**3. Conclusions**

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

A classification following the discrimination step was designed for Method III using about

(a)

(b)

For validation purposes, 30% of the measured samples were disregarded. Within the resultant restricted space, an unsupervised PCA was performed. It was then possible to establish multivariate confidence regions for the two identified classes: olive oil A and olive oil B. The assignment of a new multivariate measurement *x* to a given category *k* occurs

> 1 1 ln 2 2 *k kk d (x) = <sup>Σ</sup> m (x)*

Fig. 8. PCA (a) Method II (b) Method III (discriminating regions are shown).

when the quadratic discriminant *dk (x)* is maximized:

70% of the available samples of both A and B oils.

An easy to implement method to improve electronic nose discrimination ability of a priori similar odours has been presented. This technique has been then applied to the case of virgin olive oils. The way laser vaporization of the samples improves this task has been additionally explored. The behaviour of the gas phase headspace following pulsed and cw laser irradiation with different wavelengths has been analyzed.

The use of pulsed IR lasers increases the sensitivity of the e-nose performance. Furthermore, the use of a CO2 laser allows a better discrimination than the use of a Nd:YAG laser. When using the CO2 laser, the signal-to-noise ratio (S/N) is increased by an order of magnitude with respect to the S/N without laser vaporization effect. The IR laser wavelength influences the discrimination capabilities of the method, probably due to the different IR absorption properties of the sample compounds. Further experiments in progress may shed some light on this question.

The use of continuous wave visible diode lasers (methods II and III) produces significant changes in the V-UV spectrum of one of the EVOO, (EVOO A). Irradiation with the diode laser at 450 nm produces larger changes than those produced by the 650 nm diode laser irradiation. The 450 nm laser induces chemical reactions in the liquid oil surface and as a result precludes the discrimination. On the other hand, Laser Vaporization at 650 nm modifies the vapourliquid equilibrium conditions improving the selectivity of the electronic nose.

It is important to emphasize that although the discrimination obtained with IRLV is larger than that resulting from LV at 650 nm it is insensitive to the recognition pattern used. On the other hand, diode lasers are considerably cheaper than high power TEA CO2 lasers and they produce very good results considering the benefit-cost ratio.
