## 4 Discussion  
According to ISO 9000, quality is defined as \"the degree to which a set of inherent characteristics of an object fulfills requirements\". These requirements are imposed via rules and regulations by official authorities in order to combat fraud problems. Regarding olive oil, and especially EVOO and to a lesser extend VOO, issues of authentication are a continuous concern for authorities. Authentication issue includes a check of possible adulteration of EVOO with other types of oil of lower value and minor quality, misleading geographical indication and deceptive botanical origin. The most common adulterants usually detected at EVOO and VOO are various vegetable oils of inferior economical value and different in compositional characteristics, such as canola, sunflower, hazelnut and soybean oils. Although regulations regarding olive oil quality have been proposed and limits of various physicochemical parameters have been imposed, the drawback of these recommendations is that they are not obligatory worldwide. In addition, the common harmonized EU law 2568/91 is mandatory for all EU members; however, as described by [PERSON] et al. (2019) [64], still, minor improvement is needed. In these terms, the need for simple, rapid, environmentally friendly and reliable techniques able to confirm authentication of olive oil and consequently certify its quality is obligatory since safety is not negotiable for consumers. As has been already mentioned, EVOO and VOO contain many active constituents that belong to different chemical families. Given the fact that the chemical profile is strongly affected by numerous factors (climate, soil, cultivar, storage, collection), it is obvious that a \"standard\" chemical profile of olive oil, based on its category according to IOC guidelines, is difficult to adopt. This complexity consists of a serious advantage when cases of fraudulence are planned, and at the same time, a major disadvantage for those organizations that combat fraud. Nevertheless, the development of many analytical techniques has considerably contributed to combatting the fraud apocalypse. EVOO authenticity is guaranteed by its unique, peculiar aroma owned to the presence of multiple volatile compounds that belong to different chemical groups, including aldehydes, ketones, alcohols and esters [65; 66; 67]. Specifically, the presence of C6 and C5 aldehydes and alcohols as well as their esters, are characteristic compounds to which the sensory quality of EVOO is attributed. These compounds are produced by the lipoxygenase (LOX) pathway and are presented at high concentrations in EVOOs, on the contrary, lower quality oils are present in minor quantities or traces or are even absent [68]. Although the volatile composition of an olive oil strongly depends on climatic, geographical, cultivar and extraction methods, various analytical techniques have been developed, able to characterize the oil's authenticity, variety and geographical origin based on the volatile fraction. Differentiation of EVOOs and VOOs is a project studied by many researchers, who have concluded that, among others, certain molecules such as monoterenes, sesquiterpenes and terpen are characteristic compounds that allow the effective classification of the studied samples [57; 58; 60]. As is mentioned in this review, the volatile profile of an olive oil, as defined by SPME combined with the gas chromatography technique, has been proven to be a valuable tool to determine authenticity. The majority of the mentioned articles discriminate olive oil according to its geographical origin. The fiber used by most researchers as the most adequate to collect volatiles was the 50/30 \(\upmu\)m Divinylbenzene/Carboxen/Polydimethylsiloxane fiber. The extraction temperature of volatiles varied from 25 to 70 \({}^{\circ}\)C, while the incubation time varied from 5 min to 2 h. Extraction time also presented a great variability between the studies, from 5 to 90 min.