Antioxidant and Antibacterial compounds from the leaves of Psidium guajava

Abstract

Psidium guajava Linn., family Myrtaceae, commonly known as guava, is an important food crop and medicinal plant in tropical and subtropical countries. Previous studies reported major contribution of the ethyl acetate fraction of P. guajava leaf extract to possess antioxidant and antibacterial activities. Therefore, the ethyl acetate fraction of P. guajava was subjected to chromatographic separation to explore the bioactive molecules responsible for these activities. Five known compounds were isolated and characterized using physical, chemical and spectral analysis. Quercetin-3-O-β-arabinopyranoside was isolated for the first time from this plant. Alongside this compound, the other four compounds viz., pyrogallol, quercetin, quercetin-3-O-β-D-xylopyranoside (reynoutrin) and quercetin-3-O-α-L-arabinofuranoside (avicularin) exhibited an exceptional antioxidant activity using ABTS^●+ assay. The isolated pure compounds were further investigated for their antibacterial activity against both Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) bacteria. Pyrogallol didn't display any significant antibacterial activity against both types while, quercetin showed remarkable activity compared to ampicillin as a positive control assuming a promising antibacterial drug. Moreover, the three quercetin glycosides exhibited moderate antibacterial activity when compared to ampicillin.