A method for extracting pectin from sweet potato waste residue using lactic acid bacteria fermentation

Abstract

The present invention relates to a method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation, comprising sweet potato residue pretreatment, lactic acid bacteria fermentation, ultrasonic-assisted extraction, centrifugal separation, alcohol precipitation, cleaning and drying, and finally crushing the dried pectin to obtain sweet potato pectin raw gum. The pectin yield and purity of the present invention are higher than those of conventional acid extraction, the lactic acid bacteria fermentation process is safer, the generation of wastewater in the processing process is reduced, environmental pollution is alleviated, and it is harmless to the human body. In addition, the sweet potato waste residue after producing pectin can be used as animal feed, thereby increasing the added value and economic benefits of sweet potatoes.

Description

Technical Field

[0001] The invention relates to the technical field of pectin extraction, and in particular to a method for extracting pectin from sweet potato waste residue by utilizing lactic acid bacteria fermentation. Background Art

[0002] Pectin is an important component of plant cell walls. The peels of citrus, grapefruit, lemon and apples are rich in pectin. The main sources of commercially available pectin are the peels of citrus fruits and apple peels. At present, sweet potatoes are still one of the most important food crops. Most sweet potatoes are used to process and produce starch, and a large amount of sweet potato waste is produced during the processing. Sweet potato waste contains a lot of water and corrupt microorganisms. If not handled in time, it will produce a foul odor due to corruption and pollute the environment. Due to technical limitations, only a small amount of potato residue is used as feed or organic fertilizer, and it cannot be fully utilized. The sweet potato waste residue after sweet potato starch production contains rich natural low-ester pectin, with a content of about 10% to 30%, which can be used as a source of raw materials for pectin production.

[0003] Common pectin production methods include acid hydrolysis, microbial method, metal chelating agent method and enzyme method. Domestic production mainly uses acid hydrolysis, which is convenient, fast and easy to operate, and usually uses strong acid extraction and ethanol precipitation. Conventional acid hydrolysis method for preparing pectin uses strong acids such as nitric acid, which has high action intensity, low yield, unstable quality, and many problems such as difficult recovery and disposal after use, and environmental pollution. Summary of the invention

[0004] The purpose of the present invention is to provide a method for extracting pectin from sweet potato waste residue by using lactic acid bacteria fermentation, which replaces traditional strong acid hydrolysis to produce sweet potato pectin, has high yield and good quality, and improves the added value and economic benefits of sweet potatoes.

[0005] The technical solution of the present invention:

[0006] A method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation comprises the following steps:

[0007] Step 1: Grind the sweet potato residue, add a certain proportion of water to the sweet potato residue to form a suspension, heat to 70°C, add a certain proportion of α-amylase, and maintain a constant temperature of 70°C and stir for 1 hour.

[0008] Step 2, transferring the sweet potato residue suspension treated in step 1 to a fermentation tank for sterilization, cooling to about 40° C., inoculating Lactobacillus plantarum LD1.0026 fermentation liquid, wherein the inoculation amount of Lactobacillus plantarum LD1.0026 fermentation liquid is 3-5% of the volume of the sweet potato residue suspension, and culturing at 37° C. for 4-6 hours;

[0009] Step 3, heating the liquid obtained in step 2 to 80-100°C, and extracting it by ultrasonic assisted extraction for 90 minutes to fully dissolve the pectin; destroying the mutual links between the original pectin and other polysaccharide molecules by hydrolysis to release the pectin;

[0010] Step 4, centrifuge the mixture after water bath extraction in step 3 at 9000g for 30 min, remove the precipitate, and take the supernatant;

[0011] Step 5, mixing the supernatant obtained in step 4 with 75% to 80% ethanol in a certain proportion, and standing at 4°C for 80 minutes to fully precipitate; adding ethanol to the aqueous solution of pectin to form an alcohol-water mixed system, so that the pectin is precipitated;

[0012] Step 6, centrifuge the mixed solution obtained after step 5 at 9000g for 30 minutes, remove the supernatant, and the precipitate is the crude extracted pectin, add an appropriate amount of 75% to 80% ethanol to wash the precipitate, repeat step 6 to wash the precipitate twice, and dry to obtain pectin;

[0013] Step 7: Grind the pectin obtained in step 6 to obtain sweet potato pectin.

