UNRAVELING THE EFFECT OF ULTRASOUND ON TABLE OLIVE PROCESSING – A STUDY USING MODEL SYSTEMS

Olives cannot be consumed fresh due to the presence of oleuropein, a bitter compound. To make them edible, green olives are traditionally processed following the Spanish Style, which uses alkaline solutions to extract/hydrolyze oleuropein, thereby resulting in extensive reagent consumption and wastewater generation. In this context, high-intensity ultrasound (US) emerges as a promising process-intensification technology capable of enhancing mass transfer. Although it has been briefly reported as an assisting tool for olive debittering, its specific interactions with phenolic compounds, particularly oleuropein, remain poorly elucidated. Therefore, this study aimed at evaluating the role of US in table olive processing. For this purpose, both liquid models (water + olive leaf extract – 20% oleuropein) and solid models representing the drupes were developed and subjected to three different treatments: DCO – conventional debittering in alkaline medium (1.2x 10^-3 g NaOH per mg of oleuropein) at 23 ± 2 °C; DUS – similar debittering process assisted by US (3750 W/mL; 0.5 s on/off); and US.H2O – application of US in aqueous medium. The solid models consisted of polymeric (agar/alginate) spheres containing the same phenolic extract. Total phenolic compounds (TPC) were determined over time using the Folin–Ciocalteu method, while NaOH penetration in the solid models was assessed through a colorimetric reaction with phenolphthalein. In the solid models, the DCO treatment reduced TPC by 50% within 40 min and by 66% after 90 min, whereas in the liquid models the maximum reduction reached 70.5% during the initial 10 min (due to the direct contact between the alkali and phenolic compounds). When debittering was assisted by US, the TPC reduction in the solid models was greater, reaching 60.5% and 75.3% at the same time points, respectively, while also enhancing the NaOH penetration rate. In the liquid models, however, the DUS treatment resulted in a similar debittering behavior, as no structural barriers were present. For the US.H2O treatment, the spheres exhibited a ~10% decrease in TPC after 90 min, which was accompanied by the presence of the same amount in the external aqueous medium. In fact, the US.H2O treatment in liquid models showed no significant differences in TPC over time. Overall, US proved to be an effective technology to intensify mass transfer without directly promoting phenolic degradation under the studied conditions. These findings highlight the potential of US to enhance the extraction of phenolic compounds from olives while simultaneously facilitating NaOH diffusion into the plant matrix.