Combination of an e-nose, an e-tongue and an e-eye for the characterisation of olive oils with different degree of bitterness.

An electronic panel has been used to characterise the organoleptic characteristics of twenty-five extra virgin olive oils from varieties Hojiblanca, Picual and Arbequina, with different degree of bitterness. The method consists in the combination of three systems: electronic nose, electronic tongue and electronic eye. The Principal Component Analysis (PCA), where PC1, PC2 and PC3 explained 59% of the total variance between the samples, has demonstrated that the capability of discrimination of the combined system is superior to that obtained with the three instruments separately. This improvement is due to the increased information extracted from each sample. Partial Least Squares-Discriminant Analysis (PLS-DA) has allowed separation of the groups in function of olive variety with a root mean square error of prediction (RMSEP) lower than 0.099. Using PLS1 and PLS2 regression models, good correlations have been found between the signals obtained from the electronic tongue and the polyphenolic content (measured by chromatographic methods) or the bitterness index (scored by a panel of experts) with correlation coefficients higher than 0.9 in calibration and validation. These preliminary results indicate that the combination of an e-nose, an e-tongue and an e-eye can be a useful tool for the analysis of olive oil bitterness.

Solid-phase extraction gas chromatography-ion trap-mass spectrometry qualitative method for evaluation of phenolic compounds in virgin olive oil and structural confirmation of oleuropein and ligstroside aglycons and their oxidation products.

Phenolic compounds in Spanish virgin olive oil were analyzed by GC-MS after an SPE diol cartridge extraction and clean-up procedure. Posterior derivatization to trimethylsilyl (TMS) ethers using a mixture of hexamethyldisilazane:dimethylclorosilane (HMDS:DMCS) in pyridine (3:1:9) was performed. Several compounds were detected and 21 of them were identified. Free phenols such as hydroxytyrosol, tyrosol, tyrosyl and hydroxytyrosyl acetate, and aldehydic and dialdehydic forms of elenolic acid linked to tyrosol and hidroxytyrosol were the most abundant compounds. Likewise, oxidation products coming from the aldehydic and dialdehydic forms of elenolic acid, and of ligstroside and oleuropein aglycons, were detected, and their structure confirmed by other mass spectrometry technique, i.e., HPLC-APCI-MS. Individual oxidation products were isolated from an oxidized sample by preparative HPLC, converted to TMS ethers and re-analyzed by GC-MS. When necessary and for identification purposes, selective ion monitoring, namely, GC-MS-SIM, was employed. This is the first time that structures of oxidized forms are determined by GC-MS.

Main polyphenols in the bitter taste of virgin olive oil. Structural confirmation by on-line high-performance liquid chromatography electrospray ionization mass spectrometry.

Twenty virgin olive oils of extra quality and different bitter intensity were submitted to sensory evaluation and to the determination of polyphenols. A linear regression analysis was carried out assuming, as an independent variable, bitter intensity perceived by tasters, as an independent variable, the concentration (mmol/kg) of dialdehydic and aldehydic forms oleuropein aglycon, and dialdehydic and aldehydic forms ligstroside aglycon. Structural confirmation of these compounds was done by online high-performance liquid chromatography-electrospray ionization-collison-induced dissociation-mass spectrometry. The results obtained demonstrate the essential role played by this compound in the bitter taste of virgin olive oil.