Antioxidant and antibacterial activity of three herbs belonging to Zingiber genus of Bangladesh

Abstract

Apart from boosting flavor, herbs and spices are also known for their preservative, antioxidant, antimicrobial and other medicinal properties. Bioactive metabolites with aspiring prospect have guided the present study to screen for antibacterial and antioxidant activity of three Zingiber plants available in Bangladesh. For that purpose, rhizomes of Zingiber officinale, Z. montanum and Z. zerumbet were extracted with ethanol as solvent system for bioactivity analysis. Antioxidant activity was assessed by employing DPPH free radical scavenging assay, reducing power assay and ferric reducing antioxidant power (FRAP) assay. Z. officinale extract demonstrated the highest free radical scavenging activity (IC50: 43.65 µg/ml), reducing power (EC50: 189.026 µg/ml) and FRAP value (137.18 ± 0.116 µM Fe(II)/100 µg dry weight of extract). Moreover, total phenolic, flavonoid and tannin content were determined which significantly correlated (Pearson correlation) with the antioxidant activities. For the evaluation of antibacterial activity, zone of inhibition (ZOI) was measured by disc diffusion bioassay against four Gram positive bacteria Bacillus megaterium, Staphylococcus aureus, Micrococcus spp., and S. epidermidis as well as ten Gram negative bacteria Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, S. paratyphi, Vibrio cholera, Shigella dysenteriae, S. flexneri, Proteus spp., Mycobacterium spp., and Campylobacter spp. Z. montanum extract exhibited significant activity against E. coli (13.67 ± 0.577 mm ZOI) and Micrococcus spp. (14.33 ± 0.763 mm ZOI) if compared to standard erythromycin with ZOI 15.33 ± 0.577 mm and 15.67 ± 0.577 mm, respectively. Furthermore, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Z. montanum extract were determined against B. megaterium, Micrococcus spp., E. coli and S. paratyphi. Thus, Z. officinale and Z. montanum extracts could be utilized as source and template for the synthesis of potential drugs and food supplements as well.