A Review of Nature-Based Solutions for Valorizing Aromatic Plants’ Lignocellulosic Waste Through Oyster Mushroom Cultivation

Abstract

A creative, nature-based way to solve environmental issues and promote sustainable development could be the cultivation of Pleurotus spp. mushrooms to use the lignocellulosic waste from Medicinal and Aromatic Plants (MAPs). Pleurotus species are characterized by flexibility and biodegradative capacities to generate bioactive compounds with antibacterial, antioxidant, and nutraceutical properties using lignocellulosic substrates. Aromatic plant residues, such as those from lavender, sage, and mint, can improve the resultant mushrooms’ metabolic profiles and act as nutrient-rich substrates. Higher levels of phenols, flavonoids, and terpenoids can be among these enhancements, which could make mushrooms useful as functional foods. This strategy could provide scalable and affordable waste management solutions by utilizing already existing agricultural systems, including mushroom cultivation, during slow times. Incorporating Pleurotus-based systems can help to produce renewable bio-based products, reduce pollution, and improve soil health. This study not only attempts to demonstrate how Pleurotus species may convert industrial and agricultural waste into valuable, bioactive products, reducing waste and promoting ecological remediation in a circular economy, but also to highlight the viability of using natural processes for economic and environmental sustainability. To exploit the potential of this nature-based approach, future research should concentrate on maximizing substrate consumption, scaling these solutions to industrial levels, and guaranteeing regulatory compliance.

1. Introduction

The mushroom genus Pleurotus is the second most important in the world market and one of the most consumed worldwide. Among fungi belonging to this genus are Basidiomycota, known as “white rot fungi” [1]. They form white mycelium and are usually grown on non-composted lignocellulosic substrates. Several species of Pleurotus are commercially cultivated and of great economic importance, including P. ostreatus (Jacq.) P. Kumm. (oyster mushroom), P. eryngii (DC.) Quél. (king oyster or Cardoncello), P. pulmonarius (Fr.) Quél. (phoenix mushroom), P. djamor (Rumph. ex Fr.) Boedijn (pink oyster mushroom), P. sajor-caju (Fr.) Singer (Indian oyster), P. cystidiosus O.K. Mill. (abalone oyster), P. citrinopileatus Singer (golden oyster mushroom), and P. cornucopiae (Paulet) Quél. [1]. Medicinal and Aromatic Plants (MAPs) are vital for people’s health and well-being and provide many products [2]. Although herbs contain valuable substances, they are often disposed of by stacking, landfilling, or burning, which results in severe environmental pollution, increased greenhouse gas emissions, and the spread of pathogenic microorganisms [2]. The circular economy has the potential to become an effective method of managing lignocellulosic herb waste, and some of the most effective agents for the biodegradation of such organic waste are fungi. Circular economy strategies are increasingly recognized as sustainable options for replacing traditional linear production systems, especially in sectors that generate high levels of organic waste [3,4]. One of the major issues in this context is the use of lignocellulosic residues, particularly agricultural and industrially processed residues of medicinal and aromatic plants. They are rich in cellulose, hemicellulose, and lignin concentrations and are typically underutilized or lost, although they are high-potential renewable resources [5]. The cultivation of fungi, and specifically those species belonging to the Pleurotus genus, offers a novel and environmentally friendly method of valorizing such residues. Thanks to their lignocellulolytic enzyme systems, oyster mushrooms can break down recalcitrant plant polymers and convert waste substrates into value-added edible biomass [6,7]. This bioconversion process conforms to the principles of the circular economy by reducing environmental burdens, enabling the reuse of waste, and delivering inputs for sustainable food systems [8].

This review presents a handy checklist of the intrinsic and extrinsic factors affecting the cultivation of mushrooms of Pleurotus spp. on aromatic plants’ lignocellulosic waste. The information here will be useful to researchers, practitioners, and industry professionals in agriculture, food production, and other allied fields.

2. Methodology

The present review was created by collecting the required information from different databases, including ScienceDirect, Springer Link, PubMed, Scopus, and Google Scholar. The strategy for this review depended on gathering information from different databases during certain periods, especially during the last 10 years, to obtain the latest information. To obtain the required information, we selected the suitable keywords, which we inserted into the website of each database. The main keywords used were “waste of medicinal aromatic plants, Oyster mushrooms cultivation, Pleurotus species health food, Pleurotus species nutritional properties, herbs and lignocellulosic waste, and circular economy, novel substrates for mushrooms production, Pleurotus species growth on the waste of aromatic and medical plants”. Then we selected suitable literature based on two criteria: publication in high-impact journals and recent publication (with a preference for publications in the period 2020–2024).

3. Overview of Aromatic Plant Industries

3.1. Kinds of Products, Market Trends, and Legislation

Within the European Union (EU), MAPs are primarily utilized in the pharmaceutical and perfumery industries for their medicinal or aromatic properties [9]. The applications can be summarized as follows: essential oils, pharmaceuticals, herbal health products, dyes and colorants, cosmetics, personal care products, plant protection products, and intermediates for further processing [9,10].

