AMINO ACID COMPOSITION AND ANTIOXIDANT PROPERTIES OF FIVE EDIBLE MUSHROOM SPECIES FROM KASTAMONU , TURKEY

Background: Hydnum repandum, Cantharellus cibarius, Ramaria fennica, Boletus edulis, and Craterellus cornucopioides are all wild edible mushroom species from the Kastamonu province. The aim of this study was to investigate antioxidant properties and amino acid contents of these mushrooms. Materials and Methods: The mushrooms were analyzed for their free amino acid compositions using a high performance Amino Acid analyzer (Biochrom 30). Also, antioxidant activity and total phenolic concentrations of five different mushroom species were studied by using spectrophotometric methods. Results: The mushrooms contained 17 amino acids (g/100 g): Glutamic acid (2.56–1.11), Alanine (1.49–0.54), Arginine (1.62–6.77), Aspartic acid (1.45–0.81), Leucine (1.08–0.64), Methionine (1.05–0.06), Valine (1.05–0.66), Lysine (1.01–0.57), Serine (0.68–0.38), Cysteine (0.88–0.11), Isoleucine (0.61–0.39), Glycine (0.82–0.35), Threonine (0.82–0.44), Phenylalanine (0.66–0.42), Proline (0.60–0.47), Tyrosine (0.58–0.38), and Histidine (0.48–0.22). The total free amino acid (TAA) contents ranged from 169.2 mg/g in Boletus edulis to 89.1 mg/g in Hydnum repandum. These five different mushroom species contain eight essential amino acid species except tryptophan. The antioxidant activity of mushroom extracts was expressed as the percentage of DPPH radical inhibition and IC50 values (mg/mL). The percentage of inhibition ranged from 2.38% to 88.05% and IC50 values ranged from 0.03 to 13.98 mg/mL. The total phenolic content ranged from 0.66 to 7.74 mg/g of dry mushroom extract, expressed as gallic acid equivalents. Conclusion: Methanolic extract of Boletus edulis showed the highest phenolic content and strong antioxidant activity. As a result, the significant linear correlation between the values for the total phenolic content and antioxidant activity of mushroom extracts was corroborated in all of the investigated mushroom species, with the exception of Craterellus cornucopioides.


Introduction
Edible mushrooms are grown and consumed because of their delicious taste and a wide variety of aromatic flavors (Bailey andDay 1989, Breene 1990).They are used in traditional medicines because of their chemical properties.Mushrooms are rich in protein and carbohydrates and low in fat and calories.In addition, they contain high dietary fibers; edible vitamins (B1, B2, B12, C, D2 and E); and minerals (Kalač 2009).Phenolic acids are the major phenolic compounds found in mushrooms (Alispahić et al. 2015, Sun et al. 2017).Mushrooms are a good source of essential and non-essential amino acids (Chang and Miles 1989).The amino acid contents vary according to mushroom species (Ferreira et al. 2016) and are an indicator of the quality of the mushrooms and their nutritional value (Sudheep andSridhar 2014, Teklit 2015).The taste of a mushroom is determined by the concentrations of aspartic and glutamic acids; sweet amino acids (alanine, glycine, and serine-threonine); bitter amino acids (arginine, histidine, isoleucine, leucine, methionine, phenylalanine, and valine); and tasteless amino acids (lysine and tyrosine) (Pomeranz 2012, Kalač 2016).
Mushrooms are useful candidates in the search for an effective antioxidant because of their naturally occurring composition (Jean-Philippe 2005).Certain mushrooms have been used as supplements to improve human health.Foods rich in antioxidants are now consumed more regularly because antioxidants or molecules with radical scavenging capacity are thought to exert a potential protective effect against free radical damage.These biomolecules prevent coronary and vascular diseases and tumor formation by inhibiting oxidative reactions.
Although edible wild mushrooms are more expensive than cultivated mushrooms, their taste, nutrition, and pharmacological properties are becoming increasingly important in our diet.Cultivated and wild edible mushroom species have been widely investigated in the northern hemisphere; however, little is known about the antioxidant properties of wild edible mushrooms from Turkey (Gursoy et al. 2009), in particular, the amino acid and phenolic contents of the species Hydnum repandum (Hre), Cantharellus cibarius (Cci), Ramaria fennica (Rfe), Boletus edulis (Bed), and Craterellus cornucopioides (Cco) from the Kastamonu region.The aim of this study was to determine the antioxidant properties, phenolic compounds, and amino acid contents of these five mushroom species.

