Investigation of in-vitro antioxidant potential in crotalaria verrucosa along with identification and quantification of its polyphenolic compounds

Abstract

Crotalaria verrucosa (Fabaceae) is a local medicinal plant, native to Chittagong, Khulna, Rajshahi and Sylhet, in Bangladesh. Traditionally, C. verrucosa is used for the treatment of folkloric remedies namely, scabies, heart complaints as well as in the treatment of throat and oral diseases which may be extrapolated to its antioxidant potential as deduced from this study. In this study, the preliminary phytochemical screening of methanolic leaf extract of C. verrucosa showed the presence of flavonoids, phenolic compounds, alkaloids, tannin, steroids and glycosides. Various in-vitro antioxidant studies were performed to determine its antioxidant potential. The extract showed moderate antioxidant activity in DPPH free radical scavenging assay where ascorbic acid was used as the reference standard. Also, using the DPPH free radical scavenging assay, the IC50 values of Crotalaria verrucosa and ascorbic acid was found to be 533.738ug/mL and 154.916ug/mL, respectively. Whilst the total phenolic content was found to be 152.180mg/g of gallic acid equivalent (GAE), the total flavonoid content was found to be much higher, 184.510mg/g of quercetin equivalent (QE). The total antioxidant capacity was determined to be 32.342mg of ascorbic acid equivalent (AAE) for a concentration of 1200ug/mL of methanolic extract of C. verrucosa. In addition to the determination of in vitro antioxidant potential, HPLC coupled with a diode-array-detector was used to identify and quantify the polyphenolic compounds present in the methanolic crude extract of C. verrucosa. Amongst the polyphenolic compounds, the most notable of them were identified as gallic acid, (+)-catechin hydrate, vanillic acid, caffeic acid, syringic acid, (–)-epicatechin and vanillin were identified present in concentrations of 19.53, 5.08, 5.97, 6.22, 1.09, 7.16 and 8.05mg/100g of dried extract. Amongst the polyphenolic compounds quantified, gallic acid was most predominantly present (19.53mg/100g of dried extract). Although vanillic acid is a catechin-metabolite; (+)-catechin hydrate and (–)-epicatechin are flavonoids and gallic acid, syringic acid, caffeic acid and vanillin are polyphenolic compounds, all of these compounds possess established antioxidant activities.