A comprehensive review of the application of ultrasonication in the production and processing of edible mushrooms: Drying, extraction of bioactive compounds, and post-harvest preservation

Graphical abstract

Highlights

• •Ultrasonic technology facilitates the production and processing of edible mushroom.
• •The use of ultrasonic technology extends the shelf life of mushrooms.
• •Extensive ultrasonic application to edible mushrooms was overviewed.
• •Ultrasonic pre-treatment promotes the formation of high quality dried mushrooms.

Abstract

Edible mushrooms are high in nutrients, low in calories, and contain bioactive substances; thus, they are a valuable food source. However, the high moisture content of edible mushrooms not only restricts their storage and transportation after harvesting, but also leads to a shorter processable cycle, production and processing limitations, and a high risk of deterioration. In recent years, ultrasonic technology has been widely applied to various food production operations, including product cleaning, post-harvest preservation, freezing and thawing, emulsifying, and drying. This paper reviews applications of ultrasonic technology in the production and processing of edible mushrooms in recent years. The effects of ultrasonic technology on the drying, extraction of bioactive substances, post-harvest preservation, shelf life/preservation, freezing and thawing, and frying of edible mushrooms are discussed. In summary, the application of ultrasonic technology in the edible mushroom industry has a positive effect and promotes the development of this industry.

1. Introduction

Edible mushrooms are macrofungi with a high nutritional and medicinal value [1]. China is rich in edible mushroom resources and is also a major producer and consumer of edible mushrooms [2]. According to FAO statistics in 2021, the annual production of mushrooms in the world reached 44.97 million tons in that year, while the annual production of mushrooms in China reached 44.13 million tons [3]. Because of their unique flavor and taste, edible mushrooms are considered an integral part of gourmet cuisine as well as a culinary additive. Edible mushrooms are also a source of physiologically active compounds that have antibacterial, antioxidant, anti-hypercholesterolemic, anti-inflammatory, antiviral, antidiabetic, and cardiovascular benefits [4], [5]. For instance, as a dietary supplement, Flammulina velutipes has a positive effect on reducing high blood pressure, cholesterol, and blood sugar [4]. Over the past few years, mushrooms have been used in various products including bread [6], edible fungus protein meat production [7], mushroom pies [8], mushroom mixed meat burgers [9], and many more. In addition, because of the multiple functional properties of mushrooms, their extracts are also widely used in the medical industry. In particular, edible mushroom polysaccharides can be used for tumor immunotherapy [10] and anticancer [11] applications.

Edible mushrooms have a short post-harvest shelf life because of their high moisture content and the lack of a hard outer protective layer [12]. In addition, mushrooms are not only subject to mechanical damage during the harvesting process, but also to microbial contamination, browning, and lignification after harvesting [13]. Therefore, various processing methods such as drying, cooling, freezing, coating [14], washing with antibacterial agents, applying ozone and electrolyzed water, packing, irradiation, pulsed electric field, and ultrasonic treatment are often used to ensure the quality of mushrooms [15]. Traditional processing techniques, such as hot air drying, are simple and inexpensive but take a long time and the quality of the finished product is poor [16], [17]. Freeze-drying yields a high-quality product but is costly and energy-intensive [18]. Irradiation reduces browning but also leads to changes in the chemical composition of mushrooms [19]. Modified atmosphere packaging and cooling also have a negative impact on the quality of mushrooms [20]. Traditional processing technology is unable to meet the growing consumer demand for high-quality food [21]. Thus, to overcome the limitations of traditional processing techniques, novel processing technology is necessary.

Ultrasonication is a non-thermal processing technology that is increasingly used in the food industry because of its low cost, ease of use, and lack of need for external chemical reagents or additives for operation [22], [23]. Ultrasonication can be used for food drying/dehydration [24], food processing [25], post-harvest preservation of fruits and vegetables [26], and freeze-drying pre-treatment [27]. Ultrasonication can also aid in the freezing and thawing of food to reduce the damage to nutrients and improve quality [26]. The use of ultrasonication in the post-harvest management of fruits and vegetables can extend the post-harvest storage period and maintain the physical and chemical characteristics of the product, particularly when ultrasonication is combined with other preservation technologies [23]. Ultrasonic pretreatment increased the drying rate and improved the quality of strawberry slices [28], dry-cured yak meat [29], sweet potato slices [30], kiwifruit [31], and edible mushrooms [15]. In addition, ultrasonic technology is also used in extraction, cleaning, emulsification, homogenization, and crystallization [32].

Therefore, this paper reviews the basic principle behind ultrasonic technology and its application to the production and processing of edible mushrooms (e.g., drying, nutrient extraction, preservation, and thawing).

2. Edible mushrooms

2.1. Nutritional value of edible mushrooms

Edible mushrooms not only have a unique flavor and a high nutritional value but also a low fat content, which is desirable by consumers. Edible mushrooms can be divided into wild edible mushrooms and cultivated edible mushrooms. So far, 150,000–160,000 species of edible mushrooms have been recorded [33]. The most common edible wild mushrooms include the black morel (Morchella elata), field mushroom (Agaricus campestris), porcini mushroom (Boletus edulis), enoki (Flamumulina velutipes), and hedgehog mushroom (Hydnum repandum) [34] Only about 100 of these mushroom species are cultivated, and about 60 are widely accepted as food sources, with some of the most common being Lentinus edodes, Agaricus bisporus, Flammulina velutipe [35].

Edible mushrooms are rich in protein [36] (approximately 19 %–35 % on average, which is comparable to or higher than that in meat and similar to that in soybean). They also contain essential amino acids [37] (eight essential amino acids for humans and histidine for infants); the content and composition ratio of essential amino acids in some edible mushrooms are ideal (e.g., A. bisporus, F. velutipes, Tricholoma matsutake, and Pleurotus eryngii). In addition, they contain vitamins (B₁, B₂, B₁₂, C, D, and E) and minerals [38] (potassium, phosphorus, sodium, calcium, and magnesium, as well as essential trace minerals such as copper, zinc, iron, molybdenum, and selenium), while being low in fat (mushrooms are cholesterol-free and rich in unsaturated fatty acids, mainly in the form of linoleic acid) [39]. Edible mushrooms are also an important source of many active substances such as phenolic compounds, tocopherols, ascorbic acid, and carotenoids, which have physiological functions such as promoting human health and regulating human immunity [40].

Furthermore, edible mushrooms have medical applications, in particular, edible mushroom polysaccharides are widely used in medicine and have been researched extensively [41]. Functional polysaccharides have antitumor, anti-inflammatory, antiviral, immunoregulatory, and other bioactivities [42]. Polysaccharides isolated from Volvariella volvacea not only reduced total serum and liver cholesterol in mice but also had a positive impact on health and disease prevention by improving the gut microbial environment [43]. A review by Gong et al. concluded that different fungal polysaccharides have different functional properties. The polysaccharide from Pleurotus eryngii has tumor-inhibition, antioxidant, and bifidogenic formation activities. The polysaccharide from Grifola frondosa has antidiabetic effects. The polysaccharide from Collybia radicata has macrophage immunomodulatory function [35], whereas that from Helvella leucopus may relieve symptoms of hyperlipidemia by reducing weight gain and regulating total cholesterol, triglycerides, and LDL cholesterol in blood [44]. The active component in the polysaccharide from Hypsizygus ulmarius may help reduce oxidative damage in human cells and increase antioxidant levels to hinder the production of reactive oxygen species (ROS) [45]. In addition, the polysaccharides from L. edodes, Ganoderma lucidum, and enoki mushroom have also been researched, developed, and applied in the medical field.

