Preparation and application of microbial agent for sweetening fruits and vegetables and metabolite

Abstract

The invention discloses preparation and application of a microbial agent and a metabolite for sweetening fruits and vegetables, by introducing a specific microbial strain and the metabolite thereof, sugar accumulation of the fruits and vegetables in the growth process can be effectively promoted, and the sweetness of the fruits is directly improved. The microbial strains are carefully screened, so that a beneficial microenvironment can be established in a plant body or around a root system, the sugar metabolism process of the plant is promoted, meanwhile, the photosynthesis efficiency is improved, more carbohydrates are accumulated in fruits, and finally, the natural sweetening effect of the fruits and vegetables is achieved. Besides, natural plant extracts and microbial metabolites are adopted as main components instead of traditional chemical sweeteners, so that potential negative effects on crop quality are greatly reduced.

Description

Technical Field

[0001] The invention belongs to a fruit and vegetable sweetening microbial preparation, and specifically relates to a fruit and vegetable sweetening microbial preparation and the preparation and application of metabolites. Background Art

[0002] Although the existing sweetening technology for fruits and vegetables can quickly increase the sweetness through chemical agents or improve the growth environment through biological means, chemical agents can quickly increase the sugar content in fruits and vegetables by adding sweeteners or regulators from external sources, so that fruits and vegetables can reach the ideal sweetness level in a short period of time. This type of technology is easy to apply and has significant effects. It is particularly suitable for use in crops with a short production cycle to meet the market demand for high-sweetness fruits and vegetables. However, the negative impact of chemical sweetening cannot be ignored. First, excessive use of chemical agents will destroy the natural flavor of fruits and vegetables, resulting in a decline in the quality of fruits and vegetables. In addition, chemical residues may affect food safety, and long-term consumption of fruits and vegetables treated with these agents may have adverse effects on human health, such as causing allergic reactions or cumulative toxicity. Secondly, chemical agents may also enter the environment during application, causing soil and water pollution, negatively affecting the ecosystem, and even destroying the sustainability of agriculture. In contrast, biological sweetening technology improves the growth environment of crops and enhances plant sugar metabolism by using microbial strains or organic fertilizers. This method is more environmentally friendly, reduces the risk of chemical pollution to the soil and environment, and is in line with the trend of sustainable agricultural development. At the same time, bio-sweetening technology helps improve the overall health of crops and enhance their disease resistance. However, bio-sweetening technology also has significant limitations. First, its sweetening effect is usually slow, and it cannot significantly increase the sweetness of fruits and vegetables in a short period of time, making it difficult to meet the market demand for high-sweetness fruits and vegetables. Secondly, because the biological process is affected by external environmental factors such as temperature, humidity, soil conditions, etc., it is difficult to control and it is difficult to ensure stable and predictable results.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide a preparation and application of a microbial agent and metabolites for sweetening fruits and vegetables, and solve the problems raised in the above-mentioned background technology.

[0005] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0006] A method for preparing a microbial agent and a metabolite for sweetening fruits and vegetables, comprising the following steps:

[0007] Step (1): weigh brown sugar, dipotassium hydrogen phosphate, ammonium sulfate, magnesium sulfate, sodium chloride, peptone, yeast extract, soybean oil, plant extract, B vitamin complex and purified water according to the proportion.

[0008] Step (2): pouring the weighed raw materials of step (1) into a fermentation tank in batches for mixing to obtain a mixture A. After the mixing is completed, the pH value of the mixture A is adjusted to 7.0-7.5 using sodium hydroxide, and then the sodium hydroxide and the mixture A are stirred evenly to obtain a culture medium ①;

[0009] Step (3): steam sterilize the culture medium ①. After steam sterilization, water is introduced into the fermentation tank interlayer to cool the temperature down to 30±1°C. At this time, the strain is inoculated for fermentation culture;

