Edible fungi are typical heterotrophic organisms. How to more efficiently convert and utilize organic matter such as lignin and cellulose as well as other nutrients has always been the core issue of the development and technological innovation of the edible fungi industry [1]. As a necessary source of nutrition for the growth and development of edible fungi, cultivation substrate can provide carbon sources, nitrogen sources and a variety of trace elements. Its types, sources and treatment methods directly affect the growth cycle, yield, nutritional quality and economic benefits of edible fungi. With the acceleration of my country's high-quality economic development and industrial restructuring, the application of edible fungi cultivation substrate faces new challenges: First, the price of bulk substrate fluctuates frequently; second, under the background of increasingly strict environmental protection policies, the stable supply of sawdust substrate faces greater uncertainty, while the sources of alternative substrates are narrow and the promotion speed is slow; third, with the promotion of technologies such as straw return to the field, corn silage and perennial rice, the supply of straw substrate may further decline in the future; fourth, the current bioconversion rate of substrate is still relatively low, and the resource utilization rate needs to be improved; fifth, the factory production model has promoted a significant increase in edible fungi production capacity, and the problems of fungal residue treatment and substrate resource utilization are becoming increasingly prominent. This demonstrates that the future development of the edible fungi industry faces the risk of passively adjusting its basic cultivation formula. Developing new substrate formulas and supporting cultivation technologies with lower costs and higher yields has become a key factor for the sustainable development of the edible fungi industry.
Therefore, based on Web of Science and CNKI core journal literature data since 2015, this paper systematically summarizes the research progress in the field of edible fungi cultivation substrates in my country, discusses research hotspots, development dynamics, and future trends, aiming to provide theoretical reference for in-depth research and the high-quality and sustainable development of the edible fungi industry.
1.1 Tree branch and wood chips
Wood chips are the main source of substrate for the cultivation of wood-rotting fungi. Current research on wood chip cultivation substrates has expanded from hard wood chips represented by Fagaceae such as oak, sweetgum, beech and beech to fruit tree wood chips such as apple wood chips, mulberry wood chips, peach wood chips, kiwi fruit branch chips, walnut wood chips, pear wood chips, jujube wood chips, sour jujube branch chips, grape branch chips, as well as other economic wood chips such as camellia wood chips, tea branch chips, mulberry branch chips, rubber wood chips, pepper branch chips, wolfberry branch chips, vitex branch chips, yellow willow wood chips, moringa wood chips, eucalyptus bark, eucalyptus wood chips, etc. In addition, research on the application of oily coniferous wood chips such as Japanese cedar and spruce in the cultivation of oyster mushrooms has provided a theoretical basis for the development and utilization of wood chip resources with high content of functional components such as tannin, pectin and total flavonoids[2].
1.2 Crop Stems
Rice straw, wheat straw, corn stalks, and other crop stems are rich in cellulose and hemicellulose, making them important cultivation substrates for saprophytic edible fungi such as button mushrooms, straw mushrooms, and giant puffball mushrooms. Current research trends are expanding the range of raw materials from traditional grain crop straws such as rice straw, corn, and sorghum to stems from economic crops such as rapeseed, potato, soybean, hemp, ramie, cassava, tea stalks, and artemisia, as well as stems and leaves from vegetable crops such as asparagus, ginger, and stem mustard.
1.3 Food Processing By-products
The sources of food processing by-product substrates have expanded from traditional oilseed crop processing residues such as bran and soybean meal to various types such as oilseed cakes, seed husks, and lees. Oilseed cakes mainly include oilseed crop processing residues such as cottonseed meal, castor bean meal, and rapeseed meal, as well as peony seed meal and pepper seed meal. Seed husk research has expanded from common raw materials such as coffee shells and peanut shells to regional resources such as areca kernels, jujube kernels, grape seeds, lotus seed shells, and foxnut shells. Food lees mainly include various types such as liquor lees, beer lees, vinegar lees, water chestnut residue, prickly pear residue, sea buckthorn residue, coffee grounds, and tea residue. In addition, sugar mill filter mud is also considered a good supplementary material that can be used as a fast carbon source for edible fungi [3].
