Wild vegetable natural composite preservative and preparation method thereof

Abstract

The invention belongs to the field of agriculture, and particularly relates to a wild vegetable natural composite preservative and a preparation method thereof, the wild vegetable natural composite preservative is prepared from the following raw materials by weight: 0.6-0.9 part of a mixed flavone extract, 1-2 parts of L-malic acid, 2-3 parts of sodium lactate, 10-20 parts of a glucose solution, and 20-30 parts of glycerin. The natural composite preservative is prepared by adopting a method for extracting flavone from plants, and the prepared product is healthy and safe to use and has excellent preservative and fresh-keeping effects. L-malic acid is used as a pH regulator, so that the pH value of the preservative can be maintained in a proper range, the growth of microorganisms and the activity of enzymes are inhibited, and the preservation effect is further improved.

Description

Technical Field

[0001] The invention belongs to the field of agriculture, and in particular relates to a natural composite preservative for wild vegetables and a preparation method thereof. Background Art

[0002] Wild vegetables are highly seasonal, and a single variety is available for less than one month, let alone continuous supply, so it is difficult to preserve and store wild vegetables. Although wild vegetables have strong vitality, they will wilt, turn yellow, rot, and produce odor if they are not preserved in time after picking. The current status of wild vegetable preservation mainly relies on methods such as refrigeration, freezing, modified atmosphere packaging and chemical preservatives. Refrigeration is the most common preservation method, which slows down the growth of microorganisms and the activity of enzymes by lowering the temperature, thereby extending the shelf life of wild vegetables. Frozen preservation achieves the purpose of long-term preservation by quickly freezing wild vegetables and keeping them at a low temperature. Modified atmosphere packaging creates an environment that inhibits the growth of microorganisms by adjusting the gas composition in the package. In addition, some chemical preservatives are also used to preserve wild vegetables, but attention should be paid to their safety and residue issues. Despite this, the preservation of wild vegetables still faces many challenges, such as short shelf life and easy decay and deterioration, so new preservation technologies and methods are constantly being researched and developed.

[0003] Ginkgo biloba has a wide range of biological activities and contains a variety of chemical components, including flavonoids, terpenes, polysaccharides, phenols, organic acids, alkaloids, amino acids, steroid compounds, trace elements, etc. The flavonoid content in ginkgo leaf extract is about 28%.

[0004] Seabuckthorn, also known as Elaeagnus angustifolia, is rich in flavonoids, carotenoids, sterol hormones, tocopherols, etc. Among them, flavonoids are its most important active ingredients. Seabuckthorn flavonoids have good antioxidant effects. The flavonoid content in seabuckthorn extract is about 30%.

[0005] Berry tea, this plant contains natural active ingredients such as flavonoids. The average content of total flavonoids in young stems and leaves exceeds 26%, among which the total flavonoids content in the bud tips is as high as 43.78%. It is the plant with the highest flavonoids content among all discovered plants and is known as the "King of Flavonoids".

[0006] The flavonoids in the above plants all have strong antioxidant free radical effects. There is no relevant report in the prior art on how to apply the flavonoids in the above plants to the preservation of wild vegetables. Summary of the invention

[0007] The purpose of the present invention is to solve the deficiencies of the prior art and to provide a natural composite preservative for wild vegetables prepared by extracting flavonoids from plants.

[0008] The present invention is achieved through the following technical solutions: A wild vegetable natural composite preservative is prepared from the following raw materials in parts by weight: 0.6-0.9 parts of a mixed flavonoid extract, 1-2 parts of L-malic acid, 2-3 parts of sodium lactate, 10-20 parts of a glucose solution, and 20-30 parts of glycerol; the mixed flavonoid extract is prepared by mixing a ginkgo leaf flavonoid extract, a sea buckthorn flavonoid extract, and a berry tea flavonoid extract, and the flavonoid content of the mixed flavonoid extract is 350-500 mg / g; the concentration of the glucose solution is 10%-50%.

