The gas chromatograph was an HP-5890 (HewlettPackard, Palo Alto, CA), equipped with a quadrupole mass detector HP-5971A operating in EI mode at 70 eV. Helium was used as carrier gas with an inlet pressure of 100 kpa; a BP-20 capillary column (50 m 0.22 mm 0.25 mm) was kept at 40C for 15 min, heated at 5C/ min until 180C and then held for 15 min. MS data were acquired and processed through an HP Chemstation. Identi®cation of volatile components was carried out from their retention times and mass spectral data from the Wiley Library (McLaerty & Staue, 1989) and con®rmed by using standard compounds when available. Quantitative values (mg/l) were calculated from peak areas of volatile compounds and internal standard. Since the aim of these analyses was to compare samples submitted to similar treatments, dierences in response factor and recovery were not taken into account.