Method for preparing apple residue composite organic fertilizer by steam explosion assisted fermentation and application thereof

Abstract

This invention discloses a method for preparing apple pomace compound organic fertilizer using steam explosion-assisted fermentation and its application, belonging to the technical field of resource utilization of agricultural product processing by-products and organic fertilizer preparation. The method involves steam explosion of fresh, wet apple pomace, followed by compounding with dried and pulverized soybean residue according to the actual mass ratio, addition of urea, sterilization and cooling, and inoculation with a compound microbial agent. Aerobic solid-state fermentation is then carried out under natural pH conditions to obtain apple pomace compound organic fertilizer. Scanning electron microscopy observation shows that steam explosion can create cracks and pores on the surface of the apple pomace tissue, improving substrate accessibility. This invention can be used as organic fertilizer for fruit trees, orchard soil conditioner, or agricultural waste resource return material.

Description

Technical Field

[0001] This invention belongs to the technical fields of resource utilization of agricultural product processing by-products, preparation of organic fertilizers and orchard soil improvement, specifically involving a method for preparing apple pomace compound organic fertilizer by steam explosion-assisted fermentation and its application. Background Technology

[0002] Apple pomace is a major byproduct of apple juice, wine, and canning processes. It typically consists of peels, pulp residue, cores, stems, and a small amount of residual juice. Apple pomace is rich in cellulose, hemicellulose, pectin, protein, minerals, polyphenols, organic acids, and vitamins, making it valuable for resource utilization. However, fresh apple pomace has a high water content, making it prone to spoilage, rancidity, and leachate production, posing challenges in storage, transportation, and environmental management.

[0003] Existing methods for utilizing apple pomace include direct composting, feed production, bioenergy conversion, and functional component extraction. While direct composting or extensive piling is simple, apple pomace has a relatively low nitrogen content. When fermented alone, it is prone to problems such as unbalanced nutrient structure, slow decomposition process, insufficient product stability, and inadequate crop compatibility, making it difficult to form high-quality, standardized orchard return materials.

[0004] Soybean residue is a byproduct of soybean processing, containing high levels of protein, peptides, and nitrogenous nutrients. Combining apple pomace with soybean residue can supplement nitrogen sources, improve carbon-nitrogen structure, and enhance microbial metabolic activity. Further application with a compound microbial agent containing Bacillus, yeast, photosynthetic bacteria, acetic acid bacteria, lactic acid bacteria, actinomycetes, Trichoderma, and related enzymes can promote the degradation and transformation of proteins, cellulose, pectin, and other organic matter, improving the nutritional value and suitability for field application of the fermentation products.

[0005] However, the cell walls of apple pomace are formed by an interwoven structure of cellulose, hemicellulose, and pectin. Conventional grinding or ordinary fermentation is insufficient to fully disrupt this structure, resulting in inadequate release of intracellular nutrients and bound polyphenols, thus limiting fermentation efficiency and nutrient conversion efficiency. Steam explosion is a pretreatment technology that utilizes high-temperature, high-pressure steam to permeate materials and achieves physical cell wall disruption and tissue deconstruction through instantaneous pressure release. This technology can improve substrate porosity and accessibility, promoting the utilization of the substrate by subsequent microorganisms and their enzyme systems. However, the steam explosion intensity needs to be properly controlled: too low an intensity will result in insufficient cell wall disruption, while too high an intensity may lead to the loss of polyphenols, peptides, and other heat-sensitive active substances, and may even cause browning of the material, increased energy consumption, or a decline in fermentation quality.

