Sustainable extraction of phenolic compounds from wet olive pomace: process optimisation and storage stability

Olive pomace (OP) is the main solid by-product of olive oil production and contains more than 98% of the olive antioxidant-phenolic compounds. We developed a sustainable extraction strategy to recover phenolic compounds directly from wet OP, avoiding energy-intensive drying steps, and to evaluate the antioxidant activity (AOA) and stability of the obtained extracts. A response surface methodology approach was used to evaluate the effects of temperature, extraction time, and ethanol concentration on the recovery of free and total phenylethanoids, which were quantified by high-performance liquid chromatography with diode-array detection (HPLC-DAD), total phenolic content, and AOA. Optimal extraction conditions were identified at 95 degrees C and 40% ethanol, yielding 6.88 mg/g d.w. of total phenylethanoids. Extraction time showed no significant effect. During refrigerated storage, hydroxytyrosol and verbascoside decreased by similar to 61% and 67%, respectively, after 6 months, whereas tyrosol showed only a 7% reduction. These results highlight the effectiveness of this extraction approach, although stabilisation strategies are required to improve extract stability and applicability.