The authors are grateful to the Foundation for Science and Technology (FCT, Portugal)
for financial support by national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020
and UIDP/00690/2020), to CEB (UIDB/04469/2020) and to the Associate Laboratory SusTEC
(LA/P/0007/2020). The authors are also grateful to the “Project OLIVECOA—Centenarian olive
trees of Côa Valley region: rediscovering the past to valorize the future” (ref. COA/BRB/0035/2019),
financed by FCT (Portugal). Nuno Rodrigues thanks the National funding by FCT- Foundation for
Science and Technology, P.I., through the institutional scientific employment program-contract.
The geographical traceability of extra virgin olive oils (EVOO) is of paramount importance
for oil chain actors and consumers. Oils produced in two adjacent Portuguese regions, Côa
(36 oils) and Douro (31 oils), were evaluated and fulfilled the European legal thresholds for EVOO
categorization. Compared to the Douro region, oils from Côa had higher total phenol contents
(505 versus 279 mg GAE/kg) and greater oxidative stabilities (17.5 versus 10.6 h). The majority
of Côa oils were fruity-green, bitter, and pungent oils. Conversely, Douro oils exhibited a more
intense fruity-ripe and sweet sensation. Accordingly, different volatiles were detected, belonging to
eight chemical families, from which aldehydes were the most abundant. Additionally, all oils were
evaluated using a lab-made electronic nose, with metal oxide semiconductor sensors. The electrical
fingerprints, together with principal component analysis, enabled the unsupervised recognition
of the oils’ geographical origin, and their successful supervised linear discrimination (sensitivity
of 98.5% and specificity of 98.4%; internal validation). The E-nose also quantified the contents of
the two main volatile chemical classes (alcohols and aldehydes) and of the total volatiles content,
for the studied olive oils split by geographical origin, using multivariate linear regression models
(0.981 < R2 < 0.998 and 0.40 < RMSE < 2.79 mg/kg oil; internal validation). The E-nose-MOS
was shown to be a fast, green, non-invasive and cost-effective tool for authenticating the geographical
origin of the studied olive oils and to estimate the contents of the most abundant chemical
classes of volatiles.
