Grewia flava twigs herbal extracts: phytochemical, Antioxidant, and antimicrobial evaluations

Abstract

The ethnopharmacological properties of the medicinal plants are ascribed to their bioactive phytochemicals. Thus, the purpose of this study was to assess the phytochemical profile, antioxidant, and antimicrobial activities of Grewia flava twig extract. Infusions of this plant part are consumed to assist with kidney problems, however, there is no scientific data on the phytochemical profile, biological properties of the extract to validate its folklore use. The invitro antioxidant activity of G. flava twig extracts were evaluated using DPPH radical scavenging, reducing power and metal chelation assays and the total phenolic and flavonoid content in the extracts were determined and related to the antioxidant activity. Bioactive compounds were isolated and characterized from the twig extract on the basis of NMR and FT-IR spectroscopy. Isolates were subjected to antimicrobial screening against P. aeruginosa, S.aureus, E. coli, B. subtilis, A. niger, and R. oryzae using the agar well diffusion and microdilution methods. All crude extracts exhibited dose dependent DPPH radical quenching and chelating abilities with IC50 values ranging from 15 to 496 μg/mL and from 97 to 428μg/mL respectively. Methanol twig extract exhibited highest concentration of phenolic (250mg GAE/ g) and flavonoids (64.54 mg QUE/ g), which explains the high antioxidant ability observed. The bioactivities of the extracts can be ascribed to the presence of different bioactive phytochemical compounds including alkaloids, flavonoids, saponins, steroids, glycosides, anthraquinones and tannins which were detected in the extracts. Phytochemical study of the twig extract afforded isolation of five compounds: Lupeol, β-sitosterol, stigmasterol, eicosyl protocatechuate and kaempferol-3-O-rutinoside from aqueous methanol twig extract. All compounds except lupeol are being reported for the first time from G. flava. Eicosyl protocatechuate exhibited highest antiradical activity among the isolated compounds with an IC50 value of 120 μg/mL. Stigmasterol displayed inhibitory effect against S. aureus, E. coli, A. niger and R. oryzae with MIC values ranging from 0.40 to 1.70 mg/mL making it the most active isolated compound. Root and twig n-hexane extracts were subjected to GC-MS analysis, which identified a number of bioactive compounds like betulin, β-amyrin, palmitic acid, Lupenone, and phytol, highlighting the potential of the plant species as a botanical drug. In conclusion this study provides scientific evidence to justify the use of G. flava twigs in traditional medicine, suggestive that the plant part may serve as a medicinal agent.