CN115463622A - Gel based on oxidized pectin and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of biochemistry, and particularly relates to gel based on oxidized pectin and a preparation method thereof. The preparation method comprises the steps of adjusting the pH value of a pectin solution to be below 5.0, then adding an oxidizing agent for oxidation modification, adding a terminator for termination reaction, adjusting the pH value to be below 5.0 after redissolving the oxidized pectin, then adding a chemical cross-linking agent and a physical cross-linking agent, fully mixing, standing and gelling. According to the invention, a dialdehyde structure with higher activity is introduced into pectin molecules through oxidation modification, so that the oxidized pectin has the capability of covalent crosslinking with amino compounds, a double-gel network jointly stabilized by covalent bonds and ionic bonds is constructed by crosslinking the oxidized pectin molecules with multi-amino compounds and multivalent cations, and the prepared pectin gel has the characteristics of simple gel conditions and stronger gel elasticity, and has an application prospect in the field of biomedicine.

Description

A kind of gel based on oxidized pectin and preparation method thereof

technical field

The invention belongs to the technical field of biochemistry, and in particular relates to a gel based on oxidized pectin and a preparation method thereof.

Background technique

Pectin molecule is an anionic heteropolysaccharide widely distributed in the cell walls of higher plants. It is widely used as a gelling agent in the food industry. Its main gelation mechanism can be divided into ionic gelation mechanism according to the degree of methylation. (low ester pectin) and acid+sugar gel mechanism (high ester pectin). The two gel mechanisms are based on the ionic bond between the carboxyl group and the cation and the hydrogen bond between the hydroxyl group, which belong to the weak interaction, which limits the gel strength and application range of pectin.

CN109046190A discloses a pectin composite silica airgel and its preparation method and application, specifically disclosing the following steps: Step 1: adjusting the pH of the sodium silicate solution to 3-4, adding pectin and silica to mix , to obtain the mixture; step 2: mix the mixture with the calcium ion-containing compound and adjust the pH to 5-6 to obtain a gel; step 3: undergo aging, solvent replacement and freeze-drying of the gel in sequence to obtain pectin complex silica airgel. Calcium ions are used in this technical solution, which can well stabilize the pectin in the airgel, keep the airgel in a mesoporous structure, and prevent the network skeleton of the airgel from being affected by excessive surface tension during the drying process. Destruction, but excessive use of toxic and harmful inorganic substances, there is still room for improvement.

CN 113731307 B discloses a high-ester pectin gel containing ammonium sulfate and its preparation method and application, specifically disclosing 1) dissolving high-ester pectin in water and adjusting the pH to 4-7 to obtain high-ester pectin Solution; mixing ammonium sulfate or ammonium sulfate aqueous solution with high-ester pectin solution to obtain a mixed solution containing ammonium sulfate; 2) adjusting the pH of the mixed solution containing ammonium sulfate to 3.5, homogenizing, and standing to obtain high-ester pectin Gel; the mass concentration of ammonium sulfate in the mixed solution containing ammonium sulfate in step 1) is 25%-30%, and the mass concentration of high-ester pectin is 0.2-1.5%. This technical scheme has successfully realized the gelation of high-ester pectin under the ammonium sulfate + acid system, but this technical scheme is purely physical cross-linking without chemical modification.

In summary, the prior art still lacks a method for improving the gel strength of pectin.

Contents of the invention

In view of the above defects or improvement needs of the prior art, the present invention provides a gel based on oxidized pectin and its preparation method, the purpose of which is to modify the oxidation and introduce a more active dialdehyde group into the pectin molecule structure, so that the oxidized pectin has the ability to covalently cross-link with the amino compound, thus solving the technical problem of insufficient strength of the existing pectin gel.

