Research Journal of Biotechnology Vol. 18 (12) December (2023) Res. J. Biotech. https://doi.org/10.25303/1812rjbt1020113 102 Distinct antibacterial and antioxidative properties of Couroupita guianensis Aubl. plant parts and their relation with polyphenolic contents Bhattacharya Rupsa, Sikdar Bratati, Mukherjee Sourav, Raj Adarsha and Roy Sudipta * Department of Botany, University of Kalyani, Kalyani, Nadia 741235 West Bengal, INDIA *dr.sudiptaroy@gmail.com; sroy_bot@klyuniv.ac.in 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. Keywords: Cannonball tree, Polyphenol, Antibacterial, Antioxidant, Correlation. Introduction Plants have been used in the primary healthcare of humans since the early days of civilization 10 . They synthesize and harbor diverse phytocompounds of which secondary metabolites mostly act as defensive screens 33 . Several such compounds have also been found as bioactive and many of them act as chemical scaffolds for drug discovery. Although various successful synthetic drugs are in use or to be discovered for treating various ailments, plant-based drugs provide a relatively safe and affordable alternative to most of the underprivileged population of the world 11 . As a result, the research interests in this aspect have continued to validate the pharmacological activities of untapped plant resources for sustainable wellness programs 26 . Couroupita guianensis Aubl., with a common name of Cannonball tree, belongs to the family Lecythidaceae which is a medicinally important tropical plant native to South America and the Caribbean islands 3 . The plant was introduced in tropical South Asian countries including India 52 . All the aerial parts like bark, leaves, flowers and fruits are used in ethnomedicine to treat a wide range of ailments including fever, skin diseases, gastric complications and relieving pains 5 . The leaves and flowers are used in preparing tea for their health benefits. Pharmacologically, different plant parts are known for their antioxidant, anti-inflammatory, anti-tumor and anti- microbial properties which are contributed by their rich source of phytochemicals including polyphenols, sterols, saponins, terpenoids and alkaloids. Additionally, the plant is also a good source of vitamins, minerals and dietary fiber 32 . Bacterial infections are a menace to humans that contribute to major mortality rates globally 28 . The rapid emergence of drug-resistant bacteria over the years makes the currently used antibacterial drugs less effective leading to a serious burden to the public health system. As a consequence, explorations in new antimicrobics are sought and plant- derived compounds have emerged as therapeutic targets against bacteria 51 . The constitutive plant metabolites defending microbes are known as phytoanticipins while the inducible antimicrobial substances are known as phytoalexins. These secondary metabolites, mostly belonging to phenolic compounds including flavonoids and isoflavonoids, possess potent antimicrobial activities 50 . Many polyphenolic compounds like simple phenols, flavonoids, anthocyanins, lignans and stilbenes contribute to an antioxidant pool of plants 14 . Antioxidants act as a shield in biological systems from the damaging effects caused due