## 2 Results and Discussion
### Identification of VOCs by HS-SPME/GC-MS Analysis
The molecule 1-penten-3-ol is related to \"mouldy\" and \"rancid\" defects associated with lawn, olive, leaf, and pungency and ranged from 0.90 mg kg\({}^{-1}\) in conventional VOO of Heraklion to 2.94 mg kg\({}^{-1}\) in an organic sample of Koroneiki cultivar in Chania. (\(Z\))-2-penten-1-ol (0.60-1.87 mg kg\({}^{-1}\)) and 2-pentenal (E)- (0.1-0.51 mg kg\({}^{-1}\)) are minor compounds whose presence is correlated with banana, sweet, fruity and green, apple, and bitter almond attributes, respectively [33]. C5 ketones, pentene dimers, or monoterenes affect olive oil aroma even in low concentrations. The molecule 1-penten-3-one reached high amounts at the Koroneiki samples of Heraklion (5.75 mg kg\({}^{-1}\)) whereas it was not detected in an organic VOO of the Koroneiki variety from Rethymnon. Its presence is linked to leaf, mustard, and pungent notes [34], whereas higher amounts have been also related to metallic notes. The isomer 3-ethyl-1,5-ocadiene is produced over the oil extraction process through the same branch of the LOX pathway as the C5 compounds and was detected in all samples (0.12-4.91%) [35]. Other minor volatiles, terpene hydrocarbons (mono- and sesquiterpenes), were detected in Cretan VOOs, and despite the fact they do not contribute to VOO aroma due to their low concentration and high odor threshold, they constitute significant quality markers [29]. Among all terpenoid compounds, the most abundant in the studied VOO samples, were d-limonene (0.04-20.18 mg kg\({}^{-1}\)) with citrus, mint odor perceptions, \(\alpha\)-farnesene (0.02-0.27 mg kg\({}^{-1}\)) with floral, herb, wood, and sweet odor qualities [36], and (\(E\))-4,8-dimethyl-l,3,7-nonatriene (0.04-0.19 mg kg\({}^{-1}\)). Other terpenoid volatiles such as alpha- and beta-pinene, o-cymene, and copaene were also detected in lower amounts. Some rare terpenic compounds such as citral, (+)-cyclosativen, eremophilene, neral, 3-carene, and kessane, which so far have been reported only in a few studies [29; 37; 38], were also identified with the current method. The detection of benzenes, toluene, xylenes, and styrene (BTEXS) in olive oil is of high importance. These VOCs are widely distributed in the environment and food products mainly due to emissions from vehicles, bonfires, and paints into the ambient air near orchards. In olive oil, BTEXS are frequently identified, and their presence is attributed to several factors, such as biological processes in the fruit, the production technology used, contamination by fuel vapors, etc. [39]. In this study, toluene, styrene, xylene, propylene, 1-ethyl-2-methylbenzene, 4-ethyltoluene, 1,4-diethylbenzene, and naphthalene were identified. The presence of styrene in VOO samples has been attributed to natural causes, such as decarboxylation of the cinnamic acid that is naturally present in the olive pulp or by migration from the plastic package [39]. Naphthalene is usually hanged on treesby olive farmers, as it has a characteristic aroma that is theorised to repel the olive fly (Bactrocera oleae), and in this study was identified in low levels (0.01-0.92 mg kg\({}^{-1}\)) in 8 out of 63 samples [40]. According to our knowledge, VOCs such as 1-propanone-1-phenyl, benzene, 1,4-diethyl, 11-hexadecen-1-ol, (_Z_), and 2,_4_-di-tert-butylphenol are reported for the first time in VOO samples.