Method for preparing ecological value-added fertilizer by recycling starch process byproduct corn steep liquor

Abstract

The invention relates to the technical field of corn steep liquor resource utilization, and particularly discloses a method for preparing an ecological value-added fertilizer through starch process byproduct corn steep liquor resource, which comprises the following steps: 1, introducing oxygen into corn steep liquor for aeration oxidation, and then screening, purifying and decolorizing to obtain a clarified corn steep liquor stock solution; 2, adjusting the pH value of the clarified corn steep liquor stock solution, and adding protease for enzymolysis to obtain a primary enzymatic hydrolysate; adjusting the pH value of the primary enzymatic hydrolysate, and adding saccharifying enzyme for enzymolysis to obtain secondary enzymatic hydrolysate; 3, cooling the secondary enzymatic hydrolysate to room temperature, adjusting the pH value, adding medium trace element salt, stirring and curing to obtain a chelating solution; and 4, purifying and concentrating the chelating liquid. According to the method, potential risk factors can be effectively removed, the nutrient effectiveness can be improved, and an environment-friendly intelligent delivery system can be constructed by utilizing endogenous active components, so that the ecological value-added fertilizer with nutrition supply, biological stimulation and soil improvement functions is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of corn syrup resource utilization, and specifically discloses a method for preparing an ecological value-added fertilizer from corn syrup, a byproduct of a starch process. BACKGROUND

[0002] Corn syrup is a high-concentration organic byproduct produced in the wet corn starch processing process. It is usually obtained by concentrating the soluble components separated from corn kernels after soaking in a sulfurous acid solution. The solid content of corn syrup is as high as 40-50%, and it is rich in protein, polypeptide, amino acid, reducing sugar, organic acid, vitamin, and various mineral elements, with high organic matter and nitrogen content. Traditionally, corn syrup is mainly used as a feed additive or a nitrogen source for microbial fermentation. However, due to factors such as market capacity, transportation cost, and ingredient fluctuation, a large amount of corn syrup faces disposal problems. Some enterprises even treat it as wastewater, which not only wastes resources but also increases environmental burden.

[0003] In recent years, with the promotion of the national "double carbon" strategy and the acceleration of agricultural green transformation, the resource-based preparation of ecological fertilizers from industrial and agricultural organic waste has become a research hotspot. Corn syrup is considered a potential organic fertilizer or biological stimulant due to its natural organic nutrient characteristics. However, there are significant technical bottlenecks in directly using corn syrup to produce fertilizer. First, its high viscosity, high salt content, and complex composition result in poor flowability, easy spoilage, and low storage stability. Second, nitrogen is mainly in the form of macromolecular organic matter, which mineralizes slowly and has a lag in fertilizer effect. Third, the content of phosphorus, potassium, and trace elements is insufficient, making it difficult to meet the nutrient needs of crops throughout their growth period. Most importantly, if not properly treated, harmful substances such as mycotoxins and heavy metals that may be present in corn syrup pose a risk of entering the farmland ecosystem, threatening the safety of agricultural products.

[0004] To overcome the above problems, existing technologies attempt to treat corn syrup through dilution, drying, composting, or simple compounding. For example, CN119019199A discloses a fertilizer containing corn syrup dry powder and its application, which directly concentrates and dries corn syrup into dry powder and then compounds it with trace elements to produce organic fertilizer. However, the drying process is energy-intensive and can lead to the loss of heat-sensitive nutrients such as amino acids and vitamins. CN111606756A discloses a method for producing liquid fertilizer using corn syrup, which involves settling corn syrup and thiourea production residues, followed by enzymatic hydrolysis, and then compounding with trace elements. However, the thiourea residues contain excessive amounts of sulfite, which can cause soil acidification and environmental pollution if not treated. However, these methods generally have high energy consumption (such as spray drying), low nutrient utilization, and single product functionality, and do not fully utilize the biological stimulation potential of active small molecules (such as amino acids and oligopeptides) in corn syrup. SUMMARY

[0005] The present application provides a method for preparing an ecological value-added fertilizer from corn syrup byproduct of a starch process, which can effectively remove potential risk factors, improve nutrient availability, and utilize endogenous active ingredients to construct an environmentally friendly intelligent delivery system, thereby preparing an ecological value-added fertilizer with functions of nutrient supply, biological stimulation, and soil improvement.

