Phenolic compounds in virgin olive oil. 2. Reappraisal of the extraction, HPLC separation, and quantification procedures

The extraction procedures (solid/liquid SPE and liquid/liquid LLE) and HPLC separation and quantification methods of polyphenolic compounds have been checked in virgin olive oils in order to explain the differences in content reported in the literature. The work has been carried out on oils prepared from one cultivar and produced under the same protocol. The extraction met hods are practically equivalent, but the SPE technique is more favorable be cause it is faster and simpler. It has been proved that the chromatographic features and the method of chemical expression of the concentrations may g reatly affect the final values. Thus, under the same analytical method, the total concentration values of polyphenols of the same oil show variations from 18% to 80%, according to the formality of expression as gallic acid, c affeic acid, or tyrosol equivalents. The role of the nature and spectrophot ometric features of the phenols and of the internal standard is also discus sed, and it was found to be an important source of reported variation. A gr adient separation with an eluent mixture acetonitrile-sulfuric acid (0.1 mo l/L), detection at 225 nm, and quantitative calculation of. polyphenolic co mpounds in oils (expressed as tyrosol equivalents, THYeq) is proposed.