Research Progress of Selenium-Enriched Edible Fungi

Abstract

Selenium is a crucial trace element that necessitates exogenous supplementation and plays an essential role in human health, but its facilitation requires the conversion from inorganic to bioavailable organic forms. Selenium-enriched edible fungi provide an effective strategy for selenium fortification. Their easy cultivation, rapid growth, and excellent conversion capabilities make them ideal candidates for achieving selenium enrichment goals. This article reviews various methods for producing selenium-enriched products and highlights the benefits and functional properties of these fungi. It summarizes the mechanisms underlying selenium absorption and transformation within fungal biomass while considering influencing factors, such as environmental conditions, types of edible fungi, and sources of selenium. Furthermore, this article offers developmental recommendations to address current industrial challenges, providing theoretical references to foster healthy and sustainable advancements in this field.

1. Introduction

Selenium (Se) is a trace element essential for human health [1,2,3]. It serves as a critical component of glutathione peroxidase (GSH-Px), playing an essential role in maintaining redox balance, immune function, and thyroid function [4,5,6]. The bioavailability of selenium within the human body is influenced by various factors, including dietary intake, cooking methods employed, and individual differences in absorption and utilization [7,8,9]. Research suggests that adequate selenium intake can decrease the risk of cardiovascular diseases, cancer, and diabetes, among other health conditions [10]. In synergy with vitamin E, selenium contributes to the protection of cell membranes and helps prevent heart disease [11]. Edible fungi represent exceptional platforms for selenium biotransformation, effectively converting inorganic selenium found in the environment into bioavailable organic forms [12]. Given that 72% of soils in China are deficient in selenium [13], reliance on natural dietary sources alone is insufficient to meet the requirements for organic selenium. This situation has spurred increased research interest in the artificial cultivation of selenium-enriched crops, particularly edible fungi.

The global edible fungi industry continues to expand, demonstrating steady growth [14]. According to data from the Food and Agriculture Organization (FAO), production has increased annually, with shiitake (Lentinula edodes) and Pleurotus ostreatus dominating the market. Asia, Europe, and North America serve as primary production and consumption hubs. While international trade remains stable overall, regional patterns vary significantly: Poland, China, and other countries lead exports, whereas Japan and the United States are major importers. In 2023, the global output reached 50.101 million tons, with China contributing 43.3417 million tons—accounting for 86.6% of the total global production. Despite China’s price competitiveness driven by scale advantages, structural challenges persist; these include a prevalence of low-value-added products and insufficient branding efforts that result in a consistently low producer price index.

China’s edible fungi industry exhibited steady growth from 2023 to 2024. In 2023, the total output value of the national industry reached CNY 396.557 billion, with 16 provinces exceeding CNY 10 billion in production value. The sector has undergone structural optimization, characterized by stable shares of major varieties, expansion in the cultivation of rare fungi, accelerated modernization of production methods, and significant contributions to rural revitalization. From January to November 2024, China’s export volume remained stable; however, a notable year-on-year decline was observed in export value. The key export markets were primarily concentrated in Vietnam and nine additional countries or regions, with over 80% of the exported products categorized as low-value-added primary-processed goods. Domestically, market prices in 2024 showed seasonal fluctuations accompanied by considerable price differentiation among various types of fungi, reflecting varying consumer demands for premium products. Looking ahead to 2025, technological innovation, species diversification, and sustainable cultivation practices are anticipated to shape industry trends. As the global demand for functional foods such as selenium-enriched edible fungi (SEEF) increases, China encounters both challenges and opportunities for industrial upgrading. To transition from “volume leadership” to “value leadership” within the global competitive landscape, it is essential for China to prioritize breakthroughs in deep-processing technological constraints while establishing differentiated branding systems and extending its industrial chain into high-value-added segments.

