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.
Continuous centrifugation, a widely used procedure for extraction of
virgin olive oil, involves crushing
olives, mixing the olive paste, and centrifugation with or without
water addition (“three phase” or
“two phase” modes, respectively). Virgin olive oils were
obtained following both procedures, with
and without talc addition. Acidity value, peroxide index, UV
absorption at 270 and 232 nm, glyceridic
polar compounds, oxidized triglycerides, diglycerides, iron, copper,
tocopherols, phenolic compounds,
and oxidative stability were determined and the results statistically
analyzed. The talc addition
gave rise to a small increase in the oil stability and a slight
decrease in oxidized triglyceride levels.
The oils obtained by the “two phase” mode showed a greater
concentration of phenolic compounds
than the homologous oils obtained by the “three phase” mode.
Oils processed by the “three phase”
mode showed a significant correlation between their stability and their
phenolic concentration.
Keywords: Virgin olive oil; talc addition; centrifugation mode; quality;
stability
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