Determination of Phenols, Flavones, and Lignans in Virgin Olive Oils by Solid-Phase Extraction and High-Performance Liquid Chromatography with Diode Array Ultraviolet Detection

TLDR

The study developed a simple analytical method to quantitatively determine phenols, flavones, and lignans in virgin olive oils. The method isolates the polar fraction from 2.5 g of oil using diol‑ and amino‑phase solid‑phase extraction cartridges, then analyzes the extract by reversed‑phase HPLC with diode‑array UV detection. Chromatographic separation of key phenolic compounds was achieved with high repeatability (RSD < 6.5 %) and recovery (> 90 %), enabling the first detection of 2-(4‑hydroxyphenyl)ethyl acetate, confirmation of ligstroside aglycon structure by NMR, consistency between colorimetric and HPLC determinations, and no significant difference from liquid‑liquid extraction. Keywords: phenols, quantitative determination, solid‑phase extraction, virgin olive oil.

Abstract

A simple analytical method for the quantitative determination of phenols, flavones, and lignans in virgin olive oils was developed. The polar fraction was isolated from small amounts of oil sample (2.5 g) by solid-phase extraction (SPE) using diol-phase cartridges, and the extract was analyzed by reversed-phase HPLC coupled with diode array UV detection. Chromatographic separation of pinoresinol, cinnamic acid, and 1-acetoxypinoresinol was achieved. Repeatability (RSD < 6.5%), recovery (> 90%), and response factors for each identified component were determined. SPE on amino-phase cartridges was used for isolating acidic phenols and as an aid for phenol identification. For the first time, 2-(4-hydroxyphenyl)ethyl acetate was detected in olive oils. The aldehydic structure of the ligstroside aglycon was confirmed by NMR spectroscopy. The colorimetric determination of total o-diphenolic compounds by reaction with molybdate was consistent with their HPLC determination. Differences between results obtained by liquid−liquid extraction and SPE were not statistically significant. Keywords: Phenols; quantitative determination; solid-phase extraction; virgin olive oil