[0014] The classification of Lactobacillus plantarum LD1.0026 in step 2 is named as Lactobacillus plantarum Lactiplantibacillus plantarum , deposited on August 14, 2024 in the General Microbiology Center of China Microorganism Culture Collection Administration, with the deposit address in Beijing, China, and the deposit number is CGMCC No.31579.

[0015] Furthermore, in step 1, the volume ratio of sweet potato residue to water is 1:9, and the amount of α-amylase added is 0.1% to 0.3% of the mass of the sweet potato residue.

[0016] The volume ratio of sweet potato residue to water is 1:9, which helps the starch in the sweet potato residue to fully dissolve in water, facilitating subsequent enzymatic hydrolysis reactions.

[0017] α-amylase is an enzyme that can hydrolyze starch and break it down into small molecular sugars such as maltose. In the process of sweet potato residue treatment, adding an appropriate amount of α-amylase can accelerate the hydrolysis reaction of starch and improve the hydrolysis efficiency. The addition amount is controlled between 0.1% and 0.3% of the mass of the sweet potato residue, which can ensure the enzymatic reaction without causing enzyme waste.

[0018] α-Amylase has optimal activity within a specific pH range. Therefore, during the treatment process, the pH value of the solution needs to be adjusted to an appropriate range (usually 6.0-7.0) to ensure that the enzymatic hydrolysis reaction proceeds smoothly.

[0019] Furthermore, in step 2, the sterilization condition is 121° C. for 20 min, and the inoculation amount of Lactobacillus plantarum is 3% to 5% of the volume of the sweet potato residue suspension.

[0020] Furthermore, the ratio of the supernatant obtained in step 5 to 75% to 80% ethanol is 2:3.

[0021] Furthermore, in step 6, the drying temperature is 45-60°C.

[0022] The present invention also provides pectin prepared by the preparation method and its application in food, medical treatment, daily chemical and textile industries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The pectin prepared by the method of the present invention has higher yield and purity than pectin extracted by conventional acid method, the lactic acid bacteria fermentation process is safer, the generation of waste water in the processing process is reduced, environmental pollution is alleviated, and it is harmless to the human body. The sweet potato waste residue after producing pectin can be used as animal feed, thereby improving the added value and economic benefits of sweet potatoes.

[0025] During the fermentation process, lactic acid bacteria convert sugars in sweet potato residues into lactic acid through metabolic activities, thus creating a suitable acidic environment, inhibiting the growth of other microorganisms and ensuring the purity and effect of fermentation. In addition, the production of lactic acid also helps to improve the extraction efficiency of pectin. Compared with traditional acid extraction, lactic acid bacteria fermentation not only increases the yield and purity of pectin, but also makes the extraction process more environmentally friendly and safe.

[0026] Lactic acid bacteria ferment and metabolize the sugar in the sweet potato residue to produce metabolites such as lactic acid, which lowers the pH value and promotes the dissolution of pectin. At the same time, they secrete enzymes that help break down cell walls, thereby improving the extraction efficiency and quality of pectin. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a real picture of the sweet potato residue pectin extracted by lactic acid bacteria fermentation in the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0029] Example 1

[0030] The method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation comprises the following steps:

[0031] Step 1: Crush the sweet potato residue, add 9 times the volume of water to the sweet potato residue to form a suspension, heat to 70°C, add 0.1% α-amylase by weight of the sweet potato residue to the suspension, and maintain a constant temperature of 70°C and stir for 1 hour.

[0032] In step 1, the sweet potato residue after grinding is finer and more uniform in particles, with a larger surface area, and is less likely to agglomerate or stratify, which is beneficial to improving its adsorption, solubility and reactivity; grinding the sweet potato residue can destroy the cell walls in the sweet potato residue and release more nutrients, such as dietary fiber, vitamins and minerals.

[0033] Grinding the sweet potato residue also helps promote microbial fermentation and enzymatic hydrolysis. The crushed sweet potato residue particles are more accessible to microorganisms and enzymes, thus accelerating their decomposition and transformation process.

[0034] In step 1, a certain proportion of water is added to the sweet potato residue to prepare a suspension. After the water is added, the interaction force between the sweet potato residue particles changes, so that the overall fluidity is enhanced, making it easier to carry out subsequent processing. At the same time, the sweet potato residue particles in the suspension are easier to disperse evenly, which is conducive to improving its reaction activity and utilization rate.

[0035] In step 1, the formation of the suspension also facilitates the microbial fermentation and enzymatic hydrolysis process. In the suspension, microorganisms and enzymes can more easily contact the sweet potato residue particles, thereby accelerating their decomposition and conversion process and improving the bioavailability of the sweet potato residue.

