High-gelling low-ester pectin, its preparation and use in gels

Abstract

This invention belongs to the technical field of pectin and discloses a high-gelling-strength low-ester pectin, its preparation, and its application in gels. The preparation method of the high-gelling-strength low-ester pectin is as follows: 1) Citrus peel residue is mixed with water, the pH is adjusted to 1.5–2, extracted at 65–75°C, centrifuged, and the supernatant is subjected to alcohol precipitation and washing, filtered, dried, and pulverized to obtain primary pectin; 2) The primary pectin is reconstituted, the pH is adjusted to 0.5–1.1, reacted at 40–60°C, subjected to alcohol precipitation and washing, dried, and pulverized to obtain low-ester pectin. The method of this invention is simple, easy to operate, cost-effective, and suitable for industrial production. The prepared low-ester pectin retains a relatively complete original pectin structure, with an esterification degree of 25%–35% and a gelling-strength of 120–150, significantly superior to low-ester pectin prepared by alkaline and enzymatic methods. The low-ester pectin of this invention is used to prepare gels, and the resulting sugar-free gels and sugar alcohol gels have high hardness and water-holding capacity.

Description

Technical Field

[0001] This invention belongs to the technical field of pectin preparation, specifically relating to a low-ester pectin with high gelation degree, its preparation method, and its application in sugar-free gels and sugar alcohol gels. Background Technology

[0002] Pectin is a structurally complex anionic polysaccharide widely found in the middle lamella and primary cell walls of higher plants. Pectin is mainly composed of three domains: HG, RG-I, and RG-II. Based on the number of ester groups on the HG backbone, pectin is classified into high-ester pectin (DE ≥ 50%) and low-ester pectin (DE < 50%).

[0003] Pectin is widely used as a food additive in the production of jams, jellies, and candies. In addition, pectin can also be used in the pharmaceutical industry as a bioactive substance, by lowering blood cholesterol and inhibiting atherosclerosis.

[0004] The gelling ability of pectin plays a crucial role in the structural regulation and sensory perception of pectin-fortified foods such as jams, jellies, and candies. Therefore, gel strength is a key indicator of pectin quality. Different types of pectin often exhibit different gelling behaviors and mechanisms. High-ester pectin requires a relatively harsh environment (high acidity and high sugar) to form a gel, relying on hydrophobic interactions and hydrogen bonds between methoxy groups in the pectin chain. Low-ester pectin, on the other hand, provides more binding sites for calcium ions due to the increased carboxyl content in the pectin chain, making it more conducive to forming a stable eggshell structure. Even over a wide acidity range, and even under low-sugar or sugar-free conditions, low-ester pectin can form a gel simply with calcium. Furthermore, the lower the degree of esterification in low-ester pectin, the more favorable it is for the formation of a gel permeation network structure. Therefore, compared to high-ester pectin, low-ester pectin has a greater advantage in gelling performance applications and better aligns with consumers' health-conscious dietary concepts.

[0005] Pectin initially extracted from citrus peel pomace is mostly high-ester pectin. To expand its application, chemical and biological methods are commonly used to reduce the ester content of high-ester pectin. Chemical methods include acid and alkali treatment, with alkali treatment showing the most significant ester reduction effect. However, the β-elimination reaction accompanying the ester reduction process causes a significant decrease in the molecular weight of pectin, damaging its structure and preventing gel formation or resulting in low gel strength. Biological methods typically utilize biocatalysts such as pectin methyl esterase to assist in ester reduction. However, in large-scale industrial production, enzyme consumption significantly increases production costs, thus limiting the industrial application of enzymatic ester reduction. Furthermore, these ester reduction methods focus only on reducing the degree of esterification, with less attention paid to the application value of the pectin after ester reduction.

