Preparation method of corn vinegar through lactic acid bacteria synergistic fermentation combined with ultrasonic-microwave accelerated aging treatment

Abstract

The invention discloses a preparation method of corn vinegar through lactic acid bacteria synergistic fermentation in combination with ultrasonic-microwave accelerated aging treatment, the method adopts an ultrasonic-microwave accelerated aging treatment technology to prepare novel corn vinegar, corn is taken as a raw material, liquefaction and saccharification stages are optimized through a two-enzyme method, and efficient conversion from corn starch to fermentable sugar is realized; lactobacillus plantarum is used for synergistically performing alcoholic fermentation to generate a plurality of flavor substances such as lactic acid and ethyl lactate; and the aging process of the corn vinegar is accelerated by combining ultrasonic-microwave aging accelerating treatment. Wherein ultrasonic waves can initiate a local high-temperature and high-pressure effect and a medium cavitation effect, so that polar molecules are orderly arranged, the molecular activation energy is improved, reactions such as esterification, condensation and oxidation reduction are accelerated, the energy consumption is relatively low, and the green production requirement is met; the microwave treatment breaks the association state of molecular groups in the original system through a microwave generator, and further accelerates the alkyd esterification process. The method solves the problems of unstable components and inharmonious smell in newly brewed corn vinegar.

Description

A method for preparing corn vinegar through lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging. Technical Field

[0001] This invention belongs to the field of food processing technology and relates to a method for preparing corn vinegar, specifically a method for preparing corn vinegar by synergistic fermentation with lactic acid bacteria and combined with ultrasonic-microwave aging treatment. Background Technology

[0002] Vinegar is an acidic condiment made from grains, fruits, or other sugary or starchy substances through fermentation. Numerous studies have shown that vinegar is rich in various organic acids, amino acids, vitamins, and minerals, and has effects such as promoting metabolism, anti-aging, and lowering blood lipids. Solid-state fermentation technology is complex, has poor stability, high cost, and low yield. Liquid-state fermentation, on the other hand, is characterized by high efficiency and yield, short fermentation cycle, stable quality, and suitability for the mass market.

[0003] In my country, rice, sorghum, and wheat are the main raw materials for vinegar production. Corn, as a high-yield and low-cost grain crop, is suitable as a raw material for vinegar brewing. Its protein content is 9.6%, and its starch content is 72.0%, with a crude starch content comparable to sorghum, providing ample carbon source for acetic acid bacteria. It is also rich in amylopectin, promoting the accumulation of flavor compounds. Furthermore, corn has a wide planting area, high yield, strong resistance to adverse conditions, and is not limited by season, which is conducive to industrial production. In addition, the loose cell wall structure of corn makes it easier for enzymatic hydrolysis and saccharification after proper crushing; its moderate protein content avoids the production of excessive higher alcohols during fermentation. Finally, the decomposition of corn protein produces flavor amino acids such as valine and leucine, making corn vinegar more mellow in flavor; at the same time, corn is rich in vitamin E, and its linoleic acid gives corn vinegar higher antioxidant capacity. However, the market size of vinegar made from corn through fermentation is relatively small, with a single flavor profile, lacking the diversity and complexity of fruit vinegars, and its production technology and market awareness need to be improved.

[0004] Corn vinegar production mainly involves two continuous fermentation processes: first, alcoholic fermentation, where yeast converts fermentable sugars into ethanol under anaerobic conditions; and second, acetic acid fermentation, where acetic acid bacteria convert ethanol into acetic acid under aerobic conditions. These two processes are crucial for the formation of vinegar's flavor. Lactic acid bacteria, as a highly efficient microbial fortifier, can produce short-chain fatty acids such as lactic acid and acetic acid through fermentation and are widely used in fermented foods such as dairy products, fruit wines, pickles, and soy sauce. Existing research shows that it can interact with yeast and acetic acid bacteria during both alcoholic and acetic acid fermentation stages, thereby improving vinegar flavor and enhancing its antioxidant activity. Citrus vinegar fermented using a mixed culture of *Saccharomyces cerevisiae* and *Lactobacillus plantarum* showed higher levels of formic acid, lactic acid, and total organic acids than the pure culture, and the mixed-culture fermented citrus vinegar exhibited even higher antioxidant activity. Persimmon vinegar obtained by biofortification fermentation using one ester-producing strain and two lactic acid bacteria strains (Lactobacillus plantarum CGMCC2 and Lactobacillus acidophilus R2) has a milder taste, significantly reduced acetic acid irritation, and significantly increased content of flavor compounds such as citric acid, lactic acid, malic acid, ethyl lactate, methyl acetate, isocitrate, and acetoin.

