Introduction

Edible mushrooms have been appreciated ever since early times for their sensory characteristics and culinary suitability. Furthermore, they are well recognized for their nutritional and health benefits (Sabaratnam et al. 2011). Over the last 10 years edible mushrooms have been receiving an increased attention from researchers. Mushrooms are a great source of proteins (20–25 %), polysaccharides (37-48 %), fibers (13–24 %), vitamins and minerals (Sabaratnam et al. 2011; Alam et al. 2008) and of some secondary metabolites, including phenolic compounds, polyketides, terpenes and steroids (Cheung et al. 2003). In addition, they are low in calories (Sabaratnam et al. 2011) and in fat content (4–5 %) (Alam et al. 2008) which represents an advantage for the currently more balanced diets. From the health perspective mushrooms have been recognized for their antifungal, antibacterial, antioxidant, antimicrobial and antiviral properties, and have also been envisaged in functional foods development (Wani et al. 2010). They have been used in several therapeutical applications, including antitumor, immune-modulation and anti-diabetic treatments (Cheng et al. 2012) and are reported to have a preventive role in some cardiovascular diseases (Guillamón et al. 2010), anti-inflammatory and analgesic properties (Smiderle et al. 2008).

There are several hundreds of wild species of edible mushrooms yet only about 20 species are cultivated and used more extensively as food (Kalač 2013) and only 10 species are cultivated on an industrial scale (Reis et al. 2012a). The most commonly eaten species are Agaricus bisporus (Paris mushroom) and Lentinula edodes (Shiitake mushroom). The ‘Shiitake mushroom’ is as common in Asian countries as Agaricus bisporus is in the western world (Ghorai et al. 2009). Although cultivated mushrooms species has grown recently, there is still a lack of knowledge on their chemical composition which is essential to assess their nutritional value as well as their potential for functional ingredients provision. Therefore, the main objective of the present study was to determine the chemical composition of five cultivated edible mushrooms, some less characterized such as Pleurotus citrinopileatus var. cornucopiae or Pleurotus salmoneo stramineus, Pholiota nameko and Hericium erinaceus. Information on the proximal composition, fatty acids (FA) profile, elemental composition and main chemical compounds identified by FTIR-ATR of the five cultivated mushrooms is presented and discussed as well as their nutritive value and possible role in a healthy diet. To our knowledge this is the first study describing the FA composition of the edible P. salmoneo stramineus, P. citrinopileatus var cornucopiae, Ph. nameko and H. erinaceus and therefore this work brings valuable data about the nutritional evaluation of such mushrooms species.

Materials and methods

Mushrooms species and cultivation conditions

Dried specimens of mushrooms were supplied by Bioinvitro, Biotecnologia, Lda. (Gandra, Portugal): 3 specimens of order Agaricales and family Pleurotaceae, Pleurotus citrinopileatus var. cornucopiae, Pleurotus eryngii and Pleurotus salmoneo stramineus; 1 specimen of order Agaricales and family Strophariaceae, Pholiota nameko; and 1 specimen of order Russulales and family Hericiaceae, Hericium erinaceus. The classification of mushrooms was based on MycoKey™ (Petersen and Læssøe 2013). Mushrooms were cultivated in filter bags with sterilized organic substrate. Table 1 summarizes the cultivation conditions (Bioinvitro information) for each species of mushroom. After fructification and growth, entire clean mushrooms were dried in a ventilated drier through 24 h between 40 and 60 °C. The dried mushrooms were subsequently milled to less than 1.0 mm particle size.

Table 1 Summary of the growth conditions for each of the cultivated mushroom species
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Proximate composition

Moisture, organic matter and ash were determined according to AOAC (1990) methods. Protein content was determined by the Kjeldahl method adapted from US ISO 5983–1 (2009) using 4.38 as converting factor to protein (Kulshreshtha et al. 2013). Total fat was determined by Soxhlet extraction procedure. Total sugar was determined indirectly by calculation, subtracting protein and fat content from total organic content. Total poliphenolic content were extracted from 0.1 g of dry mushroom in 10 mL of ethyl acetate after 30 min of sonication (Ultrasonik, Germany). The extract was filtered with anhydrous sodium sulfate (Sigma) and brought to dryness with a rotary evaporator (Heidolph, Germany). The residue was re-dissolved in 5 ml of milliQ water and phenolic content of 2 mL was determined by colorimetric method of Folin-Ciocalteu (Mulinacci et al. 2001), using cathecol (0 to 75 mg/L) as standard and expressed as μg cathecol equivalent per g of dry mushroom.

