Olive Wastes as a High-Potential by-Product: Variability of Their Phenolic Profiles, Antioxidant and Phytotoxic Properties

The global world olive oil industry produces large amounts of wastes and wastewaters. However, the disposal of these polluting by-products is a significant environmental problem owing to their high polyphenolic compounds. In order to learn possible ways of exploiting this waste, we investigated the phytochemical profiles, the phytotoxicity and the antioxidant activities of olive wastes (leaves, mill wastewater (OMWW) and mill solid waste (OMSW)). Leaf extracts exhibited the highest phytotoxic and antioxidant effects, which are mainly due to its phenolic content. The chromatographic profiles depicted eleven phenolic compounds belonging to secoiridoids, phenyl alcohols, phenolic acids, phenylethanoid glycoside, and flavonoids. Hydroxytyrosol and oleuropein were the main components in leaf methanol and OMWW extracts, respectively, exhibiting an amount of 13.05 and 4.39 mg/g DW. These results will help to demonstrate the possibility of utilizing olive wastes, particularly the leaf, as an inexpensive natural product, in food and agricultural applications. Graphic Abstract: [Figure not available: see fulltext.].