Electronic nose: a tool to verify the PDO declaration of Portuguese olive oils

Abstract

The volatile and olfactory profiles of three Portuguese olive oils with protected designations of origin (PDO) were studied: Azeite do Alentejo Interior, Azeites da Beira Interior, and Azeite de Trás-os-Montes. Seven classes of volatiles were identified, with aldehydes, followed by hydrocarbons and alcohols, the most prevalent (5.63, 2.92, and 2.79 mg/kg olive oil, respectively). The Azeites da Beira Interior oils exhibited the highest amount of volatiles (18.2±4.6 mg/kg olive oil) compared to the oils from the other two PDOs. Ten positive olfactory sensations were detected, and a significant effect of the PDO on the intensities of fruity, apple, cabbage, tomato, dry and fresh herbs was observed. Specifically, Azeite do Alentejo Interior PDO oils were characterized as fruity-ripe, while Azeite de Trás-os-Montes PDO oils were labelled as fruity-green. Conversely, Azeites da Beira Interior PDO oils encompassed both fruity-ripe and fruity-green oils. Unique volatile and olfactory fingerprints were established for each PDO, allowing the linear discrimination of the oils according to the PDO, with a predictive sensitivity of 98.0±4.2% (repeated K-fold-CV). Furthermore, a lab-made electronic nose successfully discriminated the studied oils based on the PDO, with a predictive accuracy of 99.7±2.0% (repeated K-fold-CV). This device also allowed predicting the concentrations of the three main volatile classes found in the oils through multiple linear regression models (R20.923±0.101 and RMSE1.32±0.72 mg/kg oil; repeated K-fold-CV). These findings underscore the potential of the electronic nose as a reliable traceability tool to authenticate the PDO declaration of Portuguese olive oils, and broaden its use beyond non-PDO oils from a specific geographical area to encompass a national scale.