Selenium-enriched agricultural products refer to agricultural commodities that offer supplemental selenium nutrition through biotransformation technologies and the artificial application of selenium fertilizers during cultivation or breeding processes, ensuring that their selenium content complies with established standards [15]. Various categories of these products adhere to differing regulatory benchmarks, with specific industry specifications for selenium-enriched tea clearly delineating criteria such as selenium concentration [16]. The global demand for these products continues to rise in tandem with increasing trends toward health-conscious consumption. Developed economies in Europe and North America exhibit a concentrated demand for premium selenium-enriched foods within the health food sector, thereby maintaining stable market growth.

The market for selenium-enriched agriculture in China has experienced rapid expansion. Industry research indicates that the domestic market scale exceeded CNY 200 billion in 2023, underscoring significant growth potential. Staple products, such as selenium-enriched rice and eggs, have garnered considerable consumer acceptance. Within this sector, edible fungi enriched with selenium constitute a vital segment in both global research and development (R&D) and production efforts. Asian countries, like Japan and South Korea, along with various European nations, are at the forefront of advancements in mycological strain development and cultivation innovations while extensively incorporating their products into nutraceuticals and functional foods. Although China has made notable progress in fungal strain selection and cultivation optimization, its investments in the SEEF industry encounter challenges related to inconsistent product quality and inadequate standardization [17]. The absence of robust quality control systems leads to variability concerning selenium content, which hinders industrial advancement. Consequently, establishing unified industry standards alongside implementing comprehensive quality traceability mechanisms has emerged as an essential driver for enhancing the sector’s performance.

2. Main Acquisition Routes of Selenium-Enriched Products

In nature, inorganic selenium exists in four distinct oxidation states: selenate, selenite, elemental selenium, and selenides. The redox potentials of these forms decrease sequentially. Various biological systems are capable of converting these inorganic forms of selenium into more bioavailable organic compounds, primarily two selenoamino acids: selenocysteine (SeCys) and selenomethionine (SeMet). Humans, plants, and microorganisms can synthesize selenium-containing proteins by incorporating these selenoamino acids into their protein structures [17]. The primary acquisition routes of selenium-enriched products can be categorized into two technical systems: artificial synthesis and biotransformation [18].

2.1. Artificial Synthesis Technology System

The artificial synthesis method enables researchers to effectively prepare organic selenium compounds, such as SeMet and SeCys, through specific chemical reaction pathways. This is accomplished via the directed conversion of inorganic selenium sources, including Se(IV) or Se(VI). These processes further facilitate the synthesis of high-value-added products, including selenium-enriched linoleic acid and selenium-enriched lipopolysaccharides. The resultant synthetic products exhibit significant application potential within the healthcare sector [19]. The essence of this technology lies in achieving the morphological directional regulation of selenium by exercising precise control over reaction parameters—including temperature, pH value, and catalyst types—characterized by a multi-step precision reaction cascade system. Nevertheless, owing to the complexity associated with process flows, stringent requirements regarding reaction conditions, as well as rigorous equipment and technical specifications, this method encounters various technical bottlenecks. Among these are elevated production costs and substantial challenges concerning industrialization [20].

2.2. Biotransformation Technology System

The biotransformation approach facilitates the conversion of inorganic selenium into organic forms via biological metabolic pathways, with two primary technical routes: phytotransformation and microbial transformation. In comparison to chemical synthesis, this method presents several advantages, including environmental sustainability, manageable costs, and enhanced bioactivity of the resulting products. As such, it is positioned as a pivotal research avenue in the development of selenium-enriched products [21].

2.2.1. Phytotransformation Pathway

Phytotransformation facilitates the organic incorporation of selenium in plants through intrinsic physiological mechanisms, operating under two primary modes: soil-based application (the addition of inorganic selenium fertilizers to the soil for root uptake) and foliar spraying (the direct application of selenium fertilizers onto plant leaves). Research indicates that this technological approach not only significantly augments crop selenium levels but also optimizes nutritional profiles while mitigating risks associated with heavy metal contamination [22].