[0009] The preservation mechanism of the above natural composite preservative is as follows: L-malic acid as a pH regulator can ensure that the pH value of the preservative is maintained within the range of 3-5, thereby inhibiting the growth of microorganisms and the activity of enzymes, and further improving the preservation effect; the addition of sodium lactate and glucose solution not only provides necessary nutrients for wild vegetables, but also helps to maintain the osmotic pressure of the preservative, prevent cell dehydration, and maintain the freshness and taste of wild vegetables. Glycerin as a humectant can effectively prevent wild vegetables from losing water and wilting, and maintain their original color and flavor; the flavonoids in the mixed flavonoid extract have a strong antioxidant free radical effect.

[0010] The present invention also discloses a method for preparing a wild vegetable natural composite preservative, comprising the following steps: S1. Preparation of ginkgo leaf flavonoid extract. Take ginkgo leaves from Kunming, Yunnan, dry them thoroughly, grind them and pass them through a 60-mesh sieve to obtain ginkgo leaf powder; first put the ginkgo leaf powder into a filter paper bag of a Soxhlet extractor, then place the filter paper bag in a flask and add anhydrous ethanol, heat it in a water bath at a temperature of 50-60° C., and extract continuously for 2 hours; when the condensate in the siphon just falls, stop heating immediately; evaporate the solvent with a rotary evaporator to obtain a brown-black ginkgo extract crude extract; add 50% by volume ethanol to the ginkgo extract crude extract and shake well to obtain a ginkgo leaf flavonoid extract; S2. Preparation of seabuckthorn flavonoid extract. Take seabuckthorn leaves from Hotan, Xinjiang Uygur Autonomous Region, dry them thoroughly, grind them and pass them through a 60-mesh sieve to obtain seabuckthorn leaf powder; place the seabuckthorn leaf powder in a flask, add ether, stir at room temperature for 5 minutes, mix evenly, place in a constant temperature water bath at a temperature of 35-45°C, heat and reflux for 2 hours, and then perform vacuum distillation; during the vacuum distillation process, the lipid compounds in the seabuckthorn leaf powder form an azeotrope with the ether, and then enter the distillate to achieve defatting. Take the seabuckthorn leaf powder obtained after the vacuum distillation and place it in a flask together with 50% ethanol by volume, stir and extract in a constant temperature water bath at a temperature of 60-100°C for 25 minutes, and then filter to obtain the seabuckthorn flavonoid extract; S3. Preparation of berry tea flavonoid extract: berry tea leaves from Zhangjiajie, Hunan, were taken, fully dried, ground and passed through a 60-mesh sieve to obtain berry tea powder; the berry tea powder was placed in a flask, high-purity water was added, condensed and refluxed, ultrasonically extracted at a temperature of 60°C for 2 h, and the extract was filtered to obtain an extract; 10% by mass of H 2 O 2 , add water to make up to volume to obtain berry tea flavonoids extract; S4, preparing a mixed flavonoid extract, mixing the ginkgo leaf flavonoid extract obtained in step S1, the sea buckthorn flavonoid extract obtained in step S2, and the berry tea flavonoid extract obtained in step S3 evenly and making the flavonoid content in the mixed solution be 350-500 mg / g, filtering and removing impurities with a 20-mesh sieve to obtain a mixed flavonoid extract; S5, preparing a flavonoid-glycerol mixed solution, by mixing 0.6-0.9 parts of the mixed flavonoid extract obtained in step S1 and 20-30 parts of glycerol uniformly to obtain a flavonoid-glycerol mixed solution; S6, preparing a glucose-based liquid, by mixing 1-2 parts of L-malic acid, 2-3 parts of sodium lactate, and 10-20 parts of a glucose solution by weight to obtain a glucose-based liquid; S7, preparation of a composite preservative, uniformly mixing the flavonoid-glycerol mixed solution obtained in step S5 and the glucose-based solution obtained in step S6, and removing bubbles by ultrasonication to obtain a composite preservative.