2.2. Production and processing of edible mushrooms

Researchers have developed various mushroom-based products. For example, edible mushrooms can be mixed with flour and used as a meat substitute. Husain H et al. used a mixture of Pleurotus sajor-caju stalks and chickpea flour to replace chicken in chicken nuggets. Although the water content of the finished product was substantially increased, the product had adequate textural properties [46]. The use of Pleurotus eryngii to replace pork fat in the production of pork sausages resulted in finished products with reduced fat content and increased protein, moisture, total dietary fiber, and water-holding capacity. Although the color value was slightly lower than that of the control, the overall final product acceptability was increased [47]. In addition, the use of Agaricus bisporus as a partial fat substitute in the production of beef burgers resulted in improved texture and oxidative stability when the A. bisporus content was 15 % and the fat content was 5 %, making the beef burgers juicier, tenderer, and tastier [48].

Researchers have also investigated people’s preferences for different mushrooms by adding different mushroom powders to make puffed foods. A study showed that puffed foods made with the addition of Phoenix mushrooms (Pleurotus pulmonarius) were more popular with consumers than those made with straw mushrooms (Volvariella volvacea) [6]. Salehi summarized the characteristics of different mushroom powders and their application in baked foods (e.g., bread, cakes, biscuits); the powders were made using mainly Pleurotus sajor-caju, Agaricus bisporus, and Lentinus edodes. The addition of mushroom powder changed the physicochemical and textural properties of baked products. The sensory characteristics of the baked products were optimal when the amount of mushroom powder was 4 %–10 %. Moreover, as the amount of mushroom powder increased, the content of minerals (calcium, potassium, magnesium, phosphorus, iron, copper, zinc, and manganese) also increased [49].

Because of their functional properties, mushroom extracts can also be added to dietary supplements to enhance the body’s immune function, exert anti-inflammatory effects, and other functions. In particular, Ganoderma lucidum, Grifola frondosa, Cordyceps sinensis, and Agaricus blazei are used for this purpose [5]. Furthermore, the mushroom extract can also be added to frozen yogurt, fruit juice, and soybean milk for the production of functional food. Adding 0.1 % Flammulina velutipes extract to frozen whipped cream can delay the growth of ice crystals, thereby preventing the reduction in quality during frozen storage [50]. The addition of Auricularia auricula-judae extract to wheat noodles increased the hardness and stretching distance of the noodles and reduced the cooking loss and cooking yield of the noodles. The secondary structure of the gluten in the noodles containing the mushroom extract was studied and it was found that the addition of the extract increased the β-helix and decreased the α-helix, resulting in a more compact gluten network with starch particles evenly dispersed [51].

3. Ultrasonication

Ultrasonic technology is one of the most widely used non-thermal processing technologies for the “green” chemical industry. In general, the ultrasonic instruments used in the food industry can be divided into two types: water bath ultrasonic and probe-based ultrasonic (Fig. 1). According to the power frequency range, ultrasonic instruments can be divided into high-power/low-frequency (20–100 kHz), medium-power/medium-frequency (100 kHz–1 MHz), and low-power/high-frequency (1–100 MHz) instruments. Ultrasonic technology can be classified into six types based on the different working modes: sweep or fixed frequency, pulse or continuous, multi-frequency or single-frequency, sequential multi-frequency or synchronous multi-frequency, countercurrent circulation or non-forced flow, and contact or non-contact technology [52]. The ultrasonic output causes the surrounding medium to vibrate and then the ultrasonic energy is transmitted to the adjacent material. The effects of ultrasonication on the medium can be divided into thermal, mechanical, and cavitation effects (Fig. 1) [53].Fig. 2.

Fig. 1.

Types of ultrasonic waves and their effects on the medium. (A) Types of ultrasonic waves; (B) ultrasonic cavitation effect; (C) mechanical effects of the ultrasonic wave; (D) ultrasonic thermal effect [15], [62].

Fig. 2.

Ultrasonic extraction of bioactive compounds from edible mushrooms [95].

3.1. Cavitation effect

Ultrasonic waves are transmitted through the ultrasonic bath or ultrasonic probe into an aqueous medium, such as distilled water. Under the ultrasonic action, tiny bubbles are formed in the liquid nucleation, and the bubble nuclei produce oscillation, contraction, and collapse (i.e., the ultrasonic cavitation effect) [52]. The ultrasonic cavitation effect disrupts the cell walls of plant matrices, weakening and disrupting the cell membrane, and facilitating the release of bioactive compounds and their extraction [54], thus promoting the easier release of moisture from products and improving food processing [55]. The ultrasonic cavitation effect mainly includes transient cavitation and steady state cavitation, when the cavitation bubbles filled with gas or steam in the ultrasonic positive and negative pressure under the action of the cycle grow until the expansion to the critical size, when it becomes unstable and implosion occurs, transient cavitation occurs. On the other hand, the bubbles oscillate in a steady manner during the oscillation cycle and the bubble size always maintains a relatively balanced state, which is steady state cavitation. Typically, both types of cavitation bubbles coexist and interact in the ultrasonic field [56].

Cavitation effects can alter chemical processes in a system by increasing the rate of a reaction process or initiating new reaction mechanisms through the formation of various types of free radicals. These free radicals are mainly hydroxyl radicals, which are formed when water is used as a solvent, and the formation of these radicals depends on the type of gas being dissolved. The destruction of water molecules can produce highly reactive free radicals that can alter other molecules, such as proteins [57]. Ultrasonic technology has been shown to have a beneficial effect not only on food tissues and biologically active compounds, but also on other physicochemical factors (e.g. texture and nutrient content) in biological materials. This is due to the cavitation effect of ultrasound leading to cell wall rupture, particle size reduction and increased reaction rates through cell wall mass transfer [27]. In addition, the cavitation mechanism effectively removes highly bound water molecules, facilitating mass transfer during the drying process and reducing drying time to achieve high quality dehydrated products quickly and economically.

3.2. Mechanical effect

The cavitation effect will directly or indirectly cause mechanical and thermal effects, mechanical effect refers to the ultrasonic propagation in the material when the effect occurs. Ultrasonic waves have the characteristics of mechanical waves, itself has a variety of mechanical parameters, such as mass vibration velocity, acceleration, mass displacement amplitude, sound intensity and sound pressure. Ultrasonic energy applied to the medium will cause high speed vibration of the mass, resulting in changes in mechanical quantities such as velocity, acceleration, sound pressure and sound intensity of the media particles, thus producing a mechanical effect that enhances the motion of the particles in the liquid medium. This also accelerates mass-liquid transfer and biological mass transfer processes. The explosion of cavitation bubbles produces a microjet with a velocity of about 110 m/s, which creates a strong mechanical stirring effect between the phase interfaces, breaking the boundaries between the laminar flow boundary layers and can both increase the reaction efficiency by enhancing the interfacial transfer process in food processing and trigger a number of reactions in the organism [58].

