2.4. Volatile compound analysis
Aromatic compounds were extracted by purge and trap thermal desorption; 20 g of fresh and reconstituted (to a moisture equal to that of the fresh product) samples spiked with 200 μl of 2-pentanol (10 μg/ml as an internal standard), were placed in a purging vessel flask and left in a water bath at 45 °C for 20 min. During this time, purified nitrogen (200 ml min−1) was forced through a porous frit placed at the bottom of the vessel, producing a stream of bubbles which passed through the sample; then the volatile compounds were collected. These were trapped in a 100 mg of porous polymer (Tenax TA, 20–35 mesh) packed into a glass tube placed at the end of the system. In total, three extracts were obtained for each sample. The volatile compounds were subsequently thermally desorbed using a direct thermal desorber (TurboMatrix TD, Perkin ElmerTM, CT-USA). Desorption was performed under a 10 ml min−1 helium flow at 240 °C for 10 min. The volatiles were then cryofocused in a cold trap at −30 °C and transferred directly onto the head of the capillary column by heating the cold trap to 250 °C (at a rate of 99 °C/s).