Valorization of olive mill residues: antioxidant and breast cancer antiproliferative activities of hydroxytyrosol-rich extracts derived from olive oil by-products

Abstract

Phenolic composition, antioxidant and breast cancer antiproliferative activities of water and methanol/water derived extracts from olive pomace (OP) and dry olive mill residue (DOR), from Portuguese industries, were studied. DOR water (DORW) extracts showed the highest extraction yield; as well as the highest total phenolic content (TPC) and hydroxytyrosol (HT) (∼25 mg/g extract). HPLC–ESI-MS analysis identified HT in both OP and DOR, whereas HT-1-glucoside, tyrosol, oleuropein aglycone isomers, verbascoside and oleuropein were only detected in DOR. Additionally, a de(carboxymethyl)oleuropein aglycone isomer, in aldehyde form, was reported for the first time in DOR. DOR water extract also presented the most effective DPPH scavenging capacity and antiproliferative activity, comparatively to OP water (OPW) extract. Moreover, antioxidant potential of phenolic compounds present in DORW extract was comparable to HT, and to butylated hydroxyanisole (BHA), a widely used food industry antioxidant. Phenolic compounds present in DORW extract also showed comparable tumor antiproliferative activity on MDA-MB-231, relatively to HT and 5-fluorouracil (5-FU), a well-known cytostatic agent. MDA-MB-231 cell growth inhibition, upon 5-FU incubation was even incremented in the presence of DORW extract.

These results demonstrate DOR extracts potential as source of phenolic compounds for nutraceutical applications, as food supplements, opening new strategies for its olive mill residues valorization.