[0006] The present application is realized by the following technical solutions: A method for preparing an ecological value-added fertilizer from corn syrup byproduct of a starch process, comprising the following steps: Step one: oxygen is introduced into the corn syrup for aeration oxidation, and then the clarified corn syrup stock solution is obtained through screening, purification, and decolorization; Step two: the pH of the clarified corn syrup stock solution is adjusted to 8-9, and protease is added for enzymolysis to obtain a primary enzymolysis solution; the pH of the primary enzymolysis solution is adjusted to 4-5, and saccharifying enzyme is added for enzymolysis to obtain a secondary enzymolysis solution; Step three: the secondary enzymolysis solution is cooled to room temperature (25℃), the pH is adjusted to 4-5, and trace element salt is added, and then stirring and maturation are performed to obtain a chelation solution; Step four: the chelation solution is purified and concentrated to obtain the ecological value-added fertilizer.

[0007] The amphiphilic short peptides produced by protein hydrolysis can spontaneously form nanomicelle structures in an aqueous phase, the hydrophobic core of which can load metal ions, and the hydrophilic shell can impart good dispersibility and stability to the system. Therefore, the present application enriches small molecule peptides, amino acids (such as glutamic acid and proline), and organic acids (lactic acid and citric acid) in the corn syrup after directional enzymolysis, and these substances are natural biological stimulants. In-situ chelation of endogenous ligands with trace elements (Fe, Zn, Mg, and Ca) forms self-sourced biological chelates. In addition, due to the easy separation, precipitation, and metal ion precipitation of liquid fertilizer during long-term storage, the amphiphilic peptide segments (such as hydrophobic amino acids + hydrophilic carboxyl groups) in the enzymolysis products of corn syrup self-assemble into nanomicelles (<100 nm) in an aqueous phase, and trace elements are wrapped in the core or surface of the micelles to form a nanoscale stable dispersion system without the need for additional surfactants or thickeners, thereby improving the bioavailability of micro-fertilizers (nanoscale size is beneficial for stomata / root absorption). At the same time, no additional chemical chelating agents are needed, which reduces costs and is more environmentally friendly. The chelation structure has pH-responsive release characteristics (such as releasing metal ions in the rhizosphere acidic environment), and realizes intelligent slow release.

[0008] First, the protein is completely hydrolyzed by protease to generate a large number of small molecular peptides and amino acids, which provide raw materials for the self-assembly of amphiphilic. Then, the polysaccharides such as starch and dextrin are hydrolyzed by saccharifying enzyme to increase the water-soluble carbon source and reduce the viscosity of the system. The design of the enzyme hydrolysis process can guarantee the quality and yield of the peptide segment, form the core basis of the nanomicelle, and provide more small molecular sugars through subsequent saccharifying enzyme hydrolysis. The produced glucose and oligosaccharides are excellent biological stimulants, which can synergize with nanomicelles to promote plant growth.

[0009] The short peptides produced by corn syrup enzymolysis are rich in glutamic acid (Glu) and aspartic acid (Asp) which contribute to the side chain carboxyl group, and the imidazole group of histidine (His) and the amino group of lysine (Lys) are excellent coordination sites for metal ions. These groups can form stable complexes with metal ions such as calcium (Ca 2+ ), zinc (Zn 2+ ), iron (Fe 2+ / Fe 3+ ) through multi-dentate coordination mode. The hydrophobic amino acid side chains in the short peptide molecule (such as leucine Leu, valine Val, and phenylalanine Phe) provide the core driving force for self-assembly - hydrophobic interaction. These peptides have amphiphilic properties. Near the isoelectric point, the hydrophobic interaction of the amphiphilic peptide segment is enhanced, and the hydrophilic carboxyl group is oriented towards the water phase, thereby spontaneously assembling into a core-shell structure nanomicelle with hydrophobic amino acids as the core and hydrophilic carboxyl groups as the shell. This structure can effectively load Fe 2+ / Fe 3+ , Zn 2+ , Ca 2+ , Mg 2+ and other trace elements, and prevent their precipitation or oxidation. The peptide chain "anchors" the metal ion at its hydrophilic head or near the core-shell interface through multi-dentate coordination, synchronously introducing metal ions during the self-assembly of micelles, allowing metal ions to participate in the conformation adjustment and aggregation process of peptide molecules, achieving molecular-level embedding. Metal ions act as "structure directing agents" to promote the aggregation of specific conformational peptides. Some metals can be wrapped in the core of the micelle (especially when coordinated with hydrophobic residues), making the chelation more stable and resistant to pH changes.

