Comparison of Volatile Compounds of Fresh Boletus edulis and B . pinophilus in Marmara Region of Turkey

Boletus edulis and B. pinophilus are commonly consumed edible species of Boletus spp. in Turkey, which are also exported to some European countries. In this study, twenty-three volatile compounds were determined with Headspace Solid-Phase Microextraction / Gas Chromatography / Mass Spectrometry (HS-SPME/GC/MS) in both B. edulis and B. pinophilus. 1octen-3-ol (79.75), 2-octen-1-ol (13.18), 1-octen-3-one (2.52), (E)-2-octenal (1.21) in B. edulis and 1-octen-3-ol (55.97), 2octen-1-ol (13.55), 3-octanone (7.43), (E)-2-octenal (6.79), 1-octen-3-one (5.80) and 1,7,7-trimethyl-heptan-2-one (2.04), 2propenoic acid (1.95) and 1,3-octadiene (1.75) in B. pinophilus were identified as main volatile aroma compounds (%), respectively. The present study is the first report on the volatile constituents of B. edulis and B. pinophilus collected from


Introduction
Boletus edulis Bull: Fr. and Boletus pinophilus Pilât (Section Edules), which are also known as Porcini, are edible fungi widespread in the world (De Román and Boa, 2004;Sitta and Floriani, 2008).These fungi are economically significant because of wholesale average value which reached to 200 $ and the worldwide consume is ranging from 20,000 to 100,000 tons (Hall et al., 1998).
There are over a hundred Boletus species in the world.The edible Boletus spp.are popular and often harvested by European countries because of their taste, aroma and odors (Jaworska and Bernas, 2009).In the genus of Boletus, B. edulis and B. pinophilus are extremely delicious and consumed in some Asian, American and European countries.In addition to fresh consumption, dried type of B. edulis is also consumed (Tsai et al., 2008).
Porcini is an important source of income not only in Europe, but also in several rural areas of the world (Arora, 2008;Beugelsdijk et al., 2008;De Román and Boa, 2004;Leonardi et al., 2005;Sitta and Floriani, 2008).In addition, Turkey has a great potential and is becoming a major exporter of natural and edible mushrooms (Mendil et al., 2004).
Edible Boletus species are widespread and especially consumed in Marmara and Western Black Sea regions of Turkey.The quality of mushrooms depends on their aroma, taste, odor and color.Mushrooms have a lot of volatile compounds that are responsible for aroma, taste and odor.
In previous studies, elements content and antioxidant properties of some Boletus species in Turkey were reported (Elmastas et al., 2007;Gençcelep et al., 2009;Mendil et al., 2004;Sarikurkcu et al., 2008;Yamac et al., 2007).Volatile compounds of different mushrooms were studied by many researchers (Abraham and Berger, 1994;Breheret et al., 1998;Rapior et al.;1996;Taşkın et al., 2013a;Taşkın et al., 2013b).However, volatile compounds of B. edulis and B. pinophilus grown in Turkey have not been studied yet.Thus, the aim of this present study was to determine volatile aroma compounds of fresh B. edulis and B. pinophilus grown in Turkey.

Fungi material
In November 2013, fresh B. edulis and B. pinophilus samples (Fig. 1) were collected from Beypınar village (41 o 48'35"N, 27 o 33'33"E, 733 m) of Kırklareli province (Marmara region) in Turkey.Mushroom samples were transferred to the laboratory in 24 hours after collection time.Identifications of macrofungi samples were made according to Breitenbach and Kränzlin (1991) and Galli (2007).Voucher specimens were deposited in Fungarium of Selçuk University.

Solid-phase microextraction (SPME) analysis of volatile compounds
A supelco fiber holder (Bellefonte, PA-USA) and a 100 µm polydimethylsiloxane (PDMS) coated fused-silica fiber were used for adsorbing volatile compounds from B. edulis and B. pinophilus according to Taşkın (2013a), with slight modifications.Prior to first extraction, the fiber was conditioned 193 in the GC injector port at 250 °C for 1 h, according to manufacturer's recommendation.HS-SPME technique was used in the extraction of volatile compounds of B. edulis and B. pinophilus.These fungi were homogenized with saturated 5 g sodium chloride for HS-SPME.Further, 50 g of sample for each extraction was placed into 100 ml glass bottle.In HS-SPME analysis, the PDMS fibre was inserted into the headspace of the glass bottle and was immersed into the sample during 30 min at 30 °C.During this time, mushroom samples were stirred with a magnetic stirrer.After equilibration the fibre was removed from the sample and the analyses were thermally desorbed in the injector port of the GC/MS instrument for analysis.Thermal  Gas chromatography/Mass spectrometry (GC/MS) analysis Aroma compounds of the mushrooms were analysed by GC-MS.A Perkin Elmer Clarus apparatus equipped with CPSil5CB (25 m x 0.25 mm i.d., 0.4 µm film thickness) fusedsilica capillary column was used.The flow rate of helium as carrier gas was 1 ml/min.The injector temperature was 250 °C, set for splitless injection.The column temperature was 60°C/5°C/min/260°C for 20 min.Mass spectra were taken at 70 ev.Mass range was between m/z 30-425.A library search was carried out using the Wiley GC-MS Library and Flavor Library of Essential Oil Constituents.The mass spectra were compared with those of reference aroma compounds and also confirmed with retention indices in published sources.Relative percentage amounts of the separated compounds were calculated from total ion chromatograms by the computerized integrator.
As shown in Table 1, major compounds in B. edulis and B. pinophilus consisted of approximately 95-96% of total aroma, respectively.1-octen-3-ol, found as a major compound in B. edulis and B. pinophilus, is considered responsible for the characteristic aroma of many edible mushrooms (Abraham and Berger, 1994;Cho, 2006).However, it could be said that other major and minor components also contributed to taste, odor and aroma.

Conclusions
B. edulis and B. pinophilus are common mushrooms and often consumed in Marmara region of Turkey.HS-SPME / GC / MS results show clearly that these mushrooms are quite rich in terms of aroma compounds.This is why Boletus species are presumably preferred by consumers.Similar studies which will be held in the future, will help us to have more information about aromas of mushroom and to have more benefit from mushrooms in Turkey.

Table 1 .
Volatile compounds of fresh B. edulis and B. pinophilus Note: Major compounds are shown by "*"; RT: Retention Time; A: B. edulis; B: B. pinophilus; nd: not detected

Table 2 .
Comparison of the volatile compounds of Boletus species