[0011] In step S1, the amount of ginkgo leaf powder (g): the amount of anhydrous ethanol (mL): the amount of 50% ethanol by volume (mL) = (2.5-3.5): (20-40): (40-80).

[0012] In step S2, the amount of seabuckthorn leaf powder (g): the amount of ether (mL) = (1-3): (15-45); the amount of seabuckthorn leaf powder obtained after reduced pressure distillation (g): the amount of 50% ethanol by volume (mL) = 1: (10-30).

[0013] In step S3, the amount of berry tea powder (g): the amount of high-purity water (mL): the amount of H 2 O 2 Dosage (mL) = (1-3): (15-35): (0.1-0.3).

[0014] In step S4, the amount of ginkgo leaf flavonoids extract (mL): the amount of seabuckthorn flavonoids extract (mL): the amount of berry tea flavonoids extract (mL) = 1: (2-3): (3-6).

[0015] Preferably, in step S4, the amount of ginkgo leaf flavonoids extract (mL): the amount of seabuckthorn flavonoids extract (mL): the amount of berry tea flavonoids extract (mL) = 1:2:3.

[0016] The wild vegetable natural composite preservative in the present application prolongs the shelf life by adjusting the pH of wild vegetables to 3-5. The method of use is as follows: select fresh, non-rotten, and relatively uniform wild vegetables, such as broom and bracken, and spray them evenly on the surface of the wild vegetables after they are naturally dried, and then naturally air-dry and simply package them to achieve a good preservation effect.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adopts the method of extracting flavonoids from plants to prepare a natural composite preservative. The prepared product is healthy and safe to use, and has excellent antiseptic and fresh-keeping effects. L-malic acid, as a pH regulator, can ensure that the pH value of the preservative is maintained within a suitable range, thereby inhibiting the growth of microorganisms and the activity of enzymes, and further improving the preservation effect. The addition of sodium lactate and glucose solution not only provides necessary nutrients for wild vegetables, but also helps to maintain the osmotic pressure of the preservative, prevent cell dehydration, and maintain the freshness and taste of wild vegetables. Glycerol is used as a humectant, and its content is 20-30 parts, which can effectively prevent wild vegetables from losing water and wilting, and maintain their original color and flavor.

[0018] 2. The wild vegetable natural composite preservative of the present invention can enhance the freshness and durability of wild vegetables and effectively slow down the quality degradation caused by microbial activity and enzyme action.

[0019] 3. The ingredients of the wild vegetable natural composite preservative of the present invention are all of natural origin, which ensures the safety during use and satisfies consumers' pursuit of healthy food.

[0020] 4. The wild vegetable natural composite preservative of the present invention has low production cost and high market competitiveness and application potential.

[0021] 5. The wild vegetable natural composite preservative of the present invention can be directly washed with water. The use of the preservative will not cause a burden on the environment and is in line with the requirements of green ecology and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the evaluation result diagram of comparative test 2. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with embodiments, but the protection scope of the present invention is not limited by the embodiments. Example 1

[0024] A natural composite preservative for wild vegetables is prepared by the following method: (1) Ginkgo leaf flavonoids extract: Grind the fully dried ginkgo leaves from Kunming, Yunnan into powder and sieve them through a 60-mesh screen to obtain ginkgo leaf powder. Take 3 g of ginkgo leaf powder and put it into the filter paper bag of the Soxhlet extractor. Add 27 mL of anhydrous ethanol to a 100 mL round-bottom flask and heat it in a water bath at 50°C for 2.5 hours. Use a rotary evaporator to evaporate the solvent, add 60 mL of 50% ethanol by volume and shake well to obtain the ginkgo leaf flavonoids extract.

