Soybean fermented water-soluble fertilizer and preparation process thereof

Abstract

The application provides a soybean fermentation water-soluble fertilizer and a preparation process thereof. Purified water and soybean powder are put into a reaction kettle to prepare a mixed slurry, and potassium hydroxide is added to adjust the pH of the slurry; high shear circulation treatment is carried out during stirring and temperature rising, and alkaline hot soaking is carried out; after temperature reduction after the hot soaking is completed, a composite enzyme preparation is added, and an enzymolysis reaction is carried out by adopting a two-stage temperature control mode; after the enzymolysis is completed, the pH is adjusted by using a citric acid aqueous solution, and after temperature reduction, a soybean fermentation agent and molasses are added, and a soybean fermentation water-soluble fertilizer is obtained through closed anaerobic fermentation; during the fermentation process, the fermentation length and the lactic acid content are used as double indexes to determine the fermentation end point. Through alkaline hot soaking and high shear pretreatment, and in combination with stage-by-stage temperature control enzymolysis, macromolecular substances in the soybean powder are fully degraded; in the anaerobic stage, an anaerobic environment protected by inert gas is constructed, and the bottom sediment is discharged at a fixed time, and the double fermentation end point control reduces batch differences caused by fluctuations in raw material and microbial agent activity.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer technology, and in particular to a soybean fermentation water-soluble fertilizer and its preparation process. Background Technology

[0002] Liquid water-soluble fertilizers are well-suited to the integrated water and fertilizer management model of modern agriculture, enabling various application methods such as drip irrigation, fertigation, and foliar spraying. They offer rapid nutrient absorption and their application in facility agriculture and cash crop cultivation continues to expand. Currently, organic liquid water-soluble fertilizers on the market are divided into two main categories: chemically formulated and organically fermented. Chemically formulated water-soluble fertilizers have limited nutrient content and are deficient in organic matter; long-term application can easily lead to soil acidification and compaction, which is detrimental to maintaining soil fertility. Organically fermented water-soluble fertilizers are mostly prepared from plant protein raw materials such as soybean meal and soybean flour through microbial fermentation, representing an important development direction for green agricultural fertilizers.

[0003] Most existing soybean-based fermented organic water-soluble fertilizer production processes employ simple crushing and short-term heating pretreatment followed by direct inoculation with microorganisms for fermentation, which has several technical shortcomings. First, the raw material pretreatment methods are limited, relying solely on simple crushing and lacking the synergistic effect of alkaline treatment and efficient shearing. This results in insufficient delamination of large molecular structures such as soybean protein and cellulose, leading to insufficient substrate contact area for subsequent enzymatic hydrolysis, low conversion rates of macromolecular degradation, and limited production of small peptides and free amino acids in the product. Second, the enzymatic hydrolysis stage often uses a single isothermal enzymatic hydrolysis mode, which cannot match the optimal operating temperatures of various complex enzymes. This results in insufficient release of enzyme activity from various enzyme preparations, limiting the raw material degradation efficiency. Third, the fermentation process relies primarily on fermentation time as the sole endpoint. Influenced by fluctuations in soybean flour quality, the actual viable bacterial activity of the inoculated agent, and changes in ambient temperature, simple time control easily leads to incomplete or over-fermentation, resulting in significant differences in viable bacterial count and organic acid content between batches and poor product stability. Fourth, some processes lack anaerobic environment control and slag removal treatment, making it easy for contaminating microorganisms to enter the fermentation process, leading to excessive sedimentation, easy stratification of the finished product, and decreased storage performance.

[0004] Some existing processes attempt to combine hot soaking, enzymatic hydrolysis, and fermentation to prepare soybean-based liquid fertilizer, but the coordination between the processes is insufficient, the parameters of the pretreatment, enzymatic hydrolysis, and fermentation stages are fragmented, resulting in a long overall production cycle, high energy consumption, and unstable output of effective nutrients, which restricts the large-scale and stable production of high-quality soybean fermented water-soluble fertilizer.

[0005] Therefore, developing a soybean fermentation water-soluble fertilizer preparation process that features adequate pretreatment, high enzymatic degradation efficiency, controllable fermentation process, and good batch stability is a practical production need. Summary of the Invention

[0006] This invention provides a soybean fermentation water-soluble fertilizer and its preparation process to overcome the deficiencies in the prior art.

