Nutritional, Bioactive, and Flavor Components of Giant Stropharia (Stropharia rugoso-annulata): A Review

Giant Stropharia (S. rugoso-annulata) is an edible mushroom recommended for consumption by the Food and Agriculture Organization of the United Nations. It possesses significant culinary and medicinal functionalities. The characteristics of this mushroom include high protein content, abundant bioactive compounds, delicious and sweet taste, and pleasant aroma. In recent years, the S. rugoso-annulata industry has seen strong growth, especially in China. This article presents the first comprehensive and systematic review of the nutritional, bioactive, and flavor components of S. rugoso-annulata, as well as their influencing factors. This article provides scientific evidence for the production of high-quality S. rugoso-annulata mushrooms, the extraction of bioactive components, post-harvest storage, and culinary processing, aiming to promote the consumption of S. rugoso-annulata and the health of consumers.


Introduction
Stropharia rugoso-annulata, also known as Giant Stropharia, Wine-cap mushroom, is a renowned edible fungus recommended for consumption by the Food and Agriculture Organization of the United Nations due to its potential to alleviate various illnesses associated with cancer [1].Not only is it a high-protein, low-fat food rich in minerals, vitamins, and dietary fiber [2], but it is also a quality raw material for functional components such as fungal polysaccharides [3], sterols [4], and taste peptides [5], and can also be processed into various flavorful foods [6,7].With particularly simple cultivation techniques and high yield [8], it holds significant application value in various fields such as dietary nutrition supply, bioactive compound extraction, functional food production, and flavorful food processing.
S. rugoso-annulata was first domesticated in Germany in 1969.Subsequently, it was introduced for cultivation in other European countries and the United States [8].In 1989, the yearly production of S. rugoso-annulata reached approximately 1300 tons in Europe [9].China imported a strain of S. rugoso-annulata from Poland in the 1980s and began widespread cultivation in the 1990s [10].In recent years, S. rugoso-annulata has been rapidly promoted and widely cultivated throughout China.In 2021, China's fresh S. rugoso-annulata mushroom production exceeded 210,000 tons, representing a surge of 43% compared to 2019 [11].
In recent years, numerous research has been reported on the food properties of S. rugoso-annulata, particularly its flavor components.Jing et al. reported on the nutritional components, some bioactive substances, and heavy metal content of S. rugoso-annulata [2]; Chen et al. reported on the flavor components of both fresh and dried S. rugoso-annulata [12]; Li et al. reported on the flavor substances produced by the liquid fermentation of 2.1.Nutritional Components of S. rugoso-annulata Processed by Different Drying Methods Dried S. rugoso-annulata mushrooms are commonly produced using hot air drying (HAD) at temperatures ranging from 45 • C to 55 • C [12,26,27].In addition to HAD, there are also other methods for drying such as vacuum freeze-drying (VFD), natural air drying (ND, NAD), microwave drying (MWD), and microwave vacuum drying (MVD) [27][28][29][30][31].The dry matter and crude fat content of S. rugoso-annulata followed the order of VFD > HAD > ND, while the protein and polysaccharide content followed the order of VFD > ND > HAD.The differences between the three drying methods are significant.S. rugoso-annulata produced by VFD had a significantly higher content of protein (25.09%), polysaccharides (16.03%), and fat (6.05%) than those produced by HAD and ND.Additionally, VFD retained the fresh mushroom's appearance and color effectively [29].VFD is suitable for the production of high-quality S. rugoso-annulata mushrooms, while the method of ND followed by HAD is suitable for the production of regular products.

Nutritional Components of S. rugoso-annulata at Different Developmental Stages
As shown in Figure 1, the developmental process of the S. rugoso-annulata fruiting body can be divided into five stages, namely, S1 (the button stage), S2 (the gill formation stage), S3 (the early maturity stage), S4 (the maturity stage), and S5 (the parachute stage), in chronological order.The ash content reaches the highest level at the button stage and decreases significantly afterward.The total carbohydrate content increases continuously throughout the entire developmental process.The crude protein content remains relatively stable but declines during the parachute stage.The crude fiber and crude fat content did not vary much at each stage [32,33].The crude protein content of S. rugoso-annulata was significantly higher in the unopened stage than in the opened stage [34].S4 and S2 are the stages when S. rugoso-annulata exhibits a higher overall nutritional quality, providing a reference for the timely harvesting of S. rugoso-annulata [32].

