Selenium-enriched rhizoma smilacis glabrae and preparation method thereof

Abstract

The application discloses a kind of selenium-enriched rhizoma pholiopodii succis kind rod and its manufacturing method, belong to edible mushroom cultivation technical field.The method includes preparation low selenium induction culture material, nutrient transition culture material and selenium slow-release culture material;By coaxial layered filling, low selenium induction layer, nutrient transition layer and selenium slow-release layer are sequentially arranged from inside to outside;Form axial inoculation channel and access rhizoma pholiopodii spawn;Utilize composite slow-release selenium particle to control selenium element release, make mycelium growth process and selenium supply process match.Composite slow-release selenium particle includes porous biochar loaded inorganic selenium source, calcium alginate gel layer, chitosan layer and selenium yeast.The application reduces the adverse effect of early high-selenium environment on mycelium growth by culture material gradient structure and composite slow-release selenium supply structure, improves the absorption and conversion efficiency of selenium element of rhizoma pholiopodii, and obtains selenium-enriched rhizoma pholiopodii product with stable selenium content and high proportion of organic selenium.The method has the advantages of controllable cultivation process, stable selenium-enriched effect and suitability for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of edible fungus cultivation technology, and in particular to a selenium-enriched bamboo fungus substrate and its preparation method. Background Technology

[0002] Bamboo fungus (Dictyophora indusiata) is a rare edible fungus with high nutritional and culinary value. Its fruiting body contains various nutrients such as polysaccharides, proteins, amino acids, and minerals. With increasing consumer demand for functional foods, functional edible fungi products rich in trace elements are gaining attention. Selenium, as one of the essential trace elements for the human body, participates in the body's antioxidant defense, immune regulation, and various physiological metabolic processes; appropriate intake has certain nutritional value. Therefore, increasing the selenium content in bamboo fungus fruiting bodies through artificial cultivation and promoting the conversion of inorganic selenium to organic selenium has become an important research direction for the functional cultivation of bamboo fungus.

[0003] Currently, the artificial cultivation of bamboo fungus typically employs a substrate cultivation method. This involves using sawdust, bamboo powder, wheat bran, corn flour, soybean meal, and other materials as the main culture medium. After mixing, humidifying, bagging, and sterilizing, bamboo fungus spawn is inoculated, and the cultivation of the substrate is completed through the expansion of mycelium within the medium. Existing bamboo fungus substrate cultivation methods primarily focus on indicators such as mycelial germination and growth rate, cultivation cycle, contamination control, and fruiting body yield. Further improvements are still needed to achieve efficient and stable selenium-enriched cultivation while ensuring normal mycelial growth.

[0004] For example, Chinese patent CN115336502A discloses a cultivation substrate formula and preparation method for *Dictyophora indicum*. This technical solution uses sawdust, bamboo powder, wheat bran, and corn flour as the culture medium for *Dictyophora indicum*, and achieves the preparation of *Dictyophora indicum* substrate through steps such as mixing, bagging, sterilization, inoculation, and cultivation. This technology can meet the basic requirements for *Dictyophora indicum* mycelial cultivation and fruiting body formation. However, its culture medium is usually mixed as a whole, and the various nutrient components are uniformly distributed inside the substrate. The mycelium is in contact with a basically consistent nutrient environment throughout the cultivation process, making it impossible to adjust the nutrient supply environment according to different growth stages of the mycelium. When it is necessary to further increase the selenium content of *Dictyophora indicum*, if the selenium source is directly added to the culture medium, it is easy to cause the mycelium to come into contact with a high concentration of selenium source in the early stage of growth. A high concentration of inorganic selenium may inhibit mycelial germination and expansion, thereby affecting the quality of substrate formation and the subsequent yield of fruiting bodies.

[0005] Furthermore, Chinese patent CN104473141A discloses a method for producing organic selenium-rich additives using high-selenium edible fungi. This technology involves adding selenium-containing substances to the edible fungi cultivation system, enabling the fungi to absorb exogenous selenium and promoting the conversion of inorganic selenium to organic selenium. This technology discloses the use of selenite, selenate, and yeast selenium as selenium sources, and the use of carrier materials to form selenium additives with slow-release effects, thereby reducing the rapid release of selenium sources and improving the utilization efficiency of selenium by edible fungi. However, this technology mainly focuses on the selenium-rich additive itself and does not address the internal structural design of bamboo fungus substrate, nor does it consider the timing of selenium exposure during the outward expansion of bamboo fungus mycelium from the inoculation site within the substrate.

[0006] Current selenium-enriched edible fungi cultivation techniques typically involve directly mixing the selenium source into the culture medium or applying selenium nutrients through the cultivation environment to ensure a selenium supply to the entire cultivation system. While this method can increase the selenium content in edible fungi, the differences in selenium requirements and tolerance between the early and later stages of mycelial growth, coupled with maintaining the same selenium concentration throughout the cultivation cycle, can lead to the following problems: Firstly, during the early stages of mycelial germination and expansion, the mycelium is more sensitive to high-concentration selenium environments, and excessive selenium sources may affect the mycelial growth rate. Secondly, as the mycelial mass increases in the later stages, the absorption and conversion of selenium enhances, but traditional uniform selenium supply methods cannot further improve selenium utilization efficiency, resulting in some selenium in the culture medium not being fully absorbed and utilized.

[0007] Meanwhile, existing mushroom substrate structures typically employ a single-medium filling method, where the mycelial expansion path is primarily determined by the properties of the substrate itself, making it impossible to actively regulate the mycelial growth direction, expansion speed, and the time relationship with the selenium source. Although there are technical solutions in the edible fungi field that improve the mycelial expansion path through central inoculation, their main purpose is to increase mycelial germination speed or improve aeration conditions, without considering the needs of selenium-enriched cultivation and the synergistic design of the internal substrate structure, selenium release location, and mycelial growth process.

