Evaluation of Antioxidant Capacity and Identification of Bioactive Compounds of Crude Methanol Extracts of Caesalpinia pulcherrima (L.) Swartz

The study was conducted to determine the antioxidant capacity, expressed as half maximal inhibitory concentration, IC50, of Caesalpinia pulcherrima leaf, flower and seed methanol extracts, and their correlation to their total phenolic, flavonoid and triterpenoid contents. Thin layer chromatographic profiling of the methanol extracts was also conducted followed by ultra-performance liquid chromatography quadruple time-of-flight mass spectrometric analysis for the identification of antioxidant compounds. Based on the quantitative antioxidant assays, all extracts exhibited comparable activity with the reference standard at 800 mu g/ml (P>0.05). Correlation data revealed a strong negative correlation between the IC50 and the total phenolic, flavonoid and triterpenoid contents of the extracts, with statistically significant negative correlations observed between the flavonoids of leaf (r=-0.997) and flower-(r=-0.998) with reducing power assay, and triterpenoids of flower (r=-1.000) with 2,2-diphenyl-1-picrylhydrazyl scavenging assay. Two common spots with antioxidant activity in the thin layer chromatography profiles were subjected to ultra-performance liquid chromatography quadruple time-of-flight mass spectrometric. The majority of compounds were identified in the library as triterpenoids, flavonoids and phenolics, and still a large quantity of compounds were unidentified. Hyperforin, 3-(4'-hydroxy-benzyl)-5,7-dihydroxy-6,8-dimethyl-chroman-4-one and platycodigenin were identified to be the common compounds present on the three plant parts.