Nutritional Components of S. rugoso-annulata Processed by Different Drying Methods
Dried S. rugoso-annulata mushrooms are commonly produced using hot air drying (HAD) at temperatures ranging from 45 °C to 55 °C [12,26,27].In addition to HAD, there are also other methods for drying such as vacuum freeze-drying (VFD), natural air drying (ND, NAD), microwave drying (MWD), and microwave vacuum drying (MVD) [27][28][29][30][31].The dry matter and crude fat content of S. rugoso-annulata followed the order of VFD > HAD > ND, while the protein and polysaccharide content followed the order of VFD > ND > HAD.The differences between the three drying methods are significant.S. rugosoannulata produced by VFD had a significantly higher content of protein (25.09%), polysaccharides (16.03%), and fat (6.05%) than those produced by HAD and ND.Additionally, VFD retained the fresh mushroom's appearance and color effectively [29].VFD is suitable for the production of high-quality S. rugoso-annulata mushrooms, while the method of ND followed by HAD is suitable for the production of regular products.

Nutritional Components of S. rugoso-annulata at Different Developmental Stages
As shown in Figure 1, the developmental process of the S. rugoso-annulata fruiting body can be divided into five stages, namely, S1 (the button stage), S2 (the gill formation stage), S3 (the early maturity stage), S4 (the maturity stage), and S5 (the parachute stage), in chronological order.The ash content reaches the highest level at the button stage and decreases significantly afterward.The total carbohydrate content increases continuously throughout the entire developmental process.The crude protein content remains relatively stable but declines during the parachute stage.The crude fiber and crude fat content did not vary much at each stage [32,33].The crude protein content of S. rugoso-annulata was significantly higher in the unopened stage than in the opened stage [34].S4 and S2 are the stages when S. rugoso-annulata exhibits a higher overall nutritional quality, providing a reference for the timely harvesting of S. rugoso-annulata [32].

Nutritional Components of Different Parts of S. rugoso-annulata
As shown in Table 1, the nutrient components of both the pileus and the stipe of S. rugoso-annulata are the same, but their contents are different.The pileus presents a significantly higher content of crude protein, total amino acids, crude fat, ash, Mn, and Zn than the stipe, resulting in a higher nutritional value [35].[16,27,36]; * indicates significantly higher difference (p < 0.05).
Drying methods can affect the proportion of monosaccharides as well as the antioxidant activity of S. rugoso-annulata polysaccharides.The polysaccharides obtained through HAD have a higher proportion of glucose and a lower proportion of galactose compared to polysaccharides obtained through FVD, and they also exhibit stronger antioxidant activity [28].
Soluble polysaccharides of S. rugoso-annulata are traditionally extracted by the water extraction-alcohol precipitation method.Ultrasound or microwave assistance is often employed during water extraction to increase the yield and shorten the extraction time [26,28,37,49].Recently, a new method, three-phase extraction, has been reported for the extraction of S. rugoso-annulata polysaccharides.This method utilizes a tert-butanol-(NH 4 ) 2 SO 4 -water system, which avoids the need for an alcohol precipitation process and achieves the separation of polysaccharides faster [3].The highest yield from the S. rugoso-annulata fruiting body is achieved by an ultrasound-assisted extraction process (62 • C, 1:30 w/v, ultrasound 62 min), with a polysaccharide yield of 13.25% [37].The highest yield from the S. rugoso-annulata mycelium is achieved by an ultrasound-assisted extraction process (63.1 • C, 1:15 w/v, ultrasound 16.33 min), with a polysaccharide yield of 22.37% [52].Notes: --means no data.

