Biological activity of high molecular weight phenolics from olive mill wastewater

Olive oil production generates large amounts of recalcitrant compounds, the olive oil mill wastewater (OMWW), which represent one of the most contaminating effluents among those produced by the agrofood industries. Nowadays, this view has changed to one that recognizes the waste as a low-cost starting material rich in bioactive compounds, particularly biophenols, that can be extracted and applied as natural antioxidants for the food and pharmaceutical industries. The data reported in this paper indicate that the OMWW extracts, besides low molecular weight antioxidant phenolics such as tyrosol and hydroxytyrosol, also contain phenolics with a molecular weight in the range of 600-5000 Da, which exhibit efficient scavenging activities against hydroxyl and peroxyl radicals. This group of phenolics includes, besides verbascoside, isoverbascoside, and an oxidized form of verbascoside, a number of higher molecular weight phenolics arising from oxidative polymerization of hydroxytyrosol and caffeic acid. Overall, these higher molecular weight phenolics prove to be, in some in vitro tests, more efficient scavengers of hydrophilic hydroxyl radicals than hydroxytyrosol, which could be used for industrial applications as natural nontoxic antioxidants.