1.4 Medicinal Plants and Residues
The cultivation substrates for medicinal plants mainly come from plant residues after the harvest of medicinal materials, such as Evodia rutaecarpa branches and leaves, Lonicera japonica branches and leaves, Codonopsis pilosula stems and leaves, Eucommia ulmoides leaves and bark, Platycodon grandiflorus, Perilla frutescens stems, and Cinnamomum cassia wood processing by-products. Although pharmaceutical processing by-products (residues) are not a traditional source of edible fungi cultivation substrates, related research has been increasing in recent years, mainly involving residues of traditional Chinese medicinal materials, residues of traditional Chinese medicine prescriptions, and residues of Western medicines. For example, Hericium erinaceus can be cultivated using Astragalus membranaceus residue[4], and Pleurotus eryngii residue can be cultivated using Polygonum cuspidatum residue[5]. Pleurotus eryngii can be cultivated using residues from six kinds of traditional Chinese medicine preparations, namely, Agastache rugosa oral liquid, Lysimachia christinae granules, Jizhi syrup, Dabaidu capsules, Bazheng compound preparation, and Scutellaria baicalensis granules[6]. Pleurotus ostreatus can be cultivated using residues from Jizhi syrup[7]. Coprinus comatus can be cultivated using residues from Vitamin C Yinqiao tablets[8-9]. Pleurotus eryngii can be cultivated using residues from oxytetracycline Western medicine[10]. Medicinal plants and medicinal residues have great potential in the cultivation of specific nutritional or functional fruiting bodies, but their safety still needs to be systematically verified.
1.5 Other Substrates
Juncao (a type of grass) cultivation substrates are an emerging field in the research of edible fungi cultivation substrates in recent years. Commonly used juncao materials include giant reed grass, elephant grass, five-jointed miscanthus, reeds, and alfalfa, while reeds and rushes are potential resources with local characteristics. It is worth noting that the microscopic morphology of shiitake mushroom mycelium in fresh and dried juncao culture media shows obvious differences, providing a new direction for the study of its cultivation substrate [11].
The research on soil-based substrates mainly focuses on loam, sand, peat moss, wheat field soil, paddy field soil, vegetable garden soil, mushroom residue, reed residue, pond mud, etc., which are often used in the cultivation of straw-decomposing fungi such as button mushrooms, black-skinned chicken mushrooms, hairy cap mushrooms, and large-cap mushrooms.
2.1 Substrate Physicochemical Indicators
Particle size, carbon-nitrogen ratio, water content, air permeability, pH, etc. are important physicochemical indicators that affect the cultivation effect of edible fungi. Reasonable control of these indicators can improve yield and quality. Substrate particle size and air permeability directly affect the growth and yield of edible fungi. Kong Weili et al. [12] found through experiments on fermented oyster mushroom substrate with different particle sizes that the water-soluble organic carbon content of small-particle substrate is lower than that of large-particle substrate, while its ammonia content and the quality of its antimicrobial inhibitors are higher than those of large-particle substrate. The smaller the particle size of the substrate, the lower the substrate temperature, the lower the contamination rate, and the higher the bioconversion rate during the mycelial growth period after cultivating oyster mushroom. Further research based on metabolomics showed that the microbial metabolites of oyster mushroom fermented substrate prepared by adding small-particle corn cobs (D50=0.5cm) and large-particle corn cobs (D50=1.5cm) were significantly different. 464 and 201 differential metabolites were screened in positive ion (POS) and negative ion (NEG) modes, respectively [13]. Yu Hailong et al. [14] pointed out that sawdust particle size significantly affects the quality of single mushrooms, mushroom shape, biological conversion rate and production cycle in the industrial production of shiitake mushrooms. He Yan et al. [15] found through correlation analysis that the permeability of cultivation substrate and covering material directly affects the fruiting time and yield of *Agaricus bisporus*, and that oxygenated water or magnetized water has the potential to improve agronomic traits and increase yield. Xiao Lan et al. [16] applied magnetized water to the mixing and humidification of *Flammulina velutipes*, which improved the extracellular laccase, polyphenol oxidase, carboxymethyl cellulase and hemicellulase activities of *Flammulina velutipes*, shortened the production cycle, reduced the contamination rate of the mushroom bags, and increased the yield per bottle by more than 2g. Moderately alkalized substrate is beneficial to improving the yield and quality of edible fungi fruiting bodies. Zhang Weirui et al. [17] believed that this may be related to the fact that alkalization treatment improved the activity of mycelial laccase.
2.2 Substrate Treatment Methods
The substrate treatment methods for edible fungi cultivation mainly include three aspects: substrate compression, substrate fermentation, and substrate sterilization.
(1) Substrate Compression: The research focuses on the effects of different compression processes on mycelial growth and yield. Geng Yucong et al. [18] cultivated button mushrooms using compressed cow dung and wheat straw as the main materials and found that when the compaction of the compressed blocks was 500 kg/m3, it showed significant effects in saving cultivation area and cost, and increasing yield. Bao Xuxiang et al. [19] used a mechanical pressing device to prepare black fungus bags with Mongolian oak sawdust as the main material through a wet heat shaping method. The results showed that when the bulk density was 0.72 g/cm3, the black fungus mycelial growth rate was the fastest, the dry matter decomposition and utilization were the largest, the ear-forming time was short, the ear pieces were long and thick, and the hardness and soaking rate were low. In addition, Qi Jing et al. [20] used a biomass solidification molding machine to compress grape branch chips into granular substrate for cultivating oyster mushrooms, which significantly improved the yield of oyster mushrooms. (2) Substrate fermentation: This involves two aspects of research. One is the mold inhibition mechanism. Cui Xiao et al. [21] found that the extract of corn cob fermentation material can destroy the cell walls and cell membranes of Trichoderma viride and Penicillium glaucum hyphae, leading to the outflow of intracellular substances, thereby inhibiting their growth and spore germination. The other is the optimization of fermentation process. Huang Linxiang et al. [22] explored the parameters of the fermentation tunnel of Mushroom sphaerocephala; Cha Lei et al. [23] analyzed the changes in pH, conductivity, water content and nitrogen content during the fermentation process of Mushroom sphaerocephala culture medium; Wang Qian et al. [24] studied the effect of tunnel fermentation technology on the growth of Mushroom sphaerocephala hyphae and degradation of culture medium.