[0007] This invention provides a process for preparing soybean fermented water-soluble fertilizer, comprising the following steps: S1. Add 3500±100 liters of purified water to the reactor, start stirring and set the stirring frequency to 40-60 rpm. During the stirring process, add 1200-1800 kg of soybean flour to the reactor to form a mixed slurry. S2. Add 1-3 kg of potassium hydroxide to the mixed slurry to adjust the pH value of the mixed slurry to 8.5-9.5; S3. Adjust the stirring frequency of the reactor to 20-30 rpm, set the heating temperature of the reactor to 95-100℃, and start the heating program to heat the mixed slurry. During this process, pump the mixed slurry out of the reactor and pass it in series through at least one high-shear disperser for circulating shearing treatment. Then, return the sheared slurry to the reactor to accelerate the heating of the slurry. Continue until the temperature of the slurry in the reactor reaches a high temperature range of 75-85℃, and maintain hot soaking at this high temperature for 2-4 hours. S4. Cool the hot-soaked slurry to 50-55℃, add 5-10 kg of compound enzyme preparation to the slurry, and carry out the enzymatic hydrolysis reaction for 15-17 hours while maintaining a stirring frequency of 20-30 rpm. The enzymatic hydrolysis reaction is divided into two stages: in the first 8 hours, the slurry temperature is controlled at 52±1℃; in the next 8 hours, the slurry temperature is controlled at 48±1℃. S5. After the enzymatic hydrolysis reaction is completed, citric acid is added to the slurry to adjust the pH value of the slurry to 4.5-5.5. Then the slurry is cooled to 35-38℃, and 3-7 kg of soybean fermentation agent and 200-300 kg of molasses are added to the slurry. After stirring evenly, stirring is stopped, and anaerobic fermentation is carried out under sealed conditions for 22-26 hours to obtain the soybean fermented water-soluble fertilizer.

[0008] According to the preparation process of soybean fermentation water-soluble fertilizer provided by the present invention, in step S1, the soybean powder is the powder obtained by washing, drying and crushing soybeans and passing it through a 60-100 mesh sieve, with a protein content of not less than 35% and a moisture content of not more than 12%; the purified water is pure water that has undergone reverse osmosis treatment and has a conductivity of less than 10 μS / cm, and the water temperature is controlled within the range of 25-35℃ before being added to the reaction vessel.

[0009] According to the preparation process of soybean fermented water-soluble fertilizer provided by the present invention, in step S3, the cyclic shearing treatment includes: S301. The slurry in the reactor is pumped out by a main circulation pump. The slurry flows through the first high shear disperser and the second high shear disperser in sequence. The working speed of the first high shear disperser is set to 2500-3500 rpm to perform preliminary crushing and mixing of the slurry. S302. The operating speed of the second high-shear disperser is set to 4000-6000 rpm to further perform ultra-fine shearing and emulsification on the slurry; S303. The slurry after two-stage shearing treatment is returned to the lower part of the reactor through a pipeline to form a forced circulation loop. The circulation shearing treatment continues until the slurry temperature reaches above 75°C, and is intermittently started throughout the hot soaking stage to maintain the uniformity and stability of the slurry system.

[0010] According to the preparation process of soybean fermentation water-soluble fertilizer provided by the present invention, in step S3, the hot soaking process is carried out under a slight negative pressure condition. The exhaust valve of the reactor is connected to a condensation recovery device to condense and recover the evaporated water vapor and partially return it to the reactor to maintain the stability of the slurry solid concentration. During the hot soaking process, the temperature of the jacket heat transfer oil of the reactor is controlled at 105-115°C to ensure that the slurry in the reactor maintains the target temperature.

[0011] According to the preparation process of soybean fermentation water-soluble fertilizer provided by the present invention, in step S4, the compound enzyme preparation is a complex containing at least three enzymes selected from cellulase, pectinase, protease and amylase; the compound enzyme preparation is added as follows: the compound enzyme preparation is first pre-mixed and activated with 45-55 kg of purified water at a temperature below 40°C in an auxiliary material tank for 15-30 minutes to form an enzyme suspension, and then evenly sprayed into the slurry in the reaction vessel by pressurized conveying.

[0012] According to the preparation process of a soybean fermentation water-soluble fertilizer provided by the present invention, in step S5, a citric acid aqueous solution with a mass concentration of 20% to 30% is used to adjust the pH value and is slowly added by means of atomized spraying through a metering pump. At the same time, the stirring frequency is temporarily increased to 40 to 50 revolutions per minute and stirring is continued for 10 to 15 minutes.

[0013] According to the preparation process of a soybean fermented water-soluble fertilizer provided by the present invention, in step S5, the soybean fermentation agent is a compound microbial agent composed of *Lactobacillus plantarum*, *Lactobacillus acidophilus*, and *Saccharomyces cerevisiae* in a live bacteria ratio of (3-5):(1-2):(1-2), with a total live bacteria count of not less than 1.0 × 10⁻⁶. 10 CFU / g; the molasses is cane molasses or beet molasses.

