Phenolic Compounds in Virgin Olive Oil. 2. Reappraisal of the Extraction, HPLC Separation, and Quantification Procedures

Abstract

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 methods are practically equivalent, but the SPE technique is more favorable because it is faster and simpler. It has been proved that the chromatographic features and the method of chemical expression of the concentrations may greatly 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, caffeic acid, or tyrosol equivalents. The role of the nature and spectrophotometric features of the phenols and of the internal standard is also discussed, and it was found to be an important source of reported variation. A gradient separation with an eluent mixture acetonitrile-sulfuric acid (0.1 mol/L), detection at 225 nm, and quantitative calculation of polyphenolic compounds in oils (expressed as tyrosol equivalents, THY(eq)) is proposed.

Comparability and reliability of different techniques for the determination of phenolic compounds in virgin olive oil

“…The suggested explanations, such as various genetic characteristics of the olive cultivar or technological modifications during processing the olives, may partly, but not fully, explain these discrepancies. It was Pirisi and co-workers [20] who raised the question whether the discrepancies may be caused by the various analytical methods used and/or the expression of the results in various formats. In fact, individual phenolics give different responses under the UV detection after their HPLC separation.…”

HPLC and HRGC analyses of polyphenols and secoiridoid in olive oil

“…Pianella (Pe) Traditional techniques, as many compounds as possible from the polar fraction of olives and virgin olive oil [13][14][15][16][17][18][19][20]. In particular, an important component of the polar fraction of olive oil is represented by secoiridoids.…”

“…Few studies have been performed until now on the quantification of the single polyphenols present in olive oils, and often the quantitative data are related to the total polyphenolic concentration or to the total of a specific subclass, such as the "simple polyphenols" (tyrosol, hydroxytyrosol and elenolic acid) [20].…”

Analytical Methods for Determination of Polyphenols in Sweet Wort, Wort and Beer.

“…Pirisi a kol. [7] se také zabývají srovnáním SPE s C 18 a C 8 náplní a LLE s hexanem. Kvantifikace zachycených sloučenin byla provedena pomocí HPLC-DAD-MS a CZE (kapilární zónová elektroforéza) s UV-VIS detekcí.…”