Application of sulfurous acid-ascorbic acid synergistic system to increase hardness of high-gel-property hawthorn pectin saccharic acid type gel, pectin and application

Abstract

The invention belongs to the field of food processing, and particularly relates to application of a sulfurous acid-ascorbic acid synergistic system to increase hardness of hawthorn pectin with high gel property, pectin and application. According to the technical scheme, the method comprises the following steps: adding L-ascorbic acid and sulfurous acid into a hawthorn powder suspension to obtain a mixed solution, adjusting the pH value of the mixed solution to be 1.5-2.5 by using sulfurous acid, heating and extracting the mixed solution in a closed container, cooling and centrifuging the heated and extracted mixed solution, taking supernate, adding absolute ethyl alcohol, standing, taking precipitate, washing, and drying to obtain the hawthorn extract. The hawthorn pectin is obtained. The method can prevent easily oxidized polyphenol substances and procyanidine in the hawthorn from being oxidized to form quinones compounds to influence the pectin quality in the hawthorn pectin extraction process, can improve the pectin gel hardness, and improves the reduction effect of sulfurous acid in the pectin preparation process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of food processing, and particularly relates to application of a sulfurous acid-ascorbic acid synergistic system to increase hardness of hawthorn pectin with high gel properties, pectin and application. BACKGROUND

[0002] Pectin is a natural high-molecular polysaccharide, widely exists in plant cell walls, and is a complex structural polysaccharide; pectin is composed of homogalacturonan (HG), rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II) domains; pectin has good gel, thickening and emulsification properties, and is widely used in food, medicine and cosmetics fields. Hawthorn is a food with medicinal and edible properties, and is rich in pectin, polyphenols and other nutrients. Hawthorn pectin is HG type, has the characteristics of high HG (molar percentage 83-99%) and low RG-I (molar percentage 1-9%), and the high HG region makes the pectin have good gel properties.

[0003] At present, the industrialized method for extracting pectin from hawthorn mostly adopts inorganic or organic acid method such as hydrochloric acid and citric acid. These traditional methods face a significant technical bottleneck: the outstanding characteristic of hawthorn fruits, which is different from commonly used pectin raw materials such as citrus and apple, is that it is rich in a large amount of easily oxidized polyphenol substances and proanthocyanidins. In the high-temperature acid extraction process, these polyphenols and anthocyanins are easily oxidized to form quinone compounds, which in turn covalently or non-covalently combine with pectin molecules, which not only causes the browning of pectin color, but also significantly degrades the gel properties of hawthorn pectin, greatly reducing the product value.

[0004] Sulfurous acid has reducing property, can inhibit the oxidation of polyphenols, reduce the combination of oxidized polyphenols with pectin, can also destroy proanthocyanidins, and reduce their combination with pectin. After the reduction of impurities, the arrangement of pectin molecular chains is more orderly, and the three-dimensional network continuity is enhanced. However, its effect is still insufficient.

[0005] Therefore, we urgently need a comprehensive method to optimize the extraction of hawthorn pectin. The method needs to inhibit the oxidation of polyphenols and proanthocyanidins (prevent the generation of quinone compounds combined with pectin), and synergistically enhance the reducing effect of sulfurous acid, to finally improve the quality and gel hardness of pectin. SUMMARY

[0006] In view of the problems in the prior art that polyphenols and proanthocyanidins are easily oxidized to quinone compounds and combined with pectin during extraction of hawthorn pectin, resulting in decreased pectin quality and insufficient gel hardness, and the reducing effect of sulfurous acid is not good, the present application provides application of a sulfurous acid-ascorbic acid synergistic system. The system can effectively prevent the above oxidation side reactions, significantly improve the reducing efficiency of sulfurous acid, and produce hawthorn pectin with high gel hardness. To solve the technical problem, the technical scheme adopted by the present application is: The application of a sulfite-ascorbic acid synergistic system to increase the hardness of hawthorn sugar acid type pectin with high gel properties, comprising: adding L-ascorbic acid and sulfite to a hawthorn powder suspension to obtain a mixed solution, adjusting the pH of the mixed solution to 1.5-2.5 using sulfite, heating the mixed solution in a sealed container for extraction, centrifuging the mixed solution after the heating extraction is completed, adding anhydrous ethanol to the supernatant, washing and drying the precipitate to obtain hawthorn pectin.