[0010] The present application takes corn syrup, a byproduct of starch process, as the core, and through directional conversion and functional enhancement, it is prepared into a fertilizer with ecological safety and nutrient efficiency. It not only solves the problem of waste of industrial byproducts, but also provides an ecological type of increasing solution for high-value planting, realizing the unity of resources, economy and ecological benefits.

[0011] In the present application, in step one, the aeration oxidation is 2-4h, after filtering through 100-200 mesh screen, centrifuging at 3000-5000r / min for 15-20min, adding activated carbon with an addition amount of 0.1-0.5% of the supernatant quality to the supernatant, stirring and adsorbing at 45-50℃ for 15-30min, filtering to obtain the clear corn syrup stock solution.

[0012] The corn syrup (solid content 18-22%) with freshness ≤24h in the corn starch production process is selected, the sulfite is removed by aeration oxidation to make the residual amount <50 mg / L, the starch residue and fiber impurities are removed through 100-200 mesh vibrating screen, then the disc centrifuge is used for centrifugal separation to remove free oil and fine particles, and the activated carbon is used to reduce pigment and impurities to obtain the clear corn syrup stock solution.

[0013] In the present application, the specific process of step two is: a. The solid concentration of the clear corn syrup stock solution is adjusted to 10-15% with deionized water, the pH is adjusted to 8-9 with sodium hydroxide, the protease is added, and the enzymolysis is carried out at 50-55℃ for 2-4h to obtain the first enzymolysis liquid; b. The first enzymolysis liquid is cooled to 60℃, the pH is adjusted to 4-5 with food-grade citric acid, the saccharifying enzyme is added, and the enzymolysis is carried out at 60℃ for 1-2h to obtain the second enzymolysis liquid.

[0014] In the present application, the protease is alkaline protease, the addition amount of the protease is 3000-5000 U / g of substrate protein, and the addition amount of the saccharifying enzyme is 100-200 U / g of substrate total sugar. The alkaline protease cuts the main chain to generate peptide chains, controls the degree of hydrolysis (DH value) at 8-15%, retains functional peptides instead of complete mineralization into amino acids, and retains oligopeptides with plant hormone-like effects.

[0015] In the present application, after the enzymolysis, the first enzymolysis liquid and the second enzymolysis liquid are further heated to 90-95℃ and kept for 15-20min. The first enzymolysis liquid is heated to inactivate the enzyme, which can prevent the protease from being contaminated and hydrolyzed in the subsequent steps.

[0016] In the present application, the trace element salt includes calcium nitrate, magnesium sulfate, zinc sulfate and EDTA-iron with a mass ratio of 3:2:1:0.5, and the total addition amount of the trace element salt is 8-10% of the dry weight of the second enzymolysis liquid.

[0017] In the present application, in step three, the addition steps of the trace element salt are: 1) ZnSO4·7H2O and MgSO4·7H2O are respectively prepared into clear mother liquor with a mass fraction of 5-10% with deionized water, and are synchronously added to the second enzymolysis liquid at a speed of 1-2mL / min, and the total addition time is ≥15min; 2) EDTA-FeNa is prepared into a mother liquor with a mass fraction of 2-5% with warm water, and is added dropwise into the secondary enzymatic hydrolysis liquid at a speed of 0.5-1 mL / min, and the adding time is ≥10 min; 3) Ca(NO3)2·4H2O is prepared into a mother liquor with a mass fraction of 5% with deionized water, and is added dropwise into the secondary enzymatic hydrolysis liquid at a speed of 1 mL / min, and the adding time is ≥10 min.

[0018] To avoid the problems such as precipitation, competition chelation and micelle destruction of trace element salts in the in-situ co-assembly process of corn syrup enzymatic peptides, under the condition of adjusting pH to 4-5, the carboxyl part of the peptide chain is deprotonated (-COO - ), has chelation ability, Zn 2+ , Mg 2+ is kept dissolved, Fe 2+ / Fe 3+ is stable under the protection of EDTA, and Ca 2+ has a lower risk of precipitation. Therefore, magnesium sulfate and zinc sulfate are added first, so that Zn 2+ / Mg 2+ is captured by the peptide chain in the initial stage of peptide self-assembly to form a stable complex. Then EDTA-iron is added to avoid coexistence with Ca 2+ , to prevent EDTA from competing with Ca 2+ , and finally calcium nitrate is added, at which time SO4 2- has been diluted and partially combined with micelles to avoid the generation of calcium sulfate precipitation.