[0006] The application value of low-ester pectin is closely related to its gelling properties. Commercially available low-ester pectin is often defined solely by its degree of esterification, neglecting its most crucial application characteristic—gelling ability. The gelling property of low-ester pectin is vital for various applications. For low-ester pectin to have good application value, it must have an esterification degree below 50% and a gelling degree above 110. In other words, if low-ester pectin does not achieve a certain gelling degree or lacks gelling ability, its application value will be greatly reduced. For example, the dairy industry primarily utilizes the gelling properties of low-ester pectin in stirred yogurt, and its consumption is enormous. Therefore, research on low-ester pectin should not only focus on the esterification degree range; gelling properties are a crucial standard for evaluating its industrial applications.

[0007] This invention is based on low-ester pectin within the same esterification range, ensuring good gelling properties to meet product application standards. Summary of the Invention

[0008] In view of the shortcomings and deficiencies of the existing technology, the primary objective of this invention is to provide a low-ester pectin with high gelation degree and its preparation method.

[0009] Another object of the present invention is to provide applications of the aforementioned low-ester pectin. The low-ester pectin is used to prepare sugar-free gels and / or sugar alcohol gels. The low-ester pectin of the present invention is also used in jellies, jams, and gummies.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for preparing a low-ester pectin with high gelling properties includes the following steps:

[0012] (1) Mix citrus peel residue with water, add acid to adjust the pH to 1.5-2, extract at 65-75℃, centrifuge, take the supernatant for alcohol precipitation and washing, filter, dry and pulverize the precipitate to obtain primary pectin; the extraction is carried out under stirring conditions;

[0013] (2) The primary pectin obtained in step (1) is reconstituted, the pH is adjusted to 0.5-1.1 with acid, reacted at 40-60℃, washed with alcohol precipitation, and the precipitate is dried and pulverized to obtain low-ester pectin.

[0014] The citrus peel residue mentioned in step (1) is one or more of lemon peel residue, orange peel residue, grapefruit peel residue and tangerine peel residue; the material-to-water ratio of the citrus peel residue to water is 1:(20-30).

[0015] The extraction time in step (1) is 1 to 2.5 hours.

[0016] The centrifugation mentioned in step (1) refers to centrifugation at 8000-10000 rpm for 10-20 minutes.

[0017] The reconstitution mentioned in step (2) refers to adding primary pectin to water to make the pectin concentration 2-3 wt%; the reconstitution time is 1-3 h.

[0018] The reaction time in step (2) is 60 to 72 hours.

[0019] The acid mentioned in steps (1) and (2) is at least one of nitric acid, oxalic acid, hydrochloric acid, and citric acid.

[0020] The precipitant for alcohol precipitation in steps (1) and (2) is an ethanol solution, the volume concentration and purity of the ethanol solution is not less than 95%, the volume ratio of the supernatant (concentrated solution) to the ethanol solution is 1:(1-3); the precipitation time is 0.5-1.5h; and the number of washing times is 1-3.

[0021] In step (2), the pH value is adjusted to 3.5-4 with an alkaline solution before the second alcohol wash.

[0022] The drying described in steps (1) and (2) refers to blower drying, rake drying, or fluidized bed drying; the drying temperature is 50-65℃; and the drying time is 1-4 hours.

[0023] The primary pectin has an esterification degree of 55%–65%, a molecular weight of 500–600 kDa, and a gelation degree of 200–220.

[0024] The low-ester pectin prepared by this invention has an esterification degree of 25% to 35% and a gelation degree of 120 to 150.

[0025] The low-ester pectin is used to prepare gels.

[0026] The gel is prepared by the following method: after redissolving low-ester pectin, the pH of the pectin solution is adjusted with buffer solution, the mixture is boiled at high temperature, sugar alcohol or calcium chloride solution is added, and it is allowed to stand to obtain sugar alcohol gel or sugar-free gel (i.e., zero-sucrose low-ester pectin gel).

[0027] The degree of esterification of the low-ester pectin is 25% to 35%; the mass concentration of the reconstituted pectin solution is 1% to 2%.

[0028] The buffer solution is a mixture of 60 wt% citric acid solution and 2.5 M sodium hydroxide solution, with a volume ratio of 3:1.

[0029] The pH is adjusted to 3-3.3.

