Solvent-Dependent Phenolic Recovery and Biological Activities of Olive Pomace Extracts

Olive pomace, a by-product of the olive oil industry, represents an underexploited source of bioactive compounds with potential health applications. Their recovery is influenced by extraction conditions, particularly solvent polarity, which may affect extract composition and biological activity. This study aimed to evaluate the influence of extraction solvent on the phenolic content and biological properties of olive pomace extracts. Extracts were obtained by ultrasound-assisted extraction using methanol, ethanol, ethanol:water (70:30, v/v), and acetone. Extraction yield was determined gravimetrically, while total phenolic content was quantified using the Folin–Ciocalteu method. Antioxidant activity was assessed using the DPPH radical scavenging assay. Antimicrobial activity was evaluated against bacterial and yeast strains through minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays. Preliminary toxicity was assessed using the Artemia salina lethality model. Solvent selection influenced extraction yield and phenolic recovery. The ethanol:water extract showed the highest extraction yield (10.56%) and total phenolic content (29.53 mg GAE/g extract), followed by methanol (20.92 mg GAE/g extract). Ethanol:water and methanol extracts also exhibited the highest DPPH scavenging activity, reaching approximately 37% inhibition. Antimicrobial activity was comparable among the extracts for most tested microorganisms. For Enterococcus faecalis, the acetone extract showed the lowest MIC (78.1 µg/mL), compared with 156.3 µg/mL for methanol and 312.5 µg/mL for the remaining extracts. Overall, these findings demonstrate that solvent selection affects phenolic recovery and antioxidant activity, while antimicrobial activity showed a less pronounced dependence on extraction solvent.