Quantification of microstructural changes in artichoke by-products by image analysis after high-power ultrasound-assisted extraction of bioactive compounds

Abstract

Image analysis of optical and scanning electron micrographs was successfully used to quantify the microstructural effect of ultrasound application (at 200 and 335 W/L) in artichoke stem samples during the extraction of phenolic compounds and chlorogenic acid. Three temperatures were evaluated (25, 40, and 60 °C) and ultrasound-assisted extraction was compared with mechanical assisted extraction (100 rpm). The low extraction yields of phenolic compounds and chlorogenic acid at 25 °C with mechanical agitation (3.9% and 0.9%) increased up to 96.7% and 78.5%, respectively, at 60 °C and 335 W/L ultrasonic power density. Breakages in plant tissue increased from 4.3% after extraction by mechanical agitation at 25 °C to 10.7% and 16.7% at 25 °C when US at 200 W/L and 335 W/L were applied, respectively. The combined effect of temperature and ultrasound during extraction promoted cell shrinkage, and thus, an increase in cell number per area, reaching the highest increase (36%) when extraction was performed at 60 °C and 335 W/L. The intensified ultrasonic-assisted extraction process affected the microstructure of the solid, with the magnitude of the effects depending on both the extraction temperature and the ultrasonic power density, which explains the increase in extraction yields.