Edible Mushrooms as Functional Ingredients for Development of Healthier and More Sustainable Muscle Foods: A Flexitarian Approach

Consumers are increasingly interested in nutritious, safe and healthy muscle food products with reduced salt and fat that benefit their well-being. Hence, food processors are constantly in search of natural bioactive ingredients that offer health benefits beyond their nutritive values without affecting the quality of the products. Mushrooms are considered as next-generation healthy food components. Owing to their low content of fat, high-quality proteins, dietary fibre and the presence of nutraceuticals, they are ideally preferred in formulation of low-caloric functional foods. There is a growing trend to fortify muscle food with edible mushrooms to harness their goodness in terms of nutritive, bioactive and therapeutic values. The incorporation of mushrooms in muscle foods assumes significance, as it is favourably accepted by consumers because of its fibrous structure that mimics the texture with meat analogues offering unique taste and umami flavour. This review outlines the current knowledge in the literature about the nutritional richness, functional bioactive compounds and medicinal values of mushrooms offering various health benefits. Furthermore, the effects of functional ingredients of mushrooms in improving the quality and sensory attributes of nutritionally superior and next-generation healthier muscle food products are also highlighted in this paper.


Introduction
Muscle foods, such as meat and fish, play an important role in the daily diet of most consumers due to their desirable sensorial attributes and beneficial nutritional properties, including high levels of good quality proteins, vitamins, and minerals. However, muscle foods are deficient in vitamin C, calcium, dietary fibre, and antioxidants [1]. Moreover, consumption of processed food has been linked to certain chronic health problems, such as an increase in diabetes and obesity [2,3]. The increased awareness of consumers about the possible links between diet and health is leading to shifts in their dietary patterns

Mushroom as Bioactive Functional Food Ingredients
Although many ingredients are used while preparing processed food products, the role of food ingredients that merits special mention are those with inherent nutritional as well as functional properties that influence the quality of finished food products. Therefore, ingredients are now considered as an essential part and parcel of any food product development process. However, the ingredients or compounds obtained from natural sources and generally regarded as safe are of great interest because of their safety and health characteristics [34]. As per the Food and Drug Administration, these are the substances that influence various attributes and properties of any food, either directly or indirectly. They are included at any down streaming stage of processing, be it production, packaging or storage of food, till it reaches the consumer. The purpose is not only to improve nutritional quality and safety but also the freshness, appearance, and overall acceptability of the food products by modifying taste and texture. These additives are often considered as nutraceuticals when these or part of their components exert medical or positive health benefits and play a vital role in the prevention and treatment of various diseases [35,36]. The nutraceuticals could be either whole food or its part, or even a single component or extract of food which is regularly being used as a dietary supplement. A food item is termed as "Functional" only when these nutraceuticals are incorporated in the food or its formulation to achieve specific target function such as improving the well-being as well as quality of human life by reducing the risk of disease beyond its nutritional value [35,37].
Mushrooms, which belong to filamentous higher fungi, are known for their nutritional richness, low caloric value, taste, and nutraceutical properties. Due to their unique nutritional as well as textural properties, they are used as a dietary supplement and often considered as an alternative source of meat, fish, vegetables, fruits, etc. [38]. Moreover, mushrooms are a source of high-quality protein produced in huge quantity from recycling worthless agro-wastes including agro-industrial waste per unit area and time [39,40]. Therefore enriching or fortifying diets or food products with such a good source of protein containing all the essential amino acids may help in reducing the incidences of proteinenergy malnutrition in humans [41]. Furthermore, owing to the presence of numerous secondary metabolites or nutraceuticals or biologically active compounds having medicinal value, mushrooms can also be used as bio-therapeutic agents [42,43].
Generally, mushrooms possess all three functionalities of food-nutrition, taste, and physiological functionalities. Mushrooms have a peculiarly pleasant savory taste called umami due to presence of sodium salts of free amino acids such as glutamic and aspartic amino acids and 5 -nucleotides [44]. The umami taste, also called the palatable taste, is nothing but the overall food flavour enhanced by mono-sodium glutamate [45]. Hence, mushrooms are preferable and adaptable in most food formulations due to this unique flavour.
Again, the umami taste peptides and umami-enhancing peptides are also considered to be important components which influence the sensory quality of mushroom. Peptides with different structures and length possess unique taste properties including sweet, bitter, umami, sour and salty. They are usually tasteless in water, but they can increase the salty, sweet, sour, bitter or umami taste in combination with corresponding tastants [46]. Various researchers have reported that some dipeptides or tripeptides containing Glu such as Glu-Glu, Glu-Asp, Glu-Asp-Glu, Glu-Gly-Ser enhance umami taste [47]. Recently umami peptides (2 tripeptides and 3 dipeptides) were isolated from hydrolysates of dried shiitake mushroom and these peptides are believed to be responsible for specific taste of shiitake mushroom. They also contribute to the unique taste of mushrooms or even interact with other volatile compounds to influence the whole flavour of foods [48]. In an another study, umami taste peptides like Gly-Leu-Pro-Asp and Gly-His-Gly-Asp isolated from the mushroom Agaricus bisporus are reported to act as key molecules for kokumi taste [49]. Kokumi taste is best described as flavor characteristics such as mouthfulness, complexity, and continuity. Kokumi taste substances have slight taste or even no taste by themselves, but they can enhance the flavor of the basic tastes, such as sweet, salty, and umami [50]. Interestingly, when incorporated to a blank chicken broth, these peptides from Agaricus bisporus can elicit new taste sensations, such as mouthfulness and complexity [49].