[0006] Therefore, it is necessary to establish a collaborative process for the resource-based return of apple pomace to the field. By comprehensively regulating the steam explosion intensity, the ratio of apple pomace to soybean residue, nitrogen-containing regulators, compound microbial agents, and solid-state fermentation conditions, this process can improve the cell wall breaking effect and fermentation efficiency of apple pomace while obtaining a compound organic fertilizer with a more reasonable nutrient structure, better retention of functional components, and suitability for orchard return to the field. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing apple pomace compound organic fertilizer by steam explosion-assisted fermentation.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing apple pomace compound organic fertilizer by steam explosion-assisted fermentation, characterized in that it includes: Fresh, wet apple pomace was used as the raw material for steam explosion. The apple pomace to be exploded is subjected to steam explosion treatment. After reaching the set pressure, the pressure is maintained and then quickly released to obtain wet steam-exploded apple pomace. The pressure of the steam explosion treatment is 0.6 to 1.4 MPa, and the pressure maintenance time is 3 to 6 min. Wet steam-exploded apple pomace and dried and pulverized soybean residue were mixed at an actual weighing ratio of 2:1 to 5.5:1, and urea was added to obtain a compound fermentation substrate. The composite fermentation substrate was sterilized, cooled, and then inoculated with microbial agents. It was then subjected to aerobic solid-state fermentation under natural pH conditions to produce apple pomace composite organic fertilizer.

[0011] As a preferred embodiment of the method described in this invention, the apple pomace is apple peel residue, pulp residue, core residue, stem residue, or a mixture thereof produced during apple juice, cider, canned apples, or deep processing of apples; the crude fiber content of the apple pomace is not less than 23%, the protein content is not less than 7.5%, and the total organic acid content is not higher than 3.5 mg / g.

[0012] In a preferred embodiment of the method described in this invention, the pressure of the steam explosion treatment is 0.8 to 1.2 MPa.

[0013] As a preferred embodiment of the method described in this invention, the soybean residue is dried to constant weight at 60°C before compounding, pulverized, and passed through an 80-mesh standard sieve; the compounding ratio is calculated based on the actual weighing mass of wet steam-exploded apple pomace and dry soybean residue, with a mass ratio of 4.5:1 to 5.5:1; the crude protein content of the soybean residue is not less than 23%, the crude fiber content is not more than 28%, and the moisture content is not more than 85%.

[0014] In a preferred embodiment of the method described in this invention, the amount of urea added is 1.5% (w / w) based on the mass of fresh apple pomace before steam explosion treatment.

[0015] In a preferred embodiment of the method described in this invention, the sterilization temperature of the composite fermentation substrate is 110–130°C, and the sterilization time is 20–40 min.

[0016] In a preferred embodiment of the method described in this invention, the amount of the microbial agent added is 0.1% (w / w) based on the total mass of the compound fermentation substrate; based on the total mass of the agent, the microbial agent comprises 32.0% Bacillus subtilis, 16.0% Bacillus licheniformis, 13.0% Bacillus amyloliquefaciens, 4.5% Streptomyces jingyangensis, 3.0% Saccharomyces cerevisiae, 2.0% Trichoderma viride, 2.0% Rhodopseudomonas palustris, 2.0% Acetobacter pastoris, and 2.0% Lactobacillus plantarum. The microbial agent also includes 3.0% of Bacillus subtilis-derived neutral protease, 2.0% of Trichoderma reesei-derived cellulase, and 1.5% of Aspergillus niger-derived pectinase, with the remaining 17.0% being corn flour and humic acid carrier adjuvants.

[0017] In a preferred embodiment of the method described in this invention, the temperature of the aerobic solid-state fermentation is 25–35°C, and the fermentation time is 7–12 days.

[0018] Another objective of this invention is to overcome the shortcomings of the prior art and provide an apple pomace compound organic fertilizer, characterized in that: the apple pomace compound organic fertilizer contains cellulose, hemicellulose, pectin, polyphenols and organic acid components derived from apple pomace, as well as peptides, nitrogen nutrients and microbial metabolites derived from soybean residue and microbial fermentation and transformation. On a dry basis, the total nitrogen content of the apple pomace compound organic fertilizer is 2.0–5.5 g / 100 g, the total phosphorus content is 0.15–0.35 g / 100 g, and the total potassium content is 1.3–3.0 g / 100 g. On a dry basis, the total nutrient content of the apple pomace compound organic fertilizer is 3.8–7.1 g / 100 g, and the polyphenol content is 0.9–8.0 mg / g.

