Potential Use of Underutilised Mushroom Stems in Meat Products and Meat Analogues: A Mini Review

— The demand for meat has gradually increased throughout the years, and it is more widely ingested than plant products due to its sensory qualities as well as its high nutritional content, mainly protein. However, meat is low in calcium, dietary fibre, and vitamin C. Consumers' increased awareness of the possible links between nutrition and health has recently led to major dietary changes toward healthier food options. Furthermore, rising meat prices, vegetarianism, concerns about animal suffering, and sustainability issues have driven market trends toward meat alternatives from plant sources. As such, mushrooms are regarded as one of the healthier ingredients due to their nutritive, bioactive, and therapeutic values. The fibrous structure mimics the texture of meat and possesses an umami flavour, which imparts a meaty taste to the food products. Globally, Asian countries generate the highest percentage of overall mushroom production. The application of mushrooms, however, is limited to the fruiting bodies rather than the stems, which also contain high dietary fibre content. The stems are often discarded as food waste due to their tough texture. Researchers have begun to use edible mushroom waste and their by-products, especially stems, to create value-added products in a variety of sectors, such as the food industry, owing to their nutritional values and contributions to the circular economy and environmental protection. Thus, the primary intent of this review is to discuss the potential of underutilised mushroom stems in meat products.


I. INTRODUCTION
The worldwide demand for meat has been rising steadily over the years.Meat that has been considered a luxury in the past has become a staple as it can be found in almost all restaurants and kitchens across the world.Among meat categories, poultry is the most popular type of processed meat, followed by red meat, including pork and beef, accounting for 38% and 33% of the global market, respectively [1].Meat products are often consumed more than plant products due to their sensory characteristics and high nutritional content of proteins, minerals (iron, selenium, zinc), and vitamins (primarily B6 and B12) [2].However, muscle foods are deficient in calcium, dietary fibre, and vitamin C [3].
In recent years, consumers have become more aware of a possible relationship between food and health, leading to changes in eating habits towards a healthier diet [3].Additionally, an increase in meat prices, the emergence of vegetarianism [4] as well as increase in awareness pertaining to animal suffering and sustainability issues, particularly the greenhouse gas emissions from animal protein production, have shifted consumer preference towards non-meat protein sources [5] such as soybeans, legumes, wheat, oil seeds, and mushrooms.These ingredients are noticeable due to their ability to retain moisture and water during the processes of cooking, reheating, freezing, and thawing.Moreover, they are cheaper than meat and could offer nutritional and health benefits equivalent to meat [4].
In general, mushrooms are regarded as a more sustainable and healthier natural ingredient due to their nutritive, bioactive, and therapeutic values [3].Hence, the cultivation of mushrooms is rising due to the current surge in health foods.Indeed, thirty nations generate more than 10,000 tonnes of mushrooms annually, and forty-three nations produce less than 10,000 tonnes of mushrooms, with the world's total production of nearly 10.2 million tonnes [6].The worldwide mushroom market is anticipated to rise at a Compound Annual Growth Rate (CAGR) of 6.74% from 15.25 million tonnes in 2021 to 24.05 million tonnes in 2028 [7].
Mushrooms are becoming more common ingredients in muscle food due to their fibrous structure mimics the texture of meat analogues [3].Meat analogous, also known as a meat alternative, meat substitute, faux meat, mock meat, or imitation meat, is defined as food structurally similar to meat but different in composition.It demonstrates the aesthetic qualities of certain types of meat, mainly the texture, flavour, appearance, and chemical properties [4].In addition, mushrooms provide a unique taste and umami flavour due to the presence of sodium salts of free amino acids (glutamic amino acids and aspartic amino acids) as well as 5'nucleotides.As a result, it gives foods a meaty taste, which consumers favourably accept [3], thereby driving animal protein replacement with mushrooms in meat products [8][9].The application of mushrooms, however, is limited to the fruiting bodies rather than the stems, which are often discarded due to their tough texture.This leads to problems in agroindustrial waste management [10].In China, the mushroom business generated over 100,000 tonnes of stems per year, and it was assumed that the volume was similarly higher in other developed nations.These leftovers mainly go to landfills or are used as compost [11].
Recently, plant-based waste materials have gained popularity as functional food components in meat products because of their high dietary fibre content and bioactive compounds such as vitamins, minerals, and polyphenols.These dietary fibres and phenolic compounds combine to form antioxidant dietary fibres, which can be used as dietary supplements to improve gastrointestinal health or as technical ingredients to inhibit lipid oxidation in foods, increasing the food products' shelf-life [12].Over the years, several food products have been developed using mushroom stems, reducing the amount of meat present.This substitution fits with the growing need for a shift from an animal-protein diet to a plant-based diet, which encourages the reduction of animal products (Flexitarian approach), avoiding meat products (vegetarian), or avoiding animal products altogether (vegan) [3].Adding mushroom stem waste powder positively affects the cooking yield and nutritional composition, especially dietary fibre content [12].In this regard, researchers have begun to use edible mushroom stems and waste to create valueadded food products due to the good compatibility of mushrooms with meat products.

