The fungus producesspore-bearingfruit bodies above ground in summer and autumn. The fruit body has a large browncap which on occasion can reach 30 cm (12 in), rarely 40 cm (16 in) in diameter and 3 kg (6 lb 10 oz) in weight. Like otherboletes, 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 theB. edulis fruit body is whitish when young, but ages to a greenish-yellow. The stoutstipe, or stem, is white or yellowish in colour, up to 20 cm (8 in), rarely 30 cm (12 in) tall and 10 cm (4 in) thick, and partially covered with a raised network pattern, orreticulations.
The fungus grows indeciduous andconiferous forests and treeplantations, formingsymbioticectomycorrhizal associations with living trees by enveloping the tree's underground roots with sheaths of fungal tissue. Widely distributed in theNorthern Hemisphere across Eurasia and North America, it does not occur naturally in the Southern Hemisphere, although it has beenintroduced to southern Africa, Australia, New Zealand, and Brazil. Several closely related European mushrooms formerly thought to bevarieties orforms ofB. edulis have been shown usingmolecular phylogenetic analysis to be distinct species, and others previously classed as separate species areconspecific 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.
B. edulis is held in high regard in many cuisines, and is commonly prepared and eaten insoups, pasta, orrisotto. The mushroom is low in fat and digestiblecarbohydrates, and high inprotein,vitamins,minerals anddietary fibre. Although it is sold commercially, it is very difficult tocultivate. Available fresh in autumn throughout Europe and Russia, 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 also one of the few fungi soldpickled.
Boletus edulis was firstdescribed in 1782 by the French botanistPierre Bulliard and still bears its original name.[3] The starting date of fungaltaxonomy had been set as January 1, 1821, to coincide with the date of the works of the 'father of mycology', Swedish naturalistElias Magnus Fries, which meant the name required sanction by Fries (indicated in the name by a colon) to be considered valid, as Bulliard's work preceded this date. It was thus writtenBoletus edulis Bull.:Fr. A 1987 revision of theInternational Code of Botanical Nomenclature set the starting date at May 1, 1753, the date of publication ofLinnaeus' work, theSpecies Plantarum.[4] Hence, the name no longer requires the ratification of Fries' authority. Earlyalternate names includeBoletus solidus by English naturalistJames Sowerby in 1809,[5] andGray'sLeccinum edule.[6] Gray's transfer of the species toLeccinum was later determined to be inconsistent with the rules of botanicalnomenclature, and he apparently was unfamiliar with the earlier works of Fries when he published his arrangement of bolete species.[7]
Boletus edulis is thetype species of the genusBoletus. InRolf Singer'sclassification of theAgaricales mushrooms, it is also the type species ofsectionBoletus, a grouping of about 30 related boletes united by several characteristics: a mild-tasting, whiteflesh that does not change colour when exposed to air; a smooth to distinctly raised, netted pattern over at least the uppermost portion of the stem; a yellow-brown or olive-brownspore print; white tubes that later become yellowish then greenish, which initially appear to be stuffed with cotton; andcystidia that are not strongly coloured.[8][9]Molecular analysis published in 1997 established that the bolete mushrooms are allderived from a common ancestor, and established theBoletales as anorder separate from the Agaricales.[10]
Thegeneric name is derived from theLatin termbōlētus "mushroom", which was borrowed in turn from theAncient Greek βωλίτης, "terrestrial fungus".[11] Ultimately, this last word derives frombōlos/βῶλος "lump", "clod", and, metaphorically, "mushroom".[12] The βωλίτης ofGalen, like theboletus of Latin writers likeMartial,Seneca andPetronius,[13] is often identified as the much prizedAmanita caesarea.[14] Thespecific epithetedulis in Latin means "eatable" or "edible".[15]