[0030] The addition of calcium chloride results in a final gel system with a calcium ion content of 50–60 mg / g pectin.

[0031] The amount of sugar alcohol added is 0-30g / 100g gel.

[0032] The aforementioned static setting refers to cooling the thermal gel to room temperature and then placing it at 20–30°C for 24 hours.

[0033] The low-ester pectin sugar-free gel and sugar alcohol gel prepared by this invention have a hardness of 61.87g and 99.74g, respectively, and a water holding capacity of up to 97.73% and 98.92%.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) The acid-temperature incubation method of the present invention carries out the esterification reaction at a relatively mild temperature, minimizing hydrolysis and β-elimination reactions, and can preserve the original structure of pectin more completely.

[0036] (2) The acid-temperature incubation method of the present invention is simple and easy to operate, economical and feasible, and easy to industrialize.

[0037] (3) The low-ester pectin extracted by this invention has an esterification degree of 25% to 35%, which is low-ester pectin. The gelation degree after standardization is 120 to 150, which is significantly better than the alkaline method and the enzymatic method.

[0038] (4) The sugar-free gel and sugar alcohol gel formed by the low-ester pectin prepared in this invention have high hardness and water retention. Attached Figure Description

[0039] Figure 1 These are morphological images of the gels formed from the low-ester pectin in Examples 1-3 and Comparative Examples 1-3 of this invention. Figure 1 The gel in the sample is prepared by using low-ester pectin according to the SAG method in QS2484-2000. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0041] The determination of the degree of esterification was carried out by chemical titration in accordance with the national food safety standard GB25533-2010.

[0042] The gelation degree was determined according to the jelly sinking method (SAG method) specified in the light industry standard QS2484-2000.

[0043] Example 1

[0044] (1) Weigh 40g of citrus peel residue and dissolve it in 800g of water. Stir and mix evenly. Add concentrated nitric acid to adjust the pH of the system to 1.7. Stir and extract in a 70℃ water bath for 1.5h. Centrifuge the pectin suspension after reaction at 9000rpm for 15min. Precipitate the supernatant after centrifugation with 2 times the volume of 95% ethanol. Let stand for 1h and then wash with alcohol again. Filter with 400 mesh filter cloth to obtain pectin precipitate. Dry by forced air (drying temperature is 60℃, drying time is 3.5h). Crush to obtain primary pectin with esterification degree of 57.63%, molecular weight of 562kDa, and gelation degree of 209.48.

[0045] (2) Weigh 6g of the primary pectin obtained in step (1) and dissolve it in 200g of water to obtain a 3% pectin solution. After it is fully dissolved, add concentrated nitric acid to adjust the pH of the solution to 0.7. Stir and react in a 40℃ water bath for 72h. Precipitate the concentrated solution after reaction with 2 times the volume of 95% ethanol. At the same time, adjust the pH of the mixed system to 3.5 with ammonia solution. After standing for 1h, wash with alcohol again and filter with 400 mesh filter cloth to obtain pectin precipitate. Dry it with a forced air (drying temperature is 60℃, drying time is 3.5h) and pulverize it to obtain pectin with esterification degree of 29.04% and gelation degree of 125.93.

[0046] Example 2

[0047] (1) Weigh 40g of citrus peel residue and dissolve it in 800g of water. Stir and mix evenly. Add concentrated nitric acid to adjust the pH of the system to 2.0. Stir and extract in a 75℃ water bath for 2h. Centrifuge the pectin suspension after reaction at 8000rpm for 20min. Precipitate the supernatant after centrifugation with 3 times the volume of 95% ethanol. Let stand for 1h and then wash with alcohol twice. Filter with 400 mesh filter cloth to obtain pectin precipitate. Dry by rake (drying temperature is 65℃, drying time is 3h). Crush to obtain primary pectin with esterification degree of 56.45%, molecular weight of 555kDa, and gelation degree of 220.82.

