Identification of phenolic compounds from pomegranate (Punica granatum L.) seed residues and investigation into their antioxidant capacities by HPLC-ABTS+ assay

In this study, phenolic compounds were extracted and isolated from pomegranate seed residue (PSR). Phytochemicals and antioxidant capacity of extracts from PSR were firstly investigated. Total phenolic (TP) and proanthocyanidin (PC) contents of the extracts were determined as 2427.90 and 505.63 mg catechin equivalent of 100 g dry weight respectively. To evaluate the antioxidant capacity of individual compounds, on line assay of coupling high performance liquid chromatographic separation with ABTS free radical reaction system (HPLC-ABTS+) was carried out. 17 compounds in PSR extracts were detected with antioxidant capacity, and HPLC associated with electrospray ionization mass spectrometry (HPLC-ESI-MS) was used to identify them. The main phenolics in PSR identified were flavol-3-ols, phenolic acids, flavonoid glycosides, and hydrolysable tannin. The results showed that PSR contained some amount of antioxidant compounds, and the HPLC-ABTS+ on line method was fast, sensitive and effective.