Fermented mustard and preparation method thereof

Abstract

The invention relates to a preparation method of fermented leaf mustard, which comprises the following steps: S1) pretreatment: taking fresh leaf mustard, cleaning, draining water, and sterilizing the leaf mustard to obtain sterile leaf mustard; s2) blanching: blanching the sterile mustard obtained in the step S1 with hot water, draining off water after blanching, and then loading into a fermentation container; and S3) seasoning and fermentation: adding seasonings into the fermentation container, then adding the fermentation liquor into the fermentation container until the mustard is completely immersed, inoculating lactobacillus plantarum into the fermentation liquor when the temperature of the fermentation liquor is 37 + / -2 DEG C, and then performing sealed fermentation at 25 DEG C for 20-25 days to obtain the finished product. The invention further provides the fermented leaf mustard prepared by the method. According to the preparation method of the fermented leaf mustard, the content of nitrite in the leaf mustard fermentation process can be effectively reduced, so that the safety of the fermented leaf mustard is higher; meanwhile, the preparation method disclosed by the invention can also reduce the use amount of table salt and effectively guarantee the flavor of the leaf mustard.

Description

Technical Field

[0001] This invention relates to the food industry, and more particularly to a method for preparing fermented mustard greens, and the fermented mustard greens obtained according to the method. Background Technology

[0002] Traditional vegetable fermentation processes (such as kimchi and sauerkraut) have a long history in my country, primarily relying on natural fermentation and the lactic acid bacteria naturally present in the vegetables, along with environmental microorganisms. However, this process has several technical drawbacks. Firstly, there is the safety hazard of nitrites. Vegetables (such as mustard greens) accumulate large amounts of nitrates during cultivation due to nitrogen fertilizer application, harvesting, and storage. During fermentation, these nitrates are easily converted into highly toxic nitrites by nitrate-reducing bacteria. Excessive nitrite intake can lead to acute poisoning (such as methemoglobinemia) and, in the body, be converted into the potent carcinogen nitrosamine, increasing the risk of diseases such as stomach cancer. Secondly, there is the issue of high salt dependence. Traditional processes typically rely on high salt (sodium chloride) to inhibit unwanted bacteria, but long-term high sodium intake can easily lead to hypertension, cardiovascular disease, and kidney strain. Finally, the fermentation process is uncontrollable. Natural fermentation depends on environmental microorganisms, which are complex and susceptible to contamination, resulting in large fluctuations in nitrite content and unstable quality.

[0003] In recent years, attempts have been made to reduce nitrite content in fermented vegetables by inoculating with a single microbial strain. However, these strains have poor adaptability to low-salt environments, making it difficult to inhibit the entry and growth of other microbial strains. Furthermore, the conversion of nitrate to nitrite is difficult to control effectively, resulting in persistently high nitrite levels. Therefore, a fermentation process capable of reducing nitrite content is needed. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a method for preparing fermented mustard greens that can reduce nitrite production.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing fermented mustard greens, the method comprising the following steps: S1) Pretreatment: Take fresh mustard greens, wash and drain them, and then sterilize them to obtain sterile mustard greens; S2) Blanching: Blanch the sterile mustard greens obtained in step S1 with hot water, drain the water after blanching, and then put them into a fermentation container. S3) Seasoning and fermentation: Add seasoning to the fermentation container, then add fermentation liquid to the fermentation container until the mustard greens are completely submerged. When the temperature of the fermentation liquid is 37±2℃, inoculate Lactobacillus plantarum into the fermentation liquid, and then carry out sealed fermentation at 25℃ for 20-25 days to obtain the product.

[0006] In a further preferred embodiment of the present invention, the seasonings include salt, sugar, garlic, white vinegar, ginger, and chili peppers, wherein the amount of salt added is 2% to 2.5% of the weight of the mustard greens, the amount of sugar added is 1% to 2% of the weight of the mustard greens, the amount of garlic added is 0.1% to 0.2% of the weight of the mustard greens, the amount of white vinegar added is 0.1% to 0.2% of the weight of the mustard greens, the amount of ginger added is 0.1% to 0.2% of the weight of the mustard greens, and the amount of chili peppers added is 0.1% to 0.2% of the weight of the mustard greens.

