About 2 g of powdered rye-buckwheat biscuits were transferred into 22-mL headspace vials. The vials were sealed air-tight with a silicone/polytetrafluoroethylene (PTFE) septum. An aliquot of 2.5 mL of sodium chloride solution (25%) was added to each vial before capping and heating. A GC-MS method developed previously by Koutsidis et al. [38 (link)], was employed to quantitatively determine volatile compounds in the biscuits. The vials were then placed onto a COMBIPAL autosampler (CTC Analytics, Zwingen, Switzerland) coupled to an Agilent 7890A GC (Agilent Technologies, Colorado Springs, USA) and a BenchTOF-dx mass spectrometer (ALMSCO International, Llantrisant, UK).
HS-SPME of the preheated samples (40 °C, 5 min) was performed under agitation for 1 min at 500 rpm using a 50/30 μm DVB/Carboxen/PDMS stable flexTM fiber (Supelco, Bellefonte, PA, USA), followed by desorption (5 min) at 250 °C onto a 60 m DB-WAX capillary column (0.25 mm i.d. −0.25 μm film thickness). The initial oven temperature was set at 40 °C, held for 5 min, increased to 200 °C at 4 °C min−1, held for 1 min, and finally increased to 260 °C at 8 °C min−1, held for 5 min. The helium flow rate was maintained constant at a flow rate of 1 mL min−1. For quantification purposes, an external calibration method was used. Pyrazine standard solution was prepared by weighing 50 mg of pure standards of methylpyrazine, ethylpyrazine, 2,3-, 2,5- and 2,6-dimethylpyrazine in a 25 mL volumetric flask and make up the rest of the volume with de-ionized water. The 500 mL of standard solutions were added into the vial with 2 g of rye flour and 2.5 mL sodium chloride solution. All analyses were carried out in triplicate injection. Selected ions were used for quantification of the individual components. Compound identification was carried out by injection of commercial standards, by spectra comparison using the Wiley Registry 7th Edition Mass Spectral Library (Wiley and Sons Inc., Weinheim, Germany) and the National Institute Standards and Technology (NIST) 2005 Mass Spectral Library and by calculation of linear retention indexes (LRI) relative to a series of alkanes (C6–C20).
HS-SPME of the preheated samples (40 °C, 5 min) was performed under agitation for 1 min at 500 rpm using a 50/30 μm DVB/Carboxen/PDMS stable flexTM fiber (Supelco, Bellefonte, PA, USA), followed by desorption (5 min) at 250 °C onto a 60 m DB-WAX capillary column (0.25 mm i.d. −0.25 μm film thickness). The initial oven temperature was set at 40 °C, held for 5 min, increased to 200 °C at 4 °C min−1, held for 1 min, and finally increased to 260 °C at 8 °C min−1, held for 5 min. The helium flow rate was maintained constant at a flow rate of 1 mL min−1. For quantification purposes, an external calibration method was used. Pyrazine standard solution was prepared by weighing 50 mg of pure standards of methylpyrazine, ethylpyrazine, 2,3-, 2,5- and 2,6-dimethylpyrazine in a 25 mL volumetric flask and make up the rest of the volume with de-ionized water. The 500 mL of standard solutions were added into the vial with 2 g of rye flour and 2.5 mL sodium chloride solution. All analyses were carried out in triplicate injection. Selected ions were used for quantification of the individual components. Compound identification was carried out by injection of commercial standards, by spectra comparison using the Wiley Registry 7th Edition Mass Spectral Library (Wiley and Sons Inc., Weinheim, Germany) and the National Institute Standards and Technology (NIST) 2005 Mass Spectral Library and by calculation of linear retention indexes (LRI) relative to a series of alkanes (C6–C20).
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