Evaluation of the polyphenolic content of extra virgin olive oils using an array of voltammetric sensors

A novel system to evaluate the phenolic content of extra virgin olive oils is reported. The method uses an array of voltammetric electrodes. Such electrodes are chemically modified with electroactive materials (five phthalocyanines and six conducting polymers). The voltammetric responses towards the phenolic fractions extracted from extra virgin olive oils consist in complex voltammograms. Curves show redox processes related to the electrochemical activity of the phenolic fraction under study, and redox peaks associated to the electroactive material. In addition the antioxidant activity of polyphenols influences drastically the electrochemical behaviour of the electrodic material. The pattern of responses provided by the array represents the fingerprint of each sample and can be used to discriminate and evaluate the degree of phenolic content of extra virgin olive oils. Principal component analysis (PCA) conducted using kernel functions has demonstrated the capability of the array of electrodes to discriminate olive oils according to their phenolic content and bitterness index. Using partial least square discriminant analysis (PLS-DA) good correlations between the results obtained using the array of sensors and the polyphenol content, the bitterness index (analysed by chemical methods) and the bitterness degree determined by the panel of experts has been obtained.