[0007] In a further preferred embodiment of the present invention, the amount of garlic added is 0.1% of the weight of the mustard greens, the amount of white vinegar added is 0.1% of the weight of the mustard greens, the amount of ginger added is 0.1% of the weight of the mustard greens, the amount of chili pepper added is 0.1% of the weight of the mustard greens, the chili pepper is a small red chili pepper, and the white sugar is granulated sugar. In a further preferred embodiment of the present invention, the amount of *Lactobacillus plantarum* inoculated is 0.1% to 0.5% of the weight of the mustard greens.

[0008] In this invention, a further preferred embodiment is that the amount of *Lactobacillus plantarum* inoculated is 0.4% of the weight of the mustard greens.

[0009] In this invention, a further preferred embodiment is to drain the water from the blanched mustard greens in step S1 while keeping them upright.

[0010] In this invention, a further preferred embodiment is that, in step S2), the blanching process involves completely immersing the mustard greens in hot water for a blanching time of 20-30 seconds, with the hot water temperature being 85-95°C.

[0011] In this invention, a further preferred embodiment is that the hot water used to blanch the mustard greens in step S2) is used as the fermentation liquid in step S3, wherein the temperature of the hot water is 85-95℃.

[0012] In this invention, a further preferred embodiment is that the temperature of the fermentation liquid when added to the fermentation container is 80°C.

[0013] In this invention, a further preferred embodiment is that in step S3, the fermentation temperature is controlled at 25±0.5℃ and the fermentation time is 20-25 days.

[0014] In this invention, a further preferred embodiment is that the *Lactobacillus plantarum* is activated before inoculation. The activation process specifically involves: taking freeze-dried *Lactobacillus plantarum* powder, inoculating it into MRS liquid culture medium, activating it in a shaking incubator at 37±0.5℃ for 22-26 h, then centrifuging the culture medium to collect the bacterial cells, and then resuspending the bacterial cells with physiological saline.

[0015] In this invention, a further preferred embodiment is that the sterilization process in step S1 specifically involves immersing the mustard greens in 42-degree alcohol for 10-20 seconds.

[0016] In this invention, a further preferred embodiment is that the *Lactobacillus plantarum* is *Lactobacillus plantarum* obtained through a gradient salt reduction acclimatization method. The gradient salt reduction acclimatization method specifically involves gradually reducing the salt concentration in the culture medium to acclimate the *Lactobacillus plantarum*, with the salt concentration decreasing from 8-10% to 2-2.5% in a gradient of 3-6 levels.

[0017] Another aspect of the present invention is to claim protection for fermented mustard greens prepared by the above-described preparation method, wherein the fermented mustard greens contain 0.2-0.3 g / 100g of amino acid nitrogen, 0.25-0.38 mg / kg of nitrite, and have a pH value of 3.14-3.41.

[0018] In this invention, a further preferred embodiment is that the fermented mustard greens contain 0.3 g / 100g of amino acid nitrogen, 0.25 mg / kg of nitrite, and have a pH value of 3.41.

[0019] The technical effects of this invention are as follows: The fermented mustard greens preparation method of this invention can effectively reduce the nitrite content in the fermentation process of mustard greens, making the fermented mustard greens safer; at the same time, the preparation method of this invention can also reduce the amount of salt used and effectively preserve the flavor of the mustard greens.

[0020] Other features and aspects of the invention will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0021] The accompanying drawings, which are included in and form part of this specification, illustrate exemplary embodiments, features, and aspects of the invention together with the specification and serve to explain the principles of the invention.