An enhancement in crop quality via selenium fertilization has been corroborated by numerous studies. In rice cultivation, a foliar application rate of 75 g per hectare has been shown to not only increase yield but also markedly elevate the selenium content, reduce concentrations of heavy metals, such as mercury, lead, and cadmium, and improve overall rice quality and food safety [23]. In vegetable production, gradient experiments have demonstrated that foliar applications of Se(IV) can enhance the levels of selenium, vitamin C, amino acids, and other nutritional indicators in lettuce and cucumbers while simultaneously boosting yield and nutritional value [24]. Significant advancements have been achieved in the development of selenium-rich agricultural products within low-selenium tea gardens. The use of Se(IV) has elevated the selenium content in tea from 0.096 micrograms per gram to 1.14 micrograms per gram, with organic forms accounting for 81.82% [25]. Animal experimentation suggests that selenium-enriched tea improves phagocytic activity in rat cells, supporting its potential role as a functional food source. A precise regulatory system governing the selenium content in vegetables such as broccoli has also been established [26]. It was observed that foliar supplementation with selenium resulted in a linear increase in both total and organic selenium contents; additionally, the relationship between exogenous selenium concentration and vegetable-derived selenium content was quantified. Research reveals the dual effects of selenium on lead-stressed pea seedlings: concentrations below 1.0 mg/L can enhance organic selenium content and mitigate lead toxicity, while at 10.0 mg/L, the interaction between selenium and lead exacerbates plant toxicity [27]. These findings underscore the necessity for stringent standards in agricultural selenium application to strike a balance between nutritional enhancement and ecological safety, thereby ensuring both crop quality and environmental protection.

2.2.2. Microbial Transformation Pathway

Microbial transformation technology achieves the efficient conversion of inorganic selenium into organic selenium compounds through the metabolic activities of microorganisms, such as bacteria and fungi [28]. This process leverages microorganisms’ strong reducing capacity to transform inorganic selenium (e.g., Se(VI), Se(IV)) into bioactive organic forms, like SeCys and SeMet. Notably, yeast demonstrates exceptional selenium tolerance and accumulation capacity, enabling the intracellular storage of high-concentration selenium. Research indicates that utilizing ammonium chloride as a nitrogen source while maintaining a pH level of 5.5 leads to optimal biomass production and selenium accumulation levels [29,30]. As a result, selenium-enriched yeast has become a crucial carrier in food and feed biofortification, effectively enhancing dietary selenium intake [31].

In the field of selenium-rich microbial research, a study indicated that Lactobacillus paracasei strains ML13 and CH135 achieved selenium accumulation levels of 19 mg/g and 23 mg/g, respectively, in a medium containing 60 mg/L of selenium. When the selenium concentration was increased to 150 mg/L, their enrichment efficiency significantly rose to 40.7 mg/g, confirming the excellent selenium adaptability of these strains [32]. Research focusing on functional applications found that selenium-enriched Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus exhibited a 1.5-fold enhancement in inhibiting foodborne pathogens, such as Salmonella and Escherichia coli, compared to conventional strains [33]. These findings not only reveal the application value of selenium-rich microorganisms in food preservation and safety control but also provide innovative ideas for developing new biological preservatives. As a key component of microbial transformation systems, edible fungi demonstrate unique advantages in the process of selenium biotransformation. The synergistic action between their multienzyme systems and metabolic networks enables efficient conversion from the inorganic to organic forms of selenium while exhibiting remarkable tolerance and accumulation capacity for this element. Research has shown that among four types of edible mushrooms, Ganoderma lucidum exhibits particularly outstanding selenium accumulation efficiency, 10 to 20 times greater than Flammulina velutipes, L. edodes, and Hericium erinaceus [34]. In experiments focused on cultivating shiitake mushrooms with enhanced selenium content, it was confirmed that adding Se(IV) at a level of 10 mg/kg could elevate the selenium content in fruiting bodies to 225.13 mg/kg [35]. Compared with plant-based methods for enhancing selenium concentrations, fungal cultivation systems present three significant advantages: first, they achieve operational efficiency through precise substrate-mediated regulation of the selenium gradient; second, standardized cultivation protocols ensure predictability regarding production cycles; and third, increased resource allocation efficiency along with reduced soil pollution contribute to environmental sustainability [36,37]. These advantages position edible fungi as ideal biological carriers for transforming various forms of selenium while simultaneously providing essential nutrients and potential therapeutic effects along with improved sensory characteristics. Silva’s research (Silva et al. 2010, [38]) further confirmed that Se(IV) impacts P. ostreatus cultivation. Low concentrations of Se significantly enhanced mycelium growth; however, this effect was diminished or may disappear at high concentrations. Exogenous selenium notably reduced the fruiting period of Pleurotus ostreatus and improved biological efficiency, but it also affected fruiting body differentiation, leading to smaller caps and thicker stems. Research has shown that a selenium-enriched matrix was developed by utilizing the derivatives of selenium-enriched rice straw. This method not only increases the selenium content but also improves the flavor characteristics and nutritional components simultaneously [39]. Currently, the international academic community primarily employs substrate fortification strategies for achieving a biological enhancement in selenium. This involves precisely adding inorganic (Se(IV)), Se(VI)), organic (SeMet), nano-selenium, or high-selenium agricultural by-products (e.g., high-selenium wheat/straw) into growing substrates combined with accurately controlled artificial cultivation systems [40]. This technological approach achieves an optimal balance between economic feasibility and process controllability, thereby facilitating the large-scale production of functional selenium-enriched mushroom products via robust technical pathways.