Fatty acid analysis

For the analysis of total fatty acid (FA) composition, 100 mg of sample were accurately weighed and prepared according to Sánchez-Ávila et al. (2009). For quantitation purposes 100 μL of methyl tricosanoate (1.28 mg/mL) were added to samples prior to derivatization. FAME were analyzed in a gas chromatrograph HP6890A (Hewlett-Packard, USA), equipped with a flame-ionization detector (GLC-FID) and a BPX70 capillary column (50mx0.32mmx0.25 μm; SGE, France) according to the conditions described by Vingering and Ledoux (2009) Supelco 37 fatty acid methyl ester (FAME) mix (Sigma-Aldrich, USA) and butterfat CRM-164 from Fedelco Inc. (Madrid, Spain) were used for identification of fatty acids. GLC-Nestlé36 (Elysian, USA) was assayed for calculation of response factors and detection and quantification limits (LOD: 0.15 μg/mL; LOQ: 0.46 μg/mL).

Analysis of elements

The acid digestion was based on microwave-assisted digestion proposed by Speedwave MW-3+ (Berghof, Germany) for dried plant samples with some modifications for determination of Mo, B, Zn, P, Cd, Co, Ni, Mn, Fe, Mg, Ca, Cu, Na, Al and K in dried samples of mushrooms. A sample with up to 0.2 g of each dry powdered mushroom was placed in the digestion vessel and 5 mL of concentrated nitric acid were added. The vessels were capped and placed in a microwave pressure digestor Speedwave MWS-3+ (Berghof, Germany) and subjected to microwave radiation at 20 bar according to the following program: room temperature was raised first to 130 °C at 22 °C/min and 30 % of irradiation power, then to 160 °C at 6 °C/min and 40 % of irradiation power, for 5 min, and to 170 °C at 5 °C/min and 50 % of irradiation power, for 5 min. The cooling process consisted of decreasing temperature first to 100 °C for 4 min and then to room temperature. After cooling, acid digests were made up to 20 mL with Milli-Q water. Three replicates were performed for each sample as well as blanks.

Mineral content determination was performed using an inductively coupled plasma (ICP) optical emission spectrometer model Optima™ 7000 DualView ICP-OES (PerkinElmer, USA) with radial plasma configuration. Standard plasma conditions were used namely 1300 W for radio-frequency power, 1.5 mL/min pump rate, and 15.0, 0.2 and 0.8 L/min for plasma, auxiliary and nebulizer gas flow, respectively. Detection wavelengths are depicted in Table 2.

Table 2 Analysis of IPE 120 (Agaricus bisporus) certified reference material
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A multi-element standard (Inorganic Ventures) containing up to 10 mg/L of Mo, 2,5 mg/L of B, 15 mg/L of Zn, 750 mg/L of P, 0.2 mg/L of Co and Ni, 1 mg/L of Cd and Cu, 15 mg/L of Mn and Fe, 1000 mg/L of Mg, 3000 mg/L of Ca, 50 mg/L of Na, 5 mg/L of Al and 2000 mg/L of K was used for the preparation of standard solutions in 2 % HNO3. Successive dilutions of the stock reference solution (100, 50 and 10 times) were prepared and used for calibration models and the concentration of each element was determined by direct interpolation in the standard curve within its linear dynamic range. The limits of detection (LODs –Table 2) were calculated using y = yB + 3SB, where SB is the standard deviation (SD) of the blank signal estimated as sy/x, the residual SD taken from the calibration line, and yB is the blank signal estimated from the intercept, also taken from the calibration line (Miller and Miller 2005).

The accuracy of the method (microwave acid digestion and ICP-OES analysis) was assessed by analysis of certified reference material IPE 120 (Agaricus bisporus; WEPAL, Holland). Five replicates of reference material were subject to microwave digestion and analyzed three times by ICP-OES. Recovery ranged between 84 and 105 % (Table 2).