Materials and Methods
Hre, Cci, Rfe, Bed, and Cco were the five wild edible mushroom species studied herein.They are consumed regularly and are available at local markets in the Kastamonu province.
All analytical grade chemicals were purchased from Sigma-Aldrich Co. LLC.Deionized purity water was used at each stage.Absorbents were measured using a Shimadzu UVM-1240 UV-Visible spectrophotometer (Shimazu Corp., Kyoto, Japan), and Biochrom 30 was used for amino acid analysis.

Sample collection and preparation
Fresh mushrooms (Hre, Cci, Rfe, Bed, and Cco) were collected from the towns of Inebolu, Taşköprü, and Devrekani of the Kastamonu province, Turkey (Table 1).The collected mushrooms were divided into 100 g samples.The samples were then dried at 30°C for 48 h.The dried mushrooms were homogenously powdered for use in the analyses.

Mushroom identification
The mushroom species were identified by Prof. Dr. Sabri ÜNAL at the Kastamonu University Mushroom Research and Application Center.

Boletus edulis
The average cap width of Bed is 24 cm.The cap is reddish brown, flat, and slightly sticky to touch.The stipes is 17 cm long, club-shaped and yellowish white.The underside of the cap comprises thin tubes.

Cantharellus cibarius
Cci is orange or yellow, meaty, and is funnel-shaped mushroom.Beneath the smooth cap, gill-like ridges run almost all the way down the stipe.The average cap width and stipe length are 6.8 and 5 cm, respectively.

Craterellus cornucopioides
Cco is funnel shaped and gray, brown, or black.They often grow in small bunches, although sometimes they grow singly.It comprises a flower-like cap with an average width of 3.4 cm.The stipe is hollow and very thin with an average height of 6.2 cm.

Hydnum repandum
The tan-colored cap of Hre is generally irregular in shape with an average width of 11.6 cm.The underside of cap is covered with small white spines that resemble those of a hedgehog.The stipe is 7.3 cm long and white.

Ramaria fennica
The average height and width of the fruiting body of Rfe are 10.8 cm and 7.2 cm, respectively.The base is 4.8 cm wide, white, and well developed.The many branches are vertically oriented and elongated.The cap is smooth and olive-yellow.

Analysis of free amino acid concentration
Amino acid analysis was performed with a high performance amino acid analyzer (Biochrom 30).Hydrolysis was performed in a closed conical flask to determine all amino acids except tryptophan.Sample equivalent to 10 mg of protein was weighed into the conical flask and mixed with 5 mL formic acid.The flask was placed in an ice bath for 16 h and sodium disulfite was added into the flask.25 mL of HCl 6N was then added to the oxidized mixture.The flask was oven dried at 110°C for 24 h.The flask was then opened, and a Rotary evaporator was used to reduce the volume to 5-10 mL under vacuum at 60°C.The pH was adjusted to 2.20 using sodium hydroxide solution.Sodium citrate buffer (pH 2.20) was added to the hydrolyzed sample.Once all the soluble material was completely dissolved, the sample was ready for analysis (AOAC 2012).

Analysis of antioxidant components Preparation of mushroom extracts for antioxidant components
For methanolic extractions, 5 g samples of each mushroom species were extracted by mixing with 30 mL of 80% methanol at 25°C for 3 h and filtration through Whatman filter paper (No.1).The residue was then extracted with two 20 mL portions of methanol.The combined ethanolic extracts were filtered through Whatman filter paper (No.1) after storing the extracts for 2 h at room temperature.The resulting homogenate was centrifuged at 5000 rpm for 10 min (4°C).The derived supernatant was centrifuged at 7500 rpm for 10 min.The final supernatant (100 mg/mL) was used for 1,1-diphenyl-2-picrylhydrazyl (DPPH) measurements and stored at 4°C (Pedraza-Chaverri et al. 2004, Lee et al. 2004).

Evaluation of antioxidant properties using the DPPH method
The method proposed by Shimada et al. (1992) and Brand-Williams et al. (1995) was slightly modified, and free radical scavenging ability on DPPH was performed using the modified method.Different volumes (X: 0.05-0.20 mL) of the extracts in methanol (3-X mL) were mixed with 3 mL of the methanolic solution containing DPPH (Sigma) radicals; the total volume of the reaction mixture was 6 mL.This resulted in a final concentration of (stock 4.0 × 10 −4 M) DPPH.The mixture was shaken vigorously and left to stand for 30 min in the dark; the absorbance was then measured at 517 nm against a blank.The percentage radical scavenging activity was calculated from the following formula: Where A 0 is the absorbance of the control solution (no antioxidant added) and A 1 is the absorbance of the sample solution (when antioxidant was present) (Huang et al. 2005).The amount of antioxidant required to reduce the DPPH concentration by 50% is a commonly used parameter to measure the antioxidant activity and is called IC 50 (mg/mL) (Frankel and Meyer 2000).The IC 50 value was determined from the graph slope "y = mx + c" formula obtained from the inhibition (%) concentration graph for mushroom extracts (Mukherjee et al. 2011).

