A compound plant fermentation extract and its preparation method

Abstract

The present application relates to the field of natural flavonoid extraction, and more specifically, it relates to a composite plant fermentation extract and a preparation method thereof. A preparation method of a composite plant fermentation extract comprises the following steps: Step 1: crushing mulberry leaves, kudzu root, and cinnamon bark and mixing them with water to obtain a fermented material; Step 2: steaming the fermented material at 110-130°C for 25-40 minutes to obtain a steamed mixture; Step 3: cooling the steamed mixture to 25-30°C, adding Eurotium cristatum, Lactobacillus acidophilus, and Geotrichum candidum to the steamed mixture, stirring and mixing, soaking and fermenting for 5-10 days to obtain a fermentation mixture; Step 4: sterilizing and centrifuging the fermentation mixture, collecting the supernatant, and obtaining a composite plant fermentation extract. The present application has the advantages of increasing the flavonoid extraction content and enhancing the antioxidant effect.

Description

Technical Field

[0001] This application relates to the field of natural flavonoid extraction, and more specifically, it relates to a compound plant fermentation extract and its preparation method. Background Technology

[0002] In today's world, with increasing global health awareness, natural plant extracts are gradually becoming a research focus in various fields such as medicine, health products, and cosmetics, due to their absence of chemical additives, natural origin, and rich content of various bioactive components beneficial to the human body. Among them, flavonoids, as a large class of polyphenols widely found in the plant kingdom, are considered to be highly promising natural health ingredients due to their excellent antioxidant, anti-inflammatory, anti-tumor, blood sugar-lowering, and immune-regulating bioactivities.

[0003] Flavonoids are widely distributed in nature, found not only in everyday foods such as fruits, vegetables, and tea, but also in many medicinal plants, such as mulberry leaves, ginkgo leaves, and soybeans. These compounds exert positive effects on human health through various mechanisms, including scavenging free radicals, inhibiting oxidative stress responses, and regulating cell signaling. However, despite the numerous health benefits of flavonoids, their direct extraction from plants faces significant challenges.

[0004] Flavonoids in plants often exist in bound form, tightly bound to plant cell walls, pectin, cellulose, etc., making them difficult to obtain directly using conventional extraction methods. This not only leads to low extraction efficiency of flavonoids but also results in relatively low flavonoid content in the final extract, making it difficult to meet the needs of industrial production.

[0005] Therefore, in practical applications, how to steadily improve the extraction efficiency and content of flavonoids has become an urgent problem to be solved. Summary of the Invention

[0006] To improve the flavonoid content and enhance the antioxidant effect, this application provides a compound plant fermentation extract and its preparation method.

[0007] In a first aspect, this application provides a method for preparing a compound plant fermentation extract, employing the following technical solution:

[0008] A method for preparing a compound plant fermentation extract includes the following steps:

[0009] Step 1: Crush mulberry leaves, kudzu root, and cinnamon, and mix them with water to obtain the material to be fermented;

[0010] Step 2: Cook the material to be fermented at 110-130℃ for 25-40 minutes to obtain a cooking mixture;

[0011] Step 3: Cool the cooking mixture to 25-30℃, add *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to the cooking mixture, stir and mix, soak and ferment for 5-10 days to obtain the fermented mixture;

[0012] Step 4: Sterilize and centrifuge the fermentation mixture, collect the supernatant, and obtain the compound plant fermentation extract.

[0013] By adopting the above technical solution, the plant raw materials used in this application are mulberry leaves, kudzu root, and cinnamon, and a special combination of microorganisms such as *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*. With the combined effect of the specially selected plant raw materials and microorganisms, the resulting compound plant fermentation extract is rich in flavonoids and can further enhance the antioxidant capacity of the compound plant fermentation extract.

[0014] Mulberry leaves, kudzu root, and cinnamon, as plant materials rich in flavonoids, each possess unique flavonoid components and bioactivities. These flavonoids often exist in the form of glycosides within plants. When these plant materials combine with microbial extracts such as *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*, they form complex interactive systems.