FTIR-ATR analysis

Samples of milled, dried mushroom material were analyzed by Fourier Transform Infrared Spectroscopy with attenuated total reflectance (FTIR-ATR). The FTIR spectra were recorded on a Bruker Tensor 27 spectrometer (Bruker Scientific Instruments, USA), using a Golden Gate single reflection diamond ATR system (Specac Lda, USA). All spectra resulted from the average of two counts, with 128 scans each and a resolution of 2 cm−1.

Statistical analysis

One-way analysis of variance (ANOVA) was carried out with SigmaStat™ (Systat Software, USA), to assess differences between mushroom species in terms of proximate or elemental composition at a significance level of P = 0.05. The Holm-Sidak method was used for pairwise comparisons at a significance level of P = 0.05. Fatty acid data in turn, were analyzed using the IBM SPSS Statistics v22 for Mac. Normality and homogeneity were examined and One way ANOVA with the Bonferroni test for post-hoc analyses was applied to evaluate statistical differences between mushroom species (p < 0.05).

Results and discussion

Proximate composition of cultivated mushroom species

Mushrooms are known for being rich in protein and polysaccharides and poor in fat content, which from a nutritional point of view is of particular interest especially for low calorie diets with low fat content. The composition reported for the five species under evaluation (Table 3) was no different from this trend, yet among them, between the different families and within the same family, significantly different compositions were found, in particular, in what concerns protein and organic matter contents. Differences in total fat content were less relevant and only P. salmoneo stramineus presented a significantly different (p < 0.05) value; in fact the lowest fat content among the five species studied. Within the same family, i.e., Pleurotaceae family, P. eryngii was characterized by the lowest total protein content (16.2 g/100gdry mushroom) followed by the highest content in total sugar (64.9 g/100gdry mushroom) and in total fat (3.4 g/100gdry mushroom) whereas P. salmoneo stramineus, presented the highest protein content (26.6 g/100gdry mushroom) but the lowest content in total sugar (52.7 g/100gdry mushroom) and in total fat (2.3 g/100gdry mushroom). Pleurotus citrinopileatus var. cornucopiae had a similar proximate composition to P. salmoneo stramineus differing to P. eryngii (Table 3). A similar proximate composition characterized Ph. nameko and H. erinaceus with 16.8–19.2, 59.6–61.2 and 2.9–3.2 g/100gdry mushroom of total protein, total sugar and total fat content, respectively.

Table 3 Proximate composition of mushrooms and their percentage contribution in nutrients intake
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It is known that mushroom proximate composition may be affected by several factors, such as species, development stage, maturity of fruiting body, mushroom sampled part, level of nitrogen available (Colak et al. 2009) as well as by substrate composition and cultivation procedures (La Guardia et al. 2005). Our results demonstrate such interspecies variability and corroborate the importance of cultivation optimization and standardization to increase yield and nutritional value. Protein content in the five similarly cultivated mushrooms ranged between 16.2 and 26.6 g/100gdry mushroom for Pleurotus spp. and 17–19 g/100gdry mushroom for Ph. nameko and H. erinaceus, respectively (Table 3). Lower protein contents (8.5–19.7 % dried mushroom) was reported by Akyüz and Kirbağ (2010) who studied the effect of various agro-wastes (wheat straw, wheat strawcotton stalk and rice bran) on the nutritive value of cultivated P. eryngii var. ferulae. La Guardia et al. (2005) reported a proximate composition with higher levels of protein (26.6 g/100 gdry mushroom), similar to those reported for P. salmoneo stramineus herein, for P. eryngii var. eryngii cultivated in wheat straw and sugar beet based substrate. Reported values of protein content for P. citrinopileatus are lower than those reported herein and ranged between 9.2 and 17.2 g/100gdry mushroom when cultivated on substrate based on the sludge of handmade paper and cardboard industrial waste used alone or in combination with wheat straw (Kulshreshtha et al. 2013). A value of 15.6 g/100gdry mushroom for total protein was reported by Guo et al. (2007) for cultivated P. djamor (former name of P. salmoneo stramineus) purchased in a local supermarket in Guangzhou city, China. According to Khan and Tania (2012) Pleurotus species are recognized as good source of protein with values ranging from 11 to 42 g/100gdry mushroom, fitting well the results reported for the 3 species included in this study.