[0007] In some embodiments, the mass-volume ratio of L-ascorbic acid to the hawthorn powder suspension is 0.8-1 g:1 L.

[0008] In some embodiments, the hawthorn powder suspension is prepared from dry hawthorn powder and water, and the mass-volume ratio of the dry hawthorn powder to water in the hawthorn pulp is 1 g:20-30 ml.

[0009] In some embodiments, the dry hawthorn powder is obtained by freeze-drying or oven-drying hawthorn fruit, and then crushing and screening.

[0010] In some embodiments, the heating reaction conditions of the mixed solution are 80-90 DEG C stirring heating for 0.8-1.2 h.

[0011] In some embodiments, the ratio of the supernatant to anhydrous ethanol is 1:1.8-2.2, and the standing is performed at 4 DEG C for ≥12 h.

[0012] In some embodiments, the centrifugation conditions are a rotation speed of ≥5000 rpm / min and a centrifugation time of ≥10 min.

[0013] The application also discloses a hawthorn pectin prepared using the above application; the polyphenol content in the hawthorn pectin is ≤1.88%, and the proanthocyanidin content is ≤1.40%; the hardness of a pectin gel prepared from the hawthorn pectin is ≥3.08 N.

[0014] The application also discloses an application of the hawthorn pectin in producing soft candies with high hardness.

[0015] Compared with the prior art, the application has the following beneficial effects: (1) The application uses a sulfite-ascorbic acid synergistic system to prepare hawthorn pectin, which can effectively reduce the combination of oxidized polyphenols and anthocyanins with pectin, thereby reducing the competition for hydrogen bond combination sites, so that the pectin can be more effectively combined when forming a sugar acid gel, and the space steric hindrance caused by the aggregation of polyphenols and anthocyanins is reduced, further improving the gel strength of the sugar acid type gel, and the application has higher gel performance compared with common acid extraction pectin. (2) The extraction process of this invention is simple and easy to operate. By using sulfurous acid and L-ascorbic acid as a highly efficient extractant, the range of acid types that can be used to obtain high-performance hawthorn pectin is substantially broadened, breaking through the limitations of traditional strong acids (such as hydrochloric acid). Attached Figure Description

[0016] Figure 1 Schematic diagrams of the pectin gel properties of comparative examples 1-7 provided by the present invention; Figure 2 This is a schematic diagram of the pectin gel properties of Examples 1, Comparative Examples 1 and 3 provided by the present invention; Figure 3 A schematic diagram of the pectin gel properties of Comparative Example 8 provided by the present invention; Figure 4 This is a schematic diagram of the pectin-added polyphenol gel of Example 1 provided by the present invention; Figure 5 The pectin appearance diagrams of Examples 1, 1, 3, and 8 provided by this invention are shown. Detailed Implementation

[0017] The technical solutions in specific embodiments of the present invention will be described in detail and completely below. Obviously, the described embodiments are only some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0018] This invention provides an application of a sulfite-ascorbic acid synergistic system to increase the hardness of sugar-acid type gels of hawthorn pectin with high gel properties, comprising: adding L-ascorbic acid and sulfite to a hawthorn powder suspension to obtain a mixed solution; adjusting the pH of the mixed solution to 1.5-2.5 with sulfite; heating and extracting the mixed solution in a sealed container; cooling and centrifuging the mixed solution after the heating reaction is completed; adding anhydrous ethanol to the supernatant and allowing it to stand; washing and drying the precipitate to obtain hawthorn pectin.

[0019] This invention defines a pH range within which pectin extraction is high and the pectin structure is not damaged by hydrolysis due to excessively low pH. It is understood that those skilled in the art can adjust the pH within the above range according to actual conditions, and the pH can also be 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or any value within the above range.