[0010] Step (4): adding yeast metabolites to the mixture after fermentation, and stirring evenly to obtain a mixture of bacterial liquid and yeast metabolites;

[0011] Step (5): Then, the nanocomposite material is added to the mixture of the bacterial liquid and the yeast metabolites, and then the nanocomposite material and the mixture of the bacterial liquid and the yeast metabolites are stirred evenly to obtain the finished product. The nanocomposite material, due to its special structure, can form a stable microenvironment during the storage of the microbial preparation, reducing the impact of changes in the external environment on the activity of the strain. For example, nanomaterials can play a buffering role, help adjust the pH value or temperature of the microbial preparation, prevent the microorganisms from being inactivated due to environmental fluctuations, and ensure that the strain can function stably under different conditions.

[0012] Secondly, nanocomposites work synergistically with nutrients such as vitamins to improve the efficiency of plants' absorption of these nutrients. Nanomaterials can help these trace elements enter the plant faster and more effectively, increase the plant's growth rate and sugar accumulation, and thus indirectly promote the sweetening of fruits and vegetables.

[0013] Yeast metabolites provide abundant secondary metabolites, such as organic acids, amino acids, etc. These substances can enhance the plant's ability to metabolize sugars and directly promote the sweetening effect of fruits and vegetables.

[0014] Step (6): The final product is filled and stored in a warehouse, completing the preparation of microbial strains and metabolites.

[0015] Optionally, the weight proportions of the raw materials in step (1) are 1-2 parts of brown sugar, 0.2-1 parts of dipotassium hydrogen phosphate, 0.1-0.5 parts of ammonium sulfate, 0.2-1.5 parts of magnesium sulfate, 0.2-1.5 parts of sodium chloride, 0.05-0.25 parts of peptone, 0.1-0.5 parts of yeast extract, 0.05-0.25 parts of soybean oil, 80-120 parts of purified water, 2-8 parts of yeast metabolites, 0.5-2 parts of plant extracts, and 0.05-0.1 parts of B vitamin complex. Brown sugar, as a carbon source, provides energy and carbon elements for microorganisms, promotes the reproduction and metabolic activities of microorganisms, and improves the overall vitality of the strains;

[0016] Dipotassium hydrogen phosphate is used to provide phosphorus and potassium. Phosphorus is an important component of energy metabolism of microorganisms and plants, while potassium helps to improve the metabolic efficiency of microorganisms and enhance the activity of enzymes, thereby improving the sweetening effect.

[0017] As a nitrogen source, ammonium sulfate provides the necessary nitrogen elements for microorganisms, supports protein synthesis and rapid growth of microorganisms, and ensures that the strains maintain high vitality during the fermentation process;

[0018] Sodium chloride is used to adjust the osmotic pressure of the culture medium, helping to maintain the stability of the cell environment of microorganisms, preventing the inactivation of bacteria due to changes in external osmotic pressure, and ensuring the stability of the fermentation environment;

[0019] As a nitrogen source and nutrient source, peptone provides microorganisms with abundant amino acids and small peptides, promotes the growth and metabolic activities of microorganisms, and helps the bacteria maintain efficient sugar metabolism during the fermentation process.

[0020] Yeast extract is used to provide minerals and nitrogen sources to help the growth and metabolism of microorganisms, further enhancing the activity of bacteria and the production of metabolites;