[0019] In the present application, in step three, stirring and maturation are carried out at 25℃ under a nitrogen atmosphere for 2-3h. A slight positive pressure is maintained under a nitrogen atmosphere to prevent Fe 2+ oxidation, and the micelle structure is gradually improved during the maturation process, and the metal-peptide complex tends to be thermodynamically stable. After the end of stirring and maturation, the chelation rate is detected by a UV spectrophotometer to ensure that the chelation rate is ≥90%, and a stable chelate liquid is obtained.

[0020] In the present application, in step four, the chelate liquid is filtered through a 0.45μm ceramic membrane to obtain a microfiltrate; the microfiltrate is concentrated using a nanofiltration membrane with a molecular weight cut-off of 5-10KDa until the solid content is 35-40%. A small amount of large particle aggregates that may exist are removed by microfiltration, and microtrace precipitates and impurities that are not completely chelated are removed. Then a nanofiltration membrane with an appropriate molecular weight cut-off is used for concentration and desalination (to remove small molecule nutrient chelates, and to remove excess water and salt), to improve the purity of the product. In addition, the nutritional ingredients (small molecule peptides, monosaccharides, trace elements) and pH value of the concentrated liquid can be detected, and if the content of trace elements is insufficient, a small amount of chelated trace elements can be added; citric acid is used to adjust the pH to 6.5-7.0 to ensure that the product is suitable for different soil acidities.

[0021] In the application, after the chelating liquid is purified and concentrated, it is further treated at 135-140 DEG C for 3-5s, then cooled to 30-35 DEG C for sterile filling. The high-temperature instantaneous sterilization quickly kills the bacteria, mold and other microorganisms in the system, avoids the deterioration of the product during storage, and maximizes the retention of the activity of the nutritional ingredients. In the sterile filling workshop, an automatic filling machine (precision ±1%) is used to fill food-grade HDPE sealed barrels (specification 10L / 20L). The barrel body is sterilized by ultraviolet light before filling, and is immediately sealed after filling, and the product information (nutritional ingredients, shelf life, and use method) is labeled, and the final packaging is completed.

[0022] The technical scheme of the application has at least the following advantages and beneficial effects: 1. Breakthrough the limitations of traditional water-soluble fertilizer relying on chemical synthesis raw materials or single plant extracts, taking corn syrup by-product produced in the production process of corn starch as the core organic matrix, realizing high-value utilization of industrial waste. Corn syrup is rich in natural amino acids, small molecule peptides, vitamins and growth promoting factors. Compared with artificially prepared organic nutrient system, its nutritional ingredients have more natural synergy, and the raw material cost is only 1 / 3-1 / 2 of that of traditional organic raw materials, which not only reduces the environmental treatment pressure of the production end, but also endows the fertilizer with the core attribute of "source organic", which meets the core needs of the green and sustainable development of modern agriculture.

[0023] 2. Abandoning the conventional extensive hydrolysis process, using directional enzyme hydrolysis technology to accurately process corn syrup, realizing the form optimization of nutritional ingredients. By screening enzyme preparations and optimizing enzyme hydrolysis temperature, pH value and reaction time, the macromolecular proteins and polysaccharides in corn syrup are directionally decomposed into small molecule peptides, free amino acids and monosaccharides. This kind of small molecule nutrients can be directly absorbed by root hair cells without additional transformation by plant roots, and the absorption efficiency is improved by more than 60% compared with traditional organic fertilizers, solving the industry pain point of "rich in nutrients but slow in absorption" of organic water-soluble fertilizer. At the same time,.

[0024] 3. The innovation adopts a double-site chelation process, utilizes the enzymatic product-amphiphilic peptide segment, near the isoelectric point, the hydrophobic interaction of the peptide segment is enhanced, and the hydrophilic carboxyl group is oriented towards the water phase, thereby spontaneously assembling into a core-shell structure nanomicelle with hydrophobic amino acids as the core and hydrophilic carboxyl groups as the shell. This structure efficiently chelates with trace elements (such as calcium, magnesium, zinc, iron, etc.), forming a structurally stable "organic nutrient-trace element" chelate, and constructing an environmentally friendly intelligent delivery system. On the one hand, the active groups such as amino acids and carboxyl groups produced by enzymolysis can form double coordination bonds with trace elements, avoiding precipitation reactions with phosphate, carbonate, and other substances in the soil, improving the availability of trace elements in different pH soils, and increasing the utilization rate from 30-40% of traditional fertilizers to more than 80%; on the other hand, the chelate can slowly release nutrients, prolonging the duration of fertilizer effect to 45-60 days, reducing the frequency of fertilization, and reducing the cost of agricultural production.

