Ultrasound-Assisted Accelerated Penetration Extraction of Polyphenols from Pomegranate Peels: Enhanced Mass Transfer by Calcium Ion Precipitation and Utilization of Fick’s Law

The recovery of polyphenols is an attractive strategy for recycling pomegranate peel (PP) and feeding the demands of polyphenol-based functional food. However, emerging techniques are desired to elevate extraction efficiency. In this study, we developed a new method termed ultrasound-assisted accelerated penetration extraction (UAAPE), in which the precipitation effects of polyphenols by calcium ions and ultrasound-induced degradation effects of cell walls simultaneously contributed to the dissolution of PP polyphenols to enhance mass transfer. COSMOtherm was used to simplify the solvent selection, suggesting 50% aqueous ethanol as the solvent. The maximum yield of UAAPE was obtained at the condition (0.67 mg/mL of NaOH concentration, 10 mg/mL of CaCl2 concentration, 458.33W, and 30.56 min) by the optimization using the Box-Behnken design. Meanwhile, Fick’s law possessed the most accurate prediction of the polyphenol contents. The accelerated extraction kinetics showed that UAAPE could not only mitigate the reduction trends of concentration gradients of polyphenols but also improve the extraction rate coefficient. Scanning electron microscopy results showed the ultrasound-induced degradation of PPs, thus further enhancing the extraction process. Besides, UAAPE had a higher content of main polyphenols in compositions and less energy consumption compared with conventional solvent extraction and accelerated penetration extraction.