Effect of cultivar type, ontogeny and extraction methods as determinant factors of olive leaf metabolome: A case study in 8 Egyptian cultivars as analyzed using LC/MS-based metabolomics

Olive leaves (Olea europaea L.) represent a valuable by-product with potential benefits. The current study reports on leaf metabolome from 8 Egyptian cultivars based on ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) and combined with chemometrics tools. Trees’ age, cultivar type, and extraction methods were targeted as determinant factors for the first time on olive leaf metabolome. UHPLC-MS/MS resulted in the annotation of 105 metabolites, of which 10 phenolics are first time to be reported. Multivariate data analyses revealed clustering of old leaves being associated with triterpenoids, while young counterparts were more enriched in secoiridoids. In addition, ultrasound- and supercritical-assisted extraction were comparable yielding oleuropein as a main secoiridoid. In contrast, classical maceration was comparable to microwave-assisted extraction (glycerol) providing higher recovery of triterpenes viz. oleanolic and maslinic acids. This study provides new insights into the valorization potential of olive leaves based on its detailed phytochemical composition.