used to determine the viscosity, shear-thinning behavior, and gel strength of aqueous glucomannan solutions. The test subjects were aqueous solutions of glucomannan at different concentrations (0.5%, 1.0%, and 1.5%). Steady-state shear tests were conducted at 25°C with a shear rate range of 0.1-100 s⁻¹. Dynamic oscillation tests were also performed to determine the storage modulus G' and loss modulus G''. The experimental method was based on ISO 3219-1993.

[0110] Solubility Testing: The solubility and dissolution rate of glucomannan in various solvents were measured. The glucomannan products prepared in each example were tested. Solubility tests were conducted in deionized water, 0.1M NaOH solution, and 0.1M HCl solution, respectively. Stirring was performed at a constant temperature of 25°C, and the time required for complete dissolution and the maximum solubility were recorded.

[0111] The performance of glucomannan from Examples 1 to 4 and Comparative Examples 1 to 12 is summarized in Table 1. It can be seen from the table that the performance analysis of the comparative examples shows that the deviation of different process parameters has a significant impact on the preparation performance of glucomannan. The use of single-concentration ethanol extraction instead of multi-stage concentration extraction results in insufficient extraction, a significant decrease in purity, and a corresponding decrease in molecular weight. This is because multi-stage concentration extraction can more effectively remove impurities of different polarities and improve extraction efficiency. When ethanol is used instead of isopropanol for ultrasonic purification, the purity is improved but still below the optimal level because the solubility selectivity of ethanol is not as good as that of isopropanol, indicating that isopropanol has advantages in removing specific impurities. When a single polyaluminum chloride or chitosan is used as a flocculant, the purity decreases to varying degrees, proving the importance of the synergistic effect of the composite flocculant in improving the purification effect. A single component cannot achieve comprehensive removal of different types of impurities. Deviations in flocculant preparation parameters, such as low aluminum chloride concentration, insufficient alkalinization temperature, and a low hydroxide-to-aluminum ion molar ratio, all resulted in reduced flocculant activity and a significant decrease in purity, demonstrating that precise control of flocculant preparation conditions is crucial for maintaining flocculation performance. When sulfuric acid was used instead of hydrochloric acid to dissolve chitosan, purity remained high, approaching that achieved by the standard process due to its similar protonation capacity, indicating that the type of strong acid has a limited effect on chitosan protonation. Using a lower grinding speed resulted in inadequate crushing of konjac tubers and incomplete release of active ingredients, resulting in a decrease in purity and molecular weight. Using a lower ultrasonic frequency weakened the effectiveness of ultrasound-assisted purification, slightly reducing product purity. Insufficient flocculant dosage resulted in incomplete flocculation, poor impurity removal, and a significant decrease in purity. Changing the order of addition of the ingredients in the composite reaction disrupted the optimal formation conditions for the composite flocculant, affecting the formation of the flocculation network structure and significantly reducing purity, demonstrating the critical role of a correct composite reaction process in forming an efficient flocculant structure.

[0112] from Figure 7-10It can be seen from the experimental results that the embodiments of the present invention are significantly better than the comparative examples in various performance indicators, among which embodiment 3 shows the best comprehensive performance. Figure 7 The purities of Examples 1-4 reached 95.0%, 96.0%, 98.2% and 97.0%, respectively, which were significantly higher than the 87.9%-93.8% range of the comparative example, indicating that the multi-stage concentration extraction, isopropyl alcohol ultrasonic purification and composite flocculant treatment process of the present invention can effectively improve the product purity. Figure 8 The weight average molecular weight of the examples is 8.64-12.32×10 5 In the range of g / mol, the PDI value is 1.6-2.2, while the weight average molecular weight of the comparative example is only 7.85-8.71×10 5 g / mol, and the PDI value was 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 by regulating the process parameters. Figure 9 The rheological property test results show that the viscosity of the 1.0% solution of the embodiment 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 example, demonstrating that the glucomannan prepared by the present invention has better thickening and gelling properties. Figure 10 The solubility performance data show that the dissolution time in water of the embodiment is 9.8-12.3 min, and the maximum solubility is 28.5-32.6 g / L, while the dissolution time of the comparative example is 12.5-14.6 min, and the maximum solubility is 26.5-28.3 g / L, indicating that the product prepared by the process of the present invention has a faster dissolution rate and higher solubility, which is attributed to the high purity of the product, good integrity of the molecular chain structure and reasonable molecular weight distribution, which comprehensively verifies the superiority of the technical solution of the present invention and the rationality of the selection of process parameters.