[0015] Secondary metabolites produced by *Aspergillus cristatus* during fermentation, such as enzymes and organic acids, can influence the release and transformation of flavonoids. These metabolites may promote the release of flavonoids from inside the cell by regulating the permeability of the plant cell wall. Meanwhile, organic acids such as lactic acid produced by *Lactobacillus acidophilus* help regulate the pH of the extract, thereby optimizing the solubility and stability of flavonoids. The fermentation process of *Geotrichum candida* is more direct; its cellulase and pectinase enzymes can directly act on the plant cell wall, disrupting its structure and making flavonoids easier to extract with solvents. This enzymatic hydrolysis not only increases the extraction rate of flavonoids but also makes the flavonoid components in the extract richer and more diverse.

[0016] There is a synergistic antioxidant effect between these microbial metabolites and plant flavonoids. The antioxidants produced by the microorganisms work together with the plant flavonoids in the extract to form a powerful antioxidant system. This synergistic effect not only enhances the antioxidant capacity of the extract but may also give it a wider range of biological activities.

[0017] Preferably, the mass ratio of mulberry leaves, kudzu root, and cinnamon is (6-8):(2-4):(0.5-1.5).

[0018] By adopting the above technical solution and further limiting the mass ratio of mulberry leaves, kudzu root, and cinnamon, the flavonoid extraction potential of each ingredient can be maximized, while promoting the synergistic effect between flavonoid compounds, thereby obtaining an extract with higher flavonoid content and stronger biological activity.

[0019] Preferably, the mass ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* is 1:(0.1-0.3):(0.1-0.3).

[0020] By adopting the above technical solution, further limiting the mass ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum can optimize the interaction between microorganisms, thereby maximizing the extraction of flavonoids and enhancing the antioxidant properties of metabolites.

[0021] Preferably, the total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* is 0.01-0.05% of the total mass of mulberry leaves, kudzu root, and cinnamon.

[0022] By adopting the above technical solution, the total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum can be further limited to the total mass of mulberry leaves, kudzu root, and cinnamon. This can optimize the fermentation process, promote the release and transformation of flavonoids, and effectively improve the antioxidant properties of the compound plant fermentation extract.

[0023] Preferably, in step 1, the total mass of mulberry leaves, kudzu root, and cinnamon is 1:(1-3) of the mass of water.

[0024] Preferably, the sterilization conditions in step 4 are 75-85℃ for 5-10 minutes.

[0025] Preferably, the mulberry leaves, kudzu root, and cinnamon are pulverized to 1-5 mm.

[0026] By adopting the above technical solution, mulberry leaves, kudzu root, and cinnamon are pulverized to specific specifications, which helps *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to come into contact and ferment, thereby effectively increasing the flavonoid content in the extract and improving the antioxidant properties of the complex.

[0027] Secondly, this application provides a compound plant fermentation extract.

[0028] By adopting the above technical solution, and by selecting mulberry leaves, kudzu root, and cinnamon as raw materials, and combining them with a special microbial combination of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*, the content of flavonoids and antioxidant capacity of the obtained compound plant fermentation extract were significantly improved.

[0029] Microbial metabolites, such as enzymes and organic acids, promote the release, transformation, and stability optimization of flavonoids, while improving the flavonoid extraction rate and component diversity.

[0030] In addition, the synergistic effect of microbial antioxidants and plant flavonoids creates a powerful antioxidant system, endowing the extract with a wider range of biological activities and exhibiting many beneficial effects.

[0031] In summary, this application has the following beneficial effects:

[0032] 1. The compound plant fermentation extract utilizes carefully selected plant materials rich in flavonoids, such as mulberry leaves, kudzu root, and cinnamon, combined with a unique microbial blend including *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*, resulting in a significant increase in flavonoid content. During fermentation, secondary metabolites produced by microorganisms, such as enzymes and organic acids, influence the release and transformation of flavonoids, optimizing their solubility and stability. Enzymes such as cellulase and pectinase produced by *Geotrichum candida* directly act on the plant cell walls, making flavonoids easier to extract, increasing the extraction rate, and enriching and diversifying the flavonoid composition of the extract.