Ultrasonic waves cause the medium plasma to oscillate back and forth, so that the medium has a rhythmic change in density. When the sound intensity within a certain range, the elastic vibration produced by biological tissues can cause vibration of the cytoplasm within the cell or organelle, cytoplasmic mobility enhancement, cytoplasmic components of the interaction between the increase in cell metabolism enhancement. When the sound intensity exceeds a certain threshold, the amplitude of the medium plasma exceeds the elastic limit of biological tissues, and the microstructure of biological tissues is strained by the stress, and in severe cases, even fracture. The mechanical effect of ultrasound is accompanied by stirring, atomization, dispersion, impact and other effects. It has a wide range of applications, and can be used for punching, welding, cutting, cleaning, polishing and other processing treatments, as well as dispersing, emulsifying, atomizing, pulverizing, sterilizing and so on.

3.3. Thermal effect

Ultrasound in the propagation process, the medium with the vibration produces strong high-frequency oscillation, the medium internal friction heat, acoustic energy converted into thermal energy to make the medium warming, which is known as ultrasonic thermal effect. In particular, when the ultrasonic penetration characteristic impedance is different between the two media interface, the standing wave generated by reflection aggravates the molecular friction of the medium, and the ultrasonic thermal effect intensifies. In the ultrasonic field, the mass of the medium will be constantly stretched and compressed, so that the compressed part of the medium will produce a temperature rise in the center. In addition, the vibrating cavitation bubbles stir the surrounding liquid to create micro-streaming; and the imploding transient cavitation bubbles can generate localised temperatures and pressures as high as 4,000 K and 1,000 atm, resulting in strong perturbations and shear forces in the cavitation region. This produces localised high temperatures and pressures that denature enzymes and destroy biological cells. The thermal effect takes two forms, one called the continuous wave thermal effect, which is continuous friction and heat absorption over a period of time, and the other called the transient thermal effect, which is the instantaneous high temperature generated by the closure of the cavitation bubbles [56].

The heat generated by the thermal effect of ultrasound is proportional to the intensity of the ultrasound, the absorption coefficient of the medium and the duration of the ultrasound [26]. The more acoustic energy accumulated by the ultrasonic waves in the medium, the more heat is absorbed by the medium. In addition, as the temperature of the liquid medium increases, heat transfer processes occur within the medium, including heat conduction, heat convection and heat radiation [59]. Different substances have different abilities to absorb ultrasound and produce different amounts of heat based on thermal mechanisms. Factors affecting the heat absorption of a medium include the molecular structure of the medium, thermal conductivity and internal friction, which together determine the absorption coefficient of the medium. Different absorption coefficients of media, ultrasound thermal mechanism of different effects. The thermal effect produced by ultrasound can be used in sterilisation, drying and defrosting processes.

4. Application of ultrasonic technology to the production and processing of edible mushrooms

4.1. Application of ultrasonic technology to the drying of edible mushrooms

4.1.1. Ultrasonic pretreatment for drying edible mushrooms

In ultrasonic pretreatment, the sample can be immersed in a liquid, and the ultrasonic wave is propagated in the material with the liquid as the medium [25]. In an airborne ultrasonic method, the ultrasonic wave is transmitted to the product with the air as the medium through the non-contact transducer [58]. The alternating compression and expansion caused by the ultrasonic treatment creates a “sponge effect” that promotes the formation of microchannels in the solid sample, facilitating the migration of moisture from the interior of the sample to the surface and reducing drying time [60]. Secondly, ultrasonic pretreatment bursts air bubbles near the surface of the water, creating a “cavitation effect” that forms microchannels inside the sample, leading to a reduction in surface tension and promoting water removal, thus reducing drying time [61]. Finally, ultrasound destroys the cell wall of the sample, which reduces the diffusion resistance of intracellular moisture and shortens the drying time of the sample. Ultrasonic treatment can promote mass transfer in the drying process of the sample and improve the effective diffusion coefficient of water, thus reducing the drying time of the sample [62]. It improves drying efficiency, reduces energy consumption, increases nutrient retention and yields high quality products [15], [63]. This technology not only improves the limitations of drying alone but also has a positive impact on the dried product. The parameters (power, probe amplitude, time, and frequency) set in the ultrasonic pretreatment have different effects on the drying characteristics and quality of edible mushrooms.

As shown in Table 1, the application of ultrasonic pretreatment for drying edible mushrooms is mainly based on the influence of treatment duration on the mass transfer and nutrient quality of edible mushrooms during the drying process. Li et al. investigated the effects of a pulsed electric field, ultrasonication, and a combined pretreatment on the quality of Lentinus edodes and found that there was no significant difference (p＞0.05) in the total phenolic content of Lentinus edodes samples after ultrasonic pretreatment compared with the control, but there were significant differences in the soluble sugar content and antioxidant activity [15]. By contrast, Shi et al. found that the total phenolic content of shiitake mushroom slices subjected to ultrasonic pretreatment was significantly (p＜0.05) higher than that of the untreated group and the cellulase-treated group [64]. The retention of total phenolic content of edible mushrooms is closely related to the selection of ultrasonic pretreatment parameters and drying conditions, and the selection of appropriate conditions according to different raw materials can effectively improve the retention of total phenolics in edible mushrooms. For example, ultrasonic pretreatment can inhibit the oxidation of phenolic compounds by polyphenol oxidase, thus improving the retention of total phenolic content, but if the ultrasonic pretreatment time is too long, it will result in nutrient loss [62]. Similarly, the choice of ultrasonic power is also very important, in the ultrasonic pretreatment process, too much ultrasonic power will lead to a large number of phenolic degradation, which will lead to a reduction in the total phenolic content of the sample [65]. Another is the drying temperature, e.g. convection drying - the higher the air temperature, the lower the retention of phenolic compounds. Prolonged exposure of the sample to oxygen in the oven can negatively affect the total phenolic content [66]. Secondly, the increase in the number of microbubbles during the ultrasonic pre-treatment leads to the rupture of cell walls and also to the rupture of more bubbles, which in turn generates violent shock waves and high velocity jets. The bonds linking other macromolecular phenolic compounds in the sample are broken, releasing more phenolic compounds, but the increase in temperature during the drying process leads to linear degradation of the polyphenolic compounds, resulting in a decrease in phenolic compounds [67]. Ultrasound-assisted osmotic dehydration improved the osmotic efficiency of A. bisporus, resulting in a substantially higher nutrient content compared to samples treated by osmotic dehydration alone [68]. In addition, ultrasound-assisted osmotic dehydration also affected the mass transfer performance of A. bisporus. The effective diffusion coefficients of water and solid were the highest in the appropriate osmotic solution [69].

Table 1.

Parametric effects of ultrasonic pretreatment on edible mushroom drying.