[0048] (2) Weigh 12g of the primary pectin obtained in step (1) and dissolve it in 400g of water to obtain a 3% pectin solution. After it is fully dissolved, add concentrated nitric acid to adjust the pH of the solution to 0.5. Stir and react in a water bath at 45℃ for 66h. Precipitate the concentrated solution after reaction with 3 times the volume of 95% ethanol. At the same time, adjust the pH of the mixed system to 3.8 with sodium hydroxide solution. After standing for 1h, wash with alcohol again and filter with 400 mesh filter cloth to obtain pectin precipitate. Dry it by rake (drying temperature is 65℃, drying time is 3h) and pulverize it to obtain pectin with esterification degree of 29.09% and gelation degree of 124.08.

[0049] Example 3

[0050] (1) Weigh 40g of citrus peel residue and dissolve it in 800g of water. Stir and mix evenly. Add concentrated nitric acid to adjust the pH of the system to 1.5. Stir and extract in a 70℃ water bath for 1.5h. Centrifuge the pectin suspension after reaction at 8000rpm for 15min. Precipitate the supernatant after centrifugation with 3 times the volume of 95% ethanol. Let stand for 1h and then wash with alcohol twice. Filter with 400 mesh filter cloth to obtain pectin precipitate. Dry in a fluidized bed (drying temperature is 60℃, drying time is 4h). Crush to obtain primary pectin with esterification degree of 57.99%, molecular weight of 578kDa, and gelation degree of 222.97.

[0051] (2) Weigh 12g of the primary pectin obtained in step (1) and dissolve it in 400g of water to obtain a 3% pectin solution. After it is fully dissolved, add concentrated nitric acid to adjust the pH of the solution to 0.9. Stir the reaction in a 40℃ water bath for 72h. Precipitate the concentrated solution after the reaction with 3 times the volume of 95% ethanol. At the same time, adjust the pH of the mixed system to 4.0 with sodium carbonate solution. After standing for 1h, wash with alcohol again and filter with 400 mesh filter cloth to obtain pectin precipitate. Dry it in a fluidized bed (drying temperature is 60℃, drying time is 4h) and pulverize it to obtain pectin with a degree of esterification of 30.21% and a gelation degree of 120.75.

[0052] Comparative Example 1

[0053] Low-ester pectin was prepared using an alkali treatment method.

[0054] (1) Primary pectin is obtained based on step (1) of Example 1.

[0055] (2) Weigh 12g of the primary pectin obtained in step (1) and dissolve it in 400g of water to obtain a 3% pectin solution. After complete dissolution, add 15mL of 2.5M NaOH solution and stir in a 30℃ water bath for 1.5h. After the reaction, add 5mL of concentrated nitric acid and continue the reaction for 3h. Precipitate the concentrated solution after the reaction with 2 times the volume of 95% ethanol. At the same time, adjust the pH of the mixture to 3.5 with ammonia solution. After standing for 1h, wash with alcohol twice and filter with 400 mesh filter cloth to obtain pectin precipitate. Dry it with a forced air (drying temperature is 60℃, drying time is 3.5h) and pulverize it to obtain pectin with a degree of esterification of 24.62% and a gelation degree of 100.00.

[0056] Comparative Example 2

[0057] Low-ester pectin was prepared using an enzymatic treatment method.

[0058] (1) Primary pectin is obtained based on step (1) of Example 2.

[0059] (2) Weigh 12g of the primary pectin obtained in step (1), dissolve it in 400g of phosphate buffer solution, and adjust the pH of the solution to 3.5. After fully dissolving in a 50℃ water bath, add 200μL of pectin methyl esterase and react for 1.5h. Then heat at 95℃ for 5min to inactivate the enzyme. Precipitate the concentrated solution after reaction with 3 times the volume of 95% ethanol. At the same time, adjust the pH of the mixture to 3.8 with sodium hydroxide solution. After standing for 1h, wash with alcohol twice and filter with 400 mesh filter cloth to obtain pectin precipitate. Dry by rake (drying temperature 65℃, drying time 3h), and pulverize to obtain pectin with esterification degree of 30.99% and gelation degree of 105.34.

[0060] Comparative Example 3

[0061] Low-ester pectin was prepared using the citric acid / sodium citrate method.

