Method for preparing amide pectin with excellent gel properties and application thereof

Abstract

The application belongs to the technical field of amidated pectin and discloses a preparation method and application of amidated pectin with excellent gel performance. The preparation method of the amidated pectin comprises the following steps: S1. After high methoxyl pectin is dissolved, a strong acid is added, the pH is adjusted to 0.9-2, a deesterification reaction is performed, and deesterified crude pectin is obtained; S2. The deesterified crude pectin is mixed with an alcohol amine solution, an amidation reaction is performed, and then washing and drying are performed, so that the amidated pectin is obtained. In the preparation method of the amidated pectin, the simultaneously occurring deesterification and amidation reaction is split into the deesterification reaction of S1 and the amidation reaction of S2, the obtained amidated pectin DE and DA can be separately controlled, in the deesterification step S1, the high methoxyl pectin is hydrolyzed and deesterified in a strong acid environment, the acidic environment can inhibit the beta-elimination chain scission of the pectin glycosidic bond, the degradation of the macromolecular pectin in the deesterification stage is avoided, and therefore the obtained amidated pectin has high viscosity and excellent gel capacity.

Description

Technical Field

[0001] This invention relates to the technical field of amidated pectin, and more specifically, to a method for preparing amidated pectin with excellent gelling properties and its application. Background Technology

[0002] Within a certain range, the degree of esterification (DE) and degree of amidation (DA) of amidated pectin can form gels with high strength, good thermal reversibility, and excellent water retention, thus making them widely used in low-sugar jellies, yogurt products, and edible films. Currently, the method for preparing amidated pectin involves mixing a high-methoxyl pectin solution with an alcohol-ammonia solution, carrying out a deesterification and amidation reaction at 5°C, followed by washing and drying to obtain amidated pectin. However, this method has the following problems: (1) Deesterification (demethylation) and amidation (methyl ester ammonolysis) occur simultaneously in the same alkaline alcohol-ammonia system. If the degree of deesterification is insufficient, a large number of methyl ester groups on the pectin molecule will not be consumed or converted, resulting in a high methyl ester content and an excessively high DE of the resulting amidated pectin. Extending the reaction time can reduce the DE of the amidated pectin, but it will lead to an excessively high DA. The DE and DA are interdependent and cannot be controlled independently. (2) An alkaline environment will continuously induce β-elimination of pectin glycosidic bonds, causing large molecules of pectin to degrade into small molecules, resulting in low viscosity and poor gelation ability of the obtained amidated pectin. Summary of the Invention

[0003] This invention provides a method for preparing amidated pectin with excellent gelling properties and its application. It can independently control DE and DA, and the resulting amidated pectin has high viscosity and strong gelling ability, which is superior to the prior art.

[0004] Another object of the present invention is to provide the application of the amidated pectin prepared by the aforementioned amidated pectin preparation method in the preparation of amidated pectin gels.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: The preparation method of amidated pectin includes the following steps: S1. After dissolving high-methoxyl pectin, add strong acid to adjust the pH to 0.9~2 and carry out deesterification reaction to obtain deesterified crude pectin; S2. Deesterified crude pectin is mixed with an alcohol-ammonia solution to carry out an amidation reaction, followed by washing and drying to obtain amidated pectin.

[0006] The preparation method of amidated pectin described in this invention separates the simultaneous deesterification and amidation reaction into a deesterification reaction that occurs first (S1) and an amidation reaction that occurs later (S2), which has the following technical advantages: (1) The obtained amidated pectin DE and DA can be controlled separately. Specifically, S1. The deesterification reaction is fully completed by using a strong acid reaction system. The methyl ester group on the pectin molecule is consumed and converted. The methyl ester ratio is reasonable, so the pectin DE can be controlled to the target range. S2. The amidation reaction is completed by using an alkaline alcohol-ammonia reaction system, and DA can be controlled to the target range separately. (2) In the S1. Deesterification step, the high methoxyl pectin is hydrolyzed and deesterified in a strong acid environment. The acidic environment can inhibit the β-elimination chain scission of pectin glycosidic bonds, thus avoiding the large-molecule pectin from being degraded in large quantities during the deesterification stage. Therefore, the resulting amidated pectin has high viscosity and excellent gelation ability.