[0022] Figure 1 The graph shows the nitrite content-time data of fermented mustard greens prepared by inoculating different concentrations of Lactobacillus plantarum during Examples 1-7. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] A method for preparing fermented mustard greens, the method comprising the following steps: S1) Pretreatment: Take fresh mustard greens, wash and drain them, and then sterilize them to obtain sterile mustard greens; S2) Blanching: Blanch the sterile mustard greens obtained in step S1 with hot water, drain the water after blanching, and then put them into a fermentation container. S3) Seasoning and fermentation: Add seasoning to the fermentation container, then add fermentation liquid to the fermentation container until the mustard greens are completely submerged. When the temperature of the fermentation liquid is 37±2℃, inoculate Lactobacillus plantarum into the fermentation liquid, and then carry out sealed fermentation at 25℃ (if a fermentation jar is used as the fermentation container, sealed fermentation is called jar fermentation) for 20-25 days to obtain the product.

[0029] The fermented mustard preparation method of the present invention, by sterilizing the mustard, can reduce the number of contaminating bacteria when the mustard is subsequently inoculated with Lactobacillus plantarum for fermentation, thus enabling effective pure strain directional fermentation and reducing the yield of nitrite.

[0030] The seasonings in this invention can be selected based on taste, with their composition and dosage chosen from salt, sugar, garlic, vinegar, ginger, chili peppers, and other seasonings suitable for vegetable fermentation. Furthermore, to improve the taste of fermented mustard greens, the following seasonings are preferred: the seasonings include salt, sugar, garlic, white vinegar, ginger, and chili peppers, wherein the amount of salt added is 2%–2.5% of the mustard greens' weight, the amount of sugar added is 1%–2% of the mustard greens' weight, the amount of garlic added is 0.1% of the mustard greens' weight, the amount of white vinegar added is 0.1%–0.2% of the mustard greens' weight, the amount of ginger added is 0.1%–0.2% of the mustard greens' weight, and the amount of chili peppers added is 0.1%–0.2% of the mustard greens' weight. The garlic, chili peppers, etc., in this seasoning not only enrich and enhance the flavor of the fermented mustard greens but also effectively inhibit bacteria and improve fermentation efficiency. Furthermore, you can choose small red chilies; use granulated sugar; and use fresh ginger. For ginger, chilies, and garlic, you can make them into granules or mince before adding them, which will allow the fermented mustard greens to absorb the flavor more quickly.

[0031] To further reduce the nitrite content of fermented mustard greens, the inoculation amount of *Lactobacillus plantarum* is 0.1% to 0.5% of the mustard greens' weight; more specifically, the inoculation amount of *Lactobacillus plantarum* is 0.4% of the mustard greens' weight. Inoculating with this proportion of *Lactobacillus plantarum* not only reduces the nitrite content to as low as 0.25 mg / kg, but also accumulates abundant amino acid nitrogen (up to 0.3 g / 100g). This not only reduces the nitrite content but also ensures good flavor.

[0032] In this invention, the blanched mustard greens in step S1 are drained while still upright, which is more conducive to the dissipation of heat.

[0033] In this invention, in step S2), the blanching process involves completely immersing the mustard greens in hot water for 20-30 seconds. The temperature of the hot water used for blanching is 85-95°C. This process effectively kills bacteria, insects, and insect eggs on the mustard greens while preventing excessive nutrient spoilage and loss. Conversely, excessively long blanching times or high temperatures can lead to excessive nutrient spoilage and loss, while excessively low temperatures will result in poor sterilization.

[0034] In this invention, the hot water used after blanching the mustard greens in step S2) is used as the fermentation liquid in step S3. The temperature of the hot water is 85-95℃. This ensures that the hot water contains the nutrients lost during blanching, which can provide nourishment for the subsequent production of *Lactobacillus plantarum*. Furthermore, the homologous nutrients also contribute to a more stable fermentation environment. Moreover, the temperature of the fermentation liquid added to the fermentation container is 80℃. This temperature setting effectively kills microorganisms in the fermentation container, its seasonings, and on the mustard greens, while also preventing nutrient loss. This provides a favorable initial environment for subsequent inoculation with *Lactobacillus plantarum*. Testing showed that the vitamin C retention rate was higher than 85%, demonstrating that nutrient loss and damage were effectively avoided.