[0019] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of apple pomace compound organic fertilizer in the preparation of fruit tree organic fertilizer, orchard soil conditioner or agricultural waste resource return material.

[0020] Beneficial effects of this invention: (1) The present invention uses steam explosion and solid-state fermentation in a coupled manner, which can destroy the tissue structure of apple pomace and improve the porosity and bioaccessibility of the substrate. Scanning electron microscopy morphology shows that after the preferred steam explosion treatment, obvious cracks and pores are formed on the surface of the material, and the tissue structure tends to be loose, which increases the contact interface between the subsequent microorganisms and their enzyme system and the substrate, thereby facilitating the release of functional components and fermentation transformation.

[0021] (2) The present invention uses apple pomace and soybean residue in combination and supplements nitrogen source with 1.5% urea, which is beneficial to improve the nutritional structure of fermentation substrate and alleviate the problems of insufficient nitrogen in single apple pomace and unreasonable nutrient ratio of fermentation products.

[0022] (3) The present invention uses compound microbial agents and related enzymes to promote the degradation and transformation of components such as protein, cellulose and pectin, so as to release small molecule peptides, organic acids and functional components in fermentation products more fully.

[0023] (4) By controlling the steam explosion pressure and the pressure maintenance time, this invention avoids insufficient cell wall breaking caused by low-intensity treatment and reduces the risk of loss of heat-sensitive components caused by high-intensity treatment, so that the fermentation product has both nutrient supply and functional component retention effects.

[0024] (5) The process flow of the present invention is clear, the raw material sources are wide, and it is suitable for the synergistic resource utilization of apple processing by-products and soybean product by-products. It can reduce the pressure of waste treatment and form organic fertilizer products suitable for orchard return to the field and soil improvement. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 A scanning electron microscope image of fresh, wet apple pomace before steam explosion; Figure 2 This is a scanning electron microscope image of apple pomace after steam explosion under pressure of 0.8 MPa for 3 min. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0029] The apple pomace used in this embodiment of the invention is industrial apple peel pomace provided by Yantai Xingnong Fruit Juice Food Co., Ltd., and the soybean residue used is sourced from the Wuxi Xinwu District Food Processing Zone. To further clarify the basic composition of the raw materials used in this embodiment, three parallel measurements were performed on fresh apple pomace and fresh soybean residue respectively. The results of the raw material composition are shown in Table 1. Except for moisture, all percentage contents in the table are on a dry basis. Before compounding, the soybean residue was dried to constant weight at 60℃, pulverized, and passed through an 80-mesh standard sieve. The compounding mass ratios mentioned in this article are calculated based on the actual weighed mass of fresh wet apple pomace or wet steam-exploded apple pomace and dry soybean residue.

[0030] Table 1. Basic Composition of Apple Pomace and Soybean Pomace Raw Materials

[0031] The microbial agent used in this invention is an organic fertilizer compound fermentation agent provided by Shandong Junde. Based on the total mass of the agent, Bacillus subtilis (… Bacillus subtilis ) accounted for 32.0%, Bacillus licheniformis ( Bacillus licheniformis ) accounted for 16.0%, Bacillus amyloliquefaciens ( Bacillus amyloliquefaciens ) accounted for 13.0%, constituting the core microbial community; the auxiliary microbial community included *Streptomyces jingyangensis* ( Streptomyces jingyangensis 4.5%, brewer's yeast ( Saccharomyces cerevisiae 3.0%, Trichoderma viride ( Trichoderma viride ) 2.0%, Rhodopseudomonas palustris ( Rhodopseudomonas palustris 2.0%, Pasteurella multocida ( Acetobacter pasteurianus 2.0% and Lactobacillus plantarum ( Lactobacillus plantarum2.0%; the compound enzyme preparation includes 3.0% neutral protease from Bacillus subtilis, 2.0% cellulase from Trichoderma reesei, and 1.5% pectinase from Aspergillus niger; the remaining 17.0% is corn flour and humic acid carrier adjuvant. The effective viable count of the agent is greater than 20 billion / g; the neutral protease activity is not less than 500 U / g, the cellulase activity is not less than 300 U / g, and the pectinase activity is not less than 400 U / g.