[0033] 2. A synergistic antioxidant effect exists between microbial metabolites and plant flavonoids in the compound plant fermentation extract. The antioxidants produced by microorganisms and plant flavonoids work together in the extract to form a powerful antioxidant system. This synergistic effect not only enhances the antioxidant capacity of the extract, making it more resistant to oxidative stress factors such as free radicals, but may also give it a wider range of biological activities.

[0034] 3. Complex plant fermentation extracts, rich in various flavonoids and microbial metabolites, possess a wide range of biological activities. Flavonoids themselves exhibit diverse biological activities, such as antioxidant, anti-inflammatory, and anti-tumor effects, while microbial metabolites may also possess similar biological activities. The synergistic effect between the two results in extracts exhibiting more diverse and comprehensive biological activities. This broad and diverse range of biological activities makes complex plant fermentation extracts a promising candidate for applications in health supplements, functional foods, and other fields. Detailed Implementation

[0035] The present application will be further described in detail below with reference to the embodiments.

[0036] The raw materials used in the following examples and comparative examples are all commercially available products.

[0037] The following are some of the sources of raw materials:

[0038] The *Eurotium cristatum* was purchased from Wuhan Gray Algae Biotechnology Co., Ltd., C426.

[0039] Lactobacillus acidophilus was purchased from Wuhan Gray Algae Biotechnology Co., Ltd., and BIOMA 5800.

[0040] White ground fungus was purchased from Ningbo Mingzhou Biotechnology Co., Ltd., BMZ135236.

[0041] Aspergillus niger was purchased from Ningbo Taisto Biotechnology Co., Ltd., TS277286.

[0042] Lactobacillus plantarum was purchased from Ningbo Taisto Biotechnology Co., Ltd., FRI2008085 B468

[0043] Cellulase was purchased from Zhejiang Yicun Biotechnology Co., Ltd. Example 1

[0044] A method for preparing a compound plant fermentation extract includes the following steps:

[0045] Step 1: Wash the mulberry leaves, kudzu root, and cinnamon thoroughly with clean water to remove surface dust and dirt. Then, put the mulberry leaves, kudzu root, and cinnamon into a grinder and grind them to 1-5mm.

[0046] The mass ratio of mulberry leaves, kudzu root, and cinnamon is 7:3:1.

[0047] In this embodiment, 7 kg of mulberry leaves, 3 kg of kudzu root, and 1 kg of cinnamon were used.

[0048] The crushed mulberry leaves, kudzu root, and cinnamon are mixed with water in a ratio of 1:2 to the total mass of the mulberry leaves, kudzu root, and cinnamon to the mass of the water, to obtain the material to be fermented.

[0049] Step 2: Cook the material to be fermented at 120°C for 30 minutes to obtain a cooking mixture.

[0050] Step 3: Cool the cooking mixture to 28°C.

[0051] Then, add *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to the cooking mixture, maintain 28°C, stir and mix, and soak and ferment for 7 days to obtain the fermented mixture.

[0052] The total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 0.03% of the total mass of mulberry leaves, kudzu root, and cinnamon.

[0053] The mass ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 1:0.2:0.2.

[0054] Step 4: Sterilize the fermentation mixture at 80℃ for 8 minutes.

[0055] The sterilized fermentation mixture was centrifuged and the supernatant was collected to obtain a compound plant fermentation extract. Example 2

[0056] A method for preparing a compound plant fermentation extract includes the following steps:

[0057] Step 1: Wash the mulberry leaves, kudzu root, and cinnamon thoroughly with clean water to remove surface dust and dirt. Then, put the mulberry leaves, kudzu root, and cinnamon into a grinder and grind them to 1-5mm.

[0058] The mass ratio of mulberry leaves, kudzu root, and cinnamon is 6:4:1.5.

[0059] In this embodiment, the amount of mulberry leaves is 6 kg, the amount of kudzu root is 4 kg, and the amount of cinnamon is 1.5 kg.

[0060] The crushed mulberry leaves, kudzu root, and cinnamon are mixed with water in a 1:1 ratio to the total mass of the mulberry leaves, kudzu root, and cinnamon with the mass of the water, to obtain the material to be fermented.

[0061] Step 2: Cook the material to be fermented at 110°C for 40 minutes to obtain a cooking mixture.

[0062] Step 3: Cool the cooking mixture to 30°C.