[0021] Soybean oil plays multiple important roles in the fermentation process. It is not only a source of fat and energy, but also has a positive impact on the stability of the fermentation environment. First, the fatty acids in soybean oil provide additional energy reserves for fermenting microorganisms, which can support them to maintain efficient metabolic activities during the fermentation process, ensuring that the microorganisms can continue to decompose the matrix and produce metabolites. Especially in the long fermentation process, the lipid components in soybean oil help to supplement the deficiency of traditional carbohydrate sources (such as sugars), prevent the microorganisms from stopping growth or weakening metabolism due to energy exhaustion, thereby improving the fermentation efficiency and the quality of the final product. In addition, soybean oil also has a certain surface activity, which can effectively control the foam generated during the fermentation process. During the fermentation process, the active metabolism of microorganisms often produces gases, which may cause the generation of foam in the fermentation liquid. If there is too much foam, it will not only affect the stirring uniformity in the fermentation tank, but also cause the fermentation liquid to overflow, affecting the stability of the fermentation process. The addition of soybean oil can reduce the generation of foam, play a role in defoaming, ensure the smooth progress of the reaction in the fermentation tank, and avoid process interruptions or operational problems caused by foam. At the same time, the lubrication effect of fat molecules can also improve the efficiency of the stirring device in the fermentation tank, keep the fermentation liquid uniform, ensure that the microorganisms can better contact nutrients, and the overall fermentation process proceeds smoothly;

[0022] Plant extracts provide natural active ingredients, such as sugarcane juice and malic acid, which can directly increase the sweetness of fruits and vegetables, and assist the metabolism of microorganisms to improve the sweetening effect of bacteria.

[0023] During sugar metabolism and energy generation, B vitamin complex helps microorganisms improve metabolic efficiency, ensuring efficient production and application of bacterial strains.

[0024] Optionally, in step (2), during the fermentation process, the steps are:

[0025] Dilute and dissolve the peptone and yeast extract with appropriate amount of pure water respectively, add them into the fermentation tank, add water to 50% of the volume of the fermentation tank, add the remaining raw materials, stir evenly to obtain the primary product ①, continue to add water to 75% of the volume of the fermentation tank, stir evenly to obtain the primary product ②.

[0026] Optionally, in step (5), the ratio between the mixture of bacterial liquid and yeast metabolites and the nanocomposite material is 1:(0.01-0.1).

[0027] Optionally, during the steam sterilization in step (3), the temperature is 121° C., the tank pressure is 0.1 MPa, and the duration is 30 min.

[0028] Optionally, the strain is one of Bacillus subtilis, Bacillus licheniformis, Bacillus megaterium, and Paenibacillus gelatinosa.

[0029] Optionally, the natural plant extract is one of sugarcane juice or malic acid.

[0030] Optionally, the nanocomposite material is a mixture of nanoferrite, nanotitanium dioxide, and nanocarbon tubes, wherein the mixing ratios of nanoferrite, nanotitanium dioxide, and nanocarbon tubes are 50%, 30%, and 20%, respectively. Nanoferrite has good magnetic properties and can enhance the metabolic activity of microorganisms in the fermentation broth. Its magnetic effect can regulate the enzymatic reaction rate of microorganisms and promote the generation of metabolites. At the same time, the high specific surface area of ​​nanoferrite can also increase the contact area with microbial metabolites, thereby enhancing the efficiency of carbohydrate metabolism.

[0031] The strong oxidants produced by nano-titanium dioxide under light can effectively decompose any residual harmful substances that may exist and inhibit potential bacterial contamination after fermentation. This feature not only ensures that the fermentation liquid maintains a high degree of purity during storage and transportation, but also further improves the antioxidant capacity of the fermentation liquid. By reducing oxidation reactions, nano-titanium dioxide helps extend the shelf life of fermentation products and ensures that the stability and activity of microbial metabolites are not easily reduced during storage and use, thereby enhancing the overall quality and use effect of the product.

[0032] The high conductivity of carbon nanotubes can improve the metabolic efficiency of microbial cells, especially in the process of electron transfer and energy metabolism. In addition, their high specific surface area and porous structure can provide more attachment points for microorganisms, increase the contact between microorganisms and metabolites, enhance the adhesion of metabolites to the surface of fruits and vegetables, and allow sugar to penetrate more evenly into the fruits and vegetables.

[0033] Optionally, in step (3), sampling is required every 4 hours for microscopic examination to observe the growth of the bacteria. When the pH of the fermentation liquid in the fermenter reaches 5.5, the bacterial stain becomes lighter, and the bacterial count reaches the peak, the cultivation is stopped.