Low total fat contents (2.3–3.5 g/100gdry mushroom) and high total sugar contents (52.7–64.9 g/100gdry mushroom) characterize, in general, the cultivated mushrooms analyzed similarly to those found in the literature for cultivated P. eryngii var. ferulae Akyüz and Kirbağ (2010). Lower total fat content was reported for P. citrinopileatus cultivated in different substrate (0.13 to 0.46 g/ 100gdry mushroom) (Kulshreshtha et al. 2013) and for P.djamor (1.65 g/ 100gdry mushroom) (Guo et al. 2007). In turn, La Guardia et al. (2005) reported much higher values for fat content (8.6 g/100gdry mushroom) for P. eryngii var. eryngii cultivated in wheat straw and sugar beet based substrate; other reported fat values for Pleurotus species ranged between 0.5 and 8 g/100gdry mushroom (Khan and Tania 2012). The characteristic low fat content found in mushrooms coupled to its unsaturated nature provided by the predominating linoleic and oleic free fatty acids (Kalač 2013) is of great dietary importance.

Mushrooms are a good source of carbohydrates. Values ranging between 51.4 and 59.9 g/100gdry mushroom were reported by La Guardia et al. (2005) and by Guo et al. (2007) for P. eryngii var. eryngii and for P. djamor, respectively. According to Kalač (2013) the carbohydrate content constitutes about one-half of mushroom dry matter being present mainly as polysaccharides and glycoproteins making them suitable for incorporation into low-calorie diets; 36–60 g/100gdry mushroom of carbohydrates have been reported for Pleurotus species (Khan and Tania 2012) which are comparable to the data in Table 3.

Comparison between proximate composition data for cultivated Ph. nameko and H. erinaceus and published data was not possible because to the best of our knowledge the only existing characterization studies targeted wild-growing H. erinaceus. Mau et al. (2001) reported carbohydrate, moisture, crude protein, crude fat and ash content values of 57.0, 4.3, 22.3, 3.5 and 9.4 % of air dried weight for wild-growing H. erinaceus, respectively.

Edible mushrooms have been reported as a source of phenolic compounds with antioxidant properties (Preeti et al. 2012). According to Preeti et al. (2012) natural phenolic compounds are produced and accumulated with end products ranging from simple molecules (phenolic acids) to highly polymerised compounds (tannins). Among the 5 edible mushroom species tested, the Pleurotaceae family revealed great variability englobing the highest (1140 μg cathecol equiv./gdry mushroom found in P. citrinopileatus var. cornucopiae) and the lowest (464 μg cathecol equiv./gdry mushroom found in P. salmoneo stramineus) total phenolic contents. This trend somewhat contrasts with those reported by Mishra et al. (2013) who determined the total phenolic content in mushroom mycelium of the same 3 species, i.e., Pleurotus eryngii, P. djamor and of P. citrinopileatus but grown in malt extract; higher values were observed for mycelium of P. eryngii, followed by P. djamor and P. citrinopileatus, respectively.

Apparent higher phenolic content was reported by Yildirim et al. (2012) for wild-grown edible P. eryngii (29 to 32 mg of gallic acid equiv./gdry mushroom) collected from different regions of Tunceli (Turkey). However direct comparison will not be appropriate given their different origin: cultivated vs wild-growing mushrooms. In terms of cultivated Pleurotus sp., Reis et al. (2012b) reported 7.14 mg of gallic acid equiv./gmethanolic extract from P. eryngii mushrooms obtained in local supermarkets (Bragança, Northeast Portugal).

Ash content was quite variable and statistically different among the different species, ranging from 5.99 to 8.40 g/100gdry mushroom in P. eryngii and in Ph. nameko (Table 3). No statistical differences were observed between Pleurotus spp. for ash content.