Edible mushroom species	Pretreatment conditions	Drying method	Main results	Reference
Shiitake mushroom (Lentinula edodes)	Water immersion, f = 28 kHz, P = 600 W, T = 24 ± 1 °C, t = 15 min.	Short- and medium-wave infrared drying; T = 60 °C, P = 1350 W.	The total drying time of the ultrasonically pretreated samples was shortened by 21.43 %, and the dried mushrooms exhibited uniform porous microstructures.	[70]
	Water immersion (1:10), f = 40 kHz, I = 1.63 W/cm2, P = 180 W, t = 30 min.	Hot air drying.	The ultrasonic pretreatment significantly improved the hot air drying rate, maintaining high nutritional quality and good rehydration of mushrooms.	[15]
	Water immersing, f = 25 kHz, P = 240 W, T = 60 °C, t = 5 min.	Freeze-drying.	The ultrasonic pretreatment promoted the redistribution of water in the cell tissue, and the retention rate of total phenolics was high.	[64]
Pleurotus eryngii	Water immersion (1:8), f = 20–25 kHz, P = 650 W, T = 20 °C, t = 20, 40, and 60 min.	Microwave hot-air flow rolling drying.	Ultrasonic treatment for 60 min shortened the drying time of P. eryngii by 30 min; the microstructure of the mushroom was changed and energy consumption was reduced.	[62]
Oudemansiella raphanipes	Water immersion (1:10), P = 200 W, t = 5 min.	Hot air drying, T = 60 and 80 °C.	When drying at 60 °C and 80 °C, the ultrasonic pretreatment shortened the drying time by 20 % and 37.5 %, respectively, and promoted the release of aroma substances.	[96]
Button mushroom (Agaricus bisporus)	Water immersion (1:4), f = 20–25 kHz, T = 25 °C, P = 405, 612 W, t = 10, 20, and 30 min.	Electrohydrodynamic drying, hot air drying.	Increasing the ultrasonic power shortened the total drying time, and increasing the pretreatment time increased the drying speed, especially for hot air drying.	[97]
	Water immersion (1:4), f = 35 kHz, P = 480 W, T = 30 °C, t = 10, 20, and 30 min.	Hot air drying.	After ultrasonic treatment, the phenolic content and color of Lentinus edodes were preserved and the mass transfer during drying was improved.	[98]
	Probe, f = 20 kHz, P = 600 W, t = 3 and 10 min, I = 39–43 W/cm2, water immersion (1:15), f = 40 kHz, t = 3 and 10 min, P = 300 W, I = 0.5 W/cm2.	Hot air drying, T = 60 °C, freeze-drying.	The rehydration performance (weight gain rate) of the freeze-dried samples after ultrasonication was optimal.	[99]
	Water immersion (1:4), f = 40 kHz, T = 25 °C, I = 0.444 W/cm2, t = 3 and 10 min.	Hot air drying, T = 60 °C, v = 0.5 m/s; infrared drying, T = 60 °C, v = 0.6 m/s.	Increased moisture diffusivity and mass transfer coefficient of the dried mushroom flakes.	[100]
	Penetrant immersion (1:10), f = 40 kHz, P = 200 W, T = 30 °C, t = 15, 30, 45, 60, and 70 min.	Osmotic dehydration, glucose (40 %, 50 %, and 60 %, w/w), sucrose (40 %, 50 %, and 60 %, w/w), and sodium chloride (10 %, 15 %, and 20 %, w/w).	All three osmotic agents (sucrose, glucose, and sodium chloride) had a significant effect on the mass transfer of button mushrooms during ultrasound-assisted osmotic dehydration.	[69]
	Penetrant immersion (1:10), f = 40 kHz, P = 200 W, T = 30 °C, t = 45 min.	Osmotic dehydration, sucrose solution (50 %).	The ultrasonically treated samples had significantly (p＜0.05) lower reducing sugars, ascorbic acid, and soluble protein than the control.	[68]
	Water immersion, f = 25 kHz, (1) T = 60 °C, t = 20 min; (2) T = 65 °C, t = 8 min; (3) T = 70 °C, t = 5 min; (4) T = 75 °C, t = 3 min.	Microwave-vacuum drying, P = 481 W, 673 W, and 865 W, vacuum degree: 70 kPa.	The ultrasonic treatment removed 40 %–45 % of the water in the A. bisporus slices, improved the color of the product, and reduced the energy consumption by the drying process.	[71]

Zhao et al. carried out infrared drying of mushroom slices after ultrasonic treatment. The results showed that the drying time of the slices after treatment was significantly (p < 0.05) shortened by 21.43 % compared to that of the untreated samples [70]. Furthermore, Jiang et al. reached similar conclusions about the drying of A. bisporus after ultrasonic pretreatment (i.e., ultrasonic pretreatment improves the drying mass transfer and reduces energy consumption) [71]. Compared with other techniques like the pulsed electric field, the ultrasonic pretreatment has the best effect on the drying of A. bisporus. However, Li et al. obtained contradictory results. Although the mass transfer effect of the ultrasonic pretreatment was better than that of the untreated group, the effective water diffusion coefficient （D_eff） of the drying process was slightly lower than that of the pulsed electric field pretreatment. The D_eff of the ultrasonic pretreatment was 6.9520 ± 0.23, that of the pulsed electric field was 7.3328 ± 0.24, and that of ultrasonication combined with a pulsed electric field was 8.6882 ± 0.14. The effect of the combined pretreatment was significantly (p < 0.05) better than that of the single pretreatment groups. Szadzi et al. demonstrated that a higher ultrasonic power results in faster drying. The average drying speed of the ultrasonic-assisted drying process is not affected by the ambient air temperature and always remains high [66]. However, Francisca et al. found that the drying kinetics of Agaricus bisporus at 15 °C were significantly (p < 0.05) shorter than those at 5 °C and 10 °C. When using ultrasound-assisted drying at those temperatures, the drying time was reduced by 41 %, 57 %, and 66 %, respectively [72]. The ultrasonic technology used to assist in the freeze-drying of edible mushrooms affects the formation of ice nuclei and the average size of the ice crystals so that the quality of the final freeze-dried product is improved. In Carrion’s study, ultrasound-assisted atmospheric pressure freeze-drying of Agaricus bisporus was performed, resulting in a significantly (p < 0.05) shortened drying time compared to the control group. At the same time, the effective water diffusion coefficient obtained from the simulated drying process also showed an increasing trend [73].

4.1.2. Effect of ultrasonication on the nutritional and sensory quality of dried mushrooms

4.1.2.1. Color

The effects of ultrasonication on edible mushrooms are not limited to increasing the effective water diffusion coefficient of the drying process and shortening the drying time but also cause changes to the quality of the finished products. In general, the use of ultrasonic technology has both positive and negative effects on dried mushrooms, and the most intuitive effect is reflected in the color of the dried products. The application of ultrasonic technology has a positive effect on the color retention of the dried mushrooms. This may be explained by the faster drying speed and shorter drying time. A study reported that the untreated mushrooms experienced a longer drying time that promoted the Maillard reaction, resulting in a brown color [15]. By contrast, the use of ultrasonication inhibited enzymatic browning during the drying process, thus preserving the brightness of the final infrared-dried mushrooms. In the study by Shi et al., the mushrooms subjected to ultrasonic pretreatment and drying had the highest brightness [64].