[0014] According to the preparation process of soybean fermented water-soluble fertilizer provided by the present invention, in step S5, during the anaerobic fermentation process, food-grade nitrogen or carbon dioxide is introduced above the liquid surface in the reactor to expel air and construct an anaerobic environment; after 8 to 10 hours after the start of fermentation, the bottom sediment accounting for 2% to 3% of the total volume of the system is discharged through the bottom drain valve; the fermentation endpoint simultaneously meets the two conditions of fermentation duration of 22-26 hours and lactic acid content of fermentation system ≥6g / L.

[0015] A soybean fermented water-soluble fertilizer, prepared by the above-mentioned process, contains small molecule polypeptides with a molecular weight of less than 10,000 Daltons, free amino acids, oligosaccharides, organic acids, and active probiotics; the fertilizer has a pH of 4.5–5.5, a soluble solids content of not less than 25°Brix, and a total viable count of not less than 1.0 × 10⁻⁶. 8 CFU / mL, the lactic acid content in the fertilizer is 6-12g / L.

[0016] According to the present invention, a soybean fermented water-soluble fertilizer is provided, which is used for drip irrigation, fertigation or foliar spraying of crops.

[0017] The present invention provides a soybean fermentation water-soluble fertilizer and its preparation process, which has the following beneficial effects: (1) An alkaline hot soaking combined with high-shear cyclic pretreatment process is adopted. Potassium hydroxide is used to adjust the slurry to the alkaline range, which promotes the denaturation of soybean protein and the loosening and destruction of plant cell walls. Combined with the high-shear disperser cyclic shearing, the material is finely crushed and emulsified, which greatly increases the contact area between macromolecules such as protein and cellulose and subsequent complex enzymes. The shearing cycle can also generate mechanical heat to assist the material in heating up, shorten the heating time, reduce the overall heating energy consumption, solve the problem of insufficient material crushing in traditional pretreatment, and provide excellent substrate conditions for subsequent enzymatic hydrolysis. The two-stage high-shear mode can further enhance the emulsification and refinement effect of the material, maintain the uniformity of the slurry system, and reduce insoluble large particle residues.

[0018] (2) A staged temperature-controlled enzymatic hydrolysis process is adopted, maintaining 52±1℃ for the first 8 hours and 48±1℃ for the last 8 hours. This temperature-controlled process activates the optimal enzyme activity of different enzyme components in the compound enzyme preparation, enabling the stepwise degradation of soybean meal macromolecules. This efficiently breaks down soybean macromolecular proteins into small molecule peptides and free amino acids that are easily absorbed by plants. At the same time, it decomposes some polysaccharides to generate oligosaccharides, increasing the proportion of active nutrients in the fertilizer that can be directly absorbed and utilized by crops. The compound enzyme preparation is pre-activated with warm water and then atomized and sprayed into the reaction vessel. The enzyme and substrate are mixed evenly, further ensuring the efficiency of enzymatic hydrolysis.

[0019] (3) The anaerobic fermentation section constructs a closed, inert gas-protected anaerobic environment to inhibit the proliferation of aerobic bacteria and ensure that the compound fermentation microbial community of *Lactobacillus plantarum*, *Lactobacillus acidophilus*, and *Saccharomyces cerevisiae* becomes the dominant microbial community. The bottom sediment is discharged after 8-10 hours of fermentation to reduce insoluble residues in the system. Simultaneously, the traditional method of determining the fermentation endpoint solely based on time is changed; instead, a dual indicator of fermentation duration and lactic acid content is used to determine the fermentation endpoint, reducing batch-to-batch differences caused by fluctuations in raw materials and bacterial activity, and improving the quality consistency between different batches of finished products. The compound microbial community metabolizes to produce lactic acid and other organic acids, which not only enrich the active substances in the fertilizer but also play a natural antibacterial and stabilizing role in the fertilizer system.

[0020] (4) The parameters of each step in the entire process work together to ensure sufficient degradation and fermentation, and control the anaerobic fermentation time to 22-26 hours. Compared with the traditional soybean-based fermentation process with a cycle of several days, this significantly shortens the production cycle and reduces time costs. The resulting soybean fermented water-soluble fertilizer has a stable pH in the range of 4.5-5.5, soluble solids ≥25°Brix, is rich in small molecule peptides with a molecular weight of less than 10,000 Daltons, free amino acids, oligosaccharides, lactic acid content of 6-12 g / L, and total viable count of active probiotics ≥1.0×10⁻⁶. 8 CFU / mL; the product has good flowability and is suitable for various fertilization modes such as drip irrigation, fertigation, and foliar spraying. After application, it can provide crops with organic small molecule nutrients and supplement active beneficial microorganisms to improve the rhizosphere microecology. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0022] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship when the product of the invention is used, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0024] Example 1

[0025] Add 3600 liters of purified water treated by reverse osmosis with a conductivity of 8 μS / cm and a water temperature of 30°C to a 10-cubic-meter reactor. Start the stirrer and set the stirring frequency to 50 rpm.

