Method for improving quality of konjac glucomannan

Abstract

The invention discloses a method for improving the quality of konjac glucomannan. The method comprises the following steps: modifying konjac glucomannan with an esterifying agent, and treating with an alkali solution to form gel. The process is simple and convenient, the reagent is simple and safe, the gel strength and thermal stability are improved, meanwhile, the swelling dispersion effect of the konjac glucomannan is improved, the quality of the konjac glucomannan is effectively improved, and the industrial utilization value of the konjac glucomannan is improved.

Description

Technical Field

[0001] The invention relates to the field of konjac gum, and in particular to a method for improving the quality of konjac gum. Background Art

[0002] Konjac gum is a natural high molecular weight polysaccharide extracted from konjac tubers, with good hydrophilicity, thickening, rheology and gelation. As an excellent water-soluble dietary fiber, konjac gum has a variety of active functions such as lowering blood sugar, improving intestinal health, anti-inflammatory and enhancing immunity. It is widely used in the pharmaceutical and food industries in actual production activities. However, due to the strong hydrophilic effect of natural konjac gum, the actual solubility is poor, and the gel strength advantage is not enough, which makes the application range of natural konjac gum very limited. The traditional konjac gum enhancement treatment method mainly achieves a synergistic effect by compounding with other polysaccharides to improve the gel performance of konjac gum, but the gel after compounding is mostly a thermoreversible gel, and its thermal stability is destroyed.

[0003] Therefore, modifying konjac gum to improve its thermally irreversible gel properties is of great significance for expanding the application of konjac gum. Summary of the invention

[0004] The purpose of the present invention is to provide a simple and environmentally friendly method for preparing thermally irreversible konjac gel.

[0005] To achieve the above object, the present invention provides a method for improving the quality of konjac glucomannan, characterized in that the method comprises the following steps:

[0006] S1. After adding konjac gum to the alcohol aqueous solution and stirring continuously, add an esterifying agent and stir;

[0007] S2. heating reaction under alkaline conditions, the reactant is filtered and washed with an alcohol aqueous solution, and then pulverized and sieved to obtain easily dispersed konjac glucomannan, i.e. modified konjac glucomannan;

[0008] S3. Add the obtained modified konjac gum into an alkaline solution, stir until it becomes viscous, and then continue heating to react to obtain thermally irreversible konjac gel.

[0009] Furthermore, in step S1, the esterification agent is an acid anhydride.

[0010] Further, in step S1, the acid anhydride is at least one of acetic anhydride, glutaric anhydride, and octenylsuccinic anhydride;

[0011] Further, in step S1, the concentration of the acid anhydride solution is 2V / V% to 6V / V%;

[0012] Furthermore, in step S1, the usage ratio of konjac gum: esterifying agent is 10 g: (2-10) ml; preferably, the usage ratio of konjac gum: esterifying agent is 10 g: (2-6) ml.

[0013] Further, in step S2, the pH condition is alkaline, preferably, the pH is 8.0-8.5; and / or

[0014] The reaction temperature is 30-60°C; and / or

[0015] The reaction time is 1.5-5h.

[0016] Further, in step S3, the base is one or a complex of sodium hydroxide, potassium hydroxide, calcium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate; preferably, the selected base is sodium carbonate;

[0017] The concentration of the alkaline solution is greater than 0.1 mol / L. Preferably, the concentration of the alkaline solution is 0.1-5 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, 5.0 mol / L, but is not limited to these values. More preferably, the concentration of the alkaline solution is 0.1-0.5 mol / L.

[0018] Furthermore, in step S3, after the modified konjac gum is added into the alkaline solution, the concentration of the konjac gum in the alkaline solution is 2-7 w / v%.

[0019] Furthermore, in step S3, the heating is at 25-90° C. for 1-3 h.

[0020] Further, in step S3, the selected heating condition is 80° C., 1 h.

[0021] There is no limit to the concentration of the alcohol aqueous solution in step S1 of the present invention, but too low a concentration may cause the konjac flour to swell, thereby making the reaction product difficult to filter, and too high a concentration may cause the konjac gum molecular chain to be difficult to open and reduce the reaction efficiency. Therefore, a concentration of 75-85% is preferred; more preferably 80%.

[0022] The concentration of the alcohol aqueous solution used for washing in the present invention is not limited. Preferably, 75-85% concentration is a more suitable washing concentration for konjac gum. It will not cause swelling of the product due to too low concentration and can wash away the acid anhydride remaining from the reaction.