However, if the ultrasonic pretreatment conditions are not properly controlled (e.g., the ultrasonication time is too long), the proportion of pigments in the sample will decrease, resulting in a decrease in the brightness of the dry product [74]. In addition, the thermal effect of ultrasonication on the sample surface will also increase the browning index of the dry sample, resulting in a product with a poor color appearance. Vallespir et al. found that the brightness of dried shiitake mushrooms pretreated by ultrasonic lyophilization under normal pressure also showed this trend. When drying edible mushrooms at a lower temperature (5 °C), the browning index of the product obtained by ultrasound-assisted air drying was higher than that of the control and other air-dried groups. Nevertheless, low-temperature ultrasound-assisted drying does not improve the color of the finished product after drying and may even have a negative effect [72].

4.1.2.2. Texture

Texture is one of the crucial characteristics of dried mushrooms, and is usually based on the crispness and hardness of dry products, or the hardness, cohesiveness, elasticity, and chewability of the mushroom after rehydration. Research has shown that ultrasonically treated dried shiitake mushroom slices have low hardness, high crispness, and good texture. This may be due to the use of ultrasonication, which gives shiitake mushrooms a honeycomb-like structure with numerous large pores that are conducive to the formation of a brittle texture. However, other treatments result in higher hardness and lower crispness of the finished product [30]. The texture of dried edible mushrooms after ultrasonic pretreatment also changes to varying degrees after rehydration. Carrión et al. found that with the increase in the power of the ultrasonic pretreatment, the hardness of the rehydrated mushroom decreased and the sample softened. However, the cohesion and elasticity increased considerably with the increase in ultrasonic power [73]. Similarly, during post-harvest storage, the hardness of the mushrooms (cap and stalk) after ultrasonic pretreatment was higher than that of the control, and the treated mushrooms exhibited the lowest degree of softening [75].

4.1.2.3. Rehydration

Rehydration characteristics are crucial for dried edible mushrooms. Ultrasonically dried mushrooms often have better rehydration characteristics than conventionally dried ones. Pretreatment with ultrasound prior to mushroom drying promotes faster and better water absorption and accelerates the rehydration process of the dried mushrooms. Moreover, dried edible mushrooms treated with ultrasonication exhibit better rehydration performance compared to other treatments (hot blanching, infiltration, and instant low pressure). Ultrasonic pretreatment improves the rehydration characteristics of the dry products and increases their rehydration rate [76]. However, if the conditions of ultrasonic treatment are not properly selected, the rehydration performance is lowered and the cell structure is damaged, which is not conducive to the rehydration of the dried edible mushrooms. A study by Su et al. on the rehydration kinetics of dried Pleurotus eryngii after ultrasonic pretreatment with different durations reported that the rehydration capacity of the dried sample pretreated by ultrasonication for 60 min was slightly lower than that of the sample ultrasonicated for 40 min. The reason for this may be that the cell wall of the former was damaged due to the prolonged sonication time, and the degree of cell wall damage increased with the increase in sonication time; thus, the rehydration capacity of the Pleurotus eryngii was also weakened [62].

4.1.2.4. Nutritional quality

The application of ultrasonic technology to the production of dried edible mushrooms has a positive effect on the quality of the products, particularly by hindering the loss of phenolics and flavonoids and maintaining the antioxidant activity of the dried products. In addition, the use of ultrasonication has an effect on the protein, sugar, and vitamin content of the samples. In general, the use of ultrasonic technology in the drying process of edible mushrooms not only reduces the loss of sugars but also maintains the high content of total phenolics and flavonoids, which is beneficial for the health of consumers. In addition, Zhao et al. reported that the protein and vitamin B₁ contents of the dried mushrooms treated by ultrasonication were significantly higher than those of the untreated samples. However, ultrasonic pretreatment also reduced the total sugar content of the mushrooms, which is likely due to the use of water bath sonication and the immersion of the samples in water during the treatment, which promoted the dissolution of sugars, resulting in lower sugar content in the dried products [70]. Therefore, when using ultrasonic technology, it is necessary to choose the right conditions, in particular, to control the duration of the ultrasonic pretreatment, as a longer ultrasonic pretreatment will cause a loss of nutrients [64].

4.2. Application of ultrasonic technology in the extraction of bioactive substances

Mushrooms contain many bioactive ingredients that are beneficial to human health, such as functional polysaccharides, terpenes, phenolic compounds, and adenosine. Because of their functional properties (e.g., antioxidant, anti-inflammatory, and antitumor effects), mushroom extracts are used in the manufacture of healthcare products and cosmetics. [4]. In recent years, the functional properties of mushroom bioactive substances have been studied in depth. To extract bioactive substances from mushrooms, the method used should be efficient. Ultrasonic technology has been widely used in the extraction of bioactive substances from edible mushrooms as it can effectively promote the extraction of macromolecules and improve the extraction rate.

4.2.1. Ultrasonic extraction of edible mushroom polysaccharides

Edible mushroom polysaccharides have various bioactivities and can promote health through immunomodulation [77]. There are many types of edible mushroom polysaccharides (e.g., glucose-, galactose-, and mannose-based). The most common polysaccharides in mushrooms are glycogen glucans and structural cell wall polysaccharides. According to the water solubility of polysaccharides, they can be divided into water-soluble polysaccharides and water-insoluble polysaccharides. Water-soluble polysaccharides can be extracted with water combined with some physical techniques, but water-insoluble polysaccharides are not easy to extract, and the extraction process takes a long time and requires a high temperature and pressure. In addition, high-molecular-weight polysaccharides are difficult to extract because of their poor solubility and high viscosity [78]. Thus, ultrasound-assisted extraction can economically and efficiently help extract functional polysaccharides from edible fungi.

Ultrasound-assisted extraction is a gentle and efficient technology for the extraction of bioactive compounds that overcomes the shortcomings of traditional techniques, such as a long extraction cycle, low extraction efficiency, degradation of acid-base sensitive compounds, or generation of by-products. Hence, this technology has been widely studied and applied to the extraction of polysaccharides from edible mushrooms. The application of ultrasonic technology to mushroom polysaccharide extraction is mainly based on cavitation and thermal effects. When ultrasonic energy is released, the cavitation effect produces a microjet, a shock wave, and high shear force, which enhances extraction. The extraction efficiency and yield of polysaccharides are increased by promoting cell wall rupture, mass transfer, and capillary interaction between incompatible phases [78]. In addition, ultrasonication also reduces the temperature and time of extraction; thus, thermally unstable compounds can also be extracted using this method. The thermal effect of ultrasound is the result of the rupture of bubbles, which releases high local energy and promotes the diffusion of polysaccharides into the solvent, thus increasing the extraction rate of these compounds [79].

As shown in Table 2, ultrasonication can improve the extraction of bioactive compounds from most edible mushrooms. This enhancement is particularly pronounced when ultrasonic technology is used in combination with other technologies (e.g., ultrasonication and enzyme-assisted extraction, ultrasound-microwave-assisted extraction) or when water is replaced with a deep eutectic solvent during extraction. Zhang et al. investigated the ultrasonic and microwave-assisted extraction of Dictyophora indusiate polysaccharide. The D. indusiate polysaccharide yield obtained by ultrasonically assisted hot water and combined ultrasonic and microwave extraction was higher than that obtained by the single extraction, and the antioxidant capacity of the obtained polysaccharide was enhanced [80]. Vezaro et al. studied the ultrasound-assisted extraction of β-glucan from mushrooms using two solvents: water and a natural deep eutectic solvent (NADES). Ultrasonication has a positive effect on the extraction of polysaccharides from shiitake (Lentinula edodes). At higher pulse cycles and ultrasonic amplitudes, the yield and concentration of polysaccharides extracted with water and NADES were higher [81].

