Influence of storage time on the composition of volatile compounds of air dried, frozen and freeze dried thyme and rosemary cultivated in Sardinia

This paper deals with the effect of different stabilizing techniques on the evolution of the volatiles in rosemary (Rosmarinus officinalisL.) and thyme (Thymus officinalisL.) cultivated in Sardinia during nine months of storage. Fresh leaves were collected and soon divided in four batches, which were subjected to hydro distillation and GC-MS analysis, the first batch as fresh, the second one after drying in a laboratory pilot dryer, the third after freezing in a forced air freezer and the fourth after freeze drying in a laboratory freeze dryer.AlI the samples were adequately packaged and stored. Samples for analysis were taken at 3 months intervals. The fresh, stabilised and stored plant material were hydro distilled for 4 hours using a Clevenger-type. The oils were analysed in duplicate by gas chromatography, using a flame ionization detector. Qualitative analysis was done by GC /Mass and mass units were monitored from 10 to 450 at 70 eV.Results of the evolution of volatile compounds of the differently samples seem to evidence that the best way to stabilize the herbs is freezing.