Abstract

This study investigated a two-stage valorisation strategy for olive pomace, in which phenolic compounds were first recovered and the remaining residue was subsequently subjected to alkaline pretreatment for cellulose-oriented processing. In the first stage, defatting and phenolic extraction parameters were optimised based on total phenolic content (TPC). The acetone/hexane mixture at a 1:5 solid-to-solvent ratio preserved the highest TPC in defatted olive pomace (581.29 +/- 6.79 mg GAE/L). For phenolic extraction, the highest TPC was obtained using 70:30 water/ethanol at a 1:5 ratio for 3 hr (363.78 +/- 1.22 mg GAE/L), although the 2 hr treatment under the same conditions showed no significant difference. In the second stage, conventional and autoclave-assisted alkaline pretreatments were compared using 1.25, 2.5, and 3.75 M NaOH. The selected autoclave-assisted treatment with 5% NaOH increased the cellulose proportion to 50.3%, while lignin and hemicellulose decreased to 24.0% and 15.7%, respectively. Principal component analysis of Fourier transform infrared spectra explained 81.88% of the total variance and separated the 5% NaOH autoclave-treated samples. Scanning electron microscope, X-ray diffraction, colour analysis, and time-domain nuclear magnetic resonance confirmed matrix disruption, cellulose exposure, higher lightness, and treatment-dependent mobility changes. Overall, sequential phenolic recovery followed by autoclave-assisted alkaline pretreatment improved olive pomace valorisation and produced phenolic and cellulose-rich fractions.