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

Abstract Olive pomace is the main solid by-product of olive oil production and contains more than 98% of olive antioxidant phenolic compounds. We developed a sustainable extraction strategy to recover phenolic compounds directly from wet olive pomace, avoiding energy-intensive drying steps, and to evaluate the antioxidant activity 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, quantified by HPLC-DAD, total phenolic content, and antioxidant activity. Optimal extraction conditions were identified at 95 °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 ~ 61% and 67%, respectively, after six months, whereas tyrosol showed only 7% reduction. These results highlight the effectiveness of the extraction approach, although stabilization strategies are required to improve extract stability and applicability.