Phytochemical Contents and Antioxidant Activity of Medicinal Plants from the Rubiaceae Family in Thailand

Abstract

Several plants of the Rubiaceae family possess potential pharmacological properties, such as antioxidant activity, for subsequent drug development. We investigated the methanolic extracts from the bark and wood of five Rubiaceae species for phenolic and flavonoid contents and antioxidant activity. Regarding the phytochemical contents and antioxidant activity, Mitragyna diversifolia wood (437.57 ± 9.90 mg GAE g-1) and Haldina cordifolia wood (30.11 ± 0.20 mg QE g-1) displayed the highest total phenolic content (TPC) and total flavonoid content (TFC) respectively. Morinda coreia bark followed the highest antioxidant activities (IC50 = 360.58 ± 19.28 µg ml-1) in the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH), Catunaregam tomentosa bark (IC50 = 13.96 ± 5.32 µg ml-1) in the nitric oxide radical scavenging activity (NO), M. coreia wood (IC50 = 918.27 ± 0.16 µg ml-1) in the superoxide radical scavenging activity (SO) and M. coreia wood (IC50 = 236.65 ± 1.66 µg ml-1) in ferric reducing antioxidant power activity (FRAP). The TPC and TFC displayed strong correlations with DPPH in M. diversifolia wood and with FRAP in M. diversifolia bark and wood. We found high correlation between TFC and FRAP in all plant extracts except C. tomentosa wood, while no relation was detected between TFC and NO in all plant extracts. Comparing Rubiaceae species, the highest antioxidant potential were showed in C. tomentosa bark. Overall, it is worth mentioning that the Rubiaceae species exhibit potential as a promising source of natural antioxidants.