The cost of raw plant materials exhibits wide variations, influenced by numerous factors. For both pharmaceutical and cosmetic natural ingredients, prices are affected by quality and economic considerations. Moreover, documentation providing traceability and certification details, such as Fair Trade or organic certification, can also impact pricing, as can whether plants are cultivated or collected in the wild [2]. In the cosmetics sector, the price of raw materials often correlates directly with the quantity used in the final product [11].

The prices of essential oils on the open market exhibit considerable variation, often reflecting the large quantities of plant material required for oil extraction. For instance, producing 1 kg of rose oil requires 4000 kg of rose petals [11,12]. Furthermore, different essential oils can be obtained from the same plant material.

As for the latest market trends, there is a growing interest in products that improve cognitive functions [11]. Another sought-after category comprises products designed to alleviate stress and fatigue, with sustained popularity anticipated [13,14]. The Centre for the Promotion of Imports (CBI) market survey on natural ingredients for pharmaceuticals in the EU [11] identifies specific ingredients increasingly favored for product innovations and pharmaceutical applications. Overall, demand for natural ingredients in cosmetics is rising [11], driven by consumer preference for products containing naturally derived ingredients, particularly those offering functional benefits.

Legislation within the European Union primarily governs the cultivation of aromatic plants within broader agricultural and environmental frameworks. The most important regulations and directives impacting aromatic plant cultivation include Regulation (EU) No 1307/2013 [15], Regulation (EC) No 178/2002 [16], Directive 2009/128/EC [17], Regulation (EU) No 528/2012 [18], Directive 2006/118/EC [19], and Regulation (EU) No 1143/2014 [20], addressing aspects such as food safety, environmental protection, product quality, and international trade. Furthermore, compliance with European food safety standards for aromatic plants grown in the EU, control of pesticide residues, monitoring of contaminants, and labeling of food products are mandatory. Environmental standards dictate sustainable water resource use and the reduction of agricultural environmental impacts. Quality and authenticity standards may also apply, either through specific regulations or voluntary certification schemes. The EU can negotiate trade agreements and implement measures to regulate aromatic plant import/export, ensuring compliance with phytosanitary and quality standards. Financial and technical support may be extended to aromatic plant farmers through rural development programs and agricultural policies, with an overarching goal of promoting sustainable practices, product safety, quality assurance, and facilitating international trade while upholding environmental standards and consumer rights (https://agriculture.ec.europa.eu/international/agricultural-trade/wto-and-eu-agriculture_en, accessed on 15 January 2025).

In Italian legislation, the consolidated text on medicinal plants [21] defines medicinal plants and prescribes a list of species to be cultivated by decree, identifying their unique botanical and pharmacological characteristics. Currently, the cultivation and initial processing of aromatic plants are unregulated activities, requiring authorization only in the advanced processing stages. However, regulations govern aromatic plant processing, including procedures like drying and essential oil extraction, and manufacturing-derived products such as herbal teas, spices, and cosmetics. Marketing aspects such as labeling, packaging, advertising, and sales are also regulated to ensure consumer protection and fair-trade standards compliance. Italian legislation establishes quality standards for aromatic plants, covering variety selection, cultivation and harvesting methods, chemical composition, and sensory attributes. Safety and health regulations set maximum residue limits for pesticides and contaminants, along with requirements for Good Agricultural and Collection Practices (GACPs) and Good Manufacturing Practices (GMPs). Italian laws align with international standards governing aromatic plant import/export, fostering trade relations with other nations.

In this context, it is important to consider how economically viable it is to grow essential oil crops in Italy. Thanks to its lovely Mediterranean climate, Italy provides the perfect environment for cultivating various aromatic plants rich in essential oils [22,23]. Some of the most promising crops include Lavandula angustifolia Miller (lavender), Rosmarinus officinalis L. (rosemary), Salvia officinalis L. (sage), and Mentha x piperita L. (peppermint) [24,25]. These plants have shown they can thrive even in less-than-ideal soils. They are backed by regional and EU-funded rural development programs that promote sustainable and organic farming practices [26,27].

While Italy only accounts for a small portion of the global essential oil market—about 1–2% for lavender oil and under 1% for peppermint oil—Italian products are highly sought after in niche, high-value markets [28,29]. Their popularity stems from organic certification, stringent quality standards, and traceability, which are especially important in the cosmetics, pharmaceutical, and wellness industries. Consequently, essential oil crops present a financially appealing opportunity for small and medium-sized farms in Italy looking to diversify their production and boost their income.

3.2. Lignocellulosic Waste Management

While containing valuable substances, herb residues are typically disposed of through stacking, landfilling, or burning, leading to significant environmental pollution, contributing to greenhouse gas emissions, and promoting the proliferation of pathogenic microorganisms [2,11,30].

Circular economic principles offer a sustainable solution. They aim to eliminate waste by transitioning from a linear model of resource use to a circular (regenerative) model, where materials are reused whenever possible [9,31].

In the 21st century, society and industry are increasingly focused on reducing residues and recovering valuable bioactive components [32]. Traditional and novel approaches are being employed to valorize this residual biomass of MAPs, with technological advancements driving innovation.

Residual biomass refers to any biological material not deliberately produced in a production process, generated as a by-product that may or may not be considered waste [33]. The agricultural and industrial sectors based on MAPs generate various solid and liquid residues, including distillation residues from aromatic plants and unused portions of medicinal plants.