[0023] The heating treatment in the alkali treatment process of the present invention belongs to the reaction process of accelerating the gel. Preferably, 80° C. and 1 h are more suitable parameters for gel heating molding, which can effectively promote gel molding and improve production efficiency without too long a treatment time.

[0024] The invention uses an esterifying agent to perform modification treatment on konjac glucomannan and then performs alkali treatment to form gel; only common solvents are used in the treatment process, so that the actual dissolution ability of konjac glucomannan is improved, uniform gelation of konjac glucomannan in alkali solution is promoted, the strength of konjac glucomannan gel is increased to different degrees, the processing requirements of konjac glucomannan are met, and the application scenarios of konjac glucomannan are enriched.

[0025] The invention adopts an esterifying agent to chemically modify the konjac glucomannan. The addition of ester groups enables the molecules of the konjac glucomannan to be slowly connected in the process of deacetylation and gelation by adding alkali and heating, thereby improving the uniformity of the final gel and enhancing the gel strength thereof, so that the konjac glucomannan can be more widely used in industry. Meanwhile, in an alkaline environment, part of the acetyl groups of the konjac glucomannan molecular chains opened by swelling with an alcohol aqueous solution are removed, part of the active hydroxyl groups react with anhydride for esterification, new ester groups are introduced, the looseness of the konjac glucomannan particles is improved, and water solubility is promoted.

[0026] The preparation process of the invention is simple and quick, the types and quantities of reagents added are simplified, and it is more environmentally friendly and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an optical microscope comparison diagram of konjac gum powder after swelling for 3 hours before and after modification in the embodiment of the present invention and the comparative example;

[0028] Figure 2 The infrared absorption spectra of konjac gum esterified with different acid anhydrides in the embodiments and comparative examples of the present invention;

[0029] Figure 3 It is a thermogravimetric graph of konjac gel esterified with acetic anhydride at different concentrations according to the embodiments of the present invention and the comparative examples;

[0030] Figure 4 Schematic diagram of the microscopic gel network structure of the konjac thermal irreversible gel before and after modification in the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0031] Embodiments of the present invention are described in detail below, and the examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by reference to the accompanying drawings are exemplary, are intended to be used to explain the present invention, and are not to be construed as limitations of the present invention. Those who do not indicate specific techniques or conditions in the embodiments are carried out according to the techniques or conditions described in the documents in this area or according to the product specification. Those who do not indicate the manufacturer of reagents or instruments used are all conventional products that can be obtained commercially.

[0032] Determination of gel strength index: Texture test was carried out using a texture analyzer with a cylindrical probe (diameter 12.7 mm, model TA10); before, during and after extrusion, the probe tested the gel at compression speeds of 1.00 mm / s, 1.00 mm / s and 2.00 mm / s, respectively, and the trigger force and deformation were set to 5.00 g and 50%, respectively; sample parameters were recorded after all tests were completed.

[0033] Microscope observation: Dissolve the sample powder in water at a concentration of 1% (W / V) and stir continuously at 300 rpm for 3 h. After the swelling is complete, take a small amount of sol sample and observe it under a microscope.

[0034] Infrared structure characterization test: The powder sample was mixed with KBr powder in a certain proportion, ground and pressed into tablets, and then tested by Fourier infrared spectroscopy, recording 4000-500cm -1 Data within the wavenumber range, scanning time is 16s, resolution is 4cm -1 .

[0035] Thermogravimetric analysis: 5 ± 0.2 mg of sample was used for the test in an aluminum crucible. The sample was heated from 25°C to 400°C at a rate of 10°C / min, and a continuous nitrogen flow of 25 mL / min was maintained throughout the analysis to produce a nitrogen-rich atmosphere.

[0036] Microscopic morphology observation: The morphology of the sample was studied by scanning electron microscopy. The gel sample was freeze-dried and gold-sprayed on the surface before testing. The test was conducted at an acceleration voltage of 5kV, and the magnifications were ×1k, ×3k, and ×10k.