[0020] Traditional hydrochloric acid extraction of hawthorn pectin leads to the degradation of pectin chains, resulting in smaller molecular weights and weaker gel properties. Furthermore, hawthorn fruits are rich in polyphenols and proanthocyanidins, which are easily oxidized and bind to pectin during extraction, further deteriorating its gel properties. To address these technical bottlenecks, this invention employs a reducing extraction system composed of sulfurous acid and L-ascorbic acid, performed under heating conditions. This composite system effectively inhibits polyphenol oxidation, minimizing its damage to the pectin gel network, thereby obtaining hawthorn pectin products with significantly improved gel strength. While sulfurous acid, with its reducing properties, can inhibit polyphenol oxidation and reduce the binding of oxidized polyphenols to pectin, and can also destroy proanthocyanidins, reducing their binding to pectin, its effectiveness is still insufficient. This invention defines a synergistic system of L-ascorbic acid and sulfurous acid. L-ascorbic acid can efficiently reduce and regenerate oxidized sulfurous acid intermediates while delaying its own consumption, thereby greatly enhancing and maintaining the reduction potential of the entire extraction system. This synergistic effect is crucial for inhibiting the extremely high content of easily oxidized polyphenols in hawthorn and is key to achieving the high gelation properties of pectin. Furthermore, the reducing and metal-chelating abilities of sulfurous acid itself can also prevent L-ascorbic acid from reacting with oxygen, light, and metal ions (such as Fe). 3+ Cu 2+ When present in plants (either naturally occurring or introduced during processing), it is oxidized to "dehydroascorbic acid," which damages pectin molecules, causing L-ascorbic acid to exhibit only its strong reducing properties.

[0021] The present invention also specifies that the container for the heating reaction is a closed container. This is because sulfurous acid is easily decomposed into sulfur dioxide gas when heated and leaves the reaction system, causing the reaction to be unable to proceed. In a closed container, the escaped sulfur dioxide accumulates above the solution, increases in concentration, and forms a dynamic equilibrium with the sulfurous acid in the solution, ensuring that the reaction proceeds.

[0022] Therefore, this invention uses a sulfurous acid-ascorbic acid synergistic system to prepare hawthorn pectin, which can effectively reduce the binding of oxidized polyphenols and anthocyanins to pectin, thereby reducing competition for hydrogen bond binding sites. This allows pectin to bind more effectively when forming a sugar-acid gel, while reducing steric hindrance caused by polyphenol and anthocyanin aggregation, further improving the gel strength of the sugar-acid gel. Compared with common acid extraction methods for pectin, it has higher gel performance. At the same time, the extraction process of this invention is simple and easy to operate. By using sulfurous acid plus L-ascorbic acid as a highly efficient extraction agent, it substantially broadens the range of acid types that can be used to obtain high-performance hawthorn pectin, breaking through the limitations of traditional strong acids (such as hydrochloric acid).

[0023] In some embodiments, the mass-to-volume ratio of L-ascorbic acid to hawthorn powder suspension is 0.8–1 g:1 L.

[0024] This concentration range of L-ascorbic acid ensures that it can fully exert its function while meeting the standard for dosage.

[0025] It is understood that, based on actual circumstances, those skilled in the art can adjust the mass fractions of each component within the above range. For example, L-ascorbic acid can also be 0.85g, 0.9g, 0.95g, or any value within the above range. This is a suitable concentration based on experimental results and considering economic factors.

[0026] In some embodiments, the hawthorn powder suspension is prepared by mixing dried hawthorn powder and water, with a mass-to-volume ratio of dried hawthorn powder to water of 1g:20-30ml. This ratio provides a sufficient solvent environment for the raw materials, ensuring that water fully penetrates the cell structure, thereby maximizing the dissolution of pectin. A ratio that is too low will lead to incomplete extraction and reduced yield. On the other hand, it also maintains the concentration of the extract within a relatively reasonable range, avoiding excessive energy consumption in the subsequent concentration stage due to excessive solvent, thus achieving a balance between extraction efficiency, product quality, and economic efficiency.

[0027] In some embodiments, dried hawthorn powder is obtained by freeze-drying or baking pitted hawthorn fruit, followed by pulverizing and screening. Using dried hawthorn powder can avoid the impact of inconsistent moisture content in the fruit on the preparation of hawthorn powder suspension.

[0028] In some embodiments, the heating reaction of the mixed solution is carried out at 80°C–90°C with stirring for 0.8–1.2 h. The technical solution limits the extraction temperature and time because high temperature further breaks down the cell walls of plant cells, better promoting acid diffusion and the release of pectin from the plant matrix. Excessively high temperature or too long a time will damage the structure of pectin; too low a temperature or too short a time will result in insufficient pectin extraction.

