Mechanism-based antioxidant activity of Rubiaceae species collected from Ilocos Norte, Philippines

The Rubiaceae family, comprising 550 species in the Philippines, is a significant source of bioactive components with ethnopharmacological uses. This study assessed the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity of six Rubiaceae species, collected in Ilocos Norte, Philippines: Guettardella microphylla (Bartl. ex DC.) Merr., Timonius ternifolius (Bartl. ex DC.) Fern.-Vill., Kanapia monstrosa (A. Rich.) Arriola & Alejandro, Pyrostria triflora Arriola, Calaramo & Alejandro, Pyrostria subsessilifolia (Merr.) Arriola & Alejandro, and Psychotria luzoniensis (Cham. & Schltdl.) Fern.-Vill. Identification of the plant species was done using morphological characterization. The TFC results ranged between 1.86-3.81 mg quercetin equivalent/g dry weight (GAE/g DW), while TPC indicated 5.47-17.17 mg gallic acid equivalent/g dry weight (QE/g DW). G. microphylla showed the highest TFC (3.81±0.20 mg QE/g DW) while P. triflora exhibited the highest TPC (17.17±0.83 mg GAE/g DW). Antioxidant profiling showed P. luzoniensis exhibiting the highest activity in the NOS, ABTS, DPPH, and FRAP assays. G. microphylla showed the highest hydrogen peroxide scavenging activity, while T. ternifolius demonstrated the highest hydroxyl radical scavenging activity. Findings suggest that the crude methanolic extracts of the Rubiaceae species have relatively high TPC and TFC values and exhibit promising antioxidant capacities.