[0008] Therefore, the existing technology has at least the following shortcomings:

[0009] (1) Traditional bamboo fungus substrate is prepared by uniform mixing, which cannot provide a differentiated culture environment according to different growth stages of mycelium;

[0010] (2) Selenium enrichment culture usually adopts the overall selenium supply method. The selenium source release process is not matched with the mycelial growth process, which can easily lead to early selenium inhibition or insufficient selenium utilization in the later stage.

[0011] (3) Although existing slow-release selenium materials can delay selenium release, they usually only focus on selenium release performance and do not consider the synergistic relationship between selenium release performance and the spatial structure of the substrate and the mycelial migration path.

[0012] (4) The existing technology lacks a bamboo fungus stick structure that can simultaneously regulate the mycelial growth path, the physical gradient of the culture medium and the selenium release time. Summary of the Invention

[0013] This invention aims to provide a selenium-enriched bamboo fungus substrate and its preparation method, addressing the problems of mismatch between selenium source and mycelial growth stage, low selenium utilization efficiency, and inhibition of early mycelial growth by high selenium concentrations in existing bamboo fungus selenium enrichment cultivation processes. By constructing a substrate cultivation system with a radial gradient structure, bamboo fungus mycelia gradually expand in a predetermined direction, and the phased release of selenium is achieved using composite slow-release selenium particles. This enhances the absorption and conversion capacity of bamboo fungus for selenium while ensuring normal mycelial growth and stable substrate formation, resulting in a selenium-enriched bamboo fungus product with high selenium content and excellent quality.

[0014] To achieve the objectives of this invention, the following technical solution is adopted:

[0015] A method for preparing selenium-enriched bamboo fungus substrate includes the following steps:

[0016] S1. Prepare low-selenium induction culture medium, nutrient transition culture medium and selenium slow-release culture medium respectively; the selenium slow-release culture medium contains composite slow-release selenium particles, the composite slow-release selenium particles include porous biochar adsorbed with selenite ions, a calcium alginate gel layer coated on the porous biochar and a chitosan layer coated on the calcium alginate gel layer, and selenium yeast dispersed in the chitosan layer.

[0017] S2. Around the removable central core rod, the low selenium induction culture medium, nutrient transition culture medium and selenium slow-release culture medium are coaxially filled from the inside to the outside, so that the filling density and total selenium content of the three increase from the inside to the outside and the moisture content decreases from the inside to the outside. The filling density difference between two adjacent culture medium layers is not less than 0.04 g / cm³.

[0018] S3. Remove the annular separator between adjacent culture media and apply radial pressure to the outer periphery of the bag during the removal process to close the annular gap formed by the separator. Then remove the central core rod to form an axial inoculation channel that extends along the axial direction of the mushroom stick and is connected to the low selenium-induced culture media.

[0019] S4. Sterilize and cool the mushroom sticks, inoculate the bamboo fungus through the axial inoculation channel and seal the inoculation port, so that the bamboo fungus mycelium enters the low selenium induction culture medium, the nutrient transition culture medium and the selenium slow-release culture medium in sequence from the axial inoculation channel outward.

[0020] S5. Mycelial culture is carried out at 23℃~26℃, wherein the radial thickness ratio and packing density of the low selenium induction culture medium, nutrient transition culture medium and selenium slow-release culture medium are set so that the bamboo fungus mycelium reaches the selenium slow-release culture medium 18~22 days after inoculation, and the cumulative selenium release rate of the composite slow-release selenium particles is maintained at 35%~60% within 18~22 days after inoculation. Culture continues until the mycelium is fully grown and completes post-maturation to obtain selenium-enriched bamboo fungus sticks.

[0021] As a further improvement, based on dry material weight parts: the low-selenium induction culture medium includes 40-55 parts bamboo shavings, 20-30 parts broadleaf wood shavings, 12-18 parts wheat bran, 3-8 parts corn flour, 1-3 parts gypsum, and 0.2-0.8 parts potassium dihydrogen phosphate; the nutrient transition culture medium includes 30-45 parts bamboo shavings, 20-30 parts broadleaf wood shavings, 15-22 parts wheat bran, 5-10 parts soybean meal, 5-10 parts corn flour, 1-3 parts gypsum, and 0.2-0.8 parts potassium dihydrogen phosphate; the selenium slow-release culture medium includes 30-45 parts bamboo shavings, 20-30 parts broadleaf wood shavings, 10-18 parts wheat bran, 3-8 parts soybean meal, 1-3 parts gypsum, and 0.2-1.2 parts compound slow-release selenium granules.

[0022] As a further improvement, the composite sustained-release selenium particles are prepared according to the following steps: a sodium selenite aqueous solution is mixed with porous biochar, so that selenite ions are adsorbed into the pores of the porous biochar; the porous biochar with adsorbed selenite ions is dispersed in a sodium alginate solution and added dropwise to a solidification solution containing calcium ions to form calcium alginate gel particles coated with the porous biochar; the calcium alginate gel particles are placed in a chitosan solution containing selenium yeast for coating to obtain composite sustained-release selenium particles with selenium yeast dispersed on the outer layer.

[0023] As a further improvement, the thickness ratio of the low-selenium induction culture medium, the nutrient transition culture medium, and the selenium slow-release culture medium along the radial direction of the mycelium stick is 1:1.6-2.2:0.7-1.0; the diameter of the axial inoculation channel is 6%-10% of the diameter of the mycelium stick; and the low-selenium induction culture medium is continuously arranged along the outer periphery of the axial inoculation channel.

