Method for rapidly extracting pectin crude extract from citrus peel

Abstract

The invention discloses a method for rapidly extracting a pectin crude extract from citrus pericarp, and belongs to the technical field of citrus pectin extraction. The preparation method comprises the following specific steps: S1, freeze-drying and crushing citrus peel to obtain a solid material; s2, the solid material obtained in the step S1 is soaked in distilled water, after soaking is finished, liquid separation is conducted, an upper-layer water phase is collected, and a liquid material is obtained after centrifugation; s3, edible alcohol is added into the liquid material obtained in the step S2 for precipitation, and after precipitation is finished, a pectin crude extract is obtained through centrifugal separation. According to the method disclosed by the invention, the pectin is rapidly extracted by virtue of a simple process of freeze-drying, water extraction and alcohol precipitation aiming at agricultural waste, namely citrus peel, so that the problems of environmental pollution and resource waste in traditional waste treatment are solved by virtue of a simple scheme; by means of freeze-drying keep-alive and green solvent combination, operation is simplified, cost is low, efficient preparation, environmental protection and safety are both considered, operation is easy and convenient, popularization is easy, and industrial production requirements are met.

Description

Technical Field

[0001] The invention belongs to the technical field of citrus pectin extraction, and in particular relates to a method for quickly extracting crude pectin from citrus peels. Background Art

[0002] Natural pectin is a high-molecular-weight compound found extensively in plant cell walls, particularly in fruit peels and juices. Due to its excellent gelling, thickening, and stabilizing properties, pectin has found widespread application in food, medicine, cosmetics, and other fields. Pectin's primary component is a high-molecular-weight compound derived from the polymerization of galacturonic acid. Depending on its degree of polymerization, pectin can be divided into oligomeric pectins and high-molecular-weight pectins. Oligomeric pectins have excellent water solubility and rheological properties, making them useful as thickeners and suspending agents; high-molecular-weight pectins, on the other hand, possess a strong gelling ability and are used in the production of jams, jellies, and dairy products. Citrus peel, an agricultural waste product, accounts for 20%-30% of the total weight of citrus fruit and contains various substances, including pectin. Utilizing citrus peel not only mitigates environmental pollution but also allows the production of high-value products such as pectin.

[0003] Currently, pectin extraction methods are divided into traditional and novel extraction methods. Among traditional extraction methods, water extraction, acid extraction, alkaline extraction, and chelating agent extraction are the most commonly used. Compared to acid extraction (commonly used acids include nitric acid, hydrochloric acid, and sulfuric acid), alkaline extraction (commonly used alkalis include sodium hydroxide and potassium hydroxide), and chelating agent extraction (commonly used chelating agents include sodium hexametaphosphate and ammonium oxalate), which require the addition of additional chemical reagents, water extraction is divided into heating extraction and cold water extraction. While the absence of additional chemical reagents is more environmentally friendly, prolonged heating can cause pectin breakage and reduce the degree of polymerization, while cold water extraction can result in excessively long extraction times. Novel extraction methods include enzymatic extraction (commonly used enzymes include cellulase, papain, and amylase), ultrasound-assisted extraction, microwave-assisted extraction, supercritical water extraction, and subcritical water extraction. While these novel extraction methods avoid the introduction of exogenous chemicals, their high production costs hinder their widespread adoption.

[0004] Based on this, it is extremely important to provide a method for extracting citrus pectin that is efficient, green, environmentally friendly, simple, easy to use and low-cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for quickly extracting crude pectin from citrus peels, which has the characteristics of high preparation efficiency, green environmental protection, etc., and is simple to operate and low in cost, and has a guiding role in the development and utilization of citrus peel pectin.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for rapidly extracting crude pectin from citrus peels comprises the following steps:

[0008] S1. The citrus peel is freeze-dried and crushed to obtain a solid material;

[0009] S2. The solid material obtained in step S1 was soaked in distilled water. After soaking, the liquid phase was separated and the upper aqueous phase was collected and centrifuged to obtain a liquid material;

[0010] S3. Add edible alcohol to the liquid material obtained in step S2 for precipitation. After precipitation, obtain a crude pectin extract by centrifugation.

