Generality
Porcini are a group of mushrooms basidiomycetes belonging to the Boletaceae family and to the Genus Boletus.
Identified with the binomial nomenclature Boletus edulis, in French they are said Cèpe de Bordeaux, while in English they are known as cep, penny bun or king bolete.
In the past, many European mushrooms with characteristics similar to those of porcini were considered varieties of B. edulis, but the molecular phylogenetic analysis has denied this hypothesis; curiously, however, other mushrooms previously classified as species in their own right, have appeared conspecific to porcini.
The western North American species known as california king bolete (Boletus edulis var. Grandedulis) is a darker colored variety formally identified only in 2007.
Description
The surface of these pores is whitish at a young age and evolves to a greenish-yellow when fully ripe (see image).
The stem or stem porcini is robust, white or yellowish, up to 25cm long and even 10cm wide; it is superficially covered by a light layer of lattices.
Nutritional Characteristics
Porcini are foods of fungal origin (not vegetable), therefore they are allowed in lacto-ovo vegetarian, vegan diets and potentially also in raw foodists.
Fresh porcini mushrooms contain about 80% water, although this value depends on the atmospheric conditions at the time of development and processing; they have a low content of fats and carbohydrates available, while they boast a higher quantity of proteins of medium biological value.
Total carbohydrates (including those not available) make up the majority of the fruiting body of boletus, that is more than 9.23% of the fresh weight and 65.4% of the dry weight. These are mainly soluble monosaccharides - such as glucose, the mannitol (not available) and the alpha trehalose - and insoluble polysaccharides (up to 80-90% of the dry matter in the cell walls) such as glycogen and chitin.
There chitin, the "hemicellulose and the pectin (not available) represent the dietary fiber of porcini mushrooms.
In porcini mushrooms, total lipids make up 2.6% of the dry matter. The proportion of fatty acids (expressed as a% of the total) is: acid palmitic 9.8%; acid stearic 2.7%; acid oleic 36.1%; acid linoleic 42.2% and acid linolenic 0,2%.
A comparative study of the amino acid composition of eleven Portuguese edible mushrooms showed that Boletus edulis has the highest total amino acid content. All 20 essential and even many non-essential amino acids are included.
Analysis of free amino acids (ie those not bound in proteins) revealed higher concentrations of glutamine, alanine (both about 25% of the total) e lysine.
The nutritional role of porcini mushrooms is above all that of providing some vitamins, mineral salts and dietary fiber (the aforementioned carbohydrates not available).
The values on the metal and mineral composition of boletus are quite different according to the research source; this is due to the fact that the fungi accumulate different elements and that the concentrations in the fruiting bodies are often variable according to the composition of the soil.
In general, boletus contain appreciable quantities of selenium (antioxidant and useful element for the functioning of the thyroid); however, its bioavailability is considered to be rather modest.
Wild boletus contain good amounts of vitamin D2 properly called (ergocalciferol), but its concentrations appear to be lower in cultivated mushrooms (concentrations strongly depend on exposure to sunlight, even after they have been harvested). Also the amount of vitamin E (tocopherols) is not negligible.
In addition, porcini mushrooms contain good amounts of ergosterol (precursor of vitamin D); it is a relatively high intake that makes porcini extremely interesting food for vegetarians and vegans, who often suffer from a vitamin deficiency due to their diet. In order for ergosterol to be converted into vitamin D2 it is necessary that the mushroom is exposed to ultraviolet light from the sun; this reaction also occurs after harvesting, so some researchers have come to the conclusion that it would be good to expose the mushrooms for about 60 minutes to the sun before to cook and eat them.
Porcini produce other organic compounds having different biological activities; among these, antivirals, antioxidants and antioxidants are famous phytochelatins (they favor the resistance of the organism to toxic heavy metals).
Chemical structure of (from left to right): ergosterol; ergocalciferol (Vitamin D2) ergosterol peroxide.
