Type of single-cell fungal protein
Mycoprotein (lit. "protein from fungus"), also known as mycelium-based protein or fungal protein, is a form of single-cell protein derived from fungi for human consumption. 
Though these products derived from mycoprotein often are referred to as plant-based, this assortment is per definition wrong as the fungal kingdom, including mushroom-forming species as well as yeasts and molds, are separate from those of animals (Animalia) and plants (Plantae).
With that said, mycoprotein should neither be confused with mushroom-based products, as the part of fungi grown for mycoprotein is the vegetative growth of the fungi, called mycelium, which can be compared to the roots of the organism. Metaphorically, the mushroom and the mycelium are as similar as a fruit is to the roots of its tree. 
The Market.
History.
The discovery of mycoprotein was a result of "The Green Protein Revolution"-inspired British scientists looking for a sustainable alternative protein that could offset the global crisis fueled by population growth, food shortage and greenhouse gas emissions. Dr Tim Finnigan, former Chief Scientific Officer at Marlow Foods, has previously described how these scientists collected over 3000 soil organisms around the world before discovering "Fusarium venenatum": a micro fungus that grows in filaments (long thread-like cells) and effectively transforms starch into a fibrous, meat-like, and protein-rich ingredient. In 1985, almost 20 years later, Marlow Foods became the first company to launch mycoprotein-based products on the market under the brand name Quorn. 
Today.
With Quorn's patents lapsing and the increasing need for alternative proteins due to the growing world population, rising emissions, and water usage, numerous start-up companies worldwide have begun developing mycoprotein-based ingredients and products, often using new strains and innovative technologies. For example, the Swedish company Millow, along with the Scottish company ENOUGH, are developing mycoprotein ingredients. ENOUGH produces the mycoprotein ingredient ABUNDA, utilizing submerged fermentation methods, while Millow uses a dry fermentation method for its mycoprotein production. These companies focus on the business-to-business supply of their take on a mycoprotein ingredient. Other companies, such as Spanish Libre and American MyForest Foods, have instead chosen to launch mycoprotein-based products in retail, hence working business-to-consumer. 
Production &amp; Synthesis.
The production of mycoprotein takes place in vats, like in beer production. The fungi are grown under aerobic conditions, to which nitrogen, carbon and essential vitamins and minerals are supplied. Carbon dioxide is drawn from the vat. In the case of F. venenatum, glucose is supplied for carbon and ammonia for nitrogen. Parameters such as stirring, pH and temperature are also essential for optimal growth. 
At harvest, the fungus is washed and heat treated to reduce the ribonucleic acid (RNA) content according to safety regulations before undergoing further processing steps. Different flavors and tastes can be added to the mycoprotein to add variety.
A reproducible mutation occurs after 1,000 to 1,200 hours of cultivation in "F. venenatum" that greatly reduces the hypha length in the organism, which is considered unfavorable for production. Under normal conditions, this mutant strain will rapidly displace the parent strain. Replacing ammonia with nitrate as the source of nitrogen, or supplementing ammonium cultures with peptone, prevents this mutant strain from overtaking the product, but still allows development. Alternatively, the appearance of the mutant can be delayed by selection pressures such as nutrient concentrations or pH levels.
Sensory, Nutrition &amp; Health.
Due to the root-like structure of the mycelium, the texture and nutrition of mycoprotein is very different from those of plants, leading to the possibility of creating vegetarian and vegan friendly products with the fibrous texture of meat. As it is high in protein and fiber, and low in fat, cholesterol, sodium and sugar, the composition aligns with current dietary guidelines. This nutritional advantage, as mentioned in the United Nations Environment Programme (2023), is why several studies have shown that consumption of mycoprotein has been associated with several health benefits, such as improved blood levels of cholesterol and sugar. The mechanism that links fiber content and mycoprotein's effect on managing glycemia and insulinemia is not entirely understood, and often disputed by endocrinologists, but is known to decrease the rate of glucose absorption and insulin secretion, whilst lowering insulin peaks by mitigating the maximum limit an amount of insulin can process glucose. The majority of this benefit is widely believed to be down to the high protein content, which stimulates encretins and satiety; and the high fibre content which makes people feel fuller for longer.
Back in 2001, a review article published in the Food Technology Magazine summarized how a panel of experts evaluated the sustainability of mycoprotein (produced by Marlow Foods) for food use in the United States. During this evaluation, the protein quality was evaluated using both the FDA Protein Digestibility-Corrected Amino Acid Scoring (PDCAAS) as well as a human volunteer study. The evaluation showed that mycoprotein has an excellent pattern of amino acids, and a PDCAAS score of 0.91 based on an estimate of 78% digestibility, comparable to the scores of beef and soybean. In addition to this, the fatty acid pattern was concluded to be more similar to that of vegetable fat than animal fat, containing a low proportion of saturated fat and a high proportion of mono- and polyunsaturated fat. 