Table 2.

Ultrasound-assisted extraction of bioactive compounds from edible mushrooms.

Edible mushroom species	Extraction conditions	Extracted substances	Main results	Reference
Shiitake (Lentinula edodes)	m = 1.25 g, V = 50 mL, P = 400 W, f = 24 kHz, T = 25 °C, t = 60 min, solvent: water and a natural deep eutectic solvent (NADES)	β-Glucans	The ultrasonic amplitude and pulse time increased the yield and concentration of polysaccharides.	[81]
	Solvent/solid ratio = 1:30 (w/v), f = 20 kHz, P = 550 W, amplitude = 60 %, t = 60 min	Polysaccharides	Extraction of L. edodes polysaccharides using autoclaved ultrasonication resulted in a high yield and improved the quality and bioactivity of the polysaccharides.	[101]
	m = 10 g, V = 300 mL, f = 30 kHz, P = 450 W, t = 20 min	Polysaccharides	The ultrasonically extracted fungal polysaccharides had high antioxidant activity and free radical scavenging ability.	[102]
	P = 290 W, solvent/solid ratio = 1:20, t = 21 min, T = 45 °C	Polysaccharides	The optimal ultrasound-assisted polysaccharide extraction yield was 9.75 %, which was 1.62 times higher than that of conventional hot water extraction.	[103]
Dictyophora indusiata	m = 5 g, V = 200 mL, ultrasound-microwave combined reaction system: 600 W, t = 25 min, T = 80 °C	Water-soluble polysaccharides	Ultrasound-assisted microwave extraction resulted in the best comprehensive antioxidant ability, which is conducive to avoiding the intermolecular spiral of the polysaccharide.	[80]
Stalks of Agaricus bisporus	I = 187 ± 2 W/L, 321 ± 14 W/L, t = 2, 4, 6, 8, 10, 12, 15, 20, 25, 30, and 60 min, T = 25 ± 2 °C	Ergosterol, total polyphenols, antioxidants, β-glucans	Ultrasound-assisted ethanol (70 %, 96 %) extraction was performed to obtain bioactive compounds, and ultrasound significantly contributed to increase the extraction yield.	[104]
Ganoderma lucidum	m = 2 g, V = 60 mL, t = 40 min, T = 80 °C	Polysaccharides	The monosaccharide composition of Ganoderma lucidum polysaccharide obtained by ultrasound-assisted extraction was similar to that of hot water-assisted extraction, but its antioxidant activity was slightly lower.	[82]
Flammulina velutipes	m = 10 g, V = 250 mL, f = 20 kHz, P = 620 W, t = 20 min, T = 45 °C	Polysaccharides	The polysaccharide obtained by ultrasound-assisted extraction had a higher glyoxylic acid content and better antioxidant activity.	[105]
Suillus bovinus	m = 0.2 g, V = 15.3 mL, f = 20 kHz, P = 70 W, amplitude: 17 %, t = 5 min, T = 60 °C	Total phenolic compounds	The ultrasonic extraction method is suitable for the extraction of phenolic compounds from wild and cultivated edible mushrooms.	[106]
Pleurotus citrinopileatus	f = 40 kHz, P = 200 W, water extract: solvent/solid ratio = 20 mL/g, t = 14 min, T = 44 °C, ethanol extract: solvent/solid ratio = 20 mL/g, t = 13 min, T = 39 °C	Bioactive compounds	The use of ultrasonication resulted in a high extraction rate and short extraction time for total phenols and total flavonoids.	[107]
Morchella importuna	f = 40 kHz, P = 600 W, liquid–solid ratio = 32.5:1 (v/w), t = 31.2 min, T = 62.1 °C	Polysaccharides	The extraction rate of mushroom polysaccharides under optimal conditions of ultrasonication was 4.5 times higher than that using hot water.	[108]
A. bisporus by-products	m = 3 g, V = 30 mL, f = 24 kHz, P = 400 W, amplitude levels: 20, 60, and 100 µm, t = 0, 3, 5, 10, and 15 min	Water-soluble polysaccharides	Ultrasonic technology is beneficial to the extraction of water-soluble polysaccharides from byproducts of A. bisporus.	[109]
Tuber aestivum	P = 150 W, pH: 6.5, 7.0, and 7.5, amplitude = 25 %, 30 %, and 35 %, liquid–solid ratio: = 75, 80, and 85, t = 15, 20, and 25 min	Polysaccharides	Truffle polysaccharides obtained by ultrasonic extraction had comparable properties to those obtained using hot water, and ultrasonic extraction did not affect the properties of the polysaccharides.	[110]
Armillaria mellea (Vahl) P. Kumm	m = 1 g, V = 20 mL, P = 280 W, t = 40 min, T = 70 °C	Polysaccharides	The polysaccharide yield obtained with the ultrasound-assisted method was higher than that of the enzymatic method.	[111]

Nonetheless, if the selected ultrasonic parameters are inadequate, they will have a negative impact on the extraction of bioactive substances from edible mushrooms. Kang et al. compared the effects of ultrasound-assisted and hot water extraction on the polysaccharides of Ganoderma lucidum and their antioxidant activity. As a result, although the composition of the polysaccharides obtained by the two extraction methods was similar, the molecular weight of G. lucidum polysaccharides extracted by the ultrasound-assisted method was low, whereas the hydroxyl radical and DPPH scavenging ability of G. lucidum polysaccharides obtained by the hot water extraction method was stronger [82]. Therefore, when using ultrasonic technology to assist in the extraction of edible mushroom bioactives, it is necessary to select the appropriate treatment time, power, solid–liquid ratio as well as the adequate extraction method depending on the type of edible mushroom.

4.3. Other applications of ultrasonication in the production and processing of edible mushrooms

In addition to drying and bioactive extraction, ultrasonic technology has been used in other processing operations (Table 3). For example, ultrasonication has been used to improve the quality of edible mushrooms after harvesting, and ultrasound-assisted preservation of mushrooms, ultrasound-assisted freezing and thawing of mushrooms, and ultrasound-assisted frying of mushrooms have been studied.

Table 3.

Uses of ultrasonic technology in other edible mushroom applications.