[0026] 1500 kg of soybean flour is slowly added during the stirring process. The soybean flour is obtained by processing soybeans and passing them through an 80-mesh sieve. It has a protein content of 38% and a moisture content of 10%. Stirring continues until a uniform slurry is formed.

[0027] Subsequently, 1.5 kg of potassium hydroxide was added to the mixed slurry to precisely adjust the pH value of the slurry to 9.0. The stirring frequency of the reactor was adjusted to 25 rpm, and the heating temperature was set to 99°C.

[0028] Simultaneously with heating, the circulating shearing system is activated: a centrifugal pump pumps the slurry from the bottom of the reactor, allowing it to flow in series through two high-shear dispersers. The first disperser is set to a speed of 3000 rpm, and the second disperser to a speed of 5000 rpm. The treated slurry returns to the bottom of the reactor, forming a forced circulation loop. This process continues until the slurry temperature inside the reactor reaches 80°C. Continuous shearing is then stopped, and during the hot soaking stage, shearing is activated for 5 minutes every 30 minutes to maintain slurry uniformity. The hot soaking process is conducted under a slight negative pressure, with the jacket heat transfer oil temperature controlled at 110°C. Some of the evaporated water vapor is condensed and recovered, and then partially returned to the reactor to maintain a stable solids concentration. Hot soaking is maintained at 80°C for 2.5 hours.

[0029] After hot soaking, the slurry was cooled to 52℃ using cooling water from the reactor jacket. 7.5 kg of a compound enzyme preparation, composed of cellulase, pectinase, and protease in a 1:1:1 ratio of active units, was premixed with 50 kg of purified water at 35℃ and activated for 20 minutes. The enzyme suspension was then pressurized and evenly sprayed into the reactor, and the enzymatic hydrolysis reaction was carried out for a total of 16 hours with stirring at 25 rpm. The temperature was controlled at 52±1℃ for the first 8 hours of the enzymatic hydrolysis reaction and at 48±1℃ for the next 8 hours.

[0030] After enzymatic hydrolysis, a 25% (w / w) citric acid aqueous solution was prepared and added to the slurry via a metering pump using atomized spraying. The stirring frequency was temporarily adjusted to 45 rpm and stirred continuously for 12 minutes to adjust the pH to 5.0. The slurry was then cooled to 37°C, and 5 kg of a mixture of *Lactobacillus plantarum*, *Lactobacillus acidophilus*, and *Saccharomyces cerevisiae* at a live cell ratio of 4:1.5:1 was added, resulting in a total live cell count of 1.2 × 10⁻⁶. 10 Mix CFU / g of soybean starter with 250 kg of sugarcane molasses for 30 minutes until fully combined, then turn off the mixer.

[0031] Food-grade carbon dioxide was introduced into the space above the liquid surface of the reactor to expel air and create an anaerobic environment. Nine hours after the start of fermentation, the bottom sediment, which accounted for 2.5% of the total system volume, was discharged from the bottom drain valve. Anaerobic fermentation was carried out for 24 hours under sealed conditions. The lactic acid content of the fermentation system was measured to be 8.2 g / L, which met the dual fermentation endpoint of fermentation time and lactic acid content. The resulting fermentation liquid was filtered through a 100-mesh vibrating screen to obtain the finished soybean fermented water-soluble fertilizer.

[0032] The obtained liquid fertilizer was tested and found to have a pH of 5.0, a soluble solids content of 28 Brix, a small molecule polypeptide content (molecular weight less than 10,000 Daltons) of 84.7 mg / mL, a total free amino acid content of 42.1 mg / mL, and a total viable count of 4.2 × 10⁻⁶ probiotics. 8 CFU / mL, lactic acid content 8.2 g / L. All key indicators met the design expectations, proving that the combination of process parameters in this embodiment is effective and reliable.

[0033] Example 2

[0034] Add 3500 liters of purified water with a conductivity of 9 μS / cm and a water temperature of 25°C to the reactor. Start stirring at a frequency of 40 rpm. Add 1200 kg of soybean flour with a protein content of 35% and a moisture content of 12%, which has passed through a 60-mesh sieve. Add 1.0 kg of potassium hydroxide to adjust the pH value to 8.5.