[0025] 4. The product breaks through the traditional water-soluble fertilizer "single nutrient supply" functional positioning, forming a "organic nutrient supply + soil micro-ecological conditioning" dual effect. The small molecule organic matter after enzymolysis is not only a direct nutrient source for plants, but also a carbon source and nitrogen source for soil beneficial microorganisms (such as Bacillus subtilis and Actinomycetes), promoting the reproduction of beneficial bacteria and improving soil aggregate structure; at the same time, the stable chelate system can reduce the stress of heavy metal ions on plant roots, improving the stress resistance of crops (drought resistance, cold resistance, disease resistance). Field test verification shows that crops using this fertilizer not only increase yield by 15-20%, but also significantly improve the content of vitamin C and soluble sugar in fruits, achieving simultaneous improvement of crop "quantity" and "quality". DETAILED DESCRIPTION

[0026] The application will be further described below in conjunction with specific embodiments, but the embodiments do not limit the application in any form. Unless otherwise specified, the raw materials used in the embodiments of the application are conventionally purchased raw materials.

[0027] Example 1 A method for preparing an ecological value-added fertilizer from corn syrup, a byproduct of starch production, includes the following steps: Step one: select corn syrup (solid content 18-22%) with freshness ≤24h in the corn starch production process, adjust the pH of the corn syrup to 7, pass oxygen for 4h, then filter through a 100 mesh screen, centrifuge at 4000r / min for 15min, add activated carbon to the supernatant at an addition amount of 0.3% of the mass of the supernatant, stir and adsorb at 50°C for 20min, filter to obtain clear corn syrup stock solution; Step two: adjust the solid content of the clarified corn syrup stock solution to 12%, adjust the pH to 9 with sodium hydroxide, add alkaline protease, and hydrolyze at 55°C for 2h, then increase the temperature to 95°C and keep for 15min, to obtain a first enzyme hydrolysis solution; cool the first enzyme hydrolysis solution to 60°C, adjust the pH to 4.5 with food-grade citric acid, add saccharifying enzyme, and hydrolyze at 60°C for 2h, then increase the temperature to 95°C and keep for 15min, to obtain a second enzyme hydrolysis solution; the addition amount of alkaline protease is 4000 U / g substrate protein, and the addition amount of saccharifying enzyme is 150 U / g total substrate sugar; Step three: cool the second enzyme hydrolysis solution to room temperature, adjust the pH to 5, add medium and trace element salt, the medium and trace element salt includes calcium nitrate, magnesium sulfate, zinc sulfate and EDTA-iron with a mass ratio of 3:2:1:0.5, the total addition amount of medium and trace element salt is 8% of the dry weight of the second enzyme hydrolysis solution, then stir and mature at 25°C under nitrogen for 3h, to obtain a chelation solution; Among them, the addition steps of medium and trace element salt are as follows: 1) ZnSO4·7H2O and MgSO4·7H2O are respectively prepared into 10% mass fraction clarified stock solution with deionized water, and are synchronously added into the second enzyme hydrolysis solution at a speed of 2mL / min, and the total addition time is ≥15min; 2) EDTA-FeNa is prepared into a 5% mass fraction stock solution with warm water, and is added into the above system at a speed of 0.5mL / min, and the addition time is ≥10min; 3) Ca(NO3)2·4H2O is prepared into a 5% mass fraction stock solution with deionized water, and is added into the above system at a speed of 1mL / min, and the addition time is ≥10min; Step four: filter the chelation solution through a 0.45μm ceramic membrane to obtain a microfiltrate; concentrate the microfiltrate using a nanofiltration membrane with a molecular weight cut-off of 5-10KDa until the solid content is 35-40%, and then pass through an ultra-high temperature instant sterilization equipment (UHT) at 140°C for 3s, then cool to 30°C for sterile filling, to obtain an ecological value-added fertilizer.

