Assessment of polyphenolic content and in vitro antiradical characteristics of apple pomace

Abstract

Apple pomaces, a by-product in the apple juice processing, were subjected to evaluation as potential sources of antioxidant phytochemicals on the basis of their total content of phenolics (from 4.22 to 8.67mg/g), total flavonoids (from 0.45 to 1.19mg/g) and total flavan-3-ols (from 2.27 to 9.51mg/g), and in vitro antiradical activities. Some individual phenolic compounds including caffeic and chlorogenic acids, (+)-catechin and (-)-epicatechin, rutin, quercetin glycosides and phloridzin were identified and quantified by HPLC. The antiradical activity of apple pomaces was tested by measuring their ability to scavenge DPPH and hydroxyl radicals by ESR spectroscopy. The highest DPPH (EC50(DPPH)=6.33mg/ml) and hydroxyl (EC50(OH)=26.11mg/ml) radical scavenging activities were obtained in the case of Reinders pomace. The regression analysis produced moderate to high correlation coefficients between the antiradical activities (1/EC50(DPPH) and 1/EC50(OH)), and total phenolics, total flavonoids, total flavan-3-ols, and some individual phenolic compounds.

Keywords: Antiradical activity; Apple pomace; DPPH radical; ESR; HPLC; Hydroxyl radical; Phenolic compounds.