Common names forB. edulis vary by region. The standard Italian name,porcino (pl.porcini), meansporcine;[16]fungo porcino, in Italian, echoes the termsuilli, literally "hog mushrooms", a term used by the Ancient Romans[17] and still in use in southern Italian terms for this species.[18] The derivation has been ascribed to the resemblance of young fruit bodies to piglets, or to the fondness pigs have for eating them.[19] It is also known as "king bolete".[20] The Englishpenny bun refers to its rounded brownish shape. The German nameSteinpilz (stone mushroom) refers to the species' firm flesh.[21] In Austria, it is calledHerrenpilz, the "noble mushroom",[19] while in Mexico, the Spanish name ispanza, meaning "belly".[22] Another Spanish name,rodellon, means "small round boulder", while theDutch nameeekhoorntjesbrood means "squirrel's bread".[23] Russian names arebelyy grib (ru:белый гриб; "white mushroom" as opposed to less valuable "black mushrooms") andborovik (ru:боровик; frombor—"pine forest").The vernacular namecep is derived from theCatalancep or its French namecèpe, although the latter is a generic term applying to several related species. In France, it is more fullycèpe de Bordeaux, derived from theGasconcep "trunk" for its fat stalk,[24] ultimately from theLatincippus "stake".[25]Ceppatello,ceppatello buono,ceppatello bianco,giallo leonato,ghezzo, andmoreccio are names from Italian dialects,[26][27] andciurenys orsurenys is another term in Catalan.[28] The French-born KingCharles XIV John popularisedB. edulis in Sweden after 1818,[29] and is honoured in the local vernacular nameKarljohanssvamp, as well as the Danish nameKarl Johan svamp. The monarch cultivated the fungus about his residence,Rosersberg Palace.[30] The Finnish name isherkkutatti, fromherkku 'delicacy', andtatti, 'bolete'.[citation needed]
Cross-section showing white flesh, broad stem, and spore tubes on the underside of the cap
Thecap of this mushroom is 7–30 cm (3–12 in) broad at maturity. Slightly sticky to touch, it is convex in shape when young and flattens with age. The colour is generally reddish-brown fading to white in areas near the margin, and continues to darken as it matures. Thestipe, or stem, is 8–25 cm (3–10 in) in height, and up to 7 cm (3 in) thick—rather large in comparison to the cap;[31] it is club-shaped, or bulges out in the middle. It is finelyreticulate on the upper portion, but smooth or irregularly ridged on the lower part. The under surface of the cap is made of thin tubes, the site ofspore production; they are 1 to 2 cm (1⁄2 to3⁄4 in) deep, and whitish in colour when young, but mature to a greenish-yellow.[32] The angular pores, which do not stain when bruised, are small—roughly 2 to 3 pores per millimetre.[33] In youth, the pores are white and appear as if stuffed with cotton (which are actuallymycelia); as they age, they change colour to yellow and later to brown. The spore print is olive brown. The flesh of the fruit body is white, thick and firm when young, but becomes somewhat spongy with age. When bruised or cut, it either does not change colour, or turns a very light brown or light red.[34] Fully mature specimens can weigh about 1 kg (2 lb 3 oz); a huge specimen collected on theIsle of Skye, Scotland, in 1995 bore a cap of42 cm (16+1⁄2 in), with a stipe 18 cm (7 in) in height and14 cm (5+1⁄2 in) wide, and weighed 3.2 kg (7 lb 1 oz).[31] A similarly sized specimen found in Poland in 2013 made international news.[35]
Stem shape can range from club-shaped to centrally bulbous
Boletus edulis is considered one of the safest wild mushrooms to pick for the table, as few poisonous species closely resemble it, and those that do may be easily distinguished by careful examination.[19] The most similar poisonous mushroom may be the devil's bolete (Rubroboletus satanas), which has a similar shape, but has a red stem and stains blue on bruising.[19] It is often confused with the very bitter and unpalatableTylopilus felleus, but can be distinguished by the reticulation on the stalk; in porcini, it is a whitish, net-like pattern on a brownish stalk, whereas it is a dark pattern on white in the latter. Porcini have whitish pores while the other has pink. If in doubt, tasting a tiny bit of flesh will yield a bitter taste.[19] It can also resemble the "bolete-like"Gyroporus castaneus, which is generally smaller, and has a browner stem.Boletus huronensis, an uncommon mushroom of northeastern North America, is another recognized look-alike known to cause severegastrointestinal disorders.[36]