[0062] 10g of lemon peel residue was weighed and dissolved in 250mL of citric acid / sodium citrate buffer solution with pH=8. The mixture was stirred and reacted in an 85℃ water bath for 2h. The resulting pectin suspension was centrifuged at 8000rpm for 15min. The supernatant was precipitated with 3 times its volume of 95% ethanol. Simultaneously, the pH of the mixture was adjusted to 4.0 with sodium carbonate solution. After standing for 1h, the mixture was washed a second time with ethanol and filtered through a 400-mesh filter cloth to obtain pectin precipitate. The precipitate was then dried in a fluidized bed (drying temperature: 60℃, drying time: 4h) and pulverized to obtain pectin with a degree of esterification of 32.16%, which could not form a gel.

[0063] The physicochemical parameters of the pectin prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0064] Table 1. Physicochemical parameters of pectin prepared in Examples 1-3 and Comparative Examples 1-3

[0065]

[0066] As shown in Table 1, the degree of esterification of the prepared low-ester pectin was approximately 29% ± 5%. However, the gelation degree varied considerably. The gelation degree of Examples 1-3 was 120-130, while the gelation degrees of Comparative Examples 1 and 2 were only 100.00 and 105.34, respectively, and Comparative Example 3 did not even form a gel. Therefore, the low-ester pectin prepared in this invention has significant advantages in gelation ability.

[0067] Figure 1 These are morphological images of the gels formed from the low-ester pectin in Examples 1-3 and Comparative Examples 1-3 of this invention.

[0068] The following describes the application of sugar-free gel and sugar alcohol gel in Example 1, and uses Examples 1 to 3 in CN 111602804 B as comparative examples 4 to 6 of the present invention.

[0069] Example 4

[0070] Weigh 1.5g of the low-ester pectin obtained in Example 1 and dissolve it completely in 75mL of distilled water. Adjust the pH of the solution to 3.3 using a buffer solution composed of 60% (w / v) citric acid and 2.5M sodium hydroxide. Boil the mixture and add 12.5mL of 1.66% (w / v) anhydrous calcium chloride solution (the calcium ion content in the final gel system is 50mg / g pectin). The gel mass is 150g. After cooling the hot gel solution to 25°C and letting it stand for 24h, a low-ester sugar-free gel is obtained.

[0071] Example 5

[0072] The only difference from Example 4 is that 15g of erythritol was added after the mixture was boiled, so that the mass percentage of erythritol in the final gel system was 10%.

[0073] Example 6

[0074] The only difference from Example 4 is that 30g of erythritol was added after the mixture was boiled, so that the mass percentage of erythritol in the final gel system was 20%.

[0075] Example 7

[0076] The only difference from Example 4 is that 45g of erythritol was added after the mixture was boiled, so that the mass percentage of erythritol in the final gel system was 30%.

[0077] Comparative Example 4

[0078] CN 111602804 B Example 1.

[0079] Comparative Example 5

[0080] CN 111602804 B Example 2.

[0081] Comparative Example 6

[0082] CN 111602804 B Example 3.

[0083] Hardness test:

[0084] Measurements were taken using a cylindrical probe with a diameter of 0.5 inches. The gel was compressed at a constant speed of 1.0 mm / s until 50% of its initial height was reached.

[0085] Water retention test:

[0086] After the gel was allowed to stand at 4℃ for 24 hours, it was centrifuged at 8000 rpm for 10 minutes. The water expelled was blotted dry with filter paper. The mass of the gel before centrifugation was recorded as M1, and the mass of the gel after centrifugation was recorded as M2. The water holding capacity of the gel was calculated using the following formula: Water holding capacity = M2 / M1 × 100%.

[0087] The hardness and water holding capacity of Examples 4-7 and Comparative Examples 4-6 are shown in Table 2.

[0088] Table 2 shows the hardness and water holding capacity of Examples 4-7 and Comparative Examples 4-6.

