Isolation and identification of a radical scavenging antioxidant – punicalagin from pith and carpellary membrane of pomegranate fruit

Pith and carpellary membrane (CM) constitute 13% of pomegranate fruit composition. Pith acts as an anchoring tissue while CM acts as a protective membrane; both play significant roles in determining the health and disease status of pomegranate arils but remain unexplored for their nutraceutical properties. Activity-guided repeated fractionation of the methanol extract on a silica gel column, followed by preparative HPLC, yielded a compound which exhibited strong radical scavenging activity with EC50 values of 16.7 ± 2.3 and 54.2 ± 4.6 against DPPH free radical and superoxide radicals, respectively. It also showed a very strong lipid peroxidation inhibitory activity in a liposome model system with an EC50 value of 54.2 ± 0.9. However, it showed negligible metal chelating activity. Based on UV, IR, 2D-NMR, GC-Mass and MALDI-Mass studies, the compound was identified as punicalagin. The antioxidant activity of punicalagin and the methanol extract can be ascribed mainly to radical scavenging ability.