(3) Substrate sterilization: The research covers conventional high pressure, stepped high pressure, atmospheric pressure sterilization and short-time high pressure sterilization processes. Chen Qing et al. [25] found that with the increase of the number of atmospheric pressure sterilizations, the air porosity, water content and pH of the Mushroom oyster mushroom cultivation bags decreased, and the number of sterilizations was negatively correlated with the time of mycelial full bag and the bioconversion rate. Yang Hongpeng et al. [26] found that the step-high pressure sterilization method helps to increase the activity of three ligninases (laccase, manganese peroxidase and lignin peroxidase) and four cellulases (filter paper enzyme, endopeptidase, β-glucosidase and hemicellulase) in the mycelium of Crab Mushroom, and also increases the average yield of clusters.
3.1 Mineral elements
The levels and composition of mineral elements in the cultivation substrate directly affect the yield and nutritional composition of edible fungi fruiting bodies. Their important functions include maintaining the cell structure and morphology of edible fungi, participating in the regulation of extracellular enzymes, and resisting external interference such as heavy metal ions [27].
(1) Selenium: The addition of sodium selenite to the substrate has been widely applied in selenium-enriched cultivation studies of oyster mushrooms, button mushrooms, king oyster mushrooms, enoki mushrooms, shiitake mushrooms, and oyster mushrooms. Studies have shown that the selenium recovery rate of enoki mushroom fruiting bodies treated with sodium selenite is higher than that treated with selenomethionine and sodium selenite [28], and sodium selenite treatment can significantly increase the selenium content of king oyster mushroom fruiting bodies, improve their nutritional quality, and enhance their antioxidant capacity [29-30].
(2) Calcium: Calcium is an important component of cell walls and maintains cell membrane stability, and participates in regulating the osmotic pressure and enzyme activity of mycelial cells. Adding an appropriate amount of calcium carbonate to the cultivation substrate can not only provide the necessary calcium element, but also effectively neutralize the acidic substances produced during the fermentation of the culture medium or the growth of mycelium. Wu et al. [31] found that in the cultivation of button mushrooms, the calcium content decreased significantly during the composting and mycelial growth stages, and the decrease in calcium content in the casing soil was even more obvious, indicating that calcium mainly participated in mycelial metabolism and enzyme activity during this stage; while during the harvesting stage, the changes in calcium, carbon, and oxygen content in the casing soil and compost tended to be stable. (3) Regarding zinc: zinc sulfate is usually added to the substrate for regulation. Adding zinc sulfate to the cultivation substrate of nameko mushrooms can significantly increase the activity of filter paper enzyme, carboxymethyl cellulase, hemicellulase and β-glucosidase during the mycelial growth period, showing a certain yield-increasing effect [32]. (4) Other mineral elements: Sun Ya et al. [33] screened out strontium-rich black fungus varieties by adding different mass concentrations of strontium chloride to the substrate; Lin Jinsheng et al. [34] added 0.5 g/L sodium citrate to PDB liquid medium, which significantly increased the mycelial biomass of straw mushroom and shortened the culture cycle. Zhu Changwei et al. [35] found that adding yeast powder and copper sulfate to the culture medium at the same time could synergistically enhance the laccase activity in the fermentation broth of Pleurotus eryngii. Wang Jing et al. [36] confirmed that the exogenous addition of MnSO4, Na2SeO3, CaSO4 and FeSO4 could significantly increase the mycelial growth rate, biomass and the activity of antioxidant enzymes (such as superoxide dismutase and catalase) of straw mushroom. In addition, some mineral elements interact in the metabolic processes of mycelial cells. For example, the lack of phosphorus or sulfur in the culture medium may lead to a decrease in the absorption rate of sodium selenite by enoki mushroom [37], and the addition of zinc sulfate is beneficial to reduce the enrichment of cadmium by shiitake mushroom mycelium [38]. Zhang Liang et al. [39] found that under manganese ion stress, *Lycoperdon perlatum* and *Lactarius deliciosus* could activate insoluble potassium in the soil by secreting oxalic acid and hydrogen ions. It is evident that recent studies have focused more on the synergistic effects and comprehensive regulatory mechanisms of various mineral elements.