Nutritive Profile of Mushrooms
As stated earlier, mushrooms are excellent sources of dietary fibre and rich in protein possessing all nine amino acids that are essential for humans [26] but low in fat and calories [13]. In general, the mushroom fruit bodies contain 5-15% dry matter, 19-35% protein and low fat content (Table 1). Indeed, the protein content of mushrooms is almost four times greater than tomatoes and carrots, six times greater than oranges, and 12 times greater than apples [40,51]. Mushrooms, both pilei and stems are excellent source of dietary fibre mainly due to the presence of non-starch polysaccharides. Stems of mushroom are mainly composed of insoluble dietary fibre (IDF) and glucans. Hence, mushroom stem could be utilized for preparation of biologically active polysaccharide complexes as food supplement [52]. In a recent study, stem of enoki or winter mushroom (Flammulina velutipes) reported to contain 32% dietary fibre [53]. Again, the low fat and high-fibre content of mushrooms may help in preventing hypertension and hypercholesterolemia, as well as being beneficial in weight control [54]. Mushrooms are also healthy sources of essential fatty acids (52-87% unsaturated fatty acids), mostly in the form of linoleic acid, which cannot be directly synthesized in the human body but is required for health [55]. Mushrooms are also rich in indigestible carbohydrates, which makes them promising sources of novel prebiotic components [56,57]. The low glycemic index and high mannitol content of mushrooms is also believed to be beneficial for diabetics [58].
Being an excellent source of dietary fibres and proteins, mushrooms also have a low sodium content, and contain a diverse range of micronutrients, such as vitamins B 1 , B 2 , B 12 , C, D, E, niacin, and folate [59]. Despite being cultivated in the dark and being a non-animal source of food, mushrooms contain significant levels of vitamin D, which is often referred to as "the sunshine vitamin". Upon exposure to sunlight or ultraviolet (UV)-B light, the vitamin D (specially vitamin D 2 ) content of mushrooms increases appreciably, which can play a significant role in the bone and cartilage health of vegans and vegetarians [60][61][62].
Furthermore, mushrooms are a rich source of essential minerals like iron, copper, manganese, and zinc that play an important role in the proper functioning of different metabolic pathways. Indeed, the levels of some important trace elements (such as potassium and phosphorus) are typically considerably higher in mushrooms than in most vegetables [63]. Edible mushrooms can also produce a range of flavonoids, which may exhibit health benefits [64].
It should be noted that the nutritional composition of mushrooms varies considerably depending on factors such as species, intra-species genetic variability, maturity, growth conditions, geographic location, environmental conditions, and post-harvest conditions [65,66]. The chemical composition of some popular varieties of mushroom reported by different researchers, are presented in Table 1.

