Edible mushrooms from Mexico: high quality wild foods

12/11/2020

All the traditional knowledge accumulated over the years has led to the current use of world consumption of about 1,100 different species of edible mushrooms, all with different nutritional profiles and in some cases with additional medicinal benefits. This important food source has been used by humans since ancient times.

Looking back on human nutrition, history informs us that for about 2.5 million years man in his environment fed himself by hunting animals and collecting plants, and he went from that lifestyle about 10,000 years ago to a sedentary lifestyle in which his attention was focused on using and managing some animal and plant species, becoming a farmer and breeder, a producer of his food.

Wheat, for example, and animals, such as goats, were domesticated to provide food, clothing, transportation, and other needs to the societies that developed around the world. The animal species mostly bred, as well as their diverse breeds, were selected from the wild, from the large number of animals found in natural ecosystems, surely in attention to the meat and milk yield they produce, the amount of forage they consume, and the efforts that must be made to raise them.

Likewise, the cereals and other vegetables that are intensively produced by farmers around the world, proved over millennia, to be productive, nutritious, appetizing, and relatively easy to grow, which from the beginning was a benefit for the pioneer farmers who sought their domestication in relation to other plant species.

However, of the great biodiversity that exists, the proportion of species used is very low, there is a great diversity of wild foods with important nutritional and medicinal qualities, and that mainly due to ignorance, as well as difficulties in their management, have not been domesticated, much less used, despite the importance they should have and among these excellent foods, many of them quite unknown, wild mushrooms stand out.

All the traditional knowledge accumulated over the years has led to the current use of world consumption of about 1,100 different species of mushrooms whose fruit is edible, all with different nutritional profiles and in some cases with additional medicinal benefits. This important food source has been used by humans since ancient times.

The oldest written records of edible mushroom consumption come from Asia, where it is known that in 1000 BC these foods were already being consumed, although there are also archaeological remains in South America that point to the fact that this food custom existed as far back as 13,000 years ago by primitive human groups or as the discovery of pollen and spores of edible wild mushrooms in the teeth of the remains of the "Red Lady" in the Cueva del Mirón (Cantabria, Spain) dating back 19,000 years.

But it should be noted that among the group of edible mushroom species, were those that by their saprotrophic nature (ie for their nutrition from waste from other organisms) managed to be cultivated in a sense more domestication, unlike other species that are only obtained by direct collection in forests, most of the latter by establishing symbiotic relationships with plants.

The oldest date we have about the cultivation of edible mushrooms dates back to 600 AD, with the production of the fungus Auricularia sp. known as mouse-ear or wood ear, a fungus with a gelatinous texture, which although present in Mexico, is not usually consumed. The production at the industrial or semi-industrial level of edible mushrooms has been registered already in the 20th century, mainly in Europe and the Far East, and later in the United States and Mexico.

Today, approximately 92 species of edible mushrooms have been cultivated around the world, being a high percentage of all production, few species, common in supermarkets, such as the popular mushroom (Agaricus bisporus/A. bitorquis) and the so-called "mushrooms" (Pleurotus spp.) leaving aside the possibility of cultivating other species that could provide many nutraceutical benefits.

One of the possible reasons for the "delay", which compared to cereals and vegetables, has occurred in the cultivation of edible mushrooms, is their relative biological complexity. The fungi as a group of organisms different from plants and animals, naturally have different ecological strategies and life cycles.

Saprobic fungi are species that develop by feeding on decomposing organic waste, from wood to straw and leaf litter to other types of organic waste. This group includes all species of edible mushrooms that can be cultivated with relative ease for consumption purposes, since through various techniques they can be planted in nutritious substrates specially prepared for them to develop and bear fruit. Many medicinal species also belong to this group of mushrooms.

On the contrary, symbiotic mushrooms are species that live in mutual cooperation with diverse plant species and group diverse species whose fructification is edible. These mushrooms help their plant hosts to absorb water from the soil and mineral nutrients, the plants in turn provide them with nutrients produced through photosynthesis. 

This group of wild edible mushrooms is found mainly in forests and some are very selective about the tree species they are related to. This mutualistic association, occurs within the soil, in areas around the perimeter of the trees, where the cells of the fungi - called hyphae - come into contact with the cells of the roots of the trees, creating together structures known as mycorrhizae.