Thespores are elliptical to spindle-shaped, with dimensions of 12–17 by 5–7 μm. Thebasidia, the spore-bearing cells, are produced in a layer lining the tubes, and arrange themselves so their ends are facing the center of the tube; this layer of cells is known technically as ahymenium. The basidia are thin-walled, mostly attached to four spores, and measure 25–30 by 8–10 μm. Another cell type present in the hymenium is the cystidia, larger sterile cells that protrude beyond the basidia into thelumen of the hymenium, and act as air traps, regulating humidity.[37]B. edulis has pleurocystidia (cystidia located on the face of a pore) that are thin-walled, roughly spindle-shaped toventricose, and measure 30–45 by 7–10 μm; the "stuffed" feature of the hymenium is caused by cheilocystidia—cells found on the edges of the pores.[32] Thehyphae ofB. edulis do not haveclamp connections.[33]
Several similar brownish-coloured species are sometimes considered subspecies or forms of this mushroom. In Europe, in addition toB. edulis (orcèpe de Bordeaux), the most popular are:
Cèpe bronzé ("dark cep";Boletus aereus), much rarer thanB. edulis, is more highly regarded by gourmets, and consequently more expensive. Usually smaller thanB. edulis, it is also distinctively darker in colour.[19] It is especially suited to drying.[20]
Cèpe des pins ("pine tree cep";Boletus pinophilus orBoletus pinicola) grows among pine trees. Rarer thanB. edulis, it is less appreciated by gourmets than the two other kinds of porcini, but remains a mushroom rated above most others.[20]
Molecular phylogenetic analyses have proven these three are all distinctive and separate species;[38] other taxa formerly believed to be unique species or subspecies, such asB. betulicola,B. chippewaensis,B. persoonii,B. quercicola andB. venturii, are now known to be part of aB. edulisspecies complex with a widemorphological, ecological and geographic range,[39][40] and that the genetic variability in this complex is low.[41] Similar molecular technology has been developed to rapidly and accurately identifyB. edulis and other commercially important fungi.[42][43]
Three divergent lineages found in Yunnan province in China that are commonly marketed and sold asB. edulis (and are actually more closely related toB. aereus) were described in 2013 asB. bainiugan,B. meiweiniuganjun andB. shiyong.[44][45] The classification has since been updated and expanded. All lineages are still members ofBoletus sect.Boletus, the sensu sticto "porcini clade" of the genus.[46]
B. rex-veris
Western North America has several species closely related toB. edulis. The white king bolete (Boletus barrowsii), found in parts ofColorado,New Mexico,Arizona, and California (and possibly elsewhere), is named after its discoverer Chuck Barrows.[47] It is lighter in colour thanB. edulis, having a cream-coloured cap with pink tones;[48] often mycorrhizal withPonderosa pine, it tends to grow in areas where there is less rainfall. Some find its flavour as good as if not better thanB. edulis.[49] The California king bolete (Boletus edulis var. grandedulis) can reach massive proportions, and is distinguished fromB. edulis by a mature pore surface that is brown to slightly reddish. The cap colour appears to be affected by the amount of light received during its development, and may range from white in young specimens grown under thickcanopy, to dark-brown, red-brown or yellow brown in those specimens receiving more light.[50] The queen bolete (Boletus regineus), formerly considered a variety ofB. aereus, is also a choice edible. It is generally smaller thanB. edulis, and unlike that species, is typically found inmixed forests.[51] The spring king bolete (Boletus rex-veris), formerly considered a variety ofB. edulis orB. pinophilus, is found throughout western North America. In contrast toB. edulis,B. rex-veris tends to fruit in clusters, and, as its common name suggests, appears in the spring.[52]B. fibrillosus is edible but considered inferior in taste.[53]
The fruit bodies ofBoletus edulis can grow singly or in small clusters of two or three specimens. The mushroom's habitat consists of areas dominated by pine (Pinus spp.), spruce (Picea spp.), hemlock (Tsuga spp.) and fir (Abies spp.) trees, although other hosts includechestnut,chinquapin,beech,Keteleeria spp.,Lithocarpus spp., andoak. In California, porcini have been collected in a variety of forests, such as coastal forests, dry interior oak forests andsavannas and interior high-elevationmontanemixed forests,[54] to an altitude of 3,500 m (11,500 ft).[55] In northwestern Spain, they are common inscrublands dominated by therock rose speciesCistus ladanifer andHalimium lasianthum.[56] Inthe Midi region of south-west France, they are especially favoured and locally calledcèpe de Bordeaux after the town from which they are traded to the north and abroad.[57]