[0011] In the present application, freeze-drying technology is adopted in step S1 to make the moisture in citrus peel quickly sublime, pectin molecules are avoided from chain scission due to high temperature, and the peel structure after freeze-drying is loose simultaneously, and can form finer powder after pulverizing, increase the contact area with distilled water, for subsequent dissolving and extracting and laying the foundation. In step S2, using distilled water as solvent, the water-soluble pectin in the solubility peel powder can be dissolved, and liquid separation centrifugation after immersion can separate solid residue (such as insoluble impurities such as cellulose, lignin) and liquid material (the aqueous phase containing pectin), and realize preliminary purification. Edible alcohol is added in step S3, the solubility of pectin in water (hydrogen bonding between pectin molecules is enhanced, and polymerization precipitation occurs) can be reduced, and small molecule impurities (such as monosaccharide, inorganic salt) are still dissolved in alcohol-water mixed system, and pectin crude extract is obtained by centrifugation, and the separation of pectin and small molecule impurities is realized.

[0012] In summary, the present invention targets citrus peel, an agricultural waste, and realizes rapid extraction of pectin through a simple process of freeze-drying-water extraction-alcohol precipitation. It not only solves the dual problems of environmental pollution and resource waste in traditional waste treatment with a simple solution, but also conforms to the concept of circular economy. It also takes into account efficient preparation and environmental protection and safety by relying on freeze-drying preservation, green solvent combination (distilled water + edible alcohol), simplified operation and low cost (no complex equipment required), and is simple to operate and easy to promote, adapting to the needs of industrial production.

[0013] As some possible implementation methods of the present application, in step S1, ultra-low temperature liquid nitrogen freeze-drying technology is used. Specifically, citrus peels (such as grapefruit, blood orange, pomelo, and mandarin orange) are placed in a liquid nitrogen environment at -190°C to -196°C and quickly frozen for 10-15 minutes to instantly crystallize the moisture in the peel; then transferred to a low-temperature freeze drying box, sublimation drying is carried out for 2.5-3 hours at a vacuum degree of 15-25Pa to reduce the moisture content of the material to below 5%. This technology avoids the breakage of pectin molecules due to high temperature by using extremely low temperature, and at the same time makes the peel structure loose after freeze-drying, which is convenient for crushing into fine powder, laying the foundation for subsequent distilled water immersion extraction.

[0014] As some possible implementation methods of the present application, in step S2, the liquid-to-solid material ratio of distilled water is 10-15 mL:1 g; and the distilled water soaking time is 20-25 h.

[0015] As some possible implementation methods of the present application, in the centrifugation steps of step S2 and step S3, the centrifugal speed is 5000-10000 r / min, and the centrifugation time is 3-6 min.

[0016] As some possible implementation methods of the present application, in step S3, the amount of edible alcohol added is 2-5 times the volume of the liquid material.

[0017] As some possible implementation methods of the present application, in step S3, the crude pectin extract is freeze-dried to a constant weight. In this solution, the crude pectin extract is freeze-dried in a vacuum to remove residual alcohol and moisture, prevent mildew, and effectively extend the shelf life of the crude pectin extract.

[0018] As some possible implementation methods of the present application, in step S1, the crushed material is soaked in edible alcohol with a volume fraction of 25-40% for 1-2 hours, and then filtered through a 200-300 mesh 316 stainless steel mesh to obtain a solid material.

[0019] Citrus peel contains a large amount of fat-soluble impurities (such as epidermal wax, carotenoids, phytosterols, etc.). Although these impurities are insoluble in water during the subsequent distilled water soaking step S2, they will remain in the aqueous phase in the form of suspended matter, resulting in a dark color of the crude pectin extract (such as dark yellow pectin from orange peel) and affecting the uniformity of the gel (wax will destroy the pectin network structure), resulting in poor product purity and appearance.