The non-utilized portions of medicinal plants, the herbal biomass sector, and the essential oil industry distillation biomass make up the majority of aromatic waste biomass [11]. Cellulose (35–40%), hemicellulose (25–30%), and lignin (15–20%) are the main components of aromatic wasted biomass [9,34]. Rich in polyphenols and other bioactive substances, this leftover biomass can be used to make products that promote health [35]. The remaining biomass can be used to create value-added products like compost, charcoal, biofuel, biogas, and biopesticides after bioactive chemicals have been extracted [36].

Residues from agricultural waste, including residual biomass from MAPs, present a potential alternative for wastewater remediation. MAP residue can be an effective biosorbent for removing toxic compounds like metals and dyes from water [37]. Distillation biomass from plants like Mentha and lemongrass has demonstrated potential for sorbing heavy metals and dyes [38,39], owing to lingo-cellulosic materials capable of binding metal ions and dyes. The residual fiber can be used as animal feed after extracting bioactive compounds and essential oils from MAPs [37].

Lignocellulosic biomass can also be useful to produce renewable fuels. For example, ethanol production from lemongrass biomass has been successful, with lemongrass bio-oil showing potential as a renewable fuel [40,41]. Fungal conversion of cellulose and hemicelluloses from lavender and lavandin-distilled straws into fermentable sugars offers a route to obtain fuel-grade ethanol [42].

Waste biomass from MAP industries rich in organic matter can serve as soil amendments, aiding soil health improvement and promoting organic and integrated farming practices [43].

Because of their versatility in fuel and chemical synthesis, bio-based fuels like ethanol are increasingly in demand. Biomass recalcitrance can be overcome by steam distillation, which makes it possible to turn biomass into ethanol [44]. The use of MAP waste for biofuel production and co-product commercialization is encouraged, offering a nature-based solution for waste disposal in the herbal sector while minimizing pollution. Studies have demonstrated that delignified bioprocessing of residual biomass from MAPs can result in the synthesis of cellulase enzymes, reducing enzyme production costs [9].

4. Oyster Mushroom Potentiality in Biodegradation of Organic Waste: A Nature-Based Solution

Oyster mushrooms represent a relatively low return on investment and are thus considered low-value mushrooms. Other, higher value mushrooms include the shiitake (Lentinula edodes (Berk.) Pegler), maitake (Grifola frondosa (Dicks.) Gray), and truffles (Tuber spp.), which ensure higher returns due to their higher prices in the market, longer shelf life, and increased demand in gourmet and medicinal markets [8,45]. Special cultivation techniques for mushrooms of higher value include specific substrate or growing conditions and long growth cycles. This involves cultivating shiitake on hardwood logs or supplemented sawdust blocks and needs several months for fruiting. Truffles, meanwhile, involve symbiotic interactions with trees as their hosts and hence take some years to mature [8]. That just raises their value when sold, though it calls for putting a considerable investment in place.

However, several studies included in the literature comparison involve shiitake, which is often used as a benchmark species. Shiitake is one of the most widely cultivated edible mushrooms globally, following Agaricus bisporus and Pleurotus ostreatus, and is known for its high nutritional and medicinal value [46,47,48]. Because of its established market and biological efficiency, shiitake is frequently used in comparative studies to evaluate the performance of other species, including Pleurotus, particularly in terms of growth rate, yield, and bioactive compound accumulation on lignocellulosic waste substrates [49]. Its inclusion in these studies serves to highlight the potential of Pleurotus spp. species as sustainable alternatives in similar production models using agricultural and aromatic plant residues.

Oyster mushrooms represent an easily accessible entry point for small-scale farmers and entrepreneurs into the mushroom industry, while other, higher-value species might require more significant initial investments, special growing techniques, and longer cultivation cycles to become profitable.

Pleurotus mushrooms, of which more than 200 species are used worldwide, are grown for food and medicine and thrive on many lignocellulosic substrates [50]. Numerous nutritional, biotechnological, and medicinal qualities define Pleurotus mushrooms, which provide inexpensive industrial solutions to environmental problems [51]. These include the manufacture of enzymes, the creation of biomass from fruit waste, the production of bioethanol, the biodegradation of pollutants, and therapeutic qualities. Rich in polysaccharides, fatty acids, and steroids, Pleurotus species produce bioactive molecules and are widely used as functional foods [52,53]. Additionally, many Pleurotus species are disease and pest resistant and thrive in a variety of environments. [52,53]. Because they produce ligninolytic enzymes, Pleurotus species can colonize and break down different lignocellulosic wastes [54]. Using organic agricultural waste-based substrates such as sawdust and rice bran, oyster mushroom cultivation becomes an economical endeavor [31,55,56,57,58]. Its multiple fruiting capabilities (5–6 times within 120 days) and short harvesting cycle (28–35 days) further increase its allure [23]. For example, Pleurotus ostreatus exhibits mycoremediation capability for several contaminants, such as pharmaceuticals, industrial wastes, petroleum solid wastes, and chlorinated insecticides [51]. With the help of potent enzymes, including laccase, lignin peroxidase, and manganese peroxidase [16,55], Pleurotus mushrooms effectively bioremediate contaminated surroundings through mycodegradation and biosorption processes [54].