3.2 Organic Acids
Some organic acids have shown positive effects in the rejuvenation of edible fungi strains, fruiting body yield, and nutritional enhancement. Kong Zixuan et al. [40] compared the effects of adding equal amounts of 20 L-type amino acids to rejuvenate degenerated *Lycoperdon perlatum* strains and found that treatments with serine (Ser), alanine (Ala), valine (Val), leucine (Leu), and proline (Pro) all promoted mycelial growth and biomass accumulation, while increasing the content of mycelial polysaccharides, proteins, flavonoids, and polyphenols, effectively inhibiting the accumulation of reactive oxygen species and improving antioxidant enzyme activity. Further research revealed that the content of amino acids such as methionine (Met), cysteine (Cys), and Ser, as well as the content of minerals such as Mg, Cu, and Zn, were significantly increased after Ser treatment [41]. Gong et al. [42] found that the addition of exogenous citric acid and arginine could enhance the activity of the arginine synthesis branch of the citric acid cycle in the mycelial cells of Pleurotus ostreatus, which was beneficial to increasing the yield of fruiting bodies. Zhang Jinjing et al. [43] added kojic acid to the cultivation substrate to increase the activity of laccase and cellulase in the mycelium of Pleurotus ostreatus during the reproductive growth stage, thereby increasing the utilization rate of lignocellulose and thus increasing the yield. Wang Minghui et al. [44] found that adding a certain mass concentration of salicylic acid to the culture medium was beneficial to promoting the growth of Pleurotus ostreatus mycelium.
3.3 Sugars
Sugars, as carbon sources, can effectively promote the growth of mycelium. Liu Xiaoxia et al. [45] found that sucrose, fructose, mannitol, and trehalose can all increase the aerial mycelial density, mycelial growth rate, and biomass of degenerated *Pleurotus ostreatus* strains, and increase the content of mycelial polysaccharides and proteins, effectively inhibiting the accumulation of reactive oxygen species and enhancing the activities of superoxide dismutase (SOD) and peroxidase (POD). Cheng Zhihong et al. [46] also reported that exogenous addition of mannitol can largely restore the activities of filter paper enzyme, endoglucanase, laccase, and manganese peroxidase in degenerated *Pleurotus ostreatus* strains. Yang Huanling et al. [47] pointed out that the addition of trehalose can promote the mycelial growth of *Agaricus bisporus* and *Agaricus bisporus* and increase biomass, and has a significant regulatory effect on the activities of cellulase and laccase. In addition, Liu et al. [48] experimentally confirmed that a lower concentration of exogenous trehalose can alleviate the inhibitory effect of heat stress on mycelial growth. In the future, trehalose is expected to be added to the substrate as a protective agent against abiotic stress.
3.4 Plant Extracts
Adding specific plant extracts to the cultivation substrate can have multiple effects, such as inhibiting bacteria, increasing the growth rate of mycelial cells, promoting phenolic metabolism, and enhancing antioxidant activity. Adding a mixture of garlic and ginger extracts to the oyster mushroom culture medium not only has a good antibacterial effect, but also shortens the budding time, makes the oyster mushroom texture dense, and reduces the size of the cap [49]. Apricot kernel wood vinegar can effectively inhibit the occurrence of bacterial brown spot disease in oyster mushrooms and promote the growth of oyster mushroom mycelium [50]. Adding garlic and arborvitae extracts to the chicken leg mushroom cultivation substrate has a significant antibacterial effect on Penicillium and Rhizopus, and also has the effects of increasing yield, shortening the intercropping period, and increasing the cap-to-stem ratio [51]. In addition, Bao Yihong et al. [52] found that adding areca nut extract can effectively improve the antioxidant activity of oyster mushroom, elm mushroom and enoki mushroom mycelium; Wu Li et al. [53] reported that adding 8% (mass fraction) of camellia branch extract can not only significantly promote mycelial growth, but also enhance the metabolic transformation of phenolic substances and the ability to scavenge hydroxyl radicals. The extract of corn cob fermentation material fermented for 10 days can also significantly improve the growth rate and biomass of oyster mushroom mycelium, while increasing the activity of adenosine triphosphate, succinate dehydrogenase, alkaline phosphatase, laccase and protease; microscopic observation showed that the number of mitochondria and cysts in oyster mushroom mycelial cells was significantly increased compared with the control group [54].
