Valorization of olive mill solid residue through ultrasound-assisted extraction and phenolics recovery by adsorption process

Olive pomace, a solid residue generated during olive oil production process and a rich source of phenolic compounds, was dried and defatted to obtain a pomace oil rich in monounsaturated fatty acids with 64% oleic acid. The defatted pomace was further treated by ultrasound-assisted extraction (UAE). The optimal phenol extraction conditions of 10 min, 40% amplitude and 4% (w/v) solid:solvent ratio, yielded to 14.70 mg/g total phenols, 2.48 mg/g total flavonoids and 0.924 mmol Trolox/g antioxidant activity. In order to purify valuable biophenols, two polymeric resins (XAD4 and XAD16) and two activated charcoals (NPAC and GAC) were tested as adsorbents using a magnetic stirrer and an incubator shaker. XAD16 (100 g/L) in magnetic stirrer showed the optimal adsorption ratios with 74.36%, 39.25%, 68.79% and 100% for total phenols, hydroxytyrosol, tyrosol and oleuropein, respectively. Desorption using acidified 50% (v/v) ethanol-water at pH = 2.3 proved 57.65% recovery of total phenols, 19.27% of hydroxytyrosol and 45.73% of tyrosol. These results indicate that extraction and selective purification of biophenols from olive pomace can be achieved by the proposed UAE using 50% v/v ethanol-water as solvent, followed by adsorption-desorption stages with the XAD16 polymeric resin.
Spanish Agencia Estatal de Investigación [grant number PID2019-104950RB-I00/AEI/10.13039/ 501100011033] and the Junta de Castilla y León (JCyL) and the European Regional Development Fund (ERDF) [grant numbers BU301P18 and BU050P20].