[0024] As a further improvement, the low-selenium induction culture medium has a packing density of 0.36–0.42 g / cm³ and a moisture content of 62%–65%; the nutrient transition culture medium has a packing density of 0.45–0.50 g / cm³ and a moisture content of 59%–62%; and the selenium slow-release culture medium has a packing density of 0.52–0.57 g / cm³ and a moisture content of 56%–59%.

[0025] As a further improvement, based on dry materials: the total selenium content of the low-selenium induction culture medium is 0.08–0.25 mg / kg; the total selenium content of the transitional nutrient culture medium is 0.5–1.2 mg / kg; the total selenium content of the selenium slow-release culture medium is 3–10 mg / kg; the ratio of the total selenium content of the low-selenium induction culture medium to the transitional nutrient culture medium is 1:3–1:6; and the ratio of the total selenium content of the transitional nutrient culture medium to the transitional selenium culture medium is 1:4–1:8.

[0026] As a further improvement, the cumulative selenium release rate of the composite slow-release selenium particles in the simulated culture medium extract at a temperature of 24℃~26℃ and a pH value of 5.5~6.2 meets the following requirements: no more than 25% on the 10th day of culture; 35%~50% on the 18th day of culture; 45%~60% on the 22nd day of culture; and 65%~82% on the 30th day of culture.

[0027] Another aspect of the present invention provides a selenium-enriched bamboo fungus substrate, comprising a fungus bag and bamboo fungus culture medium disposed within the fungus bag. The bamboo fungus culture medium, surrounding an axial inoculation channel extending along the axial direction of the substrate, sequentially forms a low-selenium induction layer, a nutrient transition layer, and a selenium slow-release layer from the inside out. The axial inoculation channel is connected to the low-selenium induction layer. The packing density of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer increases sequentially from the inside out, and the packing density difference between adjacent layers is not less than 0.04 g / cm³. Furthermore, the water content of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer decreases sequentially from the inside to the outside; the total selenium content of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer increases sequentially from the inside to the outside; the selenium slow-release layer contains composite slow-release selenium particles, which include porous biochar adsorbed with selenite, a calcium alginate gel layer coated on the porous biochar, and a chitosan layer coated on the calcium alginate gel layer, with selenium yeast dispersed in the chitosan layer.

[0028] As a further improvement, the thickness ratio of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer along the radial direction of the mycelium substrate is 1:1.6-2.2:0.7-1.0; the packing density of the low-selenium induction layer is 0.36-0.42 g / cm³; the packing density of the nutrient transition layer is 0.45-0.50 g / cm³; the packing density of the selenium slow-release layer is 0.52-0.57 g / cm³; and the diameter of the axial inoculation channel is 6%-10% of the mycelium substrate diameter.

[0029] As a further improvement, the total selenium content of the low-selenium induction layer is 0.08–0.25 mg / kg, and the water content is 62%–65%; the total selenium content of the nutrient transition layer is 0.5–1.2 mg / kg, and the water content is 59%–62%; the total selenium content of the selenium slow-release layer is 3–10 mg / kg, and the water content is 56%–59%; the cumulative selenium release rate of the composite slow-release selenium particles on day 18 of cultivation in a simulated culture medium extract at a temperature of 24℃–26℃ and a pH of 5.5–6.2 is 35%–50%, and the cumulative selenium release rate on day 22 of cultivation is 45%–60%.

[0030] This invention establishes a low-selenium induction layer, a nutrient transition layer, and a selenium slow-release layer inside the mushroom substrate, creating a synergistic gradient in the packing density, moisture content, and selenium content of each layer. This allows bamboo fungus mycelia to gradually expand outward from the central inoculation channel. In the early stages of mycelial growth, the mycelia preferentially reside in the low-selenium, oxygen-rich induction zone, avoiding the adverse effects of high-concentration selenium sources on mycelial germination and expansion. As mycelial biomass increases and the mycelia enter the nutrient transition zone, they receive a continuous supply of nutrients and improve their adaptability to the selenium environment. Finally, they enter the selenium slow-release layer, achieving efficient absorption of selenium.

[0031] This invention employs composite slow-release selenium particles formed by porous biochar supporting inorganic selenium, a calcium alginate gel layer for slow-release isolation, and a chitosan layer carrying an organic selenium source. This allows inorganic and organic selenium to be released gradually during the cultivation of the fungus, reducing the risk of toxicity caused by the instantaneous release of selenium sources. At the same time, it improves the effective utilization rate of selenium in the cultivation system and promotes the absorption of inorganic selenium by bamboo fungus mycelium and its conversion to organic selenium.

[0032] Furthermore, by controlling the thickness of the culture medium layer, the difference in packing density, the moisture content gradient, and the release performance of the composite slow-release selenium particles, this invention enables the mycelial radial migration process to form a time-matched relationship with the selenium release process, avoiding the problems of premature release or insufficient supply of selenium in the traditional uniform selenium supply method, thereby improving the growth stability of bamboo fungus mycelium and the efficiency of selenium-enriched culture.

[0033] Furthermore, the present invention forms an axial inoculation channel through the central core rod, enabling the bamboo fungus spawn to germinate from the central area of ​​the substrate and expand radially, shortening the effective expansion path of the hyphae and improving the uniformity of hyphae migration between different culture layers; at the same time, the continuous bonding between each culture layer is maintained through layered filling and radial pressing, reducing interlayer gaps and improving the structural stability of the substrate.

[0034] In summary, this invention can improve the selenium enrichment level and organic selenium ratio in bamboo fungus fruiting bodies without reducing the growth performance of bamboo fungus mycelium, reduce the risk of selenium inhibition during the cultivation process, and improve the stability and controllability of the production process of selenium-enriched bamboo fungus, thus having good industrial application value. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the overall process for preparing selenium-enriched bamboo fungus sticks according to the present invention.