[0063] Then, add *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to the cooking mixture, maintain 30°C, stir and mix, and soak and ferment for 5 days to obtain the fermented mixture.

[0064] The total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 0.05% of the total mass of mulberry leaves, kudzu root, and cinnamon.

[0065] The mass ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 1:0.1:0.3.

[0066] Step 4: Sterilize the fermentation mixture at 75°C for 10 minutes.

[0067] The sterilized fermentation mixture was centrifuged and the supernatant was collected to obtain a compound plant fermentation extract. Example 3

[0068] A method for preparing a compound plant fermentation extract includes the following steps:

[0069] Step 1: Wash the mulberry leaves, kudzu root, and cinnamon thoroughly with clean water to remove surface dust and dirt. Then, put the mulberry leaves, kudzu root, and cinnamon into a grinder and grind them to 1-5mm.

[0070] The mass ratio of mulberry leaves, kudzu root, and cinnamon is 8:2:0.5.

[0071] In this embodiment, the amount of mulberry leaves is 8 kg, the amount of kudzu root is 2 kg, and the amount of cinnamon is 0.5 kg.

[0072] The crushed mulberry leaves, kudzu root, and cinnamon are mixed with water in a ratio of 1:3 to the total mass of the mulberry leaves, kudzu root, and cinnamon to the mass of the water, to obtain the material to be fermented.

[0073] Step 2: Cook the material to be fermented at 130°C for 25 minutes to obtain a cooking mixture.

[0074] Step 3: Cool the cooking mixture to 25°C.

[0075] Then, add *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to the cooking mixture, maintain 25°C, stir and mix, and soak and ferment for 10 days to obtain the fermented mixture.

[0076] The total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 0.01% of the total mass of mulberry leaves, kudzu root, and cinnamon.

[0077] The mass ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 1:0.1:0.3.

[0078] Step 4: Sterilize the fermentation mixture at 85℃ for 5 minutes.

[0079] The sterilized fermentation mixture was centrifuged and the supernatant was collected to obtain a compound plant fermentation extract. Example 4

[0080] A method for preparing a compound plant fermentation extract includes the following steps:

[0081] Step 1: Wash the mulberry leaves, kudzu root, and cinnamon thoroughly with clean water to remove surface dust and dirt. Then, put the mulberry leaves, kudzu root, and cinnamon into a grinder and grind them to 1-5mm.

[0082] The mass ratio of mulberry leaves, kudzu root, and cinnamon is 1:7:3.

[0083] In this embodiment, 1 kg of mulberry leaves, 7 kg of kudzu root, and 3 kg of cinnamon were used.

[0084] The crushed mulberry leaves, kudzu root, and cinnamon are mixed with water in a ratio of 1:2 to the total mass of the mulberry leaves, kudzu root, and cinnamon to the mass of the water, to obtain the material to be fermented.

[0085] Step 2: Cook the material to be fermented at 120°C for 30 minutes to obtain a cooking mixture.

[0086] Step 3: Cool the cooking mixture to 28°C.

[0087] Then, add *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to the cooking mixture, maintain 28°C, stir and mix, and soak and ferment for 7 days to obtain the fermented mixture.

[0088] The total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 0.03% of the total mass of mulberry leaves, kudzu root, and cinnamon.

[0089] The mass ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 1:0.2:0.2.

[0090] Step 4: Sterilize the fermentation mixture at 80℃ for 8 minutes.

[0091] The sterilized fermentation mixture was centrifuged and the supernatant was collected to obtain a compound plant fermentation extract. Example 5

[0092] A method for preparing a compound plant fermentation extract includes the following steps:

[0093] Step 1: Wash the mulberry leaves, kudzu root, and cinnamon thoroughly with clean water to remove surface dust and dirt. Then, put the mulberry leaves, kudzu root, and cinnamon into a grinder and grind them to 1-5mm.

[0094] The mass ratio of mulberry leaves, kudzu root, and cinnamon is 7:3:1.

[0095] In this embodiment, 7 kg of mulberry leaves, 3 kg of kudzu root, and 1 kg of cinnamon were used.