Boletus edulis has acosmopolitan distribution, concentrated in cool-temperate tosubtropical regions.[54] It is common in Europe—from northern Scandinavia, south to the extremities of Greece and Italy—and North America, where its southern range extends as far south as Mexico.[34] It is well known from theBorgotaro area ofParma, Italy, and hasPGI status there. The European distribution extends north to Scandinavia and south to southern Italy and Morocco.[54] In North America, it can be found from May to October inland[58] and August to January on the West Coast.[59] In China, the mushroom can be found from the northeasternHeilongjiang to theYunnan–Guizhou Plateau andTibet.[34] It has been recorded growing underPinus andTsuga inSagarmatha National Park in Nepal,[60] as well as in the Indian forests ofArunachal Pradesh.[61] In West Asia, the species has been reported from the northwest forests of Iran.[62]
Boletus edulis grows in some areas where it is not believed to beindigenous. It is often found underneath oak andsilver birch inHagley Park in centralChristchurch, New Zealand, where it is likely to have beenintroduced,[65] probably on the roots of container-grown beech, birch, and oak in the mid-19th century—around the time exotic trees began to be planted in the Christchurch area.[34] Similarly, it has been collected inAdelaide Hills region of Australia in association with three species of introduced trees.[66] It has been growing plentifully in association with pine forests in the southernKwaZulu-Natal Midlands in South Africa for more than 50 years and is believed to have been introduced with the import of pine trees.[67][68] It also grows in pine plantations in neighboring Zimbabwe.[69]
Italian folklore holds that porcini sprout up at the time of the new moon;[19] research studies have tried to investigate more scientifically the factors that influence the production of fruit bodies. Although fruit bodies may appear any time from summer to autumn (June to November in the UK), their growth is known to be triggered by rainfall during warm periods of weather followed by frequent autumn rain with a drop in soil temperature.[54] Above average rainfall may result in the rapid appearance of large numbers of boletes, in what is known in some circles as a "bolete year".[70] A 2004field study indicated that fruit body production is enhanced by an open and sunny wood habitat,[71] corroborating an earlier observation made in a Zimbabwean study;[69] removal of the litter layer on theforest floor appeared to have a negative effect on fruit body production, but previous studies reported contradictory results.[72][73] A Lithuanian study conducted in 2001 concluded that the maximal daily growth rate of the cap (about 21 mm or 0.8 in) occurred when therelative air humidity was the greatest, and the fruit bodies ceased growing when the air humidity dropped below 40%. Factors most likely to inhibit the appearance of fruit bodies included prolonged drought, inadequate air and soil humidity, sudden decreases of night air temperatures, and the appearance of the firstfrost.[74] Plots facing north tend to produce more mushrooms compared to equivalent plots facing south.[75]
Boletus edulis ismycorrhizal—it is in amutualistic relationship with the roots of plants (hosts), in which the fungus exchangesnitrogen and other nutrients extracted from the environment forfixed carbon from the host. Other benefits for the plant are evident: in the case of theChinese chestnut, the formation of mycorrhizae withB. edulis increases the ability of plant seedlings to resistwater stress, and increases leafsucculence, leaf area, and water-holding ability.[76] The fungus forms a sheath of tissue around terminal, nutrient-absorbing root tips, often inducing a high degree of branching in the tips of the host, and penetrating into the root tissue, forming, to some mycologists, the defining feature of ectomycorrhizal relationships, ahartig net.[77] The ectomycorrhizal fungi are then able to exchange nutrients with the plant, effectively expanding the root system of the host plant to the furthest reaches of the symbiont fungi.