[0005] Furthermore, studies have shown that appropriate ultrasound and microwave technologies can promote the aging process of vinegar, increasing the activity of various substances and their interactions, thereby accelerating various chemical reactions such as condensation, oxidation, and reduction. This improves the nutritional quality of vinegar and minimizes the loss of flavor compounds such as esters and alcohols, as well as heat-sensitive components like vitamin C and polyphenols. Ultrasonic treatment significantly enhanced several bioactivity indicators of hawthorn vinegar, including total phenolic compounds (TPC), total flavonoids (TFC), ascorbic acid (AA), DPPH free radical scavenging activity, and CUPRAC reducing capacity, thus enhancing its potential as a functional food. Strawberry vinegar optimized through ultrasonic treatment showed increased levels of malic acid, lactic acid, and oxalic acid, while also positively impacting its bioactivity and phenolic content. In addition, multiple studies have shown that ultrasonic treatment can increase the content of bioactive substances in various vinegars, including cranberry vinegar, palm vinegar, blueberry vinegar, and jujube vinegar. After treating red wine with a combination of ultrasound and microwave, the release of total polysaccharides, mannose protein, total monosaccharides, and amino acids such as proline increased. However, there are currently no reports on ultrasound-microwave aging treatment of corn vinegar. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing corn vinegar using lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging. This method addresses the problems of unstable components and unbalanced aromas in newly brewed corn vinegar by optimizing the raw material processing, lactic acid bacteria co-fermentation process, and ultrasonic-microwave aging technology. Lactic acid bacteria fermentation improves the flavor of the corn vinegar, while ultrasonic-microwave treatment promotes its subsequent maturation, ultimately producing a corn vinegar with a unique flavor, rich nutrition, and strong functional properties.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing corn vinegar by lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging includes the following steps:

[0009] Step 1: Raw material selection and pretreatment:

[0010] Step 1-1, Selection and pretreatment of corn: Select peeled and degermed corn, wash and dry it, grind it to 40-60 mesh, mix it with water at a mass ratio of 1:4-6, and heat it to gelatinize. The gelatinization temperature is 100℃ and the time is 30-90 minutes.

[0011] Steps 1-2, liquefaction: Add activated thermostable α-amylase to liquefy the corn flour. The amount of thermostable α-amylase added should be 0.4-0.8% of the corn flour mass. The liquefaction temperature should be 90-100℃ and the time should be 30-90 min.

[0012] Steps 1-3, Saccharification: Cool to 50~70℃, add saccharifying enzyme for saccharification, wherein: the amount of saccharifying enzyme added is 0.1~0.3% of the mass of corn flour, the saccharification temperature is 50~70℃, and the time is 40~60min;

[0013] Steps 1-4: Sterilization: 80~100℃, sterilize for 10~30 minutes to obtain corn saccharification residue;

[0014] Step 2: Prepare corn vinegar through liquid fermentation with the help of Lactobacillus plantarum.