[0029] In some embodiments, the ratio of supernatant to anhydrous ethanol is 1:1.8–2.2, and the mixture is allowed to stand at 1–4°C for ≥12 h. When ethanol is added at a volume ratio of 1:2 to the extract, the polarity of the mixed solvent is significantly reduced, which enhances the intermolecular forces of pectin molecules. Simultaneously, its solubility in the water-ethanol mixture decreases sharply, causing it to precipitate from the solution as a fibrous or flocculent precipitate. If the amount of ethanol is insufficient (e.g., 1 part), the change in solvent polarity is inadequate, resulting in incomplete precipitation and a significant loss of pectin yield. While excessive use of ethanol (e.g., 3 parts or more) ensures precipitation, it wastes solvent costs and increases the burden on subsequent recovery and environmental protection. Therefore, 2 parts ethanol precipitation ensures a high precipitation rate (typically over 95%) while also being operationally feasible and economical, making it an optimal process parameter choice for industrial production.

[0030] In some embodiments, the centrifugation conditions are a rotation speed ≥ 5000 rpm / min and a centrifugation time ≥ 10 min. Centrifugation can effectively separate the supernatant containing soluble pectin from insoluble plant tissue residues, impurities, and other precipitates, thereby obtaining a clear crude pectin extract. On the other hand, setting the rotation speed of 5000 rpm / min and the duration of 10 minutes are parameters optimized based on the particle size, density, and solution viscosity of solid impurity particles in the pectin extract, aiming to ensure that these small, lightweight particles can be fully settled to the bottom of the tube within the specified time, achieving maximum separation efficiency.

[0031] The present invention also discloses a hawthorn pectin, which is prepared using the above-mentioned application; the hawthorn pectin contains ≤1.88% polyphenols and ≤1.40% proanthocyanidins; the pectin gel prepared from hawthorn pectin with a pectin mass-volume concentration of 2% has a hardness ≥3.08N.

[0032] This invention also discloses the application of hawthorn pectin in the production of high-hardness soft candy. To more clearly and in detail illustrate the application of the sulfite-ascorbic acid synergistic system provided in the embodiments of this invention to increase the hardness of high-gelling-property hawthorn sugar-acid pectin, specific embodiments will be described below.

[0033] Example 1 (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0034] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and 0.1% ascorbic acid was added by liquid volume to adjust the pH to 2. The mixed solution was heated at 85℃ for 1 h with continuous stirring during the heating process. The heated mixed solution was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and 2 volumes of anhydrous ethanol were added. The mixture was allowed to stand at 4℃ for 12 h and then filtered through a 200-mesh sieve to obtain pectin precipitate. The pectin precipitate was washed once with anhydrous ethanol, filtered, and then dried at 50℃. The dried hawthorn pectin was crushed and mixed using a grinder.

[0035] Comparative Example 1 The difference from Example 1 is that hydrochloric acid is used instead of sulfurous acid and L-ascorbic acid in Example 1.

[0036] (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0037] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and the pH was adjusted to 2 with 6 M hydrochloric acid. The mixture was heated at 85℃ for 2 h with continuous stirring during the heating process. The heated mixture was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and 2 volumes of anhydrous ethanol were added. The mixture was allowed to stand at 4℃ for 12 h and then filtered through a 200-mesh sieve to obtain pectin precipitate. The pectin precipitate was washed once with anhydrous ethanol, filtered, and then dried at 50℃. The dried hawthorn pectin was crushed and mixed using a grinder.

[0038] Comparative Example 2 The difference from Example 1 is that sulfuric acid is used instead of sulfurous acid and L-ascorbic acid in Example 1.

[0039] (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0040] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and the pH was adjusted to 2 with 6 M sulfuric acid. The mixed solution was heated at 85℃ for 2 h with continuous stirring during the heating process. The heated mixed solution was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and added with 2 times the volume of anhydrous ethanol, and allowed to stand at 4℃ for 12 h. The pectin precipitate was obtained by filtering through a 200-mesh sieve. The pectin precipitate was washed once with anhydrous ethanol, filtered, and dried at 50℃. The dried hawthorn pectin was crushed and mixed with a grinder.

[0041] Comparative Example 3 The difference from Example 1 is that only sulfurous acid is used, and L-ascorbic acid is not added.

[0042] (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0043] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and the pH was adjusted to 2 with 6 M sulfurous acid. The mixed solution was heated at 85℃ for 2 h with continuous stirring during the heating process. The heated mixed solution was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and 2 volumes of anhydrous ethanol were added. The mixture was allowed to stand at 4℃ for 12 h and then filtered through a 200-mesh sieve to obtain pectin precipitate. The pectin precipitate was washed once with anhydrous ethanol, filtered, and then dried at 50℃. The dried hawthorn pectin was crushed and mixed using a grinder.