In summary, the utilization of fungi, particularly Pleurotus species, holds significant promise in driving the circular economy. It offers nature-based solutions for waste valorization, bioconversion, and environmental remediation.

5. Critical Aspects of Oyster Mushroom Cultivation on Lignocellulosic Aromatic Plants’ Waste

The cultivation of saprotrophic macrofungi depends on the specific needs of the species being grown, the facilities and technologies used, and the purpose of the cultivation, whether for scientific research, medical uses, or food production. These elements need careful consideration before starting the cultivation process. Typically, cultivating saprotrophic macrofungi involves six key stages: (1) isolation; (2) substrate preparation; (3) inoculation; (4) incubation; (5) cultivation; and (6) harvesting and transformation.

5.1. Isolation

Isolating fungal mycelium in axenic culture is a vital step in cultivating macrofungal species. For common varieties like Pleurotus, commercial mycelial cultures can be easily obtained from specialized mushroom producers or agro-industrial suppliers. However, for specific scientific purposes—such as molecular, biochemical, or comparative strain studies—mycelium must be isolated directly from fresh wild sporomata in sterile conditions. This process requires careful sampling of mycelial tissue under strict sterile protocols, usually performed in a laminar flow hood.

Common nutrient media for fungal isolation include Potato Dextrose Agar (PDA), Malt Extract Agar (MEA), and Oatmeal Agar (OA), with preparation instructions widely accessible in the mycological literature [59].

The isolation procedure for fresh sporomata involves several important steps: i. collecting healthy sporomata, making sure to avoid any specimens that show signs of damage from pests or disease; ii. extracting a small sample of mycelium from the inner tissues; iii. placing the sample onto an agarized nutrient medium, such as PDA, MEA, or OA; iv. incubating the sample at around 24 °C (the optimal temperature for the Pleurotus spp.) and checking daily for any signs of contamination; v. preserving the pure mycelium on agar slants at 4 °C or using long-term preservation methods [59].

Long-term preservation of fungal strains is crucial for both mycological research and industrial applications. Recent advancements in preservation technology have greatly improved the viability and longevity of fungal cultures [60]. However, preserving macrofungal mycelia can be challenging due to their lack of resistant structures. Protocols for ultra-low temperature preservation, such as storing at −80 °C for white-rot fungi [61] and truffles [62], or at −120 °C for Ganoderma lucidum (Fr.) P. Karst. [63] have been developed and refined, offering valuable methods for conserving strains in fungal culture banks. The long-term preservation of Pleurotus mycelium is crucial for maintaining genetic stability, ensuring consistent production, and facilitating research. Various methods have been developed to achieve effective conservation while minimizing the risk of genetic drift, contamination, and loss of viability [60]. The most employed techniques include cryopreservation, lyophilization, mineral oil overlay, and storage on solid or liquid media under refrigeration [60]. The choice of conservation method depends on factors such as available resources, intended use, and required storage duration. Cryopreservation is the most effective for long-term genetic stability, while simpler methods such as refrigerated agar slants or mineral oil overlay provide viable short-term alternatives for routine use [60]. Regular viability testing and maintenance practices are essential to ensure the successful long-term preservation of Pleurotus mycelium.

5.2. Substrate Preparation, Inoculation, and Incubation

The preparation of the substrate is crucial for successful macrofungal cultivation. As early as 1904, Minge Duggar [64] pointed out how substrate composition affects the colonization dynamics, mycelial structure, and sporomata development of fungi. It is essential to customize substrates to fulfill the nutritional needs of the target species. Recent studies [65,66] have shown that the substrate’s characteristics directly impact mycelia’s physicochemical properties, which could have significant implications for the creation of biomaterials [67].

Ideal substrates should offer a balanced nutrient profile, suitable moisture levels, and a consistent, compact yet aerated structure, preferably with a high surface-to-volume ratio. Sufficient water activity is vital to activate hydrolytic and oxidative enzymes, promoting metabolic activity and mycelial colonization [59].

Typically, substrates are packed in heat-resistant plastic bags and sterilized using autoclaving. Spawn can be prepared on various substrates, such as grains, bran, cereals, sawdust, and wood shavings, ensuring appropriate inoculation rates and environmental conditions for effective fungal growth. After sterilization, proper aseptic techniques are crucial to introduce spawn and kickstart colonization.

This careful approach guarantees optimal growth conditions, facilitating efficient fungal development and achieving the desired outcomes in experimental and production environments.

5.2.1. Medicinal Plant-Based Substrates: Pre-Treatment Protocols

Cultivation of Pleurotus mushrooms on lignocellulosic aromatic waste involves several critical aspects that must be judiciously monitored for maximum growth and yield [1]. Lignocellulosic aromatic waste, generated from agricultural residues and industrial by-products, contains complex organic compounds that may affect fungal growth and enzymatic activity. Their degradation demands proper fungal strains and optimized cultivation techniques. This concerns substrate preparation, inoculation, and environmental control as key factors.

The use of substrates from the waste of medicinal plants offers special advantages over conventional lignocellulosic biomass, such as wheat straw, rice bran, or sawdust. Medicinal plant residues often contain bioactive compounds, secondary metabolites, and enhanced antimicrobial properties, which can positively influence mushroom growth and nutritional composition [68].