Edible mushroom species	Pre-treatment conditions	Ultrasonication effects	Main results	Reference
Shiitake mushroom (Lentinula edodes)	f = 40 kHz, P = 300 W, t = 10 min; cobalt-60, 1.0 kGy	Post-harvest mushroom preservation	Ultrasonic treatment combined with irradiation prevented the deterioration of fresh mushrooms.	[84]
	f = 40 kHz, P = 80 W/L, t = 30 min, t = 10 and 20 min		Ultrasonic treatment was beneficial for maintaining post-harvest storage quality.	[75]
Button mushroom (Agaricus bisporus)	f = 20–35 kHz, P = 100 W, t = 4 and 6 min, T = 20 °C		Ultrasonic treatment preserved the color and quality of edible mushrooms during storage.	[88]
	f = 40 kHz, P = 200 W, t = 3 min,low-concentration acidic electrolyzed water (LcEW) ultrasonication		The combined treatment of LcEW and US maintained the hardness of the mushrooms, extended their shelf life, and maintained the quality of the product.	[87]
Straw mushroom (Volvariella volvacea)	f = 40 kHz, P = 300 W, t = 30 min 4 °C + 95 % RH; 15 °C +75 % RH; 15 °C + 95 % RH		The synergistic effect of ultrasonication and relative humidity prevented mushroom deterioration.	[86]
	f = 40 kHz, P = 300 W, t = 0, 3, 10, and 30 min, relative humidity = 75 % and 95 %		Ultrasonic treatment for 10 min at 95 % relative humidity inhibited respiration and extended the shelf life of mushrooms.	[83]
King oyster mushroom (Pleurotus eryngii)	f = 40 kHz, P = 253 W, t = 10–30 min, T = 25 °C		The use of organic acid or lactic acid in combination with ultrasonication controlled the growth of Listeria monocytogenes.	[112]
Button mushroom (Agaricus bisporus)	f = 28 kHz, P = 120 W, microwave power: P = 800, 900, and 1000 W, T = 80, 85, and 90 °C, vacuum pressure: 12 ± 1 kPa	Fried mushroom products	Ultrasonication combined with microwave-assisted vacuum frying sped up the frying rate and improved the quality of fried mushroom slices.	[90]
	f = 28 kHz, P = 120 W, microwave power: P = 1200 W, f = 2450 MHz, T = 150 °C		Ultrasonication combined with microwave-assisted vacuum frying shortened the frying time and lowered the oil content of the finished product.	[91]
Button mushroom (Agaricus bisporus)	ultrasonic bath-assisted thawing: f = 28 kHz, I = 16 W/kg of water, T = 4 ± 1℃; ultrasound-probe assisted thawing: f = 28 kHz, P = 150, 250, and 350 W, I = 21.25, 35.40, and 49.50 W/cm2, T = 4 ± 1℃	Freezing and thawing of mushrooms	Ultrasonic thawing of edible mushrooms reduced the thawing time and protein denaturation without damaging the structure of the product.	[93]
Lentinula edodes, Pleurotus eryngii, and Agaricus bisporus	f = 20 kHz, nominal power levels of 33.33 %, 66.66 %, and 93.33 %, I = 0.13, 0.27, and 0.39 W/cm−2		Ultrasonic impregnation reduced the freezing time, thawing time, and drip damage of mushrooms, and the quality of the product was maintained.	[113]

4.3.1. Effects of ultrasonic technology on the post-harvest quality of mushrooms

Improper post-harvest storage of edible mushrooms can result in water loss, product atrophy, and poor quality [83]. At present, low-temperature preservation and modified atmosphere packaging are widely used in the preservation of fresh edible mushrooms. However, these methods have some disadvantages. For example, long-term low-temperature storage has a negative impact on product quality. If the carbon dioxide level is too high, it causes the cell wall components of mushrooms to break down and soften [75]. In addition to low temperature and gas conditioning, fresh mushrooms can be preserved by ultrasonic treatment [13]. The use of ultrasonic technology for post-harvest preservation of fresh mushrooms can reduce the adhesion of natural microorganisms, reduce water loss during storage, and increase the retention of ascorbic acid and total phenolic substances, thus ensuring the storage quality of the mushrooms. In a study by Shi et al., mild ultrasonic treatment of shiitake mushrooms eliminated or inhibited microorganisms and improved the retention rate of ascorbic acid and total phenolics [84]. After ultrasonic treatment, the mass loss and respiration rate during storage decreased, and the color was well preserved [85]. Zan et al. investigated the mechanism of postharvest preservation through ultrasonication and relative humidity management of straw mushrooms and confirmed that ultrasonic treatment resulted in the inhibition of enzyme activities and gene transcription levels related to respiration (e.g., vvPGI, vvSDH, and vvCCO) [86]. Ultrasonic treatment reduced the post-harvest respiration rate of mushrooms, delayed their metabolic activity, and extended their post-harvest shelf life.

4.3.2. Effect of ultrasound on shelf-life/preservation of mushrooms

Once harvested, fresh mushrooms generally have a shelf life of 2–4 days at average storage temperatures, with a limited shelf life [87]. This can be effectively improved by using ultrasonic technology to pre-treat edible mushrooms. Ganjdoost et al. studied Agaricus bisporus for 12 days storage and found that pre-treatment with ultrasonic technique was able to maintain the color of Agaricus bisporus well, especially with 6 min of ultrasonic treatment with O₃ distilled water. Although the microbial counts of the samples increased throughout the storage period, the 6 min ultrasonic treatment combined with O₃ distilled water maintained the lowest microbial counts until the end of the storage period [88]. Similarly, Wu et al. investigated the synergistic effect of low concentration acidic electrolytic water and ultrasound on the storage quality of freshly sliced mushrooms. Compared with low-concentration electrolytic water alone, ultrasound combined with low-concentration electrolytic water pretreatment effectively preserved the color of sliced mushrooms during storage, reduced browning, and the brightness of sliced mushrooms at the end of storage was similar to that of fresh sliced mushrooms. In addition, they found that the microbial content of sliced mushrooms in the ultrasound-assisted pretreatment group remained at the lowest level throughout the storage period, and that ultrasound-assisted pretreatment with low-concentration acid electrolyte water was effective in delaying browning and senescence of sliced mushrooms during storage [87].

Moisture retention is very important in the marketing and storage of edible mushrooms. Water loss is an important physiological process that affects the key quality attributes of fresh mushrooms, a phenomenon that leads to shrinkage and excessive weight loss. When a harvested mushroom loses 5–10 % of its fresh mass, it begins to wilt, which in turn shortens shelf life and compromises preservation [89]. During the preservation of white mushrooms, the quality of the mushrooms decreased as the number of storage days increased. Ultrasound pretreatment was effective in reducing the mass loss of white mushrooms, and the mass loss of mushrooms was slightly less when ultrasound was combined with high-pressure argon gas treatment. Consistent with the results of other studies, ultrasonic pretreatment delayed the loss of antioxidant capacity of mushrooms during cold storage, increased the retention of total phenolics and total flavonoids during storage, and inhibited enzymatic reactions during storage [85]. Similar conclusions were reached in the study by Li et al. Ultrasonic treatment significantly delayed weight loss during storage of edible mushrooms and maintained high membrane integrity. In addition, the use of ultrasonic pretreatment significantly inhibited mushroom respiration during storage, which prolonged the shelf life of mushrooms and reduced quality deterioration [83]. What's more, ultrasound combined with gamma radiation pretreatment reduced the total number of natural flora present on the mushrooms, especially Pseudomonas and Enterobacteriaceae, and maintained the quality of fresh mushrooms during storage. In addition, ultrasound combined with γ-ray pretreatment induced PAL activity, increased the accumulation of total phenolics, improved the retention of ascorbic acid, enhanced the antioxidant activity of mushrooms, and inhibited water migration and loss during cold storage, which helped to prevent the deterioration of fresh shiitake mushrooms [84]. When used in combination with other pre-treatment technologies, ultrasound can effectively prevent browning and ageing of edible mushrooms during the preservation process, extending the shelf life of edible mushrooms and ensuring product quality.