[0044] Comparative Example 4 The difference from Example 1 is that phosphoric acid is used instead of sulfurous acid and L-ascorbic acid in Example 1.

[0045] (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0046] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and the pH was adjusted to 2 with 6 M phosphoric acid. The mixed solution was heated at 85℃ for 2 h with continuous stirring during the heating process. The heated mixed solution was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and added with 2 times the volume of anhydrous ethanol, and allowed to stand at 4℃ for 12 h. The pectin precipitate was obtained by filtering through a 200-mesh sieve. The pectin precipitate was washed once with anhydrous ethanol, filtered, and dried at 50℃. The dried hawthorn pectin was crushed and mixed with a grinder.

[0047] Comparative Example 5 The difference from Example 1 is that lactic acid is used instead of sulfurous acid and L-ascorbic acid in Example 1.

[0048] (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0049] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and the pH was adjusted to 2 with L-lactic acid (high purity). The mixed solution was heated at 85℃ for 2 h with continuous stirring during the heating process. The heated mixed solution was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and added with 2 volumes of anhydrous ethanol, and allowed to stand at 4℃ for 12 h. The pectin precipitate was obtained by filtration through a 200-mesh sieve. The pectin precipitate was washed once with anhydrous ethanol, filtered, and dried at 50℃. The dried hawthorn pectin was crushed and mixed using a grinder.

[0050] Comparative Example 6 The difference from Example 1 is that malic acid is used instead of sulfurous acid and L-ascorbic acid in Example 1.

[0051] (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0052] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and the pH was adjusted to 2 with L-malic acid. The mixed solution was heated at 85℃ for 2 h with continuous stirring during the heating process. The heated mixed solution was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and added with 2 volumes of anhydrous ethanol, and allowed to stand at 4℃ for 12 h. The pectin precipitate was obtained by filtering through a 200-mesh sieve. The pectin precipitate was washed once with anhydrous ethanol, filtered, and dried at 50℃. The dried hawthorn pectin was crushed and mixed using a grinder.

[0053] Comparative Example 7 The difference from Example 1 is that citric acid is used instead of sulfurous acid and L-ascorbic acid in Example 1.

[0054] (1) Raw material pretreatment: The freeze-dried Da Jinxing hawthorn is ground into powder by a grinder and passed through a 40-mesh sieve.

[0055] (2) Preparation of hawthorn pectin: Hawthorn powder was suspended in distilled water at a ratio of 1:30, and the pH was adjusted to 2 with citric acid. The mixture was heated at 85℃ for 2 h with continuous stirring during the heating process. The heated mixture was centrifuged at 25℃ and 5000 rpm / min for 10 min. The supernatant was taken and added with 2 volumes of anhydrous ethanol, and allowed to stand at 4℃ for 12 h. The mixture was then filtered through a 200-mesh sieve to obtain pectin precipitate. The pectin precipitate was washed once with anhydrous ethanol, filtered, and dried at 50℃. The dried hawthorn pectin was crushed and mixed using a grinder.

[0056] Comparative Example 8 (1) Citrus peel + sulfurous acid The only difference between the experimental procedure and that of Comparative Example 1 is that the raw material was replaced with citrus peel powder instead of hawthorn powder; all other steps were the same.

[0057] (2) Citrus peel + sulfurous acid The only difference between the experimental procedure and that of Comparative Example 3 is that the raw material was replaced with citrus peel powder instead of hawthorn powder; all other steps were the same.

[0058] (3) Citrus peel + sulfurous acid and ascorbic acid The experimental procedure differs from Example 1 only in that the raw material is replaced with citrus peel powder instead of hawthorn powder; all other steps are the same.

[0059] Effect Evaluation 1. Physicochemical property characterization: (1) 10 mg of hawthorn pectin obtained in Example 1 and Comparative Examples 1-7 was added to 4 ml of trifluoroacetic acid and hydrolyzed at 120 °C for 1 h. After drying the trifluoroacetic acid with a nitrogen blower, it was reconstituted to 10 ml and then diluted 20 times. The monosaccharide composition of hawthorn pectin was determined by ion chromatography (the results are shown in Table 1).

[0060] (2) Dissolve 10 mg of hawthorn pectin obtained in Example 1 and Comparative Examples 1-7 in 10 ml of distilled water, filter through a 0.22 μm microporous membrane, and determine the molecular weight using SEC-MALLS.