Nutraceutical Components in Mushrooms
Mushroom nutraceuticals are natural compounds found in mushrooms that may have health benefits by reducing the risks of certain diseases or by improving human performance [42,81,82]. The potential health-promoting and disease-preventing effects of mushroom nutraceuticals have been attributed to a broad range of biological activities, which are discussed in this section.

Prebiotic Effects of Mushrooms
There is growing evidence that human health can be promoted by consuming a diet that establishes a diverse microbiome in the colon [91]. In particular, diets that favour the growth of beneficial bacteria such as Lactobacillus and Bifidobacterium, while suppressing the growth of detrimental bacteria such as Clostridia and Bacteroides, may promote health [56,91]. Prebiotics are non-digestible and fermentable food components, such as oligosaccharides, dietary fibres, and non-digestible starches, that promote health by selectively modulating the composition and/or activity in the intestinal microbiota [61,92,93]. Mushrooms have been reported to contain numerous constituents that exhibit prebiotic activities, including chitin, hemicellulose, β-glucan, α-glucan, mannans, xylans, and galactans [57]. Some of the important mushroom species that have been reported to exhibit strong prebiotic activity include L. edodes (Shiitake), Trametes versicolor (Yunzhi), and Ganoderma lucidum (Reishi).
In a study, Chou et al. [94] reported that prebiotics (polysaccharides and proteinpolysaccharide complexes) from mushrooms passed through the human stomach and small intestine without digestion, then reached the colon where they stimulated the growth of healthy bacteria (Lactobaccilus acidophilus and Bifidobacterium longum subsp.). Similarly, glucans from P. ostreatus and P. eryngii [95] and G. lucidum [90] have also been shown to stimulate the growth of Bifidobacterium sp. and Lactobacillus sp.
Prebiotic mushroom polysaccharides are also reported to exhibit antiobesity and antidiabetic effects by regulating the energy homeostasis and plasma glucose levels of the host [61]. The restoration of energy balance is believed to be due to the supply of alternate energy sources from short-chain fatty acids produced during fermentation of the non-digestible carbohydrates in the colon [96]. Some in vitro studies have also reported that extracts from G. lucidum can modulate the gut microbiota in a manner that may help prevent obesity [97,98]. Other studies have reported that the polysaccharides from various mushroom varieties may be able to ameliorate metabolic syndromes (including diabetes), such as Agaricus brasiliensis, Agrocybe chaxingu, Catathelasma ventricosum, Pleurotus abalonus, Tremella fuciformis, G. frondosa, and G. lucidum [61,99]. The potential health promoting and medicinal properties of various bioactive ingredients found in mushrooms are summarized in Figure 1. Tremella fuciformis, G. frondosa, and G. lucidum [61,99]. The potential health promoting and medicinal properties of various bioactive ingredients found in mushrooms are summarized in Figure 1.

Effects of Edible Mushrooms on Muscle Food Products
Edible mushrooms, due to richness in nutritive value and functional food components, make them an unmatched source of healthy food and are regarded as superior nutritional supplements [36,53]. To harness the goodness of nutritional, nutraceutical and other medicinal values, mushrooms are not only used directly as food but also as raw materials in formulation and development of new functional foods for health-conscious consumers. Other than these values, mushrooms are preferred as additives by the food processors due to their aroma, taste and inherent texture-modifying functional properties [100,101] which are reported to positively influence the flavour, appearance, overall acceptance and shelf-life, when incorporated in various processed food formulations [53].
Considering their enormous benefits, varieties of food products such as breads [102], fish and meat products [103], cookies [104], other preparations like instant soups, pasta, snack seasonings, casseroles, and rice dishes [105,106] are being formulated incorporating mushrooms as functional bioactive components that is stated to improve the nutritional profile and potential health benefits [104]. Although quite a large number of research articles are available highlighting the use of mushrooms as potential functional compounds in various food applications, this review limits its focus on the potential application of mushrooms in muscle foods (meat and fish) only.
Incorporation of mushroom and its parts not only influences the desirable texture, taste, flavour, and stability of muscle food products considerably but also enriches them with nutritive and functional health values [36,104,[107][108][109]. Figure 2 indicates the bene-

