**1. Introduction**

#### **1.1 Olive oil**

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

Muick B., Lendl B., Molina-Díaz A., Pérez-Villarejo L. & Ayora-Cañada M. J. (2004).

O'Brien R.D. (2004). Fats and Oils. In: *Formulating and Processing for Applications*, 2nd ed., CRS

Ollivier D., Artaud J., Pinatel C., Durbec J.P. & Guérère M. (2003). Triacylglycerol and fatty

Ollivier D., Artaud J., Pinatel C., Durbec J.-P. & Guérère M. (2006). Diferentiation of French virgin

and chemometrics. *Food Chem.* 97, (August 2006), pp. 382-393, ISSN 0308-8146 Petrakis C. (2006). Olive oil extraction, In *Olive Oil, Chemistry and Technology*, D. Boskou

Sato T. (1994). Application of principal-component analysis on near-infrared spectroscopic

Takamura H., Hyakumoto N., Endo N. & Matoba T. (1995). Determination of lipid oxidation in edible oils by near infrared spectroscopy. *J. Near Infrared Spectrosc.* 3 (4), pp. 219-225 Tapp H.S., Defernez M. & Kemsly E.K. (2003). FTIR spectroscopy and multivariate analysis

Tay A., Singh R.K., Krisshnan S.S. & Gore J.P. (2002). Authentication of olive oil adulterated

Vlachos N., Skopelitis Y., Psaroudaki M., Konstantinidou V., Chatzilazarou A. & Tegou E.

Wahrburg U., Kratz M. & Cullen M. (2002). Mediterranean diet, olive oil and health. *Eur. J.* 

Wesley I. J., Barnes R. J. & McGill A. E. J. (1995). Measurement of adulteration of olive oils

Wesley I. J., Pacheco F. & McGill A. E. J. (1996). Identification of adulterants in olive oils. *J.* 

Wold S., Sjöström M. & Eriksson L. (2001). PLS-regression: a basic tool of chemometrics. *Chemom. Intell. Lab. Syst.* 58, (October 2001), pp. 109-130, ISSN 0169-7439 Woodcock T., Downey G. & O'Donnell C.P. (2008). Confirmation of declared provenance of

Xu Q.-S. & Liang Y.-Z. (2001). Monte Carlo cross validation. *Chemom. Intell. Lab. Syst.* 56,

Yang H. & Irudayaraj J. (2001). Comparison of near-infrared, Fourier transform-infrared,

*Lipid Sci. Technol.* 104, (October 2002), pp. 698-705, ISSN 1438-9312

*Am. Oil Chem. Soc.* 73, (April 1996), pp. 515- 518, ISSN 0003-021X

(Ed.), AOACS Press, ISBN 189399788X, Champaign, Ilinois

*Chim. Acta.* 74, (July 2006), pp. 459–465, ISSN 0003-2670

2009), pp. 187–191

pp. 293-298, ISSN 0003-021X

51, (October 2003), pp. 6110-6115

*Technol.* 35, (March 2002), 99-103

56, (November 2008), pp. 11520-11525

(April 2001), pp. 1-11, ISSN 0169-7439

889-895, ISSN 0003-021X

ISSN 0003-021X

Press, London, New York, Washington, DC

*Food Chem.* 51, (September 2003), pp. 5723-5731

Determination of oil and water content in olive pomace using infrared and Raman spectroscopy - A Comparative study. *Anal. Bioanal. Chem*. 379, (May 2004), pp. 35–41 Nunes A., Barros A., Martins J. & Delgadillo I. (2009). Estimation of olive oil acidity using

FT-IR and partial least squares regression. *Sens. & Instrumen. Food Qual.* 3, (June

acid compositions of French olive oils. Characterization by chemometrics. *J. Agric.* 

olive oil RDOs by sensory characteristics, fatty acid and triacylglycerol compositions

data of vegetable oils for their classification. *J. Am. Oil Chem. Soc.* 71, (March 1994),

can distinguish the geographic origin of extra virgin olive oils. *J. Agric. Food Chem.*

with vegetable oils using Fourier transform infrared spectroscopy. *Lebensm–Wiss U-*

(2006). Applications of Fourier transform-infrared spectroscopy to edible oils. *Anal.* 

by near-infrared spectroscopy. *J. Am. Oil Chem. Soc.* 72, (March 1995), pp. 289-292,

European extra virgin olive oil samples by NIR spectroscopy. *J. Agric. Food Chem.* 

and Fourier transform-Raman methods for determining olive pomace oil adulteration in extra virgin olive oil. *J. Am. Oil Chem. Soc.* 78(9), (March 2000), pp. Olive oil has a characteristic flavor that distinguishes it from other edible vegetable oils. Its quality depends on the aroma, taste and colour, which in turn depend on many variables including location.

The International Olive Oil Council (IOOC,2001) Standards and European Commission regulations have defined the quality of olive oil based on parameters derived from spectrophotometric studies that include free fatty acid content, but these methods only give information about the samples' oxidation level. A specific vocabulary has been developed for virgin oil sensory descriptors (IOOC, 1987). The positive attributes are classified as fruty, bitter and pungent and negative attributes as fusty, musty-humid, muddy-sediment, wineyvinegary, metallic and rancid.