[0036] Figure 2 This is a schematic diagram of the radial structure of the selenium-enriched bamboo fungus stick of the present invention;

[0037] Figure 3 This is a schematic diagram of the structure of the composite sustained-release selenium particles of the present invention;

[0038] Figure 4 This is a schematic diagram of the layered filling and central inoculation channel formation process in the preparation of selenium-enriched bamboo fungus sticks according to the present invention. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0040] This invention provides a selenium-enriched bamboo fungus substrate and its preparation method. By constructing a substrate culture system with a radial gradient structure, the growth process of bamboo fungus mycelium and the release process of selenium are matched in time, thereby improving the selenium enrichment efficiency and culture stability of the bamboo fungus substrate.

[0041] like Figure 1 As shown, the preparation method of the present invention includes the following steps: preparation of culture medium, preparation of composite slow-release selenium granules, layering and molding of mushroom sticks, sterilization and inoculation, and gradient culture.

[0042] This invention first prepares low-selenium induction culture medium, nutrient transition culture medium, and selenium slow-release culture medium respectively; then, it adopts a coaxial layered filling method to form a gradient structure of the three cultures arranged from the inside to the outside along the radial direction of the mycelium stick; further, it forms an axial inoculation channel through the central core rod, so that the bamboo fungus mycelium gradually expands from the central area to the outer area; at the same time, composite slow-release selenium particles are added to the outer selenium slow-release culture medium to release selenium at a predetermined rate, thereby achieving synergistic control of the mycelial growth process and the selenium supply process.

[0043] I. Terminology Explanation

[0044] 1. Low-selenium induction culture medium

[0045] Low-selenium induction medium refers to the medium placed in the central area of ​​the mushroom log, adjacent to the axial inoculation channel. This medium is mainly used for the initial germination and mycelial expansion of *Dictyophora indica* spawn after inoculation. Since *Dictyophora indica* mycelia are quite sensitive to the culture environment during the germination stage, the selenium content in this area is reduced, allowing the mycelia to first establish a stable growth state in a low-selenium environment.

[0046] 2. Nutrient transition medium

[0047] The transitional nutrient medium is located outside the low-selenium induction medium, connecting the early mycelial expansion zone with the selenium-enriched culture zone. This medium increases protein and mineral supply, allowing the mycelium to gradually increase biomass as it migrates outwards, thus enhancing its adaptability to the subsequent selenium-enriched environment.

[0048] 3. Selenium slow-release culture medium

[0049] The selenium slow-release culture medium is located in the outer area of ​​the mycelium substrate and contains composite slow-release selenium particles. Unlike the traditional method of directly adding selenium sources, this invention reduces the instantaneous release rate of selenium through composite slow-release selenium particles, thus matching the selenium supply process with the mycelial growth process.

[0050] 4. Composite slow-release selenium granules

[0051] The composite slow-release selenium particles comprise porous biochar loaded with an inorganic selenium source, a calcium alginate gel layer coated on the outside of the porous biochar, a chitosan layer coated on the outside of the calcium alginate gel layer, and selenium yeast dispersed in the chitosan layer. The porous biochar is used to adsorb and immobilize the inorganic selenium source; the calcium alginate gel layer is used to reduce the rate of water ingress and control selenium release; the chitosan layer is used to further regulate the release process; and the selenium yeast is used to provide an organic selenium source.

[0052] II. Preparation System Structure

[0053] The selenium-enriched bamboo fungus stick preparation system of the present invention includes a culture medium preparation unit, a composite slow-release selenium particle preparation unit, a layered molding unit, a pressing and shaping unit, a sterilization and inoculation unit, and a culture control unit.

[0054] 1. Culture medium preparation unit

[0055] The culture medium preparation unit is used to prepare low-selenium induced culture medium, nutrient transition culture medium and selenium slow-release culture medium respectively.

[0056] This unit includes a raw material weighing mechanism, a mixing mechanism, a moisture content adjustment mechanism, and a pretreatment mechanism.

[0057] By preparing different functional culture media, different regions can have different nutritional conditions, selenium content conditions, and physical structure conditions, thus preventing selenium sources from prematurely entering the mycelial germination area.

[0058] 2. Composite sustained-release selenium particle preparation unit

[0059] The composite sustained-release selenium particle preparation unit is used to prepare sustained-release selenium materials with multi-layer structures.

[0060] This unit includes: a biochar loading module; a gel coating module; a chitosan coating module; and a drying module.

[0061] The above structure transforms selenium from a traditional mixed state to a spatially distributed state, enabling the phased release of different selenium sources.

[0062] 3. Layered molding unit

[0063] like Figure 4 As shown, the layered molding unit includes a central core rod, an inner molding sleeve, and an outer molding sleeve. The central core rod is positioned along the axis of the mushroom log to form an axial inoculation channel. The inner molding sleeve is located outside the central core rod to define the filling area of ​​the low-selenium induction culture medium. The outer molding sleeve is located outside the inner molding sleeve to define the filling area of ​​the nutrient transition culture medium. A selenium slow-release culture medium filling area is formed between the mushroom bag and the outer molding sleeve. Through this coaxial structure, a continuous gradient of the three cultures is created along the radial direction of the mushroom log.

[0064] III. Step S1: Preparation of culture medium and composite sustained-release selenium particles

[0065] (I) Preparation of low-selenium induction culture medium

[0066] Low-selenium induction culture medium includes, by weight:

[0067] 40-55 parts bamboo shavings;

[0068] 20-30 parts of broadleaf wood chips;

[0069] 12-18 parts wheat bran;

[0070] 3-8 parts corn flour;

[0071] 1-3 parts plaster;

[0072] 0.2 to 0.8 parts of potassium dihydrogen phosphate.