Effects of Edible Mushrooms on Muscle Food Products
Edible mushrooms, due to richness in nutritive value and functional food components, make them an unmatched source of healthy food and are regarded as superior nutritional supplements [36,53]. To harness the goodness of nutritional, nutraceutical and other medicinal values, mushrooms are not only used directly as food but also as raw materials in formulation and development of new functional foods for health-conscious consumers. Other than these values, mushrooms are preferred as additives by the food processors due to their aroma, taste and inherent texture-modifying functional properties [100,101] which are reported to positively influence the flavour, appearance, overall acceptance and shelf-life, when incorporated in various processed food formulations [53].
Considering their enormous benefits, varieties of food products such as breads [102], fish and meat products [103], cookies [104], other preparations like instant soups, pasta, snack seasonings, casseroles, and rice dishes [105,106] are being formulated incorporating mushrooms as functional bioactive components that is stated to improve the nutritional profile and potential health benefits [104]. Although quite a large number of research articles are available highlighting the use of mushrooms as potential functional compounds in various food applications, this review limits its focus on the potential application of mushrooms in muscle foods (meat and fish) only.
Incorporation of mushroom and its parts not only influences the desirable texture, taste, flavour, and stability of muscle food products considerably but also enriches them with nutritive and functional health values [36,104,[107][108][109]. Figure 2 indicates the beneficial effect of mushrooms on quality attributes of muscle foods and associated health benefits. Further mushroom is better known for its low sodium content [110]. For example, the fruiting bodies of Agaricus sp. contain 396 mg sodium/kg [111] which is low amongst the vegetables [112]. On the other hand, processed meats contain 7-39 g sodium chloride/kg [113]. Dietary intake of such a higher amount of sodium is often linked with various diseases and increases the risk of hypertension and cardiovascular diseases [114]. Therefore, pre-mixing or blending mushrooms in processed meats may help in reduc-ing the sodium content of the products, offering more nutritional and health benefits to consumers [115].
ficial effect of mushrooms on quality attributes of muscle foods and associated health benefits. Further mushroom is better known for its low sodium content [110]. For example, the fruiting bodies of Agaricus sp. contain 396 mg sodium/kg [111] which is low amongst the vegetables [112]. On the other hand, processed meats contain 7-39 g sodium chloride/kg [113]. Dietary intake of such a higher amount of sodium is often linked with various diseases and increases the risk of hypertension and cardiovascular diseases [114]. Therefore, pre-mixing or blending mushrooms in processed meats may help in reducing the sodium content of the products, offering more nutritional and health benefits to consumers [115]. Over the years, a number of researchers have successfully incorporated mushrooms and its various parts (stipes and stem wastes) in formulation of various muscle food products like chicken sausages [70], salted cooked beef [116], tuna meat [117], kuruma shrimp [118], emulsion-type pork sausages [109], traditional Turkish meatball [108], fermented pork sausages [107], sutchi catfish patties [71] etc. A summary on the effects of edible mushrooms on physico-chemical properties, colour and oxidative stability, shelf-life and sensory attributes of muscle food products is presented in Table 2. Over the years, a number of researchers have successfully incorporated mushrooms and its various parts (stipes and stem wastes) in formulation of various muscle food products like chicken sausages [70], salted cooked beef [116], tuna meat [117], kuruma shrimp [118], emulsion-type pork sausages [109], traditional Turkish meatball [108], fermented pork sausages [107], sutchi catfish patties [71] etc. A summary on the effects of edible mushrooms on physico-chemical properties, colour and oxidative stability, shelf-life and sensory attributes of muscle food products is presented in Table 2.