[0007] Preferably, the amidation reaction temperature in S2 is -10 to -4℃.

[0008] S2. The amidation reaction temperature is controlled at -10~-4℃. This low reaction temperature further inhibits the β-elimination chain scission of glycosidic bonds and avoids the degradation of large molecular pectin into small molecular fragments. Therefore, the resulting amidated pectin has high viscosity and excellent gelation ability.

[0009] Preferably, the concentration of the S1 high-methoxyl pectin solution is 15–25 mg / mL.

[0010] Preferably, the degree of esterification (DE) of the S1 high-methoxyl pectin is 60%~72%.

[0011] In this invention, S1, the high-methoxyl pectin is selected from one or more of the following: citrus high-methoxyl pectin, apple high-methoxyl pectin, lemon high-methoxyl pectin, lime high-methoxyl pectin, grapefruit high-methoxyl pectin, guava peel high-methoxyl pectin, mango peel high-methoxyl pectin, hawthorn high-methoxyl pectin, and beet high-methoxyl pectin.

[0012] In this invention, S1, the strong acid is selected from one or more of nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, methanesulfonic acid, and p-toluenesulfonic acid.

[0013] In this invention, S1, the volume concentration of the nitric acid solution is 60%~80%.

[0014] In this invention, S1. the dissolution and reaction are both carried out under magnetic stirring conditions.

[0015] Preferably, after the S1. deesterification reaction is completed, the product is subjected to alcohol precipitation, washing, filtration, drying and pulverization to obtain deesterified crude pectin.

[0016] The deesterification reaction described in this invention is carried out at a temperature of 38~42℃ for a time of 24~72h.

[0017] More preferably, the precipitant for alcohol precipitation is an ethanol solution with a concentration of not less than 95% (volume fraction). After the deesterification reaction, the volume ratio of the resulting mixture to the ethanol solution is 1:(2~4), the time is 0.5~1.5h, and then a washing operation is performed, with the number of washing operations being 1 to 3.

[0018] The filter used in this invention is 400-mesh gauze, and the drying is done by forced air drying at a temperature of 55~65℃ for 3h~6h. After pulverization, it is sieved through an 80-mesh screen.

[0019] Preferably, the S2. alcohol-ammonia solution is specifically an ethanol solution or concentrated ammonia solution, wherein the volume fraction of the ethanol solution is 70-85% and the volume fraction of the concentrated ammonia solution is 22-28%.

[0020] The S2 amidation reaction described in this invention is carried out under high-speed stirring with a stirring paddle; S2. The detergent is a 68%~80% (volume fraction) ethanol solution, and the washing operation involves 6 to 8 washing cycles. The washing steps are as follows: After the amidation reaction is completed, the product is washed twice. Then, the pH of the reaction system is adjusted to the range of 2.9 to 3.2 with an appropriate amount of ammonia. After that, it is washed four times with 80% (w / w) ethanol solution at 10°C. Nitric acid is added dropwise during the washing process to make the pH of the system finally stabilize at about 4.40. In the present invention S2, the filter uses 400-mesh gauze, the drying is done by forced air drying at a temperature of 55~65℃ for 3h~6h, and the powdered product is sieved through an 80-mesh screen.

[0021] The S2 amidation reaction time described in this invention is 150~210 min.

[0022] The amidated pectin prepared by the above method of the present invention has a DE of 28%~33%. DA is 20%~24%.

[0023] This invention also provides the preparation of the amidated pectin prepared by any of the above-described methods. The application of amidated pectin in the preparation of amidated pectin gel.

