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Porcino: Boletus edulis

A penny bun or a penny loaf was a small bread bun or loaf which cost one old penny at the time when there were 240 pence to the pound. A penny loaf was a common size loaf of bread in England regulated by the Assize of Bread Act of 1266. The size of the loaf could vary depending on the prevailing cost of the flour used in the baking. The nursery rhyme London Bridge Is Falling Down has a version which includes the line “Build it up with penny loaves”.

The expression ‘penny bun’ is Cockney rhyming slang for one, sun and son. ‘Penny bun’ is also the common English name for the cep (French), or Boletus edulis, an edible basidiomycete mushroom. Native to Europe and North America, it is Europe’s second most sought-after fungus after truffles.

‘Cockle to a penny bun’ is British slang for racing odds of 10 to 1
Boletus edulis (English: penny bun, cep, porcino or porcini) is a basidiomycete fungus, and the type species of the genus Boletus. Widely distributed in the Northern Hemisphere across Europe, Asia, and North America, it does not occur naturally in the Southern Hemisphere, although it has been introduced to southern Africa, Australia, and New Zealand. Several closely related European mushrooms formerly thought to be varieties or forms of B. edulis have been shown using molecular phylogenetic analysis to be distinct species, and others previously classed as separate species are conspecific with this species. The western North American species commonly known as the California king bolete (Boletus edulis var. grandedulis) is a large, darker-coloured variant first formally identified in 2007.

The fungus grows in deciduous and coniferous forests and tree plantations, forming symbiotic ectomycorrhizal associations with living trees by enveloping the tree’s underground roots with sheaths of fungal tissue. The fungus produces spore-bearing fruit bodies above ground in summer and autumn. The fruit body has a large brown cap which on occasion can reach 35 cm (14 in) in diameter and 3 kg (6.6 lb) in weight. Like other boletes, it has tubes extending downward from the underside of the cap, rather than gills; spores escape at maturity through the tube openings, or pores. The pore surface of the B. edulis fruit body is whitish when young, but ages to a greenish-yellow. The stout stipe, or stem, is white or yellowish in colour, up to 25 cm (10 in) tall and 10 cm (4 in) thick, and partially covered with a raised network pattern, or reticulations.

Prized as an ingredient in various foods, B. edulis is an edible mushroom held in high regard in many cuisines, and is commonly prepared and eaten in soups, pasta, or risotto. The mushroom is low in fat and digestible carbohydrates, and high in protein, vitamins, minerals and dietary fibre. Although it is sold commercially, it is very difficult to cultivate. Available fresh in autumn in Central, Southern and Northern Europe, it is most often dried, packaged and distributed worldwide. It keeps its flavour after drying, and it is then reconstituted and used in cooking. B. edulis is one of the few fungi sold pickled.

The fungus also produces a variety of organic compounds with a diverse spectrum of biological activity, including the steroid derivative ergosterol, a sugar binding protein, antiviral compounds, antioxidants, and phytochelatins, which give the organism resistance to toxic heavy metals.

Boletus edulis fruit bodies contain about 500 mg of ergosterol per 100 g of dried mushroom. Ergosterol is a sterol compound common in fungi. Additionally, the fruit bodies have about 30 mg of ergosterol peroxide per 100 g of dried mushroom.

Ergosterol peroxide is a steroid derivative with a wide spectrum of biological activity, including antimicrobial and anti-inflammatory activity, and cytotoxicity to various tumor cell lines grown in laboratory culture.
The mushroom also contains a sugar-binding protein, or lectin, that has affinity for the sugars xylose and melibiose.

The lectin is mitogenic—that is, it can stimulate cells to begin the process of cell division, resulting in mitosis. Further, the lectin has antiviral properties: it inhibits the human immunodeficiency virus enzyme reverse transcriptase. Other studies suggest that B. edulis also has antiviral activity against Vaccinia virus and tobacco mosaic virus grown in culture. Antiviral compounds from mushrooms are a subject of interest in biomedical research for their potential to advance the knowledge of viral replication, and as new drugs in the treatment of viral disease.

The fruit bodies have a high antioxidative capacity, due probably to a combination of various organic acids (such as oxalic, citric, malic, succinic and fumaric acids), tocopherols, phenolic compounds and alkaloids; the highest antioxidant activity is in the mushroom caps. Furthermore, fruit bodies were determined to have 528 mg of the antioxidant compound ergothioneine per kilogram of fresh mushroom; this value was the highest among many food items tested in one study. Porcini were thought to have anti-cancer properties according to Hungarian research conducted in the 1950s, but later investigations in the United States did not support this.

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