Comparative phytochemical profiling and bioactivity evaluation of three Indonesian pomegranate (Punica granatum) peel varieties: Antioxidant, antibacterial, and in vitro antiproliferative activities

Antioxidants are compounds that inhibit, prevent, and reduce free radical activity caused by reactive oxygen species (ROS), thereby protecting cells from oxidative damage. Pomegranate (Punica granatum L.) is recognized as a valuable source of antioxidants, largely due to the phenolic and flavonoid compounds concentrated in its peel. Variations in cultivar, geographical region, and extraction methods are known to influence its bioactive composition. This study aimed to analyze the antioxidant capacity of the exocarp and mesocarp of three pomegranate varieties (red, yellow, and purple), grown in Indonesia, characterized by their different peel colors, extracted using ethanol (96%) and n-hexane, analyzed separately with total phenolic content (TPC), total flavonoid content (TFC), ABTS, and DPPH assays. The results showed variation in antioxidant capacity and biological compounds depending on both plant tissue and solvent used. Ethanolic extracts generally yielded higher phenolic and flavonoid contents, with the purple exocarp recording the highest TPC (721 mg GAE g-1) and TFC (161 mg QE g-1). In contrast, n-hexane extracts produce a lower yield, with the red mesocarp as the richest in bioactive compounds, with TPC (70.21 mg GAE g-1) and TFC (12.07 mg QE g-1). The ethanolic extracts consistently exhibited markedly stronger antioxidant activity, reflected by low IC50 values in both ABTS and DPPH assays, with the purple pomegranate exocarp showing the highest potency (IC50 value < 50 μg mL-1), followed by the red and yellow varieties. In contrast, n-hexane extracts demonstrated substantially weaker activity, indicated by IC50 > 200 ppm. Phytochemical profiling through LC-HRMS revealed the presence of diverse polar antioxidants, including phenolic acids, flavonoid glycosides, and anthocyanin derivatives, particularly abundant in the purple peel. Complementary GC-MS analysis confirmed the presence of non-polar constituents such as fatty acids, sterols, terpenoids, and other lipophilic metabolites. The antibacterial activity of the ethanolic peel extracts was evaluated against Staphylococcus aureus and Escherichia coli using the broth microdilution method, revealing inhibitory effects across all varieties with IC50 values ranging from 1417.41 to 5063.08 µg mL-1. The ethanolic extract of yellow pomegranate mesocarp exhibited the strongest antibacterial activity, while the ethanolic extract of yellow pomegranate exocarp showed the weakest inhibition. In the MTT assay, all ethanolic extracts of pomegranate peel from three varieties demonstrated antiproliferative effects against Huh7it cells after 48 h incubation. Notably, the purple pomegranate exocarp showed the highest cytotoxic potency (IC50 = 231.22 µg mL-1). This research can be used as initial information about new sources of antioxidants.