**1.3 Electronic nose**

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

Fusty Ethyl butanoate, propanoic and butanoic acid Winey-vinegary Acetic acid, 3-methyl butanol and ethyl acetate

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

(lower quality). The first two categories can be bottled and consumed.

EVOO with the names of the areas where they are produced.

depends on the extraction used (S. Vichi, 2010).

**1.2 Analytical techniques** 

Morales, Rios, & Aparicio, 1997).

Rancid Several saturated and unsaturated aldehydes and acids

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

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

The methods used and / or proposed to evaluate the oxidative deterioration of olive oil based on the determination of volatile compounds are HPLC / GC-MS, analytical methods associated with some headspace extractive techniques. The volatile profile of VOO closely

Some of the traditional distillation methods applied in the analysis of plant materials as steam distillation (SD), simultaneous distillation/extraction (SDE) and microwave-assisted

Among these distillation techniques, SDE appeared to provide the most favourable uptake for mono- and sesquiterpenes, as well as for their oxygenated analogues (Marriott et al., 2001). Hydro distillation (HD) has been applied for the analysis of leaf, fruit and virgin oil volatiles of an Italian olive cultivar (Flamini, Cioni, & Morelli, 2003). With hydro distillation, the volatiles in the steam distillate are strongly diluted in water when collected in cold traps. This can be overcome in simultaneous distillation/extraction (SDE) via solvent extraction of the distillate. Dynamic headspace techniques have been used to correlate the composition of the olive oil headspace to sensory attributes (Angerosa et al., 1996; Angerosa et al., 2000; Morales et al., 1995; Servili et al., 1995) and or avors ''defects" (Angerosa, Di Giacinto, & Solinas, 1992;

extraction (MAE) were used for this purpose (Marriott, Shellie, & Cornwell, 2001).

**Descriptor Volatile compounds** 

Mustiness-humidity 1-octen-3-ol

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 patternrecognition system, capable of recognizing simple or complex odours.

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 dimensions (Schaller et al., 1998).

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 interpreted by multivariate pattern recognition techniques.

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 developmental stage.

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).

Innovative Technique Combining Laser Irradiation Effect and

amount of vapour to be generated in a short time period.

(Taglauer, E, A. W. Czanderna and D. M. Hercules, 1991).

olive oil quality determination are reported.

**2.1 Pulsed laser irradiation** 

it was mentioned in Section 1.4.

**2. E-nose + laser vaporization technique** 

to allow the laser beam admission, referred to as vials. The following analytical methods were undertaken:

this application.

Electronic Nose for Determination of Olive Oil Organoleptic Characteristics 151

Laser vaporization (LV) produces a local heating of the irradiated liquid surface and, in consequence, some molecules are driven to the gas phase. This phenomenon can be produced by the use of either pulsed or continuous wave (cw) lasers. For a fixed wavelength, the main difference lies in the amount of energy emitted per unit time, or power. Pulsed lasers produce an increase of the liquid surface temperature without producing a significant change of the bulk volume temperature (Christensen, B., and M. S. Tillack, 2003). These lasers produce only a local heating of the surface allowing a large

Due to the intrinsic nature of the LV this surface effect is produced immediately after the irradiation time lapse. Therefore, it is common to speak of a "thermal spike" rather than simply "thermal heating", because of the transient nature of the high temperature. The characteristics of this spike are determined by the laser fluence and its pulse length

The cw lasers used to vaporize liquids can cause an increase of the bulk sample temperature and can induce chemical reactions, thus, modifying the sample's properties. However, the appropriate choice of the irradiation time lapse and the laser power make them suitable for

In the present work the results of experiments carried out to illustrate the use of the combined techniques of electronic nose and pulsed or continuous wave laser irradiation for

In this experiment the Infrared Laser Vaporization, IRLV, properties to improve the e-nose selectivity are investigated. The role of the laser wavelength is additionally analyzed. This is due to the fact that the quality and the quantity of the chemical compounds incorporated the headspace depend on the laser parameters, particularly, the fluence and the pulse length, as

Two extra virgin olive oils produced in the same geographical region of Argentina (San Juan) classied as A and B, were tested. Three samples of 15 ml of each oil were subjected to three different analytical methods in order to compare the effects of the laser vaporization. All analytical methods were carried out under the same temperature and humidity conditions, of 25 °C and 43%, respectively. The samples were introduced in 100 ml T-shaped Pyrex test tubes with screw-caps in air inlet and outlet channels and a CaF2 window in order

**Method I:** Vial with oil sample A is kept closed during 2 minutes. Immediately afterwards the vial headspace is subjected to 35 seconds sampling with a Cyranose® 320. This

**Method II:** Vial with oil sample A is kept closed for 1min. The sample is subsequently irradiated with Nd:YAG laser pulses of 1064 nm at a repetition rate of 10 Hz during 1

procedure is repeated 5 times. The same operation is performed with oil sample B.