Determination of total phenolic content
The concentration of phenolics in the mushroom extracts was determined using a spectrophotometric method (Singleton et al. 1999).A methanolic solution was used at a concentration of 1 mg/mL.The reaction solution was prepared by mixing 0.5 mL of methanolic solution of mushroom extracts, 2.5 mL of 10% Folin Ciocalteu's reactant, which was dissolved in water, and 2.5 mL 7.5% NaHCO 3 .The blank was prepared by adding 0.5 mL methanol to 2.5 mL 10% Folin Ciocalteu's reactant dissolved in water, and 2.5 mL of 7.5% NaHCO 3 .The samples were then incubated at 45°C for 45 min.The same procedure was repeated for the gallic acid solution.The absorbance was determined using a spectrophotometer at λmax = 765 nm.The phenolic content of the extracts was expressed in terms of gallic acid equivalent (mg of GA/g of extract) after the concentration of phenolics (ppm) was read from the calibration line.

Statistical analysis
For each mushroom species, three samples were used; the antioxidant content of each was calculated using descriptive statistical analysis with Microcal Origin Pro 8.5.1 (Origin Lab.Corp., Northampton, MA, USA).Statistically significant effects were investigated using SPSS software (SPSS Inc., Chicago, IL, USA) for Windows version 13.

Free amino acid concentrations in the five mushroom species
In this study, eight essential and nine non-essential amino acid species were identified in the five wild mushroom species.In all five of the mushroom species, glutamic acid was the predominant non-essential amino acid.It was the main compound in Bed followed by Ref, Cci, Cco, and Hre.These results clearly indicate that glutamic acid, which is the major compound in all species, contributes to the primary taste of the mushrooms (Yamaguchi et al. 1971, Dutta et al. 2013).Several reports have shown that glutamic acid, which is an anti-cancer agent, is the highest total free amino acid (TAA) in mushrooms (Sato et al. 1985).
The free amino acid content ranged from 5.8 ± 0.01 to 25.6 ± 0.05 mg/g in Bed, from 0.6 ± 0.00 to 11.1 ± 0.03 mg/g in Hre, from 1.1 ± 0.00 to 17.5 ± 0.02 mg/g in Cci, from 1.8 ± 0.00 to 19.4 ± 0.04 mg/g in Ref, and from 1.1 ± 0.00 to 13.7 ± 0.04 mg/g in Cco (Table 2 and Figure 1).Several factors can affect the composition of mushrooms, including time of harvest, species, environmental factors, and method analysis (Manzi et al. 2001).Sun et al. (2017) reported that the total amino acid composition of 13 popular wild edible mushroom species from the Yunnan Province ranged from 14.62 to 131.06 mg/g.The synergistic effect of glutamic and aspartic acid are thought to contribute to the umami taste of mushrooms (Baars et al. 2014).We found the maximum concentration of aspartic acid in Bed (14.5 ± 0.04 mg/g) and the minimum aspartic acid concentration in Hre (8.1 ± 0.03 mg/g).
Aspartic acid had the second largest concentration in four of the studied species (except Cci), and the methionine concentration was low in Hre, Cco, and Cci, as reported by Ribeiro (2008).
Alanine was the most abundant compound in Bed.The concentration of serine was the highest in Bed, and lowest in Cco compared to all the other mushroom species.Cci had the highest concentration of arginine, and the maximum concentration of cysteine was recorded in Bed, proline in Ref, and tyrosine in Bed.Bed is the most abundant mushroom species in terms of essential amino acids.Histidine content was the lowest compared to the other amino acids.The highest concentrations of glutamic acid, methionine and valine were found Bed.The lowest concentrations of valine and lysine were found in Cco; the lowest concentration of isoleucine (3.9 ± 0.01 mg/g), glycine (3.5 ± 0.01 mg/g), and threonine (4.4 ± 0.01 mg/g) were found in Hre.Phenylalanine concentration was the highest in Bed and lowest in Cco.These results agree with those reported by Petrovska (2002) The amino acid composition in Rfe was similar in comparison to other Ramaria species, e.g., León-Guzmán et al. (1997) reported similar results in Ramaria flava, and Agrahar-Murugkar and Subbulakshmi (2005) also found low levels of amino acids in Ramaria brevispora.The lowest amino acid content in the mushroom samples was 89.1 mg/g in Hre, which was in agreement with the results presented by Kalač (2016).
The correlation between each mushroom species was significant at p<0.01 and (r) values ranged from 0.728 to 0.962 for the 17 amino acids.When the correlation coefficients (r) were examined for the 17 amino acid species statistically, it was found that the lowest correlation existed between arginine (Arg) and proline (Pro).Arginine exhibited lower correlation values than the other amino acids.In contrast, the highest correlation coefficient was found to be 0.998 for (p < 0.01, n = 5) significance between aspartic acid (Asp) and glutamic acid (Glu).