Bio-Active Compounds of Porcini
As anticipated, porcini mushrooms contain excellent amounts of ergosterol. In addition, they bring ergosterol peroxide, a steroid derivative with a broad spectrum of biological activity, including antimicrobial, anti-inflammatory and cytotoxic functions for some cancer cells (effect observed in vitro).
Porcini also contain lectin, which has an affinity for it xylose and the melibiose. Lectin is a mitogenic compound, meaning it can stimulate cells to initiate the replication process resulting in mitosis. In addition, lectin has known antiviral properties as it inhibits the "viral reverse transcriptase enzyme of human immunodeficiency.
Other studies suggest that porcini also have an antiviral activity against the virus Vaccinia and the tobacco mosaic.
Antiviral compounds from fungi are of interest in biomedical research due to their power to improve knowledge on viral replication and their potential utility in treating infections.
Porcini mushrooms have a "high antioxidant capacity, probably due to the combination of various organic acids (oxalic, citric, malic, succinic And fumaric), tocopherols, compounds phenolics and alkaloids.
The most developed antioxidant activity is localized inside the mushroom caps. Additionally, boletus is estimated to contain up to 528mg of ergothioneine (sulfur amino acid with antioxidant action) per kilogram of fresh mushrooms, one of the highest values found in the foods examined.
According to a Hungarian research conducted in 1950, boletus may boast some anti-cancer capacity but, following other US investigations, the hypothesis has been disproved.
Gastronomic notes
Appreciated as ingredients of great value in many recipes, porcini are edible mushrooms both raw and cooked.
The gastronomic use of porcini includes the formulation of some first courses such as soups, pasta dishes, risottos, polenta etc. In addition, they enrich numerous meat-based dishes such as, for example, stews in fricassee; there are also some combination of crustaceans (prawns) and porcini mushrooms.
Porcini mushrooms are also added in intermediate recipes, appetizers, salads or single dishes, such as bruschetta, pizza, raw salads, sandwiches, etc.
Heavy Metal Contamination
Boletus are known to be able to tolerate and even thrive on soils contaminated with toxic heavy metals, such as near foundries.
As anticipated, the resistance of the fungus to heavy metal toxicity is conferred by a biochemical compound called phytochelatine oligopeptide, whose production is induced by exposure to the metal itself.
Phytochelatins are chelating agents capable of forming multiple bonds with the metal. In this form, the contaminant is unable to react with other surrounding elements or ions and is stored in a non-toxic variant within the tissues.
Commodity study
Despite being very commercially sold, porcini are still very difficult to grow.
In Europe, porcini mushrooms are available in fresh form especially in late summer and autumn; in the other seasons, however, they are distributed frozen or dried or in brine.
Famous, and awarded the IGP (Typical Geographical Indication) mark, are the porcini mushrooms of Borgotaro.
Habitat
Porcini mushrooms grow in deciduous and coniferous forests, or in plantations, forming associations ectomycorrhizal symbiotic that envelop the underground roots of plants with sheaths of fungal tissue.
The fungus produces fruiting bodies (what is commonly understood as a fungus) of spores that come out of the soil in the summer and autumn seasons.
Related Species
Various Species of mushrooms similar to porcini proper are considered subspecies or simple varieties. In Europe, in addition to B. edulis (o Cèpe de Bordeaux), the most popular pseudo-porcini (Boletus species) are:
- Tête de Nègre ("Negro's head" or better Boletus aereus), much rarer than B. edulis, is the most appreciated by gourmets and also the most expensive. It is usually smaller and darker than B. edulis and is very suitable for drying
- Cèpe des pins ("porcino of the" pine tree "or better Boletus pinophilus or Boletus pinicola); obviously it grows among the pines. Rarer than B. edulis, it is less appreciated by gourmets than the other two types but remains superior to almost all others
- Cèpe d "été ("summer porcino" or Boletus reticulatus), is even less common and earlier than the others.
Including edulis, these are the four independent Boletus species found in Europe; as regards the subspecies of edulis, on the other hand, we can deduce: betulicola, chippewaensis, persoonii, oak tree And venturii.