II. BACKGROUND OF MUSHROOM
A mushroom is a fleshy, spore-bearing fruiting body of a fungus that is recognised by a stem (stipe), cap (pileus), and gills (lamellae) [13].Mushrooms have been consumed since antiquity and recognised by many civilisations, including the Greeks, Romans, and Chinese culture, due to their unique flavour and therapeutic properties [14], nutritional content, and healing properties [15].Mushrooms were widely used for culinary purposes by the upper class during the previous era [16].In addition, mushrooms have a peculiarly pleasant savoury taste, which is known as umami due to the presence of sodium salts of free amino acids such as glutamic and aspartic amino acids and 5-nucleotides, which makes them a popular choice in food [3].Currently, mushrooms are consumed in households all over the world as they possess a unique texture and desirable taste [16] that are compatible with meat and fish products [3].
Mushrooms can be classified into three categories: edible, medicinal, and wild.It is believed that there are at least 12,000 mushroom species worldwide, with around 2000 of them ideal for edible and/or medicinal use [3].Globally, Asian countries generate the highest percentage of overall mushroom production (74.64%) [17].In 2011, China was reported to be the world's largest mushroom producer, along with the United States, Italy, The Netherlands, and Poland [18].The most cultivated edible mushroom species are Pleurotus ostreatus, Lentinula edodes, Agaricus bisporus, Flammulina velutipes, and Auricularia auricular.Meanwhile, Ganoderma lucidum, Cordyceps sinensis, and Poria cocos are the most harvested medicinal mushrooms [15].The most important factors influencing the production of grown edible mushrooms are temperature, humidity, fresh air, and compact material.In general, mushroom production is more sustainable than meat products, hence causing less damage to the environment [3].

III. NUTRITIONAL PROPERTIES OF MUSHROOM
Mushrooms are known for their nutritional richness and have been applied in various products such as patties [8], bread [19], muffins [20], pasta [21], snacks [22], soup [23], cookies [24][25], and biscuits [26].Mushrooms are high-quality protein source as they contain all nine amino acids essential for humans [27].Mushrooms contain about four times the protein content of tomatoes and carrots, six times that of oranges, and twelve times that of apples [3].However, the amount of crude protein of mushrooms is mainly differ and affected by development stage, and species [28].
Mushrooms are high in indigestible carbohydrates, which contribute to a low glycemic index as well as contain high mannitol making them apt for diabetic patients.Both caps and stems are also high in dietary fibre due to the presence of nonstarch polysaccharides (predominantly composed of insoluble dietary fibre and glucans) which may help prevent hypertension and hypercholesterolemia and be beneficial in weight control.Moreover, they are an excellent source of polysaccharides (α-glucan, β-glucan chitin, mannans, galactans, and xylans), minerals (copper, iron, manganese, zinc, phosphorus and potassium), vitamins (B1, B2, B12, C, D, E, folate, and niacin), and unsaturated fatty acids primarily linoleic acid [3].
Since mushrooms are plant-based source foods, thus, they are cholesterol-free and contain low amounts of sodium [29].For example, the fruiting bodies of Agaricus sp.contain 396 mg sodium/kg (n=14) [30] compared to processed meats containing 7 to 39 g sodium chloride/kg [31].Mushrooms are also gluten-free [29] and a rich source of bioactive compounds such as phenolics and flavonoids that could be vital to human health in lowering the risk of diseases such as oral health and cancer [18].In addition, mushrooms act as an immune system enhancer, antibacterial, and cholesterol-lowering agents.Consumers consume almost 5 kg of mushrooms per person per year on average, which is projected due to consumer awareness of a healthy diet [32].