Periodic acid oxidation can oxidize adjacent hydroxyl groups into dialdehyde structures, and the introduction of active aldehyde groups in pectin molecules can further enrich its gelation mechanism. Schiff base reaction is a chemical process in which amino groups and aldehyde groups are cross-linked to form dynamic covalent imine bonds. Different types of Schiff base gels prepared from polysaccharides can obtain tunable mechanical properties and chemical stability. It has broad application prospects in medical fields such as tissue repair and drug sustained release.

To achieve the above object, according to one aspect of the present invention, a kind of preparation method of gel based on oxidized pectin is provided, comprising the following steps:

(1) Preparation of oxidized pectin: adjust the pH of the pectin solution to below 5.0, then add an oxidizing agent for oxidative modification, add a terminator to terminate the reaction, then precipitate the reaction solution with alcohol to obtain a precipitate, and separate the alcohol solvent in the precipitate to obtain an oxidized pectin pectin;

(2) After redissolving the oxidized pectin, adjust the pH to below 5.0, then add a chemical crosslinking agent and a physical crosslinking agent, mix well and leave to stand for gelation, wherein the chemical crosslinking agent is used to combine with the oxidized pectin The gum undergoes a Schiff base reaction to form co-bond crosslinks, and the physical crosslinker is used to form ionic crosslinks with the oxidized pectin.

Preferably, the aldehyde group content of the oxidized pectin is above 0.75mmol/g.

Preferably, the oxidant is at least one of sodium periodate, hydrogen peroxide and sodium hypochlorite, preferably sodium periodate.

As preferably, the terminator includes at least one of polyethylene glycol, ascorbic acid and sodium thiosulfate.

As preferably, the chemical crosslinking agent is at least one of adipic acid dihydrazide (ADH), ** and **, polyamino compounds can be cited, preferably adipic acid dihydrazide.

As preferably, the physical cross-linking agent is at least one of calcium chloride, zinc chloride, ferric chloride, magnesium sulfate and magnesium chloride.

As preferably, the pectin raw material described in step (1) is at least one of lemon peel pectin, orange peel pectin, apple peel pectin.

As a preference, alkali is added in the step (1) and step (2) to adjust the pH, and the pH is 4.0-5.0.

As a preference, the reaction temperature in the step (1) and step (2) is 20°C-30°C.

According to another aspect of the present invention, there is provided a gel of oxidized pectin prepared by the preparation method of the gel based on oxidized pectin.

Pectin polysaccharides contain a large number of hydroxyl groups and carboxyl groups, and their gels are mainly stabilized by ionic bonds and hydrogen bonds. They have the disadvantage of weak gel strength, and gel conditions require additional high-temperature cooking and a large amount of co-solutes. This not only makes the gel preparation process complicated and increases energy consumption, but also limits the application of pectin gel.

The invention introduces a more active dialdehyde structure into the pectin molecule through oxidation modification, so that the oxidized pectin has the ability to covalently cross-link with amino compounds. By controlling the amount of oxidant, the ratio of oxidant to pectin and the oxidation time, pectin with different oxidation degrees can be prepared; then the oxidized pectin molecules are cross-linked with polyamino compounds and multivalent cations, and a covalent and ionic bond is jointly stabilized. double gel network. The pectin gel prepared by this method has the characteristics of simple gel conditions and stronger gel elasticity, and has application prospects in the field of biomedicine. The pectin gel preparation method proposed by the present invention is simple to operate, and the gel strength and elasticity are much higher than the traditional pectin gel based on physical interaction, which enriches the gelation strategy and application scenarios of pectin.

In general, compared with the prior art, the above technical scheme conceived by the present invention can obtain the following beneficial effects:

(1) The oxidized pectin containing dialdehyde structure was prepared in the present invention, and the gelation was easily realized under the double cross-linking of ADH and Ca ²⁺ .

(2) The present invention can control the degree of oxidation of pectin according to the amount of oxidant, the ratio and the oxidation time, and then control the mechanical properties of the pectin gel with the degree of oxidation of the oxidized pectin, the content and the amount of crosslinking agent, which broadens the scope of the pectin gel. scope of application.