[0020] Based on this, the present invention introduces edible alcohol with a volume fraction of 25-40%, which can specifically dissolve fat-soluble impurities, effectively improve the removal rate of fat-soluble impurities, make the color of the crude pectin extract lighter (such as blood orange pectin from light red to light pink), improve the uniformity of the gel, and reduce the subsequent pigment adsorption pressure of activated carbon.

[0021] As some feasible embodiments of the present application, in step S1, the liquid-solid ratio of edible alcohol with a volume fraction of 25-40% to the crushed material is 5mL:(0.5-1.5)g.

[0022] As some possible implementation methods of the present application, in step S2, the aqueous phase after centrifugation is treated as follows:

[0023] First, adjust the pH to 3.5-4.0 with 0.8-1.5% citric acid solution, then add 0.05%-0.1% modified activated carbon based on the mass of the aqueous phase and 0.1-0.15% sodium chloride based on the mass of the aqueous phase, stir thoroughly, and centrifuge to obtain a liquid material;

[0024] The modified activated carbon is obtained by modifying activated carbon with 0.3-0.8% by mass of citric acid.

[0025] The natural pH of the aqueous phase mixture of citrus peel fluctuates greatly due to differences in varieties (for example, the pH of grapefruit is about 3.0, and the pH of mandarin orange is about 4.0). Pectin molecules are prone to hydrolysis (glycosidic bond breakage) in a strongly acidic (pH < 3.0) or weakly alkaline (pH > 4.5) environment, resulting in a decrease in the degree of polymerization (especially the gel activity of high-polymer pectin depends on the long-chain structure). If the pH is not controlled, the pectin yield and activity will be unstable.

[0026] Based on this, the present invention adjusts the pH to 3.5-4.0 to stabilize the pectin molecules in this pH range. Adjusting the pH by citric acid can avoid pectin hydrolysis, thereby reducing the pectin molecular chain breakage rate, and improving the high-polymer pectin retention rate and gel strength.

[0027] In addition, water-soluble pigments in the citrus aqueous phase (such as anthocyanins and hesperidin in blood oranges) are difficult to be completely adsorbed by unmodified activated carbon, resulting in uneven color of the pectin crude extract (such as light red or yellow-brown), affecting the appearance quality of food-grade pectin. At the same time, the porous structure of unmodified activated carbon will non-selectively adsorb some pectin (especially oligomeric pectin), resulting in a reduced pectin yield. Based on this, the present invention uses citric acid to modify activated carbon, which can introduce carboxyl groups on the activated carbon surface, reducing the adsorption of negatively charged pectin molecules through charge repulsion, while enhancing the targeted adsorption of polar pigment molecules, thereby effectively improving the removal rate of water-soluble pigments (such as the color of blood orange pectin close to white), pectin yield, and pectin purity.

[0028] Furthermore, pectin molecules in the aqueous phase are negatively charged due to the ionization of carboxyl groups, and are easily electrostatically adsorbed with the positive potential points on the surface of activated carbon (especially the small amount of positive groups remaining after modification), resulting in part of the pectin being retained by the modified activated carbon, especially the low-molecular-weight pectin (with higher charge density).

[0029] Based on this, the present invention introduces sodium chloride, the Na + It can neutralize the negative charge of pectin molecules, reduce the electrostatic attraction between them and modified activated carbon, and further increase the pectin yield (especially the oligomeric pectin is more completely retained) without affecting the adsorption efficiency of modified activated carbon on pigments.