[0036] α-Amylase is an enzyme that can randomly hydrolyze the α-1,4 glucosidic bonds within starch at higher temperatures.

[0037] In step 1, under the constant temperature of 70°C, the activity of α-amylase is high, which can effectively hydrolyze the starch in the sweet potato residue into soluble dextrin, a small amount of oligosaccharides, and even further hydrolyze into glucose and maltose. This process helps to reduce the starch content in the sweet potato residue, while increasing the proportion of its soluble components, which facilitates subsequent processing and utilization.

[0038] In step 1, the physical properties of the sweet potato residue suspension are improved by heating and enzymatic hydrolysis. The hydrolysis of starch reduces the viscosity of the suspension, enhances fluidity, and makes it easier to carry out subsequent processing. At the same time, the enzymatic hydrolysis process also destroys part of the fiber structure in the sweet potato residue, making it easier to be degraded and utilized by microorganisms.

[0039] In the embodiment of the present invention, the sweet potato residue suspension treated with α-amylase has a reduced starch content and increased soluble components, which provides more favorable conditions for microbial fermentation. In the subsequent fermentation process, microorganisms can more easily utilize these soluble components for growth and metabolism, thereby accelerating the fermentation process and improving the yield and quality of the fermentation product.

[0040] In an embodiment of the present invention, a certain proportion of water is added to the sweet potato residue to form a suspension, and a certain proportion of α-amylase is added after heating to 70°C, and the suspension is stirred at a constant temperature of 70°C for 1 hour. This can effectively hydrolyze the starch components in the sweet potato residue, improve its physical properties, promote microbial fermentation, and improve resource utilization.

[0041] Step 2, transferring the sweet potato residue suspension treated in step 1 to a fermentation tank, sterilizing under high pressure at 121° C. for 20 min, cooling to 40° C., inoculating Lactobacillus plantarum LD1.0026 fermentation liquid, wherein the inoculation amount of Lactobacillus plantarum LD1.0026 fermentation liquid is 3% of the volume of the sweet potato residue suspension, and culturing at 37° C. for 4 to 6 h;

[0042] In step 2, the sweet potato residue suspension is transferred to a fermentation tank for sterilization. High-temperature sterilization can effectively reduce or eliminate the number of microorganisms in the sweet potato residue, providing a relatively sterile environment for the subsequent fermentation process.

[0043] In step 2, the temperature is lowered to about 40° C., which will not cause excessive damage to the nutrients in the sweet potato residue, but can also ensure the activity of the Lactobacillus plantarum LD1.0026 fermentation liquid, which is beneficial to the fermentation process.

[0044] In step 2, Lactobacillus plantarum LD1.0026 will rapidly proliferate under suitable temperature (37°C) and nutritional conditions, becoming the dominant strain in the fermentation process. When cultured at 37°C for 4 to 6 hours, Lactobacillus plantarum LD1.0026 will proliferate in large quantities and decompose pectin and other components in the sweet potato residue.

[0045] Lactobacillus plantarum LD1.0026 can convert sugars into lactic acid through fermentation. In the fermentation process of sweet potato residue, Lactobacillus plantarum LD1.0026 plays a vital role. As a fermentation substrate, sweet potato residue is rich in sugars, which provides a sufficient source of nutrition for the growth and metabolism of Lactobacillus plantarum LD1.0026.

[0046] In an embodiment of the present invention, grinding and crushing sweet potato residue can destroy the cell wall in the sweet potato residue, discharges more nutrients, such as dietary fiber, vitamins and mineral substances, and dietary fiber has a certain promoting effect on plant lactobacillus LD1.0026.Dietary fiber can be used as the food source of plant lactobacillus, helps the growth and breeding of probiotics.Mineral substances provide the mineral elements required for plant lactobacillus LD1.0026 growth, and these mineral elements play an important role in the metabolic process of plant lactobacillus, such as participating in processes such as energy metabolism, material transport.

[0047] When Lactobacillus plantarum LD1.0026 comes into contact with the sugars in the sweet potato residue, it uses these sugars as an energy source and metabolic substrate. Through a series of enzymatic reactions, Lactobacillus plantarum LD1.0026 can gradually convert sugars into lactic acid. This conversion process not only provides Lactobacillus plantarum LD1.0026 with the energy needed for its growth, but also produces a large amount of lactic acid, thereby changing the pH value of the fermentation environment.

