Authentication of concentrated orange essential oils using photoacoustic spectroscopy

Photoacoustic spectroscopy (PS) was used to study the thermal diffusivity and its relation with the composition in folded (concentrated) cold-pressed Mexican orange essential oils. A linear relation between the amplitude (on a semi-log scale) and phase, as functions of the sample thickness, for PS was obtained through a theoretical model to fit the experimental data for thermal-diffusivity measurements in concentrated orange essential oils. Experimental results showed a linear increase in thermal-diffusivity values with the folding degree: 5-fold, 10-fold, 20-fold, and 35-fold due to a decrease in terpenes (mainly D-limonene) related with the folding process that can be correlated with the thermal diffusivity of the orange essential oils. The obtained values in this study and those previously reported (see Int. J. Thermophys. 32, 1066, 2011) showed the possibility of using this thermal property to make distinctions between citrus oils obtained by different extraction processes and also between concentrated citrus oils. This provides the viability of a new complementary method for this purpose, contrasting with the use of density and refraction index, physical properties commonly used in the authentication of citrus essential oils.