[0025] (2) Seabuckthorn flavonoids extract: Grind the fully dried seabuckthorn leaves from Hotan, Xinjiang Uygur Autonomous Region into powder, sieve with a 60-mesh screen, and obtain seabuckthorn leaf powder. Take 3 g of seabuckthorn leaf powder in a 100 mL round-bottom flask, add 30 mL of ether, and stir at room temperature for 5 min. After mixing evenly, place in a 45 ℃ constant temperature water bath and heat under reflux for 2 h, then perform vacuum distillation. The lipid compounds in the seabuckthorn leaf powder form an azeotrope with the ether, and then enter the distillate for defatting. Take 1 g of defatted seabuckthorn leaf powder in a 50 mL round-bottom flask, add 20 mL of 50% ethanol by volume, stir and extract in a constant temperature water bath at 80 ℃ for 25 min, and then filter to obtain seabuckthorn flavonoids extract.

[0026] (3) Berry tea flavonoid extract: Take an appropriate amount of dried berry tea from Zhangjiajie, Hunan, put it into a mortar, grind it into powder, and pass it through a 60-mesh sieve to obtain berry tea powder. Quantitatively take 1g of berry tea powder into a round-bottom flask, add 25mL of high-purity water, condense and reflux, perform ultrasonic extraction at 60℃ for 2h, filter to obtain the extract, add 0.2mL of 10% H 2 O 2 , add water to make the volume to 100 mL, and finally obtain the berry tea flavonoids extract.

[0027] (4) Take, by mass, 0.1 part of ginkgo leaf flavonoids extract, 0.3 part of seabuckthorn flavonoids extract, 0.5 part of berry tea flavonoids extract, 20 parts of glycerol, 1 part of L-malic acid, 2 parts of sodium lactate, and 10 parts of 50% glucose solution.

[0028] (5) The ginkgo leaf flavonoids extract, the sea buckthorn flavonoids extract and the berry tea flavonoids extract were mixed to obtain a mixed flavonoids extract, wherein the flavonoids content in the mixed flavonoids extract was 410 mg / g.

[0029] (6) mixing glycerol and the mixed flavonoid extract, and stirring evenly to obtain a flavonoid-glycerol extract; (7) mixing L-malic acid, sodium lactate, and 50% by mass glucose solution to obtain a glucose-based solution containing an acidity regulator; (8) The flavonoid-glycerol extract and the glucose-based liquid are mixed and stirred evenly, and then the bubbles are removed by ultrasonication to obtain a natural composite preservative for wild vegetables. Example 2

[0030] A natural composite preservative for wild vegetables is prepared by the following method: (1) Ginkgo leaf flavonoids extract: Grind the fully dried ginkgo leaves into powder and sieve them through a 60-mesh screen to obtain ginkgo leaf powder. Take 2.5 g of ginkgo leaf powder and put it into the filter paper bag of the Soxhlet extractor. Add 40 mL of anhydrous ethanol to a 100 mL round-bottom flask and heat it in a water bath at 60°C for 3 hours. Use a rotary evaporator to evaporate the solvent, add 40 mL of 50% ethanol by volume and shake well to obtain the ginkgo leaf flavonoids extract.

[0031] (2) Seabuckthorn flavonoids extract: Grind the fully dried seabuckthorn leaves into powder and sieve them with a 60-mesh screen to obtain seabuckthorn leaf powder. Take 2g of seabuckthorn leaf powder in a 100mL round-bottom flask, add 45mL of ether, and stir at room temperature for 5min. After mixing evenly, place in a 35℃ constant temperature water bath and heat under reflux for 2.5h, then perform vacuum distillation to defat. Take 1g of defatted seabuckthorn leaf powder in a 50mL round-bottom flask, add 30mL of 50% ethanol by volume, stir and extract in a 100℃ constant temperature water bath for 25min, and then filter to obtain seabuckthorn flavonoids extract.

[0032] (3) Berry tea flavonoid extract: Berry tea leaves are produced in Zhangjiajie District, Hunan Province. Take an appropriate amount of dried berry tea raw materials, put them into a mortar, grind them into powder, and pass them through a 60-mesh sieve to obtain berry tea powder. Take 2g of the quantitative berry tea powder in a round-bottom flask, add 15mL of high-purity water, condense and reflux, perform ultrasonic extraction at 60℃ for 2h, filter to obtain the extract, add 0.3mL of 10% H 2 O 2 , add water to make the volume to 100 mL, and finally obtain the berry tea flavonoids extract.

