Isolation of antioxidative secoiridoids from olive wood (Olea europaea L.) guided by on-line HPLC–DAD–radical scavenging detection

The woody portion of olive tree pruning is a source of natural antioxidants of potential interest for the food industry. This work deals with the isolation and identification of further antioxidants present in an ethyl acetate extract of olive (Olea europaea L.) wood. Thus, a new secoiridoid, oleuropein-3″-methyl ether (1), together with six known secoiridoids, 7″S-hydroxyoleuropein (2), jaspolyanoside (3), ligustroside 3′-O-β-d-glucoside (4), jaspolyoside (5), isojaspolyoside A (6) and oleuropein 3′-O-β-d-glucoside (7) were isolated by combining HPLC with fast on-line post-column radical scavenging activity evaluation. The structures of these compounds were determined by spectroscopic methods. The antioxidant activity of the pure compounds was determined by measuring the radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl radical (DPPH). Compounds 2, 5 and 7 displayed a higher antioxidative effect than the synthetic antioxidant BHT and lower than rosmarinic acid, whereas compounds 3 and 4 showed weak DPPH scavenging activity.