GC–MS analyses were performed using a Finnigan TRACETM MS (TermoQuest, Austin, USA). Volatile compounds were separated using a BP-20 capillary column (SGE, Australia) (60 m length, 0.32 mm i.d., 1.0 lm film thickness). Helium, at a constant flow rate of 1 ml min−1, was used as a carrier gas. The temperature was programmed to increase from 40 °C (2 min hold time) to 190 °C at 4 °C min−1 and finally to 230 °C at 10 °C min−1. The MS interface and source temperatures were 250 and 200 °C, respectively. Electron impact mass spectra were recorded in impact ionisation mode at 70 eV and with a mass range of m/z 33–433. In total, three extracts were obtained for each sample.