Collected material

The specimens were bought in Tesquedó community, and were used to determine the species taxonomic keys of ^{Singer et al. (1991)}. About 700 g of fresh mushroom were collected from Xajay community (a locality near to Tesquedó), covered with aluminum foil, placed inside a plastic bag and transported to the laboratory in a cooler with refrigerant.

Color determinations

Color determination was made on pileus, context and pores, of three fresh mushrooms of F. wolfeana. Measurements were taken five times per structure (pileus, context and pores) with a Minolta spectrophotometer (CM-2002). The parameters L* (Luminosity), a* (red/Green coordinates), b* (yellow/blue coordinates), c* (chrome and clarity) and h° (tone angle) were averaged and compared using standard deviation. For pore surface and context, precautions were taken to avoid any damage that could induce color changes, caused by touching these parts. The colors are important since wild mushrooms are an important source of bioactive compounds, such as pigments (^{Ferreira et al., 2009}).

Proximal analysis

One sample of 300 g of fresh mushrooms and one sample of 300 g of dried mushrooms were processed to determine their nutritional values. The proximal analysis was conducted in the Unit of Chemical Services at the Faculty of Chemistry of the Universidad Autónoma de Querétaro, using the methods established by the Mexican norms: NMX-F-607-NORMEX-2002) for ash determination, NMX-F-613-NORMEX-2003 for raw fiber determination, NMX-F-608-NORMEX-2002 for protein determination, NMX-F-089-S-1978 for ethereal extracts determinations (Soxhlet method), and NMX-AA-051-SCFI-2001 for the use of atomic absorption spectrophotometer (Perkin Elmer, 2002).

Antioxidant activity

Mushroom extracts were prepared according to ^{Elmastas et al. (2007)} with some modifications. For methanolic extraction, 1 g of powdered lyophilized mushrooms was resuspended in 40 mL of methanol and then mixed with a homogenizer (IKA T25 Basic) into Falcon tubes, and were covered with aluminum foil and placed on an orbital shaker (Orbital shaker Midi OM10E) for 24 h. The extract was filtered with a Whatman no. 2 paper and the remaining extract was collected. Methyl alcohol was removed in a rotatory evaporator at 40°C and 70 rpm at 175 mbar to obtain the dried extract (Büchi, Heating Bath B490, Rotovapor R-205 and Vacuum V-800). The final amount of the extract was resuspended in 2 mL of HPLC water and stored at 4°C for one day, to avoid oxidative damage.

The radical scavenging activity was determined with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, as reported by ^{Brand-Williams et al. (1995)}, and was modified to read in a 96-well microplate. Aliquots of 280 µL of DPPH (100 µM) in methanol were deposited with 20 µL of mushroom extract at 1:10 and 1:100, and completed to 300 µL each. Samples were incubated in the dark for 45 min, and then measured at 490 nm (Microplate reader). Samples were processed in triplicate. Trolox reagent was used as standard, and was prepared at 0, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8 and 1 µM to determine Trolox equivalents.

Ethnomycological importance

Fistulinella wolfeana was found in local markets for the first time in the Tesquedó community, and then was mentioned by several people who live in the three communities (Tesquedó, Xajay and Tenasdá). It is known as "Ushki jieth´e" in otomí dialect, meaning "salted mushroom", beacuse people attribute it a salty taste, even though some call it "sweet mushroom", due to a mild flavor when the mushroom is mature. It is collect either for self-consumption, economic purposes (Figure 2), or even to exchange for main supplies, such as vegetable oil, bread, rice or corn. This is important to emphasize, because there are no previous reports of its edibility. Therefore, F. wolfeana could be used both as a food source or an economical income source. An important feature is that people dry and keep the mushrooms (Figure 3) for almost a year, to consume them during dry season, when there are not mushrooms and food is scarce. The preservation is possible because this species is rarely invaded by larvae, even when it is left on the soil exposed to sunlight. In fact, this is the first report of conservation of a bolete, because Boletus spp., and other genera of the Boletaceae family, are frequently infected by larvae, therefore, people cannot conserve them. ^{Estrada-Torres and Aroche (1987)} indicated that people from Acambay, Estado de México, dry their mushrooms hanging them with a thread, and exposing them to the sunlight; but there was no mention of any bolete among them. In our study, we have observed that people place the mushrooms over a rock or a tree during the day, and at night they keep them inside to avoid rehydration, and repeat the same process for few days until the mushrooms are completely dry. During this study, F. wolfeana was consumed for two consecutive seasons by the authors and at least seven more people, who indicated that the taste was exquisite.

Figure 1: Location of the study area. 

Figure 2: People from Tesquedó community who collect Fistulinella wolfeana for sale. 

Figure 3: Dry specimens of sun-dried Fistulinella wolfeana. 

Color determination

There is a lack of reported quantitative color determination for wild mushrooms, and most determinations have been done on cultivated species with industrial purposes (^{Mohapatra et al., 2010}; ^{Qi et al., 2014}). We made a complementation of the original color description, with the values obtained in the test. Pileus and pores show similar values, while context presented differences due to its whitish color. According to color scores, luminosity (L*) had the following order: context > pores > pileus; coordinates red/green (a*): pores > pileus > context; and coordinates yellow/blue (b*): pores > pileus > context. On the other hand, c* and h° parameters had the following order, chrome (c*): pores > pileus > context; and tone angle (h°): context > pores > pileus. The parameter in the pileus had the major deviation in color, including pinkish, pinkish-violet or pinkish-brownish, probably due to sun exposure. Pores change their color, from white to pinkish-lilac, when touched. It could explain the minimal variation and similarity between the values of both parts. The high value in context explains the white color and the low variation in color change, as indicated by ^{Singer et al. (1991)} in the original description. The above values, suggest a variation depending on where the mushroom is growing, and if it is directly influenced by the sunlight, because specimens found in the inner part of the forest had lower L* values, indicating a higher color tone, while those exposed to sunlight had paler tones, showing higher L* values. Pileus and pores had similar values; context does not change since it is inside, and only pileus shows a considerable variation (Table 1). Thus, this difference may suggest a variation in the amount of pigments that decrease in exposed specimens. It would be convenient to determine pigments, to find out which are the most important that make up the colors of this species, and how they are modified by environmental conditions.