3. Multiple Biological Functions of SEEF

Selenium significantly enhances the antioxidant capacity of edible fungi. Adding selenium during L. edodes cultivation not only accelerates mycelial growth but also improves resistance to bacterial invasion and elevates antioxidant activity, thereby increasing adaptability to adverse environments [41]. Selenium-bound polysaccharides from Pleurotus pulmonarius exhibit synergistic free radical scavenging effects, effectively mitigating oxidative stress damage and delaying the aging process [42]. Additionally, SEEF demonstrate remarkable heavy metal detoxification properties: selenium-enriched L. edodes reduces lead accumulation in rats, alleviating lead-induced toxicity [43]; selenium-enriched Agrocybe cylindracea mitigates arsenic-induced immunotoxicity in mouse macrophages [44]; and selenium-enriched Stropharia rugosoannulata counters cadmium-induced inhibition of mycelial growth and biomass by activating antioxidant enzymes (e.g., glutathione peroxidase (GPX), glutathione reductase (GR), and glutathione S-transferase (GST)) while promoting osmotic regulators, such as proline and soluble proteins [45].

The anticancer efficacy of SEEF primarily stems from the synergistic effects of selenium polysaccharides (e.g., from L. edodes and Ganoderma lucidum) and selenoproteins. These compounds act through dual pathways: enhancing immune responses by activating macrophage phagocytosis and inhibiting tumor progression by inducing cancer cell apoptosis and suppressing proliferation (e.g., blocking T-lymphocyte activity) [46,47]. Research has demonstrated that selenium polysaccharides from L. edodes mycelia possess potent anticancer properties. Additionally, polysaccharides enriched with selenium derived from G. lucidum have been shown to reduce breast cancer incidence by modulating gene expression, promoting apoptosis, and halting cell cycle progression [48]. Furthermore, selenium-enriched Hericium erinaceus contributes to disease resistance and enhances tolerance to radiotherapy and chemotherapy by increasing the production of immunoglobulins, leukocyte counts, and lymphocyte transformation, all of which serve to inhibit cancer cell growth. Importantly, L. edodes-derived selenium polysaccharides also suppress abnormal T-lymphocyte proliferation while protecting normal cells through antioxidant stress mechanisms [49]. This provides novel molecular insights for cancer prevention.