[0030] As some feasible implementation methods of the present application, the specific steps of step S3 are: adding 1-2 times the volume of edible alcohol to the liquid material obtained in step S2, standing at 0-4°C for 45min-70min, then filtering and adding edible alcohol to the filter residue, the liquid-to-material ratio of edible alcohol to the filter residue is 1-3mL:1g, then freezing at -6 to -3°C for 25-35min, and finally centrifuging to obtain a crude pectin extract.

[0031] The aqueous phase of citrus pectin contains small molecular impurities (such as monosaccharides, oligosaccharides, and organic acids). These impurities can still be dissolved in high-concentration edible alcohol. However, if precipitated in one step, the sudden increase in alcohol concentration will cause some small molecular impurities to co-precipitate with the pectin (especially low-molecular pectin, which is easy to wrap impurities), reducing the purity.

[0032] Based on this, the present invention first introduces 1-2 times the volume of edible alcohol, which can fully dissolve small molecular impurities (pectin has a high solubility at this concentration and is not easy to precipitate). The low temperature of 0-4°C can reduce the solubility of impurities and promote their diffusion into the solution, thereby reducing impurity interference for subsequent pectin precipitation.

[0033] After the initial precipitation, a small amount of pectin still remains in the residual liquid (especially high-polymer pectin is not completely dissolved at low alcohol concentrations), and the pectin molecules are easily partially degraded due to thermal motion at room temperature, affecting the gel activity.

[0034] Based on this, the present invention can significantly reduce the solubility of pectin by adding 1-3 times the volume of edible alcohol again, and freezing at -6 to -3°C can promote the formation of a stable hydrogen bond network between pectin molecules (accelerate polymerization precipitation), while low temperature inhibits pectinase activity.

[0035] In summary, the present invention can significantly increase the pectin precipitation rate by adding edible alcohol in batches.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. Efficient preparation: Liquid nitrogen freeze-drying is used to quickly dehydrate citrus peels while retaining pectin activity. The powder formed after crushing is fully contacted with distilled water, and efficient separation is achieved through soaking and centrifugation. Combined with edible alcohol precipitation and centrifugation, the overall process is simple, with low equipment requirements and high extraction rate, which is suitable for rapid preparation needs.

[0038] 2. Safe preparation: The entire process uses a solvent combination of "distilled water + edible alcohol" without the intervention of acids, alkalis or chemical chelating agents to avoid chemical contamination. Residual alcohol can be removed through freeze-vacuum drying. The resulting crude pectin extract is highly safe and meets food-grade application standards.

[0039] 3. Low cost: No expensive equipment or reagents such as enzymatic methods and ultrasound-assisted methods are required. It only relies on conventional freeze-drying, centrifugal equipment and cheap solvents (distilled water, edible alcohol), which significantly reduces the company's production costs.

[0040] 4. Waste resource utilization: For citrus peel waste, a simple process is used to turn waste into treasure, which not only solves the problems of environmental pollution and resource waste in traditional treatment, but also conforms to the concept of circular economy.

[0041] In summary, this solution integrates basic technologies such as freeze-drying, water extraction, and alcohol precipitation. While ensuring safety and extraction efficiency, it lowers the threshold for industrialization with its low cost and easy operation, and has both environmental and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a crude extract of blood orange pectin;

[0043] Figure 2 It is a crude extract of grapefruit pectin;

[0044] Figure 3 It is crude extract of pectin from citrus aurantium;

[0045] Figure 4 It is a crude extract of pectin from Wogan.

[0046] Figure 5 For blood orange pectin gel formation test;

[0047] Figure 6 This is a test for the gel formation of grapefruit pectin;

[0048] Figure 7 This is a test for the gel formation of pectin from the rake mandarin orange;

[0049] Figure 8 This is a test on the gel formation of Wogan pectin. DETAILED DESCRIPTION

[0050] Example 1 (Grapefruit Peel)

[0051] S1: 4 g of grapefruit peel was taken, the white sponge layer removed, freeze-dried using ultra-low temperature liquid nitrogen freeze-drying technology, and then fully ground using a grinder to obtain a solid material;

[0052] S2: Add 40 mL of distilled water to the solid material obtained in step S1 and soak at room temperature for 24 hours; after soaking, separate the liquids and collect the upper aqueous phase, and centrifuge at 10,000 rpm for 3 minutes to obtain a liquid material;

[0053] S3: Add 2 times the volume of edible alcohol to the liquid material obtained in step S2, mix well and centrifuge at 10000r / min for 3min. The obtained precipitate is the crude extract of grapefruit pectin. Figure 1 shown.