Flavor Components of S. rugoso-annulata
The flavor of edible mushrooms includes aroma and taste.The aroma is mainly produced by volatile compounds that are perceived by the nose, while the taste is produced by non-volatile compounds that are perceived by the tongue.The intensity of the flavor is determined by the concentration of flavor compounds and their perception thresholds [67].The taste activity value (TAV) and odor activity value (OAV) are commonly used to evaluate the non-volatile or volatile compounds in edible mushrooms.TAV or OAV is the ratio of the concentration of a certain non-volatile or volatile compound to its taste or odor threshold concentration, reflecting the contribution of a single compound to the overall taste or odor.
TAV or OAV > 1 indicates that the compound contributes to the taste or odor, and the larger the value, the greater the contribution [6,12].The equivalent umami concentration (EUC) is often used to evaluate the umami taste compounds in mushrooms.EUC is the total amount of umami substances (umami amino acids and 5 -nucleotides) per 100 g of dry sample, usually expressed in terms of monosodium glutamate (MSG) content, also known as MSG equivalence, with units of g MSG•100 g −1 .The higher the EUC value, the stronger the umami taste [12].The relative odor activity value (ROAV) is another index commonly used to evaluate the key aroma compounds in mushrooms.A compound with an ROAV ≥ 1 is considered a key aroma compound, while substances with an ROAV 0.1-1 are considered to have a modifying effect on the aroma [68,69].
The summary of reports on the flavor components from multiple samples and processes of S. rugoso-annulata is shown in Table 4.
Table 4. Research reports on the flavor components of S. rugoso-annulata.

Samples
Processing Methods

Soluble Sugars
Soluble sugars are sweet in taste.As shown in Table 6, the fruiting body of S. rugoso-annulata contains various soluble sugars or polyols such as trehalose, arabinose, glucose, mannose, fructose, galactose, xylose, ribose, mannitol, erythritol, and arabitol, with a total content range of 10.01-13.06%[12,27].Trehalose (7.82-11.03%)or arabinose (5.46-26.54%)have the highest content [12,27], indicating that S. rugoso-annulata mushrooms, particularly the stipes, are excellent raw materials for extracting these two sugars.The mycelium of S. rugoso-annulata contains glucose, gluconic acid, galactose, rhamnose, and ribose, with a total content of 8.32-8.65%.Glucose has the highest content (7.92-8.25%) in the mycelium [13].4.1.3.Free Amino Acids In terms of free amino acids, Glu and Asp provide the umami taste while Thr, Ser, Pro, Gly, and Ala provide the sweet taste.Phe, Arg, His, Val, Met, Ile, Leu, and Trp provide the bitter taste, and other amino acids are tasteless [27].As shown in Table 7, the fruiting body of S. rugoso-annulata contains 15-21 free amino acids, with a total content range of 3.07-9.38%.Thr or Glu have been reported to have the highest content [12,27,30,32].The content of taste amino acids follows the order of sweet amino acids > bitter amino acids > umami amino acids [14,30,32].In the fermented mycelium of S. rugoso-annulata, there are 20 free amino acids with a total content of 2.27-2.48%,and Arg has the highest content.The content of taste amino acids follows the order of bitter amino acids > sweet amino acids > umami amino acids [13].4.1.5.Organic Acids Organic acids provide a sour taste.S. rugoso-annulata contains seven organic acids, including malic acid, tartaric acid, ascorbic acid, acetic acid, citric acid, fumaric acid, and succinic acid (Table 9).The total content of these organic acids ranges from 11.10 to 24.14% [13,14,27,30].
In the fruiting body, malic acid has the highest content (9.2-16.77%)[27,30], while in the fermented mycelium, acetic acid has the highest content (0.42%) [13].Alkaloids and flavonoids provide a bitter taste, with contents of 0.016-0.020%and 0.35-0.41%respectively, in the mycelium of S. rugoso-annulata.Polyphenols produce astringency, with a content of 0.0063-0.014% in the mycelium [13].S. rugoso-annulata mushrooms contain a relatively high amount of K (3.41%) and Na (0.12%) [2], which also contribute to their taste.K + and Na + provide a salty taste [76], and Na + can also combine with glutamine or succinic acid to form MSG or sodium succinate, respectively.Both of these compounds are important umami substances [77].

Aroma (Volatile Flavor) Components of S. rugoso-annulata
The odor of fresh S. rugoso-annulata mushrooms is primarily characterized by mushroomy, earthy, and grassy aromas [12,70].During the drying process of fresh mushrooms, the earthy and grassy aroma gradually decreases, while a burnt and malty odor emerges and becomes stronger.However, the mushroomy and earthy aroma remains the key characteristic aroma of both fresh and dried S. rugoso-annulata mushrooms.

Taste Components in Different Parts of S. rugoso-annulata
There was no difference in the variety of taste components between the pileus and stipe of S. rugoso-annulata, but there were significant differences in the content (Table 10).The pileus's content of free amino acids, organic acids, 5′-nucleotides, and EUC were significantly higher than those in the stipe.The content of soluble sugars in the stipe was significantly higher than that in the pileus [27].These indicate that the pileus of S. rugosoannulata is more umami-rich, whereas the stipe tends to be sweeter in taste.