[0015] Step 2-1, Alcoholic fermentation: Add activated yeast to the corn saccharification mash, inoculate the activated Lactobacillus plantarum culture into the corn saccharification mash, seal and ferment at 30℃ for 5-7 days to obtain corn wine, wherein: the amount of yeast added is 0.1-0.3% of the mass of corn flour, the amount of Lactobacillus plantarum culture inoculation is 5-10%, the alcohol content of corn wine is 7% vol, and the Lactobacillus plantarum culture is obtained according to the following method: (1) MRS broth culture medium used for activating Lactobacillus plantarum (10g peptone, 10g beef extract, 5g yeast extract, 2g diammonium citrate, 5g sodium acetate, 20g glucose, Tween 80) 1 mL, magnesium sulfate 0.2 g, manganese sulfate 0.05 g, dipotassium hydrogen phosphate 2 g, heated and dissolved in 1 L of distilled water, sterilized at 121℃ for 15 min) to prepare and sterilize; (2) Activation and subculturing of strains: inoculate Lactobacillus plantarum into liquid culture medium at an inoculation rate of 4%, culture at 37℃ for 12 h, subculture 2-3 times, and obtain Lactobacillus plantarum culture medium for later use;

[0016] Step 2-2, Acetic acid fermentation: Inoculate acetic acid bacteria seed liquid into 7% vol corn wine, seal the container, and culture in a shaker until the acidity is basically stable. The inoculation amount of acetic acid bacteria seed liquid is 5~10%, the culture temperature is 30℃, and the rotation speed is 160~200r / min. The acetic acid bacteria seed liquid is obtained by the following method: (1) Prepare and sterilize the liquid culture medium (10g glucose, 10g yeast extract, 5mL anhydrous ethanol, 1000mL distilled water, pH natural) used for activating acetic acid bacteria; (2) Activation, subculturing, and acclimatization of the strain: Inoculate acetic acid bacteria into the liquid culture medium at an inoculation amount of 5%, culture in a shaker at 30℃ and 180r / min for 24h, subculture twice, and obtain the culture medium for later use. Inoculate 7% vol corn wine at an inoculation amount of 5% for acclimatization, and the acid production reaches 2g / 100mL to obtain the acetic acid bacteria seed liquid for later use.

[0017] Steps 2-3: Centrifugation and filtration: Centrifuge and collect the supernatant, then filter it again using an ultrafiltration membrane and sterilize it. The centrifugation speed is 6000~10000 r / min, the time is 10~30 min, the pore size of the ultrafiltration membrane is 0.22 μm, the sterilization temperature is 80~100℃, and the time is 10~30 min.

[0018] Step 3: Perform ultrasonic-microwave aging treatment on the corn vinegar:

[0019] The corn vinegar prepared in step 2 is first subjected to ultrasonic treatment, and then to microwave treatment. The ultrasonic treatment power is 600~800W and the time is 10~30min; the microwave treatment power is 300~500W and the time is 10~30s, and the number of times is 2~4.

[0020] Step 4: Determination of flavor compounds and bioactive substances in corn vinegar:

[0021] The corn vinegar prepared in step 3 was stored in a refrigerator at 4°C, and the flavor compounds and bioactive substances were determined.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention utilizes ultrasonic-microwave aging technology to prepare a novel corn vinegar. Using corn as raw material, it optimizes the liquefaction and saccharification stages through a dual-enzyme method, achieving efficient conversion of corn starch into fermentable sugars. It employs *Lactobacillus plantarum* for synergistic alcoholic fermentation, generating various flavor compounds such as lactic acid and ethyl lactate. The ultrasonic-microwave aging process is then accelerated. Ultrasonic waves induce localized high-temperature, high-pressure effects and cavitation, promoting the orderly arrangement of polar molecules, increasing molecular activation energy, and accelerating esterification, condensation, and redox reactions. This process is energy-efficient and meets green production requirements. Microwave treatment breaks down the association of molecular groups in the original system using a microwave generator, further accelerating the alcohol and acid esterification process. This invention, by combining lactic acid bacteria bio-enhanced fermentation with ultrasonic-microwave aging technology, produces a corn vinegar product rich in various bioactive substances, suitable for long-term consumption. Attached Figure Description

[0024] Figure 1 is a flowchart of the preparation route of corn vinegar by lactic acid bacteria co-fermentation and combined ultrasonic-microwave aging treatment;

[0025] Figure 2 shows the content of flavor compounds in vinegar;

[0026] Figure 3 shows the content of bioactive substances in vinegar. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0028] Comparative Example 1:

[0029] Step 1: Preparation of corn vinegar:

[0030] Step 1-1, Raw material selection: Select peeled and germ-free corn, wash and dry it, and grind it to 40 mesh.