[0024] Preferably, the amidated pectin prepared by the amidated pectin preparation method is used in the preparation of... The application of amidated pectin gels includes the following steps: Dissolve the amidated pectin obtained from any of the above methods, heat to boiling, and then add... Water-soluble polyhydroxy food-grade sweeteners are mixed thoroughly; finally, the mixture is left to stand and cool at room temperature to form an amidated pectin gel.

[0025] In the preparation of amidated pectin gel described in this invention, the water-soluble polyhydroxy food filler sweetener is selected from sucrose. One or more of the following: sugar, maltose, lactose, trehalose, glucose, fructose, galactose, fructooligosaccharides, maltose oligosaccharides, isomaltooligosaccharides, sorbitol, xylitol, maltitol, erythritol, mannitol, high-fructose corn syrup, maltose syrup, glucose syrup, and honey.

[0026] The preparation method of the amidated pectin gel of the present invention is as follows: (1) Redissolve the amidated pectin and adjust the pH of the solution to the set range using a buffer solution; (2) Heat the resulting mixture to boiling and maintain it for a period of time, then add sucrose and let it dissolve completely to obtain a thermogel; (3) Let stand to form a stable amidated pectin gel.

[0027] The mass concentration of the reconstituted pectin solution is 10 mg / mL to 20 mg / mL; The buffer solution is a mixture of 60 wt% citric acid solution and 2.5 M sodium hydroxide solution, with a volume ratio of (2~3):1. The pH is adjusted to 3.15~3.20; The amount of sucrose added is 20-40g / 100g amidated pectin; The term "static setting" refers to placing the thermogel at 20-30°C for 20-24 hours after cooling it to room temperature. Attached Figure Description

[0028] Figure 1 The images show the appearance of the amidated pectin gels obtained in Examples 1-3 and Comparative Examples 1-2. Figure 2 The SAG test results are for the amidated pectin gels obtained in Examples 1-3 and Comparative Examples 1-2, where ND indicates gel collapse. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments.

[0030] Example 1 A method for preparing and applying amidated pectin with excellent gelling properties includes the following steps: S1. Dissolve citrus high-methoxyl pectin. After dissolution, the concentration of the high-methoxyl pectin solution is 20 mg / mL. Then, add 70% nitric acid to adjust the pH to 1.0 and carry out the deesterification reaction. After the deesterification reaction is completed, perform alcohol precipitation, washing, filtration, drying and pulverization to obtain deesterified crude pectin. The degree of esterification (DE) of the S1 high-methoxyl pectin is 64.47%. The deesterification reaction was carried out at a temperature of 40°C for 48 hours. The precipitant for alcohol precipitation is an ethanol solution with a concentration of not less than 95% (volume fraction). After the deesterification reaction, the volume ratio of the resulting mixture to the ethanol solution is 1:3, the time is 1 hour, and then a washing operation is performed, with the number of washing operations being 1 to 3. The filter uses 400-mesh gauze, the drying is done by forced air drying at 60℃ for 4 hours, and the powder is then sieved through an 80-mesh screen. Both the dissolution and deesterification reactions were carried out under magnetic stirring.

[0031] S2. Mix the deesterified crude pectin with an alcohol-ammonia solution to carry out an amidation reaction, and then wash and dry to obtain amidated pectin; The amidation reaction was carried out under high-speed stirring with a stirrer at a reaction temperature of -6°C for 180 min. The alcohol-ammonia solution specifically comprises an ethanol solution and concentrated ammonia, wherein the volume fraction of the ethanol solution is 80% and the volume fraction of the concentrated ammonia solution is 25%. The detergent is an 80% (volume fraction) ethanol solution, and the washing operation involves 6 to 8 washes. The washing steps are as follows: After the amidation reaction is completed, the product is washed twice. Then, the pH of the reaction system is adjusted to the range of 2.9 to 3.2 with an appropriate amount of ammonia. After that, it is washed four times with 80% (w / w) ethanol solution at 10°C. Nitric acid is added dropwise during the washing process to make the pH of the system finally stabilize at about 4.40. The filtration process used 400-mesh gauze, the drying process used was blower drying at 60℃ for 4 hours, and the powdered product was sieved through an 80-mesh screen.