Besides having important nutritional characteristics, fine flavors and aromas that make them appreciated worldwide, their scarce natural availability, since until now the cultivation of their fruits is difficult, makes them highly valued, and their production volume depends on the conservation of forests and natural areas where they develop.

As Mexico is a very diverse country in terms of mushrooms, it has a great variety of edible species from the aforementioned groups. The records indicate that around 400 species are used as food and medicine among all the country's ethnic groups, an outstanding number worldwide. However, the vast majority of Mexicans are unaware of this potential, which can be seen in part, for example, during the rainy season in traditional markets.

With a large number of edible mushroom species in Mexico, the potential for cultivation and use of these species is vast. These mushrooms could be catalogued as a good food because of the nutritional and medicinal benefits, proven throughout history, being even a cultural vestige of the harvesting activities of our ancestors.

In addition, they provide important sources of economic income for rural communities, which is why they are an important reason to promote the conservation of threatened forest ecosystems where these mushrooms grow and ensure their sustainable use and management.

Edible mushrooms against pathogenic bacteria

In the last decades, the production of edible mushrooms has shown remarkable growth, China and the USA contribute more than half of the world production. Currently, the production of mushrooms is led by Lentinula edodes (shiitake) with the first place, Pleurotus spp. (mushroom) and Auricularia spp. (mouse-ear) compete for second and third place, followed by Agaricus bisporus (mushroom).

Mexico is the second-largest producer of edible mushrooms in Latin America, after Brazil, with more than 60 thousand tons of fresh mushrooms per year.

Edible mushrooms contain proteins, polysaccharides, essential fatty acids, dietary fiber, minerals, and vitamins. Compared to other conventional sources of fiber, such as cereals, fruits, legumes, and vegetables, the mushrooms consumed provide more fiber content than the above-mentioned foods. They are constituted mainly by insoluble fiber, which includes the chitin and the beta-glucans, and by soluble fiber that represents less than 10% in dry weight.

The consumption of mushrooms as part of the daily diet can provide up to 25% of the recommended dietary intake. Consumption of fiber-rich foods has been shown to produce health benefits such as the maintenance and prevention of cardiovascular disease, improved digestive system function, lowered blood glucose, and minimized high cholesterol levels. On the other hand, due to their functional properties, fungi are considered anti-cancer, anti-cholesterolemic, hypolipemic, and hepatoprotective agents.

Mushrooms have been widely used as food for centuries and are characterized by their texture and flavor. However, the knowledge of mushrooms as an important source of bioactive compounds with medicinal value has also highlighted.

Scientific evidence over the last decade has pointed to various species of fungi as a source of antioxidants. The main antioxidants in edible mushrooms are carbohydrates such as beta-glucans, phenolic compounds, and vitamins such as ascorbic acid and tocopherols.

Phenolic compounds identified in mushrooms include gallic acid, caffeic acid, quercetin, and rutin, among others. They play an essential role in protecting against oxidative damage phenomena, and have therapeutic effects in a large number of pathologies, including ischemic heart disease, atherosclerosis, or cancer.

Considering the current problems that humanity faces in terms of chronic-degenerative diseases and the need for nutritious food, the study of edible and medicinal mushroom species, which present bioactive molecules of interest to health is of vital importance.

In addition to the antioxidant capacity, fungi may contain molecules that inhibit the growth of microorganisms and viral infections, some compounds with these properties are the phenols mentioned above. This also highlights the importance of the antibiotic and antiviral potential of fungi.

In some studies with cultivated fungi species of commercial interest, it has been demonstrated the activity of compounds with antibacterial activity. Most of the compounds with antimicrobial activity are secondary metabolites such as polyethylene and terpenoids, among others.

It has been described that certain secondary metabolites obtained from edible fungi show antibacterial activity against bacteria such as Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Typhimurium, Listeria monocytogenes, and Staphylococcus aureus, among other pathogens in humans. In a study, it was documented that the fungal production of the metabolite 2-aminoquinoline, shows antibacterial activity.

In conclusion, secondary metabolites of fungi represent a source of compounds with antioxidant and antibacterial activity. These properties depend on the species of fungus, the growth substrate of the fungus, the age of the fungus, among other factors. Therefore, fungi represent a viable alternative to develop new drugs, alternatives to conventional synthetic drugs.

By Enrique César, Leticia Montoya, Víctor M. Bandala, and Rigoberto Gaitán-Hernández, J. Fernando Ayala-Zavala, Randy Ortiz-Castro

Sources: Inecol