[0031] Steps 1-2: Raw material pretreatment: Mix 120g corn flour with 600g purified water and soak for at least 12 hours. Heat at 100℃ for 60 minutes to gelatinize. Add 0.72g activated α-amylase and liquefy at 90℃ for 60 minutes. Cool to 60℃ and add 0.24g saccharifying enzyme, then saccharify at 60℃ for 50 minutes. Sterilize in a water bath at 80℃ for 20 minutes, then seal and store for later use.

[0032] Steps 1-3: Alcoholic fermentation: Add 0.12g of activated yeast to 720g of corn saccharification dregs, seal and ferment at 30℃ for 6 days until the alcohol content reaches 7% vol.

[0033] Steps 1-4: Acetic acid fermentation: Pick a certain amount of bacterial cells with an inoculation loop and directly inoculate them into 5 mL of liquid culture medium to activate the acetic acid bacteria. Incubate at 30℃, 180 rpm for 24 hours, then perform two more expansion cultures to obtain acetic acid bacteria seed culture. Inoculate 5% of this seed culture into 7% vol corn alcohol to obtain acetic acid bacteria seed culture. Add 10% of the acetic acid bacteria seed culture to the 7% vol corn alcohol, seal with four layers of gauze, and incubate at 30℃ and 180 rpm in a shaker until the acidity no longer changes.

[0034] Step 2: Sterilize the corn vinegar prepared in Step 1 by centrifugation and filtration.

[0035] Step 2-1, Centrifugation and filtration: Centrifuge at 8000 r / min for 10 min, collect the supernatant, and filter again using a 0.22 μm ultrafiltration membrane.

[0036] Step 2-2, pasteurization: pasteurize at 80℃ for 20 minutes.

[0037] Step 3: Determination of flavor compounds and bioactive substances:

[0038] The corn vinegar prepared in step 2 was stored in a refrigerator at 4°C and the flavor and bioactive substances were determined.

[0039] As shown in Figures 2 and 3, the flavor compounds include acids, alcohols, esters, ketones, aldehydes, and others, with proportions of 63%, 16%, 17%, 1%, 2%, and 1%, respectively. The main acids are acetic acid, isobutyric acid, and isovaleric acid; the main alcohols are ethanol, phenethyl alcohol, isoamyl alcohol, and isobutanol; the main esters are ethyl acetate, isoamyl acetate, and phenethyl acetate; the main aldehydes are acetaldehyde, benzaldehyde, and nonanal; and the main ketone is 3-hydroxy-2-butanone. The total flavonoid content was 53.19 ± 3.49 mg / L, and the total phenolic content was 143.34 ± 1.86 mg / L. The phenolic compounds mainly originate from corn raw materials (such as ferulic acid and p-coumaric acid) and microbial transformation during fermentation. Flavonoids in corn mainly exist in the form of flavonoid glycosides, and their transformation mechanism is similar to that of phenols, but more dependent on the hydrolysis of glycosidic bonds.

[0040] Example 1

[0041] Step 1: Preparation of corn vinegar:

[0042] Step 1-1, Raw material selection: Select peeled and germ-free corn, wash and dry it, and grind it to 40 mesh.

[0043] Steps 1-2: Raw material pretreatment: Mix 120g corn flour with 600g purified water and soak for at least 12 hours. Heat at 100℃ for 60 minutes to gelatinize. Add 0.72g activated α-amylase and liquefy at 90℃ for 60 minutes. Cool to 60℃ and add 0.24g saccharifying enzyme, then saccharify at 60℃ for 50 minutes. Sterilize in a water bath at 80℃ for 20 minutes, then seal and store for later use.