[0054] Example 2 (Blood Orange Peel)

[0055] S1: Take 4g of blood orange peel, freeze-dry it using ultra-low temperature liquid nitrogen freeze-drying technology, and grind it thoroughly with a grinder to obtain a solid material;

[0056] S2: Add 40 mL of distilled water to the solid material obtained in step S1 and soak at room temperature for 24 hours; after soaking, separate the liquids and collect the upper aqueous phase, and centrifuge at 10,000 rpm for 3 minutes to obtain a liquid material;

[0057] S3: Add 2 times the volume of edible alcohol to the liquid material obtained in step S2, mix well, and centrifuge at 10000r / min for 3min. The resulting precipitate is the crude extract of blood orange pectin. Figure 2 shown.

[0058] Example 3 (Pomelo peel)

[0059] S1: 4 g of citrus peel was freeze-dried using ultra-low temperature liquid nitrogen freeze-drying technology, and then fully ground using a grinder to obtain a solid material;

[0060] S2: Add 40 mL of distilled water to the solid material obtained in step S1 and soak at room temperature for 24 hours; after soaking, separate the liquids and collect the upper aqueous phase, and centrifuge at 10,000 rpm for 3 minutes to obtain a liquid material;

[0061] S3: Add 2 times the volume of edible alcohol to the liquid material obtained in step S2, mix well and centrifuge at 10000r / min for 3min. The obtained precipitate is the crude extract of pectin from citrus aurantium. Figure 3 shown.

[0062] Example 4 (Mandarin orange peel)

[0063] S1: Take 4g of Wogan peel, freeze-dry it using ultra-low temperature liquid nitrogen freeze-drying technology, and grind it thoroughly with a grinder to obtain a solid material;

[0064] S2: Add 40 mL of distilled water to the solid material obtained in step S1 and soak at room temperature for 24 hours; after soaking, separate the liquids and collect the upper aqueous phase, and centrifuge at 10,000 rpm for 3 minutes to obtain a liquid material;

[0065] S3: Add 2 times the volume of edible alcohol to the liquid material obtained in step S2, mix well and centrifuge at 10000r / min for 3min. The obtained precipitate is the crude extract of Wogan pectin. Figure 4 shown.

[0066] The gel formation tests of the crude pectin extracts obtained in Examples 1-4 were performed as follows: Figure 5-8 As shown, through Figure 5-8 It can be seen that the gels formed by the crude pectin extracts of Examples 1-4 have uniform textures, and the pectin gel properties of different citrus varieties vary, which is related to the pectin polymerization degree and composition of the variety itself.

[0067] Example 5 (Grapefruit Peel)

[0068] S1: 4 g of grapefruit peel with the white sponge layer removed was freeze-dried with liquid nitrogen and then ground into powder. The peel was then soaked in 30% ethanol (liquid-to-solid ratio: 5 mL:1 g) for 1.5 h and filtered through a 200-mesh 316 stainless steel mesh to obtain a solid material.