[0037] Example 1

[0038] S1. 10g of konjac gum was dispersed in 80% ethanol system for stability, 4mL of acetic anhydride solution was measured and diluted with 4 times its volume of isopropanol; after the system was evenly dispersed, the diluted acetic anhydride solution was added dropwise to the system within 1h and stirred to make the total volume of the system finally 100mL;

[0039] S2. Add 1M NaOH to control the system pH to maintain between 8.0 and 8.5, heat at 40°C, and the entire reaction lasts for 2 hours; filter, wash and filter the mixture after precipitation with 80% ethanol solution, and repeat three times to remove the remaining reactants;

[0040] The obtained product was dried at 55° C. for 24 h, and crushed through an 80-mesh sieve to obtain an acetic anhydride esterified konjac gum powder sample;

[0041] S3. The obtained 1.00 g esterified konjac gum sample was added to 25 mL of 0.2 M Na2CO3 solution, and the solution was stirred until viscous and allowed to stand for 30 min;

[0042] The mixture was placed in a 80°C water bath and heated for 1 hour. The gel was cooled at room temperature and then refrigerated in a 4°C refrigerator overnight to obtain a thermally irreversible gel of konjac gum.

[0043] Example 2

[0044] S1. 10 g of konjac gum was dispersed in 80% ethanol to stabilize the system, 4 mL of octenyl succinic anhydride solution was measured and diluted with 4 times its volume of isopropanol; after the system was evenly dispersed, the diluted octenyl succinic anhydride solution was added dropwise to the system within 1 h and stirred to make the total volume of the system finally 100 mL;

[0045] S2. Same as Example 1S2;

[0046] S3. Same as Example 1S3.

[0047] Example 3

[0048] S1. 10 g of konjac gum was dispersed in 80% ethanol to stabilize the system, 4 g of glutaric anhydride was weighed and diluted with 4 times its volume of isopropanol; after the system was evenly dispersed, the diluted glutaric anhydride solution was added dropwise to the system within 1 h and stirred to make the total volume of the system finally 100 mL;

[0049] S2. Same as Example 1S2.;

[0050] S3. Same as Example 1S3.

[0051] Example 4

[0052] S1. 10g of konjac gum was dispersed in 80% ethanol system for stability, 2, 3, 6mL of acetic anhydride solution was measured and diluted with 4 times its volume of isopropanol; after the system was evenly dispersed, the diluted acetic anhydride solution was added dropwise to the system within 1h and stirred to make the total volume of the system finally 100mL;

[0053] S2. Same as Example 1S2.;

[0054] S3. Same as Example 1S3.

[0055] Example 5

[0056] S1. Same as Example 3S1.;

[0057] S2. Add 1M NaOH to control the system pH to maintain between 8.0 and 8.5, heat at 30, 50, and 60°C, and the entire reaction lasts for 2 hours; filter, wash and filter the mixture after precipitation with 80% ethanol solution, and repeat three times to remove the remaining reactants;

[0058] The obtained product was dried at 55° C. for 24 h, and crushed through an 80-mesh sieve to obtain a glutaric anhydride esterified konjac gum powder sample;

[0059] Example 6

[0060] S1. 10g of konjac gum was dispersed in 80% ethanol system for stability, 6mL of acetic anhydride solution was measured and diluted with 4 times its volume of isopropanol; after the system was evenly dispersed, the diluted acetic anhydride solution was added dropwise to the system within 1h and stirred to make the total volume of the system finally 100mL;

[0061] S2. Same as Example 1S2.;

[0062] S3. 0.5, 1.25, 1.5 g, 1.75 g of the above-obtained esterified konjac gum sample was added to 25 mL of 0.2 M Na2CO3 solution, and the solution was stirred until viscous and allowed to stand for 30 min;

[0063] The mixture was placed in a 80°C water bath and heated for 1 hour. The gel was cooled at room temperature and then refrigerated in a 4°C refrigerator overnight to obtain a thermally irreversible gel of konjac gum.

[0064] Example 7

[0065] S1. Same as Example 7S1.;

[0066] S2. Same as Example 1S2.;

[0067] S3. 1.00 g of the esterified konjac gum sample obtained above was added to 20 mL of 0.1, 0.3, 0.4, and 0.5 M Na2CO3 solutions, and the solution was stirred until viscous and allowed to stand for 30 min;

[0068] The mixture was placed in a 80°C water bath and heated for 1 hour. The gel was cooled at room temperature and then refrigerated in a 4°C refrigerator overnight to obtain a thermally irreversible gel of konjac gum.

[0069] Comparative Example 1

[0070] S1. 10 g of konjac gum was dispersed in 80% ethanol and stirred to stabilize the system so that the total volume was finally 100 mL;

[0071] S2. Same as Example 1S2.;

[0072] S3. Same as Example 1S3.