(3) The pectin gel prepared by the present invention is jointly stabilized by ionic bonds and covalent bonds, and the gel strength and elasticity are significantly better than traditional physical crosslinked pectin gels.

(4) The imine bonds formed in the preparation of the oxidized pectin gel in the present invention are reversible.

Description of drawings

Fig. 1 is the test chart of the gel morphology and rheological properties of Example 1 and Comparative Examples 1-2.

Fig. 2 is the gel rheological strength of Comparative Example 3 and Examples 1-3.

Fig. 3 is a graph of the gel morphology of Comparative Examples 1-3 and Examples 1-3.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Example

Comparative example 1

(1) Add 2.5g of pectin to 100mL of distilled water, stir in a magnetic stirrer at 30 degrees Celsius until fully dissolved to obtain a pectin solution, and adjust the pH to 5.0; do not add sodium periodate, stir for 12 hours and then add 10 mL of ethylene glycol, pour the above pectin solution into 3 times the volume of absolute ethanol to precipitate, repeat this 3 times, and finally freeze-dry to remove the ethanol to obtain pectin.

(2) Weigh 1g of the above pectin and dissolve it in 20mL of distilled water, adjust the pH of the pectin solution to 5.0, add 2mL of CaCl ₂ (0.1M) to the above pectin solution, mix well and let stand to gel.

Comparative example 2

The difference between this example and Example 1 is that the pectin is oxidized and modified in step (1), as described below.

(1) Add 2.5g of pectin to 100mL of distilled water, stir in a magnetic stirrer at 30 degrees Celsius until fully dissolved to obtain a pectin solution, and adjust the pH to 5.0; add solid sodium periodate to the pectin solution In the solution, the mass ratio of pectin to periodic acid in the solution was 10:1, and the pectin solution was continuously stirred while adding periodic acid, and after 12 hours of reaction, 10 mL of ethylene glycol was added to terminate the oxidation reaction, and the above pectin The solution was poured into 3 times the volume of absolute ethanol for precipitation, and this was repeated 3 times, and finally lyophilized to remove ethanol to obtain oxidized pectin. Through testing, the aldehyde group content of the oxidized pectin is 0.75 mmol/g.

(2) Weigh 1g of oxidized pectin and dissolve it in 20mL of distilled water, adjust the pH of the pectin solution to 5.0, add 2mL of CaCl ₂ (0.1M) to the above pectin solution, mix well and let stand to gel.

Comparative example 3

The difference between this example and Comparative Example 2 is that the pectin is not oxidatively modified in step (1), and the chemical crosslinking agent adipate dihydrazide (ADH) is added in step (2), specifically as follows mentioned.

(1) Add 2.5g of pectin into 100mL of distilled water, stir in a magnetic stirrer at 30 degrees Celsius until fully dissolved to obtain a pectin solution, and adjust the pH to 5.0; add 10mL of ethylene glycol after stirring for 12 hours, and mix the above The pectin solution was poured into 3 times the volume of absolute ethanol for precipitation, and this was repeated 3 times, and finally freeze-dried to remove the ethanol to obtain pectin.

(2) Weigh 1g of pectin and dissolve it in 20mL of distilled water, adjust the pH of the pectin solution to 5.0, add 0.8mL of adipic acid dihydrazide (ADH) solution (0.5M) and 2mL of CaCl2 (0.1M), mixed well and left to gel.

Example 1

The difference between this example and Comparative Example 3 is that the pectin is oxidized and modified in step (1), as described below.

(1) Add 2.5g of pectin to 100mL of distilled water, stir in a magnetic stirrer at 30 degrees Celsius until fully dissolved to obtain a pectin solution, and adjust the pH to 5.0; add solid sodium periodate to the pectin solution In the solution, the mass ratio of pectin to periodic acid in the solution was 50:1, and the pectin solution was continuously stirred while adding periodic acid, and after 12 hours of reaction, 10 mL of ethylene glycol was added, and the above pectin solution was poured into Precipitate in 3 times the volume of absolute ethanol, repeat this three times, and finally freeze-dry to remove ethanol to obtain oxidized pectin. Through testing, the aldehyde group content of the oxidized pectin is 0.35mmol/g.