[0069] S2: distilled water (liquid-to-solid ratio of 10 mL: 1 g) was added to the solid material obtained in step S1, and the mixture was soaked at room temperature for 24 h; the upper aqueous phase was separated and collected, and the mixture was centrifuged at 10,000 rpm for 3 min. The aqueous phase after centrifugation was adjusted to pH 3.8 with 1.0 wt% citric acid solution, and 0.08% modified activated carbon and 0.12% sodium chloride were added to the aqueous phase by weight. The mixture was stirred for 10 min and then centrifuged to obtain a liquid material;

[0070] S3: adding 1.5 times the volume of edible alcohol to the liquid material obtained in step S2, allowing the mixture to stand at 0° C. for 60 min, filtering, adding 2 times the volume of edible alcohol to the residue, freezing the mixture at -5° C. for 30 min, and centrifuging the mixture at 10,000 rpm for 3 min to obtain a crude pomelo pectin extract.

[0071] The preparation method of modified activated carbon is as follows:

[0072] Take 20-40 mesh granular coconut shell activated carbon, rinse it with deionized water three times, and place it in a 50°C oven to dry for 6-8 hours to remove surface water and light impurities to obtain pretreated activated carbon. Then, the pretreated activated carbon is mixed with a 0.5% mass fraction of citric acid solution at a solid-liquid ratio of 1:15 (g / mL) and stirred in a constant temperature water bath at 40-50°C for 2.5 hours (stirring rate 2500r / min). Then filter it with qualitative filter paper, wash it with deionized water until the filtrate pH is 4.5-5.0, and then place the activated carbon in a vacuum drying oven at 60°C to dry for 5.5 hours to obtain modified activated carbon.

[0073] Example 6 (Blood Orange Peel)

[0074] S1: 4 g of blood orange peel was freeze-dried with liquid nitrogen and then ground into powder. The peel was then soaked in 35% alcohol (liquid-to-solid ratio: 5 mL:1 g, i.e., 20 mL of alcohol corresponds to 4 g of the material) for 1 h. The solid material was filtered through a 250-mesh 316 stainless steel mesh.

[0075] S2: distilled water (liquid-to-solid ratio of 10 mL: 1 g) was added to the solid material obtained in step S1, and the mixture was soaked at room temperature for 24 h; the upper aqueous phase was separated and collected, and the mixture was centrifuged at 10,000 rpm for 3 min. The aqueous phase after centrifugation was adjusted to pH 3.8 with 1.0 wt% citric acid solution, and 0.08% modified activated carbon (prepared as in Example 5) and 0.12% sodium chloride were added to the aqueous phase by weight, and the mixture was stirred for 10 min and centrifuged to obtain a liquid material;

[0076] S3: adding 1 volume of edible alcohol to the liquid material obtained in step S2, allowing the mixture to stand at 2° C. for 50 minutes, filtering, adding 2.5 volumes of edible alcohol to the residue, freezing the mixture at -4° C. for 30 minutes, and centrifuging the mixture at 10,000 rpm for 3 minutes to obtain a crude blood orange pectin extract.

[0077] Example 7 (Pomelo peel)

[0078] S1: 4 g of citrus peel was freeze-dried with liquid nitrogen and then ground into powder. The mixture was soaked in 25% ethanol for 2 h (liquid-to-solid ratio: 5 mL:1.2 g, i.e., 17 mL of ethanol corresponds to 4 g of material). The solid material was filtered through a 300-mesh 316 stainless steel mesh to obtain a solid material.

[0079] S2: distilled water (liquid-to-solid ratio of 10 mL: 1 g) was added to the solid material obtained in step S1, and the mixture was soaked at room temperature for 24 h; the upper aqueous phase was collected by separation, and the mixture was centrifuged at 10,000 r / min for 3 min. The aqueous phase after centrifugation was adjusted to pH 3.8 with 1.0 wt% citric acid solution, and 0.08% modified activated carbon (prepared by the same method as in Example 5) and 0.12% sodium chloride were added to the aqueous phase by weight. The mixture was stirred for 10 min and then centrifuged to obtain a liquid material;

[0080] S3: Add 2 times the volume of edible alcohol to the liquid material obtained in step S2, let it stand at 4°C for 60 minutes, add 1.5 times the volume of edible alcohol to the residue after filtering, freeze it at -3°C for 35 minutes, and centrifuge it at 10,000 r / min for 3 minutes to obtain a crude extract of pectin from the mandarin orange.