[0061] (3) 10 mg of hawthorn pectin obtained in Example 1 and Comparative Examples 1-7 were dissolved in 10 ml of distilled water, filtered through a 0.22 μm microporous membrane, and examined by infrared spectrophotometry. The degree of esterification of hawthorn pectin was calculated by FT-IR according to the formula DE= A1753 / (A1753+A1641) (the results are shown in Table 1).

[0062] Table 1 Physicochemical Properties of Hawthorn Pectin Wherein, HG is galacturonic acid minus rhamnuronic acid, RG-I is 2*rhamnose + arabinose + galactose, RG-I represents the content of branched chains in the pectin chain, and HG is the content of straight chains (main chain) in the pectin chain.

[0063] As shown in Table 1, the extraction rate, degree of esterification, and monosaccharide composition of hawthorn pectin extracted with different acids are similar. The extraction of hawthorn pectin with different acids does not have a significant impact on its structure, indicating that the structure of hawthorn pectin extracted with different acids does not affect the gel properties.

[0064] 2. Determination of polyphenol and proanthocyanidin content in pectin (1) Determination of polyphenol content in pectin: S1: Take 0 μL, 50 μL, 75 μL, 100 μL, 125 μL, 150 μL, 175 μL, and 200 μL of 100 mg / L gallic acid standard solution, add deionized water to 1 ml, then add 1 ml of Folin-Ciocalteu reagent and shake well. Add 1 ml of 7.5% (m / v) sodium carbonate solution, shake thoroughly, let stand for 10 min, transfer to the dark and react for 1 h. Zero the instrument with deionized water and measure the absorbance at 765 nm to prepare a standard curve.

[0065] S2: Take the hawthorn pectin obtained in Example 1, Comparative Example 1, and Comparative Example 3, and the citrus pectin obtained in Comparative Example 8, and prepare pectin solutions with a concentration of 5 mg / mL. Take 1 ml of each solution, add 1 ml of Folin-Ciocalteu reagent, and shake well. Add 1 ml of 7.5% (m / v) sodium carbonate solution, shake thoroughly, let stand for 10 min, transfer to the dark, and react for 1 h. Measure the absorbance at 765 nm. Compare with the standard curve to obtain the polyphenol content in the pectin (results are shown in Table 2).

[0066] (2) Determination of proanthocyanidin content in pectin: S1: Prepare a 1 mg / ml proanthocyanidin standard solution. Take 2 ml, 3 ml, 4 ml, 5 ml, and 6 ml of the standard solution respectively, and dilute to 10 ml with methanol. Take 1 ml of each gradient concentration standard solution, add 2.5 ml of 1% vanillin-methanol solution and 2.5 ml of concentrated hydrochloric acid, shake well, and incubate in a water bath at 30℃ for 30 min under light-protected conditions. Use methanol as a blank control and measure the absorbance value at a wavelength of 502 nm to prepare a standard curve.

[0067] S2: Hawthorn pectin obtained in Example 1, Comparative Example 1, and Comparative Example 3, and citrus pectin obtained in Comparative Example 8, were used to prepare pectin solutions with a concentration of 50 mg / mL. 1 ml of each solution was added to 2.5 ml of 1% vanillin-methanol solution and 2.5 ml of concentrated hydrochloric acid. The solutions were thoroughly mixed and incubated in a water bath at 30°C for 30 min in the dark. The absorbance was measured at a wavelength of 502 nm. The proanthocyanidin content in the pectin was obtained by comparing the results with the standard curve (see Table 2).

[0068] Table 2. Content of polyphenols and proanthocyanidins in pectin As shown in Table 2, the extraction rates of the combined sulfurous acid and ascorbic acid were close to those of hydrochloric acid, but the content of polyphenols and anthocyanins bound to the pectin was significantly reduced. Extraction of citrus pectin using both the sulfurous acid method and the combined sulfurous acid and ascorbic acid method revealed that the polyphenol content in the pectin prepared by the combined method was significantly lower than that in hawthorn pectin, and slightly higher than that prepared by the sulfurous acid method alone. This is because the characteristic polyphenol of citrus peel is hesperidin, which is chemically stable and not easily oxidized. In the antioxidant system composed of ascorbic acid and sulfurous acid, it is more conducive to its stable existence in an intact form, while the content of anthocyanins and other substances in citrus is extremely low and negligible.