3.5 Other exogenous factors
Plant growth regulators can regulate the metabolic process of edible fungi, promote mycelial growth and improve enzyme activity. Indoleacetic acid, naphthaleneacetic acid, 6-benzylaminopurine, cytokinin KT-30, gibberellin, and sodium humate have all been shown to promote the growth of Balkhash mushroom mycelium to a certain extent [55]. Adding 2.0 mL of β-oligomeric acid to 1 kg of dry material promotes the growth of mycelium of Erycibe obtusifolia, Coprinus comatus, Ganoderma lucidum, and Hericium erinaceus [56]. In addition, chlorophenoxyacetic acid, naphthaleneacetic acid, and zeatin have also been used in liquid culture, and are expected to be more widely used as substrate additives in the future.
Enzyme preparations have the dual function of increasing yield and improving the marketability of fruiting bodies. Zhang Heying et al. [57] added a compound enzyme preparation composed of enzymes, enzyme gene expression inducers, and enzyme activators to the shiitake mushroom cultivation substrate, which advanced the time for mycelium to fill the bag by 15 days compared with the control group, significantly increased the activity of cellulase, protease, and amylase in the mycelium during the color change period, and increased the bioconversion rate by 21.99%. Xin Yu et al. [58] reported that adding 1% acidic cellulase, 1% neutral cellulase, and 0.5% hemicellulase (all by mass fraction) to compost before primary fermentation significantly increased the diameter of straw mushroom buds.
Mushroom root and residue extracts were added to the cultivation substrate as exogenous nutrient solutions, showing good application prospects. Yin Chuan et al. [59] mixed mushroom, erythrina, and white jade mushroom root extracts with soil and covered the ring-cut surface of white lingzhi mushroom bags. They found that the yield of mushroom root extracts applied to mushrooms increased by 54.6% compared with the control, and also increased the nitrate and protein content in the fruiting bodies. Zhang Ting et al. [60] sprayed enoki mushroom residue extracts onto the casing layer of button mushrooms and measured that the amino acid score (AAS), chemical score (CS), essential amino acid ratio coefficient (SRC), essential amino acid index (EAAI), biological value (BV), and nutrient index (NI) of the fruiting bodies were all higher than those of the control group, indicating that enoki mushroom residue extracts are beneficial to improving the protein nutritional quality of the fruiting bodies.
4.1 Isolation, identification and screening of functional strains in fermentation substrate
The bacterial community in fermentation substrate is highly diverse, and there are significant differences in the dominant bacterial groups and relative abundance at different fermentation stages. A decrease in the relative abundance of dominant bacterial groups may cause fermentation failure, while the absence of specific bacterial groups during the fruiting period may cause abnormal fruiting. Therefore, isolating, identifying and screening strains with specific functions such as antibacterial, growth-promoting and detoxifying functions from fermentation substrate to regulate and optimize the fermentation process is a research hotspot in this field. Currently, 16S rRNA gene sequencing technology has been widely used in this type of research [61].
Zhang Junjie et al. [62] isolated 94 bacterial strains from fermentation substrate of oyster mushrooms at different stages, of which 11 strains showed a dual effect of simultaneously inhibiting Trichoderma and promoting the growth of oyster mushrooms. Further research found that some of the growth-promoting strains had a strong ability to synthesize indoleacetic acid (IAA) [63]. Cui et al. [64] found that the change in aflatoxin content during the fermentation of oyster mushroom culture medium was significantly negatively correlated with the relative abundance of Bacillus and Luteinobacter, suggesting that these two genera may be involved in the degradation process of aflatoxin. Wu et al. [65] isolated and screened a type of aggregate microbial agent from distiller's grains. After adding this agent to the fermentation medium of oyster mushrooms, it significantly accelerated the rate of carbohydrate metabolism, increased the temperature of the medium, and prolonged the thermophilic stage. At the same time, the content of fungal ergosterol, the degradation rate of lignocellulose, and the activity of related enzymes in the fermentation medium were all higher than those in the control group, which promoted the faster colonization of oyster mushroom mycelium.
4.2 Changes in the community structure and dominant microbial community of casing microorganisms
Casing microorganisms play an important role in the mycelial growth, primordia formation, and yield increase of saprophytic fungi. Usually, there are significant differences in the abundance and dominant microbial community composition of casing microorganisms in different flushes. Wang et al. [66] found that in the first flush of Agaricus bisporus, the dominant genera were Sphingomonas, Dongia, and Achromobacter; while in the third flush, the dominant strains were mainly Norank, Pseudomonas, Flavobacterium, and Brevundimonas. In addition, there may be extensive interactions among the microbial communities in the casing soil, which was confirmed in Yang et al. [67]’s study on Boletus stalk. Some researchers have also isolated strains with specific functions from the casing soil. Hua et al. [68] isolated the rhizobium strain CACMS001 from the soil of Agaricus bisporus 'Polyporus'. This strain not only promoted the mycelial growth of Agaricus bisporus and Armillaria mellea, but also significantly enhanced the xylanase activity of Armillaria mellea.
