Valorisation of By-Products Resulting from Olive Processing and Olive Oil Production - Extraction and Quantification of Polyphenols

Carolina Conde Monteiro

Key information

Authors:

Carolina Conde Monteiro (Carolina Conde Monteiro)

Supervisors:

Luís Joaquim Pina da Fonseca (Luís Joaquim Pina da Fonseca); Susete Maria Martins Dias (Susete Maria Martins Dias)

Published in

November 24, 2025

Abstract

The olive oil industry generates substantial quantities of solid residues, including pomace and olive stones coated with residual pulp, which remain underexploited despite their richness in bioactive compounds. This study aimed to quantify and recover polyphenols from olive pomace and wet stone samples using sustainable, water-based extraction. Total phenolic content was determined by the Folin-Ciocalteu method, and possible protein interference in the TPC measurements was evaluated using the Bradford assay. The influence of solid-to-liquid ratio, pH, and extraction time was assessed, and extraction kinetics were modelled with the Peleg equation, which showed a good fit. Optimal conditions were 25 °C, natural pomace pH, a 1:80 kg/L solid-to-liquid ratio (wet weight basis), and 30 min extraction time, yielding 16.5 mg GAE/gdry weight in pomace and up to 38.5 mg GAE/gdry weight in wet stones. The higher TPC in wet stones was attributed to a more favourable matrix with greater accessibility of residual pulp. Polyphenol separation from the aqueous pomace extract (1:80 kg/L) using XAD16N resin achieved recoveries between 13.3% and 21.7% across two column configurations, with methanol proving to be the most effective eluent. HPLC analysis confirmed hydroxytyrosol and tyrosol as the main phenolics in the pomace aqueous supernatant, quantified at 8.22 mg/gdry pomace and 1.95 mg/gdry pomace, respectively. Recovery yields in XAD16N chromatography were 2.6% for hydroxytyrosol and 36.4% for tyrosol. Overall, these results demonstrate that aqueous extraction coupled with resin purification enables the recovery of high-value phenolics, supporting a circular and sustainable valorisation pathway for olive-processing by-products.