[0035] Adjust the stirring frequency to 20 rpm and set the heating temperature to 95℃. Start the two-stage circulating shearing process, with the first high-shear disperser running at 2500 rpm and the second high-shear disperser running at 4000 rpm. After heating the slurry to 75℃, stop continuous shearing. During the hot soaking process, intermittently start the shearing to ensure the slurry is uniform. Operate under slight negative pressure during the hot soaking process, control the jacket heat transfer oil temperature at 105℃, and partially reflux the condensed water vapor. Maintain hot soaking for 4 hours. Then cool the slurry to 50℃, add 5.0 kg of a compound enzyme preparation composed of cellulase, pectinase, and protease, pre-activate with 45 kg of purified water at 38℃ for 30 minutes, and then pressurize and spray it into the reactor.

[0036] The enzymatic hydrolysis reaction was carried out for a total of 17 hours with stirring at 20 rpm; the temperature was 52±1℃ for the first 8 hours and 48±1℃ for the last 8 hours. After enzymatic hydrolysis, a 20% citric acid aqueous solution was prepared and sprayed through atomization to adjust the pH to 4.5. The temperature was then lowered to 35℃, and 3.0 kg of a total viable bacteria count of 1.0 × 10⁻⁶ was added. 10 CFU / g of soybean starter culture and 200 kg of beet molasses were mixed evenly and then sealed. Nitrogen gas was introduced into the reactor to create an anaerobic environment. At the 8th hour of fermentation, 2% of the bottom sediment was discharged. After 26 hours of anaerobic fermentation, the lactic acid content was measured to be 6.3 g / L, reaching the endpoint of double fermentation. After fermentation, the product was obtained by filtering through a 100-mesh vibrating sieve.

[0037] The resulting fermented soybean water-soluble fertilizer had a pH of 4.5 and a soluble solids content of 25 Brix. It contained 75.3 mg / mL of small molecule peptides, 37.6 mg / mL of total free amino acids, and 3.1 × 10⁻⁶ live probiotics. 8The concentration of CFU / mL and the lactic acid content were 6.3 g / L. The results indicate that even at the lower limit of the parameters, the core product indicators still met the standards, demonstrating the tolerance and stability of the process.

[0038] Example 3

[0039] Add 3700 liters of purified water with a conductivity of 7 μS / cm and a water temperature of 35℃ to the reactor. Start stirring at a frequency of 60 rpm, and add 1800 kg of soybean flour with a protein content of 40% and a moisture content of 8%, sieved through a 100-mesh sieve. Add 3.0 kg of potassium hydroxide to adjust the pH value to 9.5.

[0040] Adjust the stirring frequency to 30 rpm and set the heating temperature to 100℃. Start the two-stage circulating shearing: the first stage shearing speed is 3500 rpm and the second stage is 6000 rpm. After heating the slurry to 85℃, start shearing for 5 minutes every 30 minutes during the hot soaking stage. The total hot soaking time is 2 hours. The hot soaking is operated under slight negative pressure, with the jacket heat transfer oil temperature at 115℃, and some of the condensed water vapor is returned to the reactor.

[0041] The slurry was then cooled to 55°C, and 10.0 kg of a compound enzyme preparation consisting of cellulase, pectinase, protease, and amylase was added. After pre-activation with 55 kg of purified water at 36°C for 15 minutes, the mixture was sprayed under pressure. The enzymatic hydrolysis reaction was completed over a total of 15 hours with stirring at 30 rpm; the temperature was 52±1°C for the first 8 hours and 48±1°C for the last 8 hours. After hydrolysis, a 30% citric acid aqueous solution was prepared and sprayed through atomization to adjust the pH to 5.5. The temperature was then lowered to 38°C, and 7.0 kg of a total viable bacteria count of 1.5 × 10⁻⁶ was added. 10 CFU / g of soybean starter culture and 300 kg of sugarcane molasses were mixed evenly and then sealed. Nitrogen gas was introduced to maintain an anaerobic environment. After 10 hours of fermentation, 3% of the bottom sediment was discharged. After 22 hours of anaerobic fermentation, the lactic acid content was measured to be 11.1 g / L, reaching the endpoint of double fermentation. The material was filtered through a 100-mesh vibrating screen to obtain the finished product.

[0042] The resulting fermented soybean water-soluble fertilizer had a pH of 5.5 and a soluble solids content of 32 Brix. It contained a high content of small molecule peptides (91.8 mg / mL), a total free amino acid content of 47.9 mg / mL, and a total viable count of 6.0 × 10⁻⁶ probiotics. 8 The concentration of CFU / mL and the lactic acid content were 11.1 g / L. The results showed that using the upper limit of parameters significantly increased the content of active ingredients and the number of viable bacteria in the final product. All product indicators were within the expected range, demonstrating that this process can optimize product quality within a certain range by adjusting parameters.

