3.2. Extraction and Analysis of Volatile Sulfur Compounds

The isolation of headspace volatiles was performed by using a manual SPME fiber with the layer of carboxen/polydimethylsiloxane (CAR/PDMS). For HS-SPME extraction, 1 g of the sample was placed in a 15 mL glass vial, and the vial was maintained in the water bath at 40 °C, during the equilibration period (15 min) and the extraction period (40 min). After the sampling, the SPME fiber was withdrawn into a needle, removed from the vial, and inserted into injector for 7 min, where the extracted volatiles were thermally desorbed directly to the GC column. The samples were analyzed by GC–MS system (Agillent Technologies GC 7820A and MSD 5977E, Palo Alto, CA, USA). Operating conditions were as follows: column HP-5MS ((5%-phenyl)-methylpolysiloxane), 30 m × 0.25 mm i.d., coating thickness 0.25 μm) and column temperature was programmed at 70 °C isothermal for 2 min, and then increased to 200 °C at a rate of 3 °C/min and held isothermal for 15–18 min; helium as the carrier gas at 1 mL/min; injector temperature 250 °C; the split ratio 1:50; ionization voltage 70 eV; ion source temperature 230 °C; the mass range at m/z 30–350. The individual peaks were identified by comparison of their retention indices (relative to C₉-C₂₅ n-alkanes) to available authentic samples and literature data [79], as well as by comparison of the mass spectra with the Wiley 9 MS library (Wiley, New York, USA) and NIST 14 (Gaithersburg, Germany) databases. The percentage composition was calculated by using the normalization method (without correction factors) from the GC peak areas. The HS-SPME/GC–MS analyses were performed in triplicate.