[0035] In this invention, a further preferred embodiment is that in step S3, the fermentation temperature is controlled at 25±0.5℃ and the fermentation time is 20-25 days.

[0036] To facilitate the inoculation of Lactobacillus plantarum, an activation treatment is performed before inoculation. The activation treatment specifically involves: taking freeze-dried Lactobacillus plantarum powder, inoculating it into MRS liquid culture medium, activating it in a shaking incubator at 37±0.5℃ for 22-26 hours (preferably 24 hours), then centrifuging the culture medium to collect the bacterial cells, and then resuspending the bacterial cells with physiological saline.

[0037] The sterilization process in this invention can be achieved by immersing the mustard greens in 42-degree liquor for 5-10 seconds; or by immersing the mustard greens in 42-degree alcohol for 10-20 seconds. This can effectively kill bacteria and pests attached to the mustard greens.

[0038] In this invention, to further enhance the low-salt environment adaptability of *Lactobacillus plantarum*, the *Lactobacillus plantarum* is obtained through a gradient salt reduction acclimation method. Specifically, this method involves gradually reducing the salt concentration (mass concentration) in the culture medium to acclimate the *Lactobacillus plantarum*, with the salt concentration decreasing from 8-10% to 2-2.5%, and the gradient set in 3-6 levels. Further, the salt concentration is decreased from 8% to 2%, with a gradient set in 4 levels, and each level representing a decrease of 1.5%.

[0039] Another aspect of the present invention is to claim protection for fermented mustard greens prepared by the above-described preparation method, wherein the fermented mustard greens contain 0.2-0.3 g / 100g of amino acid nitrogen (i.e., 0.2-0.3g of amino acid nitrogen per 100g of fermented mustard greens), 0.25-0.38mg / kg of nitrite, and have a pH value of 3.14-3.41.

[0040] In this invention, a further preferred embodiment is that the fermented mustard greens contain 0.3 g / 100g of amino acid nitrogen, 0.25 mg / kg of nitrite, and have a pH value of 3.41.

[0041] When selecting mustard greens, choose fresh, moderately mature, dense, undamaged, and pest-free mustard greens that meet pollution-free hygiene standards. Before sterilization, the mustard greens can be further processed by washing and cutting them, then placing them in a cool, ventilated place to dry until they are slightly wilted and a little water seeps out when gently squeezed.

[0042] The present invention will be further illustrated by the following embodiments. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0043] The *Lactobacillus plantarum* in the following examples (Examples 1-7) are derived from a commercially available *Lactobacillus plantarum* obtained through a gradient salt reduction acclimatization method. The gradient salt reduction acclimatization method specifically involves gradually reducing the salt concentration in the culture medium to acclimate the *Lactobacillus plantarum*. The salt concentration is gradually reduced from 8% to 2%, with the gradient set to 4 levels: 8% → 6.5% → 5% → 3.5% → 2%.

[0044] Example 1 A method for preparing fermented mustard greens, the method comprising the following steps: S1) Pretreatment: Take fresh mustard greens, wash and drain the water, and then sterilize the mustard greens to obtain sterile mustard greens; the sterilization treatment specifically involves immersing the mustard greens in 42-degree alcohol for 15 seconds. S2) Blanching: The sterile mustard greens obtained in step S1 are blanched in hot water. After blanching, the mustard greens are drained while standing upright in a draining basin, and then placed into a fermentation container. The blanching process involves completely immersing the mustard greens in hot water for 20 seconds. The temperature of the hot water used for blanching is 90°C. S3) Seasoning and Fermentation: Add seasonings to the fermentation container, then add fermentation liquid to the fermentation container until the mustard greens are completely submerged. Use the hot water from blanching the mustard greens in step S2) as the fermentation liquid in step S3. The temperature of the fermentation liquid when it is added to the fermentation container is 80℃. Then, inoculate Lactobacillus plantarum when the temperature of the fermentation liquid is 37±2℃, seal the container and ferment for 25 days to obtain the product. The fermentation environment temperature is 25℃ and the fermentation environment is an anaerobic environment. The seasonings include salt, granulated sugar, garlic, white vinegar, ginger, and chili peppers. The amount of salt added is 2% of the weight of the mustard greens, the amount of granulated sugar added is 1.5% of the weight of the mustard greens, the amount of garlic added is 0.1% of the weight of the mustard greens, the amount of white vinegar added is 0.1% of the weight of the mustard greens, the amount of ginger added is 0.1% of the weight of the mustard greens, and the amount of chili peppers added is 0.1% of the weight of the mustard greens.