5.1 Correlation between extracellular enzyme activity and fruiting body yield
The utilization process of nutrients in the cultivation substrate by edible fungi mainly includes the degradation of macromolecular organic matter (lignin, cellulose, hemicellulose, protein, etc.), the absorption of mineral elements (nitrogen, phosphorus, potassium, etc.), and the metabolism of small molecule organic matter (amino acids, peptides, lipids, vitamins, phenylpropanoids, polyketides, pyranoic acid, pyranone, plant hormones, antibacterial substances, etc.). The degradation of macromolecular organic matter by edible fungi depends on the extracellular enzymes secreted by edible fungi, which decompose macromolecular organic matter into absorbable small molecule components. Therefore, the activity of extracellular enzymes is closely related to the mycelial growth rate and the yield of fruiting bodies. Xie et al. [69] found in a comparative experiment on different substrates that the degradation rate of lignocellulose by Pleurotus eryngii and the activity of lignocellulase were positively correlated with its bioconversion rate. Lin Hui et al. [70] showed that the yield of fresh mushrooms of *Agaricus bisporus* was significantly positively correlated with the activities of carboxymethyl cellulase, xylanase, filter paper enzyme, and amylase. Liu Shunjie et al. [71] cultivated straw mushrooms with waste cotton substrate, and the activities of carboxymethyl cellulase and xylanase in high-yield batches were significantly higher than those in low-yield batches. In addition, Cai Panpan et al. [72] also reported that the activities of carboxymethyl cellulase and xylanase were positively correlated with the yield of button mushrooms.
5.2 Changes in extracellular enzyme activities at different growth stages
Extracellular enzyme activities show obvious stage-specific changes during the growth and development of edible fungi. Lei Ping et al. [73] found that the activities of filter paper cellulase, carboxymethyl cellulase, β-glucosidase, amylase, and hemicellulase in the mycelial cells of *Agaricus bisporus* all showed a trend of first increasing and then decreasing, and the enzyme activities remained at a high level until the young mushroom stage; while laccase and peroxidase had high activities in the early stage of mycelial growth and decreased with the extension of cultivation time. Yue et al. [74] found that carboxymethyl cellulase, pectinase, filter paper cellulase, and hemicellulase in *Hericium erinaceus* reached their peak activity during the growth and development of the fruiting body; while amylase, pectinase, and peroxidase had higher activity during the mycelial growth period. Li et al. [75] measured the laccase activity of *Pleurotus eryngii* during the mycelial, twisting, primordia, young mushroom, and fruiting body stages. The results showed that the laccase activity during the fruiting body stage was significantly higher than that during other stages, while the differences between the other four developmental stages were not significant.
5.3 Effect of carbon source on extracellular enzyme activity
The type and proportion of carbon source can affect the activity of extracellular enzymes in edible fungi. Compared with the culture medium containing cottonseed hulls, sawdust, and corn cobs, *Auricularia auricula-judae* grown in the culture medium containing wheat bran had higher laccase activity [76]; the activities of carboxymethyl cellulase, laccase, and neutral protease in *Pleurotus ostreatus* cultivated with cottonseed hull fermentation material were higher than those in *Pleurotus ostreatus* cultivated with corn cob fermentation material [77]. Differences in the proportion of carbon source addition can also cause changes in enzyme activity. Chen Hui et al. [78] showed that during the mycelial growth period, the activity of lignin peroxidase was highest when the mass fraction of corn cob in the Auricularia auricula-judae culture medium was 70%, the activity of manganese peroxidase was highest when the mass fraction of corn cob was 50%, and the activity of carboxymethyl cellulase was highest when the mass fraction of corn cob was 30%. With the increase of the mass fraction of corn cob, the activity of laccase decreased, while the activity of N-acetyl-β-D-glucosidase increased. The activities of β-1,3-glucanase, β-glucosidase and endoglucanase showed a trend of first increasing and then decreasing. It is worth noting that some studies have begun to explore the regulatory mechanism of different carbon sources on extracellular enzyme activity at the molecular level. Xiao Donglai et al. [79] used Hydrangea macrophylla as the test material and conducted a systematic analysis from the perspective of the expression of genes related to cellulose and hemicellulose degradation.