[0034] A microbial agent for sweetening fruits and vegetables and its metabolites are applied to fruit trees and melon crops.

[0035] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art. Of course, any product implementing the present invention does not necessarily need to achieve all the advantages described below at the same time:

[0036] 1. The present invention can effectively promote the accumulation of sugars in fruits and vegetables during their growth process and directly improve the sweetness of fruits by introducing specific microbial strains and their metabolites. These microbial strains are carefully screened and can establish a beneficial microenvironment in the plant body or around the root system, promote the sugar metabolism process of the plant, and improve the photosynthesis efficiency, so that more carbohydrates accumulate in the fruit, and finally achieve the natural sweetening effect of fruits and vegetables. In addition, the present invention uses natural plant extracts and microbial metabolites as the main ingredients, rather than traditional chemical sweeteners, which greatly reduces the potential negative impact on crop quality.

[0037] 2. Through the addition of nano-composite materials, the stability of microbial agents has been significantly enhanced, and pH fluctuations, temperature changes and microbial activity during the storage period have been effectively controlled. The improved quality of fermentation products not only enables them to maintain higher stability during storage, but also continues to play a sweetening role. During the processing of fruits and vegetables, the efficient dispersibility and stability of nanomaterials promote the uniform distribution and penetration of sugars on the surface of fruits and vegetables, thereby significantly improving the sugar content and sensory sweetness scores of fruits and vegetables. Compared with traditional methods, nanomaterials not only improve the sweetness, but also enhance the uniformity and persistence of the sweetness of fruits and vegetables, making fruits and vegetables more competitive in the market.

[0038] 3. The microbial strains of the present invention can not only increase sweetness, but also improve the overall growth environment of fruits and vegetables, enhance the disease resistance and stress resistance of crops, increase the yield and quality of fruits and vegetables, and make fruits and vegetables have a stronger advantage in market competition.

[0039] The specific implementation modes of the present invention are described in further detail below. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0042] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0044] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0045] A method for preparing a microbial agent and a metabolite for sweetening fruits and vegetables, comprising the following steps:

[0046] Step (1): weigh brown sugar, dipotassium hydrogen phosphate, ammonium sulfate, magnesium sulfate, sodium chloride, peptone, yeast extract, soybean oil, plant extract, B vitamin complex and purified water according to proportion;

[0047] Step (2): Pour the weighed raw materials of step (1) into a fermentation tank in batches for fermentation treatment, adjust the pH to 7.0-7.5 with sodium hydroxide, and then stir evenly to obtain culture medium ①;

[0048] Step (3): steam sterilize the culture medium ①. After steam sterilization, water is introduced into the fermentation tank interlayer to cool the temperature down to 30±1°C. At this time, the strain is inoculated for fermentation culture;

[0049] Step (4): adding yeast metabolites to the mixture after fermentation, and stirring evenly to obtain a mixture of bacterial liquid and yeast metabolites;

[0050] Step (5): adding the nanocomposite material to the mixture of the bacterial liquid and the yeast metabolites, and stirring the nanocomposite material and the mixture of the bacterial liquid and the yeast metabolites evenly to obtain a finished product;

[0051] Step (6): The final product is filled and stored in a warehouse, completing the preparation of microbial strains and metabolites.

[0052] In the following examples, the weight parts of the raw materials in step (1) are 1-2 parts of brown sugar, 0.2-1 parts of dipotassium hydrogen phosphate, 0.1-0.5 parts of ammonium sulfate, 0.2-1.5 parts of magnesium sulfate, 0.2-1.5 parts of sodium chloride, 0.05-0.25 parts of peptone, 0.1-0.5 parts of yeast extract, 0.05-0.25 parts of soybean oil, 80-120 parts of purified water, 0.5-2 parts of plant extract, and 0.05-0.1 parts of B vitamin complex.