[0043] The data results from the three embodiments show that, although there are differences in specific process parameters among the embodiments, covering different combinations of key steps such as low temperature-short time, medium temperature-standard, and high temperature-long time, the core indicators of the prepared soybean fermented water-soluble fertilizer products all exhibit good consistency and stability. The pH value of all products remained stable within the design range of 4.5 to 5.5, and the soluble solids content was greater than 25 Brix. More importantly, the key indicators representing the degradation effect of soybean flour, namely the content of small molecule peptides and the total amount of free amino acids, as well as the active probiotics and lactic acid content representing the success of fermentation, all reached excellent levels in all embodiments, and the values ​​showed a positive correlation with the amount of raw materials input and the treatment intensity. This fully demonstrates that the preparation process provided by this invention has clear causal logic and excellent repeatability, a wide range of process parameters, is easy to operate and control, and can continuously and stably produce high-quality soybean fermented water-soluble fertilizer products.

[0044] Comparative Example 1 The process of this comparative example is basically the same as that of Example 1, except that the two-stage high-shear cyclic shearing treatment is cancelled in step S3. Instead, the temperature is raised to 80°C by stirring the built-in stirrer at 25 rpm and maintained at 80°C for 2.5 hours. All other raw materials and operating parameters are the same as those in Example 1. The subsequent enzymatic hydrolysis and fermentation processes are carried out in accordance with those in Example 1.

[0045] The resulting fertilizer was tested and found to have the following characteristics: pH 5.1, soluble solids 27 Brix, small molecule polypeptides 56.2 mg / mL, free amino acids 26.4 mg / mL, and total viable probiotic count 2.3 × 10⁻⁶. 8 CFU / mL, lactic acid content 5.1g / L.

[0046] Compared with the test results of Example 1, it can be seen that after canceling the high-shear cycle pretreatment, the material was not sufficiently pulverized and emulsified, the soybean macromolecules were not fully exposed, the enzymatic degradation efficiency decreased, the production of small molecule peptides and free amino acids in fertilizer was significantly reduced, and the decline in substrate quality further reduced the fermentation lactic acid production capacity and the number of live bacteria.

[0047] Comparative Example 2 The process of this comparative example is basically the same as that of Example 1, except that the two-stage temperature control mode is no longer used in the enzymatic hydrolysis section. The temperature is kept constant at 50°C throughout the enzymatic hydrolysis process, and the total enzymatic hydrolysis time of 16 hours remains unchanged. All other raw materials and operating parameters are the same as those in Example 1.

[0048] The resulting fertilizer was tested and found to have the following characteristics: pH 5.0, soluble solids 28 Brix, small molecule polypeptides 63.5 mg / mL, free amino acids 31.7 mg / mL, and total viable probiotic count 2.7 × 10⁻⁶. 8 CFU / mL, lactic acid content 6.0g / L.

[0049] The results showed that a single constant temperature condition could not simultaneously adapt to the optimal operating temperature of multiple complex enzymes. The overall enzyme activity of the complex enzymes was limited, the degree of macromolecular degradation was reduced, and the output of active small molecule nutrients in fertilizers was significantly lower than that in Example 1 of this invention.

[0050] Comparative Example 3 The process of this comparative example is basically the same as that of Example 1, except that: the dual endpoint control of fermentation time and lactic acid content is not used, but only a fixed fermentation time of 24 hours is used as the fermentation endpoint; at the same time, to simulate the fluctuation of microbial activity in industrial production, the actual inoculation amount of live bacteria in soybean fermentation agent is reduced by 40%, while the other raw materials and operating parameters remain unchanged.

[0051] The resulting fertilizer was tested and found to have the following characteristics: pH 5.7, soluble solids 27 Brix, small molecule polypeptides 83.9 mg / mL, free amino acids 41.5 mg / mL, and total viable probiotic count 7.2 × 10⁻⁶. 7 CFU / mL, lactic acid content 4.4g / L.

[0052] The test results show that when the activity of the inoculum decreases, relying solely on a fixed fermentation time to control the process will result in incomplete fermentation, leading to substandard lactic acid content and probiotic count in the product. Therefore, this invention employs a dual endpoint determination method based on fermentation time and lactic acid content, which effectively overcomes batch variations caused by fluctuations in raw material and inoculum activity, thus improving product batch stability.