Fatty acids profile of cultivated mushrooms

From the analysis of data in Table 4, it was found that total FA concentration ranged from 22.75 to 14.12 μg/mgdry mushroom in P. eryngii and in P. salmoneo stramineus (p < 0.05). All samples showed concentrations of linoleic acid (C18:2 c9 c12) above 30 g FA/100gfat, indicating that this is main FA in the composition for P. salmoneo stramineus and P. citrinopileatus var cornucopiae (69.09–78.33 g FA/100gfat). The other mushroom species had significantly lower values especially in H. erinaceus (38.69 g FA/100gfat). The FA composition of the mushroom species was characterized by much higher content of mono (MUFA) and polyunsaturated FA (PUFA) than of saturated FA (SFA). The SFA distribution was characterized by palmitic (C16) and stearic acids (C18). Higher content was observed in H. erinaceus and in P. citrinopileatus var cornucopiae (16.52–18.60 g FA/100gfat) whereas values between 10.3 and 12.5 g FA/100gfat were observed for the other mushroom species. For C18 the highest amount for this FA was observed in H. erinaceus (6.15 g FA/100gfat; p < 0.05) which was 3.3 to 3.7 times higher compared to the other mushroom species (1.64–1.85 g FA/100gfat).

Table 4 Fatty acid composition (g FA/100gfat) and total content (μg FA/mgdry mushroom) of cultivated edible mushroom species
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Interestingly, in P. salmoneo stramineus and P. citrinopileatus var cornucopiae the concentration of linoleic acid was higher than 65 % but the concentration of oleic acid (C18:1 c9) was the lowest (3.7–5.5 g FA/100gfat). For the other mushroom species this ratio was lower and more variable (Table 4).

The FA composition of edible mushrooms can comprise from butyric acid (C4) to docosahexanoic acid (C22:6) depending on the mushroom species but in general C16, C18:1 c9 and C18:2 c9 c12 are among the main FA (Ergönül et al. 2013). Previous studies reporting the FA composition of wild P. eryngii or obtained from local supermarkets in Portugal, showed that SFA content were 25.8–17.4 %, MUFA were 49–13.1 % and PUFA were 69.4–25.2 % (Reis et al. 2012a, 2014). Such variation were associated to the values of palmitic (14.9–12.8 %), oleic (47.5–12.3 %) and linoleic acids (68.8–24.7 %). However the detailed profile was solely focused on the mentioned FA as well as on the stearic and linolenic acids.

To our knowledge this is the first study describing the FA composition of the edible P. salmoneo stramineus, P. citrinopileatus var cornucopiae, Ph. nameko and H. erinaceus and therefore this work brings valuable data about the nutritional evaluation of such mushrooms species.

Elemental composition of cultivated mushroom

Cultivated mushrooms have been reported as a good source of minerals, and may contain calcium(Ca), magnesium (Mg), sodium (Na), potassium (K), phosphorus (P), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) (Cheung 2008). In this study, the species analyzed revealed to be good sources of macroelements such as K, Mg, and P, where K stood out as the most predominant macroelement with values ranging between 26,274 and 37,368 mg/Kgdry mushroom followed by P (7623–10,892 mg/Kgdry mushroom) and Mg (949–1572 mg/Kgdry mushroom). Their combined percentage was about 98–99 % where K represented 6–76 %, followed by P with 20–27 % and Mg with 2.5–3.9 %. Higher contents, but not statistically different (p > 0.05), of K, P and Mg were observed for both P. eryngii and P. salmoneo stramineus. Higher content of K was observed in Ph. nameko (p < 0.05) in comparison to H. erinaceus. Potassium and Mg were also the predominant elements in other cultivated Pleurotus spp. For example, Lee et al. (2009) reported 26,273 and 1233 mg/Kgdry mushroom for K and Mg for P. eryngii cultivated in complex substrate based on pine sawdust, corncob and rice bran with beet pulp (sawdust and beet pulp are two common organic substrates also used to cultivate P. eryngii -Table 1). Akyüz and Kirbağ (2010) reported 14.3–18.8 mg/gdry mushroom for K for P. eryngii var. ferulae. Phosphorus content was not reported in both studies. Guo et al. (2007) also reported abundance of these macroelements in P. djamor: 1.21, 7.57 and 12.3 mg/gdry mushroom for Mg, P and K. According to Kalač (2013) K is highly accumulated in mushroom fruit bodies, reaching 20–40-fold higher values than in the substrate.

Among the remaining macroelements, Ca was found at rather low levels with values ranging from 170 to 226 mg/Kgdry mushroom and sodium (Na) was not detected above limit of detection. According to Cashman (2002), Ca is the specific nutrient most important for preventing and treating osteoporosis. This finding coupled to the non-detection of Na may be considered as good advantages from a nutritional aspect.