[0089]

[0090] Table 2 shows that the hardness and water retention of Examples 5-7 are higher than those of Example 4, indicating that the addition of a certain amount of erythritol is beneficial to gel formation. The hardness and water retention of Example 6 are higher than those of Examples 5 and 7, indicating that there is an optimal range for the amount of erythritol added; beyond this optimal amount, the gel begins to weaken, and the network structure becomes unstable. Compared with Comparative Examples 4-6, at the same amount of erythritol added, the low-ester pectin extracted in Examples 5-7 forms a erythritol gel with higher hardness and stronger water retention.

[0091] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and essence of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A method for preparing a low-ester pectin with high gelling properties, characterized in that: Includes the following steps: (1) Mix citrus peel residue with water, add acid to adjust pH to 1.5~2, extract at 65~75℃, centrifuge, take the supernatant for alcohol precipitation and washing, filter, dry and pulverize the precipitate to obtain primary pectin. (2) The primary pectin obtained in step (1) is reconstituted, the pH is adjusted to 0.5~0.9 with acid, reacted at 40~60℃, washed with alcohol precipitation, and the precipitate is dried and pulverized to obtain low-ester pectin. The extraction time in step (1) is 1~2.5 h; The reaction time in step (2) is 60-72 h; The citrus peel residue mentioned in step (1) is one or more of lemon peel residue, orange peel residue, grapefruit peel residue and tangerine peel residue; the mass ratio of citrus peel residue to water is 1: (20~30). The extraction described in step (1) is carried out under stirring conditions; The centrifugation mentioned in step (1) refers to centrifugation at 8000~10000 rpm for 10~20 min; The reconstitution mentioned in step (2) refers to adding primary pectin to water to make the pectin concentration 2-3 wt%; The precipitant for alcohol precipitation in step (1) is an ethanol solution with a volume concentration ≥95%; the volume ratio of supernatant to ethanol solution is 1:(1~3); the precipitation time is 0.5~1.5 h; and the number of washing cycles is 1~3. The acid mentioned in steps (1) and (2) is at least one of nitric acid, oxalic acid, hydrochloric acid, and citric acid; The drying described in steps (1) and (2) is respectively blower drying, rake drying or fluidized bed drying; the drying temperature is 50~65℃; the drying time is 1~4 h; The precipitant for alcohol precipitation in step (2) is an ethanol solution with a volume concentration ≥95%; the volume ratio of the supernatant to the ethanol solution is 1:(1~3); the washing is performed 2~3 times, and the pH of the precipitation system is adjusted to 3.5~4 with an adjusting agent before the second or third alcohol washing, and then allowed to stand for 0.5~1.5 h; the adjusting agent is ammonia water, sodium hydroxide or sodium carbonate solution; The primary pectin has an esterification degree of 55%~65%; a molecular weight of 500~600kDa; and a gelation degree of 200~220. The low-ester pectin has an esterification degree of 25%~35% and a gelation degree of 120~150.

2. The application of the high-gelling-strength low-ester pectin obtained by the preparation method according to claim 1, characterized in that: The low-ester pectin is used to prepare gels.

3. The application according to claim 2, characterized in that: The gel was prepared by the following method: after reconstituted low-ester pectin, the pH of the pectin solution was adjusted with buffer solution, boiled at high temperature, and then sugar alcohol or calcium chloride solution was added and allowed to stand to obtain sugar alcohol gel or sugar-free gel. The degree of esterification of the low-ester pectin is 25%~35%; the mass concentration of the reconstituted pectin solution is 1%~2%. The buffer solution is a mixture of 60 wt% citric acid solution and 2.5 M sodium hydroxide solution, with a volume ratio of 3:

1. The pH is adjusted to 3-3.3; The addition of the calcium chloride solution resulted in a final gel system containing 50-60 mg / g pectin with calcium ions. The term "static setting" refers to placing the thermogel at 20-30°C for 24 hours after cooling it to room temperature.

4. The application of the high-gelling-strength low-ester pectin obtained by the preparation method according to claim 1, characterized in that: The high-gelling-strength, low-ester pectin is used in jellies, jams, and gummies.

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