[0073] Preferred ingredients: 50 parts bamboo shavings; 25 parts broadleaf wood shavings; 15 parts wheat bran; 5 parts corn flour; 2 parts gypsum; 0.5 parts potassium dihydrogen phosphate.

[0074] After the above raw materials are mixed evenly, sterile water is added to make the moisture content reach 62% to 65%.

[0075] The total selenium content of the culture medium was controlled at 0.08–0.25 mg / kg.

[0076] (II) Preparation of transitional nutrient culture medium

[0077] Nutritional transitional culture medium includes, by weight, the following components:

[0078] 30-45 parts bamboo shavings;

[0079] 20-30 parts of broadleaf wood chips;

[0080] 15-22 parts wheat bran;

[0081] 5-10 parts soybean meal;

[0082] 5-10 parts corn flour;

[0083] 1-3 parts plaster;

[0084] 0.2 to 0.8 parts of potassium dihydrogen phosphate.

[0085] Preferably, the ingredients are: 40 parts bamboo shavings; 25 parts broadleaf wood shavings; 18 parts wheat bran; 8 parts soybean meal; 7 parts corn flour; 2 parts gypsum; and 0.5 parts potassium dihydrogen phosphate. Adjust the moisture content to 59%–62%.

[0086] (III) Preparation of Composite Slow-Release Selenium Particles

[0087] like Figure 3 As shown, the present invention uses composite slow-release selenium particles as the selenium supply material.

[0088] The specific preparation process is as follows: First, sodium selenite is added to water to form a selenium-containing solution. Then, porous biochar is added, allowing selenite ions to enter the pores of the biochar and be fixed inside the porous structure through adsorption. After loading is complete, the selenium-containing biochar is added to the sodium alginate solution and then dropped into a calcium ion-containing curing solution, causing the sodium alginate to undergo ionic cross-linking and form a calcium alginate gel layer. Further, the particles forming the gel layer are added to a chitosan solution containing selenium yeast, allowing chitosan to form a coating layer on the outside of the particles, while simultaneously dispersing the selenium yeast within the chitosan layer. Finally, composite slow-release selenium particles with a multi-layered structure are obtained.

[0089] (iv) Mechanism of action of compound sustained-release selenium particles

[0090] The composite slow-release selenium particles of this invention achieve selenium release regulation through spatial stratification. Specifically: a chitosan layer controls the rate of external moisture ingress; a calcium alginate gel layer forms an intermediate diffusion barrier; and porous biochar controls the release of internal inorganic selenium. Therefore, the composite slow-release selenium particles can reduce the peak selenium release, making the selenium supply process more gradual. Simultaneously, the selenium yeast provides an organic selenium source, which is beneficial for increasing the enrichment ratio of organic selenium in the fruiting body of *Dictyophora indica*.

[0091] IV. Step S2: Coaxial layered filling to form a gradient mycelium structure

[0092] like Figure 2 As shown, the selenium-enriched bamboo fungus sticks prepared by the present invention do not adopt the traditional uniform mixed culture medium structure, but instead form gradient culture zones with different functions in the radial direction inside the stick.

[0093] Specifically, it includes: a low-selenium induction layer in the central region; a nutrient transition layer in the middle region; and a selenium slow-release layer in the outer region. These three regions are continuously arranged radially along the mushroom stick, allowing the bamboo fungus mycelium to gradually expand from the center to the periphery, successively experiencing a low-selenium environment, a nutrient-fortified environment, and a selenium-rich environment.

[0094] (a) Coaxial layered filling process

[0095] After preparing the three types of culture media, the mushroom bags were installed in the layered molding unit. First, a central positioning axis for the mushroom log was formed using a central core rod. Then, a low-selenium induction culture medium was filled around the outer periphery of the central core rod. After filling, the low-selenium induction culture medium was kept coaxial with the central core rod. Next, a nutrient transition culture medium was filled around the low-selenium induction culture medium. Finally, a selenium slow-release culture medium was filled between the inner wall of the mushroom bag and the nutrient transition culture medium. Through this process, a three-layered structure was formed inside the mushroom log, arranged sequentially from the inside out.

[0096] Among them: the low-selenium induction layer is close to the inoculation area; the nutrient transition layer serves as the transition area for mycelial migration; and the selenium slow-release layer serves as the selenium-enriched area in the later stage.

[0097] (II) Radial Gradient Structure Design

[0098] Specifically: Low selenium induction layer: packing density of 0.36-0.42 g / cm³; moisture content of 62%-65%; total selenium content of 0.08-0.25 mg / kg.

[0099] Nutrient transition layer: packing density is 0.45-0.50 g / cm³; moisture content is 59%-62%; total selenium content is 0.5-1.2 mg / kg.

[0100] Selenium slow-release layer: packing density is 0.52-0.57 g / cm³; moisture content is 56%-59%; total selenium content is 3-10 mg / kg.

[0101] (III) The regulatory effect of packing density gradient on mycelial migration

[0102] The expansion rate of *Dictyophora indica* mycelia in the culture medium is affected by the pore structure of the medium. When the packing density of the culture medium is low: the gaps between the culture medium particles are larger; the air exchange capacity is enhanced; and the mycelia can easily penetrate. Therefore, this invention sets the low-selenium induction layer to a low packing density, enabling the mycelia to expand rapidly in the early stage of inoculation. As the mycelia migrate to the periphery: entering the nutrient transition layer; the packing density gradually increases; and the porosity decreases.

[0103] This change can appropriately reduce the mycelial expansion rate, allowing the mycelium sufficient growth time before entering the selenium slow-release layer.