4.3.3. Ultrasound-assisted deep-frying of sliced mushrooms

Fried products are popular for their unique flavor and crunchy texture. However, the high oil content of fried products limits consumer purchases because of the public’s demand for healthy food. Ultrasound-assisted frying of mushroom slices improved the frying rate while reducing the amount of oil in the products [90]. During the frying process, the ultrasonic waves that are transmitted to the inside of the mushrooms, using oil as a medium, make the mushroom structure rigid, resulting in surface hardening, which in turn prevents the penetration of oil. The sponge effect of ultrasonication also affects the viscosity of the oil, hindering its absorption by the fried mushrooms. In addition, ultrasonication shortened the heating time, preventing non-enzymatic reactions, and thus preserving the color of the finished products. More importantly, the resulting fried mushrooms had the most acceptable flavor parameters according to their odor characterization. Therefore, the use of ultrasonication results in high-quality mushroom-based fried products [91].

4.3.4. Ultrasound-assisted freezing and thawing of edible mushrooms

Ultrasonic technology is also used to freeze and thaw edible mushrooms. While studying the ice crystal growth and size distribution of frozen Agaricus bisporus, Nahidul et al. found that the application of ultrasonication ruptured the cavitation bubbles, creating microflows in the cavitation fluid, and resulting in rapid nucleation and the formation of smaller ice crystals. Moreover, the ice crystals were needle- and column-like rather than dendritic. The smaller the ice crystals, the smaller the pores of the frozen mushrooms, the higher their density, the more uniform their structure, and the better their quality [92]. Similarly, the thawing of edible mushrooms by ultrasonication is mainly based on the cavitation effect. The microcurrent generated by the ultrasonic cavitation effect enhances heat transfer. If the ultrasonication treatment is long, the cavitation bubbles will tend to burst because the instability limit will have been reached, which will cause strong turbulence in the medium and increase the heat transfer coefficient. The strong turbulence caused by the bursting of the bubbles due to the cavitation effect causes the ice crystals to break into smaller pieces, thus shortening the thawing time of the mushrooms [93]. Thus, the use of ultrasonic technology reduces the thawing time of frozen mushrooms and prevents their browning, so that their color is preserved. In addition, the mushrooms frozen and then thawed with the aid of ultrasonication have not only a better microstructure but also higher hardness and chewing values and lower cohesion and elasticity values.

4.4. Limitations of ultrasound technology in processing and preservation of mushrooms

The application of ultrasonic technology in the processing and preservation of mushrooms can not only extend the shelf life of mushrooms, but also facilitate the post-harvest preservation of mushrooms, improve the quality of dried and fresh mushrooms, and promote the extraction of biologically active substances; it can also help in the production of high-quality fried mushrooms, as well as in the freezing and thawing of mushrooms. However, the application of ultrasonic waves often requires the selection of parameters such as ultrasonic power, ultrasonic time and ultrasonic frequency, which limits the application of ultrasonic technology in the processing and preservation of edible mushrooms.

Too long ultrasonic pre-treatment of edible mushrooms increases the degree of cell wall damage, destroys the cells and negatively affects the rehydration capacity of dried mushrooms [62]. Similarly, higher power ultrasonic pretreatment caused tissue damage and pigment degradation, increased the color difference between fresh and dried samples and affected the final hardness of the samples. Different ultrasound frequencies resulted in different porosities and inhomogeneous cell alignment or separation [27]. When using ultrasound for freezing and thawing of food products, the thermal effects of freezing/thawing increase with increasing ultrasound intensity/power, which can negatively affect the freezing/thawing efficiency and quality attributes of the food product. Surface overheating due to high ultrasonic attenuation occurs when the ultrasonic frequency exceeds the maximum suitable value. The attenuation coefficient of ultrasonic waves is higher for parallel propagation than for perpendicular propagation. The composition of the product to be defrosted affects the ultrasonic transmission coefficient and thus the total defrosting time [26].

The use of ultrasound for pre-treatment is also limited by the size, dimensions of the instrument. The effective area of ultrasound is a ring that decreases with distance. In the extraction of bioactives from edible mushrooms, differences in the diameter of the extraction tank may result in a blank ultrasonic area, reducing the extraction rate [94]. In the case of non-contact ultrasound, the low acoustic impedance and high acoustic absorption of the gas can limit the effectiveness of ultrasound by the weak transmission of sound waves through the gas, resulting in high ultrasonic energy loss in the medium [58].

5. Conclusion and future prospects

This paper summarizes the application of ultrasonic technology in the production and processing of edible mushrooms, and the application of ultrasonic technology has a positive effect on the production and processing of edible mushrooms. The selection of appropriate ultrasonic pre-treatment parameters can promote drying mass transfer, reduce non-enzymatic reactions in the drying process, shorten the drying time and improve the quality of dried mushrooms. Appropriate ultrasonic pretreatment can also help to maintain color, ensure good texture and rehydration of dried mushrooms, increase the retention of total phenolics and total flavonoids and obtain high quality dried mushrooms. In addition, the use of ultrasonic pre-treatment also facilitates the extraction of bioactive compounds from edible mushrooms, particularly the extraction rate of mushroom polysaccharides, while maintaining their functional properties. Ultrasonic technology applied to post-harvest preservation can extend the post-harvest storage period and ensure the quality of fresh mushrooms. Ultrasonic technology also has a positive effect on frying, freezing and thawing of edible mushrooms. In conclusion, the use of ultrasonic technology in the edible mushroom industry is highly recommended, but more in-depth research is needed.

For the future application of ultrasonic technology in the production and processing of edible mushrooms, the optimization of ultrasonic pretreatment parameters should be considered in order to reduce the damage of ultrasonic pretreatment to the raw materials of edible mushrooms. Different edible mushrooms have different intrinsic characteristics, and suitable processing conditions should be selected according to their characteristics in order to promote the production and processing of edible mushrooms and better preserve the initial characteristics of various edible mushrooms. The distribution of ultrasonic power in the medium may not be uniform during the ultrasonic pretreatment process, and more basic research is needed to construct a pretreatment apparatus with uniform distribution of ultrasonic power and intensity. In addition to the use of distilled water as a pretreatment medium, the effects of more other media on the ultrasonic pretreatment of edible mushrooms can be explored in order to seek better pretreatment methods and obtain better quality edible mushroom products. In addition, the high energy requirements and expensive equipment of ultrasound have limited the commercial use of ultrasound, and future research must also thoroughly investigate the effects of other energy sources and synergistic effects with ultrasound technology to ensure that the use of ultrasound technology is economical and to save energy consumption and costs. Last but not least, although a lot of research has been done on the application of ultrasonic technology in the production and processing of edible mushrooms, most of them are only at the laboratory research stage, and there are still some technical challenges in actual practice, and large-scale industrial application still needs a lot of efforts.

CRediT authorship contribution statement

Mianli Sun: Data curation, Writing – original draft. Yongliang Zhuang: Resources, Software. Ying Gu: Conceptualization, Formal analysis, Investigation, Methodology, Visualization. Gaopeng Zhang: Conceptualization, Formal analysis, Investigation, Methodology, Visualization. Xuejing Fan: Conceptualization, Funding acquisition, Supervision, Writing – review & editing. Yangyue Ding: Conceptualization, Funding acquisition, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

No data was used for the research described in the article.