In detail, residues from medicinal plants may contain higher levels of bioactive compounds like flavonoids, phenolics, and alkaloids that enhance the medicinal properties of the mushrooms harvested [69]. Certain medicinal plant substrates have inherent antimicrobial properties that will reduce the risk of contamination compared to conventional substrates [70,71]. Moreover, medicinal plants, due to their complex phytochemical composition, are degraded at a slow rate, which includes the need for different pre-treatment strategies [72,73]. However, unlike wheat straw and sawdust, which are widely available, medicinal plant residues may be more expensive and region specific [73].

Despite these advantages, substrates from medicinal plants can pose several challenges, including the variability in their composition, possible residual pesticides, and the need for specific pre-treatment protocols to optimize nutrient availability for fungal growth. Among the well-known pre-treatment protocols are the following: i. grinding and sieving—breaking down plant materials to increase surface area and ensure uniform particle size distribution; ii. soaking—hydrating the substrate in water or nutrient-rich solutions to improve digestibility and leach out inhibitory compounds; iii. fermentation—pre-treatment through microbial fermentation to partially degrade complex compounds and enhance bioavailability; iv. alkaline treatment—involving the use of lime or sodium hydroxide to depolymerize lignin and facilitate fungal enzyme access; and v. steam explosion—a high-pressure treatment that disrupts plant cell walls, making the polysaccharides more amenable to fungal metabolism [74,75,76]. These pre-treatment protocols are employed to overcome problems in the complex phytochemical matrix of medicinal plant residues, thereby improving fungal colonization and nutrient uptake.

Additionally, proper substrate treatment is necessary for eliminating competing microorganisms and improving bioavailability. Conventional methods are i. sterilization, wherein autoclaving at 121 °C for 15–30 min ensures complete eradication of microbes; ii. pasteurization, where heating of the substrate is conducted at 60–80 °C for several hours to reduce microbial load with preservation of helpful microbes; and iii. chemical application of lime or hydrogen peroxide to repress contaminants and promote fungal colonization [1].

5.2.2. Inoculation and Incubation

Successful inoculation dictates quick colonization of the substrate and minimizes the chances of contamination. Some of the key parameters are (1) spawn quality, high-quality actively growing spawn is used for heavy mycelial expansion, (2) inoculation rate, usually 5–10% of the weight of the substrate for quicker colonization, and (3) aseptic techniques, sterile conditions to be maintained during inoculation to avoid contamination [1].

For mycelial growth and fruiting body development, optimum environmental conditions should be maintained. The most important parameters include the following: temperature, the optimum temperature range is 20–25 °C for colonization and 15–20 °C for fruiting; relatively high humidity of 85–95% to avoid desiccation and to stimulate fruiting; air exchange must be provided to remove CO₂ and provide fresh oxygen; and light exposure—for initiating primordia formation, indirect light (500–1000 lux) is required [77,78]. Sudden changes in these conditions can significantly lower yields or, in extreme cases, lead to total crop failure. To enhance the cultivation environment, it is crucial to consider the specific needs of the species, the chosen cultivation method, and the local climate conditions.

5.3. Cultivation Systems

Cultivation systems can be divided into three categories based on the level of environmental control. The first is Free/Open-Field Cultivation: substrates are placed in natural or semi-natural settings that mimic the species’ natural growth conditions [77,79]. Environmental factors are not regulated, leading to growth, ripening, and harvesting cycles that closely follow natural seasonal patterns. The second system is Semi-Controlled Cultivation: this method employs partially protected environments like greenhouses, shaded structures, or cultivation tunnels [77,79]. While some environmental factors (such as temperature and humidity) are monitored and somewhat regulated, the system remains affected by external conditions. This approach often prolongs the fruiting and harvesting period beyond the limits of natural seasons. The last method is Controlled Management Cultivation: in this carefully regulated environment, substrates are placed in incubation chambers or growth cells, where every environmental factor—such as temperature, humidity, light, and ventilation—can be finely tuned [77,79]. This precise control enables cyclic fruiting and harvesting, regardless of natural or seasonal changes. It is essential to maintain stable environmental conditions that meet the specific physiological needs of the species for successful fruiting and consistent yields. Controlled systems provide the benefit of dependable and ongoing production, though they come with increased technological and operational expenses.

6. Oyster Mushroom vs. Aromatic Plant Lignocellulosic Waste: Feasibility and Economic Advantages

Agro-industrial wastes involve residues resulting from agricultural and industrial activities and have found successful use as growth substrates in mushroom cultivation. Many of these wastes have low nitrogen content, a crucial factor for mushroom growth. The protein content in mushroom fruiting bodies depends on the C–N ratio of substrates, their chemical composition, and the cultivated mushroom species [80,81]. Mushrooms of the Pleurotus genus can be cultivated on various phenolic wastes and lignocellulosic substrates, utilizing their complex enzymatic system with applications in the beverage and food industry [82].