[0033] (4) Take, by mass, 0.1 part of ginkgo leaf flavonoids extract, 0.2 part of seabuckthorn flavonoids extract, 0.3 part of berry tea flavonoids extract, 25 parts of glycerol, 1.5 parts of L-malic acid, 2.5 parts of sodium lactate, and 15 parts of 30% glucose solution.

[0034] Step (5) to step (8) are the same as Example 1, wherein the content of flavonoids in the mixed flavonoid extract is 350 mg / g. Example 3

[0035] A natural composite preservative for wild vegetables is prepared by the following method: (1) Ginkgo leaf flavonoids extract: Grind the fully dried ginkgo leaves into powder and sieve them through a 60-mesh screen to obtain ginkgo leaf powder. Take 3.5 g of ginkgo leaf powder and put it into the filter paper bag of the Soxhlet extractor. Add 20 mL of anhydrous ethanol to a 100 mL round-bottom flask and heat it in a water bath at 55°C for 3.5 hours. Use a rotary evaporator to evaporate the solvent and add 80 mL of 50% ethanol by volume and shake well to obtain the ginkgo leaf flavonoids extract.

[0036] (2) Seabuckthorn flavonoids extract: Grind the fully dried seabuckthorn leaves into powder and sieve them with a 60-mesh screen to obtain seabuckthorn leaf powder. Take 1g of seabuckthorn leaf powder in a 100mL round-bottom flask, add 15mL of ether, and stir at room temperature for 5min. After mixing evenly, place in a 40℃ constant temperature water bath and heat under reflux for 3h, then perform vacuum distillation to defat. Take 1g of defatted seabuckthorn leaf powder in a 50mL round-bottom flask, add 10mL of 50% ethanol by volume, stir and extract in a 60℃ constant temperature water bath for 25min, and then filter to obtain seabuckthorn flavonoids extract.

[0037] (3) Berry tea flavonoid extract: Take an appropriate amount of dried berry tea raw material, put it into a mortar, grind it into powder, and pass it through a 60-mesh sieve to obtain berry tea powder. Take 3g of the quantitative berry tea powder in a round-bottom flask, add 35mL of 50% ethanol, condense and reflux, perform ultrasonic extraction at 60℃ for 2h, filter to obtain the extract, add 0.3mL of 10% H 2 O 2 , add water to make the volume to 100 mL, and finally obtain the berry tea flavonoids extract.

[0038] (4) Take 0.1 parts of ginkgo leaf flavonoids extract, 0.2 parts of seabuckthorn flavonoids extract, 0.6 parts of berry tea flavonoids extract, 30 parts of glycerol, 2 parts of L-malic acid, 3 parts of sodium lactate, and 20 parts of glucose solution by mass.

[0039] Step (5) to step (8) are the same as Example 1, wherein the content of flavonoids in the mixed flavonoid extract is 500 mg / g. Comparative Example 1

[0040] A wild vegetable natural composite preservative, wherein the mixed flavonoid extract is from Example 1. In parts by mass, 20 parts of glycerol, 1 part of L-malic acid, 2 parts of sodium lactate, 10 parts of 50% glucose solution by mass fraction and 0.9 parts of the mixed flavonoid extract are directly stirred and mixed evenly to obtain a mixed solution; the mixed solution is subjected to ultrasonic degassing to obtain the wild vegetable natural composite preservative. Comparative Example 2

[0041] A natural composite preservative for wild vegetables, the mixed flavonoid extract is from Example 1. In parts by mass, 30 parts of glycerol, 2 parts of L-malic acid, 20 parts of 30% glucose solution by mass fraction, and 0.6 parts of mixed flavonoid extract. The preparation method is as follows: (1) directly mixing L-malic acid and glucose solution to obtain a mixed solution; (2) mixing glycerol with the mixed flavonoid extract, and stirring evenly to obtain a flavonoid-glycerol extract; (3) The flavonoid-glycerol extract and the mixed solution are mixed and stirred evenly, and bubbles are removed by ultrasonication to obtain a natural composite preservative for wild vegetables. Comparative test 1

[0042] The natural composite preservatives prepared in Examples 1-3 and Comparative Example 1 were used to carry out a preservation test on broom.