[0113] Table 1 Performance of glucomannan in Examples 1 to 4 and Comparative Examples 1 to 12

[0114] Sample number purity(%) <![CDATA[Weight-average molecular weight (×10 5 g / mol)]]> <![CDATA[Number-average molecular weight (×10 5 g / mol)]]> PDI 1.0% solution viscosity (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

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that any equivalent structural transformations made within the scope of the present invention using the contents of the present invention's description and drawings should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-purity glucomannan, characterized in that: The following steps are involved: S1: Fresh konjac tubers were pretreated and then subjected to multi-stage concentration extraction using 60 wt% ethanol, 70 wt% ethanol, and 80 wt% ethanol to obtain crude glucomannan; S2: Ultrasound-assisted purification of crude glucomannan using isopropanol; S3: The purified product is subjected to hydrosolization, flocculation with an aluminum chloride / chitosan composite flocculant, ethanol precipitation, and drying to obtain high-purity glucomannan; The preparation of the aluminum chloride / chitosan composite flocculant comprises the following steps: preparing aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution with a concentration of 0.45 to 0.55 mol / L; preparing sodium hydroxide to prepare a sodium hydroxide aqueous solution with a concentration of 0.45 to 0.55 mol / L for later use; placing the aluminum chloride aqueous solution in a reaction container, heating it to 72.0 to 78.0° C., and slowly dripping the sodium hydroxide aqueous solution into the aluminum chloride aqueous solution at a dripping rate of 25.0 to 35.0 mL / h under a stirring rate of 800 to 1200 rpm to perform an alkalization reaction; during the alkalization reaction, the molar ratio of hydroxide ions to aluminum ions is controlled to be 1.8 to 2.2, and the alkalization reaction time is 60 to 90 minutes; after the alkalization reaction is completed, cooling the resulting solution to room temperature, and then diluting it with deionized water to an aluminum ion concentration of 0.08 to 0.12 mol / L, to obtain a polyaluminium chloride stock solution, and then dropwise add the chitosan stock solution into the polyaluminium chloride stock solution to carry out a composite reaction to obtain an aluminium chloride / chitosan composite flocculant; The purity of the high-purity glucomannan is 95.0-98.2%, and the molecular weight polydispersity index (PDI) is 1.6-2.

2.

2. The method for preparing high-purity glucomannan according to claim 1, wherein: The preparation method of the chitosan stock solution comprises: adding 0.08 to 0.12 parts of chitosan by weight to 0.12 to 0.20 parts of a 0.08 to 0.12 mol / L hydrochloric acid aqueous solution, stirring at 200 to 400 rpm at room temperature for 50 to 70 minutes until completely dissolved, and then diluting with deionized water to a volume of 180 to 220 mL.

3. The method for preparing high-purity glucomannan according to claim 1, wherein: The fresh konjac tubers in S1 are pretreated by peeling, washing, and chopping into small pieces with a side length of 3 to 5 mm, drying at a temperature of 45 to 55° C. for 20 to 28 h, and grinding to a particle size of 80 to 100 meshes after drying; The multi-stage concentration extraction in S1 includes: mixing the ground konjac tuber with 60wt% ethanol in 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 minutes, filtering and collecting the filter residue, mixing the filter residue with 70wt% ethanol in a weight ratio of 1:(5.0-6.0) and repeatedly grinding and filtering, mixing the filter residue with 80wt% ethanol in a weight ratio of 1:(5.5-6.0) and repeatedly grinding and filtering, collecting all the filtrates and drying them at 45-55°C for 20-28 hours to obtain crude glucomannan.

4. The method for preparing high-purity glucomannan according to claim 1, wherein: 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), ultrasonically treat the mixture at a frequency of 20-25 kHz and a power of 200-300 W for 8-12 minutes, and dry the product after ultrasonic purification at a temperature of 45-55°C for 10-14 hours.

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

6. The method for preparing high-purity glucomannan according to claim 1, wherein: The ethanol precipitation in S3 includes: adding 3 to 4 times the volume of 90wt% ethanol to the clarified liquid obtained by centrifugation, mixing thoroughly, and then standing for 1.5 to 2.5 hours to precipitate glucomannan, then filtering under reduced pressure to collect the precipitate, drying the collected precipitate at a temperature of 45 to 55°C and a vacuum degree of -0.08 to -0.1 MPa for 20 to 28 hours, grinding it after drying, and passing it through a 60-mesh sieve.

Images