Statistically higher content of Ca was observed in Ph. nameko (p < 0.05) in comparison to other mushrooms tested, but the content of Ca was not statistically different among the three cultivated Pleurotus spp. and H. erinaceus. Variable content of Ca and Na were reported in the literature for cultivated Pleurotus spp. For example higher content of Ca (120–700 mg/kgdry mushroom) in comparison to Na (100–307 mg/kgdry mushroom) were reported in P. eryngii var. ferulae (Akyüz and Kirbağ 2010) but the opposite was observed in other cultivated P. eryngii: 8 and 147 mg/100gmushroom reported by La Guardia et al. (2005) and 162.5 and 253.6 mg/kgdry mushroom reported by Lee et al. (2009) for Ca and Na, respectively. According to Lee et al. (2009) their reported Ca content in the mushroom fruit bodies was very low despite high concentrations in the substrate. The authors suggest that either Ca was present in the substrate in a less bioavailable form or mushrooms do not have efficient Ca uptake channels.

The most predominant observed microelements were Zn and Fe in the 5 cultivated mushroom species analyzed (Fig. 1). According to Khan and Tania (2012) Fe and Zn are the most abundant elements among the trace minerals in mushrooms. In particular, Fe content was high in P. salmoneo stramineus and in Ph. nameko (233 and 278 mg/Kgdry mushroom) whereas Zn was high in P. salmoneo stramineus, P. citrinopileatus var. cornucopiae and in Ph. nameko (155, 104 and 121 mg/Kgdry mushroom). The reported values were, in general, higher than those reported by Gençcelep et al. (2009) for various edible mushrooms collected from the Erzurum region of Turkey. Lee et al. (2009) reported 39.0 mg/Kgdry mushroom for Fe and 52.2 mg/Kgdry mushroom for Zn for cultivated P. eryngii whereas Akyüz and Kirbağ (2010) reported 519–620 mg/kgdry mushroom for Fe, 40.5–102.5 mg/kgdry mushroom for Zn for P. eryngii var. ferulae. Iron is known to be essential for cellular energy and metabolism (Jankowska et al. 2013) and its deficiency is associated to anaemia which affect adversely patients with chronic heart disease (Comín-Colet et al. 2013). Zinc is present in all organs, tissues, fluids, and secretions participating in all major biochemical pathways playing multiple roles in the perpetuation of genetic material (Brown et al. 2004). Zinc deficiency may be associated to adverse outcomes of pregnancy (King 2000), sickle cell disease (Prasad 2002) or metabolic syndrome and diabetes (Miao et al. 2013). Among the remaining trace elements it is worthwhile referring Cu contents that were clearly higher in P. salmoneo stramineus and in Ph. nameko (24.7 and 27.3 mg/Kgdry mushroom) than in the other cultivated species analyzed. According to Khan and Tania (2012) the inclusion of Pleurotus spp. mushrooms in the diet could help to minimize Fe, Zn, Cu and other micronutrients deficiencies, but their bioavailability still have to be tested in animal and human studies since contradictory results still do persist in literature.

Fig. 1
figure 1

Elements content (mg/kgdry mushroom) in the different cultivated mushroom species: a P. citrinopileatus var. cornucopiae; b P. salmoneo stramineus; c P. eryngii; d H. erinaceus; e Ph. nameko. For each element, different letters indicate significant differences (p < 0.05) between mushroom species

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In general, the five cultivated mushrooms studied were of important nutritional value not only due to their proximate composition but especially due to their elemental composition. Taking current trends into account, studied mushrooms offer a wide array of nutrients, at concentrations that may meet with nutritional requirements, particularly in what concerns elements and, in some cases, may even allow for application of nutritional claims. Data on daily intake of mushrooms are unavailable for the Portuguese population and according to O’Neil et al. (2013) mushroom intake data are sparse. Considering a serving size of 84 g of fresh mushroom, reported by O’Neil et al. (2013) based on FDA food labelling information (2013) the possible contribution of analyzed mushrooms to daily nutritional requirements was calculated (Table 3). Whereas such daily intake contributes with a small fraction to protein, carbohydrate and fat requirements, in terms of microelements some of the mushrooms contribute over 15 % (minimum requirement for nutritional claim) of the recommended daily intakes (RDIs). Variable contribution to the RDI for the elements is observable in Table 3. In terms of macro-elements all species can be considered good contributors to RDI of K, especially Ph. nameko with values as high as 15.7 %. In terms of P, values between 9.2 and 13.1 % RDI are reported with higher values found in Ph. nameko. Lower Ca and Mg suppliers characterized the cultivated species. In terms of microelements, interesting values of contribution to Fe, Cu and Zn RDI was observed in P. salmoneo and Ph. nameko with values ranging between 10 and 23 %. Lower values were, in general, found for Mn.