[0028] Example 2 A method for preparing an ecological value-added fertilizer from starch process by-product corn syrup resources, comprising the following steps: Step one: select corn syrup (solid content 18-22%) with freshness ≤24h in the corn starch production process, adjust the pH of the corn syrup to 6, pass through oxygen aeration oxidation for 2h, then filter through a 200 mesh screen, centrifuge at 5000r / min for 15min, add activated carbon with an addition amount of 0.1% of the mass of the supernatant to the supernatant, stir and adsorb at 45°C for 30min, filter, to obtain a clarified corn syrup stock solution; Step two: adjust the solid content of the clarified corn syrup stock solution to 10-15%, adjust the pH to 8 with sodium hydroxide, add alkaline protease, and hydrolyze at 50°C for 4h, then increase the temperature to 90°C and keep for 20min, to obtain a first enzyme hydrolysis solution; cool the first enzyme hydrolysis solution to 60°C, adjust the pH to 4 with food-grade citric acid, add saccharifying enzyme, and hydrolyze at 60°C for 1h, then increase the temperature to 95°C and keep for 15min, to obtain a second enzyme hydrolysis solution; the addition amount of alkaline protease is 3000 U / g of substrate protein, and the addition amount of saccharifying enzyme is 100 U / g of total substrate sugar; Step three: cool the second enzyme hydrolysis solution to room temperature, adjust the pH to 5, add medium and trace element salt, the medium and trace element salt includes calcium nitrate, magnesium sulfate, zinc sulfate and EDTA-iron with a mass ratio of 3:2:1:0.5, the total addition amount of medium and trace element salt is 10% of the dry weight of the second enzyme hydrolysis solution, then stir and mature at 25°C under nitrogen for 2h, to obtain a chelation solution; The addition steps of the medium and trace element salt are as follows: 1) ZnSO4·7H2O and MgSO4·7H2O are respectively prepared into 5% clarified stock solutions with deionized water, and are synchronously added into the second enzyme hydrolysis solution at a speed of 1mL / min, and the total addition time is ≥15min; 2) EDTA-FeNa is prepared into a 2% stock solution with warm water, and is added into the above system at a speed of 1mL / min, and the addition time is ≥10min; 3) Ca(NO3)2·4H2O is prepared into a 5% stock solution with deionized water, and is added into the above system at a speed of 1mL / min, and the addition time is ≥10min; Step four: filter the chelation solution through a 0.45μm ceramic membrane to obtain a microfiltrate; concentrate the microfiltrate using a nanofiltration membrane with a molecular weight cut-off of 5-10KDa, until the solid content is 35-40%, and then pass through an ultra-high-temperature instant sterilization equipment (UHT) at 135°C for 5s, then cool to 35°C for sterile filling, to obtain an ecological value-added fertilizer.

[0029] Example 3 A method for preparing an ecological value-added fertilizer from starch process by-product corn syrup resources, comprising the following steps: Step one: select corn syrup (solid content 18-22%) with a freshness of ≤24h in the corn starch production process, adjust the pH of the corn syrup to 6.5, pass through oxygen aeration oxidation for 3h, then filter through a 150 mesh screen, and centrifuge at 3000r / min for 18min, then add activated carbon with an addition amount of 0.5% of the mass of the supernatant to the supernatant, stir and adsorb at 48°C for 20min, filter, to obtain a clarified corn syrup stock solution; Step 2: Adjust the solids concentration of the clarified corn steep liquor to 10-15% with deionized water, adjust the pH to 8.5 with sodium hydroxide, add protease, and hydrolyze at 52℃ for 3 hours. Then, raise the temperature to 92℃ and hold for 18 minutes to obtain the first hydrolysate. Cool the first hydrolysate to 60℃, adjust the pH to 5 with food-grade citric acid, add saccharifying enzyme, and hydrolyze at 60℃ for 1.5 hours. Then, raise the temperature to 93℃ and hold for 17 minutes to obtain the second hydrolysate. The amount of alkaline protease added is 5000 U / g substrate protein, and the amount of saccharifying enzyme added is 200 U / g total substrate sugar. Step 3: Cool the secondary enzymatic hydrolysate to room temperature, adjust the pH to 4.5, and add trace element salts, which include calcium nitrate, magnesium sulfate, zinc sulfate and EDTA-iron in a mass ratio of 3:2:1:0.5. The total amount of trace element salts added is 9% of the dry weight of the secondary enzymatic hydrolysate. Then, stir and mature the solution at 25°C under nitrogen for 2.5 hours to obtain the chelate solution. The steps for adding trace element salts are as follows: 1) Prepare clear mother liquors of ZnSO4·7H2O and MgSO4·7H2O with deionized water to a mass fraction of 8%, and add them dropwise to the secondary enzymatic hydrolysis solution at a rate of 1.5 mL / min, with a total addition time of ≥15 min; 2) Prepare a 4% (w / w) stock solution of EDTA-FeNa with warm water, and add it dropwise to the above system at a rate of 0.7 mL / min for ≥10 min; 3) Prepare a 5% (w / w) stock solution of Ca(NO3)2·4H2O with deionized water, and add it dropwise to the above system at a rate of 1 mL / min for ≥10 min. Step 4: Filter the chelate through a 0.45μm ceramic membrane to obtain a microfiltrate; concentrate the microfiltrate using a nanofiltration membrane with a molecular weight cutoff of 5-10KDa until the solid content is 35-40%, then pass it through an ultra-high temperature instantaneous sterilization device (UHT) at 138℃ for 4 seconds, and then cool it to 32℃ for aseptic filling to obtain an eco-friendly value-added fertilizer.