[0069] (3) The content of oxidized polyphenols and pigments (anthocyanins) in pectin was judged by the appearance of pectin. Take dried pectin samples from Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 8 respectively, and place them in transparent glass bottles (see...). Figure 5 ).

[0070] Depend on Figure 5 It can be visually determined from the color of the pectin that hawthorn pectin extracted using a combination of ascorbic acid and sulfite is the lightest in color, proving that the combination of sulfite and ascorbic acid can effectively inhibit the binding of oxidized polyphenols and pigments (anthocyanins) to pectin. However, the color difference of citrus pectin prepared using different methods is relatively small.

[0071] 3. Hawthorn pectin gel performance evaluation (1) The hawthorn pectin obtained in Example 1 and Comparative Examples 1-8 were dissolved in distilled water, and the mass volume concentration of pectin was 2%. The solution was stirred and dissolved for 8 hours. The pH of the solution was adjusted to 2 with 6 M hydrochloric acid. Sucrose was added so that its concentration in the final solution was 75% (w / v). The solution was stirred until the sucrose was completely dissolved and then allowed to stand at room temperature for 12 hours to form a stable gel.

[0072] The gel properties of pectin were tested using a texture analyzer. The gel sample used for structural testing had a diameter of 27 mm and a height of 18 mm. The hawthorn pectin gel was placed on a fixed base plate under a probe (P / 0.5 probe, 25 mm diameter), and pressure was applied until the deformation reached 40%. The speeds before, during, and after the test were set to 1.0, 1.0, and 1.0 mm / s, respectively. The triggering force was 1 g (0.0098 N), and the time between two loadings was 5 s. The gel hardness was calculated using Texture Expert 1.22 software (results are shown in...). Figure 1 , Figure 2 and Figure 3 ).

[0073] Depend on Figure 1 and Figure 2 It can be seen that the pectin gel prepared by sulfurous acid + ascorbic acid has a higher hardness than the gel hardness of pectin extracted by sulfurous acid method and hydrochloric acid method, which proves that the combination of sulfurous acid and ascorbic acid can effectively inhibit the binding of oxidized polyphenols and pigments (anthocyanins) with pectin and further improve the gel properties of pectin.

[0074] Depend on Figure 3 It can be seen that the hardness of citrus pectin prepared by different methods is not significantly different.

[0075] (2) Preparation of polyphenol-containing sulfite + ascorbic acid pectin gel: Add epicatechin, chlorogenic acid and proanthocyanidins to 2% pectin solution, stir and dissolve for 8 hours, adjust the pH of the solution to 2 with 6 M hydrochloric acid, add 75% sugar, stir until the sugar is completely dissolved, and let stand at room temperature for 12 hours to form a stable gel.

[0076] The gel properties of pectin were tested using a texture analyzer. The gel sample used for structural testing had a diameter of 27 mm and a height of 18 mm. The hawthorn pectin gel was placed on a fixed base plate under a probe (P / 0.5 probe, 25 mm diameter), and pressure was applied until the deformation reached 40%. The speeds before, during, and after the test were set to 1.0, 1.0, and 1.0 mm / s, respectively. The triggering force was 1 g (0.0098 N), and the time between two loadings was 5 s. The gel hardness was calculated using Texture Expert 1.22 software (results are shown in...). Figure 4 ).

[0077] Depend on Figure 4 It can be seen that adding polyphenols and anthocyanins, which are abundant in hawthorn, to the gel prepared by the sulfurous acid + ascorbic acid method with the highest gel hardness will cause a decrease in gel hardness. Therefore, polyphenols and anthocyanins will affect the gel strength of pectin.

[0078] In summary, as shown in Table 1, the extraction rates, degrees of esterification, and monosaccharide compositions of hawthorn pectin extracted with different acids were similar. Different acid extraction methods did not significantly affect the structure of hawthorn pectin, indicating that the structure of hawthorn pectin extracted with different acids does not affect its gel properties. However, from... Figure 4 There are significant differences in gel hardness between pectin extracted using different acids. Adding polyphenols and anthocyanins, abundant in hawthorn, to the gel prepared using the sulfite + ascorbic acid method (which has the highest gel hardness) shows that polyphenols and anthocyanins decrease gel hardness. Therefore, polyphenols and pigments (anthocyanins) affect the gel strength of pectin.