[0073] Comparative Example 2

[0074] S1. The same as Example 7S1. and Comparative Example 1S1.;

[0075] S2. Same as Example 1S2.;

[0076] S3. 0.25g of the above-obtained konjac gum or esterified konjac gum sample was dissolved in 25mL of 0.2M Na2CO3 solution, and the solution was stirred to a viscous state and then allowed to stand for 30min;

[0077] The mixture was placed in a 80°C water bath and heated for 1 hour. The gel was cooled at room temperature and then refrigerated in a 4°C refrigerator overnight to obtain a thermally irreversible gel of konjac gum.

[0078] Comparative Example 3

[0079] S1. Same as Comparative Example 2S1.;

[0080] S2. Same as Example 1S2.;

[0081] S3. 1.00 g of the above-obtained konjac gum or esterified konjac gum sample was dissolved in 20 mL of 0.05 M Na2CO3 solution, and the solution was stirred until viscous and allowed to stand for 30 min;

[0082] The mixture was placed in a 80°C water bath and heated for 1 hour. The gel was cooled at room temperature and then refrigerated in a 4°C refrigerator overnight to obtain a thermally irreversible gel of konjac gum.

[0083] Test example

[0084] Performance tests were performed on the products obtained from Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0085] Table 1 Comparison of gel strength of samples modified by different anhydride types

[0086] Sample No. Anhydride type Gel strength (gf) Comparative Example 1 none 376.17±13.62 Experimental Example 1 Acetic anhydride 775.02±35.22 Experimental Example 2 Octenyl succinic anhydride 575.07±12.99 Experimental Example 3 (40°C) Glutaric anhydride 501.15±66.02

[0087] Table 2 Comparison of gel strength of samples modified with different anhydride concentrations

[0088] Sample No. Anhydride concentration (%, V / V) Gel strength (gf) Comparative Example 1 0 376.17±13.62 Example 4 2 565.79±33.27 Example 4 3 729.48±62.03 Example 1 4 775.02±35.22 Example 4 6 835.99±54.50

[0089] Table 3 Comparison of gel strength of modified samples at different reaction temperatures

[0090] Sample No. Temperature(℃) Gel strength (gf) Comparative Example 1 40 376.17±13.62 Experimental Example 5 30 425.83±30.79 Experimental Example 3 40 501.15±66.02 Experimental Example 5 50 464.55±23.02 Experimental Example 5 60 439.50±17.58

[0091] Table 4 Comparison of gel strength at different konjac gum concentrations

[0092]

[0093]

[0094] Table 5 Comparison of gel strength of samples modified with different alkali concentrations

[0095]

[0096] The results are shown in Tables 1-6. The gel strength of the anhydride-modified konjac glucomannan obtained by the method of the present invention is improved to varying degrees compared with the unmodified konjac glucomannan in the comparative example; this is because the increase in the acyl content makes the konjac glucomannan particles evenly dispersed in the swelling stage, and the heating deacetylation process slowly and evenly gels, which is conducive to the formation of a stronger gel.

[0097] like Figure 1 As shown, the left side is the optical microscope image after the swelling 3h of the konjac glucomannan powder obtained in comparative example 1, and the right side is the optical microscope image after the swelling 3h of the konjac glucomannan powder obtained in embodiment 1. It can be seen that after 3h of stirring and swelling, the unmodified konjac glucomannan (i.e., obtained in comparative example) still has a large amount of incompletely swollen block structures under an optical microscope, indicating that its swelling degree is restricted; and only a small amount of block structures appear in the microscope image after the swelling of the konjac glucomannan (i.e., obtained in embodiment) esterified by the present method, and a large amount of small-volume point-like objects exist, proving that its block structure swelling and fracture trace, swelling and dissolution effect is improved.

[0098] like Figure 2 As shown, the esterified konjac glucomannan with octenylsuccinic anhydride is obtained in Example 2, the esterified konjac glucomannan with glutaric anhydride is obtained in Example 3, the esterified konjac glucomannan with acetic anhydride is obtained in Example 1, and the konjac glucomannan is obtained in Comparative Example 1. It can be seen that in the infrared absorption spectrum of the modified konjac glucomannan (i.e., obtained in Examples 1, 2, and 3), the 1732 cm -1 The absorption peak of konjac gum showed an enhanced peak intensity compared with that of original konjac gum, which was attributed to the esterification between the acyl group in the acid anhydride and the hydroxyl group in konjac gum, proving the successful esterification of konjac gum.