Odour is an important parameter determining the sensory quality of olive oils and it is therefore of interest to investigate if volatile compounds contributing to the characteristic odour can be measured.

In the last decades many efforts have been made to study the aromatic fraction of olive oils based mainly on chromatographic determinations (S. de Koning et al 2008, S. Mildner-Szkudlarz, H. H. Jeleń 2008, C. M. Kalua 2007). The presence or absence of particular volatile compounds is a good indicator of olive oil quality.

The aroma of olive oil is attributed to aldehydes, alcohols, esters, hydrocarbons, ketones, furans and probably, other volatile compounds, not yet identified. More than 120 volatile compounds that contribute both positively and negatively to the sensory properties of olive oil have been identified (Aparicio, R., Morales, M .T. & Luna, G. 2006). Table 1 lists some volatile compounds associated with negative attributes determined by Morales et al. in 2005.

Innovative Technique Combining Laser Irradiation Effect and

related to their volatility.

**1.3 Electronic nose** 

developmental stage.

checks on extra virgin olive oil is required.

dimensions (Schaller et al., 1998).

Electronic Nose for Determination of Olive Oil Organoleptic Characteristics 149

More recently, the solid-phase microextraction (SPME) technique has been introduced as a sample pre-concentration method prior to chromatographic analysis as an alternative to the dynamic headspace technique. Among other applications, SPME allowed the characterization of virgin olive oils from different olive varieties and geographical production areas (Temime et al., 2006; Vichi et al., 2003a), and the evaluation of varietal and processing effects (Dhi et al., 2005; Tura et al., 2004). Since the SPME uptakes are strongly dependant on the distribution of analytes among the sample matrix, the gas phase and the ber coating (Pawliszyn, 1999), some compounds present in virgin olive oil may remain undetected. In the case of other techniques such as SDE, the recovery of analytes is mainly

These last techniques are complex, expensive and time-consuming. They generally highlight only one or few aspects of the oxidation process, providing only partial information. On the other hand, the olive oil industry needs a rapid assessment of the level of oil oxidation in order to predict its shelf-life. Consumers usually expect manufacturers and retailers to provide products of high quality and seek for quality seals and brands. Therefore, the development of innovative analytical tools for quick and reliable quality

Gardner and Barllet (1993) defined the electronic nose as an instrument which comprises an array of electronic chemical sensors of partial specificity and an appropriate pattern-

The sensors used in the array of an electronic nose should have the following characteristics: high sensitivity to chemical compounds, low sensitivity to humidity and temperature, medium selectivity, high stability, high reproducibility and reliability; short reaction and recovery time; robustness and durability; easy calibration and data processing and small

The chemical interaction between the odour compounds and the gas sensors alters the state of the sensors giving rise to electrical signals which are registered by the instrument. Since each sensor is sensitive to all odour components, the signals from the individual sensors determine a pattern which is unique for the gas mixture measured and that is then

Nowadays, there are different gas sensor technologies available, but only four of them are currently used in commercialized electronic noses: metal oxide semiconductors (MOS); metal oxide semiconductor field effect transistors (MOSFET); conducting organic polymers (CP); piezoelectric crystals (Bulk Acoustic (Wave–BAW), Surface Acoustic (Wave SAW)). Others, such as fiber-optic, electrochemical and bi-metal sensors, are still in the

The processing of the multivariate output data generated by the gas sensor array signals represents another essential part of the electronic nose concept. The statistical techniques used are based on commercial or specially designed software using pattern recognition routines like principal component analysis (PCA), cluster analysis (CA), partial least squares

(PLS), linear discriminator analysis (LDA) and artificial neural network (ANN).

recognition system, capable of recognizing simple or complex odours.

interpreted by multivariate pattern recognition techniques.


Table 1. Volatile compounds associated with negative attributes of olive oils

Odour activity is a measure of the importance of a specific compound for the odour of a sample. It is calculated as the ratio between the concentration of an individual substance in a sample and the threshold concentration of this substance. The minimum concentration of a compound able to give rise to an olfactory response is the compound´s odour thereshold value. For this reason, high concentration of volatile compounds is not necessarily the main contribution to odour. For example, Reiners and Grosch reported a concentration of 6770 μg/g of trans-2-hexenal with an odour activity value of 16 whereas 1-penten-3-one with a much lower concentration of 26 μg/g had a higher odour activity value of 36 (C. M. Kalua, 2007).

According to the European Community Regulations (ECR 640/2008,ECR 1989/2008) olive oil can be classified in extra-virgin (high quality), virgin (medium quality) and lampante (lower quality). The first two categories can be bottled and consumed.

The quality and uniqueness of specific extra virgin olive oils is the result of different factors such as cultivar, environment and cultivation practices. The European Community (ECR 2081/1992) allows the Protective Denomination of Origen (PDO) labeling of some European EVOO with the names of the areas where they are produced.