4. Absorption and Conversion Mechanism of Selenium by Edible Fungi

In edible fungi, selenium exists in two primary forms: inorganic and organic selenium. Inorganic selenium encompasses elemental selenium (Se), selenite (Se(IV)), and selenate (Se(VI)), which are characterized by higher toxicity and lower bioavailability. Conversely, organic selenium includes low-molecular-weight compounds such as SeCys, SeMet, and dimethyl selenide (DMSe), as well as macromolecules like selenoenzymes and selenoproteins [50]. Compared to their inorganic counterparts, organic Se exhibits significantly reduced toxicity while possessing multifunctional physiological properties, including antioxidant and immunomodulatory activities. The distribution of the various speciation forms of organic selenium directly influences both the nutritional value and food safety of edible fungi [51].

The mechanisms by which microorganisms, including edible fungi, absorb and transform selenium fundamentally differ from those found in plants. These microorganisms achieve efficient conversion through unique metabolic networks that do not rely on chloroplasts. The absorption and transport mechanisms of Se vary among different microbial species. For instance, in yeast, Se(VI) undergoes a multi-step enzymatic reduction process: it is first catalyzed by ATP sulfurylase to form APSe, which is then converted to PAPSe before being reduced to Se(IV) through the activity of reductases, ultimately yielding H₂Se. The absorption of Se(IV) is influenced by phosphate concentration: low concentrations engage the high-affinity transporter Pho84p, whereas higher concentrations utilize lower-affinity transporters such as Pho87p [52,53,54,55,56,57]. Bacteria primarily absorb Se(VI) or Se(IV) via the sulfate ABC transport system or specialized transport proteins (e.g., gutS, YbaT). In edible fungi, functional groups, such as thiol and amino groups present on the cell wall, facilitate selenium enrichment through biosorption. For instance, in selenium-enriched P. ostreatus, approximately 56% of the selenium accumulates within the cell wall. Additionally, ion channels and transport proteins—including phosphate and sulfate transporters—play critical roles in transmembrane selenium transport; their absorption efficiency is modulated by environmental factors such as temperature, pH levels, and carbon sources [58,59,60,61].

The metabolic process of Se in edible fungi primarily comprises three key steps: reduction and assimilation, methylation, and biosynthesis. The mechanism by which exogenous Se(VI) is reduced to selenide (Se²⁻) is similar to that observed in yeast. These selenide ions are then converted into selenocysteine (SeCys) via the action of selenocysteine synthase. SeCys undergoes further transformation into SeMet through the trans-sulfuration pathway (Figure 1). Ultimately, SeMet may be incorporated into selenoproteins to participate in functional metabolism or may be methylated to yield volatile methylselenide compounds, such as dimethyl selenide (DMSe) [62]. Importantly, metabolic pathways vary markedly among fungal species. For instance, Agaricus brasiliensis and Pleurotus eryngii predominantly utilize Se(VI) reduction pathways mediated by selenium reductase. In contrast, L. edodes and Tricholoma matsutake rely on selenium methyltransferase for methylselenium synthesis. This strain-specific metabolic divergence may correlate with genetic backgrounds, environmental adaptability, and functional requirements [63,64].

To elucidate the distribution and functionality of organic selenium in edible fungi, multi-omics approaches have been systematically applied. Transcriptome sequencing revealed a total of 1036 differentially expressed genes in Se-enriched Flammulina velutipes, comprising 987 up-regulated genes and 49 down-regulated genes. These genes were associated with 20 metabolic pathways. Notably, sulfur metabolism and ABC transporters displayed significant correlations with selenium metabolism [65]. Furthermore, genome sequencing of G. lucidum indicated that Se predominantly contributes to the synthesis of selenium-containing amino acids (such as SeMet, SeCys, and MSeCys) [66], while the biosynthetic pathways for Se polysaccharides and other Se-containing compounds warrant further investigation. Research has demonstrated that organic Se may accumulate within edible fungi cells through mechanisms such as transport proteins, ion channels, and hydrogen sulfide reactions [67,68]. The transport and accumulation mechanisms for Se are species-specific and exhibit heterogeneity [69]; they are influenced collectively by cellular signal transduction pathways, gene regulation processes, and environmental factors [70]. The intricate regulatory network concerning these mechanisms necessitates additional exploration. Remarkably, edible fungi demonstrate significantly higher absorption efficiency for organic versus inorganic Se [71]. It is hypothesized that SeMet may be actively absorbed via aquaporins, ion channels, or methionine transporters; however, this hypothesis demands experimental validation.