[0104] Furthermore, the outer selenium slow-release layer uses a higher packing density, so that the selenium element is mainly concentrated in the outer area, reducing the possibility of the selenium element rapidly migrating to the central area.

[0105] (iv) The regulatory effect of moisture content gradient on the selenium release process

[0106] In addition to packing density, this invention further regulates selenium release behavior through a moisture content gradient. The low-selenium induction layer has a high moisture content. Its functions include:

[0107] To improve the germination rate of the inoculum; promote mycelial formation; and maintain a stable initial culture environment. The nutrient transition layer uses a medium moisture content.

[0108] This area satisfies the needs of mycelial expansion while avoiding excessive moisture that could lead to oxygen deficiency in the culture medium. The selenium slow-release layer uses a low moisture content. Its functions include: reducing the water absorption rate of the composite slow-release selenium particles; reducing the rapid diffusion of selenium; and extending the selenium supply time.

[0109] V. Step S3: Compression and shaping of the mycelium sticks and formation of axial inoculation channels

[0110] like Figure 4 As shown, after the three layers of culture medium are filled, the layered molding structure needs to be removed.

[0111] (a) Radial pressing process

[0112] Specifically, when removing the separators between adjacent culture media, uniform radial pressure is applied to the outer periphery of the mycelium stick. This pressure acts on the outer edge of the mycelium stick, causing the culture media particles to rearrange and fill the space created by the removal of the separators. Through the pressing process: interlayer voids are reduced; the continuity of culture media contact is improved; and the stability of the three-layer structure is maintained. After pressing, the interior of the mycelium stick still retains: a central low-selenium induction zone; a central nutrient transition zone; and a peripheral selenium slow-release zone.

[0113] (ii) Formation of axial inoculation channels

[0114] After radial pressing is completed, the central core is removed. Once the central core is removed, an axial inoculation channel is formed in the center of the substrate. This channel extends continuously along the axial direction of the substrate and connects with the low-selenium induction layer. The axial inoculation channel serves the following functions: first, it allows the bamboo fungus spawn to enter the center of the substrate; second, it allows the mycelium to spread evenly from the center outwards; and third, it shortens the path differences for the mycelium to reach the outer cultivation area.

[0115] VI. Step S4: Sterilization, inoculation, and directional mycelial propagation culture

[0116] After the mushroom logs are formed, they undergo sterilization. This process includes: placing the formed logs in a sterilization device; using steam sterilization; and cooling them to the inoculation temperature after sterilization. The sterilization process serves to: reduce the risk of contamination by other microorganisms; enhance the competitive advantage of the bamboo fungus strain; and ensure the stability of subsequent cultivation processes.

[0117] (I) Inoculation process

[0118] After cooling, the mushroom logs are inoculated with bamboo fungus spawn through the axial inoculation channel. After inoculation, the inoculation port is sealed. Because the axial inoculation channel is located in the center of the mushroom log, the spawn can directly enter the low-selenium induction zone.

[0119] (II) Mycelial growth process

[0120] In the initial inoculation stage: Bamboo fungus mycelia first grow in the low-selenium induction layer. Due to the low selenium content, sufficient moisture, and good oxygen supply in this area, the mycelia can quickly establish colonies. Subsequently, the mycelia enter the nutrient transition layer. During this stage, the mycelial quantity increases, metabolic capacity improves, and tolerance to the selenium environment strengthens. Finally, the mycelia enter the selenium slow-release layer. At this point, the mycelia have formed a relatively complete network, and the release of the composite slow-release selenium particles is at an optimal stage, thus achieving high-efficiency selenium absorption.

[0121] VII. Step S5: Timing-matched culture of mycelial growth and selenium release

[0122] (a) Selenium release process control

[0123] When composite slow-release selenium particles are added to selenium slow-release culture medium, selenium is gradually released during the culture process.

[0124] Early stage of cultivation: Due to the barrier effect of the chitosan layer and calcium alginate gel layer, the selenium release rate is slow. During this stage, the mycelium is mainly located in the low-selenium induction layer. This avoids a high-selenium environment affecting mycelial germination. Mid-stage of cultivation: As water gradually enters the interior of the composite particles, the selenium release rate increases. At this time, the mycelium gradually enters the nutrient transition layer and the selenium slow-release layer. Late stage of cultivation: Inorganic selenium is continuously released from the pores of the biochar. Simultaneously, selenium yeast releases organic selenium, increasing the selenium enrichment level of the bamboo fungus fruiting body.

[0125] (ii) Matching of mycelial migration time with selenium release time

[0126] This invention adjusts the following: the thickness of the culture medium layer; the packing density; the moisture content; and the structure of the composite slow-release selenium particles, enabling *Dictyophora indica* mycelia to enter the selenium slow-release layer 18–22 days after inoculation. Simultaneously, the cumulative selenium release rate of the composite slow-release selenium particles is controlled within this time range of 35%–60%. This matching relationship has the following effects: when the mycelia have not yet entered the selenium slow-release layer, the selenium release is low, avoiding early selenium stress. When the mycelia have entered the selenium slow-release layer, an adequate amount of selenium has been released, meeting the mycelial absorption requirements. Therefore, a synergistic relationship is formed between mycelial growth and selenium supply.

[0127] To further verify the technical effect of matching the mycelial migration process with the selenium release process in this invention, a comparative experiment was conducted on the growth of bamboo fungus mycelium and the selenium enrichment effect under different selenium release timing conditions.

[0128] This experiment uses the mushroom stick structure of the example as a basis, and only adjusts the release performance of the composite slow-release selenium particles to advance or delay the selenium release time.