[0053] In the following examples, the steps in step (2) during the fermentation process are:

[0054] Dilute and dissolve the peptone and yeast extract with appropriate amount of pure water respectively, add them into the fermentation tank, add water to 50% of the volume of the fermentation tank, add the remaining raw materials, stir evenly to obtain the primary product ①, continue to add water to 75% of the volume of the fermentation tank, stir evenly to obtain the primary product ②.

[0055] The ratio between the mixture of bacterial liquid and yeast metabolites and the nanocomposite material in Examples 1-3 is 1:0.1.

[0056] In the following examples, the temperature during steam sterilization was 121° C., the tank pressure was 0.1 MPa, and the duration was 30 min.

[0057] In the following examples, in step (3), sampling is required every 4 hours for microbial growth observation. When the fermentation liquid in the fermenter reaches pH 5.5, the bacterial stain becomes lighter, and the bacterial count reaches the peak, the cultivation is stopped.

[0058] In the following examples, the strain is one of Bacillus subtilis, Bacillus licheniformis, Bacillus megaterium, and Paenibacillus gelatinosa.

[0059] In the following examples, the natural plant extract is one of sugarcane juice or malic acid.

[0060] The nanocomposite materials in Examples 1-3 are mixtures of nanoferrite, nanotitanium dioxide and nanocarbon tubes, wherein the mixing ratios of nanoferrite, nanotitanium dioxide and nanocarbon tubes are 50%, 30% and 20% respectively.

[0061] The present invention will now be further described in detail with reference to embodiments.

[0062] It should be noted that all raw materials in the examples of the present invention were obtained through commercial sources.

[0063] Example 1: A method for preparing a microbial agent and metabolites for sweetening fruits and vegetables, comprising the following steps:

[0064] Step (1): 0.08 parts of peptone and 0.1 parts of yeast extract are diluted and dissolved with appropriate amount of purified water respectively, the diluted peptone and yeast extract are added to a fermentation tank, and water is added to 50% of the volume of the fermentation tank to obtain a primary product ①.

[0065] Step (2): add 1.5 parts of brown sugar, 0.5 parts of potassium dihydrogen phosphate, 0.2 parts of ammonium sulfate, 0.5 parts of magnesium sulfate, 0.4 parts of sodium chloride, 0.08 parts of soybean oil, 0.07 parts of B vitamin complex and 5 parts of sugarcane juice to the primary product ①, stir evenly to obtain the primary product ②, continue to add water to 75% of the volume of the fermentation tank, and stir evenly to obtain the primary product ③.

[0066] Step (3): The primary product ③ is subjected to steam sterilization at a temperature of 121° C., a tank pressure of 0.1 MPa, and a duration of 30 minutes.

[0067] Step (4): After steam sterilization, water is introduced into the fermentation tank interlayer to cool the temperature down to 30±1°C, and then Bacillus megaterium is inoculated for fermentation culture.

[0068] Step (5): after the fermentation of Bacillus megaterium is completed, yeast metabolites are added, and the mixture of bacterial liquid and yeast metabolites is obtained after being stirred evenly, and then the nano-mixture is added to the mixture of bacterial liquid and yeast metabolites, and the mixture is mixed evenly to obtain the finished product.

[0069] Step (6): Finally, the final product is filled and stored in a warehouse, completing the preparation of microbial strains and metabolites.

[0070] The difference between Example 2 and Example 1 is the ratio of raw materials, and the remaining steps are the same as Example 1, wherein the ratio of raw materials is:

[0071] Brown sugar: 2 parts, dipotassium hydrogen phosphate: 0.8 parts, ammonium sulfate: 0.5 parts, magnesium sulfate: 1.3 parts, sodium chloride: 1.2 parts, peptone: 0.2 parts, yeast extract: 0.4 parts, soybean oil: 0.25 parts, yeast metabolites: 8 parts, malic acid: 1.5 parts, B vitamin complex: 0.1 parts, purified water: 120 parts.