Mushrooms on the Physicochemical Properties of Muscle Foods
The quality and acceptability of muscle foods depends on a number of different physicochemical properties including chemical composition, pH, water-holding capacity (WHC), emulsion stability, and cooking yield [8,132]. The pH of muscle foods is particularly important because it influences their WHC, juiciness, cooking yield, texture, and shelf-life by regulating microbial growth [1,133]. Studies have shown that incorporation of winter mushroom (F. velutipes) powder into emulsion-type pork sausages increased their pH, WHC, and cooking yield by decreasing the exudation of fat and water from the sausages [109]. Similarly, Cha et al. [126] reported that the incorporation of white jelly mushroom (T. fuciformis) into pork patties significantly increased their oil retention and cooking yield. Moreover, the introduction of 25% fresh mushroom into chicken patties has been reported to give an improved moisture retention (77%) and cooking yield (81%) [134]. The increase in cooking yield and water/fat retention are not only beneficial from technological and sensorial, but also from an economic viewpoint. In a recent study, the inclusion of enoki mushroom (F. velutipes) stem wastes into goat meat nuggets was shown to give a higher pH, emulsion stability, cooking yield, and WHC [53]. Likewise, Bao et al. [135] reported a slight increase in the pH of beef and fish products after addition of enoki mushroom extracts. The observed increase in pH after mushroom addition could be due to the relative abundance of basic amino acids compared to acidic amino acids in these products [136], as well as the natural buffering capacity of the mushroom proteins [137]. In contrast, shiitake (L. edodes) extracts were found to reduce the pH of fermented sausages during 30 days storage at 15 • C [130], which may have been due to the presence of lactic acid bacteria that generated acids within the fermented sausages.
The addition of mushroom also influences the chemical composition and nutritional profil of muscle foods. As discussed earlier, these effects can be attributed to the presence of relatively high levels of protein, minerals, and dietary fibres in mushrooms. The incorporation of dried mushroom (P. ostreatus) into beef patties has been reported to increase the protein, fat, and ash content of the end product [67]. Similarly, the incorporation of dried grey oyster mushrooms significantly decreased the fat content of cooked chicken patties [68]. The incorporation of dried enoki mushroom extracts into goat meat nuggets has been reported to increase their dietary fibre and ash contents [53]. Wan Rosli et al. [124] reported that the incorporation of oyster mushroom (P. sajor caju, PSC) powder into chicken meat decreased the fat content but increased the dietary fibre content in frankfurters in a dose-dependent manner.
Taken together, these studies clearly show that the composition of muscle-based foods can be manipulated by adding different types and amounts of mushrooms during processing. Incorporation of mushrooms either in the form of powder or extract influences the physicochemical properties, sensory attributes, and nutritional profiles of muscle foods.

Mushrooms on Lipid Oxidation in Muscle Foods
The oxidation of the lipids and proteins in muscle foods is undesirable because it leads to rancid odours, off-flavours, discolouration of the products [138][139][140]. Again, lipid oxidation by different means produces free radicals (such as alkyl, alcoxyl, and peroxyl radicals) which have been observed to induce protein oxidation [141]. For example, cooking or heating muscle food products above 60 • C initiate oxidative cleavage of the porphyrin ring, resulting in release of heme iron, which can lead to increased lipid and protein oxidation [142,143]. These oxidative reactions are extremely complex and lead to the loss of valuable nutrients, as well as the generation of numerous types of reaction products [116,140]. For instance, the essential amino acids and fatty acids may be lost [144], whereas volatile off-flavours are produced [145,146]. Many factors influence the lipid and protein oxidation, including oxygen, temperature, light, and transition metal ions. Researchers are increasingly trying to identify and utilize natural antioxidants to inhibit lipid and protein oxidation in muscle foods [147][148][149][150]. The utilization of these antioxidants helps in improving the food quality, shelf life, and nutritional profile [8,151,152].
Mushroom extracts from the fruiting bodies of edible mushrooms (F. velutipes) have been reported to inhibit lipid and protein oxidation in raw beef and fish (bigeye tuna) during storage, which was attributed to the presence of natural antioxidants [103,135]. Alnoumani et al. [116] incorporated dried A. bisporus powder into salted cooked ground beef and tested its ability to protect the lipids and proteins from oxidation during storage. The mushroom extract was found to effectively inhibit lipid and protein oxidation, with about 88-94% lower malonaldehyde values and 99% lower volatile aldehydes being produced after 16 days storage compared to the control sample. In another study, Nayak et al. [71] reported significantly lower oxidative changes in sutchi catfish (Pangasius hypophthalmus) patties after a button mushroom (A. bisporus) extract was incorporated, leading to an appreciable increase in shelf life. The antioxidative activity of mushrooms and their extracts have also been demonstrated in various other studies, including B. edulis extracts in beef burger patties [119], ground white mushroom in dry-fermented beef products [63], F. velutipes extract in bigeye tuna [117], F. velutipes extract in kuruma shrimp [118], and L. edodes extracts in fermented pork sausages [130].
These studies clearly show that mushrooms and their extracts contain a diverse range of natural antioxidants that can improve the quality and shelf-life of muscle food products by inhibiting lipid and protein oxidation.