[0032] Example 2 The process is basically the same as in Example 1, except that the degree of esterification (DE) of the S1 high-methoxyl pectin is 60.82%; and the deesterification reaction temperature is 35°C and the time is 24 hours.

[0033] Example 3 The process is basically the same as in Example 1, except that the degree of esterification (DE) of the S1 high-methoxyl pectin is 71.28%; and the deesterification reaction temperature is 45°C and the time is 72 hours.

[0034] Example 4 The process is basically the same as in Example 1, except that the S1. high-methoxyl pectin... The degree of esterification (DE) was 67.93%; the deesterification reaction temperature was 40℃, and the reaction time was 60 hours. Example 5 The process is basically the same as in Example 1, except that the amidation reaction in S2 is carried out under high-speed stirring with a stirrer, the reaction temperature is -10°C, and the reaction time is 150 min.

[0035] Example 6 The reaction is basically the same as in Example 1, except that the amidation reaction in S2 is carried out under high-speed stirring of a stirrer, the reaction temperature is -4°C, and the reaction time is 210 min.

[0036] Example 7 Similar to Example 1, except that S1. Citrus high-methoxyl pectin was dissolved, and the concentration of the high-methoxyl pectin solution after dissolution was 15 mg / mL. Then, 60% nitric acid was added to adjust the pH to 0.9 and a deesterification reaction was carried out. After the deesterification reaction was completed, the solution was washed with alcohol precipitation, filtered, dried and pulverized to obtain deesterified crude pectin. The precipitant for alcohol precipitation is an ethanol solution with a concentration of not less than 95% (volume fraction). After the deesterification reaction, the volume ratio of the resulting mixture to the ethanol solution is 1:2, the time is 0.5h, and then a washing operation is performed, with the number of washing operations being 1 to 3. The filter used 400-mesh gauze, the drying was done by forced air drying at 55°C for 3 hours, and the powder was then sieved through an 80-mesh screen.

[0037] S2. The alcohol-ammonia solution specifically comprises an ethanol solution and concentrated ammonia solution, wherein the volume fraction of the ethanol solution is 70% and the volume fraction of the concentrated ammonia solution is 22%. The detergent is a 68% (volume fraction) ethanol solution, and the washing operation involves 6 to 8 washes. The filter used 400-mesh gauze, the drying was done by forced air drying at 55°C for 3 hours, and the powder was then sieved through an 80-mesh screen.

[0038] Example 8 Similar to Example 1, except that S1. Citrus high-methoxyl pectin was dissolved, and the concentration of the high-methoxyl pectin solution after dissolution was 25 mg / mL. Then, nitric acid with a volume concentration of 80% was added to adjust the pH to 2 and carry out the deesterification reaction. After the deesterification reaction was completed, alcohol precipitation, washing, filtration, drying and pulverization were carried out to obtain deesterified crude pectin. The precipitant for alcohol precipitation is an ethanol solution with a concentration of not less than 95% (volume fraction). After the deesterification reaction, the volume ratio of the resulting mixture to the ethanol solution is 1:4, the time is 1.5 hours, and then a washing operation is performed, with the number of washing operations being 1 to 3. The filtration process used 400-mesh gauze, the drying process used was blower drying at 65°C for 6 hours, and the powdered product was sieved through an 80-mesh screen.

[0039] S2. The alcohol-ammonia solution is specifically an ethanol solution and concentrated ammonia solution, wherein the volume fraction of the ethanol solution is 85% and the volume fraction of the concentrated ammonia solution is 28%. The detergent is an 80% (volume fraction) ethanol solution, and the washing operation involves 6 to 8 washes. The filtration process used 400-mesh gauze, the drying process used was blower drying at 65°C for 6 hours, and the powdered product was sieved through an 80-mesh screen.

