**1.2 Analytical techniques**

The methods used and / or proposed to evaluate the oxidative deterioration of olive oil based on the determination of volatile compounds are HPLC / GC-MS, analytical methods associated with some headspace extractive techniques. The volatile profile of VOO closely depends on the extraction used (S. Vichi, 2010).

Some of the traditional distillation methods applied in the analysis of plant materials as steam distillation (SD), simultaneous distillation/extraction (SDE) and microwave-assisted extraction (MAE) were used for this purpose (Marriott, Shellie, & Cornwell, 2001).

Among these distillation techniques, SDE appeared to provide the most favourable uptake for mono- and sesquiterpenes, as well as for their oxygenated analogues (Marriott et al., 2001). Hydro distillation (HD) has been applied for the analysis of leaf, fruit and virgin oil volatiles of an Italian olive cultivar (Flamini, Cioni, & Morelli, 2003). With hydro distillation, the volatiles in the steam distillate are strongly diluted in water when collected in cold traps. This can be overcome in simultaneous distillation/extraction (SDE) via solvent extraction of the distillate.

Dynamic headspace techniques have been used to correlate the composition of the olive oil headspace to sensory attributes (Angerosa et al., 1996; Angerosa et al., 2000; Morales et al., 1995; Servili et al., 1995) and or avors ''defects" (Angerosa, Di Giacinto, & Solinas, 1992; Morales, Rios, & Aparicio, 1997).

More recently, the solid-phase microextraction (SPME) technique has been introduced as a sample pre-concentration method prior to chromatographic analysis as an alternative to the dynamic headspace technique. Among other applications, SPME allowed the characterization of virgin olive oils from different olive varieties and geographical production areas (Temime et al., 2006; Vichi et al., 2003a), and the evaluation of varietal and processing effects (Dhi et al., 2005; Tura et al., 2004). Since the SPME uptakes are strongly dependant on the distribution of analytes among the sample matrix, the gas phase and the ber coating (Pawliszyn, 1999), some compounds present in virgin olive oil may remain undetected. In the case of other techniques such as SDE, the recovery of analytes is mainly related to their volatility.

These last techniques are complex, expensive and time-consuming. They generally highlight only one or few aspects of the oxidation process, providing only partial information. On the other hand, the olive oil industry needs a rapid assessment of the level of oil oxidation in order to predict its shelf-life. Consumers usually expect manufacturers and retailers to provide products of high quality and seek for quality seals and brands. Therefore, the development of innovative analytical tools for quick and reliable quality checks on extra virgin olive oil is required.
