Application of an electronic nose to differentiate extra virgin olive oils according to the geographical origin: Côa versus Douro regions
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Olive oils produced in the Douro’s region (north of Portugal) are greatly appreciated due to their specific chemical-sensory characteristics, which can be associated to the region’s “Terroir”. Thus, for olive oil producers and consumers, the capability to guarantee the authenticity of the geographical origin of these oils is of utmost importance. In this sense, this study aimed to evaluate the possibility of using an electronic nose (E-nose), with nine metal oxide semiconductors (MOS), as a non-invasive analytical tool to recognize the geographical origin of olive oils from two geographical sub-regions: “Côa” and “Douro”
Olive oils produced in the Douro’s region (north of Portugal) are greatly appreciated due to their specific chemical-sensory characteristics, which can be associated to the region’s “Terroir”. Thus, for olive oil producers and consumers, the capability to guarantee the authenticity of the geographical origin of these oils is of utmost importance. In this sense, this study aimed to evaluate the possibility of using an electronic nose (E-nose), with nine metal oxide semiconductors (MOS), as a non-invasive analytical tool to recognize the geographical origin of olive oils from two geographical sub-regions: “Côa” and “Douro”. For each region, 40 different oils were collected, and the chemical quality (acidity, peroxide value and extinction coefficients) and sensory profiles were evaluated. From the initial samples, only those fulfilling the legal thresholds of extra virgin olive oil (EVOO) category were further used [1], being kept 38 and 31 different EVOO from “Côa” and “Douro” regions, respectively. For the majority of the oils, 9 olfactory attributes were perceived by the panellists (fruity – green or ripe; apple; banana; tomato and tomato leaves; dry fruits; cabbage; fresh and dry herbs) and 14 gustatory attributes (sweet; bitter; pungent; fruity – green or ripe; apple; banana; tomato and tomato leaves; dry fruits; cabbage; fresh and dry herbs; plum; olive leaves). Oils from “Douro” region were more sweet and had greater intensities of fruity-ripe, banana and dry herbs sensations. On the other hand, “Côa” oils were bitter and pungent showing higher intensities of fruity-green, tomato and tomato leaves, cabbage, fresh herbs and olive leaves sensations. Considering the differences perceived at the sensory level, namely at the olfactory profile, a lab-made E-nose [2] was applied. The results showed that this sensor-based device could identify the geographical origin of the studied olive oils. In fact, the principal component analysis (PCA) of the average response curve of the sensors’ signals (resistance data) enabled a satisfactory unsupervised differentiation of the 69 olive oils according to the two geographical regions studied (Figure 1). The satisfactory performance could be tentatively attributed to the abovementioned different olfactory profiles found for the oils, depending on their origin.