[0043] Test method: 5 groups of freshly picked broom flowers with no withered petals were selected, and the preservatives prepared in Examples 1-3 and Comparative Example 1 were evenly sprayed on the surfaces of the broom flowers in groups 1-4. The fifth group was a blank control group, which was not treated with any treatment and naturally air-dried. 1 kg of broom flowers were treated with 20 mL of the preservative and stored at an average room temperature of 20±2°C for 14 days. The weight loss rate and quality of the broom flowers were statistically analyzed. The specific results are shown in Table 1.

[0044] Table 1 Comparative test 1 test results

[0045] Direct mixing in Comparative Example 1 easily leads to uneven mixing of flavonoids and the solution, resulting in some leaves not being sprayed, causing bacterial colonies to form, and microorganisms to multiply rapidly and rot.

[0046] Sodium lactate is mainly used as a moisture retainer and has a certain antioxidant effect. However, in Comparative Example 2, no sodium lactate was added, resulting in rapid water loss and enhanced oxidation, leading to decay. Comparative test 2

[0047] The natural composite preservatives prepared in Examples 1-3 and Comparative Example 1 were used to carry out a preservation test on bracken.

[0048] Test method: Freshly picked bracken with a length of 15-20 cm and appropriate maturity were divided into 5 groups, each group weighing 1 kg. The preservatives prepared in Examples 1-3 and Comparative Example 1 were evenly sprayed on the surface of the bracken in Groups 1-4. Group 5 was a blank control group without any treatment. Each 20 mL of the composite preservative was used to treat 1 kg of bracken. Groups 1-5 were stored at room temperature and 10 sensory evaluators were asked to conduct sensory evaluation. The evaluation criteria are shown in Table 2 below.

[0049] Table 2 Evaluation criteria for comparative test 2

[0050] The effect of the preservation treatment on the bracken was evaluated on the 2nd, 4th, 6th, 8th and 10th days. The specific evaluation results are shown in the attached manual. Figure 1 .

[0051] Attached to the instruction manual Figure 1 It can be seen that on the 10th day, only the natural composite preservatives in Examples 1-3 meet the second-class standard.

Claims

1. A natural composite preservative for wild vegetables, characterized in that: The invention is prepared from the following raw materials in parts by weight: 0.6-0.9 parts of mixed flavonoid extract, 1-2 parts of L-malic acid, 2-3 parts of sodium lactate, 10-20 parts of glucose solution and 20-30 parts of glycerol.

2. The natural composite preservative for wild vegetables according to claim 1, characterized in that: The flavonoid content in the mixed flavonoid extract is 350-500 mg / g.

3. The natural composite preservative for wild vegetables according to claim 1, characterized in that: The mixed flavonoids extract is prepared by mixing ginkgo leaf flavonoids extract, seabuckthorn flavonoids extract and berry tea flavonoids extract.

4. The natural composite preservative for wild vegetables according to claim 1, characterized in that: The concentration of the glucose solution is 10%-50%.