[0032] The materials obtained in the embodiments of the present invention were subjected to performance testing according to the following method: (1) Moisture content determination: Take the fermentation sample and dry it in an oven at 105℃ until constant weight. Calculate the moisture content according to the mass difference before and after drying.

[0033] (2) Determination of soluble peptide content: Weigh an appropriate amount of sample, add water and mix well, centrifuge and take the supernatant, and use the BCA kit to determine the content of soluble peptides or soluble protein hydrolysates.

[0034] (3) Determination of total polyphenol content: Weigh the sample, extract it with ethanol aqueous solution, take the supernatant, and determine it by the Folin-Ciocalteu method, or refer to GB / T 44349-2024 for determination, and convert it with gallic acid standard curve.

[0035] (4) Determination of organic acid content: After extraction, centrifugation and filtration, the sample is determined by high performance liquid chromatography. The test objects include tartaric acid, malic acid, lactic acid, citric acid, fumaric acid and succinic acid; or GB 5009.157-2016 can be used for determination.

[0036] (5) Determination of total nitrogen, total phosphorus, total potassium and total nutrients: After the sample is digested, total nitrogen can be determined by the Kjeldahl method, total potassium can be determined by atomic absorption spectrophotometry, and total phosphorus can be determined by the ammonium vanadate colorimetric method; total nitrogen, total phosphorus, total potassium and total nutrients can also be determined with reference to NY / T 2017-2011.

[0037] (6) Scanning electron microscopy observation: Fresh wet apple pomace before steam explosion and apple pomace after steam explosion under pressure of 0.8 MPa for 3 min were taken respectively. Both groups of samples were freeze-dried or low-temperature dried in the same way, then fixed on the sample stage and sputtered with gold. Their surface morphology was observed at the same or comparable magnification.

[0038] Example 1: Screening of the mass ratio of fresh apple pomace to dried soybean residue Fresh, moist apple pomace was collected; soybean residue was dried at 60℃ to constant weight using a forced-air drying process, then pulverized using a high-speed grinder and passed through an 80-mesh standard sieve. Composite substrates were prepared for each group according to actual weight ratios of fresh, moist apple pomace to dried soybean residue of 2:1, 4.5:1, 5:1, and 5.5:1. A urea aqueous solution was added to each group, with the urea addition amount being 1.5% (w / w) based on the mass of the fresh apple pomace.

[0039] The resulting composite substrate was sterilized at 121℃ for 30 min and then cooled. Subsequently, it was inoculated with the above-mentioned organic fertilizer composite fermentation agent, the amount of which was 0.1% (w / w) based on the total mass of the composite substrate.

[0040] Each group of samples underwent aerobic solid-state fermentation at 30℃ and natural pH for 10 days.

[0041] Representative samples were taken during or after fermentation for testing. Except for moisture content determination, the test samples were dried to constant weight at 60℃, pulverized, and passed through an 80-mesh standard sieve. The contents of soluble peptides, total polyphenols, organic acids, total nitrogen, total phosphorus, and total potassium were then determined. The test results are shown in Table 2.

[0042] Table 2. Fermentation screening data of different ratios of apple pomace and soybean residue.

[0043] As shown in Table 2, the mass ratio of fresh apple pomace to dried soybean residue has a significant impact on the nutrient composition, functional component release, and fermentation conversion state of the fermentation products.

