FROM WASTES TO ADDED VALUE BY-PRODUCTS: AN OVERVIEW ON CHEMICAL COMPOSITION AND HEALTHY PROPERTIES OF BIOACTIVE COMPOUNDS OF OLIVE OIL CHAIN BY-PRODUCTS

The production of olive oil originates a huge amount of residues like aqueous waste (50%) called olive mill wastewater and olive leaves that represent up to 10% of the weight of olive oil extraction and olive pomace. Moreover, other wastes were generated during the filtration processes and during the storage time when suspended solids tend to migrate at the bottom of the tanks originating sediments. However, it has been demonstrated that these wastes are rich in bioactive compounds and, thus, they can be considered as useful by-products for the recovering of these compounds to further uses. The olive oil mill wastewater is a problematic and polluting effluent which may degrade the soil and water quality, with critical negative impacts on ecosystems functions and services provided. Nevertheless, literature highlights its high concentration of antioxidants, especially phenolic compounds. However, the qualitative phenolic profiles of olive oil mill wastewater differ depending on the technological process of production of olive oil and the time of storage. Because of that, it is very important to evaluate the technological processes and the shelf life of olive oil mill wastewater to obtain a good source of bioactive compounds. In fact, the biological activities of phenolic compounds from olive mill wastewater have been studied, and they show a spectrum of highly interesting bioactivities. Olive leaves also represent a significant by-product of the cultivation and harvesting of olive. Historically, olive leaf has also been used as a folk remedy for combating fevers and other diseases, such as malaria. Several pharmacological reports have shown that olive leaf extracts have the property to lower blood pressure, increase blood flow in the coronary arteries, and exhibit a wide antiviral activity including anti-HIV activity, or have been cited for their antitumor activity, particularly against different types of breast cancer. Olive pomace can reach up to 30% of olive oil manufacturing, depending on the milling process which, after oil extraction, is generally distributed by means of controlled spreading on agricultural soil. However, a large quantity of olive mill solid residue remains without actual application because only small amounts are used as natural fertilizers, combustible biomass and additives in animal feeding and activated carbon. But theses residues are a valuable starting material for the production of phenol extracts that could be used in the industries. Because of that, research for valorization of olive pomaces has so far been mainly focused on panels or target known compounds considered of interest.