Phenolic composition and in vitro bioactivities of olive leaf infusions: influence of cultivar and infusion temperature

Olive leaves ( Olea europaea L.), an abundant by-product of olive cultivation, are a rich source of secoiridoids and other phenolic compounds with recognised bioactivity. In this study, aqueous infusions prepared from leaves of five Spanish cultivars at 70 ˚C and 90 ˚C were characterised in terms of phenolic profile and in vitro activities related to metabolic health. HPLC-DAD-TOF-MS analysis revealed a predominance of secoiridoids—particularly oleuropein and elenolic acid–derived glucosides—together with simple phenols, flavonoid glycosides and highly polar constituents. Extraction efficiency varied with cultivar and temperature, with 90 ˚C generally enhancing total phenolic diffusion, although individual compounds exhibited distinct temperature-dependent behaviours. All infusions exhibited antioxidant activity in DPPH, ABTS and FRAP assays, together with inhibitory effects against pancreatic lipase, α-glucosidase and angiotensin-converting enzyme (ACE) under the experimental conditions tested. Strong correlations between phenolic composition and antioxidant activity were observed for infusions prepared at 70 ˚C at 70 ˚C, whereas enzyme inhibitory responses showed a more complex behaviour not directly explained by total phenolic content alone. Infusions from Hojiblanca, Picual and Manzanilla prepared at 70 ˚C exhibited the strongest pancreatic lipase inhibitory activity among the samples evaluated. Overall, the results demonstrate that olive leaf infusions retain a chemically diverse mixture of secoiridoids and related phenolic compounds with measurable in vitro bioactivities. These findings contribute to the characterisation of olive leaf infusions as plant-based beverages and provide a basis for further studies addressing bioaccessibility, bioavailability and physiological relevance under in vivo conditions.