[0040] Comparative Example 1 Similar to Example 1, except that after the citrus high-methoxyl pectin was dissolved, nitric acid was not added for deesterification; instead, an alcoholic amine solution was directly added for simultaneous deesterification and amidation reactions, as detailed below: Citrus high-methoxyl pectin is dissolved, and after dissolution, it is mixed evenly with an 80% (v / v) ethanol solution and a 25% (v / v) concentrated ammonia solution. The mixture was placed at -6°C and reacted for 3 hours.

[0041] Comparative Example 2 It is basically the same as Example 1, except that the amidation temperature of S2 is 5°C.

[0042] Comparative Example 3 It is basically the same as Example 1, except that the degree of esterification (DE) of the S1 high-methoxyl pectin is 56.47%.

[0043] Performance testing: 1. Adipic acid (DA) and diethylsaturated (DE) of amidated pectin According to GB 25533-2010 National Food Safety Standard for Food Additives Pectin, the degree of methyl esterification (DE) and degree of amidation (DA) of amidated pectin were tested.

[0044] The DA and DE detection results of amidated pectin in Examples 1-8 and Comparative Examples 1-4 are shown in Table 1.

[0045] Table 1. DA and DE of amidated pectin in Examples 1-8 and Comparative Examples 1-4

[0046] In Table 1, Comparative Example 1: without prior deesterification, direct simultaneous deesterification and amidation resulted in a final DE of 39.24% (far exceeding the upper limit of 33%) and DA of 14.68% (far below the lower limit of 20%), demonstrating the advantages of the deesterification-before-amidation approach.

[0047] Comparative Example 2: Amide temperature 5℃ (outside the range of -10~-4℃), final DE 24.76% and DA 17.95%. High temperature leads to pectin degradation and a significant decrease in amidation efficiency.

[0048] Comparative Example 3: Initial pectin DE 56.47% (below the 60% lower limit), final DE 25.89% and DA 19.34%. Insufficient initial ester groups resulted in too few carboxyl groups after deesterification and insufficient amidation sites.

[0049] 2. Gel strength of the amidated pectin gel prepared from amidated pectin.

[0050] The preparation method of amidated pectin gel is as follows: Prepare 150g of the amidated pectin obtained from any of Examples 1-3 and Comparative Examples 1-2. An aqueous solution of amidated pectin with a concentration of 20 mg / mL was diluted to a total weight of 162.5 g and then heated to 35 °C. Subsequently, 2.85 mL of citric acid solution with a concentration of 0.6 g / mL and 1.0 mL of sodium hydroxide solution with a concentration of 2.5 mol / L were added sequentially to adjust the pH of the system to 3.18 ± 0.01. Deionized water was then added again to bring the total mass of the solution to 227.5 g. The mixture was heated to boiling under continuous stirring, and 90 g of sucrose and 12.5 mL of anhydrous calcium chloride solution with a concentration of 16.6 mg / mL were added in sequence. The mixture was kept boiling until the total mass of the system reached 300 g. The obtained hot solution was transferred to a beaker, cooled to room temperature, and then allowed to stand at 25°C for 24 hours to obtain amidated pectin gel.

[0051] The strength tests of the amidated pectin gels obtained in Examples 1-3 and Comparative Examples 1-2 are as follows: The hot solutions obtained in Examples 1-3 and Comparative Examples 1-2 were rapidly dispensed into two prepared standard SAG gel test cups. After cooling to room temperature, they were placed in a 25°C incubator for 24 hours. Subsequently, the fully formed gel was removed from the cups and inverted onto a glass plate for 2 minutes. The gel height (h) and center temperature (T) were measured using a gel strength tester and a thermometer, respectively. Based on the standard reference table, the corresponding height correction factor (F) and temperature correction factor (C) were obtained from the measured height (h) and temperature (T), respectively. The gel strength grade (G) was calculated using the following formula: G = 100 × F × C F is the height correction factor; C is the temperature correction factor; 100 is the set reference gelation degree base.

