## 1 Introduction
The obtained spectrum is unique for each tested sample and represents a distinctive chemical fingerprint. Raman spectroscopy, such as with IR, provides a unique spectrum for each sample. However, the difference between these two techniques lays in the characteristic absorption bands. Unlike IR, intense and well-distinctive bands of symmetric vibrations of non-polar groups appear in Raman spectroscopy, thus making able to determine, for example, the type of unsaturated fatty acids and ensure the presence of cis configuration. Both techniques are quick since no preparation of the sample is required; consequently, the use of solvents is limited to the minimum and the sample remains intact. Time of analysis is short and information obtained, when combine results, complete the profile of the studied sample and allow researchers to guarantee its authenticity [15] (Table 1). \begin{table}
\begin{tabular}{c c c} \hline
**Authors** & **Method/Sample Preparation** & **Focus** & **Chemometrics** \\ \hline \multicolumn{3}{c}{**Detection of Adulteration**} \\ \hline
[7] & FT-NIR spectroscopy/the method requires no sample preparation & Authenticity and adulteration of EVOO with vegetable oils & PLS1 analysis \\
[10] & FT-NIR spectroscopy/the method requires no sample preparation & Screening of commercial oils labeled as EVOOs to identify their authenticity & PCA and PLS analysis \\
[16] & NIR Raman spectroscopy/the method requires no sample preparation & Adulteration with hazelnut oil as well as botanical and geographical discrimination of & PLS and PCA analysis \\
[17] & FT-NIR Raman spectroscopy/the method requires no sample preparation & EVOO & PCA analysis \\
[18] & Vis-Raman/the method requires no sample preparation & Geographical discrimination and & PCA analysis \\
[19] & Raman and visible spectroscopy/both methods require no sample preparation & Quantitative determination of EVOO & PLS and PCA analysis \\
[20] & Raman spectroscopy/the method requires no sample preparation & Detection of derek EVOO adulteration with sunflower oil & PLS method \\  & FT-IR, FT-NIR and Raman & Detection of adulteration of EVOO with & PCA and LDA analysis \\
[21] & spectroscopy/transesterification of the sample & Discrimination of pure olive oil from & PCA, PLS-DA analysis \\
[22] & FT-IR/the method requires no sample preparation & Detection of adulteration EVOO with & DA and PLS \\
[23] & FT-IR/the method requires no sample preparation &
\begin{tabular}{c} Detection of EVOO adulteration with canola, \\ hazelnut, pomace and high linoleic/oleic \\ sunflower oils \\ \end{tabular} & PLS analysis \\ \hline \end{tabular}
\end{table} 
Table 1: Infrared and Raman spectroscopic methods used to evaluate authenticity of EVOO and VOO. [PERSON] et al. (2015) [7], using Near-Infrared Spectroscopy (NIRS), developed a novel protocol to confirm the authenticity and adulteration of EVOO based on the creation of an FT-NIR index, determined by specific wavelengths. Authenticity was achieved thanks to two characteristic absorption bands, at 5180 cm\({}^{-1}\), which corresponds to non-volatile compounds or esters and at 5280 cm\({}^{-1}\), which equals to volatile compounds bearing carbonyl groups. Detection of adulteration was evaluated based on the spectral differences between the fatty acid (FA) composition among EVOO and adulterant oil. In cases of similarities between the FA composition of EVOO and the adulterant, a higher level of adulteration was necessary. According to the FT-NIR index, a classification model using Partial Least Square Regression analysis (PLS) was built, and results evidencedthat the method developed by the authors is of high reliability. A similar study analyzed commercial samples of EVOO for their authentication with the FT-NIR technique [10]. Authors' prerequisites in order to define a sample as EVOO were an FT-NIR index greater than 75%, the content of the main FA was according to official criteria guidelines and the adulterant content at the level of limit \(\pm\)2 SD (standard deviation), as established by other studies [7].