[0044] The 2:1 group has a higher proportion of soybean residue, resulting in higher soluble peptide and total nitrogen content and a higher level of total nutrients. However, its nitrogen level is significantly higher, with an excessively large proportion of nitrogen in the N:P:K ratio. This poses a risk of nitrogen redundancy when used as a material for returning fertilizer to orchards.

[0045] The 5.5:1 ratio of apple pomace is relatively high, which is beneficial for increasing the utilization of apple pomace, but the soybean residue provides insufficient nitrogen, resulting in low levels of soluble peptides, total polyphenols, total organic acids, and total nutrients. This indicates that the microbial metabolic activity and substrate transformation are insufficient at this ratio.

[0046] In contrast, the 5:1 group showed a better overall balance in terms of total nutrients, soluble peptides, total polyphenols, and organic acids. The total nutrient content at the end of fermentation in this group was 6.32%, with total nitrogen, total phosphorus, and total potassium at 4.20 g / 100 g, 0.32 g / 100 g, and 1.80 g / 100 g, respectively. Meanwhile, on day 7, the soluble peptide content was 6.72%, the total polyphenol content was 5.03 mg / g, and the proportion of lactic acid in the total organic acids reached 85.34%, indicating that fermentation was relatively complete, functional components were well released, and fermentation conversion was relatively complete under this compound ratio.

[0047] Therefore, a ratio of 5:1 of actual weighed fresh wet apple pomace to dry soybean residue was selected as the compounding ratio for subsequent steam explosion parameter screening and process optimization.

[0048] Example 2: Screening of Steam Explosion Parameters Based on the optimal compound ratio obtained in Example 1, fresh wet apple pomace was subjected to steam explosion. The steam explosion pressure was set to 0.6 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa and 1.4 MPa. After reaching the set pressure, the pressure was maintained for 3 min and 6 min respectively, and then the pressure was rapidly released to atmospheric pressure. A total of 10 groups of wet steam-exploded apple pomace samples were obtained.

[0049] Soybean residue was dried to constant weight at 60℃, pulverized, and passed through an 80-mesh standard sieve. Each group of wet steam-exploded apple pomace and dry soybean residue were mixed at an actual weight ratio of 5:1, and a urea aqueous solution of 1.5% (w / w) based on the weight of fresh apple pomace before steam explosion treatment was added. The mixture was sterilized at 121℃ for 30 min, cooled, and then inoculated with the above-mentioned organic fertilizer compound fermentation agent at 0.1% (w / w) of the total mass of the composite substrate. Aerobic solid-state fermentation was carried out at 30℃ and natural pH for 10 days.

[0050] After 10 days of fermentation, apple pomace compound organic fertilizer was obtained. Representative samples were then tested using the methods described above to determine the moisture, soluble peptides, total polyphenols, organic acids, and nitrogen, phosphorus, and potassium content. Samples requiring a dry basis were dried to constant weight at 60℃, pulverized, and passed through an 80-mesh standard sieve.

[0051] The optimal steam explosion conditions are not based solely on maximizing a single indicator, but rather on a comprehensive consideration of factors such as cell wall disruption and release, retention of heat-sensitive components, treatment intensity, energy consumption, and suitability for orchard return to the field.

[0052] The effects of steam explosion conditions on the moisture, functional components, and nitrogen, phosphorus, and potassium content of fermentation products are shown in Table 3.

[0053] Table 3. Moisture, functional components, and nutrient data of fermentation products under different steam explosion conditions.

[0054] Note: Total nutrients are the sum of total nitrogen, total phosphorus, and total potassium.

[0055] As shown in Table 3, after the steam explosion intensity increases, the release of some nutrients and functional components in the fermentation products tends to increase, but different indicators do not change synchronously.

[0056] Under low pressure conditions, the release of peptides, polyphenols and mineral nutrients is relatively limited, indicating that the cell wall deconstruction of apple pomace is insufficient. Higher pressure or longer maintenance time can improve some indicators, but at the same time, it will increase the processing intensity and energy consumption, and may cause fluctuations in fermentation quality.