The activity of lignocellulolytic enzymes can be regulated by fermentation parameters such as temperature, air composition, C–N ratio, pH, and medium composition [80,81,82]. Depending on the substrate, the ideal C–N ratio for Pleurotus ostreatus culture has been observed to range from 45 to 60:1 [80,81,82]. Solid residues high in lignin, hemicellulose, cellulose, minerals, carbon, and phenolic chemicals are produced during the lavender extraction process. These residues are often discarded, leading to environmental concerns. A study by Atila and Cetin [83] investigated the cultivation of Pleurotus eryngii var. ferulae (Lanzi) Sacc. using a growing medium comprising poplar sawdust (PS), lavender straw (LS), and lavender extraction waste (LFW). The experimental design included seven different substrate formulations. The highest yield (216.3 ± 6.4 g/kg) and biological efficiency (61.8 ± 1.8%) were recorded in the substrate composed of PS, LS, and LFW in a 5:3:2 ratio. In contrast, the most favorable nutritional and antioxidant profiles were obtained from the medium composed of PS and LS in a 7:3 ratio.

Various agricultural by-products rich in phenols, such as olive press waste, green walnut husks, tea wastes, and coffee pulp have been identified [10,84,85]. While their high polyphenol content may pose risks to soil and flora, using these wastes as mushroom cultivation substrates offers ecological, environmental, and economic benefits [86]. Pleurotus sajor-caju (Fr.) Singer has been shown to eliminate tannin in the coffee-spent ground, demonstrating its potential for phenol degradation [86]. It was determined that tannin content (79.2%) and caffeine content (60.7%) were decreased in the substrate after cultivation [86]. Semenova et al. [10] explored cultivating edible basidiomycetes on lavender, sage, mint, and rose wastes, yielding enriched fodder products with proteins and vitamins. According to their results, the content of the sulfur-containing amino acid methionine in the biomass of the studied strains is 0.31–0.35% (in terms of protein in champignon—0.9%, in shiitake—1.6%, in oyster mushroom—1.2–1.3%). Significant increases in the protein content during the bioconversion of all the studied types of solid waste by at least 1.4 times were found in this study.

Studies by Omarini et al. [87], Mandeel et al. [57], and Sharma et al. [50] further underscore the potential of utilizing waste from the essential oil industry and various organic substrates for mushroom cultivation. For example, Omarini et al. [87] showed that Pleurotus ostreatus onset was observed after 3 days on lavender-derived agro-industrial waste and wheat straw, and 5 days on essential oil waste. However, essential oil waste substrate resulted in lower biological efficiency, likely due to antifungal compounds present in essential oil residues. This highlights the versatility of mushrooms like Pleurotus in utilizing diverse waste streams for biomass production.

Feasibility and Economic Benefits of the Process

Pleurotus spp. mushrooms hold significant economic importance as the third-largest mushroom species. The infrastructure requirements for cultivating Pleurotus mushrooms are minimal, making them an attractive option for utilizing agricultural wastes as substrates [53].

The minimal infrastructure required for the efficient cultivation of Pleurotus fungi can enable the establishment of specific areas for waste biodegradation and the production of fungi directly in situ within farms. This latter possibility significantly reduces ex situ biomass transport costs.

Studies by Mandeel et al. [57], Di Piazza et al. [88], and Sharma et al. [50] demonstrate the feasibility and benefits of using agricultural residues in mushroom cultivation. Mandeel et al. [57] found that Pleurotus columbinus Quél. and Pleurotus ostreatus showed superior biological efficiency compared to Pleurotus sajor-caju when grown on cardboard and paper substrates. Di Piazza et al. [88] cultivated Pleurotus ostreatus on solid waste from lavender production, yielding mushrooms with biochemical profiles containing antioxidant and pharmacological properties. Sharma et al. [50] reported high biological efficiency in Pleurotus floridanus Singer cultivated on substrates such as rice straw and wheat straw supplemented with rice bran and in Pleurotus ostreatus supplemented with lavender and barley straw. The highest biological efficiency was observed in the case of rosagrass, with 32.8%, followed by wheat straw, lemongrass, and Java citronella with 25.3%, 21.6%, and 18%, respectively. In addition to this, a high amount of the minerals zinc (97 ± 0.6 mg/kg), manganese (11 ± 0.2 mg/kg), and copper (18 ± 0.2 mg/kg) were observed in the fruiting bodies of mushrooms obtained from Java citronella as compared to the control [50].

These studies highlight the potential of utilizing agricultural wastes as substrates for mushroom cultivation, offering economic benefits and opportunities for waste reduction and recycling. Further research and optimization of cultivation methods using agricultural residues can contribute to sustainable farming practices and enhance the efficiency and profitability of mushroom production.

To achieve full productive maturity, it is considered essential to first assess the product’s compliance with regulatory standards, particularly focusing on the authorization process as a novel food. Additionally, it is necessary to address and optimize technical aspects of the production process that are critical for ensuring efficiency and economic sustainability. Specifically, (1) determine the optimal cultivation area for mushrooms, considering that the structures required are relatively simple and intended for seasonal use, particularly during the months of March to October, without requiring disassembly between cycles.; (2) establish organizational procedures for the production of substrates, with a focus on assessing the optimal shape and size of the substrate blocks to maximize their performance; (3) development of a protocol for substrate utilization based on the available equipment within the facility; (4) economic evaluation of the production activities related to substrate creation, particularly consideration of the possibility of outsourcing production to specialized third parties, and identification of any necessary authorization processes for the commercial production of substrate blocks.

