Phenolic content and antioxidant activity of olive extracts

The phenolic component of freeze-dried olive fruit was fractionated by high -performance liquid chromatography using ultraviolet, atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) detection. The fractions together with several standards were tested for antioxidant acti vity in an aqueous and a lipid system. The negative ion mode of APCI and ES I showed less fragmentation than positive ion mode. The latter was generall y more useful in obtaining fragmentation data and hence structural informat ion. Some olive phenolics notably tyrosol exhibited a low ionisation effici ency in both APCI and ESI. There was no simple relationship between antioxi dant activity and chemical structure. The ranking of antioxidant activity w as strongly dependent on both the test system and on the substrate demonstr ating the need to examine activity in both aqueous and lipid systems. Signi ficant antioxidant activity was seen in most olive fractions and this was r elated to phenolic content. The kinetics of the oxidation process are compl ex and suggest that multiple pathways may be involved at different antioxid ant concentrations. (C) 2001 Elsevier Science Ltd. All rights reserved.