[0048] The accumulation of plant lactobacillus LD1.0026 causes the pH value of the fermentation environment to reduce gradually, forming an acidic microenvironment. This acidic environment is favourable to plant lactobacillus LD1.0026, because it can usually grow and breed under a lower pH value, but has an inhibitory effect on other microorganisms. This inhibitory effect not only helps to maintain the purity and effect of fermentation, prevents other bacteria from contaminating and interfering, but also can prolong the shelf life and stability of the fermented product. In the sweet potato residue fermentation process, the above-mentioned inhibitory effect of plant lactobacillus LD1.0026 is particularly important, which ensures that the fermentation process can be carried out according to a predetermined direction, and finally obtains a product that meets expectations.

[0049] As an organic acid, Lactobacillus plantarum LD1.0026 can reduce the pH value of the solution, thereby changing the solubility of pectin. Under acidic conditions, the solubility of pectin increases, which helps to release pectin from the plant cell wall. Lactobacillus plantarum LD1.0026 molecules can penetrate into the plant cells, destroy the cell wall structure, and make pectin easier to extract. Lactobacillus plantarum LD1.0026 can also chelate with certain metal ions (such as calcium ions) in pectin to form stable compounds, which helps to separate and purify pectin.

[0050] Step 3: Heat the liquid obtained in step 2 to 80° C. and perform ultrasonic-assisted extraction for 90 minutes to fully dissolve the pectin.

[0051] In step 3, after fermentation is completed, the liquid is heated to 80°C to make it easier for pectin to dissolve out of the liquid. Ultrasonic waves are used to assist extraction for 90 minutes. Ultrasonic waves generate high-frequency vibrations and cavitation effects in the liquid, which destroy the binding of pectin with other ingredients, making it easier to dissolve in the liquid and increasing the dissolution rate of pectin.

[0052] In the embodiments of the present invention, pectin in sweet potato residue is released by fermentation, and the extraction efficiency of pectin is improved by heating and ultrasonic treatment.

[0053] Step 4: Centrifuge the mixture after water bath extraction in step 3 at 9000 g for 30 min, remove the precipitate and take the supernatant.

[0054] In step 4, after the extraction is completed, the mixture is placed in a centrifuge and centrifuged at a relative centrifugal force of 9000g for 30 minutes to fully separate the solid and liquid components in the mixture. After the centrifugation is completed, the precipitate in the centrifuge tube is removed by pouring or pipetting, and then the supernatant is carefully taken out. The supernatant contains dissolved pectin and other soluble components and is the target solution for subsequent purification or application.

[0055] Step 5: Mix the supernatant obtained in step 4 with 75% ethanol in a ratio of 2:3, and let stand at 4°C for 80 minutes to fully precipitate.

[0056] In step 5, in order to precipitate the pectin from the solution, the supernatant needs to be mixed with 75% to 80% ethanol in a certain ratio. The ratio is usually determined according to the concentration of the pectin and the required purity.

[0057] In step 5, the mixed solution is placed in an environment of 4°C for 80 minutes. Low temperature helps to slow down the movement of molecules and increase the interaction between pectin molecules, which is conducive to the precipitation of pectin. The standing time is a key factor to ensure that the pectin is fully precipitated. During the standing process, the pectin molecules will gradually aggregate and form a visible precipitate, which usually appears as a white or light yellow granular substance.

[0058] In step 5, when ethanol is added to the aqueous solution of pectin, an alcohol-water mixed system is formed. Pectin molecules have a certain solubility in water, but a lower solubility in ethanol. Therefore, as the concentration of ethanol increases, the solubility of pectin molecules in water gradually decreases, and finally precipitates out in the form of precipitation.

[0059] Step 6: centrifuge the mixed solution obtained in step 5 at 9000g for 30 minutes, remove the supernatant, and the precipitate is the crude extracted pectin. Add an appropriate amount of 75% ethanol to wash the precipitate, repeat step 6 to wash the precipitate twice, and dry it at a temperature of 45-60°C to obtain pectin.

[0060] In step 6, in order to remove impurities in the precipitate, it is necessary to add an appropriate amount of 75% ethanol to wash the precipitate. The addition of ethanol can further dissolve and remove soluble impurities in the precipitate, and also help to maintain the stability of pectin. When washing, the precipitate should be gently stirred to ensure that the ethanol can fully contact the surface of the precipitate.