[0072] The difference between Experimental Example 3 and Example 1 lies in the ratio of raw materials, wherein the ratio of raw materials is:

[0073] Brown sugar: 1 part, dipotassium hydrogen phosphate: 0.3 parts, ammonium sulfate: 0.2 parts, magnesium sulfate: 0.5 parts, sodium chloride: 0.3 parts, peptone: 0.1 parts, yeast extract: 0.2 parts, soybean oil: 0.1 parts, yeast metabolites: 4 parts, natural plant extract (sugarcane juice): 0.8 parts, B vitamin complex: 0.06 parts, purified water: 110 parts.

[0074] The difference between Control Example 1 and Example 1 is that no nanocomposite material is used and Bacillus megaterium is not introduced during the fermentation process.

[0075] Experimental Example 1: Samples were taken from Example 1, Example 2, Example 3 and Control Example 1 to ensure that the samples were uniform and free of contamination. Then, the samples were packaged in sterile containers for fermentation effect experiments;

[0076] Use an acidity meter to measure the pH value of the fermentation broth and evaluate the fermentation effect. Then, determine the main products produced during the fermentation process and use corresponding detection instruments for analysis. Finally, use an optical densitometer or other bacterial concentration measurement methods to determine the bacterial concentration in each culture medium.

[0077] The appearance and pH value data of each culture medium were compared to evaluate the influence of the raw material ratio on the quality of the culture medium. The fermentation rate, fermentation product and bacterial concentration of each culture medium were compared to evaluate the influence of the raw material ratio on the fermentation effect. The experimental results were compared and statistically analyzed to obtain the performance advantages and disadvantages of each culture medium and summarize the influence of different factors on the quality of the culture medium and the fermentation effect. The experimental results are shown in Table 1.

[0078] Table 1: Summary of fermentation effect experimental results

[0079]

[0080] As can be seen from Table 1, the huge increase in fermentation rate is mainly attributed to the introduction of Bacillus megaterium. Bacillus megaterium has extremely high metabolic activity, and its rapid reproduction and metabolic capacity significantly increase the fermentation rate. In Control Example 1, since Bacillus megaterium was not used, the fermentation rate was significantly reduced, indicating that this strain played a key role in improving the fermentation efficiency.

[0081] The huge increase in the amount of fermentation products is closely related to the efficient metabolic process of Bacillus megaterium. The strain can produce a large number of metabolites such as organic acids and enzymes through its unique metabolic pathways, which play an important role in sweetening fruits and vegetables. The fermentation product production of Control Example 1 is the lowest, further indicating that the absence of Bacillus megaterium will significantly reduce the production of metabolites, thereby weakening the effect of sweetening fruits and vegetables.

[0082] The difference in bacterial concentrations indicates that Bacillus megaterium can proliferate rapidly during the fermentation process, significantly increasing the overall bacterial concentration. The higher the bacterial concentration, the more active the microorganisms grow and reproduce during the fermentation process, and the more metabolites are produced. In Control Example 1, due to the lack of Bacillus megaterium, the bacterial concentration is significantly lower, showing its important role in the proliferation of microorganisms during the fermentation process.

[0083] Experimental Example 2: By adding nanocomposites, the effects on the stability of fermented products and the efficiency of enhancing the sweetness of fruits and vegetables were tested. The results are shown in Tables 1 and 2.

[0084] The fermentation broth (Example 1 and Control Example) was stored in containers under the same conditions (stored at room temperature). The following parameters were tested every day for 7 days: The pH value of the fermentation broth was measured using a pH meter. The temperature of the fermentation broth was measured using a thermometer, and the temperature fluctuation was recorded. Next, a certain amount of the fermentation broth was extracted, and the microbial activity was detected using a microbial counter, and the number of viable bacteria was calculated. The test results are shown in Table 2.