Based on the unpublished data collected in the framework of the FINNOVER PROJECT (Interreg, France-Italy ALCOTRA, founded by European Commission—https://www.interreg-alcotra.eu/it/finnover-strategie-innovative-lo-sviluppo-di-filiere-verdi-transfrontaliere, accessed on 15 January 2025), Di Piazza and Zotti proposed a production model that can seamlessly integrate into the floriculture business by utilizing existing spaces during periods of reduced activity.

The assumptions of the proposal are summarized in the following cycle (Figure 1).

The figure emphasizes how a relatively low-complexity cultivation infrastructure (such as the ombraio) can support mushroom production from agro-industrial waste. It also represents graphically the potential of Pleurotus cultivation embedded in circular economy systems, converting lavender waste into high-value food and soil amendments.

The figure depicts an entire and replicable cycle of production from waste to harvest.

Thanks to the FINNOVER PROJECT, Di Piazza and Zotti also proposed a theoretically projected income statement. The primary cost drivers are expected to be labor expenses, particularly given the assumption that bag production will occur in-house. They estimated the labor demand, with the most substantial effort projected to be from bag preparation. Additionally, estimates have been made for the labor requirements associated with sales activities, including market attendance and transportation logistics. The costs of the process are listed in

Table 1. Schematic list of the fungal production costs extracted from data from the FINNOVER PROJECT (2019–2022). Regarding the estimated costs, depreciation values are presented in the table referring to the new values and the quota utilized. The shading structure has been valued at EUR 1.500 when new and depreciated in 20 years (5%); the land where the shading structure is placed is owned. The processing facility has been supposed to be owned and valued at EUR 10.000 (50 sqm * EUR 200/sqm), depreciated at 3%. The value of the equipment serving both the processing facility and the shading structure was estimated to be EUR 3000, with a depreciation of 12.5%. Equipment for the packaging of products and pallets costs EUR 2000 with a depreciation of 9%. A van used for the transport of products to the market has a new value assumed at EUR 16,000 depreciable in 10 years. The annual utilization rate was fixed at 20% for the activity with mushrooms. Such a vehicle may be used at the same time for other farms’ purposes. The packaging system is estimated at EUR 5000 and depreciated at 12.5%. The cold storage unit was valued at EUR 3000 and depreciated at 12.5%. The shading structure covers a small area; hence, remuneration of the land capital has been considered at only EUR 25. The total costs for two production cycles are EUR 8545. A relatively low average selling price of EUR 2 per kg has been assumed, and the total revenues exceed EUR 9000. At this price too, the business is profitable with remarkable figures for both gross and net income.

Costs	Unit of Measurement	Amount	Unit Cost	Tot	Variable Costs	Express Costs
Cost of plastic bags and inoculum	Number	1.805	0.15	270.78	X	x
Purchases of various means, boxes, and minute tools	Estimation	1	200.00	200.00	X	x
Insurances	Estimate—breakdown from total company	1	50.00	50.00	X	x
Tax consulting	Estimate—breakdown from total company	1	50.00	50.00	X	x
Membership costs	Estimate—breakdown from total company	1	50.00	50.00		x
Waste disposal costs (plastic wrap)	Estimate—breakdown from total company	1	50.00	50.00	X	x
Fuels for the marketing of the product	Estimation	1	100.00	100.00	X	x
Electricity for a packaging machine, fans, and refrigerator	Estimation	1	300.00	300.00	X	x
Plastic maintenance and renewal	Estimation	1	200.00	200.00	X	x
Waged labor	Hours	120	14.00	1680.00	X	x
Entrepreneur labor and family	Hours	218	14.00	3052.00	X	x
Taxes and contributions	Estimate—breakdown from total company	1	50.00	50.00		x
Land capital depreciation (wood shade)	Calculated quotas	1	75.00	75.00		x
Processing room depreciation	Calculated quotas	1	300.00	300.00		x
Depreciation of electrical and similar equipment	Calculated quotas	1	375.00	375.00		x
Depreciation of pallets and structures for processing/conditioning	Calculated quotas	1	180.00	180.00		x
Transport van depreciation	Calculated quotas	1	320.00	320.00		x
Bag wrapping machine depreciation	Calculated quotas	1	625.00	625.00		x
Cold storage depreciation	Calculated quotas	1	375.00	375.00		x
Directional work of the entrepreneur	Hours	8	18.00	144.00		x
Interests	Computation			73.77	X	x
Land capital cost	Estimation	1	25.00	25.00
Total Costs				8545.44
Aggregation of Cost Items				Tot
Total attrition factors				470.68
Other costs				800.00
Partial attrition factors				2250.00
Waged labor				1680.00
Labor entrepreneur and family				3052.00
Directional work of the entrepreneur				144.00
Taxes				50.00
Interests				73.77
Land capital cost				25.00
TOTAL COSTS				8545.44
Variable costs				6026.44
Express costs				5004.44
Revenue by Product Type	Unit of Measure	Total Product in kg (2 Cycles)	Price in Euro/KG	Total
Fungi, 2 cycles	kg	4511.28	2.00	9022.56
Total Income or Plv.				9022.56
Results				Total
Gross income = revenue—variable costs				2996.11
Net income = revenue—explicit costs				4018.11
Profit = revenue—total costs				477.11

.

