Theoyster mushroom (Pleurotus ostreatus, English - oyster mushroom, Japanese - hiratake) is a well-known mushroom worldwide, which is available in every store and fresh.

The names of the mushroom are based on the shape of its fruit. In Latin, pleurotus is a sideways/sideways growing mushroom, this is how the foot is positioned to the mushroom's cap. Ostreatus then refers to the shape of the mushroom, which resembles an oyster. Even the names in other languages are based on this similarity. It is said that the mushroom is also close to the oyster in taste.

Themushroom is a wood-destroying fungus that prefers colder geographical zones. It grows in clusters on damaged and dead deciduous trees, obtaining nutrients by decomposing the wood. However, little known, fungi of the genus Pleurotus are also 'carnivorous'. Their mycelium can kill and digest nematodes (nematodes). Because the fungus is not a parasite to trees, but a saprophyte, it helps return nutrients to the soil as dead or damaged wood decomposes, thereby supplying them to other plants.

Oyster mushrooms have been part of traditional Chinese medicine for thousands of years. The first written references to the fungus are found in the Shennong Bencao Jing materia medica. In ancient history, the mushroom was so sought after that it was cultivated and targeted. This was described in 199 AD. The inclusion of the mushroom in scientific texts took place in 1775, when it was described by the Danish naturalist N. J. Freiherr. At that time, however, he placed it in the genus Non-archeae, only later was the fungus reclassified into the genus Pleurotus by the German mycologist P. Kummer.

Apart from traditional medicine, the mushroom is also used in cuisine, especially in Asian cuisine. It is an integral part of Japanese, Korean and Chinese cuisine. It can be served on its own, but also in soups, sauces, vegetable and meat mixtures. The mushroom tastes best when picked young, it becomes tougher as it ages and the smell also becomes quite unpleasant. Some people may find it harder to digest and have digestive problems, this is due to the presence of arabitol, a sugar alcohol.

As the mushroom is in high demand, it is commercially grown, cultivated.

It can grow in open spaces, on specially constructed substrates or on substrates in polythene bags.

The substrates are designed to provide the best possible growth and nutrients for the mushroom. The most common materials include sawdust, starch, cereals, coffee bean pulp, cocoa, nut and coconut husks, cotton seeds, bananas, grass and corn stalks, clover, rice and much more. The substrate must be pasteurised or otherwise ensured to be free of bacteria, mould and other possible contaminants. The prepared substrate is inoculated with prepared fungal mycelia, which colonise it and then produce fruiting bodies. During this process, the correct temperature, humidity and carbon dioxide concentration must be maintained.

Of course, it is also grown on trees, mainly logs, and there are also methods of growing on straw.

The composition of the hawthorn

Theoyster mushroom is very rich in bioactive compounds that can be involved in the processes taking place in the body and modify them.

Sugar components

Like other mushrooms, oyster mushrooms are very rich in sugar components. Polysaccharides, complex sugars, are the most abundant. Polysaccharides include compounds that are not water-soluble and are so-called coarse fibre (cellulose, chitin), but more important are the water-soluble polysaccharides, i.e. glucans.

These are mainly beta glucans, which are branched at positions (1→3), (1→6). A polysaccharide that has been called pleuran is typical of the fungus. In this polysaccharide there are beta bonds between glucose molecules (1→3), the side chains are formed by glucopyranose molecules. The glucose molecules in the side chains are attached to the main chain via a (1→4) or (1→6) bond. The molecular weight is 600-700 kDa. We attach a part of the pleuran molecule:

Other compounds containing sugars are mannans, galactins and xylans.

In addition to polysaccharides, individual sugar molecules, i.e. monosaccharides, can also be extracted from tubers. These are glucose and galactose.

Amino acids and proteins

Polysaccharides, although the majority, are not the only component of fungi. Mushrooms are also rich in amino acids and proteins. Amino acids are the building blocks of protein and many can also be used to make the main energy compound for brain and muscle function, glucose, in times of nutrient deficiency.

Mushrooms contain both non-essential amino acids, which the body can create itself, and essential amino acids, which must be supplied to the body. Glutamic acid, aspartic acid, tyrosine, alanine, histidine, glycine, arginine, serine, tryptophan, leucine, isoleucine, threonine, methionine, etc., are the most abundant amino acids in mushrooms.