. rugoso-annulata
There was no difference in the variety of taste components between the pileus and stipe of S. rugoso-annulata, but there were significant differences in the content (Table 10).The pileus's content of free amino acids, organic acids, 5 -nucleotides, and EUC were significantly higher than those in the stipe.The content of soluble sugars in the stipe was significantly higher than that in the pileus [27].These indicate that the pileus of S. rugoso-annulata is more umami-rich, whereas the stipe tends to be sweeter in taste.Notes: Data obtained from reference [27]; * indicates significantly higher difference (p < 0.05).

Aroma Components in Different Parts of S. rugoso-annulata
The fresh pileus and stipe of S. rugoso-annulata were found to contain 15 and 14 volatile components, respectively, with 3-octanone, schisterol, and hexanal being the same major ones.3-octanone was the compound with the highest content (>70%) in both parts.Hexanal, 3-ethyl-2-methyl-1, 3-hexadiene, and pentadecane were found in the pileus but not in the stipe, while α-bisabolene and dehydrovomifoliol were detected in the stipe but not in the pileus.The pileus had a higher content of aldehydes, esters, alkenes, and alkanes, while the stipe had a higher content of alcohol [31].
The dried pileus and stipe of S. rugoso-annulata (first subjected to HAD and then FVD) were found to contain a total of 50 volatile components, respectively, with alcohols, esters, and alkanes being the main constituents in the pileus, and alcohols, esters, and ketones being the main constituents in the stipe.The dried pileus exhibited a higher content of alkanes, whereas the dried stipe showed a higher content of ketones [72].

Taste Components of S. rugoso-annulata at Different Developmental Stages
As shown in Figure 4, the content of free amino acids (2.48%) and 5 -nucleotides (0.0067%) in fermented mycelium is obviously lower than in the fruiting body [13], resulting in an almost negligible umami taste (EUC) in the fermented mycelium.The total content of free amino acids, 5 -nucleotides, EUC, and TAV in the fruiting body showed a trend of first increasing and then decreasing [32].
being the main constituents in the stipe.The dried pileus exhibited a higher content o alkanes, whereas the dried stipe showed a higher content of ketones [72].

Taste Components of S. rugoso-annulata at Different Developmental Stages
As shown in Figure 4, the content of free amino acids (2.48%) and 5′-nucleotide (0.0067%) in fermented mycelium is obviously lower than in the fruiting body [13], resul ing in an almost negligible umami taste (EUC) in the fermented mycelium.The total con tent of free amino acids, 5′-nucleotides, EUC, and TAV in the fruiting body showed a tren of first increasing and then decreasing [32].

Taste Components of S. rugoso-annulata with Different Processing Methods
In the preparation of S. rugoso-annulata soup (water extracts of fruiting body pow der), processing methods present a significant influence on the content of taste compo nents.The non-thermal treatment of HHP resulted in the highest levels of 5′-nucleotide (1.46-1.82%)and free amino acids (10.43-12.36%)and the highest EUC (827.44-1411.79MSG•100 g −1 ), while thermal treatments (70 °C and 90 °C heating) led to the highest con centration of organic acids (6.55-9.84%).Other non-thermal treatments, including UT an HG, led to higher levels of soluble sugars (1.56-3.05%)[14].These findings are helpful i the cooking of highly flavorful S. rugoso-annulata soup.
Grinding the S. rugoso-annulata powder (particle size) also has a significant impact o S2 showed the highest 5 -nucleotide content (0.91%), TAV (112.15), and EUC (788.66 g MSG•100 g −1 ).S4 showed the highest content of total free amino acids (9.38%), umami amino acids (1.29%), and sweet amino acids (1.70%) [32].These findings serve as a reference for determining the optimal timing for harvesting.S. rugoso-annulata.This study provides a reference for the timely harvesting of S. rugoso-annulata rich in nutrition and taste components.

