3.5. Production of volatile compounds
In order to determine the optimum conditions for SPME-GC/MS
analysis the following parameters were studied: fibre type, absorption
and desorption time, sample weight in the vial, extraction time, and
temperature. Six fibres with different coating materials were
examined: polyacrylate 85 mm in thickness, PDMS 100 mm in
thickness; CAR/PDMS 75 mm in thickness, PDMS/DVB 65 mm in
thickness, CAR/DVB 65 mm in thickness and DVB/PDMS/CAR 50–
30 mm in thickness. The results showed that the 75-mm CAR/PDMS
fibre had the highest sorptive capacity. Extraction time was carried
from 5 to 30 min. The optimum signal areas were obtained with an
extraction time of CAR/PDMS for 15 min into the headspace of the vial
after allowing the sample to equilibrate for 15 min at 60 °C. Extraction
temperature was varied between 30 and 70 °C. The optimum signal
areas were obtained at 60 °C. In order to determine the optimum
sample weight samples (0.1 to 0.5 g) were placed in the vial and
conditioned as described above. The sample weight was chosen to be
0.1 g chocolate, along with 1 mL of distilled water and 1 mL of 0.1 M
NaCl. The addition of water was necessary to generate a homogenous
slurry of crushed chocolate and to disperse the internal standard
homogeneously throughout the sample. The addition of NaCl to the
sample showed a positive effect on the reproducibility and the
extraction yield of the headspace compounds. 4-methyl-2-pentanone
was chosen as the internal standard as it does not occur naturally in
dark chocolate or hazelnut and it does not interfere with flavor
compounds of dark chocolate with hazelnuts in the chromatographs.
Our experimental conditions with regard to SPME fibre selection
contradict those of Ducki, Miralles-Garcia, Zumbé, Tornero, and Storey
(2008) who reported that DVB/PDMS/CAR 50–30 mm showed the