IV. POTENTIAL APPLICATION OF MUSHROOMS IN MEAT PRODUCTS
Mushrooms are a source of healthy food and are recognised as superior nutritional supplements.They are being used directly in food as well as raw materials in the formulation of novel functional foods development due to their taste, aroma, and inherent texture-modifying functional properties, which have been found to positively affect the appearance, flavour, overall acceptance, and shelf-life of food products, especially in meat products.Various meat products have been developed using mushrooms as functional bioactive components to improve the nutritional content and potential health benefits.Adding mushrooms to processed meats may help lower the salt levels of the products, providing more nutritional and health advantages to consumers.Mushrooms have been successfully added in many formulations of meat products [3], such as chicken sausage [33], chicken frankfurter [34], pork frankfurter [35], emulsion-type sausage [36], Cantonese sausage [37], chicken burger [38], chicken patties [8], pork patty [39], and beef burger [40].Indeed, the incorporation of mushrooms influences the cooking characteristics, physicochemical properties, and nutritional composition of the meat products.

IV. APPLICATION OF MUSHROOM STEMS IN MEAT PRODUCTS OR MEAT ANALOGUE
Consumers ingest meat products for their sensory properties and essential nutritional components [2].It is anticipated that booming population, education, urbanisation, industrialisation, and affluence will result in a 72% increase in meat consumption by 2030.It is forecasted that worldwide meat production will more than double from 229 million tonnes in 1999/01 to 465 million tonnes in 2050 [41].However, the reputation of meat products has recently been impacted due to high levels of saturated fatty acids, cholesterol, salt, and synthetic additives, which are frequently linked to a variety of diseases such as diabetes, obesity, cardiovascular disease, and cancer.The suggestion to restrict the intake of red meat and processed meat has influenced the consumer's perception of meat products.As a result, meat is replaced with various plants, including co-products and by-products, with the added benefit of dietary fibre, which is not common in meat products [2].
The use of plant-based waste materials as a functional ingredient in meat products is gaining popularity [12,[42][43][44].As such, mushrooms are considered a promissory source of bioactive compounds that can be utilised to develop healthier meat products [2].Total mushroom production in Asian countries contributes the highest percentage of total worldwide production [17].However, the potential values of the stems or stalks were often omitted and considered as food loss, which led to challenges in agro-industrial waste management [45].Data on the global or country-specific allocation of crop residues to mushroom production are scarce in the literature [46].In fact, for every kg of mushrooms harvested, approximately 25% is left behind and is treated as waste, and this consists of the mushroom stems that connect the mushroom to the compost [47].In the past few years, the agroindustrial waste from mushrooms has attracted the attention of researchers from all over the world due to the presence of bioactive compounds [45].Recently, mushroom stems were successfully added to several meat products, and the effects of mushroom stems and their waste in meat and meat analogue products are presented in Table 1.

TABLE I. EFFECTS OF MUSHROOM STEMS IN MEAT PRODUCTS OR MEAT ANALOGUES
V. CONCLUSIONS Mushrooms are widely used in various products, but the potential values of the stems, stipes or stalks are usually omitted and considered food waste, which poses a challenge in agro-industrial waste management.The underutilised mushroom stems have the potential to be incorporated into meat products as they mimic the texture of meat as well as contribute to the appealing umami flavour.Furthermore, mushroom stems possess a high nutritional value, especially fibre and phytochemical content that could be a promising ingredient to produce a value-added meat product in the current sector aligned with consumers' preferences and recent trends.