[0045] Example 2 A method for preparing fermented mustard greens, the method comprising the following steps: S1) Pretreatment: Take fresh mustard greens, wash and drain the water, and then sterilize the mustard greens to obtain sterile mustard greens; the sterilization treatment specifically involves immersing the mustard greens in 42-degree alcohol for 15 seconds. S2) Blanching: The sterile mustard greens obtained in step S1 are blanched in hot water. After blanching, the mustard greens are drained while standing upright in a draining basin, and then placed into a fermentation container. The blanching process involves completely immersing the mustard greens in hot water for 20 seconds. The temperature of the hot water used for blanching is 90°C. S3) Seasoning and fermentation: Add seasoning to the fermentation container, then add fermentation liquid to the fermentation container until the mustard greens are completely submerged. Use the hot water after blanching the mustard greens in step S2) as the fermentation liquid in step S3. The temperature of the fermentation liquid when it is added to the fermentation container is 80℃. Then, when the temperature of the fermentation liquid is 37±2℃, inoculate Lactobacillus plantarum into the fermentation liquid, and then seal the container for fermentation for 25 days to obtain the product. The seasonings include salt, granulated sugar, garlic, white vinegar, ginger, and chili peppers. The amount of salt added is 2% of the weight of the mustard greens, the amount of granulated sugar added is 1% of the weight of the mustard greens, the amount of garlic added is 0.1% of the weight of the mustard greens, the amount of white vinegar added is 0.1% of the weight of the mustard greens, the amount of ginger added is 0.1% of the weight of the mustard greens, and the amount of chili peppers added is 0.1% of the weight of the mustard greens.

[0046] The inoculation amount of *Lactobacillus plantarum* was 0.1% of the weight of the mustard greens. Activation treatment was performed before inoculation, specifically as follows: freeze-dried *Lactobacillus plantarum* powder was inoculated into MRS liquid medium and activated in a 37°C shaking incubator for 30 hours. Then, the culture medium was centrifuged (centrifugation speed 4000 r / min, centrifugation time 10 min) to collect the bacterial cells. The bacterial cells were then resuspended in physiological saline to obtain a *Lactobacillus plantarum* resuspension before inoculation. The fermentation environment was 25°C and anaerobic.

[0047] Examples 3-7 Unlike Example 2, the amount of *Lactobacillus plantarum* inoculated in Examples 3-7 is different. Specifically, in Example 3, the amount of *Lactobacillus plantarum* inoculated is 0.2% of the weight of mustard greens; in Example 4, the amount of *Lactobacillus plantarum* inoculated is 0.3% of the weight of mustard greens; in Example 5, the amount of *Lactobacillus plantarum* inoculated is 0.4% of the weight of mustard greens; in Example 6, the amount of *Lactobacillus plantarum* inoculated is 0.5% of the weight of mustard greens; and in Example 7, the amount of *Lactobacillus plantarum* inoculated is 1% of the weight of mustard greens. All other steps and parameters are the same as in Example 2.