The use of an electronic nose for quality evaluation as a means of olfactory sensing is becoming widespread due to its advantages of low cost, reliability and high portability. Electronic noses based on different sensor technologies and using different recognition schemes have been employed for this task.

When samples of olive oil are analyzed with an electronic nose, the standard procedure is to put a fixed quantity in a vial and sense the headspace. The main drawback of this method is that the concentration of some compounds in the headspace may be quite different from their concentration in the liquid phase. For example, the concentration of methanol and ethanol is usually much higher in the vapor phase than in the liquid. However, these substances have been found to be irrelevant in the definition of the olive oil characteristics (S. de Koning, 2008). On the other hand, substances such as hexanal and trans-2-hexanal which are responsible for the organoleptic properties, are more abundant than methanol and ethanol (Cosio et al, 2006, C. Di Natale et al, 2001) in the oil, but are scarcely present in the headspace. It is well known that the odour activity of hexanal and trans-2-hexanal is higher than that of those alcohols because of their low odour thresholds (Morales et al., 2005, J. Reiners, W. Grosch 1998, A. Runcio et al., 2008). Despite the abovementioned drawback, several efforts have been made to use the electronic nose for olive oil quality control (Guadarrama et al., 2000). The combination of electronic nose fingerprinting with multivariate analysis enabled the study of the profile of olive oil in relation to its geographical origin (Ballabio et al., 2006; Cosio et al., 2006). García Gonzalez and Aparicio, 2002, detected the vinegary defect in Spanish VOO with the use of metal oxide sensors. They used an Alpha MOS e-nose equipped with 18 MOS sensors distributed in three chambers, and heated the samples to 34 °C during 10 minutes before testing the headspace. Servili et al., 2009, reported the first study of the use of an Electronic Olfactory System (EOS 835) online to control the formation and evolution of the volatile compounds that characterize the most important sensory notes of VOO during the malaxation process.

In 2010, M. J. Lerma-García et al. compared the response of an electronic nose (EOS 507) to classify oils containing the five typical virgin olive oil sensory defects with that of a sensory panel. They demonstrated the usefulness of this tool when combined with panels to perform a fast screening of a large set of samples with the aim of discriminating defective oils. Each sample was incubated at 37°C for 7 minutes before injection.

In the same year, Massacane et al. proposed a method to improve the electronic nose performance for discriminating among different olive oils without changing the properties of the original oil sample. This task is carried out by IR laser vaporization (IRLV) which seems to be a promising technique that modifies only slightly the headspace by volatilizing certain organic compounds or by cracking them. Thus IRLV improves the selectivity of the overall response of the electronic nose. Due to the extremely low sample vaporization that it produces this method can be considered non-destructive as most ablation laser Analytical methods (C. A. Rinaldi and J. C. Ferrero, 2001).

### **1.4 Laser irradiation effect**

Normal vaporization occurs when the vapour pressure in the ambient gas is lower than the saturation pressure of the liquid at the liquid temperature (Xu, X., and D. A. Willis, 2002). As the liquid's temperature increases, so do the saturation pressure and the rate of vaporization.

Laser vaporization (LV) produces a local heating of the irradiated liquid surface and, in consequence, some molecules are driven to the gas phase. This phenomenon can be produced by the use of either pulsed or continuous wave (cw) lasers. For a fixed wavelength, the main difference lies in the amount of energy emitted per unit time, or power. Pulsed lasers produce an increase of the liquid surface temperature without producing a significant change of the bulk volume temperature (Christensen, B., and M. S. Tillack, 2003). These lasers produce only a local heating of the surface allowing a large amount of vapour to be generated in a short time period.

Due to the intrinsic nature of the LV this surface effect is produced immediately after the irradiation time lapse. Therefore, it is common to speak of a "thermal spike" rather than simply "thermal heating", because of the transient nature of the high temperature. The characteristics of this spike are determined by the laser fluence and its pulse length (Taglauer, E, A. W. Czanderna and D. M. Hercules, 1991).

The cw lasers used to vaporize liquids can cause an increase of the bulk sample temperature and can induce chemical reactions, thus, modifying the sample's properties. However, the appropriate choice of the irradiation time lapse and the laser power make them suitable for this application.

In the present work the results of experiments carried out to illustrate the use of the combined techniques of electronic nose and pulsed or continuous wave laser irradiation for olive oil quality determination are reported.