(2) Weigh 1 g of oxidized pectin and dissolve it in 20 mL of distilled water, adjust the pH of the pectin solution to 5.0, add 0.8 mL of adipic acid dihydrazide (ADH) solution (0.5 M) and 2mL CaCl2 (0.1M), mix well and let stand to gel.

Example 2

The difference between this embodiment and Example 1 is that the amount of oxidizing agent used in step (1) is different, specifically as follows.

(1) Add 2.5g of pectin to 100mL of distilled water, stir in a magnetic stirrer at 30 degrees Celsius until fully dissolved to obtain a pectin solution, and adjust the pH to 5.0; add solid sodium periodate to the pectin solution In the solution, the mass ratio of pectin to periodic acid in the solution was 10:1, and the pectin solution was continuously stirred while adding periodic acid, and after 12 hours of reaction, 10 mL of ethylene glycol was added, and the above pectin solution was poured into Precipitate in 3 times the volume of absolute ethanol, repeat this three times, and finally freeze-dry to remove ethanol to obtain oxidized pectin. Through testing, the aldehyde group content of the oxidized pectin is 0.75mmol/g.

(2) Weigh 1 g of oxidized pectin and dissolve it in 20 mL of distilled water, adjust the pH of the pectin solution to 5.0, add 0.8 mL of adipic acid dihydrazide (ADH) solution (0.5 M) and 2mL CaCl2 (0.1M), mix well and let stand to gel.

Example 3

The difference between this embodiment and Example 1 is that the amount of oxidizing agent used in step (1) is different, specifically as follows.

(1) Add 2.5g of pectin to 100mL of distilled water, stir in a magnetic stirrer at 30 degrees Celsius until fully dissolved to obtain a pectin solution, and adjust the pH to 5.0; add solid sodium periodate to the pectin solution In the solution, the mass ratio of pectin to periodic acid in the solution was 8:1, and the pectin solution was continuously stirred while adding periodic acid, and after 12 hours of reaction, 10 mL of ethylene glycol was added, and the above pectin solution was poured into Precipitate in 3 times the volume of absolute ethanol, repeat this three times, and finally freeze-dry to remove ethanol to obtain oxidized pectin. Through testing, the aldehyde group content of the oxidized pectin is 1 mmol/g.

(2) Weigh 1 g of oxidized pectin and dissolve it in 20 mL of distilled water, adjust the pH of the pectin solution to 5.0, add 0.8 mL of adipic acid dihydrazide (ADH) solution (0.5 M) and 2mL CaCl2 (0.1M), mix well and let stand to gel.

Test Example

The high-esterified orange peel pectin used in the following manufacturing examples was purchased from Guangzhou Limen Biotechnology Co., Ltd.

The instrument used in the embodiment: the homogenizer model is T10 homogenizer (IkA).

Determination of aldehyde content of pectin:

Refer to the literature "Liu Wenying. Preparation and performance research of oxidized cellulose/chitosan composite hemostatic material [D].", weigh a certain amount of oxidized pectin, add a certain volume of 0.25M hydroxylamine hydrochloride-methyl orange solution , fully stirred for 4h. Finally, it is titrated with 0.1M standard NaOH solution until the color of the solution changes from pink to yellow, and its titration result is a solution pH=5.0. Aldehyde content [CHO] calculation formula is as follows:

[CHO]=(V ₂ -V ₁ )×c/m

Among them, the unit of aldehyde group content [CHO] is mmol/g; c: NaOH solubility, mol/L; V ₂ : the volume of NaOH required for the end point of titration, mL; V ₁ : the volume of NaOH consumed by blank titration, mL; m: oxidation Pectin mass, g.

