2.9. Statistical analysis of GC-FIDdata
Multivariate analysis was employed in cluding the five majormcompounds, i.e. compounds with concentration equal or higher than 20% in any sample and extraction technique (pulegone,carvacrol, thymol, p-cymene and -terpinene). Area percentages(%of totalarea)of each peak were used,as the relative concentration of each compound has been reported to be less dependent on plant material treatment spriorto analysis than its absolute
concentration (Hillig, 2004). Cluster analysis was performed for each essential oil isolation technique in order tovalidate samples chemotype, using hierarchical centroid method.Linear discriminant analysis was used to classify samples in to the a priori defined chemotypes regardless of acquisition technique.Statistical analysis
of GC-FID data was performed using JMP version8.0(SAS Institute,2008).