[77] Compatible hosts may belong to multiple families ofvascular plants that are widely distributed throughout the Northern Hemisphere; according to one 1995 estimate, there are at least 30 host plant species distributed over more than 15 genera.[34] Examples of mycorrhizal associates includeChinese red pine,[78]Mexican weeping pine,[79]Scots pine,Norway spruce,[80]Coast Douglas-fir,[81]mountain pine,[82] andVirginia pine.[83] The fungus has also been shown to associate withgum rockrose, apioneer early stage shrub that is adapted for growth in degraded areas, such as burned forests.[84] These and otherrockrose species are ecologically important as fungal reservoirs, maintaining an inoculum of mycorrhizal fungi for trees that appear later in theforest regrowth cycle.[85]
The mushroom has been noted to often co-occur withAmanita muscaria orA. rubescens, although it is unclear whether this is due to a biological association between the species, or because of similarities in growing season, habitat, and ecological requirements.[54] An association has also been reported betweenB. edulis andAmanita excelsa onPinus radiata ectomycorrhizae in New Zealand, suggesting that other fungi may influence the life cycle of porcini.[86] A 2007 field study revealed little correlation between the abundance of fruit bodies and presence of its mycelia below ground, even when soil samples were taken from directly beneath the mushroom; the study concluded that the triggers leading to formation of mycorrhizae and production of the fruit bodies were more complex.[87]
Boletus edulis is known to be able to tolerate and even thrive on soil that is contaminated with toxic heavy metals, such as soil that might be found nearmetal smelters. The mushroom's resistance to heavy-metal toxicity is conferred by a biochemical called aphytochelatin—anoligopeptide whose production is induced after exposure to metal.[88] Phytochelatins arechelating agents, capable of formingmultiple bonds with the metal; in this state, the metal cannot normally react with other elements or ions and is stored in a detoxified form in the mushroom tissue.[citation needed]
The fruit bodies ofB. edulis can be infected by the parasitic mould-like fungusHypomyces chrysospermus, known as the bolete eater, which manifests itself as a white, yellow, or reddish-brown cottony layer over the surface of the mushroom.[89] Some reported cases ofstomach ache following consumption of dried porcini have been attributed to the presence of this mould on the fruit bodies.[90] The mushroom is also used as a food source by several species of mushroom flies,[54] as well as other insects and theirlarvae.[91] An unidentified species of virus was reported to have infected specimens found in the Netherlands and in Italy; fruit bodies affected by the virus had relatively thick stems and small or no caps, leading to the name "little-cap disease".[92][93]
A porcini mushroom and noodle soup served in a bread bowl at a Polish restaurantA porcini mushroom sandwich in Stockholm, Sweden
Boletus edulis, as the speciesepithetedulis (Latin:edible) indicates, is an edible mushroom. Italian chef and restaurateurAntonio Carluccio has described it as representing "the wild mushroompar excellence", and hails it as the most rewarding of all fungi in the kitchen for its taste and versatility.[19] Considered a choice edible, particularly in France, Germany, Poland and Italy,[20] it was widely written about by the Roman writersPliny the Elder and Martial, although ranked below the esteemedAmanita caesarea. When he was servedsuilli[a] instead ofboleti,[99] the disgruntled Martial wrote:
sunt tibi boleti; fungos ego sumo suillos (Ep. iii. 60) ("You eat the choice boletus, I have mushrooms that swine grub up.")[100]
The flavour of porcini has been described as nutty and slightly meaty, with a smooth, creamy texture, and a distinctive aroma reminiscent ofsourdough. Young, small porcini are most appreciated, as the large ones often harbourmaggots (insect larvae), and become slimy, soft and less tasty with age. The fruit bodies are collected by holding the stipe near the base and twisting gently. Cutting the stipe with a knife may risk the part left behind rotting and the mycelium being destroyed. Peeling and washing are not recommended.[19] The fruit bodies are highlyperishable, due largely to the high water content (around 90%), the high level ofenzyme activity, and the presence of a flora of microorganisms.[101] Caution should be exercised when collecting specimens from potentially polluted orcontaminated sites, as several studies have shown that the fruit bodies canbioaccumulate toxic heavy metals likemercury,[102]cadmium,[103]caesium andpolonium.[104][105] Bioaccumulated metals orradioactive fission decay products are like chemical signatures:chemical andradiochemical analysis can be used to identify the origin of imported specimens,[106] and for long-termradioecological monitoring of polluted areas.[107]