[0085] Select apple and grape samples, wash and air-dry. Spray or soak the processed fermentation liquid on the fruit and vegetable samples to ensure uniform coverage, and let it stand for 1 hour for absorption. Store the processed fruits and vegetables at room temperature for 24 hours until the sugar is evenly distributed. Use a Brix meter to measure the sugar content (Brix value) of the processed fruits and vegetables. Measure multiple fruit and vegetable samples and take the average value. The test results are shown in Table 3.

[0086] Table 2: Results of the stability test of fermentation products

[0087] index Comparison Example Example 1 pH change (storage for 7 days) 7.0→6.2 7.0→6.8 Temperature fluctuation(℃) ±3℃ ±1℃ Decrease in microbial activity (%) 20％ 8％

[0088] Table 3: Experimental results of sweetening effect of fruits and vegetables

[0089]

[0090] According to the data in Tables 2 and 3, after the nanocomposite material was added in Example 1, the fermentation product showed remarkable stability during storage. Specifically, the pH value of the fermentation broth fluctuated less and the temperature remained relatively stable. At the same time, the rate of decline of microbial activity was significantly lower than that of the control example, which shows that the nanocomposite material can effectively enhance the stability of the fermentation product.

[0091] Furthermore, the apple and glucose levels (Brix value) of the experimental group increased by 1.7 and 1.8 units respectively compared with the control group, indicating that the addition of nanomaterials promoted the effective penetration of microbial metabolites, thereby increasing the sugar accumulation inside the fruits and vegetables. In addition, the sensory test results showed that the subjective scores of the fruits and vegetables in the experimental group on sweetness and taste were significantly higher. This means that the nanocomposite material not only improves the overall sweetness of fruits and vegetables, but also makes the sweetness more evenly distributed, reducing the phenomenon of uneven local sweetness, such as areas that are too sweet or too light.

[0092] This effect can be attributed to the high specific surface area of ​​the nanocomposite material, which provides more active surfaces, allowing microbial metabolites to fully contact the surface of fruits and vegetables and penetrate into the interior of fruits and vegetables, thereby improving the sweetness of fruits and vegetables. In addition, nanomaterials may enhance the permeability of sugars through interaction with the cell walls of fruits and vegetables, making fruits and vegetables show better absorption capacity in terms of sweetness accumulation. At the same time, the antioxidant properties of nanomaterials may delay the decomposition of sugars, making the sweetness of fruits and vegetables more lasting.

[0093] 1. Application method:

[0094] Foliar application: Spray directly on the leaves of the plant to allow it to absorb nutrients.

[0095] Root application: Apply the product directly to the roots of the plant through root irrigation.

[0096] Soil application: Mix the formula into the soil for absorption by plant roots.

[0097] For use on fruit trees:

[0098] Foliar application: The dosage is 1kg / mu. Dilute the formula in an appropriate amount of water, mix well and spray on the leaves of fruit trees. It is recommended to apply once every 7-10 days, especially during the fruit expansion and ripening stage, to enhance the sweetness and hardness of the fruit.

[0099] Root irrigation: The dosage is 10kg / mu. Mix the formula with an appropriate amount of water and dilute it. It is recommended to irrigate once every 10-15 days. This method helps improve the efficiency of root nutrient absorption, enhance the overall health of fruit trees and fruit quality.

[0100] For use in melon crops such as watermelon and cantaloupe:

[0101] Foliar application during the fruit expansion period: the dosage is 1kg / mu. Dilute the formula with an appropriate amount of water and spray evenly on the leaves of melon crops. It is recommended to apply once every 7-10 days during the fruit expansion period to promote rapid expansion of the fruit and increase sweetness.

[0102] Soil application: Mix an appropriate amount of formula into the soil to enhance root absorption, improve the overall growth of crops and the quality of fruits.

