Bioactivity, DNA damage protecting, and aroma potential of oleuropein enriched olive leaf extract by optimization of ultrasound‐assisted process

Abstract

In this study, Box–Behnken experimental design was employed to optimize Ultrasound‐assisted extraction (UAE) method to obtain oleuropein‐rich extract from olive leaf. The effect of three parameters, ethanol concentration (30%–70%), amplitude (30%–50%), and ultrasonication time (5–15 min) on oleuropein content were evaluated through experimental design. The total phenolic content, antioxidant capacity, DNA damage scavenging activity, aroma profile, and antimicrobial activity of olive leaf were also investigated. The optimum extraction condition was determined as 30% amplitude, 70% ethanol, and 5 min extraction time. The amount of oleuropein was found to be 42.621 mg/g dry leaves at the optimum condition. The total phenolic content of the optimized extract was found as 45.13 mg GAE/g dry leaves while the antioxidant capacity of the optimized extract was 216 µmol Trolox/g in DPPH and 213.19 µmol Trolox/g in ABTS method. Twenty‐three volatile compounds were identified in extracts, mainly aldehydes and alcohols. The extracts showed high antimicrobial activity against selected bacterial strains. DNA damage protecting activity of extracts on plasmid DNA was clearly demonstrated. UAE has an important effect on the phenolic content and antioxidant capacity of olive leaves. Moreover, oleuropein‐rich extract can have potential as a therapeutic agent depending on its antimicrobial and DNA‐protecting activity.