Also mentioned in this review, as well as in more recent articles, is that mycoprotein contains no or very low levels of phytic acids (also known as phytates), which are notorious anti-nutrients present in many plant-based protein sources. This means that in contrast to most beans and legumes, consumption of mycoprotein does not inhibit the absorption of essential trace elements and minerals like iron, zinc, calcium, and manganese. 
It has also been found that mycoprotein produced by "F. venenatum" can consist of up to 42% protein while the fungal β-glucan present may also function as a prebiotic, stimulating the growth of health associated bacteria in the lower gut.
The texture and taste of mycoprotein may vary as different producers use different strains of fungi to produce their unique protein. For example, Nature's Fynd, a company founded in Chicago 2021, produce their Fy Protein™ from "Fusarium yellowstonensis" (also known as "Fusarium strain flavolapis" or "Fusarium oxysporum MK7"), an extremophile discovered in Yellowstone National Park, whilst Meati Inc. since 2022 produces their MushroomRoot™ from "Neurospora crassa" based on patented research by the Better Meat Co. The texture and taste are also influenced by different downstream technology, i.e., the treatment after harvesting the vats. Mycoprotein produced by "F. venenatum" has, for example, been described as a pale yellow solid with a faint taste of mushrooms.
Allergies &amp; Hypersensitivity.
Hypersensitivity reactions caused by ingestion of mycoprotein is very rare, though it has previously occurred in people allergic to mold or other fungi. For most individuals, mycoprotein is safe to eat. The fact is that 72.4% of allergic reactions and 67.6% of the gastrointestinal reactions that have been reported after ingestion of a Quorn product occurred on an individual's first consumption of Quorn's products, which is an indication of cross-allergenicity with other antigens. There is, however, continual testing for concerns of allergic reactions, which can range from abdominal pain, nausea, and vomiting to severe asthmatic reactions, especially when crossed with inhaled mold spores.
A few but not all strains involved in mycoprotein production are known to produce mycotoxins in very low concentrations, amongst others some strains of "F. venenatum," which in Quorn's case is prohibited by continuous testing every 6th production hour. "Fusarium yellowstonensis," on the other hand, is an example of a strain that has been found to have low allergenic potential and no mycotoxins has been detectable.
Law, Legislation &amp; Recognition.
Although mycoprotein is considered a new generation of alternative protein, most microorganisms used to produce mycoprotein have been used for decades, some for centuries, and do not fall under the Novel Food Regulation in the European Union. Mycoprotein has been considered Generally Recognized as Safe (GRAS) by the Food and Drug Administration in the US since 2002. 
However, looking across the globe, mycoprotein has still not been fully recognized as the sufficient protein source it is, despite its nutritional and sustainable benefits and advantages. An open access article was published in early 2022 on the topic of the lack of a global uniformity when it comes to Food-Based Dietary Guidelines (FBDG). The author, reviewed by Marlow Foods, points out that the global protein guidance tends to be dichotomous and exclusively focuses on comparing animal and plant proteins, resulting in alternative proteins, such as fungal proteins, being overlooked. Subsequently, the author calls for fungal protein to be included in the forthcoming EAT-Lancet 2.0 publication, due in 2024, and the Nordic Dietary Guidelines. 
This article is certainly not the only call for acknowledgement of fungal protein. In 2022, several companies pioneering for food sustainability united to form a new trade association: The Fungi Protein Association (FPA). One of the purposes of the association is to united advocate for mycoprotein in public policy. The founding members of the association include previous mentioned companies such as Quorn, ENOUGH, Mycorena and Nature's Fynd, but also companies as The Better Meat Co. and Prime Roots. Two members of the FPA, Mycorena and Quorn, published in 2022 an open letter to urge the Nordic Nutrition Recommendations (NNR) committee to review their selection of recommended protein sources and recognize fungi-derived proteins in food-based dietary guidelines. The NNR committee responded by including fungi as a source of non-animal protein in their nutrition recommendations published in June 2023.
Environmental Impact.
Several producers of mycoprotein have reported that production of mycoprotein has an environmental impact (including land-use, water consumption and carbon footprint) over 90% less than beef. Additionally, a study published in Nature 2022 found that replacing 20 percent of per-capita ruminant meat, such as beef, with fermentation derived microbial protein, such as mycoprotein, could cut global deforestation and carbon dioxide emissions by 50% in addition to lowering methane emissions. These numbers are under the assumption of consumer acceptance.
References.
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