[0044] Steps 1-3: Alcoholic fermentation: Add 0.12g of activated yeast and 10% of Lactobacillus plantarum that has been passaged 3 times to 720g of corn saccharification lees. Seal and ferment at 30℃ for 6 days until the alcohol content reaches 7% vol.

[0045] Steps 1-4: Acetic acid fermentation: Pick a certain amount of bacterial cells with an inoculation loop and directly inoculate them into 5 mL of liquid culture medium to activate the acetic acid bacteria. Incubate at 30℃, 180 rpm for 24 hours, then perform two more expansion cultures to obtain acetic acid bacteria seed culture. Inoculate 5% of this seed culture into 7% vol corn alcohol to obtain acetic acid bacteria seed culture. Add 10% of the acetic acid bacteria seed culture to the 7% vol corn alcohol, seal with four layers of gauze, and incubate at 30℃ and 180 rpm in a shaker until the acidity no longer changes.

[0046] Step 2: Centrifuge, filter, and sterilize the corn vinegar prepared in Step 1.

[0047] Step 2-1, Centrifugation and filtration: Centrifuge at 8000 r / min for 10 min, collect the supernatant, and filter again using a 0.22 μm ultrafiltration membrane.

[0048] Step 2-2, pasteurization: pasteurize at 80℃ for 20 minutes.

[0049] Step 3: Determination of flavor compounds and bioactive substances

[0050] The corn vinegar prepared in step 2 was stored in a refrigerator at 4°C and the flavor and bioactive substances were determined.

[0051] As shown in Figures 2 and 3, the flavor compounds include acids, alcohols, esters, ketones, aldehydes, and others, with proportions of 63%, 11%, 22%, 1%, 3%, and 1%, respectively. The total flavonoid content is 71.59 ± 1.87 mg / L, and the total phenol content is 183.79 ± 3.16 mg / L. The increased proportion of esters is mainly due to the production of new acids and esters by *Lactobacillus plantarum* fermentation, primarily lactic acid and ethyl lactate. Furthermore, the newly introduced lactic acid substrate undergoes esterification reactions with alcohols, especially the conversion of ethanol and lactic acid into ethyl lactate. The aldehydes are mainly nonanal and hexanal. *Lactobacillus plantarum* produces acid, creating a low pH environment that accelerates fatty acid oxidation and the oxidation of alcohols into aldehydes, thus increasing the proportion of aldehydes.

[0052] Lactobacillus plantarum has abundant esterase and glycosidase activity, which can effectively hydrolyze bound polyphenols, such as phenolic acids and polysaccharides, in the cell wall of corn, converting bound, inactive phenols and flavonoids into free, highly active forms, thereby increasing the content of total phenols and total flavonoids.

[0053] Example 2

[0054] Step 1: Preparation of corn vinegar:

[0055] Step 1-1, Raw material selection: Select peeled and germ-free corn, wash and dry it, and grind it to 40 mesh.

[0056] Steps 1-2: Raw material pretreatment: Mix 120g corn flour with 600g purified water and soak for at least 12 hours. Heat at 100℃ for 60 minutes to gelatinize. Add 0.72g activated α-amylase and liquefy at 90℃ for 60 minutes. Cool to 60℃ and add 0.24g saccharifying enzyme, then saccharify at 60℃ for 50 minutes. Sterilize in a water bath at 80℃ for 20 minutes, then seal and store for later use.

[0057] Steps 1-3: Alcoholic fermentation: Add 0.12g of activated yeast and 10% of Lactobacillus plantarum that has been passaged 3 times to 720g of corn saccharification lees. Seal and ferment at 30℃ for 6 days until the alcohol content reaches 7% vol.

[0058] Steps 1-4: Acetic acid fermentation: Pick a certain amount of bacterial cells with an inoculation loop and directly inoculate them into 5 mL of liquid culture medium to activate the acetic acid bacteria. Incubate at 30℃, 180 rpm for 24 hours, then perform two more expansion cultures to obtain acetic acid bacteria seed culture. Inoculate 5% of this seed culture into 7% vol corn alcohol to obtain acetic acid bacteria seed culture. Add 10% of the acetic acid bacteria seed culture to the 7% vol corn alcohol, seal with four layers of gauze, and incubate at 30℃ and 180 rpm in a shaker until the acidity no longer changes.