[0061] Repeat step 6 to wash the precipitate twice to ensure the purity of the precipitate. Through multiple washings, impurities in the precipitate can be removed to the greatest extent, thereby improving the purity and quality of pectin.

[0062] In step 6, after washing, the precipitate is placed in an oven for drying. The drying temperature and time should be adjusted according to the actual situation to ensure that the pectin can be completely dried and will not be denatured due to excessive temperature. After drying, the purified pectin product is obtained. The product can be used in the fields of food, medicine, cosmetics, etc.

[0063] Step 7: Grind the pectin obtained in step 6 to obtain sweet potato pectin.

[0064] In an embodiment of the present invention, the pectin extracted by lactic acid bacteria fermentation is usually of higher purity. During the fermentation process, lactic acid bacteria can consume some impurities and undesirable components in the raw materials, thereby improving the purity of pectin. In addition, lactic acid bacteria fermentation can also improve the physical and chemical properties of pectin, such as viscosity, stability, etc.

[0065] Example 2

[0066] A method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation comprises the following steps:

[0067] Step 1, crush the sweet potato residue, add 9 times the volume of water to the sweet potato residue to prepare a suspension, heat to 70°C, add 0.3% α-amylase by weight of the sweet potato residue to the suspension, maintain a constant temperature of 70°C and stir for 1h;

[0068] Step 2, transferring the sweet potato residue suspension treated in step 1 to a fermentation tank, sterilizing under high pressure at 121° C. for 20 min, cooling to 40° C., inoculating Lactobacillus plantarum LD1.0026 fermentation liquid, wherein the inoculation amount of Lactobacillus plantarum LD1.0026 fermentation liquid is 5% of the volume of the sweet potato residue suspension, and culturing at 37° C. for 4 to 6 h;

[0069] Step 3, heating the liquid obtained in step 2 to 100°C, and extracting with ultrasound for 90 minutes to fully dissolve the pectin;

[0070] Step 4, centrifuge the mixture after water bath extraction in step 3 at 9000g for 30 min, remove the precipitate, and take the supernatant;

[0071] Step 5: Mix the supernatant obtained in step 4 with 80% ethanol in a ratio of 2:3, and let stand at 4°C for 80 minutes to fully precipitate;

[0072] Step 6, centrifuge the mixed solution obtained after step 5 at 9000g for 30min, remove the supernatant, and the precipitate is the crude extracted pectin, add an appropriate amount of 80% ethanol to wash the precipitate, repeat step 6 to wash the precipitate twice, and dry it at a temperature of 45-60°C to obtain pectin;

[0073] Step 7: Grind the pectin obtained in step 6 to obtain sweet potato pectin.

[0074] Comparative Example 1

[0075] The difference from the preparation method of Example 1 is that the comparative example 1 is inoculated with fermentation liquid of Lactobacillus plantarum LD1.0010.

[0076] Lactobacillus plantarum LD1.0010 is classified and named as Lactobacillus plantarum Lactobacillus plantarum , deposited in the General Microbiology Center of China Microorganism Culture Collection Administration on June 9, 2021, with the deposit address in Beijing, China, and the deposit number is CGMCC No.20050.

[0077] Comparative Example 2

[0078] Different from the preparation method of Example 1, the comparative example 2 does not inoculate the fermentation liquid.

[0079] Comparative Example 3

[0080] The difference from the preparation method of Example 1 is that in Comparative Example 3, 0.1 mol / L nitric acid is added to a pH of 2-3.

[0081] Comparative Example 4

[0082] The difference from the preparation method of Example 1 is that in Comparative Example 4, 0.1 mol / L hydrochloric acid is added to a pH of 2-3.

[0083] Comparative Example 5

[0084] The difference from the preparation method of Example 1 is that in Comparative Example 5, 0.1 mol / L lactic acid is added until the pH is 2-3.

[0085] Performance Testing

[0086] The sweet potato pectin prepared in Example 1 and Example 2 are respectively marked as Example 1 and Example 2, and the sweet potato pectin prepared in Comparative Examples 1-5 are respectively marked as Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5. The performance of Examples 1, 2 and Comparative Examples 1-5 is tested. The test method is as follows:

[0087] 1. Determine the pectin yield of sweet potato residue. The calculation method of pectin yield is generally: pectin yield (%) = (pectin mass / raw material mass) × 100%, usually expressed as a percentage; pectin yield is a comprehensive indicator that reflects the efficiency and effect of extracting pectin from raw materials;

[0088] 2. Determine the purity of sweet potato residue pectin, usually using the galacturonic acid content as an indicator. The higher the content, the higher the purity of the pectin. The method used is carbazole sulfate-ultraviolet spectrometry;

[0089] 3. Determine the esterification degree of sweet potato residue pectin by acid-base titration;

[0090] 4. Determine the gelling degree of sweet potato residue pectin by using the calibration curve method and a jelly strength tester to determine the gelling degree of low-ester pectin;

[0091] The data obtained are recorded in Table 1 below.