Mushrooms on the Textural Properties of Muscle Foods
The quality attributes and acceptability of muscle foods is strongly influenced by their textural properties. Muscle foods are compositionally and structurally complex soft materials with semi-solid textures that influence their preparation, mastication, and digestion. The textural attributes of muscle foods is not only largely governed by the gel-forming and emulsification properties of the proteins they contain, but also effect by other components, such as lipids and minerals [151,163]. The incorporation of mushrooms into muscle foods influence their rheological characteristics, which must be accounted for when designing mushroom-enriched products. One of the advantages of using mushrooms in meat products is that they already have quite meat-like textures themselves because they have a very firm texture, and their dietary fibre fractions form a dense meaty texture when processed with muscle foods. As a result, they can often be incorporated up to a certain percentage into muscle foods without causing major adverse effects on their textural attributes [53,127]. Changes in quality aspects especially textural attributes of muscle foods due to incorporation of mushroom can be assessed from different studies is listed in Table 2.
A number of researchers have examined the impact of mushrooms on the textural properties of muscle foods. Choe et al. [109] reported a decrease in hardness, springiness, gumminess, and chewiness of sausages after incorporation of a mushroom powder. Similarly, Banerjee et al. [53] reported that the hardness, springiness, cohesiveness, and gumminess of meat nuggets decreased after addition of mushroom extracts, but these effects were not statistically significant. The hardness and other textural attributes of chicken patties have been reported to decrease after replacement of 25% or 50% of chicken meat with oyster mushroom [120,134]. Decreased hardness, cohesiveness, and gumminess but increased springiness have been reported when king oyster mushroom is incorporated into surimi gel prepared from cuttlefish (Sepia esculenta) meat paste [121].
In general, these results suggest that incorporation of mushrooms into muscle foods usually leads to softening of the final products. There are a number of possible physicochemical phenomena that may account for this effect. For instance, mushrooms contain relatively high levels of dietary fibres that can form a 3D biopolymer network that traps fluids, thereby leading to a softer texture in the muscle food products [164,165]. Moreover, the incorporation of high levels of mushrooms into muscle foods reduces the concentration of solubilized muscle proteins, thereby decreasing their ability to form strong gels.