6.1 Effects of different cultivation substrates on the nutritional composition of fruiting bodies
This type of study usually uses multiple substrates to cultivate the same mushroom species, and measures different nutritional components such as protein, amino acids, total sugar, polysaccharides, polysaccharide peptides, and dietary fiber in the fruiting bodies. The effects of different substrates on nutritional value are evaluated through differences in nutritional components, providing a scientific basis for the development and utilization of new cultivation substrates. On the one hand, there are many studies on the content and composition of amino acids. Hu Yingping [80] used a mixture of mushroom grass and lotus seed shells and lotus pods to cultivate oyster mushrooms, and the amino acid and fatty acid composition of the fruiting bodies were diverse and rich. Lin Xingsheng et al. [81] added fresh mushroom grass to cottonseed hull cultivation material, which significantly increased the amino acid content of Tremella fruiting bodies. Ke Binrong et al. [82] used enoki mushroom residue and erythrina variegata residue as the main substrate to cultivate button mushrooms. The results showed that the amino acid composition and flavor amino acid content of the fruiting bodies were better than those of the rice straw formula. On the other hand, more and more studies are focusing on the effects of different substrates on specific nutrients in fruiting bodies, providing a reference for the development of edible fungi products with special nutritional value or health benefits. Wen Qing et al. [83] revealed that increased nitrogen source (such as urea) concentration can promote the accumulation of γ-aminobutyric acid (GABA) in the fruiting bodies of various edible fungi; the addition of sea buckthorn sawdust, sea buckthorn pomace, and sea buckthorn leaves can significantly increase the flavonoid content in the fruiting bodies of *Pleurotus ostreatus* [84]; the addition of cassava stems can increase the trehalose content in the fruiting bodies of *Auricularia auricula-judae*, *Pleurotus ostreatus*, and *Pleurotus ostreatus* [85]; the addition of *Astragalus membranaceus* stems and leaves can increase the content of terpenoids, flavonoids, and other bioactive substances of *Astragalus membranaceus* in the fruiting bodies of *Pleurotus ostreatus* [86].
6.2 Effects of different cultivation substrates on the flavor substances of fruiting bodies
Different cultivation substrates have different effects on the volatile flavor substances, flavor amino acids, and other non-volatile flavor substances of edible fungi fruiting bodies. Some substrates may contain a relatively high amount of flavor amino acids, which are absorbed during the growth of edible fungi, thereby increasing the content of flavor amino acids in the fruiting body. For example, the content of umami and sweet amino acids in the fruiting body of *Pleurotus ostreatus* cultivated with Chinese medicinal residue is higher than that in the sorghum husk treatment [87]. Different substrates can change the types and contents of volatile compounds in the fruiting body and promote the generation of certain aroma components, thereby affecting the overall aroma quality of the fruiting body. Yu Changxia et al. [88] found through the analysis of major volatile flavor substances such as isovaleraldehyde, hexanal, 1-octen-3-ol, methanethiol, 2-pentylfuran, and dimethyl sulfide that the aroma of *Pleurotus ostreatus* fruiting bodies cultivated with different culture media is significantly different. The aroma quality of *Pleurotus ostreatus* cultivated with *Pleurotus ostreatus* residue is the best, while the aroma quality of *Pleurotus ostreatus* cultivated with *Flammulina velutipes* residue is the worst. The comparative experiment of Yin Chaomin et al. [89] showed that cottonseed hull substrate is conducive to the generation of flavor ester compounds in *Pleurotus ostreatus* edible fungi, while hardwood sawdust substrate is conducive to the generation of free amino acids. The cultivation substrate may also affect the content and composition of other flavor substances in edible fungi. Yu Changxia et al. [90] found that the hydrolyzed amino acid content and composition of straw mushrooms cultivated with cottonseed hulls as substrate were the best in the experimental treatment, while the content of soluble sugar alcohols and organic acids of straw mushrooms cultivated with rice straw as substrate was the highest in the experiment. Li Jing et al. [91] used corn steep liquor fermentation liquid to partially replace wheat bran in the cultivation of Pleurotus eryngii, and the results showed that the content of soluble sugar alcohols, organic acids and 5′-nucleotides in its fruiting bodies were higher than those in the control group.
7.1 Types and Utilization Methods of Fungal Residue
In terms of fungal residue types, in recent years, domestic scholars have focused more on the fungal residues of industrially cultivated fungi such as Pleurotus eryngii, Enoki mushroom, Pleurotus ostreatus, and Seafood mushroom, as well as the fungal residues of traditional large-scale cultivated varieties such as Shiitake mushroom and Auricularia auricula-judae. In addition, the reuse of new fungal residue waste such as waste bags of Morel mushroom nutrient bags, waste fungal materials of Gastrodia elata, and waste rice base of Cordyceps militaris has also attracted increasing attention from researchers.
In terms of the utilization methods of fungal residue, the most important path is to cultivate straw-rotting fungi with fungal residues of wood-rotting fungi. In this case, the fungal residue usually needs to be used in combination with other fresh raw materials. Some fungal residues, such as waste fungal materials of Tremella fuciformis and fungal residues of Auricularia auricula-judae, can also partially replace fresh sawdust for the cultivation of other wood-rotting fungi. Most fungal residues, while providing a cultivation substrate, also have the function of supplementing carbon and nitrogen sources. For example, waste rice base of Cordyceps militaris can be used as a typical nitrogen substitute material [92]. Besides directly mixing fresh mushroom residue with other materials after crushing, Zhang Tengxiao et al. [93] used four methods—alkaline reaction, composting, baking, and ultrasound—to modify the mushroom residue, effectively improving the yield and quality of enoki mushrooms under mushroom residue cultivation conditions.