[0129] The experiment was divided into: Experimental Group A:

[0130] By using the composite slow-release selenium particles of this invention, the cumulative selenium release rate is maintained at 45% to 55% when the mycelium enters the selenium slow-release layer.

[0131] Experimental Group B:

[0132] The structure of the composite slow-release selenium particles was adjusted so that when the hyphae entered the selenium slow-release layer, the cumulative selenium release rate was less than 20%.

[0133] Experimental group C:

[0134] By adjusting the structure of the composite slow-release selenium particles, the cumulative selenium release rate is higher than 70% when the mycelium enters the selenium slow-release layer.

[0135] The cultivation conditions remain consistent.

[0136] Table 3. Effects of different selenium release sequences on the cultivation effect of bamboo fungus.

[0137] Experimental Group A 20 50 31 175.2 5.36 88.1 Experimental Group B 20 18 34 158.4 3.72 76.5 Experimental group C 20 72 39 149.6 5.61 68.9

[0138] As can be seen from Table 3, when the mycelium enters the selenium slow-release layer, if the release of the composite slow-release selenium particles is insufficient, that is, the cumulative release rate of selenium is less than 20%, although it will not cause obvious selenium inhibition, the total selenium content and the proportion of organic selenium in the fruiting body are low because the mycelium cannot obtain sufficient selenium supply after entering the selenium-rich area.

[0139] In experimental group B, the total selenium content was only 3.72 mg / kg, and the proportion of organic selenium was 76.5%.

[0140] Compared to experimental group A: the total selenium content decreased by 30.6%; the proportion of organic selenium decreased by 11.6 percentage points.

[0141] When the hyphae enter the selenium slow-release layer, the cumulative selenium release rate exceeds 70%. Although this can increase the selenium concentration in the culture system, the hyphae will not be fully adapted to the high selenium environment, which will lead to a decrease in the hyphae expansion rate.

[0142] In experimental group C:

[0143] The mycelium reached full colony size in 39 days, significantly longer than the 31 days in experimental group A. Meanwhile, the proportion of organic selenium decreased to 68.9%.

[0144] This indicates that premature or rapid selenium release will lead to: (1) increased local selenium concentration in the culture medium; (2) impaired mycelial metabolism; and (3) reduced efficiency of inorganic selenium to organic selenium conversion.

[0145] To verify the role of different structural layers in the composite sustained-release selenium particles, the following experiment was further conducted:

[0146] Experimental group D: Intact composite slow-release selenium particles were used: porous biochar loaded with selenite; calcium alginate gel coating; chitosan outer coating; and selenium yeast dispersed in the chitosan layer.

[0147] Experimental group E: Chitosan layer removed, only biochar + calcium alginate gel retained.

[0148] Experimental group F: The calcium alginate gel layer was removed, and only biochar-supported selenium was used.

[0149] Table 4. Effect of different sustained-release selenium particle structures on selenium release performance

[0150] Experimental group D 22 48 75 88.1 Experimental group E 35 65 86 79.4 Experimental group F 62 88 95 65.7

[0151] Table 4 shows that the release rate of the intact composite slow-release selenium particles was low in the early stage of cultivation, gradually increasing in the middle and later stages. This is because the porous biochar restricts the rapid diffusion of inorganic selenium within; the calcium alginate gel layer forms the first diffusion barrier; and the chitosan layer further reduces the rate of external moisture ingress. Therefore, the combined effect of these three layers makes the selenium release curve smoother.

[0152] In experimental group E, after the chitosan layer was removed, the release rate increased to 65% on day 20. This indicates that the chitosan layer can further delay selenium release.

[0153] After the gel layer was removed in experimental group F:

[0154] The release rate reached 62% on day 10. This indicates that biochar adsorption alone cannot achieve the phased release required by this invention.

[0155] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A method for preparing selenium-enriched bamboo fungus sticks, characterized in that, Includes the following steps: S1. Prepare low-selenium induction culture medium, nutrient transition culture medium and selenium slow-release culture medium respectively; the selenium slow-release culture medium contains composite slow-release selenium particles, the composite slow-release selenium particles include porous biochar adsorbed with selenite ions, a calcium alginate gel layer coated on the porous biochar and a chitosan layer coated on the calcium alginate gel layer, and selenium yeast dispersed in the chitosan layer. S2. Around the removable central core rod, the low selenium induction culture medium, nutrient transition culture medium and selenium slow-release culture medium are coaxially filled from the inside to the outside, so that the filling density and total selenium content of the three increase from the inside to the outside and the moisture content decreases from the inside to the outside. The filling density difference between two adjacent culture medium layers is not less than 0.04 g / cm³. S3. Remove the annular separator between adjacent culture media and apply radial pressure to the outer periphery of the bag during the removal process to close the annular gap formed by the separator. Then remove the central core rod to form an axial inoculation channel that extends along the axial direction of the mushroom stick and is connected to the low selenium-induced culture media. S4. Sterilize and cool the mushroom sticks, inoculate the bamboo fungus through the axial inoculation channel and seal the inoculation port, so that the bamboo fungus mycelium enters the low selenium induction culture medium, the nutrient transition culture medium and the selenium slow-release culture medium in sequence from the axial inoculation channel outward. S5. Mycelial culture is carried out at 23℃~26℃, wherein the radial thickness ratio and packing density of the low selenium induction culture medium, nutrient transition culture medium and selenium slow-release culture medium are set so that the bamboo fungus mycelium reaches the selenium slow-release culture medium 18~22 days after inoculation, and the cumulative selenium release rate of the composite slow-release selenium particles is maintained at 35%~60% within 18~22 days after inoculation. Culture continues until the mycelium is fully grown and completes post-maturation to obtain selenium-enriched bamboo fungus sticks.

