Antioxidant activity of polar extracts from olive oil and olive mill wastewaters: an EPR and photometric study

Abstract

AbstractPolar extracts from olive oil and olive mill wastewaters (OMW) were isolated and examined as direct scavengers of free radicals. In order to evaluate their potent antioxidant capacity, two experimental procedures were undertaken: electron paramagnetic resonance (EPR) in combination with a spin‐trapping technique and a photometric procedure based on the formation of the N,N‐dimethyl‐p‐phenylenediamine colored radical cation (DMPD+.). In the EPR study, free radicals were generated by oxidizing the lipid moiety of low‐density lipoprotein or lecithin micelles by Cu2+. Stable radical spin adducts were produced using the spin trap α‐phenyl‐t‐butylnitrone. The formation of the three‐line EPR signal was inhibited in the presence of compounds with known antioxidant activity or of polar extracts with potent antioxidant activity. The antioxidant activity of polar extracts from olive oil and OMW was also measured using the N,N‐dimethyl‐p‐phenylenediamine (DMPD) colorimetric procedure. The antioxidant capacity of the extracts tested was expressed as trolox equivalents per mg of antioxidant. The extraction procedures of olive oil seem to affect olive oil content in antioxidants and, consequently, the corresponding antioxidant capacity. Tannin‐rich polar extracts isolated from the OMW are much more potent in scavenging free radical formation than polyphenol‐rich polar extracts from olive oil.