[0096] The crushed mulberry leaves, kudzu root, and cinnamon are mixed with water in a ratio of 1:2 to the total mass of the mulberry leaves, kudzu root, and cinnamon to the mass of the water, to obtain the material to be fermented.

[0097] Step 2: Cook the material to be fermented at 120°C for 30 minutes to obtain a cooking mixture.

[0098] Step 3: Cool the cooking mixture to 28°C.

[0099] Then, add *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to the cooking mixture, maintain 28°C, stir and mix, and soak and ferment for 7 days to obtain the fermented mixture.

[0100] The total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 0.03% of the total mass of mulberry leaves, kudzu root, and cinnamon.

[0101] The mass ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* was 0.3:1:0.1.

[0102] Step 4: Sterilize the fermentation mixture at 80℃ for 8 minutes.

[0103] The sterilized fermentation mixture was centrifuged and the supernatant was collected to obtain a compound plant fermentation extract.

[0104] Comparative Example 1

[0105] A method for preparing a compound plant fermentation extract differs from Example 1 in that mulberry leaves are replaced with licorice.

[0106] Comparative Example 2

[0107] A method for preparing a compound plant fermentation extract differs from Example 1 in that kudzu root is replaced with yam.

[0108] Comparative Example 3

[0109] A method for preparing a compound plant fermentation extract differs from Example 1 in that cinnamon is replaced with hawthorn.

[0110] Comparative Example 4

[0111] A method for preparing a compound plant fermentation extract differs from Example 1 in that kudzu root and cinnamon are replaced with mulberry leaves.

[0112] Comparative Example 5

[0113] A method for preparing a compound plant fermentation extract differs from Example 1 in that Aspergillus niger is replaced with Aspergillus cristatus.

[0114] Comparative Example 6

[0115] A method for preparing a compound plant fermentation extract differs from Example 1 in that Lactobacillus acidophilus is replaced with Lactobacillus plantarum.

[0116] Comparative Example 7

[0117] A method for preparing a compound plant fermentation extract differs from Example 1 in that Geotrichum can be replaced with cellulase.

[0118] Comparative Example 8

[0119] A method for preparing a compound plant fermentation extract differs from Example 1 in that Lactobacillus acidophilus and Geotrichum candida are replaced with Aspergillus cristatus.

[0120] Comparative Example 9

[0121] A method for preparing a compound plant fermentation extract differs from Example 1 in that *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* are replaced with *Lactobacillus plantarum*.

[0122] 1. Total flavonoid content: Accurately weigh 20 mg of rutin reference standard dried to constant weight at 105℃, dissolve in 60% ethanol, and dilute to 100 mL to prepare the stock solution. Using the NaNO2-Al(NO3)3-NaOH complex chemical method, with a reagent blank as a reference, plot the rutin standard curve at 510 nm. The linear equation is: A = 0.0109C - 0.012 (C: concentration, mg·mL). -1 A: Absorbance), R=0.9997.

[0123] Take 1.0 mL of the compound plant fermentation extracts from Examples 1-5 and Comparative Examples 1-9 respectively, dilute to 10 mL, and measure the absorbance at 510 nm using the working curve method to calculate the total flavonoid yield. Record the total flavonoid yield in Table 1.

[0124]

[0125] Where: C is the mass concentration of flavonoids in the extract, mg·mL -1 V is the total volume of the extract, mL; M is the dry weight of the analyte, g.

[0126] 2. Antioxidant properties: DPPH free radical inhibition rate test

[0127] Weigh 0.5g of the compound plant fermentation extracts from Examples 1-5 and Comparative Examples 1-9 respectively, dissolve them in pure water, transfer them to 100mL volumetric flasks, and make up to volume to prepare a solution with a mass concentration of 5.00×10⁻⁶. -3 a sample solution of g / mL.

[0128] Transfer 3 mL of the sample solution to a 10 mL volumetric flask, then add 3 mL of a 2×10⁻⁶ solution. -4 Prepare a DPPH solution at a concentration of g / mL. Stopper the container, shake well, and allow to react for 30 min. Measure the absorbance (A) at 517 nm. i ; Measure the absorbance A of a mixture of 3 mL sample solution and 3 mL ethanol. j The concentration was determined to be 2×10 in 3 mL. -4 The absorbance A0 of a DPPH solution of g / mL mixed with 3 mL of pure water.

