Oleuropein extraction from olive leaves assisted by moderate electric fields and high-power ultrasound. A parametric study

Moderate electric field (MEF) or power ultrasound (US) are alternative technologies that could enhance conventional extraction processes, increasing yield and quality, shortening processing and reducing energy needs. This study analyses the feasibility of using MEF and US to improve oleuropein extraction from olive leaf. For this purpose, extraction kinetics (distilled water, 50 degrees C) were carried out in different olive leaf/water ratios (OLWR: 1, 5, 10, 15 % w/v), with and without the application of MEF (12.5 V cm(-1)) at different electric frequencies (MEF-FR: 300, 600, 900 and 1200 Hz). Furthermore, the sequential application of MEF and US (3.2 W/L; 21.48 kHz) was also assessed. The experimental extraction kinetics were modelled using Two Terms, Naik and Peleg models. Multi-Factor ANOVAs (p < 0.05) permitted the analysis of the influence of OLWR, MEF-FR and US on the yield. The results showed that the maximum yield (0.016 mg oleuropein/g olive leaf d.m) was found at the lowest OLWR tested (1 % w/v) with MEF application, increasing a 34.2 % the yield of the conventional extraction. As regards the electric frequency, the fastest kinetics and the greatest yield (0.022 mg oleuropein/g olive leaf d.m) were achieved at 300 Hz. The combined application of MEF and US shortened the extraction, finding the maximum yield (0.024 mg oleuropein/g olive leaf d.m) after 10 min instead of the 40 min needed for conventional extraction (0.012 mg oleuropein/g olive leaf d.m), which means an extraction time reduction of 75 %. The modified Peleg model provided the best fit. Therefore, MEF and US significantly improved the efficiency of oleuropein extraction, thus highlighting their potential in extraction processes.