Antioxidant properties and total phenolics
The antioxidant properties and total phenolics assayed here are summarized in Table 3, and the results were explained as IC 50 values (mg dry weight of various extracts per mL) for comparison.Percent inhibitions for each mushroom species increased in direct proportion with increasing mushroom concentration (0.83-3.33 mg/mL).Bed showed the highest antioxidant activity and Cco showed the lowest antioxidant activity when the concentrations were considered separately.DPPH radical scavenging capacities for mushroom species were determined by IC 50 value.In scavenging ability on DPPH radicals, the effectiveness was in descending order: (Bed) > (Rfe) > (Cco) > (Cci) > (Hre).
Total phenols were found in the range of 7.74-0.66mg gallic acid equivalents/g for methanolic extracts as a major naturally occurring antioxidant component.The contents of total phenols were found in descending order of (Bed) > (Rfe) > (Cci) > (Hre) > (Cco).The order of total phenolic contents exhibited similar results with IC 50 values, with the exception of Cco.
A relative correlation between concentration and the percent of inhibition for each mushroom species was obtained.Cco and Cci, which were measured by the DPPH method, showed a good significance (p<0.01,n=4).The values ofr were 0.999 and 0.996 between concentration and the percent of inhibition, respectively.Likewise, Rfe showed good significance (p<0.05,r=0.955).Bed and Hre, which were also measured by the DPPH method, the values of r were 0.797 and 0.895, respectively.
The 95% confidence interval of the difference test for the concentration-inhibition pairs was at a level of significance p<0.01 for Bed, Hre, Cci, and p<0.05 for Rfe.The standard deviation value (SD) for concentrationinhibition comparisons was 1.075.
Total phenolics are directly correlated with the change in antioxidant properties.Therefore, statistically correlation coefficients were found (r= −0.887) at the significant level (p<0.05) between total phenolic contents values and IC 50 values for all mushrooms.Accordingly, the negative correlation found confirmed the inverse relation between IC 50 and total phenolic concentration.Ahmad and Mukhtar (1999) proposed good antioxidant properties of phenols because of their scavenging abilities on free radicals and chelating abilities on metal ions.Tsai et al. (2007) and Dubost et al. (2007) found a good correlation between total antioxidant components and polyphenols.

Conclusion
This study was conducted to assess the nutritional value of mushroom species that are widely consumed and form a commercial source of income in the Kastamonu region.
The results of the analysis show the essential and non-essential amino acid compositions of the mushrooms.In particular, non-essential amino acids such as glutamic acid, which also play a role in the formation of the essential amino acids, were found extensively in the studied mushroom species.Among these mushroom species, Bed and Rfe had the highest antioxidant activity and amino acid contents.In addition, antioxidant activity and total phenolic substance concentrations for these mushroom species followed a linear correlation, with the exception of Cco.As a result, it was found that the total phenolic contents had a significant effect on the antioxidant activity, but the antioxidant activity was also determined by the different compositions.Antioxidant activity may also be affected by the amino acid content, which is responsible for typical mushroom tastes and natural values of these five mushroom species.
, and the Boletus species are similar to those reported by Sun et al. (2017).In contrast, Ribeiro et al. (2008) and Tsai et al. (2008) reported low amino acid levels in Bed.Our findings for the amino acid distribution in Cci are similar to those reported by Danell and Eaker (1992), whereas Mdachi et al. (2004), Agrahar-Murugkar and Subbulakshmi (2005) and Ribeiro et al. (2008) found different values.Our findings for Cco are in agreement with those reported by Liu et al. (2012); however, although Beluhan and Ranogajec (2011) reported similar results for threonine and lysine, their findings for the other amino acids were different.

Table 1 :
Collection points and voucher numbers for each mushroom species

Table 2 .
Free amino acid content in Bed, Hre, Cci, Ref, and Cco

Table 3 .
Inhibition (%) and IC 50 values calculated using the DPPH method and total phenolic values measured using Folin Ciocalteu method for mushroom species Mushroom extract concentrations (c*): 0.83, 1.67, 2.50, 3.33 mg/mL The 95% confidence interval of the difference test for the concentration-inhibition pairs are significant at the *p < 0.01 and **p < 0.05 level.