1. Rheology test of pectin gel:

Refer to the literature "Tian Yan. Effects of environmental conditions and glycosylation on soybean 7S protein oil-water interface properties and emulsification mechanism [D]. ", the pectin gel was tested on a rheometer using a parallel plate with a diameter of 35 mm. Set the spacing to 1mm, and the test temperature to 25°C. The shear frequency is fixed at 5rad/s, and the strain sweep (0.1%-1000%) is performed.

Figure 1 is the gel rheological strength of Comparative Example 1 and Comparative Example 2.

Fig. 2 is the gel rheological strength of Comparative Example 3 and Examples 1-3.

Fig. 3 is the gel form figure of comparative example 1-3 and embodiment 1-3

As can be seen from Figure 1, the method of the present invention adopts ADH+Ca ²⁺ cross-linked oxidized pectin to form a stable gel structure. According to Comparative Examples 1 and 2 (Fig. 1), it can be seen that the oxidation leads to the breakage of the pectin molecular chain, which is not applicable to the physical cross-linking mode based on ionic bonds. From Comparative Example 3 and Examples 1-3 (Fig. 2), it can be seen that when ADH+Ca ²⁺ is used as the cross-linking mode, the pectin with a lower degree of oxidation (the content of aldehyde group is less than 0.75mmol/g) is due to the decrease in molecular weight and the aldehyde If the base content is not enough, the strength of the formed pectin gel is not as good as that of Ca ²⁺ cross-linked oxidized pectin; and with the increase of oxidation degree, the strength of the pectin gel based on ADH+Ca ²⁺ cross-linked mode gradually increases , and the oxidized pectin gel crosslinked by ADH+Ca ²⁺ can resist stronger denaturation and keep the gel structure stable, indicating that the oxidized pectin gel prepared by the present invention has unique gel properties.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. a preparation method based on the gel of oxidized pectin, is characterized in that, comprises the following steps: (1) Preparation of oxidized pectin: adjust the pH of the pectin solution to below 5.0, then add an oxidizing agent for oxidative modification, add a terminator to terminate the reaction, then precipitate the reaction solution with alcohol to obtain a precipitate, and separate the alcohol solvent in the precipitate to obtain an oxidized pectin. pectin; (2) After redissolving the oxidized pectin, adjust the pH to below 5.0, then add a chemical crosslinking agent and a physical crosslinking agent, mix well and leave to stand for gelation, wherein the chemical crosslinking agent is used to combine with the oxidized pectin The gum undergoes a Schiff base reaction to form co-bond crosslinks, and the physical crosslinker is used to form ionic crosslinks with the oxidized pectin. 2. The preparation method according to claim 1, characterized in that the aldehyde group content of the oxidized pectin is more than 0.75mmol/g. 3. The preparation method according to claim 1 or 2, characterized in that the oxidizing agent is at least one of sodium periodate, hydrogen peroxide and sodium hypochlorite, preferably sodium periodate. 4. The preparation method according to claim 3, wherein the terminator comprises at least one of polyethylene glycol, ascorbic acid and sodium thiosulfate. 5. preparation method according to claim 1, is characterized in that, described chemical linking agent is at least one in adipate dihydrazide, chitosan and ethylenediamine, is preferably adipate dihydrazide Hydrazine. 6. The preparation method according to claim 5, wherein the physical crosslinking agent is at least one of calcium chloride, zinc chloride, iron chloride, magnesium sulfate and magnesium chloride. 7. The preparation method according to claim 2, characterized in that, the pectin raw material described in step (1) is at least one of lemon peel pectin, orange peel pectin, and apple peel pectin. 8. The preparation method according to claim 1, characterized in that alkali is added in the step (1) and step (2) to adjust the pH, and the pH is 4.0-5.0. 9. The preparation method according to claim 1, characterized in that, the reaction temperature in the step (1) and step (2) is 20°C-30°C. 10. The oxidized pectin gel prepared according to the preparation method of the oxidized pectin-based gel according to any one of claims 1-9.

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