Kinetics of Ultrasound-Assisted Flavonoid Extraction from Agri-Food Solid Wastes Using Water/Glycerol Mixtures

Red grape pomace (RGP) and onion solid wastes (OSW) were used as raw material to produce flavonoid-enriched extracts, using ultrasound-assisted solid-liquid extraction. The extraction medium used was composed of water and glycerol and under the conditions used the extraction of flavonoids from both materials was shown to obey first-order kinetics. Maximum diffusivities (D-e) values were 4.01 x 10(-11) and 2.35 x 10(-11) m(2).s(-1), for RGP and OSW extraction, respectively, while the corresponding activation energies (E-a) were 14.00 and 15.23 kJ.mol(-1).