[0059] Step 2: Centrifuge, filter, and sterilize the corn vinegar prepared in Step 1.

[0060] Step 2-1, Centrifugation and filtration: Centrifuge at 8000 r / min for 10 min, collect the supernatant, and filter again using a 0.22 μm ultrafiltration membrane.

[0061] Step 2-2, pasteurization: pasteurize at 80℃ for 20 minutes.

[0062] Step 3: Perform ultrasonic-microwave aging treatment on the corn vinegar prepared in Step 2:

[0063] The corn vinegar was subjected to ultrasonic treatment at 600W for 20 minutes, followed by microwave treatment at 400W for 20 seconds three times.

[0064] Step 4: Determination of flavor compounds and bioactive substances:

[0065] The corn vinegar prepared in step 3 was stored in a refrigerator at 4°C and the flavor and bioactive substances were determined.

[0066] As shown in Figures 2 and 3, the flavor compounds include acids, alcohols, esters, ketones, aldehydes, and others, with proportions of 61%, 10%, 25%, 1%, 2%, and 1%, respectively. The total flavonoid content is 103.52 ± 0.39 mg / L, and the total phenol content is 221.86 ± 1.56 mg / L. Ultrasound-microwave stimulation generates a large number of hydroxyl radicals in the solution. By creating localized high temperature and pressure, it accelerates molecular collisions, producing cavitation and thermal effects, which greatly promotes the esterification reaction rate of acids and alcohols, especially non-enzymatic esterification. Ultrasound-microwave stimulation also alters the degree of hydrogen bonding in the solution molecules, thereby increasing the number of molecules involved in bonding and reducing the number of irritating free molecules. This is the fundamental reason for the increased proportion of esters and the rapid "mellowing" of the flavor. Furthermore, aldehydes are chemically reactive and are easily reduced to their corresponding alcohols or oxidized to acids during the aging process. This process reduces the content of aldehydes that contribute to a raw, pungent odor, thus contributing to a smoother flavor.

[0067] The increase in total phenols and flavonoids is mainly due to the strong shearing force generated by the "cavitation effect" of ultrasound, which can destroy the molecular structure and dissolve more bound and embedded phenolic substances. The combined action of ultrasound and microwave can more thoroughly destroy the microstructure of corn residue, releasing more bound flavonoid glycosides and providing more substrates for subsequent enzymatic or acid hydrolysis.

Claims

1. A method for preparing corn vinegar by synergistic fermentation with lactic acid bacteria combined with ultrasonic-microwave aging, characterized in that... The method includes the following steps: Step 1, Raw material selection and pretreatment: Step 1-1, Selection and pretreatment of corn: Select peeled and degermed corn, wash and dry it, crush it to 40-60 mesh, mix it with water at a mass ratio of 1:4-6, and heat to gelatinize; Step 1-2, Liquefaction: Add activated heat-resistant α-amylase for liquefaction; Step 1-3, Saccharification: Cool to 50-70℃, add saccharifying enzyme for saccharification; Step 1-4, Sterilization: Sterilize at 80-100℃ for 10-30 minutes to obtain corn saccharification mash; Step 2, Preparation of corn vinegar by liquid fermentation with Lactobacillus plantarum: Step 2-1, Alcoholic fermentation: Add activated yeast to the corn saccharification mash, inoculate the activated Lactobacillus plantarum solution into the corn saccharification mash, seal and ferment at 30℃ for 5-7 days to obtain corn wine; Step 2-2, Acetic acid fermentation: Add 7%... Inoculate acetic acid bacteria seed liquid into vol corn wine, seal the container, and culture in a shaker until the acidity is basically stable; Steps 2-3: Centrifugation and filtration: Centrifuge to collect the supernatant, filter it again using an ultrafiltration membrane, and sterilize; Step 3: Ultrasonic-microwave accelerated aging treatment of corn vinegar: Sonicate the corn vinegar prepared in step 2 first, and then microwave it.

