## 4 Conclusions  
The combined use of GC-MS and GC\(\times\)GC-TOF-MS analysis for volatile aroma compounds proved to be a powerful analytical option, providing broad coverage of the volatilome, which is useful for the differentiation of the two classes of EVOO with respect to the origin of purchase: monovarietal PDO EVOO from family farms vs. commercial-blended EVOO from supermarkets, respectively. To our knowledge, this study provided one of the most detailed and comprehensive qualitative and quantitative analytical characterizations of the volatile profile in EVOO up to date, with many compounds being identified (or tentatively identified) in EVOO for the first time. Among them, many potential markers were extracted, despite the known (for PDO) and presumed (for commercial-blended) geographical and pedoclimatic heterogeneity and large variations in olive growing and oil producing parameters among EVOOs. Monovarietal PDO EVOOs were characterized by notably higher concentrations of desirable LOX-derived C6 and C5 volatiles, including the major ones that are known to be crucial contributors to the characteristic and appreciated EVOO green and fruity flavor. Such findings basically confirmed the results of the sensory analysis, which described the monovarietal PDO EVOOs by higher intensities and grades for positive sensory descriptors and attributes. On the other hand, the commercial-blended EVOOs had larger quantities of many volatiles that are known to originate from undesirable chemical and microbiological processes in olive and in olive oil, such as saturated esters, alcohols, acids, and aldehydes, which corresponded to the occurrence of sensory defects in many of the samples from this group. It is worth highlighting that a very large array of minor and unbeknown compounds, not reported or neglected in previous studies, was found to differentiate each of the two investigated EVOO groups, which point to the possibility that they also contributed to the perceived sensory notes. Targeted HPLC-DAD-ESI/MS profiling of phenols succeeded in differentiating monovarietal PDO from commercial-blended EVOOs to a much smaller extent, which was mostly due to the diversity of the concentration in monovarietal oils. Additionally, the differences that were observed during sensory analysis related to the corresponding taste attributes were not large. Nevertheless, the results of this study undoubtedly confirmed the large heterogeneity of oils, which are sold declared as EVOO in Italy, both in terms of chemical composition and sensory attributes, and in a way pointed to the possible reasons behind the existing large span of prices within this quality category. The approach that was proposed in this study is universal in nature and it could be applied for the characterization and differentiation of various other types of EVOO. The detailed profiles of volatile aroma compounds and phenols that can be obtained by the reported combination of powerful yet complementary techniques may serve experts, producers, and suppliers to better define typical sensory characteristics of EVOO in question, and in this way strengthen their identity and position on the market. From the technological point of view, understanding the compositional origins of thesensory typicity of particular EVOO might allow for more efficient quality management and control in production and more precise information to the consumers. The following are available online, Figure S1: Chromatograms of volatile aroma compounds found in monovarietal PDO and commercial-blended extra virgin olive oil by headspace solid-phase microextraction combined with gas chromatography/mass spectrometry (HS-SPME-GC-MS). Figure S2: Contour plots (2D-chromatograms) of volatile aroma compounds found in a) monovarietal PDO and commercial-blended extra virgin olive oils by headspace solid-phase microextraction combined with comprehensive two-dimensional gas chromatography-mass spectrometry (HS-SPME-GC-GC-TOF-MS).