[0030] Comparative Example 1 The difference between this comparative example and Example 1 is that only alkaline protease was used for enzymatic hydrolysis.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 is that the secondary enzymatic hydrolysate was cooled to room temperature and then the pH was adjusted to 7.5.

[0032] Comparative Example 3 The difference between the present comparative example and Example 1 is that in step three, after the secondary enzymatic hydrolysate is cooled to room temperature, the pH is adjusted to 5, and then a mixture of calcium nitrate, magnesium sulfate, zinc sulfate and EDTA-iron with a mass ratio of 3:2:1:0.5 is directly added to the secondary enzymatic hydrolysate.

[0033] Comparative Example 4 The difference between the present comparative example and Example 1 is that in step three, after the secondary enzymatic hydrolysate is cooled to room temperature, the pH is adjusted to 5, and then a mixture of calcium nitrate, magnesium sulfate, zinc sulfate and EDTA-iron with a mass ratio of 3:2:1:0.5 is directly added to the secondary enzymatic hydrolysate.

[0034] <Experimental design> Ten mu of vegetable base were randomly divided into 10 equal areas numbered 1-10, wherein 1-3 correspond to the use of fertilizers of Examples 1-3, 4-7 correspond to the use of fertilizers of Comparative Examples 1-4, 8 is not used any fertilizer, as a blank control group, 9 uses conventional chemical fertilizer, and 10 uses ordinary liquid fertilizer. The soil of the vegetable base is sandy loam, with pH 7.2, organic matter 18.5 g / kg, available Fe 4.2 mg / kg, and available Zn 0.9 mg / kg (mild zinc deficiency). The test crops are: tomato ('Jinpen 1'), and the fertilization period is 20 days, 35 days and 50 days after planting, with 3 times of drip irrigation and fertilizer, and the amount of the fertilizer of the present application is 5 L / mu / time.

[0035] Among them, the conventional chemical fertilizer is compound fertilizer NPK (Hubei Yuanfeng Chemical Co., Ltd.), and the ordinary liquid fertilizer is amino acid water-soluble fertilizer containing EDTA-Fe (Shanghai Zhongfeng Biological Technology Co., Ltd.).

[0036] Vitamin C: GB 5009.86-2016 (fluorescence method); soluble sugar: NY / T 2742-2015 (anthrone colorimetric method); total iron and total zinc: GB / T 15396-2023 (atomic absorption method); yield: NY / T 1388-2007.

[0037] Table 1 Test results

[0038] According to Table 1, compared with Comparative Examples (4-7), the crop yield of Examples (1-3) is higher, and the content of vitamin C, soluble sugar, total iron and total zinc of the crops is higher. It shows that the ecological value-added fertilizer provided by the present application can improve the crop yield and improve the quality of the crops.

