Determination of Bitterness of Extra Virgin Olive Oils by Amperometric Detection

A flow injection system with amperometric de- tection at potentials poised at + 0.4 and + 0.9 V was used to evaluate intensity of the bitter taste in monovarietal Extra Virgin Olive Oils (EVOO). Results from the pro- posed method were based on the extraction of the bitter constituents of the virgin olive oil samples in methanol- water, followed by the direct amperometric measurement. These potentials were selected according to the hydrody- namic voltammogram of oleuropein, one of the most prominent and bitter phenolic compound found in EVOO. The amperometric detection was applied on 32 monovariatal EVOO samples. Results were correlated with the phenolic profile measured by high performance liquid chromatography (HPLC). The amperometric signal at + 0.9 V mainly correlated with the total phenols of the samples (R2 = 0.81), whereas the signal at + 0.4 V mainly correlated with oleuropein aglycone (3,4 DHPEA-EDA, R2 = 0.79). Bitterness intensity of the samples was evalu- ated by a trained sensory panel of experts and the results compared to those obtained by the amperometric flow system. The best correlation with the bitter taste was ach- ieved by the sensor at + 0.4 V (R2 = 0.72). A calibration model based on partial least squares was built with three variables, namely the sensors set at + 0.4 and + 0.9 V and the total phenol content of the EVOO extracts. The model showed a moderate capacity to predict the bitter- ness of the EVOO samples using leave one out method, (R2 = 0.75) and in prediction of a test set of samples (R2 = 0.7). Such approach is very promising for future studies.