# Olive Oils Classification via Laser-Induced Breakdown Spectroscopy
## 1 Introduction  
Olive oil is a key element of the Mediterranean diet because of its excellent nutritional and organoleptic properties. Extra Virgin Olive Oils (EVOOs), in particular, usually attain much higher price than other types of vegetable oils; this difference resulted from the increased demand of the markets and the preferences of the consumers, the latter being oriented during recent years, progressively, towards higher quality and more healthy food products and ingredients. Inevitably, this situation makes EVOOs more prone to adulteration by other lower cost vegetable oils (as e.g., pomace oil). In addition, when the olive oil of a region is recognized for its unique properties (as e.g., taste, odor, color, etc.) and assessed for that by the specialists and the consumers, its designation of origin and/or geographical indication is becoming finally a brand name, giving added value and therefore resulting in higher market prices. Thus, Protected Designation of Origin (PDO) and/or Protected Geographical Indication (PGI) protocols can significantly differentiate the different types of olive oils [1; 2; 3; 4]. In that view, the control of the authenticity of foodstuff is essential and necessary for the fair trade between the producers and the consumers, and there are several national (e.g., Hellenic Food Authority-EFET in Greece) and international (e.g., European Commission) organizations in charge to set and control the frameworks about the allowed concentration of the different food ingredients while they are often responsible to prepare the necessary legislation in order to preserve the PDO and the PGI of food. Then, according to this legislation, food's categorization, which is based on its variety and designation of origin, is set as a criterion of their authenticity and quality. During the last twenty years, there have been several common methodologies for olive oil testing, which are mainly used for assessing the oil's suitability as an edible product (e.g., by labeling it as extra virgin, virgin, lampante, etc. ), for determining the amounts of substances which are relatedwith its quality, such as the phenolic content and stigmatadienes [5], and for determining its regional provenance. The most standard and common methods employed are liquid and gas chromatographic techniques. However, they require significant laboratory workload for the full characterization of an olive oil sample; despite the high accuracy and excellent results they offer, there is need for new techniques that can alleviate the workload associated with their use. In addition, some important issues that need to be resolved are the identification of geographical origin, and/or the classification of olive oils based on their acidity, etc. As an alternative to the chromatographic techniques, different spectroscopic techniques have been proposed and applied for the analysis of olive oils, with different degree of success, such as NMR spectroscopy [6; 7], FT-IR spectroscopy [8; 9], Raman spectroscopy [10; 11; 12] and, recently, Laser-Induced Breakdown Spectroscopy (LIBS) [13; 14; 15]. LIBS is a laser based analytical technique that uses an intense enough laser beam to induce a dielectric breakdown in a sample or on its surface [16; 17]. The result is the formation of a spark, i.e., a plasma, which contains atoms and small (mainly diatomic) molecules (that can be excited or not), ions and electrons. The so produced plasma lives, in general, for a short time (e.g., up to some tens/hundreds of \(\upmu\)s), depending on the material, while during this time, it emits some characteristic spectral radiations arising from its different excited constituents and the physical processes occurring in the hot plasma. The spectral analysis of the plasma radiation contains information about the sample's elemental composition, being a kind of spectral fingerprint. The collection of such LIBS spectra is rapid, does not require any previous time-consuming preparation of the sample and it can be performed on-line, in situ and even remotely.