Applications of by-products from the olive oil processing: Revalorization strategies based on target molecules and green extraction technologies

During the last decades, olive oil consumption has experienced a continuous increase due to its unique organoleptic properties and its related beneficial properties. Consequently, waste and by-products derived from the olive production have also increased causing environmental problems and economic losses. However, the low-cost and huge availability of these by-products is an opportunity for their valorization and the obtaining of high added-value compounds such as tyrosol, hydroxytyrosol (HT), oleocanthal, oleuropein (OLE), ligstroside, squalene, fatty acids, etc. The development of innovative extraction and characterization technologies is a key factor for the olive sector. In addition, a deeper knowledge about the biological properties of the compounds present in the recovered products and their mechanism of action is crucial to allow their reintegration in the food chain and their potential uses in the food and pharmaceutical industries. This review encompasses all these aspects showing the advances achieved to date in the olive oil by-products valorization focusing on their biological properties, including cardioprotective, antioxidant, anticancer, anti-inflammatory and antidiabetic effects. The by-products derived from the Olea europaea L. processing industry are secondary but valuable products, from which different biologically active molecules can be recovered by green extraction technologies (PLE, SFE, etc. ) and reused for food, pharmaceutical and cosmetic purposes following the circular economy policies. One of the main advantages on recovering valuable molecules from olive by-products is their incorporation to functional foods. A direct effect was proved between the use of olive by-products in human consumption and the heath claims. In this context, different food industries have used the phenolic fraction of olive by-products, holding mostly HT and OLE, as food additives and as preserving agents due to their antioxidant properties.