Porcini are sold fresh in markets in summer and autumn in Europe and Russia, and dried or canned at other times of the year, and distributed worldwide to countries where they are not otherwise found.[108] They are eaten and enjoyed raw, sautéed with butter, ground into pasta, in soups, and in many other dishes. In France, they are used in recipes such ascèpes à la Bordelaise,cèpe frits andcèpe aux tomates.[109] Porcinirisotto is a traditional Italian autumn dish.[110] Porcini are a feature of many cuisines, includingProvençal,[111] andViennese.[112] InThailand they are used in soups and consumed blanched in salads.[113] Porcini can also be frozen, either while raw or after cooking in butter. The colour, aroma, and taste of porcini deteriorate noticeably after being frozen for four months.Blanching (or soaking and blanching) as a processing step before freezing can extend the freezer life to 12 months.[101] They are also one of the few species sold commercially aspickled mushrooms.[114]
A pile of dried porcini at theBorgotaro porcino festival in Italy
Boletus edulis is well suited to drying—its flavour intensifies, it is easily reconstituted, and its resulting texture is pleasant.[115] Reconstitution is done by soaking in hot, but not boiling, water for about twenty minutes; the water used is infused with the mushroom aroma and it too can be used in subsequent cooking. Dried porcini have more protein than most other commonly consumed vegetables, apart fromsoybeans. Some of their protein is indigestible, though digestibility is improved with cooking.[116]
Like other boletes, porcini can be dried by being strung separately on twine and hung close to the ceiling of a kitchen. Alternatively, the mushrooms can be dried by cleaning with a brush (washing is not recommended), and then placing them in a wicker basket orbamboo steamer on top of a boiler or hot water tank.[117] Another method is drying in an oven at 25 to 30 °C (77 to 86 °F) for two to three hours, then increasing the temperature to 50 °C (122 °F) until crisp or brittle.[118] Once dry, they must be kept in an airtight container.[117] Importantly for commercial production, porcini retain their flavour after industrial preparation in apressure cooker or after canning or bottling, and are thus useful for manufacturers of soups or stews. The addition of a few pieces of dried porcino can significantly add to flavour, and they are a major ingredient of the pasta sauce known ascarrettiera (carter's sauce).[119] The drying process is known to induce the formation of variousvolatile substances that contribute to the mushroom's aroma. Chemical analysis has shown that the odour of the dried mushroom is a complex mixture of 53 volatile compounds.[120]
A 1998 estimate suggested that the total annual worldwide consumption ofBoletus edulis and closely related species (B. aereus,B. pinophilus, andB. reticulatus) was between 20,000 and 100,000 tons.[54] Approximately 2,700 tonnes (3,000 tons) were sold in France, Italy and Germany in 1988, according to official figures. The true amount consumed far exceeds this, as the official sales figures did not account for informal sales or consumption by collectors.[55] They are widely exported and sold in dried form, reaching countries where they do not occur naturally, such as Australia and New Zealand. The autonomous community ofCastile and León in Spain produces 7,700 tonnes (8,500 tons) annually.[84] In autumn, the price of porcini in the Northern Hemisphere typically ranges between $20 and $80 per kilogram, although in New York in 1997 the wholesale price rose to more than $200 per kilogram due to scarcity.[55]