[0103] The present invention is not limited to the above-mentioned embodiments. Anyone should be aware that any structural changes made under the enlightenment of the present invention, and any technical solutions that are the same or similar to the present invention, fall within the protection scope of the present invention. The technology, shape, and structural parts not described in detail in the present invention are all well-known technologies.

Claims

1. A method for preparing a microbial agent and metabolites for sweetening fruits and vegetables, characterized in that: The following steps are involved: Step (1): weigh brown sugar, dipotassium hydrogen phosphate, ammonium sulfate, magnesium sulfate, sodium chloride, peptone, yeast extract, soybean oil, plant extract, B vitamin complex and purified water according to proportion; Step (2): pouring the weighed raw materials of step (1) into a fermentation tank in batches for mixing to obtain a mixture A. After the mixing is completed, the pH value of the mixture A is adjusted to 7.0-7.5 using sodium hydroxide, and then the sodium hydroxide and the mixture A are stirred evenly to obtain a culture medium ①; Step (3): steam sterilize the culture medium ①. After steam sterilization, water is introduced into the fermentation tank interlayer to cool the temperature down to 30±1°C. At this time, the strain is inoculated for fermentation culture; Step (4): adding yeast metabolites to the mixture after fermentation, and stirring evenly to obtain a mixture of bacterial liquid and yeast metabolites; Step (5): adding the nanocomposite material to the mixture of the bacterial liquid and the yeast metabolites, and then uniformly stirring the nanocomposite material and the mixture of the bacterial liquid and the yeast metabolites to obtain a finished product; Step (6): The final product is filled and stored in a warehouse, completing the preparation of microbial strains and metabolites.

2. The method for preparing a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: The weight proportions of the raw materials in step (1) are 1-2 parts of brown sugar, 0.2-1 parts of dipotassium hydrogen phosphate, 0.1-0.5 parts of ammonium sulfate, 0.2-1.5 parts of magnesium sulfate, 0.2-1.5 parts of sodium chloride, 0.05-0.25 parts of peptone, 0.1-0.5 parts of yeast extract, 0.05-0.25 parts of soybean oil, 80-120 parts of purified water, 2-8 parts of yeast metabolites, 0.5-2 parts of plant extracts, and 0.05-0.1 parts of B vitamin complex.

3. The method for preparing a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: The steps in step (2) during the fermentation process are: Dilute and dissolve the peptone and yeast extract with appropriate amount of pure water respectively, add them into the fermentation tank, add water to 50% of the volume of the fermentation tank, add the remaining raw materials, stir evenly to obtain the primary product ①, continue to add water to 75% of the volume of the fermentation tank, stir evenly to obtain the primary product ②.

4. The method for preparing a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: In step (5), the ratio between the mixture of bacterial liquid and yeast metabolites and the nanocomposite material is 1:(0.01-0.1).

5. The method for preparing a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: During the steam sterilization process in step (3), the temperature is 121° C., the pressure is 0.1 MPa, and the duration is 30 min.

6. The method for preparing a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: The strain is one of Bacillus subtilis, Bacillus licheniformis, Bacillus megaterium, and Paenibacillus gelatinosa.

7. The preparation and application of a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: The natural plant extract is one of sugar cane juice or malic acid.

8. The method for preparing a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: The nano composite material is a mixture of nano ferrite, nano titanium dioxide and nano carbon tube, wherein the mixing ratios of nano ferrite, nano titanium dioxide and nano carbon tube are 50%, 30% and 20% respectively.

9. The preparation of a microbial agent and metabolites for sweetening fruits and vegetables according to claim 1, characterized in that: In step (3), samples need to be taken every 4 hours for microbial growth observation. When the pH of the fermentation liquid in the fermenter reaches 5.5, the bacterial stain becomes lighter, and the bacterial count reaches the peak, the cultivation is stopped.

10. A microbial agent for sweetening fruits and vegetables and its metabolites as claimed in any one of claims 1 to 9, applied to fruit trees and melon crops.

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