[0099] like Figure 3 As shown, the high-substituted acetic anhydride esterified konjac gum is the 6% concentration acetic anhydride esterified konjac gum sample in Example 4, and the low-substituted acetic anhydride esterified konjac gum is the esterified konjac gum sample in Example 1. It can be seen that the konjac gel has a first weight loss due to the volatilization of water and solvent in the temperature range of 30 to 150°C, indicating that the hygroscopicity of the konjac gel obtained after the modification treatment is reduced; and the second round of obvious weight loss occurs between 150 and 300°C, which is mainly attributed to the destruction of the gel structure and the molecular chain, indicating that the weight loss rate of the modified konjac gel is reduced, indicating that esterification improves the thermal stability of konjac gel; because the esterification treatment promotes the aggregation of konjac gum molecular chains, its hydrophobic interaction is enhanced, thereby leading to the improvement of the thermal properties of konjac gel.

[0100] like Figure 4 As shown, wherein the konjac gel is obtained by comparative example 1, and the modified konjac gel is obtained by embodiment 1. It can be seen that there are a large number of incomplete dot-shaped objects in the konjac gel microstructure, and the overall structure presents an uneven sheet pore structure; this is because some particles swell too fast to block water from entering during the dissolution of konjac glucomannan, resulting in incomplete dissolution of internal particles, and this situation does not occur in the modified konjac gel; compared with the unmodified konjac glucomannan, the filamentous structure formed by the modified gel increases, the pores are more and the pore size is smaller, and the three-dimensional network structure is more compact and uniform.

[0101] According to the embodiments of the present invention, konjac glucomannan is subjected to esterification modification treatment, the process is simple, the reagents are streamlined and safe, it is conducive to the uniform formation of gel, the gel strength and thermal stability are improved, and the swelling effect of konjac glucomannan is improved, and water solubility is promoted, indicating that the anhydride-modified konjac glucomannan effectively improves the quality of konjac glucomannan and enhances its industrial utilization value.

[0102] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for improving the quality of konjac gum, characterized in that, The steps include: S1. After adding konjac gum to the alcohol aqueous solution and stirring continuously, add an esterifying agent and stir; S2. heating reaction under alkaline conditions, the reactant is filtered and washed with an alcohol aqueous solution, and then pulverized and sieved to obtain easily dispersed konjac glucomannan, i.e. modified konjac glucomannan; S3. Add the obtained modified konjac gum to an alkaline solution, stir until it becomes viscous and then let it stand, and then continue heating to react to obtain a thermally irreversible konjac gel.

2. The method for improving the quality of konjac gum as claimed in claim 1, wherein In step S1, the esterification agent is an acid anhydride.

3. The method for improving the quality of konjac glucomannan as claimed in claim 1, wherein In step S1, the acid anhydride is at least one of acetic anhydride, glutaric anhydride, and octenylsuccinic anhydride.

4. The method for improving the quality of konjac glucomannan as claimed in claim 1, wherein In step S1, the concentration of the acid anhydride solution is 2 V / V% to 6 V / V%.

5. The method for improving the quality of konjac glucomannan as claimed in claim 1, wherein: In step S1, the usage ratio of konjac gum: esterifying agent is 10 g: (2-10) ml; preferably, the usage ratio of konjac gum: esterifying agent is 10 g: (2-6) ml.

6. The method for improving the quality of konjac gum as claimed in claim 1, wherein In step S2, the pH condition is alkaline, preferably, the pH is 8.0-8.5; and / or The reaction temperature is 30-60°C; and / or The reaction time is 1.5-5h.

7. The method for improving the quality of konjac glucomannan as claimed in claim 1, wherein: In step S3, the base is one or a complex of sodium hydroxide, potassium hydroxide, calcium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate; preferably, the selected base is sodium carbonate; The concentration of the alkaline solution is greater than 0.1 mol / L. Preferably, the concentration of the alkaline solution is 0.1-5 mol / L; more preferably, the concentration of the alkaline solution is 0.1-0.5 mol / L.

8. The method for improving the quality of konjac glucomannan as claimed in claim 1, wherein: In step S3, after the modified konjac gum is added into the alkaline solution, the concentration of the modified konjac gum in the alkaline solution is 2-7 w / v%.

9. The method for improving the quality of konjac glucomannan as claimed in claim 1, wherein: In step S3, the heating is at 25-90°C for 1-3h.

10. The method for improving the quality of konjac gum as claimed in claim 9, wherein: In step S3, the heating condition is selected as 80°C for 1 h.

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