Table 1: Color values of pileus, pores surface and context of Fistulinella wolfeana 

L* (Luminosity), a* (red/green coordinates), b* (yellow/blue coordinates), c* (chrome and clarity) and h° (tone angle). Values averaged ± standard deviation.

Proximal analysis

Results of proximal analysis are shown in Table 2, which are compared with data from other foods, such as mushrooms and some meats frequently consumed. Protein levels, in dry weight, were similar to those in Agaricus bisporus and Pleurotus ostreatus, but with less than half of fat and carbohydrates. Therefore, F. wolfeana is a food with high protein content.

Table 2: Comparison of fresh and dry proximal analysis of Fistulinella wolfeana with other foods 

Data taken from ^{1De Moreno et al. (2000)}; ^{2Juárez-Luna (2012)}; ³Sánchez et al. (2007); ^{4Sadler (2003)}; ^{5Manzi et al. 2004}; ^{6Castro-González et al. (2007)}; N= No data available.

In addition, its sodium content, was very low compared to another mushrooms species. This is important because of potential health problems, such as hypertension that can be caused by excess of sodium. Finally, F. wolfeana had more fiber content, in both fresh and dry weight, than any of the commercial mushrooms compared, which means that it can help lower cholesterol levels and promote digestion.

Regarding to comparison with some meats of frequent consumption, protein values (in dry weight) were similar to those in chicken, beef, tuna fish and blacktip shark. Fistulinella wolfeana had fewer carbohydrates and fats than meat; such as the case with commercial mushrooms. Two important aspects to consider in F. wolfeana, the presence of fiber and the low amount of sodium, indicate that this species is a good nutritional alternative, even compared to meat.

Comparison with other wild mushrooms

The comparison of proximal analysis results of F. wolfeana with wild mushrooms, are shown in Table 3, and data are shown in grams per 100 g of dry material. The average amount of protein in F. wolfeana is 29.83 g; Amanita caesarea had a higher value (34.77 g), while Armillaria tabesceus had a lower content (22.90 g). However, the contents of fat, carbohydrates and ash were the lowest for these two species. Therefore, we consider that F. wolfeana is a good diet alternative for people looking for foods low in fat and carbohydrates. This species is abundant in oak forests in Mexico, and large specimens grow there, which can weigh up to half a kilogram when fresh; that is why it is a highly prized species, because with a few basidiomata, they can cook for a family (six to eight members).

Table 3: Basic comparison of Fistulinella wolfeana with other wild edible mushrooms (g/100g), data of dry material 

Data taken from ^{Ouzouni et al. (2009)}. The underlined number represents the highest value for each category.

During the rainy season, F. wolfeana can replace other foods, such as meat, which in many cases is not accessible for most of the people of the communities. Also, this species could be dried and preserved for almost a year in a freezer.

Antioxidant activity

Many common wild boletes are known to have a considerable antioxidant activity, comparable with our results (Figure 5), as indicated by several previous studies (^{Elmastas et al., 2007}; ^{Ribeiro et al., 2006}; ^{Sarikurkcu et al., 2008}; ^{Tsai et al., 2007}). Looking for organic compounds profiles in boletes, we could find different values for fatty acids and phenolic compounds, that show high levels of linoleic, oleic and stearic acids (^{Kalaç, 2009}). In general, mushrooms have low fat content, but in some cases, unsaturated acids such as oleic acid (C18:1) and linoleic acid (C18:2) are predominant over saturated fats (León-Guzmán et al., 1997; ^{Ribeiro et al., 2009}; ^{Guillamón et al., 2010}). Some members of the Boletaceae family have shown the same predominance of unsaturated acids (^{Pedneault et al., 2006}). In this work, we report an increase in fat content when mushrooms were dried, but more studies are needed to determine the profile of fatty acids in raw, dry and even cooked mushrooms, in order to know if heat modifies the amount of fat. This could have implications as people dry them to consume them later.

Figure 5: Percentage of radical scavenging activity with 2,2-diphenyl-1-picrylhydrazyl (DPPH) from methanol extracts diluted 1:10 and 1:100. Data were averaged from N=6, bars are standard deviation. 

It is important to notice that some species are considered health enhancers by people who consume them (^{Garibay-Orijel et al., 2007}; ^{Alonso-Aguilar et al., 2014}), which makes sense, because it has been reported that the consumption of wild mushrooms play a role in the prevention of cardiovascular diseases (^{Guillamón et al., 2010}). ^{Bautista (2013)} published one of the most recent and complete reports about Mexican medicinal mushrooms traditionally used by Nahuas, Tseltales and Otomíes. The author cited a traditional medicine man, stating that: "not all the mushrooms are medicinal, but all edible mushrooms are potentially medicinal". In the case of F. wolfeana, we could hypothesize that it has medicinal properties, but its use as one of the Mexican traditional wild mushrooms has not been reported. ^{Elmastas et al. (2007)} and ^{Puttaraju et al. (2006)} indicated that boletes contain phenolic compounds, suggesting that it is possible to find them in Fistulinella genus. In addition, many phenolic compounds have antioxidant potential (^{Ribeiro et al., 2006}). These components could also have the capacity to repel insects, as we have noticed in all the mushrooms collected for this work.