The role of cyclodextrins in ORAC-fluorescence assays. Antioxidant capacity of tyrosol and caffeic acid with hydroxypropyl-ß-cyclodextrin
Tyrosol and caffeic acid are biophenols that contribute to the beneficial properties of virgin olive oil. The influence of hydroxypropyl-beta-cyclodextrin (HP beta-CD) on their respective antioxidant capacities was analyzed. The ORAC antioxidant activity of tyrosol (expressed as mu M Trolox equivalents/mu M Tyrosol) was 0.83 +/- 0.03 and it increased up to 1.20 +/- 0.11 in the presence of 0.8 mM HP beta-CD. However, the ORAC antioxidant activity of caffeic acid experienced no change. The different effect of HP beta-CD on each compound was discussed. In addition, the effect of increasing concentrations of different cyclodextrins in the development of ORAC-fluorescence (ORAC-FL) assays was studied. The ORAC signal was higher for HP beta-CD, followed by M beta-CD, beta-CD, gamma-CD and finally alpha-CD. These results could be explained by the formation of inclusion complexes with fluorescein.