[0092] Table 1

[0093]

[0094] It can be seen from the data in Table 1 that the pectin extracted in Examples 1 and 2 has a higher yield than that in Comparative Examples 1 to 5, and the yield in Example 2 is 10.5%, which is higher than the yield using strong acids such as nitric acid and hydrochloric acid, and weak acids such as lactic acid; the purity of the pectin obtained in Examples 1 and 2 is higher than that in Comparative Examples 1 to 5, wherein Example 2 reaches 72%, which meets the requirement of GB25533-2010 that the purity of pectin is greater than or equal to 65%; in addition, the purity and yield of pectin from sweet potato residues after fermentation with different lactic acid bacteria are different; the pectin esterification degree of Examples 1, 2 and Comparative Examples 1-5 is all below 50%, belonging to low-ester pectin, and can be used in low-sugar foods; the FCC standard stipulates that the standard gelling degree is 100, and the measured gelling degree of 100±5 is a qualified product. The pectin gelling degree of Examples 1, 2 and Comparative Examples 1-5 all meets the standard requirements.

[0095] Figure 1 This is a physical picture of the sweet potato residue pectin extracted by lactic acid bacteria fermentation of the present invention. It can be seen from the figure that the pectin extracted from the sweet potato residue is an off-white powdery substance.

[0096] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. All equivalent changes made to the contents described in the claims of the present invention are included in the protection scope of the present invention.

Claims

1. A method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation, characterized in that: The following steps are involved: Step 1, grind the sweet potato residue, add a certain proportion of water to the sweet potato residue to make a suspension, heat to 70°C, add a certain proportion of α-amylase, maintain a constant temperature of 70°C and stir for 1h; Step 2, transferring the sweet potato residue suspension treated in step 1 to a fermentation tank for sterilization, cooling to 40°C and inoculating Lactobacillus plantarum LD1.0026 fermentation liquid, Lactobacillus plantarum LD1.0026 is classified and named as Lactobacillus plantarum, and is deposited in the General Microbiology Center of China Microbiological Culture Collection Administration on August 14, 2024, with a deposit address of Beijing, China, and a deposit number of CGMCC No.31579. The inoculation amount of Lactobacillus plantarum LD1.0026 fermentation liquid is 3-5% of the volume of the sweet potato residue suspension, and cultured at 37°C for 4-6 hours; Step 3, heating the fermentation liquid of Lactobacillus plantarum LD1.0026 obtained in step 2 to 80-100° C., and subjecting the fermentation liquid to ultrasonic-assisted extraction for 90 minutes to fully dissolve the pectin; Step 4, centrifuge the mixture after water bath extraction in step 3 at 9000g for 30 min, remove the precipitate, and take the supernatant; Step 5: Mix the supernatant obtained in step 4 with 75% to 80% ethanol in a certain proportion, and let stand at 4°C for 80 minutes to fully precipitate; Step 6, centrifuge the mixed solution obtained after step 5 at 9000g for 30 minutes, remove the supernatant, and the precipitate is the crude extracted pectin, add an appropriate amount of 75% to 80% ethanol to wash the precipitate, repeat step 6 to wash the precipitate twice, and dry to obtain pectin; Step 7: Grind the pectin obtained in step 6 to obtain sweet potato pectin.

2. The method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation according to claim 1, characterized in that: In step 1, the volume ratio of sweet potato residue to water is 1:9, and the amount of α-amylase added is 0.1% to 0.3% of the mass of the sweet potato residue.

3. The method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation according to claim 1, characterized in that: The sterilization condition in step 2 is 121° C. for 20 min.

4. The method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation according to claim 1, characterized in that: The ratio of the supernatant obtained in step 5 to 75% to 80% ethanol is 2:

3.

5. The method for extracting pectin from sweet potato waste residue by lactic acid bacteria fermentation according to claim 1, characterized in that: The drying temperature in step 6 is 45-60°C.

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