According to O’Neil et al. (2013) mushroom consumption is associated with a better nutrient profile and higher diet quality. For example higher intakes of Cu and K are reported by these authors for mushroom consumers than non-consumers. The recommendations by O’Neil et al. (2013) go further and state that mushroom consumption should be encouraged by health professionals. In a meta-analysis on mushroom intake and its relation to the reduction of breast cancer, Li et al. (2014) concluded that greater edible mushroom consumption may be associated with a lower risk of breast cancer.

FTIR-ATR characterization

Mushrooms are rich in polysaccharides followed by protein content with low fat content (Table 3) yet a more specific characterization of these macrostructures is a further asset to establish structure-function relationships. Several authors (Zhao et al. 2006a, b) describe the chemical characteristic features of specific regions of FTIR spectra for mushrooms truffles (Tuberaceae) and for different Amanita species, according to:

  1. i)

    4000–1800 cm−1 with a prominent broad band centered around 3300 cm−1, that could be assigned to O-H and C-H stretching vibrations and two sharper bands around 2900–2880 cm−1 assigned to CH2 and CH3 stretching of fatty acids from the cell wall;

  2. ii)

    1800–1500 cm−1 with two major bands around 1650 and 1560 cm−1 assigned to amide I and amide II of proteins; a band around 1740 cm−1 that could correspond to carbonyl stretching vibration of alkyl-esters indicating the presence of oil;

  3. iii)

    1500–750 cm−1 region associated with vibrations of proteins, lipids but also polysaccharides - 1077 and 1042 cm−1 have been assigned to C-O stretching of polysaccharides;

  4. iv)

    950–750 cm−1 region that has been associated with identification of anomeric configuration of polysaccharides - 890 cm−1 band has been assigned to β-glycosides and 860–810 cm−1 for α-glycosides. This information is equally supported by Mohaček-Grošev et al. (2001) studies who used vibrational spectroscopy to characterize several wild growing mushroom species.

In Fig. 2, the 4 specific regions are observable for the 5 mushroom species. At first sight there seems to be little qualitative difference between spectra of the 3 cultivated Pleurotus species (Fig. 2i); apparent differences are more evident in Ph. nameko spectrum especially in the 1500–750 cm−1 region which is associated with vibrations of proteins, lipids but also polysaccharides (Fig. 2ii). Evidence of presence of proteins (due to 1650 and 1560 cm−1 bands), fatty acids (due to two sharper bands around 2900–2880 cm−1) and polysaccharides (bands in 1500–750 cm−1 region) are easily perceived in the 5 cultivated mushroom species spectra taking into account the band assignments by Zhao et al. (2006b) and Mohaček-Grošev et al. (2001) According to Liu et al. (2006) the region between 750 and 1200 cm−1 could serve as fingerprints to discriminate mushrooms whereas according to Mohaček-Grošev et al. (2001) the spectral region between 1200 and 1000 cm−1 could serve as an indicator of mushroom genus.

Fig. 2
figure 2

FTIR-ATR spectra of the five cultivated mushroom species: i P. eryngii, P. salmoneo stramineus and P. citrinopileatus var. cornucopiae; ii Ph. nameko and H. erinaceus

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In Figs. 3 and 4, the 1500–750 cm−1 region is amplified enabling a more detailed observation of the bands present in this region. Characteristic bands found in the 5 spectra are 1400, 1375, 1315, 1237–1240, 1204–1212, 1148, 1074–1079, 1026–1029, 995–988, 890–910 and 801–803 cm−1. The majority coincide with main observed bands in the 5 Amanitas species and the 5 truffles studied (Zhao et al. 2006a, b). According to Gonzaga et al. (2005) 1028 cm−1 is assigned to C-O stretching, 1074 cm−1 to anomeric C1H group vibration and 1165 to C-O-C stretching of glycosidic structures. Protein patterns have been associated with characteristic absorption at 1654, 1544, 1409 and 1242 cm −1; a similar pattern was found in the 5 cultivated mushroom species studied which according to Gonzaga et al. (2005) may be evidence of the presence of a glucan-protein complex.