[0081] Example 8 (Mandarin orange peel)

[0082] S1: 4 g of mandarin orange peel was freeze-dried with ultra-low temperature liquid nitrogen and then crushed. The mixture was soaked in 40% edible alcohol for 1 h (liquid-solid ratio 5 mL:0.8 g, i.e., 25 mL of alcohol corresponds to 4 g of material). The solid material was filtered through a 250-mesh 316 stainless steel mesh.

[0083] S2: distilled water (liquid-to-solid ratio of 10 mL: 1 g) was added to the solid material obtained in step S1, and the mixture was soaked at room temperature for 24 h; the upper aqueous phase was collected by separation, and the mixture was centrifuged at 10,000 r / min for 3 min. The aqueous phase after centrifugation was adjusted to pH 3.8 with 1.0 wt% citric acid solution, and 0.08% modified activated carbon (prepared by the same method as in Example 5) and 0.12% sodium chloride were added to the aqueous phase by weight. The mixture was stirred for 10 min and then centrifuged to obtain a liquid material;

[0084] S3: Add 1.2 times the volume of edible alcohol to the liquid material obtained in step S2, let it stand at 1°C for 55 minutes, add 3 times the volume of edible alcohol to the residue after filtering, freeze it at -6°C for 25 minutes, and centrifuge it at 10,000 r / min for 3 minutes to obtain a crude extract of Wogan pectin.

[0085] Experimental Example: The key data (wet weight state, not dried) of the crude pectin extracts of Examples 1-8 were collated and analyzed.

[0086] Among them, the key data include: the precipitate mass, purity (galacturonic acid content as the core indicator, determined by carbazole colorimetry) and actual pectin yield (actual pectin amount = precipitate mass × purity) of the original process (Examples 1-4) and the improved process (Examples 5-8). The results are shown in Table 1.

[0087] Table 1:

[0088]

[0089]

[0090] The data in Table 1 are analyzed as follows:

[0091] 1. Example 1 vs. Example 5:

[0092] Example 1: Only water extraction and single alcohol precipitation were performed, and a small amount of cellulose and pigment impurities were contained in the precipitate, resulting in limited purity. The actual pectin amount was 2.115 g.

[0093] Example 5: Pretreatment with edible alcohol removes fat-soluble impurities (such as naringin) and reduces non-pectin components in the subsequent precipitation. Modified activated carbon is used to adsorb residual pigments, and citric acid is used to adjust the pH to the optimal pectin precipitation point to promote pectin molecular aggregation.

[0094] Compared with Example 1, the pectin purity (47%→66%) and the actual pectin amount (2.115→2.77 g) in Example 5 were both improved, achieving a double increase in purity and yield.

[0095] 2. Example 2 vs Example 6:

[0096] Example 2: Blood orange anthocyanidins were co-precipitated with pectin, resulting in extremely low purity (37%), with the actual pectin amount being only 1.295 g, and the pigment residues affecting the pectin quality.

[0097] Example 6: Pretreatment with edible alcohol initially removes water-soluble anthocyanins, reducing pigment interference in subsequent precipitation. Modified activated carbon deeply adsorbs residual anthocyanins, while citric acid pH control prevents pectin degradation.

[0098] Compared with Example 2, the purity (37%→55%) and the actual pectin amount (1.295→1.76 g) of Example 6 were both improved, solving the problem of difficult purification of high-pigment raw material pectin.

[0099] 3. Examples 3 and 4 vs. Examples 7 and 8:

[0100] Examples 3 and 4: only water extraction + single alcohol precipitation, the pectin dissolution is insufficient (the precipitate mass is only 0.5g), and the actual pectin amount (0.21g, 0.20g) cannot be used industrially.