[0129] According to the formula P = [1 - (A) i -A j The measured absorbance is used to calculate the inhibition rate of the test solution against DPPH free radicals by substituting the measured absorbance into the formula ) / A0]×100%.

[0130] The inhibition rates are recorded in Table 1.

[0131] Table 1

[0132]

[0133] Comparative Examples 1-3 were based on Example 1, with mulberry leaves, kudzu root, and cinnamon replaced by other plants; Comparative Example 4 was based on Example 1, with kudzu root and cinnamon replaced by mulberry leaves, meaning flavonoids were extracted only from mulberry leaves. According to the comparison of the detection data in Table 1, the total flavonoid content of Comparative Examples 1-4 was lower than that of Example 1, and the DPPH· free radical inhibition rate of Comparative Examples 1-4 was also far lower than that of Example 1.

[0134] Comparative Examples 5-7 were based on Example 1, with *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* replaced by other microorganisms; Comparative Example 8 was based on Example 1, with *Lactobacillus acidophilus* and *Geotrichum candida* replaced by *Aspergillus cristatus*, meaning it contained only *Aspergillus cristatus*; Comparative Example 9 was based on Example 1, with *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* replaced by *Lactobacillus plantarum*, meaning it contained only *Lactobacillus plantarum*. According to the test data in Table 1, after disrupting the specific combination of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*, the total flavonoid content of the resulting compound plant fermentation extract was lower than that of Example 1, and its antioxidant properties were also inferior.

[0135] This indicates that disrupting the combination of plant raw materials such as mulberry leaves, kudzu root, and cinnamon, or disrupting the combination of microorganisms such as *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*, destroys the synergistic effect, thus failing to effectively increase the flavonoid content of the prepared compound plant fermentation extract, and also resulting in poor antioxidant properties.

[0136] Example 4 was based on Example 1, but with a different ratio of mulberry leaves, kudzu root, and cinnamon. Example 5 was based on Example 1, but with a different ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*. According to the test data in Table 1, Examples 4 and 5 showed a decrease in total flavonoid content and free radical inhibition rate. This indicates that further limiting the ratio of mulberry leaves, kudzu root, and cinnamon, or further limiting the ratio of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida*, can improve the synergistic effect between plants and microorganisms, thereby further enhancing the performance of the compound plant fermentation extract.

[0137] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a compound plant fermentation extract, characterized in that, Includes the following steps: Step 1: Crush mulberry leaves, kudzu root, and cinnamon, and mix them with water to obtain the material to be fermented; Step 2: Cook the material to be fermented at 110-130℃ for 25-40 minutes to obtain a cooking mixture; Step 3: Cool the cooking mixture to 25-30℃, add *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* to the cooking mixture, stir and mix, soak and ferment for 5-10 days to obtain the fermented mixture; Step 4: Sterilize and centrifuge the fermentation mixture, collect the supernatant, and obtain the compound plant fermentation extract; The mass ratio of mulberry leaves, kudzu root, and cinnamon is (6-8):(2-4):(0.5-1.5). The mass ratio of *Aurotium cristatum*, *Lactobacillus acidophilus*, and *Geotrichum candida* is 1:(0.1-0.3):(0.1-0.3).

2. The method for preparing the compound plant fermentation extract according to claim 1, characterized in that: The total mass of *Aspergillus cristatus*, *Lactobacillus acidophilus*, and *Geotrichum candida* is 0.01-0.05% of the total mass of mulberry leaves, kudzu root, and cinnamon.

3. The method for preparing the compound plant fermentation extract according to claim 1, characterized in that: In step 1, the total mass of mulberry leaves, kudzu root, and cinnamon is 1:(1-3) of the mass of water.

4. The method for preparing the compound plant fermentation extract according to claim 1, characterized in that: The sterilization conditions in step 4 are 75-85℃ for 5-10 minutes.

5. The method for preparing the compound plant fermentation extract according to claim 1, characterized in that: The mulberry leaves, kudzu root, and cinnamon are pulverized to 1-5mm.

6. A compound plant fermentation extract prepared by the method of any one of claims 1-5.

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