Fig. 3
figure 3

FTIR-ATR spectra of the three Pleurotus sp. (P. eryngii, P. salmoneo stramineus and P. citrinopileatus var. cornucopiae) mushrooms between 1500 and 750 cm−1

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Fig. 4
figure 4

FTIR-ATR spectra of Ph. nameko and H. erinaceus between 1500 and 750 cm−1

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Although bands between 950 and 750 are very weak they are considered important for the identification of anomeric configuration of polysaccharides (Mohaček-Grošev et al. 2001; Barbosa et al. 2003). According to Zhao et al. (2006a, b) β-glucan and chitosan standards with β-glycosidic linkage presented bands at 889 and 897 cm−1, respectively, whereas α-glycosidic linkage typical in a standard starch presented a characteristic band at 858 cm−1. According to Barbosa et al. (2003) bands at 890 and 1370 cm−1are typical of (1 → 3)-β-glucans and of β-glucans, respectively. In P. citrinopileatus var. cornucopiae and P. salmoneo stramineus spectra (Fig. 3) as well as in Ph. nameko and H. erinaceus spectra (Fig. 4), two weak bands at 890–910 cm−1 and 801–803 cm−1 were observable; such could indicate that both α- and β-glycosidic linkages exist in these mushroom species. In addition, the detection of the band at 1375 cm-1 in the five cultivated mushroom species suggests the existence of β-glucans. According to Wasser (2002) mushroom polysaccharides are present mostly as glucans with different types of glycosidic linkages, such as (1 → 3), (1 → 6)-β-glucans and (1 → 3)-α-glucans but also as heteroglucans; in this case, side chains contain glucuronic acid, xylose, galactose, mannose, arabinose, or ribose as a main component or in different combinations.

Possible discriminant bands between the 3 cultivated Pleurotus species are the bands at 943 and 840 cm−1 only present in P. eryngii, 953 and 875 cm−1 only present in P. salmoneo stramineus, whereas the band at 931 cm−1 is visible in P. salmoneo stramineus and P. citrinopileatus var. cornucopiae (Fig. 3). In turn, possible discriminant bands for Ph. nameko are observable in the 1500–1000 cm−1 region such as 1124, 1100, 1014 cm−1 and in the 950–750 cm−1 region such as 956, 842 and 851 cm−1. The Ph. nameko spectrum is characterized by more and diverse distinct bands than the other 4 cultivated mushroom species including in the 1500–1200 cm−1 region. A broad weak band around 867 cm−1 appears to be discriminative for H. erinaceus (Fig. 4).

Zhao et al. (2006a, b) suggested several absorption ratios to discriminate between mushroom species. In accordance, the absorption ratios A1029/1148, A1029/1074 were calculated for each cultivated mushroom species. The ratio A1029/1148 did not reveal to be discriminant (1.29–1.10), which is not the case for the A1029/1074 ratio where clear differences were detected; calculated values were 1.24, 1.18, 0.41, 0.41 and 0.38 for P. eryngii, P. salmoneo stramineus, P. citrinopileatus var. cornucopiae, H. erinaceus and Ph. nameko, respectively.

Conclusions

The chemical composition of five cultivated edible mushrooms in terms of proximate composition, fatty acids profile and elemental composition showed significant differences among the different species, emphasizing the nutritional potential of the five different cultivated edible mushrooms to be consumed in a healthy diet. High contents in proteins and polysaccharides associated with low content of fat, which profile is characterized by higher concentration in mono and polyunsaturated FA than in saturated FA, being also interesting sources of phenolic compounds as well as of some macro and micronutrients highlights its potential as healthy food. According to FTIR-ATR spectra, the presence of β-glucans, α-glucans and glucan-protein complexes are among main representative polysaccharides in the five species. The presence of these polysaccharides further upholds the interest in exploring these mushrooms for applications in health-related fields, for example, drug or nutraceutical delivery approaches.