5. A method for preparing a natural composite preservative for wild vegetables, characterized in that: The following steps are included: S1. Preparation of ginkgo leaf flavonoid extract. Take ginkgo leaves from Kunming, Yunnan, dry them thoroughly, grind them and pass them through a 60-mesh sieve to obtain ginkgo leaf powder; first put the ginkgo leaf powder into a filter paper bag of a Soxhlet extractor, then place the filter paper bag in a flask and add anhydrous ethanol, heat it in a water bath at a temperature of 50-60°C, and extract continuously for 2 hours; when the condensate in the siphon just falls, stop heating immediately; evaporate the solvent with a rotary evaporator to obtain a brown-black ginkgo extract crude extract; add 50% by volume ethanol to the ginkgo extract crude extract and shake well to obtain a ginkgo leaf flavonoid extract; S2. Preparation of seabuckthorn flavonoid extract: seabuckthorn leaves from Hotan, Xinjiang Uygur Autonomous Region are taken, fully dried, ground and passed through a 60-mesh sieve to obtain seabuckthorn leaf powder; the seabuckthorn leaf powder is placed in a flask, ether is added, stirred at room temperature for 5 minutes, and after mixing evenly, the mixture is placed in a constant temperature water bath at a temperature of 35-45°C, heated under reflux for 2 hours, and then vacuum distilled; the seabuckthorn leaf powder obtained after vacuum distillation is placed in a flask together with 50% ethanol by volume, stirred and extracted in a constant temperature water bath at a temperature of 60-100°C for 25 minutes, and then filtered to obtain a seabuckthorn flavonoid extract; S3, preparation of berry tea flavonoid extract, taking berry tea leaves from Zhangjiajie, Hunan, fully drying them, grinding them and passing them through a 60-mesh sieve to obtain berry tea powder; placing the berry tea powder in a flask, adding high-purity water, condensing and refluxing, ultrasonically extracting at a temperature of 60°C for 2 h, and filtering to obtain an extract; adding 10% H2O2 by mass to the extract, and adding water to the fixed volume to obtain a berry tea flavonoid extract; S4, preparing a mixed flavonoid extract, mixing the ginkgo leaf flavonoid extract obtained in step S1, the sea buckthorn flavonoid extract obtained in step S2, and the berry tea flavonoid extract obtained in step S3 evenly and making the flavonoid content in the mixed solution be 350-500 mg / g, filtering and removing impurities with a 20-mesh sieve to obtain a mixed flavonoid extract; S5, preparing a flavonoid-glycerol mixed solution, by mixing 0.6-0.9 parts of the mixed flavonoid extract obtained in step S1 and 20-30 parts of glycerol uniformly to obtain a flavonoid-glycerol mixed solution; S6, preparing a glucose-based liquid, by mixing 1-2 parts of L-malic acid, 2-3 parts of sodium lactate, and 10-20 parts of a glucose solution by weight to obtain a glucose-based liquid; S7, preparation of a composite preservative, uniformly mixing the flavonoid-glycerol mixed solution obtained in step S5 and the glucose-based solution obtained in step S6, and removing bubbles by ultrasonication to obtain a composite preservative.

6. The method for preparing a natural composite preservative of wild vegetables according to claim 5, characterized in that: In step S1, the amount of ginkgo leaf powder (g): the amount of anhydrous ethanol (mL): the amount of 50% ethanol by volume (mL) = (2.5-3.5): (20-40): (40-80).

7. The method for preparing a natural composite preservative of wild vegetables according to claim 5, characterized in that: In step S2, the amount of seabuckthorn leaf powder (g): the amount of ether (mL) = (1-3): (15-45); the amount of seabuckthorn leaf powder obtained after reduced pressure distillation (g): the amount of 50% ethanol by volume (mL) = 1: (10-30).

8. The method for preparing a natural composite preservative of wild vegetables according to claim 5, characterized in that: In step S3, the amount of berry tea powder (g): the amount of high-purity water (mL): the amount of H2O2 with a mass fraction of 10% (mL) = (1-3): (15-35): (0.1-0.3).

9. The method for preparing a natural composite preservative of wild vegetables according to claim 5, characterized in that: In step S4, the amount of ginkgo leaf flavonoids extract (mL): the amount of seabuckthorn flavonoids extract (mL): the amount of berry tea flavonoids extract (mL) = 1: (2-3): (3-6).

10. The wild vegetable natural composite preservative according to any one of claims 1 to 4, or the wild vegetable natural composite preservative prepared by the method according to any one of claims 6 to 9, characterized in that: The wild vegetable natural composite preservative prolongs the preservation period by adjusting the pH value of the wild vegetables to 3-5.

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