[0057] Therefore, this invention does not use the highest single indicator as the sole screening criterion, but makes a comprehensive judgment based on cell wall breaking and release, component retention, mild processing and applicability to subsequent production.

[0058] The effects of steam explosion conditions on the organic acid composition of fermentation products are shown in Table 4.

[0059] Table 4. Organic acid composition data of fermentation products under different steam explosion conditions

[0060] As shown in Table 4, the composition of organic acids in the fermentation products differs under different steam explosion conditions, indicating that the pretreatment intensity affects the release of apple pomace structure and the direction of subsequent microbial metabolism.

[0061] Moderate steam explosion is beneficial for forming a more stable composition of fermentable organic acids; insufficient release occurs when the treatment intensity is too low, while large fluctuations may occur in the organic acid spectrum when the treatment intensity is too high.

[0062] Based on the data on moisture, peptides, polyphenols, and nitrogen, phosphorus, and potassium in Table 3, although 0.8 MPa and 3 min are not the highest values ​​for all individual indicators, they are relatively balanced in terms of process mildness, retention of functional components, and scalability. Therefore, they are determined to be the preferred steam explosion conditions.

[0063] Scanning electron microscopy morphology of apple pomace before and after steam explosion as follows: Figure 1 and Figure 2 As shown.

[0064] Depend on Figure 1 and Figure 2 It is evident that fresh, wet apple pomace, before steam explosion and prepared using the same SEM, maintained a relatively continuous and dense microstructure with a relatively smooth surface. After steam explosion at 0.8 MPa for 3 minutes, the surface roughness of the samples significantly increased, with visible cracks, pores, and lamellar peeling, and some tissues becoming loose and locally collapsing. These morphological differences indicate that high-pressure steam infiltration and instantaneous depressurization can effectively deconstruct the microstructure of apple pomace, increasing the contact interface between subsequent microorganisms and enzymes and the substrate.

[0065] The aforementioned changes in microstructure are consistent with the changes in functional components, mineral nutrients, and organic acid composition in Tables 3 and 4, indicating that steam explosion can reduce the density of apple pomace tissue, increase the reaction interface, and improve substrate accessibility through high-pressure steam permeation and rapid depressurization, creating conditions for subsequent action of compound microbial agents and enzyme systems. 0.8 MPa for 3 min can achieve relatively significant structural deconstruction while avoiding overtreatment that may be caused by excessively high pressure and prolonged pressure; therefore, it can be considered the preferred steam explosion condition.

[0066] Example 3: Optimized process for preparing apple pomace compound organic fertilizer Fresh, wet apple pomace was loaded into a steam explosion device, and after maintaining pressure at 0.8 MPa for 3 minutes, the pressure was rapidly released to atmospheric pressure, and the wet steam-exploded apple pomace was collected.

[0067] To characterize the effect of steam explosion on the structure of apple pomace, wet apple pomace before steam explosion and apple pomace after steam explosion at 0.8 MPa and 3 min were collected from the same batch of fresh apple pomace for observation using scanning electron microscopy.

[0068] The soybean residue was dried at 60℃ to constant weight, pulverized, and passed through an 80-mesh standard sieve. The wet steam-exploded apple residue and the dry soybean residue were mixed at an actual weight ratio of 5:1, and a urea aqueous solution was added. The amount of urea added was 1.5% (w / w) based on the weight of the fresh apple residue before steam explosion treatment.

[0069] The obtained composite substrate was sterilized at 121℃ for 30 min, cooled, and then inoculated with the above-mentioned organic fertilizer composite fermentation agent. The amount of the organic fertilizer composite fermentation agent added was 0.1% (w / w) based on the total mass of the composite substrate.

[0070] The above composite substrate was subjected to aerobic solid-state fermentation at 30°C and natural pH for 10 days.