2. The method for preparing selenium-enriched bamboo fungus sticks according to claim 1, characterized in that, By dry weight: the low-selenium induction culture medium comprises 40-55 parts bamboo shavings, 20-30 parts broadleaf wood shavings, 12-18 parts wheat bran, 3-8 parts corn flour, 1-3 parts gypsum, and 0.2-0.8 parts potassium dihydrogen phosphate; the nutrient transition culture medium comprises 30-45 parts bamboo shavings, 20-30 parts broadleaf wood shavings, 15-22 parts wheat bran, 5-10 parts soybean meal, 5-10 parts corn flour, 1-3 parts gypsum, and 0.2-0.8 parts potassium dihydrogen phosphate; the selenium slow-release culture medium comprises 30-45 parts bamboo shavings, 20-30 parts broadleaf wood shavings, 10-18 parts wheat bran, 3-8 parts soybean meal, 1-3 parts gypsum, and 0.2-1.2 parts compound slow-release selenium granules.

3. The method for preparing selenium-enriched bamboo fungus sticks according to claim 1, characterized in that, The composite sustained-release selenium particles are prepared according to the following steps: sodium selenite aqueous solution is mixed with porous biochar, so that selenite ions are adsorbed into the pores of the porous biochar; the porous biochar with adsorbed selenite ions is dispersed in sodium alginate solution and added dropwise to a solidification liquid containing calcium ions to form calcium alginate gel particles coated with the porous biochar; the calcium alginate gel particles are placed in a chitosan solution containing selenium yeast for coating to obtain composite sustained-release selenium particles with selenium yeast dispersed on the outer layer.

4. The method for preparing selenium-enriched bamboo fungus sticks according to claim 1, characterized in that: The thickness ratio of the low-selenium induction culture medium, the nutrient transition culture medium, and the selenium slow-release culture medium along the radial direction of the mycelium stick is 1:1.6-2.2:0.7-1.0; the diameter of the axial inoculation channel is 6%-10% of the diameter of the mycelium stick; the low-selenium induction culture medium is continuously arranged along the outer periphery of the axial inoculation channel.

5. The method for preparing selenium-enriched bamboo fungus sticks according to claim 1, characterized in that: The low-selenium induction culture medium has a packing density of 0.36–0.42 g / cm³ and a moisture content of 62%–65%; the nutrient transition culture medium has a packing density of 0.45–0.50 g / cm³ and a moisture content of 59%–62%; and the selenium slow-release culture medium has a packing density of 0.52–0.57 g / cm³ and a moisture content of 56%–59%.

6. The method for preparing selenium-enriched bamboo fungus sticks according to claim 1, characterized in that, Based on dry materials: the total selenium content of the low-selenium induction culture medium is 0.08–0.25 mg / kg; the total selenium content of the transitional nutrient culture medium is 0.5–1.2 mg / kg; the total selenium content of the selenium slow-release culture medium is 3–10 mg / kg; the ratio of the total selenium content of the low-selenium induction culture medium to the transitional nutrient culture medium is 1:3–1:6; and the ratio of the total selenium content of the transitional nutrient culture medium to the transitional selenium culture medium is 1:4–1:

8.

7. The method for preparing selenium-enriched bamboo fungus sticks according to claim 1, characterized in that, The cumulative selenium release rate of the composite slow-release selenium particles in the simulated culture medium extract at a temperature of 24℃~26℃ and a pH value of 5.5~6.2 meets the following requirements: no more than 25% on the 10th day of culture; 35%~50% on the 18th day of culture; 45%~60% on the 22nd day of culture; and 65%~82% on the 30th day of culture.

8. A selenium-enriched bamboo fungus substrate, comprising a fungus bag and a bamboo fungus culture medium disposed within the fungus bag, characterized in that: The bamboo fungus culture medium forms a low-selenium induction layer, a nutrient transition layer, and a selenium slow-release layer sequentially from the inside out around an axial inoculation channel extending along the axis of the fungus stick. The axial inoculation channel is connected to the low-selenium induction layer. The packing density of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer increases sequentially from the inside out, with a packing density difference of not less than 0.04 g / cm³ between adjacent layers. The moisture content of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer decreases sequentially from the inside out. The total selenium content of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer increases sequentially from the inside out. The selenium slow-release layer contains composite slow-release selenium particles, which include porous biochar adsorbed with selenite, a calcium alginate gel layer coated on the porous biochar, and a chitosan layer coated on the calcium alginate gel layer. Selenium yeast is dispersed in the chitosan layer.

9. The selenium-enriched bamboo fungus stick according to claim 8, characterized in that: The thickness ratio of the low-selenium induction layer, the nutrient transition layer, and the selenium slow-release layer along the radial direction of the substrate is 1:1.6-2.2:0.7-1.0; the packing density of the low-selenium induction layer is 0.36-0.42 g / cm³; the packing density of the nutrient transition layer is 0.45-0.50 g / cm³; the packing density of the selenium slow-release layer is 0.52-0.57 g / cm³; and the diameter of the axial inoculation channel is 6%-10% of the substrate diameter.

10. The selenium-enriched bamboo fungus stick according to claim 8, characterized in that, Based on dry matter: the total selenium content of the low-selenium induction layer is 0.08–0.25 mg / kg, and the water content is 62%–65%; the total selenium content of the nutrient transition layer is 0.5–1.2 mg / kg, and the water content is 59%–62%; the total selenium content of the selenium slow-release layer is 3–10 mg / kg, and the water content is 56%–59%; the cumulative selenium release rate of the composite slow-release selenium particles on day 18 of cultivation in a simulated culture medium extract at a temperature of 24℃–26℃ and a pH of 5.5–6.2 is 35%–50%, and the cumulative selenium release rate on day 22 of cultivation is 45%–60%.

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