7.2 Effect Evaluation and Formula Optimization
The safety of mushroom residue used for the cultivation of other edible fungi is the primary focus of current research. Chen Furong et al. [94] used Erycibe lanceolata mushroom residue as an additive for the re-cultivation of oyster mushrooms, Erycibe lanceolata, and enoki mushrooms. The results showed that the contents of As, Hg, Pb, and Cd in the fruiting bodies were all lower than the relevant national standards.
Current research focuses on screening the optimal formula for mushroom residue cultivation by comprehensively comparing indicators such as mycelial growth, yield performance, fruiting body nutritional components, and economic benefits. Wen Qing et al. [95] explored the effects of different proportions of industrialized enoki mushroom residue on the agronomic traits and fruiting body nutritional components of oyster mushrooms cultivated with cooked substrate, and proposed the most suitable amount. Li Zhengpeng et al. [96] replaced waste cotton with 60% eryngii and oyster mushroom residue and button mushroom residue respectively, which shortened the straw mushroom production cycle by 1.6 days and increased the yield by 15% and 17% respectively. Chen Hua et al. [97] found that replacing rice straw with 30% eryngii and oyster mushroom residue could achieve the highest yield for Agaricus blazei cultivation, and the mass fractions of crude protein, amino acids and polysaccharides in the fruiting bodies were all better than the traditional formula, and the raw material cost was reduced by more than 35%.
Ahead, my country has achieved fruitful results in multiple fields of edible fungi cultivation substrate research over the past 10 years, showing a trend of diversified substrate sources, diversified treatment methods, and complex substrate formulation combinations. The understanding of the succession patterns of microbial community structure in cultivation substrates, extracellular enzyme activity and substrate degradation and utilization mechanisms, as well as the influence of cultivation substrates on the nutritional components and flavor substances of fruiting bodies, has been continuously deepened. Future research can focus on the following directions:
(1) In-depth analysis of the influence mechanisms of substrate components. Research will further focus on the regulatory mechanisms of different substrate components on the growth and development of edible fungi, especially revealing the molecular regulatory mechanisms in key processes such as substrate degradation, nutrient storage and transportation, and secondary metabolite synthesis. Among these, the key gene regulatory network related to nutrient transformation and metabolite synthesis will become a research hotspot [98].
(2) Rapid development and industrial application of commercial cultivation substrates. With the continuous advancement of industrialized production of edible fungi, the industrial chain is becoming increasingly refined. Specialized commercial substrate manufacturers will accelerate the development of efficient, safe, and functional cultivation substrates suitable for different types of edible fungi, especially specialized compound products with diverse additive formulations. Meanwhile, developing modified substrates with stress-resistant properties for non-traditional habitats such as high-altitude, desert, and saline-alkali land will also become an important research direction.
(3) Expansion of research on the structure and function of microbial communities in fermented materials and casing soil. Current research focuses on the growth-promoting and antibacterial mechanisms of beneficial microorganisms at different growth stages. In the future, more research will be conducted from the perspective of microbial ecology to explore the interaction relationships, functional redundancy, and regulatory networks among microbial communities, in order to achieve precise regulation and efficient utilization of microbial resources.
(4) Construction of an ecological risk and biosafety evaluation system for new cultivation substrates. With the continuous expansion of the application of new materials in cultivation substrates, the assessment of their potential impact on ecosystems and human health is becoming increasingly important. Therefore, it is urgent to establish a scientific and systematic evaluation system to comprehensively assess the ecological safety, fruiting body nutritional quality, and potential toxicological effects of new cultivation substrates, ensuring that they do not have a negative impact on the environment and human health while guaranteeing yield [99], so as to promote human well-being.
(5) Research and development of microbial residue recycling and substrate reuse technologies. With the continuous expansion of production capacity, improving resource utilization efficiency and reducing costs have become urgent problems for the industry. Exploring the feasibility of reusing substrates, revealing the evolution of their physicochemical properties during reuse and their impact on the yield and quality of edible fungi, will provide theoretical basis and technical support for building a green, low-carbon, and sustainable edible fungi industry system.
(6) Development and application of intelligent substrate management system. With the help of technologies such as the Internet of Things, big data, and artificial intelligence, the development of an intelligent substrate management system suitable for different types of edible fungi and with self-learning and evolution capabilities, to realize real-time monitoring and precise control of all process parameters such as traceability of cultivation substrate sources, substrate treatment, nutrient analysis, and degradation utilization, is one of the key paths for future industrial production technology upgrades [100].
Copyright © China Chamber of Commerce of Food, Native Produce and Animal Products Edible Fungi and Products Branch
京公网安备11010102004652号 京ICP备05021290号-29 | Technical Support: Starify Privacy Policy Sitemap Contact Us