[0071] After 10 days of fermentation, apple pomace compound organic fertilizer was obtained. A representative fermentation product was dried at 60℃ to constant weight, pulverized using a high-speed pulverizer, and passed through an 80-mesh standard sieve for various index determinations.

[0072] The resulting apple pomace compound organic fertilizer contains nitrogen, phosphorus, potassium nutrients, soluble peptides, polyphenols, organic acids, and fiber structural components derived from apple pomace. It can be used as organic fertilizer for fruit trees, soil conditioner for orchards, or material for returning agricultural waste to the field.

[0073] The total nitrogen, total phosphorus and total potassium contents of the fermentation products obtained under the conditions of 0.8 MPa and 3 min steam explosion were determined to be 2.29 g / 100 g, 0.22 g / 100 g and 1.58 g / 100 g (dry basis), respectively, the total nutrient content was 4.09 g / 100 g (dry basis) and the polyphenol content was 3.52 mg / g. The relevant results are shown in Table 3.

[0074] Comparative Example 1 The only difference between this comparative example and Example 3 is that the steam explosion step is omitted for the fresh wet apple pomace, and it is compounded with dried soybean residue that has been dried to constant weight at 60°C, crushed and passed through an 80-mesh standard sieve at an actual weighing ratio of 5:1 and then carried out solid-state fermentation; all other parameters and conditions are the same as in Example 3.

[0075] In Comparative Example 1, after omitting the steam explosion step, the fresh wet apple pomace mainly relied on subsequent microorganisms and their enzyme systems for structural degradation, and the release efficiency of functional components and nutrients was relatively low, indicating that steam explosion pretreatment helps to improve the bioavailability of the substrate.

[0076] Comparative Example 2 The only difference between this comparative example and Example 3 is that the steam explosion conditions were adjusted to 0.6 MPa and 3 min; all other parameters and conditions are the same as in Example 3.

[0077] Comparative Example 2 adjusted the steam explosion conditions to 0.6 MPa and 3 min. The treatment intensity was too low, and the release levels of peptides, polyphenols, and nitrogen, phosphorus, and potassium were lower than those of most medium- and high-intensity treatment groups. This indicates that an excessively low explosion intensity is insufficient to fully exert the cell wall breaking effect.

[0078] Comparative Example 3 The only difference between this comparative example and Example 3 is that the steam explosion conditions were adjusted to 1.4 MPa and 6 min; all other parameters and conditions are the same as in Example 3.

[0079] Comparative Example 3 adjusted the steam explosion conditions to 1.4 MPa and 6 min. Although the release level of some mineral nutrients was relatively high, the treatment intensity and energy consumption increased significantly. Moreover, the excessive treatment may cause the loss of heat-sensitive components or fluctuations in fermentation quality, so it is not suitable as a comprehensive optimal condition.

[0080] Comparative Example 4 The only difference between this comparative example and Example 3 is that the ratio of apple pomace to soybean pomace is adjusted to 2:1 or 5.5:1; all other parameters and conditions are the same as in Example 3.

[0081] Comparative Example 4 adjusted the mass ratio of fresh apple pomace to dried soybean residue to 2:1 or 5.5:1. The 2:1 group was more of a high-nitrogen formula, while the 5.5:1 group had the problem of insufficient nitrogen supply from the soybean residue. Neither of them was as balanced as the 5:1 group in terms of sufficient nutrients, not excessive amounts, and suitability for returning to the field.

[0082] In summary, the technical advantages of this invention stem from the combination of "moderate steam explosion + reasonable blending of fresh apple pomace and dried soybean residue + 1.5% urea + compound microbial agent solid-state fermentation". This combination can simultaneously address the issues of apple pomace substrate cell wall disruption and release, nitrogen source replenishment, fermentation conversion, and orchard return to the field.