2. The method for preparing corn vinegar by lactic acid bacteria synergistic fermentation combined with ultrasonic-microwave aging according to claim 1, characterized in that... In step 1-1, the gelatinization temperature is 100℃ and the time is 30~90min.

3. The method for preparing corn vinegar by lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging according to claim 1, characterized in that... In steps 1-2, the amount of heat-resistant α-amylase added is 0.4-0.8% of the corn flour mass, the liquefaction temperature is 90-100℃, and the time is 30-90 min.

4. The method for preparing corn vinegar by lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging according to claim 1, characterized in that... In steps 1-3, the amount of saccharifying enzyme added is 0.1-0.3% of the corn flour mass, the saccharification temperature is 50-70℃, and the time is 40-60 min.

5. The method for preparing corn vinegar by lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging according to claim 1, characterized in that... In step 2-1, the amount of yeast added is 0.1-0.3% of the mass of corn flour, the inoculation amount of Lactobacillus plantarum culture is 5-10%, the alcohol content of corn wine is 7% vol, and the Lactobacillus plantarum culture is obtained by the following method: (1) Prepare and sterilize the MRS broth medium used for activating Lactobacillus plantarum; (2) Activation and subculturing of the strain: Inoculate Lactobacillus plantarum into the liquid culture medium at an inoculation amount of 4%, culture at 37℃ for 12h, and subculture 2-3 times to obtain Lactobacillus plantarum culture medium for later use.

6. The method for preparing corn vinegar by lactic acid bacteria synergistic fermentation combined with ultrasonic-microwave aging according to claim 5, characterized in that... The MRS broth culture medium formula used for activating *Lactobacillus plantarum* is as follows: 10g peptone, 10g beef extract, 5g yeast extract, 2g diammonium citrate, 5g sodium acetate, 20g glucose, 1mL Tween 80, 0.2g magnesium sulfate, 0.05g manganese sulfate, and 2g dipotassium hydrogen phosphate, dissolved in 1L distilled water and sterilized at 121℃ for 15min.

7. The method for preparing corn vinegar by lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging according to claim 1, characterized in that... In step 2-2, the inoculation amount of acetic acid bacteria seed liquid is 5-10%, the culture temperature is 30℃, and the rotation speed is 160-200r / min. The acetic acid bacteria seed liquid is obtained by the following method: (1) Prepare and sterilize the liquid culture medium used for activating acetic acid bacteria; (2) Activation, subculturing, and acclimatization of the strain: Inoculate acetic acid bacteria into the liquid culture medium at an inoculation amount of 5%, culture at 30℃ and 180r / min for 24h, subculture twice, and obtain the culture medium for later use. Inoculate acetic acid bacteria into 7% vol corn wine at an inoculation amount of 5% for acclimatization, and the acid production reaches 2g / 100mL, and obtain the acetic acid bacteria seed liquid for later use.

8. The method for preparing corn vinegar by lactic acid bacteria synergistic fermentation combined with ultrasonic-microwave aging according to claim 7, characterized in that... The liquid culture medium formula used for activating acetic acid bacteria is as follows: 10g glucose, 10g yeast extract, 5mL anhydrous ethanol, 1000mL distilled water, and natural pH.

9. The method for preparing corn vinegar by lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging according to claim 1, characterized in that... In steps 2-3, the centrifugation speed is 6000~10000 r / min, the time is 10~30 min, the pore size of the ultrafiltration membrane is 0.22 μm, the sterilization temperature is 80~100℃, and the time is 10~30 min.

10. The method for preparing corn vinegar by lactic acid bacteria co-fermentation combined with ultrasonic-microwave aging according to claim 1, characterized in that... In step 3, the power of ultrasonic treatment is 600~800W, the time is 10~30min; the power of microwave treatment is 300~500W, the time is 10~30s, and the number of times is 2~4.

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