[0053] Therefore, this invention provides a soybean fermentation water-soluble fertilizer and its preparation process, employing an alkaline hot soaking combined with a high-shear cyclic pretreatment process. Potassium hydroxide is used to adjust the slurry to the alkaline range, promoting soybean protein denaturation and the loosening and destruction of plant cell walls. Combined with a high-shear disperser for cyclic shearing, the material is finely pulverized and emulsified, significantly increasing the contact area between macromolecules such as protein and cellulose and subsequent complex enzymes. The shearing cycle also generates mechanical heat, assisting in material heating, shortening heating time, reducing overall heating energy consumption, and solving the problem of insufficient material crushing in traditional pretreatment, thus providing excellent substrate conditions for subsequent enzymatic hydrolysis. The two-stage high-shear mode further enhances the emulsification and refinement effect of the material, maintains the homogeneity of the slurry system, and reduces insoluble large particle residues. A staged temperature-controlled enzymatic hydrolysis process is employed, maintaining a temperature of 52±1℃ for the first 8 hours and 48±1℃ for the following 8 hours. This temperature-zoned approach activates the optimal enzyme activity of different enzyme components in the compound enzyme preparation, achieving a stepwise degradation of soybean meal macromolecules. It efficiently breaks down soybean macromolecular proteins into easily absorbed small-molecule peptides and free amino acids, while simultaneously decomposing some polysaccharides to generate oligosaccharides, increasing the proportion of bioactive nutrients in the fertilizer that can be directly absorbed and utilized by crops. The compound enzyme preparation is pre-activated with warm water and then atomized into the reaction vessel, ensuring uniform mixing of the enzyme and substrate, further guaranteeing the efficiency of the enzymatic hydrolysis conversion.

[0054] The anaerobic fermentation section creates a closed, inert gas-protected anaerobic environment to inhibit the proliferation of aerobic bacteria and ensure that the combined fermentation microbial community of *Lactobacillus plantarum*, *Lactobacillus acidophilus*, and *Saccharomyces cerevisiae* becomes the dominant microbial community. The bottom sediment is removed after 8-10 hours of fermentation, reducing insoluble residues in the system. Furthermore, it departs from the traditional method of determining the fermentation endpoint solely based on time, employing both fermentation duration and lactic acid content as dual indicators to reduce batch-to-batch variations caused by fluctuations in raw materials and microbial activity, thereby improving the quality consistency between different batches of finished products. The combined microbial community metabolizes and produces lactic acid and other organic acids, which not only enrich the active substances in the fertilizer but also play a natural antibacterial and stabilizing role in the fertilizer system.

[0055] The entire process utilizes coordinated parameters across all steps, ensuring thorough degradation and fermentation while controlling anaerobic fermentation within 22-26 hours. Compared to traditional soybean-based fermentation processes that take several days, this significantly shortens the production cycle and reduces time costs. The resulting fermented soybean water-soluble fertilizer exhibits a stable pH between 4.5 and 5.5, soluble solids ≥25°Brix, and is rich in small-molecule peptides (molecular weight less than 10,000 Daltons), free amino acids, oligosaccharides, lactic acid content of 6-12 g / L, and a total viable count of ≥1.0 × 10⁻⁶ probiotics. 8 CFU / mL; the product has good flowability and is suitable for various fertilization modes such as drip irrigation, fertigation, and foliar spraying. After application, it can provide crops with organic small molecule nutrients and supplement active beneficial microorganisms to improve the rhizosphere microecology.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation process for a soybean fermentation water-soluble fertilizer, characterized in that, Includes the following steps: S1. Add 3500±100 liters of purified water to the reactor, start stirring and set the stirring frequency to 40-60 rpm. During the stirring process, add 1200-1800 kg of soybean flour to the reactor to form a mixed slurry. S2. Add 1-3 kg of potassium hydroxide to the mixed slurry to adjust the pH value of the mixed slurry to 8.5-9.5; S3. Adjust the stirring frequency of the reactor to 20-30 rpm, set the heating temperature of the reactor to 95-100℃, and start the heating program to heat the mixed slurry. During this process, pump the mixed slurry out of the reactor and pass it in series through at least one high-shear disperser for circulating shearing treatment. Then, return the sheared slurry to the reactor to accelerate the heating of the slurry. Continue until the temperature of the slurry in the reactor reaches a high temperature range of 75-85℃, and maintain hot soaking at this high temperature for 2-4 hours. S4. Cool the hot-soaked slurry to 50-55℃, add 5-10 kg of compound enzyme preparation to the slurry, and carry out the enzymatic hydrolysis reaction for 15-17 hours while maintaining a stirring frequency of 20-30 rpm. The enzymatic hydrolysis reaction is divided into two stages: in the first 8 hours, the slurry temperature is controlled at 52±1℃; in the next 8 hours, the slurry temperature is controlled at 48±1℃. S5. After the enzymatic hydrolysis reaction is completed, citric acid is added to the slurry to adjust the pH value of the slurry to 4.5-5.