[0079] Based on the above, three methods were selected for extracting hawthorn and citrus pectin: hydrochloric acid (the most commonly used commercially available), sulfurous acid (which has reducing properties), and a combination of ascorbic acid and sulfurous acid (which has a stronger reducing system). Table 2 shows that for hawthorn pectin, the extraction rate of the combination of sulfurous acid and ascorbic acid was close to that of hydrochloric acid, but the content of polyphenols and anthocyanins bound to the pectin was significantly reduced. Visually, the color of the pectin extracted using the combination of ascorbic acid and sulfurous acid indicates that the hawthorn pectin is the lightest in color. Figure 5 The gel hardness of the pectin extracted using the sulfite method and the hydrochloric acid method was further improved compared to that extracted using the sulfite method and the hydrochloric acid method, proving that the combination of sulfite and ascorbic acid can effectively inhibit the binding of oxidized polyphenols and pigments (anthocyanins) with pectin, further improving the gel properties of pectin. The extraction of citrus pectin using the sulfite method and the combination of sulfite and ascorbic acid showed that the polyphenol content in the citrus pectin prepared by the combination method was significantly lower than that in hawthorn pectin, and slightly higher than that obtained by the sulfite method alone. This is because the characteristic polyphenol of citrus peel is hesperidin, which is chemically stable and not easily oxidized. In the antioxidant system composed of ascorbic acid and sulfite, it is more conducive to its stable existence in an intact form, while the content of anthocyanins and other substances in citrus is extremely low and negligible. Despite the difference in polyphenol content, the gel hardness of the citrus pectin obtained by the two methods did not show a significant difference, suggesting that anthocyanins may have a more significant effect on pectin.

[0080] This result contrasts sharply with the hawthorn system: in hawthorn, high levels of easily oxidized proanthocyanidins and polyphenols readily cross-link with pectin, severely degrading gel properties. In contrast, this compound system effectively blocks this process, significantly improving gel strength. This contrasting effect demonstrates that the present invention does not provide a universal strong reducing technique, but rather a targeted solution specifically addressing the bottleneck problem of gel degradation caused by the cross-linking of easily oxidized polyphenols and anthocyanins with pectin in hawthorn fruit, fully reflecting its raw material specificity and technological ingenuity.

Claims

1. An application of a sulfite-ascorbic acid synergistic system to increase the hardness of hawthorn pectin-acid gel with high gelling properties, characterized in that, include: L-ascorbic acid and sulfurous acid were added to hawthorn powder suspension to obtain a mixed solution. The pH of the mixed solution was adjusted to 1.5-2.5 with sulfurous acid. The mixed solution was placed in a sealed container and heated for extraction. After the heating reaction was completed, the mixed solution was cooled and centrifuged. The supernatant was added to anhydrous ethanol and allowed to stand. The precipitate was washed, dried, and hawthorn pectin was obtained.

2. The application according to claim 1, characterized in that, The mass-to-volume ratio of L-ascorbic acid to hawthorn pulp is 0.8–1 g: 1 L.

3. The application according to claim 1 or 2, characterized in that, The hawthorn powder suspension is prepared by mixing dried hawthorn powder and water, wherein the mass-to-volume ratio of the dried hawthorn powder to the water in the hawthorn powder suspension is 1g:20-30ml.

4. The application according to claim 3, characterized in that, The dried hawthorn powder is obtained by freeze-drying or baking pitted hawthorn fruits, followed by pulverizing and screening.

5. The application according to claim 1, characterized in that, The conditions for heating and extracting the mixed solution are 80℃~90℃ with stirring for 0.8~1.2 h.

6. The application according to claim 1, characterized in that, The ratio of the supernatant to the anhydrous ethanol is 1:1.8 to 2.2:2, and the mixture is allowed to stand at 4°C for ≥12 h.

7. The application according to claim 1, characterized in that, The centrifugation conditions are: rotation speed ≥ 5000 rpm / min, centrifugation time ≥ 10 min.

8. A type of hawthorn pectin, characterized in that, The hawthorn pectin is prepared using any one of claims 1-7; the polyphenol content in the hawthorn pectin is ≤1.88%, and the proanthocyanidin content is ≤1.40%; the pectin gel prepared from the hawthorn pectin with a pectin mass-volume concentration of 2% has a hardness ≥3.08N.

9. The application of hawthorn pectin according to claim 8 in the production of high-hardness soft candy.

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