Novel method based on carbon paste electrodes for the evaluation of bitterness in extra virgin olive oils

A new method has been developed to evaluate the bitterness of extra virgin olive oils. The method employs carbon paste electrodes where olive oils are used as the electroactive binder material. Electrodes have been fabricated with nine extra virgin olive oils differing in their degree of bitterness. The features observed in the voltammograms reflect the reactions of electroactive compounds (such as polyphenols), which are present in the virgin olive oils mixed with the carbon paste matrix. For this reason, the voltammetric responses of the electrodes are specific for each type of oil. In addition, each electrode shows a variety of responses immersed in different electrolytic solutions. Such pattern of responses can be considered as a characteristic fingerprint of the oil. The Principal Component Analysis (PCA) and the Partial Least Squares Discriminant Analysis (PLS-DA) of the electrochemical signals obtained by immersing the electrodes in different solutions has allowed a clear discrimination of the nine virgin olive oils according to their degree of bitterness. Good correlations between redox processes observed in the electrodes and the analytical and sensorial characteristics of the virgin olive oils under study have been found.