Mushrooms on the Appearance of Meat Products
The appearance of muscle foods, such as their opacity, colour, and surface sheen, provide a visible indication of their quality and freshness, thereby playing an important role in determining consumer purchasing decisions [166,167]. The incorporation of mushrooms into muscle foods may impact their appearance in a number of ways. Mushrooms naturally have a different colour to meat or fish and, therefore, blends will have a different appearance than meat or fish alone. Moreover, the mushroom extracts may contain particles that have sizes and shapes that are different from those present in muscle foods, which can alter their visual texture. Finally, mushrooms contain antioxidants and other molecules that may inhibit colour changes in muscle foods. In this section, we provide a brief overview of studies that have examined the impact of mushrooms on the appearance of muscle foods.
Bao et al. [135] monitored changes in the met-myoglobin concentration and colour of minced beef and bigeye tuna meat products containing winter mushroom extract during cold storage. The authors reported that the presence of the mushroom extracts significantly decreased the met-myoglobin concentration in the meat products. As a result, the desirable colour of the beef and tuna products was maintained for up to 12 and 7 days storage compared to 6 and 2 days for the control samples (no mushroom), respectively. The colour stabilizing effect of the mushroom extract was attributed to the presence of ergothioneine, which reduced the rate of met-myoglobin formation, which is known to promote discolouration in muscle foods [135,168]. Similarly, an ergothioneine extract from mushroom was shown to prolong the stability of the red colour of yellowtail and tuna fish meat during cold storage [123].
In another study, researchers reported that the presence of 50% oyster mushroom in cooked chicken patties did not affect their redness (a*) but did decrease their lightness (L*) and yellowness (b*) [134]. Incorporation of white winter mushroom powder into emulsion-type pork sausages was reported to have little impact on their appearance [109]. Similarly, incorporation of up to 20% A. bisporus mushroom into beef burgers did not strongly affect their appearance [127]. The introduction of shiitake mushroom powder into frankfurters had little impact on their initial colour but did increase their yellowness during storage [169]. In a study on cooked beef taco, Wong et al. [170] reported a decrease in lightness (L*) with increasing level of mushroom (25-75%). In addition, the incorporation of 75% mushroom into the taco meat led to a lower redness (a*) than the all-meat control samples. These effects might arise due to the fact that the mushrooms were darker than the meat products, and because the myoglobin content in the final products was reduced after addition of the mushrooms.
In contrast to the above studies, the addition of white jelly mushroom was found to slightly decrease the redness and increase the yellowness of cooked pork patties, which might be due to the transparent white colour of these mushrooms [126]. In general, the impact of mushrooms on muscle foods depends on the initial colour of the mushrooms and muscle foods, as well as any physical interactions or chemical reactions that can occur between them [171].

Mushrooms on the Microbiological Quality of Muscle Foods
Muscle foods contain high levels of macronutrients and micronutrients that spoilage or pathogenic microorganisms can utilize to grow. Therefore, it is important to have effective strategies to extend the shelf-life and ensure the safety of this type of food [172]. Many mushrooms and their constituents exhibit antibacterial and antifungal properties [154,173]. Consequently, their incorporation into muscle food products may have the added advantage of improving their safety and shelf-life. These antimicrobial properties have been attributed to a number of different mushroom constituents, including high-molecular weight (peptides and proteins) and low-molecular weight (terpenes, steroids, anthraquinones, benzoic acid derivatives and quinolones) compounds secreted by the mushroom fruiting body for its own survival [36,174]. Medicinal mushrooms like Aleurodiscus, Coprinus, Clitocybe, Daedalea, Marasmius, Merulius, Pleurotus, Polyporus, Poria, Psathyrella, and Tricholoma spp. have been used as a source of natural antibiotics for the treatment of various types of disease because of the immunomodulatory properties of β-glucans and the antibacterial properties of secondary metabolites [175,176]. In this section, we review studies on the antimicrobial properties of mushrooms and their constituents, with a focus on their application in muscle foods.
Chowdhury et al. [155] reported that extracts of L. edodes, P. ostreatus and Hypsizigus tessulatus demonstrated antimicrobial activity against all bacteria and fungi tested, with minimum inhibitory concentration (MIC) values ranging from 1 to 9 mg/mL. In this study, the L. edodes extracts were more effective than those from the other two mushroom species. Similarly, shiitake (L. edodes) mushroom extracts, isolated using organic solvents and supercritical fluids, exhibited antibacterial effects against pathogenic microorganisms such as Streptococcus pyogenes and Staphylococcus aureus [177], whereas extracts isolated using only supercritical fluid revealed antimicrobial activity against Micrococcus luteus and Bacillus cereus [178]. Extracts from Pleurotus florida mushroom have also been reported to exhibit strong inhibitory effects on the growth of both Gram-positive and Gram-negative bacteria and could, therefore, be considered as an alternative to traditional antibiotics [179].
Other studies suggest that mushrooms or their extracts can be used as natural preservatives that improve the shelf-life of foods by inhibiting the growth of spoilage microorganisms in muscle foods. Button mushrooms have been reported to exhibit antimicrobial activity in sutchi catfish patties, leading to a considerable extension in their shelf-life [71]. In another study, shitake (L. edodes) extracts were shown to exhibit good antimicrobial activity in fermented sausages, thereby extending their shelf-life and inhibiting the growth of pathogens such as S. aureus, Listeria monocytogenes, and Escherichia coli O157 [130]. Stojković et al. [180] reported that a methanolic extract from Boletus aereus was effective at controlling microbial growth against food-poisoning organisms in pork meat, including S. aureus, L. monocytogenes, E. coli, and Salmonella Typhimurium. Overall, these studies show that incorporating mushrooms into muscle foods, like meat or fish, may be an effective means of increasing their shelf-life and safety.