In the vicinity ofBorgotaro in theProvince of Parma of northern Italy, the four speciesBoletus edulis,B. aereus,B. aestivalis andB. pinophilus have been recognised for their superior taste and officially termedFungo di Borgotaro. Here these mushrooms have been collected for centuries and exported commercially. Owing to the globalisation of the mushroom trade most of the porcini commercially available in Italy or exported by Italy no longer originate there. Porcini and other mushrooms are also imported into Italy from various locations, especially China and eastern European countries; these are then often re-exported under the "Italian porcini" label.[121][122]
In Italy the disconnect with local production has had an adverse effect on quality; for example in the 1990s some of the dried porcino mushrooms exported to Italy from China contained species of genusTylopilus, which are rather similar in appearance and when dried are difficult for both mushroom labourers and mycologists alike to distinguish fromBoletus.Tylopilus species typically have a very bitter taste, which is imparted to the flavour of the porcini with which they are mixed.[123]
After thefall of the Iron Curtain and the subsequent reduction of economic and political barriers, central and eastern European countries with local mushroom harvesting traditions, such as Albania, Bulgaria, Macedonia, Romania, Serbia and Slovenia, developed into exporters of porcini, concentrating primarily on the Italian market.[122] Porcini and other wild fungi from these countries are also destined for France, Germany and other western European markets, where demand for them exists but collection on a commercial scale does not.[122] PickingB. edulis has become an annual seasonal income earner and pastime in countries likeBulgaria, especially for manyRoma communities and theunemployed.[124] A lack of control of the harvest has led to heavy exploitation of the mushroom resource.[125]
Like many other strictly mycorrhizal fungi,B. edulis has eluded cultivation attempts for years.[116][126][63] The results of some studies suggest that unknown components of the soil microflora might be required forB. edulis to establish a mycorrhizal relationship with the host plant.[127][128][129] Successful attempts at cultivatingB. edulis have been made by Spanish scientists by mycorrhization ofCistus species,[63] withPseudomonas fluorescens bacteria helping the mycorrhiza.[64]
Boletus edulis mushrooms are 9%carbohydrates, 3% fat, and 7%protein (table). Fresh mushrooms consist of over 80% moisture,[133] although reported values tend to differ somewhat as moisture content can be affected by environmental temperature andrelative humidity during growth and storage.[134] The carbohydrate component contains themonosaccharidesglucose,mannitol and α,α-trehalose, thepolysaccharideglycogen, and the water-insoluble structural polysaccharidechitin, which accounts for up to 80–90% of dry matter in mushroomcell walls. Chitin,hemicellulose, andpectin-like carbohydrates—all indigestible by humans—contribute to the high proportion of insoluble fibre inB. edulis.[135]
A comparative study of theamino acid composition of eleven Portuguese wild edible mushroom species showedBoletus edulis to have the highest total amino acid content.[137][138]
Aroma compounds givingB. edulis mushrooms their characteristic fragrance include some 100 components, such asesters andfatty acids.[148] In a study of aroma compounds,1-octen-3-one was the most prevalent chemical detected in raw mushrooms, withpyrazines having increased aroma effect and elevated content after drying.[149]
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^Šutara J. (1985). "Leccinum and the question of superfluous names (Fungi: Boletaceae)".Taxon.34 (4):678–86.doi:10.2307/1222214.JSTOR1222214.
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^Peter Howell,A Commentary on Book One of the Epigrams of Martial, The Athlone Press, 1980 p.152-3. Howell doubts the identification, and mentions the view advanced by Augusta A. Imholtz Jr., 'Fungi and piace- names, thè origin of boletus,' inAJP Vol.98, 1977 pp.71f., that the Latin word may derive from the Spanish town Boletum, modern-dayBoltaña, south of thePyrenees, which is still famous for its mushrooms.
^Ramsbottom J. (1953).Mushrooms & Toadstools. London, England: Collins. p. 6.ISBN1-870630-09-2.
^Pliny,Natural History, Bk. 16, 11, 31: "Such is the multiplicity of products in addition to the acorn that are borne by hard-oaks; but they also produce edible fungi (boletos) and hog mushrooms (suillos)." Pliny,Natural History, 10 vols., tr. H. Rackham, Harvard University Press/Heinemann, (1945) 1968, vol. 4, pp. 408–409.
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