Olive oil dregs: an underexploited source of valuable compounds with health benefits

The olive oil industry produces large amounts of wastes that are disposed-off, although rich in bioactive compounds with valuable properties. In particular, phenolic compounds (PC), widely recognized as powerful antioxidants and provided with significant therapeutic properties, represent a non-negligible fraction [1]. As cellular studies demonstrated that olive oil PC enhance the proliferation of pre-osteoblasts and the differentiation in osteoblasts [2], the phenolic fraction recovered from olive oil mills by-products can be regarded as an effective treatment in bone tissue regeneration [3]. Furthermore, hydroxytyrosol (HT), one of the main PC contained in by-products from olive oil production, is used as active ingredient in cosmetic formulations and has a high commercial value. Consequently, its recovery greatly contributes to valorise these residues. In the present work, a poorly exploited by-product from olive oil mills: the sediment of unfiltered olive oils, namely Olive Oil Dregs (OOD), was chosen as a novel and cheap source for the production of PC. An eco-sustainable and simple process was developed for the extraction of PC from OOD provided by an oil mill located in Campania (South Italy). The total phenolic and HT contents in the crude extract were 6.80 ± 0.16 mg Gallic Acid Equivalents/g OOD and 519.86 ± 9.08 ug/g OOD, respectively. The OOD aqueous extract showed no cytotoxicity in in vitro tests performed using human osteoblasts compared to the OOD alcoholic extract. Furthermore, OOD aqueous extract exhibited antimicrobial activity toward Staphylococcus epidermidis and Staphylococcus aureus and antioxidant effect in a monocyte oxidative model. The purification of HT from OOD aqueous extract using absorption matrices, such as activated charcoal, and resins with different polarity, such as XAD-7 and XAD-16, is in progress.