Taste Components of S. rugoso-annulata with Different Processing Methods
In the preparation of S. rugoso-annulata soup (water extracts of fruiting body powder), processing methods present a significant influence on the content of taste components.The non-thermal treatment of HHP resulted in the highest levels of 5 -nucleotides (1.46-1.82%)and free amino acids (10.43-12.36%)and the highest EUC (827.44-1411.79g MSG•100 g −1 ), while thermal treatments (70 • C and 90 • C heating) led to the highest concentration of organic acids (6.55-9.84%).Other non-thermal treatments, including UT and HG, led to higher levels of soluble sugars (1.56-3.05%)[14].These findings are helpful in the cooking of highly flavorful S. rugoso-annulata soup.
Grinding the S. rugoso-annulata powder (particle size) also has a significant impact on the release of taste components into soup.Moderately ground powder (36.63 µm) leads to the highest concentration of free amino acids and soluble sugars in the soup.These findings suggest that HHP and moderately fine grinding are beneficial for the extraction of taste components from S. rugoso-annulata powder [14].
HAD-dried S. rugoso-annulata exhibited the highest EUC value, while VFD-dried samples had the highest levels of taste components [27,30].HAD and VFD have been found to be beneficial for preserving and enhancing the taste components in S. rugoso-annulata, making them suitable for the production of tasteful dried mushrooms [12,30].Among them, HAD is the most economical and convenient drying method.On the other hand, MWD was shown to cause a significant decrease in the content of taste components and therefore is not suitable for drying.

Aroma Components of S. rugoso-annulata with Different Processing Methods
A total of 47 volatile components were identified in the S. rugoso-annulata soup, primarily consisting of alcohols, aldehydes, ketones, esters, hydrocarbons, and a small number of heterocyclic compounds (Figure 5).The main odor components (with higher concentrations) were hexanol, 1-octen-3-ol, and hexanal.The ranking of the processing methods for the aroma intensity of S. rugoso-annulata soup from high to low was UT > HHP > RT > HG > 70 • C > 90 • C. The non-thermal-treated soup displayed a more intense aroma than the thermal-treated soup.Thermal treatment reduced the volatile components of the soup, and the higher the processing temperature, the more severe the loss of volatile compounds.Grinding the mushroom powder (particle size) influenced the odor of the mushroom soup.Ultrafine grinding probably destroyed the volatile components of S. rugoso-annulata powder.The soup of non-ultrafine-ground mushroom powder (181.25 µm) had the strongest aroma [15].
Drying significantly affects the odor of S. rugoso-annulata; the variety of odor compounds in dried S. rugoso-annulata (59-68) is significantly higher than that of fresh S. rugoso-annulata (47).Different drying methods result in different aroma profiles-fresh mushrooms have a slightly grassy and earthy aroma, while HAD mushrooms have a mild nutty aroma with a decrease in grassy flavor.VFD mushrooms retain a more distinct grassy flavor; MWD mushrooms have a slightly nutty, burnt, and sulfurous smell; ND mushrooms have a slight sulfur odor.Among the drying methods, VFD can best preserve the odor quality of fresh mushrooms [12].Drying significantly affects the odor of S. rugoso-annulata; the variety of odor compounds in dried S. rugoso-annulata (59-68) is significantly higher than that of fresh S. rugoso-annulata (47).Different drying methods result in different aroma profiles-fresh mushrooms have a slightly grassy and earthy aroma, while HAD mushrooms have a mild nutty aroma with a decrease in grassy flavor.VFD mushrooms retain a more distinct grassy flavor; MWD mushrooms have a slightly nutty, burnt, and sulfurous smell; ND mushrooms have a slight sulfur odor.Among the drying methods, VFD can best preserve the odor quality of fresh mushrooms [12].
Deep frying significantly increased the richness of the aromas of S. rugoso-annulata stipe, adding roasted nut and chocolate aromas.In the unfried samples, the volatile flavor compounds were mainly alcohols and esters, and 1-octene-3-one contributed the most to the aroma.In the fried samples, aldehydes were found the most, mainly including n-hexanal, octanal, nonanal, and (E)-2-nonenal, with (E)-2-nonenal making the largest contribution to the aroma [7].This finding provided a reference for the deep-frying processing of S. rugoso-annulata.Deep frying significantly increased the richness of the aromas of S. rugoso-annulata stipe, adding roasted nut and chocolate aromas.In the unfried samples, the volatile flavor compounds were mainly alcohols and esters, and 1-octene-3-one contributed the most to the aroma.In the fried samples, aldehydes were found the most, mainly including n-hexanal, octanal, nonanal, and (E)-2-nonenal, with (E)-2-nonenal making the largest contribution to the aroma [7].This finding provided a reference for the deep-frying processing of S. rugoso-annulata.[68].The results revealed that fresh S. rugoso-annulata after harvest can be stored at 15 • C for 4-6 days and at 0 • C for 12 days while maintaining good quality without decaying.3-octanol, 1-octene-3-ol, (E)-2-octenal, nonanal, decanal, 3-octanone, and 2-pentylfuran were the characteristic flavor substances in fresh S. rugoso-annulata.As the storage time extended, 3-octanol and hexanal were the key substances for the aroma deterioration of post-harvest S. rugoso-annulata.Compared to the samples stored at 15 • C, S. rugoso-annulata samples stored at 0 • C showed a lower ROVA of undesirable aroma components and a greater variety of aroma compounds [68].This result indicated that 0 • C storage could effectively maintain the post-harvest quality of S. rugoso-annulata and inhibit its flavor deterioration, providing valuable references for maintaining the post-harvest storage of S. rugoso-annulata.
The processing temperature adopted for preparing S. rugoso-annulata soup led to significant differences in the content of 5'-nucleotides.When the soup is prepared at 70 • C or 90 • C, 5 -CMP and 5 -XMP are detected, unlike in soups prepared at room temperature.The total content of 5 -nucleotides in the soup follows a descending order of RT > 70 • C > 90 • C [14].Additionally, the total concentration of volatile flavor components in S. rugoso-annulata soup follows a descending order of RT > 70 • C > 90 • C [15].
Qin et al. reported on the effect of various drying temperatures of HAD on the volatile flavor components of S. rugoso-annulata [38].Within the range of 30-90 • C, as the HAD temperature increased, the diversity of volatile components decreased, and more alkanes were produced.A HAD temperature of 30 • C led to the most abundant volatile components (58) in S. rugoso-annulata [31].
Bao et al. reported the effects of roasting on the volatile flavor compounds of S. rugoso-annulata [6].The result showed that roasting S. rugoso-annulata within the temperature range of 100-180 • C improved the richness of flavor, increased the malty, rose-like, nut-like, and cocoa-like aromas, and improved the overall flavor of S. rugoso-annulata.The largest number (63) of flavor components was found in S. rugoso-annulata roasted at 140 • C. With the increase in roasting temperature, the content of alcohols decreased significantly, while the content of aldehydes, alkanes, and pyrazines increased [6].The results indicated that roasting enhanced the volatile flavor of S. rugoso-annulata.
The adsorption temperature (40-100 • C) in the microextraction step of headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) significantly influenced the detection result of volatile components.The number of detected volatile compounds was positively correlated with the adsorption temperature, with only one for 40 • C and 18 for 100 • C. The optimal adsorption temperature was found to be 80 • C [31].