5. Then the slurry is cooled to 35-38℃, and 3-7 kg of soybean fermentation agent and 200-300 kg of molasses are added to the slurry. After stirring evenly, stirring is stopped, and anaerobic fermentation is carried out under sealed conditions for 22-26 hours to obtain the soybean fermented water-soluble fertilizer.

2. The preparation process of a soybean fermentation water-soluble fertilizer according to claim 1, characterized in that: In step S1, the soybean powder is obtained by washing, drying, crushing soybeans and passing them through a 60-100 mesh sieve. Its protein content is not less than 35% and its moisture content is not more than 12%. The purified water is pure water that has undergone reverse osmosis treatment and has a conductivity of less than 10 μS / cm. The water temperature is controlled within the range of 25-35℃ and added to the reaction vessel.

3. The preparation process of a soybean fermentation water-soluble fertilizer according to claim 1, characterized in that: In step S3, the cyclic shearing process includes: S301. The slurry in the reactor is pumped out by a main circulation pump. The slurry flows through the first high shear disperser and the second high shear disperser in sequence. The working speed of the first high shear disperser is set to 2500-3500 rpm to perform preliminary crushing and mixing of the slurry. S302. The operating speed of the second high-shear disperser is set to 4000-6000 rpm to further perform ultra-fine shearing and emulsification on the slurry; S303. The slurry after two-stage shearing treatment is returned to the lower part of the reactor through a pipeline to form a forced circulation loop. The circulation shearing treatment continues until the slurry temperature reaches above 75°C, and is intermittently started throughout the hot soaking stage to maintain the uniformity and stability of the slurry system.

4. The preparation process of a soybean fermentation water-soluble fertilizer according to claim 1, characterized in that: In step S3, the hot soaking process is carried out under a slight negative pressure condition. The exhaust valve of the reactor is connected to the condensation recovery device to condense and recover the evaporated water vapor and partially return it to the reactor to maintain the stability of the slurry solid concentration. During the hot soaking process, the temperature of the heat transfer oil in the jacket of the reactor is controlled at 105-115℃ to ensure that the slurry in the reactor maintains the target temperature.

5. The preparation process of a soybean fermentation water-soluble fertilizer according to claim 1, characterized in that: In step S4, the compound enzyme preparation is a complex containing at least three enzymes selected from cellulase, pectinase, protease and amylase. The compound enzyme preparation is added as follows: the compound enzyme preparation is first pre-mixed and activated with 45-55 kg of purified water at a temperature below 40°C in an auxiliary material tank for 15-30 minutes to form an enzyme suspension, and then evenly sprayed into the slurry in the reaction vessel by pressurized conveying.

6. The preparation process of a soybean fermentation water-soluble fertilizer according to claim 1, characterized in that: In step S5, a citric acid aqueous solution with a mass concentration of 20% to 30% is used to adjust the pH value. The solution is slowly added via a metering pump in the form of atomized spray, while the stirring frequency is temporarily increased to 40 to 50 rpm and stirring is continued for 10 to 15 minutes.

7. The preparation process of a soybean fermentation water-soluble fertilizer according to claim 1, characterized in that: In step S5, the soybean fermentation agent is a compound microbial agent composed of Lactobacillus plantarum, Lactobacillus acidophilus, and Saccharomyces cerevisiae in a live cell ratio of (3-5):(1-2):(1-2), with a total live cell count of not less than 1.0 × 10⁻⁶. 10 CFU / g; the molasses is cane molasses or beet molasses.

8. The preparation process of a soybean fermentation water-soluble fertilizer according to claim 1, characterized in that: In step S5, during the anaerobic fermentation process, food-grade nitrogen or carbon dioxide is introduced above the liquid surface in the reactor to expel air and create an anaerobic environment. After 8 to 10 hours of fermentation, the bottom sediment, which accounts for 2% to 3% of the total system volume, is discharged through the bottom drain valve. The fermentation endpoint simultaneously meets the two conditions of fermentation duration of 22-26 hours and lactic acid content of the fermentation system ≥6g / L.

9. A soybean fermentation water-soluble fertilizer, characterized in that: Prepared by the process described in any one of claims 1-8, the soybean fermented water-soluble fertilizer contains small molecule polypeptides with a molecular weight of less than 10,000 Daltons, free amino acids, oligosaccharides, organic acids, and active probiotics; the fertilizer has a pH of 4.5-5.5, a soluble solids content of not less than 25°Brix, and a total viable count of not less than 1.0 × 10⁻⁶. 8 CFU / mL, the lactic acid content in the fertilizer is 6-12g / L.

10. A soybean fermentation water-soluble fertilizer according to claim 9, characterized in that: The fermented soybean water-soluble fertilizer is used for drip irrigation, fertigation, or foliar spraying of crops.