Metabolomic characterization and antioxidant activity of three varieties of Olea europaea growing in Aljouf region, Saudi Arabia.

The objective of this study was to evaluate the metabolomic profiling and antioxidant activity of olive leaves in three varieties (K18, improved Napali and Galat) growing under the same environmental conditions in Aljouf region in Saudi Arabia. High performance liquid chromatography (HPLC) and spectrophotometry coupled with multivariate data analysis (MVDA) were used to evaluate the metabolomics and antioxidant activity of the varieties under evaluation. MVDA discriminated the three varieties into three distinct groups based on their metabolomic profiling by spectrophotometer and HPLC analyses. The first group included the variety of K18 characterized with higher content of total phenolics, total tannins, salicylic acid and luteolin-4-glucoside. The second group included Improved Napali and characterized with higher content of total flavonols, total anthocyanins, naringenin and quercetin. The third group included Galat and characterized with higher content of total saponins, total flavonoids, luteolin, luteolin-7-glucoside, caffeic acid and oleuropein. All the three varieties showed very high reducing power (RP) and DPPH radical scavenging activity and consequently very low IC50. Galat and K18 showed higher contents of bioactive secondary metabolites and antioxidant activity than improved Napali. The metabolomic profiling and the antioxidant activity of the three varieties will be discussed not only in the light of leaves application in pharmacological studies, but also in the light of the effect of metabolomic composition of leaves in plant resistance mechanism under extreme environmental conditions.