Comparison of Aroma Components between S. rugoso-annulata and Other Edible Mushrooms
The aroma components of S. rugoso-annulata are also related to its genetic characteristics.Different edible mushroom species have their own characteristic odor components, and there can be significant differences in aroma profiles between them (Table 11).The aroma components of S. rugoso-annulata do not contain sulfur compounds [12,70], whereas those of shiitake (Lentinula edodes) and straw mushroom (Volvariella volvacea) include sulfur compounds as the main and characteristic aroma components [78,79].Sulfur compounds generally release a strong, unpleasant smell [80].Therefore, unlike shiitake or straw mushrooms, S. rugoso-annulata mushrooms do not have an unpleasant odor, giving a mild earthy and grassy aroma.
Generally, the flavor components of S. rugoso-annulata are influenced by various internal factors such as genetic characteristics, developmental stages, and parts of the mushroom, and external factors such as processing methods and temperature conditions.

Zero Research Report on Chitin
As the main component of fungal cell walls, chitin is a structural polysaccharide composed of N-acetylglucosamine linked by β-1, 4 glycosidic linkages.It is widely present in fungi and crustaceans and was first discovered in mushrooms [81].It is insoluble in water but can only be dissolved in strong acids [82].The reason why mushrooms are not easily cooked to softness after prolonged cooking is because they contain a large amount of chitin [83].
The chitin contents of A. bisporus, P. ostreatus, L. edodes, F. velutipes, P. eryngii, and V. volvacea have been reported, ranging from 4.77% to 19.6% [84].However, the chitin content of S. rugoso-annulata has not yet been reported and related studies are still lacking.