Among the important proteins in mushrooms are enzymes. The fungus is capable of breaking down woody matter and thus contains cellulases, hemicellulases, laccases, amylases, etc. It also contains enzymes that reduce oxidative stress, interact with and neutralise free radicals, such as superoxide dismutase, peroxidases and catalases.

The fungus can also be used to break down certain toxic substances that accumulate in nature and are irreducible. These include some herbicides, pesticides, antibiotics, etc. Enzymes from the fungus can break them down into inactive and harmless substances.

Thefungus also releases small secreted proteins, these are made up of less than 300 amino acids. They play an important role in e.g. infection affecting the fungus and modulate its defence response, they are also important for symbiotic life and the degradation of many substances, including wood and toxic substances.

Another important component of the fungus is gamma aminobutyric acid, known mainly by the acronym GABA, which is also a neurotransmitter. Also present is ornithine, which is a precursor to the synthesis of arginine (a precursor is a substance from which the final product is 'made').

The fungus also contains two proteins not found in any other fungus. These are osteolysin and pleurotolysin. The proteins have a cytolytic effect, i.e. they disrupt cell membranes, leading to cell damage and death. But for these effects to take effect when we eat the tubers, we would have to consume literally tens of kilograms. In experiments, a dose of 1,170 micrograms per kilogram of live weight in a mouse has been shown to be dangerous to rodents when given in pure form into a vein. Intoxication with osteolysin and pleurotolysin manifests itself as slowing of cardiac activity, lowering of blood pressure, cardiac ischemia. There is damage to erythrocytes, release of hemoglobin and potassium into the bloodstream. Impairment of pulmonary function also occurs, but this is closely related to damage to the cardiovascular system.

Lipids

Fungi are one of the few non-animal representatives that contain fats not only in their seeds. The mushroom is a carrier of both saturated fatty acids and unsaturated ones. The unsaturated fatty acids found in mushrooms include oleic, linoleic and arachidonic acids. Of the saturated ones, we can mention stearic or palmitic acid.

Other important components: phenols, terpenes, sterols...

Vital mushrooms, and therefore also the mushroom, are rich in phenols, terpenes and other compounds derived from them. These substances have significant antioxidant effects and have been tested in experiments on cancer cells and with pathogens. The results are positive.

The group of these substances (among sterols and steroids) includes vitamin D2, ergosterol, and cerevisterol.

Among the terpenes that give the mushroom a slightly bitter taste are ergosta-5,7,22-trien-3-ol, ergosta-5,7,9(11),22-tetraen-3, ergosta-5,8(14)-dien-3-ol, D-xenialactol.

Furthermore, phenyl and phenolic compounds are present in the mushroom: coumarins, e.g. 3-(2-indolyl)isocoumarin, 2,4-bis(1,1-dimethyl ethyl or 2,5-di-tertbutylphenol, 2,5-dihydroxybenzoic acid, ferulic acid, cinnamic acid, vanillic acid, naringenin, etc.

It is also possible to extract the flavone compounds morin, quercetin and resveratrol from hawthorn.

In a recent study (2018), the authors also described 5 naphtho-gamma-pyrones, 2 groups of isomers: fonsecinone B, asperpyrone F; asperpyrone C, fonsecinone A and aurasperone A. These substances were tested for their antibacterial effects, even on multidrug-resistant staphylococcus or E. coli.

Minerals and vitamins

The mushroom also contains many minerals that it obtains from its environment. These are mainly potassium, calcium, sodium, magnesium, zinc, selenium, iron, manganese, etc.

For illustrative purposes, here is an overview of the phytoconstituents of the mushroom. It shows how complex the mushroom is. There are, of course, polysaccharides and proteins

Lovastatin

Lovastatin is also an important and unique part of the mushroom, it is a secondary metabolite that is involved in cholesterol metabolism. As its name suggests, it is a statin that is also commonly used to treat high cholesterol in humans. Statins actually block HMG-CoA reductase, an enzyme involved in cholesterol synthesis.

For illustrative purposes, a summary of the phytocompounds of hawthorn is attached. It shows how complex the mushroom is. There are, of course, polysaccharides and proteins

Deepalakshmi, Krishnamoorthy & Mirunalini, Sankaran. (2016). Antiproliferative and apoptotic effect of Pleurotus ostreatus on human mammary carcinoma cell line (michigan cancer foundation-7). Cancer Translational Medicine. 2. 95. 10.4103/2395-3977.189303.