**1. Introduction**

130 Olive Oil – Constituents, Quality, Health Properties and Bioconversions

Sinesio, F.; Moneta, E. & Esti M. (2005). The dynamic sensory evaluation of bitterness

Tsimidou, M. Z.; Georgiou, A.; Koidis, A. & Boskou, D. (2004). Loss of stability of ''veiled'' (cloudy) virgin olive oils in storage. *Food Chemistry*, Vol. 93, pp. 377-383.

564.

and pungency in virgin olive oil. *Food Quality and Preference*, Vol. 16, pp. 557–

Olive oil extraction starts by crushing olives and ends by obtaining olive oil, vegetative water and partially de-oiled olive pomace (Petrakis 2006; Di Giovacchino 2000). In the industry it is important to know the amount of oil and water present in both olive fruits and olive pomace. In fact, the amount of oil is the parameter that establishes the price of raw materials and by-products and is critical for the optimization of extraction procedures.

There are publications compiling the various technological aspects of olive oil production, its quality, authenticity, chemical composition and the numerous analytical methodologies used for its characterization (Boskou 2006; Hardwood & Aparicio 1999; Hardwood & Aparicio 2000 Kiritsakis 1998; EC Reg No 2568/1991 and its amendment EC Reg No 1989/2003).

The intrinsic characteristics of the production demand fast decisions based on rapid analytical results. Therefore, conventional analytical determinations of oil, water and acid value should be replaced by short time or real-time/in-line measurements. Rapid characterization of raw material allows the selection of olives according to quality, enabling the production of higher quality oils.

Nowadays, infrared spectroscopy has become widely used as a non-invasive tool for fast analyses with less to no sample pre-preparation. There are numerous publications on the use of infrared spectroscopy for the analysis of oils, some of them will be referred, later in this document.

Baeten et al. (2000) published a paper on infrared and Raman spectroscopies and their potential for olive oil analysis. They described the instrumental techniques, interpretation of the spectra, data treatment and present potential applications.

This chapter reviews various applications of infrared spectroscopy for the analysis of olive oil, presents some results of the authors' work and emphasizes that infrared spectroscopy coupled with proper chemometric tools is an advantageous instrument, to be used in the industry, for olive quality evaluation and olive oil characterization.

Quality Evaluation of Olives, Olive Pomace and Olive Oil by Infrared Spectroscopy 133

Near-infrared spectra present less well resolved bands in the range of 14000 to 4000 cm−1

Figure 2 a) and b) show NIR spectra of olive oil, hammer milled olive and olive pomace. The following main spectroscopic regions can be observed: the region between 9000 – 8000 cm-1, can be ascribed to the second overtone of the C–H stretching vibration of modes of methyl, methylene and ethylene groups of fatty acids and triacylglycerols; the region between 7500 and 6150 cm-1 can be attributed to the first overtone of the O-H stretching vibrations; whereas the absorptions located around 6000 – 5700 cm-1 correspond to the first overtone of the C-H stretching vibration modes of methyl, methylene and ethylene groups; in next region bands between 5350 and 4550 cm-1 result from combinations of fundamentals of the C-H stretching vibration and of bands of water molecules (specially in olives and olive pomace); finally, the 4370 – 4260 cm-1 region can be ascribed to the C–H stretching

combination of methyl and methylene groups (Galtier et al. 2007; Muick et al. 2004).

Several aspects must be considered when spectroscopic data are used in order to achieve multiple parameter determination, by direct analysis of spectra. A careful calibration framework should be devised, comprising: 1) an adequate sampling strategy, taking in account sampling variability and a suitable physicochemical range set; 2) a robust spectroscopic equipment in order to detect and quantify olive oil parameters in lower amounts, which is particularly important in the industrial in-line process; 3) a proper validation of the results given by infrared spectra and multivariate models; 4) a careful control of the outcome from the instrumental results and chemometric models, by employing control charts to evaluate the performance of the methodology and 5) a plan to address models sustainability through a periodic assessment of models performance, e.g. by performing traditional analysis and comparing to the outcome of the infrared spectra, in order to correct possible deviations. This last aspect is very important due to the nature of the samples (e.g. different harvest periods and samples origin, etc.) and equipment efficacy.

corresponding to overtones and combinations of fundamental vibrations.

Fig. 1. Typical ATR-Mid-IR spectrum of olive oil.