High Protein Content Distortion
S. rugoso-annulata mushrooms have a significantly high protein content (25.75-34.17%),being 1.8 times that of A. bisporus, 1.4 times that of L. edodes, and 1.3 times that of P. ostreatus [16,85].However, in some studies, the protein content of S. rugoso-annulata has been reported to exceed 50% [32].This could be due to the incorrect conversion factor when measuring the protein content using the Kjeldahl method.
The Kjeldahl method is a classic method for measuring the nitrogen and protein contents of samples and is included in the standard for determining protein content in food.This method determines the protein content by measuring the total nitrogen content and multiplying it by a conversion factor (nitrogen to protein factor, NPF), generally taken as 6.25 [86].However, because edible mushrooms contain a large amount of nonprotein nitrogen, in chitin, the content of non-protein nitrogen needs to be excluded when measuring the protein content of edible mushrooms using the Kjeldahl method.
To obtain a more accurate protein content, the NPF for edible mushrooms is generally modified to 4.38 [27,87].After modifying the conversion factor, the protein content of S. rugoso-annulata, which was originally reported to exceed 50%, decreased to around 35%, which is a more realistic and accurate figure.

Little Research on the Bioactive Components in the Fermentation Mycelium and Liquid of S. rugoso-annulata
Mycelium and fermentation liquid produced through the liquid fermentation of edible mushrooms are important sources of pharmacologically active ingredients.Liquid fermentation has advantages such as a short cycle, year-round production, and controllable quality.Secondary metabolite production can also be increased intentionally by changing fermentation parameters and cultivation methods [88].Currently, the bioactive ingredients of S. rugoso-annulata are mainly derived from its fruiting bodies, and there is little research on the bioactive ingredients and pharmacological activities of mycelium and fermentation liquids.Therefore, it is necessary to further conduct research on the liquid culture of S. rugoso-annulata mycelium and the bioactive components of its products.

Genes Related to the Metabolism of Nutritional and Flavoring Components Have Not Been Reported
Currently, research progress in the biosynthetic pathways and metabolic regulation mechanisms of key volatile components in S. rugoso-annulata has already been made.For example, the biosynthetic pathway of the main odor components (aldehydes, ketones, and alcohols) generated during the drying process of S. rugoso-annulata was found to be the lipoxygenase (LOX) metabolic pathway, and the key enzymes involved in regulation are lipoxygenase and alcohol dehydrogenase (ADH).LOX catalyzes the formation of aldehydes and ketones of C 6 , C 8 , and C 9 , while ADH catalyzes the reduction of aldehydes and ketones into corresponding alcohols [70], but the research findings are still in the preliminary stage.Research on nutritional and flavor components needs to delve into the genetic level in order to fully understand the mechanisms of component metabolism.So far, there have been no reports on the important functional genes of S. rugoso-annulata.

The Deep-Processed Products Are Almost Blank
In the current Chinese market, S. rugoso-annulata products are mainly limited to fresh mushrooms, with only a small quantity of dried and pickled mushrooms available [89].The products are limited and quite primary.As an excellent raw material, S. rugoso-annulata mushroom can be used to extract various nutrients, bioactive ingredients, and flavor components.
Compared with other edible mushroom varieties, S. rugoso-annulata is not only rich in nutritional value such as protein and amino acids, but also abundant in bioactive and flavor substances such as polysaccharides, sterols, and taste peptides.There are great application prospects for S. rugoso-annulata in the fields of dietary nutrition supply, bioactive compound extraction, functional food production, flavor food processing, etc.

4. 3 . 6 .
Flavor Components of S. rugoso-annulata at Different Temperatures Rao et al. reported the effects of storage temperature (0 • C, 15 • C) on post-harvest quality and volatile flavor components

Table 1 .
Content of nutritional components in S. rugoso-annulata pileus and stipe.

Table 2 .
Monosaccharide components, structure and optimum extraction conditions of soluble polysaccharides in S. rugoso-annulata.

Table 3 .
Bioactivity and optimal extraction conditions of other bioactive components in the S. rugoso-annulata fruiting body.

Table 10 .
Content of taste components in S. rugoso-annulata pileus and stipe.
Parts of S.

Table 10 .
Content of taste components in S. rugoso-annulata pileus and stipe.

Table 11 .
Comparison of aroma components in S. rugoso-annulata and other edible mushrooms.