It is important that the concentration of selenium is strictly regulated within an appropriate range. Elevated levels of selenium can yield a plethora of adverse effects on edible fungi. Firstly, excessive selenium may disrupt normal physiological functions at the cellular level, inhibiting mycelial growth and resulting in morphological abnormalities of fruiting bodies, ultimately leading to reductions in both yield and quality. Secondly, selenium has the potential to compromise the integrity of cell membranes and organelles, thereby impairing processes related to substance transport and energy metabolism. Furthermore, selenium can bind to enzymes or interfere with their synthesis and degradation mechanisms, diminishing enzyme activity and disrupting metabolic pathways. Lastly, elevated selenium concentrations can initiate oxidative stress responses that generate significant amounts of reactive oxygen species (ROS), which subsequently damage biological macromolecules within cells, severely impeding the normal growth and development of edible fungi.

5. Main Influencing Factors of Selenium Enrichment in Edible Fungi

The Se enrichment effect of edible fungi is regulated by multiple factors, including strain characteristics, types of Se sources, selenium application methods, concentration, growth stages, and environmental conditions.

5.1. Influence of Selenium Source Types and Addition Concentrations

The Se enrichment effect of edible fungi is closely linked to the types and concentrations of Se sources used. There are significant differences in the bioavailability and conversion efficiency among various selenium sources. For instance, during the cultivation of Auricularia auricula, when nano-Se (0–250 mg/kg) is added, the Se content in the fruiting bodies varies between 0.03 and 85.7 mg/kg. Conversely, using Se(IV) as a Se source can result in a maximum Se content reaching up to 100 mg/kg [72,73]. The impact of Se concentration on enrichment demonstrates a pattern, whereby low concentrations promote accumulation, while high concentrations inhibit it. Specifically, for F. velutipes, when the substrate’s Se concentration is less than 300 mg/kg, increasing this concentration leads to higher levels of Se in the fruiting bodies; however, once this threshold is surpassed, accumulation decreases [74]. Additionally, spraying nano-Se onto Pleurotus pulmonarius reveals that a concentration of 5 mg/L enhances growth, while concentrations ranging from 6.7 to 40 mg/L diminish biological efficacy [75]. Moreover, the type of selenium source used directly affects the composition of the selenium forms in fungi (

Table 1. Absorption and transformation of selenium by representative edible fungi.

Types of Edible Fungi	Methods of Selenium Application	Selenium Source	Selenium Concentration in the Culture Medium	Selenium Content in Fruiting Bodies (mg/kg)	Main Composition of Selenium Forms; Content of Organic Selenium (mg/kg); Conversion Rate of Organic Selenium (%)	References
H. erinaceus	/	Sodium selenite	12 mg/L	/	0.9837	[80]
P. pulmonarius	/	Sodium selenite	55 mg/kg	2.812	/	[81]
S. rugosoannulata	/	Sodium selenite	150 mg/L	4727.68	96.27%	[82]
A. auricula	/	Biological nano-selenium	0~250 mg/kg	0.03~85.70	/	[83]
	/	Sodium selenite	250 mg/kg	>100	/	[83]
G. lucidum	/	Sodium selenite	1~15 mmol/L	28~73	1	[84]
A. aegerita	/	Sodium selenite	1~15 mmol/L	12~34	0.84	[84]
A. blazei	/	/	/	9.15	SeCys2 (5.734), MeSeCy (1.84), SeMet (0.22)	[85]
	/	Selenium-enriched yeast	/	3	/	[86]
P. ostreatus	Mixing with the cultivation material	Sodium selenite	/	267.6	SeMet, SeCys2, Se(IV),	[87]
	Soaking	Sodium selenite	/	/	Se(IV)	[88]
L. edodes	Irrigation	Sodium selenite	/	/	MeSeCys, SeCys, SeMet	[89]
	Soaking	Sodium selenate	/	174.5	SeMet, Se(IV)	[87]
F. velutipes	Mixing with the cultivation material	Sodium selenite	5 mg/kg	132	/	[90]
	Mixing with the cultivation material	Selenium-enriched yeast	/	/	MeSeCys, SeCys2, SeMet, Se(IV)	[91]
A. bisporus	Mixing with the cultivation material	Sodium selenite	/	/		[92]
	Spraying	Sodium selenite	10~40 mg/kg	12.2~415	MeSeCys, SeCys2, SeMet	[77]
	Irrigation	Sodium selenite	10~40 mg/kg	798	MeSeCys, SeCys2, SeMet	[92,93]