Mushroom on Sensory Attributes of Muscle Foods
The sensory attributes of food products play an important role in determining their quality and desirability. The overall sensory impression of muscle foods depends on their appearance, flavour, texture, and oral processing [181]. The incorporation of edible mushrooms into meat and fish products changes these physicochemical characteristics to an extent that depends on the type and level of mushrooms used, thereby altering their sensory attributes. Choe et al. [109] reported that incorporation of 1% winter mushroom powder into emulsion-type pork sausages led to better sensory scores (texture, flavour, and acceptability) than sausages with 2%. Wan Rosli et al. [134] reported that incorporation of 25% to 50% oyster mushrooms into chicken patties led to blended products that had similar sensory and liking scores as the all-meat control patties. Likewise, incorporation of 25% oyster mushrooms into meat patties was also shown to have no adverse effects on their sensory attributes [68].
Myrdal Miller et al. [122] found that incorporating 80% of white button mushrooms into reduced-salt ground beef tacos did not impact their flavour intensity. This study suggests that in some cases it is possible to include high levels of mushrooms into muscle food products while maintaining their desirable flavour profiles. This effect may be due to the relatively high content of free amino acids in mushrooms, which generate desirable meat-like umami, sweet, and bitter tastes [182,183]. The umami taste makes the edible mushrooms palatable and adaptable in most food preparations [44]. Chun et al. [125] reported that incorporating different levels (2%, 4% and 6%) of shiitake mushroom powder into pork patties increased their firmness, juiciness, flavour, and overall acceptability in a dose dependent manner. Similarly, incorporation of king oyster mushroom (30%, 40%, and 50%) into cuttlefish (S. esculenta) paste led to higher overall acceptability scores than the control paste [121]. A number of other studies have also reported no changes or an improvement in the sensory attributes of muscle food products after addition of mushrooms or their extracts, e.g., enoki mushroom powder (2%, 4% and 6%) to mutton nuggets [53] and ground white jelly mushrooms (10%, 20%, and 30% ground) to pork patties [126].

Conclusions
Mushrooms are a rich source of important nutrients and bioactive components, including proteins, fibres, vitamins, minerals, and nutraceuticals, while also being low in calories, sodium, fat, and cholesterol. They can also be produced more sustainably than meat products, with less damaging effects on the environment [6]. Moreover, they have many flavor and textural attributes that are compatible with meat and fish products. Consequently, they are an extremely valuable functional ingredient for creating muscle food products with enhanced nutritional and sustainability profiles. In particular, they can be used to create foods designed for a flexitarian diet where a fraction of the meat or fish in a product is reduced.
There are many species of edible mushrooms that have not yet been explored for their potential application in food products. These novel mushroom species may have different nutritional, sensory, and environmental impacts than those exhibited by the species used so far. Consequently, there is a need for research on these other species. Moreover, further research is required to identify the mechanisms of action of different constituents in mushrooms, e.g., their antimicrobial activity, antioxidant activity, structures, textural attributes, and flavour profiles. Given the increasing demand of consumers for healthier and more sustainable foods, it is likely that the utilization of mushrooms within muscle foods is likely to continue to grow.