## 1 Introduction  
According to the International Olive Council (IOC), olive oil can be defined as the product of the fruits from _Olea europen_ L\({}_{v}\), trees obtained physically or mechanically by washing, decantation, centrifugation and filtration. These processes alter neither the nutritional composition of the final product nor interfere with its organoleptic characteristics, namely, taste and aroma. Regulation of the European Union (Reg. (EEC) 2568/91) and IOC have introduced specific requirements, according to which olive oil is classified in different categories which (a) define its quality, namely: alkyl esters of fatty acids composition (which are constituents connected to quality decline when their estimated value is greater than those imposed by legislative authorities), degree of acidity (expressed as a percentage of g of oleic acid in 100 g of oil), determination of peroxides (expressed as milliequivalents of active oxygen per kilogram which oxidize potassium iodide), spectrophotometric indices and sensory characteristics (flavor and aroma) and (b) are characteristic parameters of its purity such as quantification of waxes (the limit is set at 150 mg/kg for EVOO and VOO), sterols (total sterol content (mg/kg) as well as % of free sterols), 2-glycerol mono-palmitic [1]. This classification includes Extra Virgin Olive Oil (EVOO), which is directly produced from olives using mechanical means. EVOOs' aroma and taste are attributed to the presence of volatile and non-volatile compounds and their free acidity is lower than 0.8%. Virgin Olive Oil (VOO) is produced similarly to EVOO; however, its free acidity is higher but not greater than 2%, and its organoleptic properties are of inferior quality with respect to EVOO. Olive Oil (OO), is a mixture of refined and edible virgin olive oil, with acidity lower than 1%, and it is often labeled as virgin, light or pure olive oil. Refined olive oil is obtained from lower quality VOOs in terms of the degree of acidity and organoleptic characteristics. However,during refining processes such as deacidification, deodorization and decolorization, which require the use of organic solvents, these \"defects\" are usually eliminated. In particular, deodorization aims at removing off-flavor compounds from VOO, among which volatile compounds are included, that are produced via degradation/oxidation pathways due to long/inappropriate storage of olives before processing and/or of VOO. Deodorization requires high temperature under vacuum, which gradually degrades those unpleasant volatile compounds. Ordinary virgin oil is produced from olive oil fruits using the same processes as for EVOO; however, its acidity is 3.3%. This category has been excluded by the EU classification of olive oil, a strategy that will also follow other regulatory organizations. Lampante virgin olive oil is produced from low-quality fruits and is not destined for consumption. Its level of acidity is higher than 2%, and its organoleptic characteristics are rather poor (displeasing taste and smell). Finally, a distinct category that includes three subcategories is that kind of oil derived from pomace. Pomace is the residue of olive oil fruits after mechanical extraction of EVOO, which is treated with organic solvents, most common of which is hexane. Pomace oils include crude olive pomace oil, which is not adequate for human consumption; refined olive pomace oil, which is also not proposed for consumption and olive pomace oil, derived from olive pomace and VOO and is considered ideal for culinary purposes. EVOO is a mixture of numerous bioactive compounds, the majority of which belong to monounsaturated fatty acids (MUFAs) such as oleic acid (18:1, n-9) and palmitoleic acid (16:1, n-7), with the first one being presented in abundance, and polyunsaturated fatty acids (PUFAs) such as linoleic acid (18:2, n-6) and linolenic acid (18:3, n-3).