Distinct antibacterial and antioxidative properties of Couroupita guianensis Aubl. plant parts and their relation with polyphenolic contents

Abstract

Couroupita guianensis is an arboreal flowering plant of the family Lecythidaceae with diverse pharmacological effects and a myriad of folk-medicinal uses. The study aims to compare the antibacterial and antioxidant efficacies of different plant parts like bark, leaf, flower and fruit with their polyphenolic contents. Methanolic extracts of different plant parts were prepared to assess their bioactivities and to estimate phytochemicals. The antibacterial activities of different extracts against six pathogenic bacteria were examined following the agar diffusion method and broth microdilution assays to determine inhibition zones, MIC and MBC. Among the different plant parts, the fruit methanolic extract represented the highest antibacterial activity with the highest inhibition zones and consequential lowest MIC/MBC values. On the contrary, the antioxidant activities revealed the superiority of bark over other plant parts in the total antioxidant, ferric reducing and radical scavenging assays. Phytochemical analyses by qualitative assays and HPTLC highlighted the presence of diverse phytocomponents in different extracts. Among different plant parts, quantitative estimates of polyphenolic contents exhibited the highest total phenolics (TPC; 37.32±2.47 mg GAE/g extract) in bark, the highest flavonoid content (TFC; 25.78±1.56 mg QE/g extract) in flower while the highest tannin content (TTC) was noted in leaf (34.35±0.40 mg GAE/g extract). Pearson’s correlation analyses concerning the polyphenolic contents and the bioactivities like antioxidant and antibacterial efficacies in different plant parts highlighted an explicit role of total phenols and flavonoids in the antioxidative properties. However, the role of polyphenols in the antibacterial activities of Couroupita was meager and pointed out the involvement of non-phenolic compounds in such activities. Despite the low polyphenol contents in Couroupita fruit extract, its potent antibacterial activities have grown our interest in future studies to find out the bioactive compound(s) with therapeutic potential.