[0052] The gels obtained in Examples 1-3 and Comparative Examples 1-2 have the following appearance: Figure 1 As shown; the gel strength SAG test results of Examples 1-3 and Comparative Examples 1-2 are as follows. Figure 2 As shown. From Figure 1 and Figure 2 It can be seen that: Among the amidated pectin samples prepared under the same conditions, Examples 1-3 all formed smooth, structurally stable, and self-supporting gels with gel strengths ranging from 105 to 130 SAG°. The gel strength showed a significant increasing trend with increasing initial esterification degree of the raw materials. Specifically, Example 1 had the highest SAG value, reflecting that its internal network structure was the densest and most robust, exhibiting the strongest resistance to external forces and its own gravity.

[0053] In contrast, the two groups of samples in Comparative Examples 1 and 2 failed to form a complete self-supporting gel. During inversion or demolding, their structures were prone to collapse or could not be completely separated from the container, indicating that a three-dimensional through-network structure with sufficient mechanical strength could not be formed under these conditions.

[0054] The above description is merely an embodiment of the present invention and does not limit the scope of patent protection. Any non-substantial changes or substitutions made by those skilled in the art based on the present invention will still fall within the scope of patent protection.

Claims

1. A method for preparing amidated pectin, characterized in that, Includes the following steps: S1. After dissolving high-methoxyl pectin, add strong acid to adjust the pH to 0.9~2 and carry out deesterification reaction to obtain deesterified crude pectin; S2. Deesterified crude pectin is mixed with an alcohol-ammonia solution to carry out an amidation reaction, followed by washing and drying to obtain amidated pectin.

2. The method for preparing amidated pectin according to claim 1, characterized in that, The amidation reaction temperature in S2 is -10 to -4℃.

3. The method for preparing amidated pectin according to claim 1, characterized in that, The concentration of the S1 high-methoxyl pectin solution is 15–25 mg / mL.

4. The method for preparing amidated pectin according to claim 2, characterized in that, The degree of esterification (DE) of the S1 high-methoxyl pectin is 60%~72%.

5. The method for preparing amidated pectin according to claim 1, characterized in that, The S1 deesterification reaction is carried out at a temperature of 35–45°C for 24–72 hours.

6. The method for preparing amidated pectin according to claim 4, characterized in that, After the S1 deesterification reaction is completed, the product is subjected to alcohol precipitation, washing, filtration, drying and pulverization to obtain deesterified crude pectin.

7. The method for preparing amidated pectin according to claim 1, characterized in that, The S2. alcohol-ammonia solution specifically refers to an ethanol solution and concentrated ammonia water, with the ethanol solution having a volume fraction of 70-85% and the concentrated ammonia water having a volume fraction of 22-28%.

8. The method for preparing amidated pectin according to claim 5, characterized in that, The precipitant for S1. alcohol precipitation washing is an ethanol solution with a concentration of not less than 95%. The volume ratio of the mixture obtained after the deesterification reaction to the precipitant is 1:(2~4), and the precipitation time is 0.5~1.5h.

9. The use of the amidated pectin prepared by the method according to any one of claims 1 to 8 in the preparation of amidated pectin gel.

10. The application of the amidated pectin prepared by the method for preparing amidated pectin according to claim 9 in the preparation of amidated pectin gel, characterized in that, Includes the following steps: The amidated pectin obtained by any one of the amidated pectin preparation methods of claims 1 to 8 is dissolved, heated to boiling, and then a water-soluble polyhydroxy food filler sweetener is added and stirred evenly; finally, it is allowed to stand and cool at room temperature to form an amidated pectin gel.

Images