7. Oyster Mushrooms with High Nutritional Value

Because of their nutritional worth and possible health advantages, edible mushrooms have long been used as food. Because of their low calorie and fat content, high protein, mineral, and dietary fiber content, and availability of vital nutrients including vitamins, amino acids, and fatty acids, mushrooms—especially Pleurotus species—are acknowledged as healthful meals [89]. According to studies, Pleurotus mushrooms are nutrient-dense and may even be medicinal due to their numerous bioactive components, including anti-inflammatory, antioxidant, antiviral, antibacterial, and immunomodulatory qualities [90].

Oyster mushrooms (Pleurotus spp.) cultivated on lignocellulosic waste derived from aromatic plants offer a unique combination of nutritional and medicinal properties. Aromatic plant residues, such as those from lavender, rosemary, and mint, contain bioactive compounds like polyphenols, flavonoids, and essential oils, which can enhance the functional properties of the mushrooms [88,91]. These bioactive compounds are known for their antioxidant, antimicrobial, and anti-inflammatory properties, potentially augmenting the health benefits of the cultivated mushrooms.

Recent studies have shown that mushrooms grown on substrates rich in aromatic compounds exhibit higher levels of bioactive secondary metabolites, such as ergothioneine, polysaccharides, and beta-glucans, which contribute to immune modulation and oxidative stress reduction [88,92,93]. Additionally, the absorption of phenolic compounds from the substrate may enhance the mushrooms’ anti-cancer and neuroprotective effects, making them a valuable dietary supplement for promoting overall health [94].

Moreover, mushrooms cultivated on aromatic plant waste have been reported to possess enhanced antimicrobial activity, which can be attributed to the residual essential oils present in the substrate [94,95]. This unique property makes them an excellent functional food with potential applications in preventing bacterial and fungal infections.

Furthermore, the cultivation of oyster mushrooms on such substrates contributes to sustainable agricultural practices by utilizing plant residues that would otherwise be discarded, promoting environmental conservation while producing nutraceutical-rich food sources [94,95].

These benefits are well-documented in many studies [50,58,87,88]. Aromatic plant wastes improved the sensory qualities of mushrooms, influencing elements including color, flavor, and texture, according to Omarini et al. [87]. Di Piazza et al. [88] demonstrated that lavender-enriched substrates boosted the secondary metabolism of mushrooms, producing chemicals that are not normally present in the primary metabolomic pattern of the fungi. According to Sharma et al. [50], mushrooms grown on aromatic crop distillation wastes showed higher concentrations of vital elements, including copper, manganese, and zinc, than those grown on conventional substrates, suggesting they may have immune-boosting qualities.

These investigations highlight the possibility of using herbal substrates and agricultural waste to improve the nutritional value, bioactivity, and therapeutic potential of mushrooms, hence aiding in the creation of functional meals with extra health advantages. Additional investigation in this field may result in the improvement of farming methods and the creation of novel products derived from mushrooms that enhance human health and welfare.

8. Composition and Potential Applications of Spent Substrates

After mushroom harvest, the spent substrate still contains substantial residual nutrients and organic matter, hence, it is a valuable by-product with various potential applications. The general composition of the spent substrate includes partially degraded lignocellulose, fungal biomass, a diverse microbial community, and residual nutrients such as nitrogen, phosphorus, and potassium [96,97]. These components are useful in various industries, from agriculture to bioenergy production.

Among all the uses of the spent substrate, it is very well utilized as a soil amendment [97]. It helps in the structure, water retention, and nutrient supply of the soil due to its organic matter and diverse microbial population, and thereby facilitates plant growth, improving soil health. The fiber-rich composition in the spent substrate also makes it an adequate candidate for use as supplementary animal feed; it adds useful roughage and other nutrients to livestock [96,98].

Within the bioenergy realm, it has been realized that spent mushroom substrate could act as a good feedstock for biofuels. Due to the residual carbohydrate it contains, it can be anaerobically digested into biogas or utilized in the production of bioethanol [97,98]. What is more, the spent substrate can be composted into high-quality organic fertilizer, further enhancing its sustainability credentials. Another promising avenue is its application in bioremediation, whereby microbial communities within the substrate can help degrade environmental pollutants and contribute toward ecosystem restoration [99,100].

9. Conclusions and Future Trends

Production of Pleurotus spp. on the lignocellulosic waste of aromatic plants is a concrete demonstration of the circular economy, with a sustainable model of bioconversion and value recovery of agro-industrial residues. Apart from waste valorization, the process can yield nutritionally and functionally improved edible mushrooms, with advantages to environmental mitigation and human health.

This review points out the promising aspect of incorporating oyster mushroom cultivation into present agricultural systems, particularly those that involve the production of aromatic plants, using their residues as substrates. Minimal infrastructure is needed in the process, which is economically viable and easily implementable at the local or regional levels.

To advance this field, future studies should be aimed at standardizing substrate compositions, optimizing cultivation techniques, and elucidating biochemical processes associated with waste degradation and the enrichment of bioactive compounds. Harmonization of these processes with food safety procedures and scalability testing for industrial applications will also be critical to commercialization.

Overall, Pleurotus spp. bioconversion of aromatic plant waste offers a replicable and promising model of sustainable food production and environmental robustness—a path that is in line with broader sustainability goals and promotes innovation in circular bioeconomy strategies.