Antioxidant properties and phenolic profile characterization by LC-MS/MS of selected Tunisian pomegranate peels

Abstract

Antioxidant contents and activities of different extracts from four Tunisian pomegranate peels, locally called "Acide", "Gabsi", "Nebli" and "Tounsi", were studied. Peels samples were extracted with three solvents (water, ethanol and acetone). For each extract, the total phenol contents and antioxidant activity were evaluated. The highest values of polyphenol, tannins, flavonoids and anthocyanins were recorded in the acetone extract of Acide ecotype with 304.6 mg gallic acid equivalent/g; 292.23 mg gallic acid equivalent/g; 15.46 mg Quercetin/g and 54.51 mg cy-3-glu/100 g, respectively. The acetone extract of Acide ecotype also showed the highest free radical-scavenging and reducing power activity compared to other extracts. Besides, the phytochemical analysis by LC-MS/MS revealed a high content of ellagitannins with punicalagin and punicalagin derivatives as the major compounds that might be responsible for promising antioxidant activity of pomegranate peel extracts. Two compounds (Castalagin derivative and Galloyl-bis-HHDP-hex derivative) were detected only in "Acide" ecotype in important contents.

Keywords: Antioxidant propreties; LC–MS/MS analysis; Punica granatum L.; Punicalagin.

Fig. 1

Identification of phenolic compounds in acetone extracts. a Acide ecotype, b Gabsi ecotype, c Nebli ecotype, d Tounsi ecotype

Fig. 2

MS–MS spectra of punicalagin (M–H m/z 1083) and the subsequent fragment ions of punicalin (M–H m/z 781), ellagic acid (M–H m/z 301) and then gallagic acid (M–H m/z 601)