[0048] Experimental Example 1 After fermentation, the nitrite content, pH value, total acid concentration, and amino acid nitrogen content of the fermented mustard greens from Examples 1-7 were tested. Nitrite content was detected using a nitrite test kit from Shanghai Tongwei Company. Total acid was detected using the method for "Determination of Total Acid in Food" in GB12456-2021 standard. pH was measured using a digital pH meter. Amino acid nitrogen was detected using the acidity meter method in GB 5009.235-2016 "National Food Safety Standard: Determination of Amino Acid Nitrogen in Food". Detailed test data are shown in Table 1 below: Table 1: Physicochemical Data Test Table of Fermented Mustard Greens Obtained in Examples 1-7

[0049] As can be seen from the data in Table 1, the fermented mustard obtained by the preparation method of the present invention (Examples 2-7) has a significantly lower nitrite content than that of Example 1, and the fermented mustard obtained in Example 5 has the lowest nitrite content. Furthermore, the nitrite content does not continuously decrease with the increase of the inoculum amount. The inoculum amounts of Examples 6 and 7 are higher than those of Example 5, but the nitrite content is significantly higher than that of Example 5. When the inoculum amount is too high as 1.0% (Example 7), the nitrite content rises to 0.89 mg / kg, indicating that an excessively high concentration of bacteria may disrupt the bacterial community balance and affect the degradation of nitrite. Combination Figure 1 The data show that after inoculation with *Lactobacillus plantarum*, the peak nitrite level (on day 2) was significantly reduced (only 0.89 mg / kg at 0.5% concentration and 3.89 mg / kg at 0% concentration), indicating that it can competitively inhibit nitrate-reducing bacteria. At concentrations of 0.1-0.5%, inoculation with different concentrations of *Lactobacillus plantarum* effectively reduced nitrite, with the best inhibitory effect at 0.4% concentration, resulting in a final nitrite content of 0.25 mg / kg. The highest final nitrite content was observed at 1.0% concentration, at 0.89 mg / kg, indicating that *Lactobacillus plantarum* rapidly became dominant, possibly inhibiting nitrite-degrading bacteria, but its own nitrite-degrading capacity was insufficient, leading to nitrite retention. In addition, since no *Lactobacillus plantarum* was added in Example 1, the amino acid nitrogen was low (0.09 g / 100g), and the total acid and pH value showed weak fermentation, possibly due to insufficient bacterial activity. Example 7 had extremely low amino acid nitrogen (0.02 g / 100g) but the highest total acid, and the kimchi had a poor taste, indicating that the *Lactobacillus plantarum* concentration was too high. The rapid acid production in the early stages inhibited other bacteria that could degrade proteins, ultimately affecting the taste of the mustard greens. Examples 5 and 6 had higher amino acid nitrogen (0.25%~0.30 g / 100g), moderate total acid (0.59~0.76 g / 100g), and pH values ​​between 3.15 and 3.50. The synergistic effect between *Lactobacillus plantarum* and protease-producing bacteria was good, achieving a balance between acidity and flavor. Considering the three key indicators of total acidity, pH value and amino acid nitrogen, Example 5 achieved the highest amino acid nitrogen content (0.30 g / 100g) while maintaining a moderate acidity (total acid 0.59 g / 100g, pH 3.41), indicating that it has the most prominent umami flavor and a mild acidity, achieving the best balance between flavor and quality.

[0050] The nitrite content in all the above embodiments is far below the national limit (20 mg / kg), proving the safety of this process.

[0051] For other technical solutions of the present invention, such as those using similar methods as in Example 2, based on other process parameters (such as sterilization time, blanching time, and the composition or ratio of seasonings), the nitrite content of the fermented mustard greens obtained is far lower than the national limit standard, and will not be listed here.

[0052] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "a," "an," "the," and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms "comprising," "including," "having," and any variations thereof used in this application are intended to cover non-exclusive inclusion. The terms "connected," "linked," "coupled," and similar words used in this application are not limited to physical or mechanical connections but include electrical connections, whether direct or indirect. The term "multiple" used in this application refers to two or more, and "and / or" describes the relationship between related objects, indicating that three relationships may exist. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. The terms "first," "second," "third," etc. used in this application are merely to distinguish similar objects and do not represent a specific ordering of objects.

