Chemical Characterization and Phenolic Profiling of Commercial Olive Leaf Extracts Using LC-Q-TOF-MS and HPLC-DAD

This study comparatively evaluated the chemical fingerprints and oleuropein contents of commercially available olive leaf extracts on the Turkish dietary supplement market. Six independent commercial products, comprising three liquid and three powder/capsule formulations, were characterized by LC-Q-TOF-MS, while oleuropein was quantified by targeted HPLC-DAD analysis. Among the LC-Q-TOF-MS annotations, 288 compounds were operationally classified as phenolic or phenolic-related compounds. Of these, 114 were annotated only in liquid products, 113 only in powder/capsule products, and 61 in both groups. Powder/capsule products showed greater phenolic-class richness, particularly in flavonoid annotations. HPLC-DAD confirmed oleuropein in all six products, although concentrations varied markedly among samples. However, because the products were independent commercial preparations, these differences cannot be attributed solely to physical form. Overall, combining LC-Q-TOF-MS profiling with targeted HPLC-DAD quantification provided complementary information on phytochemical heterogeneity and product-to-product variability in commercial olive leaf extracts.