Ultrasound-Assisted Extraction of Polyphenols from Olive Pomace: Scale Up from Laboratory to Pilot Scenario

Abstract

Power ultrasound application has been proven to intensify the extraction of biocompounds from plant materials. In this work, the ultrasound-assisted extraction (UAE) of polyphenols from olive pomace (OP) has been studied at three different scales: laboratory (batch, 400 W, 0 barg), medium (continuous, 1000 W, 1.0 barg), and pilot (continuous, 2000 W, 1.0 barg) taking into consideration the influence of technological parameters: extraction time (s), solvent to solid ratio (mL/g), mixture pH, and acoustic parameters: amplitude (µm), intensity (W/cm2), and applied energy (Wh). A central composite design was used to optimize the UAE at laboratory scale (0.2 kg). The optimal conditions were: time: 490 s; ratio: 2.1 mL H2O/g OP; pH: 5.6 at an acoustic amplitude of 46 µm for a maximum extraction yield of 3.6 g GAE/L of extract. At medium scale (2.2 kg) the UAE was carried out using amplitudes from 41 to 57 µm. The effect of the pressure (1.0 barg) on the UAE was positive, in terms of higher extraction yield (2.9 g GAE/L) and faster extraction rates compared to the non-pressurized UAE (2.5 g GAE/L), however, the extraction yield was lower than the one observed at laboratory scale. At pilot scale (120 kg), the UAE involved different ultrasound constellations (booster + sonotrode) to deliver the ultrasound energy at different acoustic intensities from 23 to 57 W/cm2. The acoustic intensity (W/cm2) exerts an important effect on the extraction yield, and should be tailored to each process scale. The highest yield obtained at pilot-scale was 3.0 g GAE/L, and it was 58% higher than the one observed in the conventional extraction without ultrasound assistance (stirring and heating). In all tests, regardless of the scale, higher yields were observed between 80 and 85 °C. The application of this technology at the industrial scale to evaluate if the improvement of the extraction caused by the application of ultrasound could is still important when other operations like centrifugation, ultrafiltration, and reverse osmosis are included in the system and to evaluate its techno-economic feasibility.