Oyster mushroom (Pleurotus ostreatus)

The second most popular edible mushroom in the world, oyster mushrooms are found in the wild but can be cultivated on straw and a variety of other substrates. The mushrooms come in a range of colours — the most common being white or grey but can also be golden yellow, pink, tan or dark brown. The flesh and gills are white.

Oyster mushrooms are widespread in temperate and subtropical forests and are called “saprotrophs”, meaning they are a primary decomposer (digestor) of dead wood of deciduous trees, particularly beech trees.

Commercial cultivation first started in Germany as a subsistence food in World War 1. Today, its cultivation comprises 27 per cent of the world’s total mushroom production and is viewed as a potential step towards food security.

Oyster mushrooms can be prepared in a variety of ways such as soups, stir-fries, stuffed or breaded and as a tasty alternative to meat. A delicacy in Asian cooking, oyster mushrooms can also be used as a vegetarian alternative to oyster sauce in Asian cooking.

Bioremediation — an environmental restorer
Oyster mushrooms bioaccumulate lithium and a range of other environmental compounds. They are lignocellulolytic fungi that can use lignin, cellulose and hemicellulose as carbon and energy sources, giving them spectacular bioremediation properties. Due to their highly efficient enzymatic system, they are able to degrade a large range of compounds and can be grown on a substrate of a variety of toxic chemicals and plastics.

Therapeutic uses in human trials
Oyster mushrooms have traditionally been used as foods and as medicines. Medicinal properties have show numerous benefits. These include immunomodulation, antioxidant, antifungal, antibacterial, antiparasitic and antiviral, cardiovascular, antihypertensive and anti-hypercholesterolaemic, detoxification, anti-inflammatory and anti-diabetic effects.

Active ingredients in oyster mushrooms
Oyster mushrooms are highly nutritious, containing polysaccharides, beta-glucans, phenolics, flavonoids, vitamins C, B1, B2, B3, B6, B9 as well as vitamins A, D and E, minerals (potassium, phosphorus, selenium, zinc), glycoproteins, steroids, lectins, alkaloids, superoxide dismutase, fibre and bioactive proteins including ergothioneine. They are also low in calories, fat and sodium.

Gastrointestinal: The beta-glucan levels in oyster mushrooms make them an ideal prebiotic that has the potential to restore gut microbial balance, particularly evident as people age.

Cardiovascular: Research shows oyster mushrooms act as anti-hypertensives capable of inhibiting ACE and blocking calcium channels with their powerful antioxidant activity. A small human trial on hypertensive and diabetic patients showed consuming oyster mushrooms daily for three months lowered both systolic and diastolic blood pressure significantly (with reductions in HbA1c).

Further studies showed a lowering of high cholesterol level  — long-term supplementation of 5 per cent oyster mushrooms effectively suppressed diet–induced hypercholesterolemia in rats by inhibiting cholesterol absorption and VLDL synthesis, with a reduction in atherosclerosis risk factors.

Immune: Regular consumption of oyster mushrooms can play a significant role in prevention or treatment of infectious diseases, including acute respiratory viruses, herpes II viral infections, adenoviruses and possibly COVID infections.

Neurological: A Korean study on 87,822 participants showed that consuming mushrooms regularly — particularly oyster mushrooms (more than one serving per month) — demonstrated significantly decreased levels of depressive symptoms, with women and older participants showing a stronger association. The explanations for these findings centered around the reduction in proinflammatory cytokines and oxidative stress, both of which have been shown in previous meta-analyses to contribute to neuropsychiatric disorders.

Endocrine: Rodent studies have demonstrated that consuming oyster mushrooms reduces blood sugar in diabetics. The polysaccharides have beneficial effects on NIDDM, reducing blood glucose, as well as glucose and ketones in the urine.

In further rat studies, the anti-hyperglycaemic effect was thought to be due to the healing of damaged pancreatic B cells, partially restoring their hormonal activity, increasing peripheral sensitivity to insulin and modulation of its synthesis and increasing glucose utilisation in muscle cells.

Oyster mushrooms constitute an incredible resource for sustainable human and environmental needs. They are exceptional both as foods and medicines and are easily cultivated. They play a crucial role in recycling agricultural, pharmaceutical and chemical wastes into valuable compounds to enhance both the environment and human health.

References available on request.