Olive cake and leaf extracts as valuable sources of antioxidant and antimicrobial compounds: a comparative study

Abstract

Aiming to exploit the remediation of olive cake and leaves, a comparative study between these extracts from the same trees has been carried out to explore them as a source of bioactive compounds with added value. Olive cake (OCE) and leaf (OLE) methanolic extracts were chemically characterized by UPLC-QTOF-MS, and tested for their in vitro antimicrobial activity using a broth microdilution method. The antioxidant activity was evaluated using the DPPH scavenging, ferric reducing-antioxidant power and iron chelation assays. Our results demonstrated that Gram-positive bacteria were more sensitive to the extracts tested than Gram-negative bacteria, with the exception of Yersinia enterocolitica and Campylobacter jejuni. OLE have higher amounts of ash, carbohydrates, total phenolic content and flavonoids than OCE. UPLC-ESI-TOF-MS allowed the putative identification of 48 and 45 compounds in OLE and OCE, respectively, with three newly identified compounds in OLE. OLE had the highest antioxidant activity based on DPPH, ferrozin and FRP. This study provides novel information on the presence of bioactive compounds, antioxidant and antibacterial capacity of Olea europaea L. leaf and cake extracts, which can lead to the use of these by-products as sources of natural-based bioactive compounds suitable for numerous applications.