Minor compounds in the phenolic fraction of virgin olive oils

The phenolic fraction of 34 virgin olive oils was analysed by gas chromatography–mass spectrometry (GC–MS) with the aim to identify new compounds at low level. Twenty-seven compounds previously described in olive oils were identified; several new minor compounds with phenolic structure were detected in the samples: amongst them, 4-hydroxyphenylacetaldehyde, trans-isoeugenol (trans-2-methoxy-4-(1-propenyl)-phenol), 1,4-dihydroxy-2,6-dimethoxybenzene, 3,4-dihydroxybenzyl alcohol and 3,4-dihydroxyphenylacetic acid were identified by their mass spectra and confirmed using standards. In 34 virgin olive oils (cv. Nocellara del Belice) the mean concentrations for these five substances were always below 0.2 mg kg−1 and only in two samples the level of 3,4-dihydroxyphenylacetic acid reached 1.47 and 1.97 mg kg−1, respectively. These compounds could be used to characterise olive oils; low concentrations of 3,4-dihydroxyphenylacetic acid may show the initial autoxidation processes of olive oils.