). For example, when selenite (Se(IV)) is utilized for treatment, the predominant selenium compounds identified in L. edodes, A. bisporus, and Hericium erinaceus are SeMet and MeSeCys. Conversely, in C. militaris, selenocystine (SeCys₂) and SeMet are the primary forms present [76,77,78,79].

5.2. Types of Edible Fungi and Selenium Metabolism Specificity

Edible fungi exhibit remarkable species-specific characteristics in Se metabolism, particularly evidenced by their selenium absorption and conversion efficiency, as well as their preferences for organic Se speciation. Research has demonstrated that under a treatment condition of 12 mg/L of Se(IV), the total Se content in the fruiting bodies of Hericium erinaceus can reach up to 139.1 mg/kg, with an organic selenium conversion rate as high as 98.37% [94,95,96]. In contrast, when the culture medium contains 55 mg/kg of selenium, Pleurotus eryngii accumulates only 2.812 mg/kg [97,98]. This significant disparity arises from strain-specific variations in Se uptake efficiency, reductase activity, and methylation capacity—factors potentially linked to genetic backgrounds and metabolic regulatory networks.

With regard to organic Se speciation, distinct biochemical preferences are evident among various species. L. edodes and Hericium erinaceus predominantly accumulate SeMet and MeSeCys; Agaricus bisporus additionally synthesizes SeCys₂ besides these two forms; and Cordyceps militaris preferentially incorporates both SeCys₂ and SeMet [76,77,78,79]. These specificities reflect significant divergences across edible fungi regarding the key biochemical nodes involved in Se metabolism, including reduction pathways, methylation mechanisms, and protein incorporation processes. The differential evolution of these metabolic pathways may represent crucial adaptive strategies for fungi thriving in diverse ecological environments.

5.3. Regulatory Effects of Selenium Application Methods on Selenium Speciation

The method of selenium application, which includes substrate addition and fruiting body spraying, significantly influences the distribution of selenium forms as well as their biological transformation efficiency. For instance, in L. edodes, when subjected to Se(IV) immersion treatment, primarily Se(IV), SeMet, and SeCys₂ were detected. In contrast, during irrigation treatment, in addition to the aforementioned forms, MeSeCys was also produced [88]. In A. bisporus, mixing substrates promotes the accumulation of Se(IV) and SeCys₂, whereas fruiting body spraying enhances the biosynthesis of SeMet and MeSeCys [99]. Notably, while irrigation treatments may yield similar Se speciation profiles in both L. edodes and A. bisporus [77,89], their underlying metabolic mechanisms likely exhibit strain-dependent variations.

Methodological limitations and advantages coexist within these approaches. Spraying allows for the direct deposition of selenium onto fruiting bodies; however, it encounters challenges related to bioavailability due to inefficient cuticular penetration. Conversely, substrate supplementation facilitates sustained Se enrichment through mycelial absorption but necessitates careful optimization of the selenium dosage to prevent growth inhibition. For example, Pleurotus pulmonarius achieves an equilibrium between biomass yield and Se accumulation at a concentration of 55 mg/kg substrate Se [100], underscoring the critical balance between Se fortification and fungal viability.