[0054] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications or improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing fermented mustard greens, characterized in that... The preparation method includes the following steps: S1) Pretreatment: Take fresh mustard greens, wash and drain them, and then sterilize them to obtain sterile mustard greens; S2) Blanching: Blanch the sterile mustard greens obtained in step S1 with hot water, drain the water after blanching, and then put them into a fermentation container. S3) Seasoning and fermentation: Add seasoning to the fermentation container, then add fermentation liquid to the fermentation container until the mustard greens are completely submerged. When the temperature of the fermentation liquid is 37±2℃, inoculate Lactobacillus plantarum into the fermentation liquid, and then carry out sealed fermentation at 25℃ for 20-25 days to obtain the product.

2. The preparation method according to claim 1, characterized in that: The seasonings include salt, sugar, garlic, white vinegar, ginger, and chili peppers. The amount of salt added is 2% to 2.5% of the weight of the mustard greens, the amount of sugar added is 1% to 2% of the weight of the mustard greens, the amount of garlic added is 0.1% to 0.2% of the weight of the mustard greens, the amount of white vinegar added is 0.1% to 0.2% of the weight of the mustard greens, the amount of ginger added is 0.1% to 0.2% of the weight of the mustard greens, and the amount of chili peppers added is 0.1% to 0.2% of the weight of the mustard greens.

3. The preparation method according to claim 1, characterized in that: The inoculation amount of *Lactobacillus plantarum* is 0.1% to 0.5% of the weight of the mustard greens.

4. The preparation method according to claim 1, characterized in that: The inoculum amount of *Lactobacillus plantarum* is 0.4% of the weight of the mustard greens.

5. The preparation method according to claim 1, characterized in that: After blanching the mustard greens in step S1, drain the water while keeping them upright.

6. The preparation method according to claim 1, characterized in that: In step S2), the blanching process involves completely immersing the mustard greens in hot water for 20-30 seconds, with the hot water temperature being 85-95°C.

7. The preparation method according to claim 1, characterized in that: The hot water used to blanch the mustard greens in step S2) is used as the fermentation liquid in step S3, and the temperature of the hot water is 85-95℃.

8. The preparation method according to claim 7, characterized in that: The temperature of the fermentation broth when added to the fermentation container is 80℃.

9. The preparation method according to claim 1, characterized in that: In step S3, the fermentation temperature is controlled at 25±0.5℃ and the fermentation time is 25 days.

10. The preparation method according to claim 1, characterized in that, The sterilization process in step S1 specifically involves immersing the mustard greens in 42-degree alcohol for 10-20 seconds.

11. The preparation method according to claim 1, characterized in that, The *Lactobacillus plantarum* is obtained through a gradient salt reduction acclimatization method. Specifically, the gradient salt reduction acclimatization method involves gradually reducing the salt concentration in the culture medium to acclimate the *Lactobacillus plantarum*, with the salt concentration decreasing from 8-10% to 2-2.5% in a gradient of 3-6 levels.

12. The preparation method according to claim 11, characterized in that, The salt concentration is reduced from 8% to 2% in a gradient of 4 levels, with each level decreasing by 1.5%.

13. The preparation method according to claim 1, characterized in that, The *Lactobacillus plantarum* was activated before inoculation. The activation process specifically involved: taking freeze-dried *Lactobacillus plantarum* powder, inoculating it into MRS liquid culture medium, activating it in a shaking incubator at 37±0.5℃ for 22-26 hours, then centrifuging the culture medium to collect the bacterial cells, and then resuspending the bacterial cells in physiological saline.

14. The fermented mustard greens prepared by the method according to any one of claims 1-13, characterized in that, The fermented mustard greens contain 0.2-0.3 g / 100 g of amino acid nitrogen and 0.25-0.38 mg / kg of nitrite. The pH value of the fermented mustard greens is 3.14-3.

41.

15. The fermented mustard greens according to claim 14: characterized in that, The fermented mustard greens contain 0.3 g / 100g of amino acid nitrogen and 0.25 mg / kg of nitrite. The pH value of the fermented mustard greens is 3.41.

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