[0039] The above merely describes the preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an ecological value-added fertilizer from corn syrup resources in a starch process, characterized in that, The method comprises the following steps: Step one: oxygen is introduced into the corn syrup to perform aeration oxidation, and then the corn syrup is screened, purified, and decolorized to obtain a clarified corn syrup stock solution; Step two: the pH of the clarified corn syrup stock solution is adjusted to 8-9, a protease is added to perform enzymolysis to obtain a first enzymolysis solution; the pH of the first enzymolysis solution is adjusted to 4-5, a saccharifying enzyme is added to perform enzymolysis to obtain a second enzymolysis solution; Step three: the second enzymolysis solution is cooled to room temperature, the pH is adjusted to 4-5, and a trace element salt is added, and then the solution is stirred and matured to obtain a chelation solution; Step four: the chelation solution is purified and concentrated to obtain an ecological value-added fertilizer.

2. The method for preparing ecological value-added fertilizer from corn syrup resources in starch process according to claim 1, characterized in that, In step one, the aeration oxidation is performed for 2-4 hours, the solution is filtered through a 100-200 mesh screen, and then centrifuged at 3000-5000 r / min for 15-20 minutes; activated carbon is added to the supernatant at an amount of 0.1-0.5% of the mass of the supernatant, and then stirred and adsorbed at 45-50°C for 15-30 minutes; and then filtered to obtain the clarified corn syrup stock solution.

3. The method for preparing ecological value-added fertilizer from corn syrup resources in a starch process according to claim 1, characterized in that, The specific process of step two is as follows: a. The solid content concentration of the clarified corn syrup stock solution is adjusted to 10-15% with deionized water, the pH is adjusted to 8-9 with sodium hydroxide, a protease is added, and then enzymolysis is performed at 50-55°C for 2-4 hours to obtain the first enzymolysis solution; b. The first enzymolysis solution is cooled to 60°C, the pH is adjusted to 4-5 with a food-grade citric acid, a saccharifying enzyme is added, and then enzymolysis is performed at 60°C for 1-2 hours to obtain the second enzymolysis solution.

4. The method for preparing ecological value-added fertilizer from corn syrup resources in starch process according to claim 3, characterized in that, The protease is an alkaline protease, the addition amount of the protease is 3000-5000 U / g of substrate protein, and the addition amount of the saccharifying enzyme is 100-200 U / g of substrate total sugar.

5. The method for preparing ecological value-added fertilizer from starch process by-product corn syrup resources according to claim 3, characterized in that, After the enzymolysis, the first enzymolysis solution and the second enzymolysis solution are further heated to 90-95°C and kept for 15-20 minutes.

6. The method for preparing ecological value-added fertilizer from corn syrup resources in starch process according to claim 1, characterized in that, The trace element salt comprises calcium nitrate, magnesium sulfate, zinc sulfate, and EDTA-iron in a mass ratio of 3:2:1:0.5, and the total addition amount of the trace element salt is 8-10% of the dry weight of the second enzymolysis solution.

7. The method for preparing ecological value-added fertilizer from starch process by-product corn syrup resources according to claim 6, characterized in that, In step three, the addition steps of the trace element salt are as follows: 1) ZnSO4·7H2O and MgSO4·7H2O are respectively dissolved in deionized water to prepare a 5-10% mass fraction clarified mother liquor, which is synchronously added to the second enzymolysis solution at a speed of 1-2 mL / min, and the total addition time is ≥15 min; 2) EDTA-FeNa is dissolved in warm water to prepare a 2-5% mass fraction mother liquor, which is added to the second enzymolysis solution at a speed of 0.5-1 mL / min, and the addition time is ≥10 min; 3) Ca(NO3)2·4H2O is dissolved in deionized water to prepare a 5% mass fraction mother liquor, which is added to the second enzymolysis solution at a speed of 1 mL / min, and the addition time is ≥10 min.

8. The method for preparing ecological value-added fertilizer from corn syrup resources in starch process according to claim 1, characterized in that, In step three, the solution is stirred and matured at 25°C under a nitrogen atmosphere for 2-3 hours.

9. The method for preparing ecological value-added fertilizer from corn syrup resources in a starch process according to claim 1, characterized in that, In step four, the chelation solution is filtered through a 0.45 μm ceramic membrane to obtain a microfiltrate; the microfiltrate is concentrated by a nanofiltration membrane with a molecular weight cut-off of 5-10 KDa until the solid content concentration is 35-40%.

10. The method for preparing ecological value-added fertilizer from corn syrup resources in starch process according to claim 1, characterized in that, After the purification and concentration of the chelation solution, the solution is further treated at 135-140°C for 3-5 seconds, and then cooled to 30-35°C for sterile filling.

Images