Pharmacognosy and Antioxidant Activity of Pruned Leaves from the Unexplored Olea europaea L. ‘Lavagnina’ (Liguria, Italy)

Olea europaea L. ‘Lavagnina’ is cultivated in the Eastern Ligurian coast (Italy), and during the pruning process a huge amount of pruning residues is produced. This by-product is generally disposed of by burning, despite still containing bioactive compounds. In particular, olive leaves are indeed rich in secondary metabolites, which can vary both in quality and quantity in relation to the cultivar considered and the area of cultivation. For this reason, we aimed to carry out a pharmacognostic study of the pruned leaves of the unexplored local cultivar ‘Lavagnina’, evaluating the possibility of reusing this by-product for new health applications. The micromorphological characterization was conducted by light and scanning electron microscopy. ‘Lavagnina’ leaf was micromorphologically similar to that of other olive cultivars; however, it differed in terms of midrib structure. Leaf extracts were obtained using solvents of increasing polarity (petroleum ether, chloroform, methanol) and the food-grade solvent, 70% ethanol. A high antioxidant activity was found only for the methanolic (ME) and hydroalcoholic (HAE) extracts, and, therefore, they were then characterized from a phytochemical point of view by LC-ESI-HR-MS. Such analysis allowed the identification of secondary metabolites belonging mainly to secoiridoids, flavonoids, and iridoids. Overall, the HAE had the highest antioxidant activity (17.3 ± 0.6 μg/mL), and it is, therefore, the best candidate for health applications related to a protective effect on a variety of inflammation-related diseases, also considering that inflammation may play a role in cancer progression.