[0083] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing apple pomace compound organic fertilizer by steam explosion-assisted fermentation, characterized in that: include, Fresh, wet apple pomace was used as the raw material for steam explosion. The apple pomace to be exploded is subjected to steam explosion treatment. After reaching the set pressure, the pressure is maintained and then quickly released to obtain wet steam-exploded apple pomace. The pressure of the steam explosion treatment is 0.6 to 1.4 MPa, and the pressure maintenance time is 3 to 6 min. Wet steam-exploded apple pomace and dried and pulverized soybean residue were mixed at an actual weighing ratio of 2:1 to 5.5:1, and urea was added to obtain a compound fermentation substrate. The composite fermentation substrate was sterilized, cooled, and then inoculated with microbial agents. It was then subjected to aerobic solid-state fermentation under natural pH conditions to produce apple pomace composite organic fertilizer.

2. The method as described in claim 1, characterized in that: The apple pomace is apple peel residue, pulp residue, core residue, stem residue, or a mixture thereof produced during apple juice, cider, canned apples, or deep processing of apples; the crude fiber content of the apple pomace is not less than 23%, the protein content is not less than 7.5%, and the total organic acid content is not more than 3.5 mg / g.

3. The method as described in claim 1, characterized in that: The pressure of the steam explosion treatment is 0.8 to 1.2 MPa.

4. The method as described in claim 1, characterized in that: The soybean residue is dried to constant weight at 60°C before compounding, then crushed and passed through an 80-mesh standard sieve. The compounding ratio is calculated based on the actual weighing mass of wet steam-exploded apple pomace and dry soybean residue, with a mass ratio of 4.5:1 to 5.5:

1. The crude protein content of the soybean residue is not less than 23%, the crude fiber content is not more than 28%, and the moisture content is not more than 85%.

5. The method as described in claim 1, characterized in that: The amount of urea added is 1.5% (w / w) based on the mass of fresh apple pomace before steam explosion treatment.

6. The method as described in claim 1, characterized in that: The sterilization temperature of the composite fermentation substrate is 110–130℃, and the sterilization time is 20–40 min.

7. The method as described in claim 1, characterized in that: The amount of the microbial agent added is 0.1% (w / w) based on the total mass of the compound fermentation substrate; based on the total mass of the agent, the microbial agent includes 32.0% Bacillus subtilis, 16.0% Bacillus licheniformis, 13.0% Bacillus amyloliquefaciens, 4.5% Streptomyces jingyangensis, 3.0% Saccharomyces cerevisiae, 2.0% Trichoderma viride, 2.0% Rhodopseudomonas palustris, 2.0% Acetobacter pastoris, and 2.0% Lactobacillus plantarum. The microbial agent also includes 3.0% of Bacillus subtilis-derived neutral protease, 2.0% of Trichoderma reesei-derived cellulase, and 1.5% of Aspergillus niger-derived pectinase, with the remaining 17.0% being corn flour and humic acid carrier adjuvants.

8. The method as described in claim 1, characterized in that: The aerobic solid-state fermentation was carried out at a temperature of 25–35°C for 7–12 days.

9. An apple pomace compound organic fertilizer prepared by the method according to any one of claims 1 to 8, characterized in that: The apple pomace compound organic fertilizer contains cellulose, hemicellulose, pectin, polyphenols and organic acid components derived from apple pomace, as well as peptides, nitrogen nutrients and microbial metabolites derived from soybean residue and microbial fermentation. On a dry basis, the total nitrogen content of the apple pomace compound organic fertilizer is 2.0–5.5 g / 100 g, the total phosphorus content is 0.15–0.35 g / 100 g, and the total potassium content is 1.3–3.0 g / 100 g. On a dry basis, the total nutrient content of the apple pomace compound organic fertilizer is 3.8–7.1 g / 100 g, and the polyphenol content is 0.9–8.0 mg / g.

10. The application of the apple pomace compound organic fertilizer as described in claim 9 in the preparation of fruit tree organic fertilizer, orchard soil conditioner, or agricultural waste resource return material.

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