[0101] Examples 7 and 8: Pretreatment with edible alcohol can dissolve substances that inhibit pectin dissolution (such as oligosaccharides and proteins), thereby improving pectin extraction efficiency. Modified activated carbon removes insoluble impurities such as lignin fragments (from tangerine peel) and wax (from tangerine peel), reducing the ineffective mass in the precipitate.

[0102] Compared with Examples 3 and 4, the precipitate mass (0.5→1.3g, 1.1g), actual pectin amount (0.21g→0.69g; 0.2g→0.55g) and purity in Examples 7 and 8 were all improved, breaking through the bottleneck of low pectin raw material extraction.

[0103] In summary, Examples 5-8 significantly improved the purity and yield of pectin through the synergistic strategy of pretreatment and impurity removal → directional purification → gradient enrichment, solving the technical problem of "purity and yield being mutually exclusive" in traditional processes.

Claims

1. A method for rapidly extracting crude pectin from citrus peels, characterized in that: The steps include: S1. The citrus peel is freeze-dried and crushed to obtain a solid material; S2. The solid material obtained in step S1 was soaked in distilled water. After soaking, the liquid phase was separated and the upper aqueous phase was collected and centrifuged to obtain a liquid material; S3. Add edible alcohol to the liquid material obtained in step S2 for precipitation. After precipitation, obtain a crude pectin extract by centrifugation.

2. The method for rapidly extracting crude pectin from citrus peels according to claim 1, characterized in that: In step S1, ultra-low temperature liquid nitrogen freeze-drying technology is used.

3. The method for rapidly extracting crude pectin from citrus peels according to claim 1, characterized in that: In step S2, the liquid-to-solid ratio of distilled water to solid material is 10-15 mL:1 g; and the distilled water soaking time is 20-25 h.

4. The method for rapidly extracting crude pectin from citrus peels according to claim 1, characterized in that: In the centrifugation steps of step S2 and step S3, the centrifugal speed is 5000-10000 r / min and the centrifugal time is 3-6 min.

5. The method for rapidly extracting crude pectin from citrus peels according to claim 1, characterized in that: In step S3, the amount of edible alcohol added is 2-5 times the volume of the liquid material.

6. The method for rapidly extracting crude pectin from citrus peels according to claim 1, characterized in that: In step S3, the crude pectin extract is freeze-dried to a constant weight.

7. The method for rapidly extracting crude pectin from citrus peels according to claim 1, characterized in that: In step S1, the crushed material is soaked in edible alcohol with a volume fraction of 25-40% for 1-2 hours, and then filtered through a 200-300 mesh 316 stainless steel mesh to obtain a solid material.

8. The method for rapidly extracting crude pectin from citrus peels according to claim 7, characterized in that: In step S1, the liquid-solid ratio of edible alcohol with a volume fraction of 25-40% to the crushed material is 5mL:(0.5-1.5)g.

9. The method for rapidly extracting crude pectin from citrus peels according to claim 7, characterized in that: In step S2, the aqueous phase after centrifugation is treated as follows: First, adjust the pH to 3.5-4.0 with 0.8-1.5% citric acid solution, then add 0.05%-0.1% modified activated carbon based on the mass of the aqueous phase and 0.1-0.15% sodium chloride based on the mass of the aqueous phase, stir thoroughly, and centrifuge to obtain a liquid material; The modified activated carbon is obtained by modifying activated carbon with 0.3-0.8% by mass of citric acid.

10. The method for rapidly extracting crude pectin from citrus peels according to claim 9, characterized in that: The specific steps of step S3 are: adding 1-2 times the volume of edible alcohol to the liquid material obtained in step S2, standing at 0-4°C for 45min-70min, then filtering and adding edible alcohol to the filter residue, the liquid-to-material ratio of edible alcohol to the filter residue is 1-3mL:1g, then freezing at -6 to -3°C for 25-35min, and finally centrifuging to obtain a crude pectin extract.

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