5.4. Differences in Growth Stages and Parts of Fruiting Bodies

The efficiency of Se absorption and conversion by edible fungi varies across different growth stages and within various parts of the fruiting bodies. During the mycelium stage, characterized by high metabolic activity, the efficiency of Se conversion is particularly favorable. For instance, the mycelium of F. velutipes can convert approximately 70% of inorganic Se into organic forms [101]. In the fruiting body development stage, while the overall absorption increases, the conversion efficiency may decline due to energy allocation prioritizing growth processes. Moreover, the Se distribution within different parts of the fruiting bodies is uneven. For example, L. edodes exhibits a higher Se content in its gills compared to its caps and stalks [102]. Likewise, P. ostreatus displays significantly greater Se levels in its caps (25 μg/g) than in its stalks (10 μg/g) [103]. This disparity in distribution could be attributed to factors such as tissue metabolic activity, variations in Se-binding protein localization, or spatial specificity within their transport systems.

6. Concluding Remarks and Future Perspectives

Se is a vital trace micronutrient—particularly in its organic forms—that plays an indispensable role in enhancing immune function, augmenting antioxidant activity, and inhibiting the proliferation of cancer cells. Edible fungi, recognized as optimal carriers for Se transformation, face three primary challenges in the efficient conversion of inorganic Se to its organic counterparts.

Firstly, the mechanisms that govern the absorption and transportation of Se in edible fungi remain insufficiently understood. The interactions involving multiple pathways—such as sulfur metabolism and redox regulation—remain ambiguous. Furthermore, there is a noticeable lack of quantitative research addressing the synergistic or antagonistic effects between environmental factors (including temperature, humidity, light, etc.) and selenium metabolism. Critical scientific issues that necessitate resolution include variations in conversion efficiency among different sources of Se, metabolic regulatory targets, and human bioavailability.

Secondly, the existing studies are hindered by an absence of standardized evaluation systems, which complicates comparisons of Se enrichment data across diverse experimental conditions. It is imperative to establish a multi-dimensional evaluation model that encompasses environmental parameters, characteristics of fungal strains, and analyses of Se speciation. This framework should be integrated with advanced sensing technologies and artificial intelligence algorithms to facilitate dynamic regulation of Se supplementation, precise monitoring throughout the growth cycle, and optimization of processing techniques—all aimed at facilitating the transfer of laboratory results into scalable industrial practices.

Lastly, production norms and quality standards for Se-enriched edible fungi are not yet fully developed. Although China has established certain agricultural industry standards for Se-enriched products, such as “Se-enriched Tea” and “Se-enriched Garlic”, these standards exhibit limited coverage. Consequently, this results in significant fluctuations in Se content while posing challenges to product safety assurance. Therefore, it is vital to establish comprehensive guidelines that effectively address these gaps.

To promote the sustainable development of the Se-enriched edible fungi industry, a tripartite strategy involving fundamental research, technological advancement, and standardization is essential. Fundamental research should combine genomics, proteomics, and metabolomics to identify key genes and protein networks in Se metabolism. In vitro simulation systems can measure how environmental factors, like temperature and humidity, affect Se transformation, laying the groundwork for precision enrichment. Regarding technology, integrating intelligent sensors with AI models allows for real-time monitoring of selenium levels while optimizing cultivation parameters to ensure consistent quality and safety. Standardization requires collaboration among governments, enterprises, and research institutions. Governments must establish regulatory frameworks for Se content and labeling standards. Enterprises are responsible for implementing standardized protocols and utilizing blockchain technology for traceability. Research institutions should focus on developing cost-effective enrichment technologies. Educating consumers about the benefits and safety of Se-enriched products is crucial for building market confidence. Through interdisciplinary collaboration between policy initiatives and market dynamics, the industry can transition from experience-based practices to data-driven innovation, enhancing global nutritional solutions.