Untargeted gas chromatography–mass spectrometry analysis and evaluation of antimicrobial and antioxidant activity of Zingiber nimmonii (J. Graham) Dalzell rhizome extracts

Abstract

Background: Zingiber nimmonii (J. Graham) Dalzell (syn. Z. cernuum) endemic to peninsular India have been documented to be in use since ancient times in several traditional systems of medicine. Z. nimmonii with ethnomedicinal applications constitute a rich source of secondary metabolites toward identifying potential bioactive constituents with antioxidant and antimicrobial properties. Objective: Rhizomes of Z. nimmonii (J. Graham) Dalzell, endemic to the Western Ghats, were analyzed for bioactivity and phytochemical composition. Materials and Methods: Polyphenolic contents, namely total phenolics (TPs), total flavonoids (TFs) and total tannin (TT), were determined and expressed using gallic acid (GA), catechin (C) and tannic acid (TA) as standards. Antibacterial and antifungal activities were evaluated against two Gram-positive, three Gram-negative bacteria and three fungi by agar well diffusion method. Antioxidant activity was determined by 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and Ferric Reducing Antioxidant Power (FRAP) assay, and volatile metabolite composition was determined by gas chromatography–mass spectrometry (GC-MS) analysis. Results: THE highest TF and TT contents were detected in ethyl acetate (557.64 ± 41.74 mg CE. 100 g-1 DW) and isopropanol (63.995 ± 2.062 mg TA equivalent. 100 g-1 DW) extract, respectively. High TP content in isopropanol extract (112.80 ± 10.99 mg GA equivalent. 100 g-1 DW) contributed to antimicrobial activity against Gram-positive Staphylococcus aureus (16.3 ± 0.6 mm) and antifungal activity against Aspergillus flavus (11.7 ± 0.6 mm). Methanol extracts showed high antioxidant activity as determined by DPPH (67.4 ± 12.5 μg/ml) and FRAP (127.8 ± 12.4 μg/ml) assays. Major bioactive phytochemical constituents in Z. nimmonii rhizome following GC-MS analysis included heptanediamide, N, N'-di-benzoyloxy (arachidonic acid inhibitor), n-hexadecanoic acid (antibacterial, cytotoxic, and antioxidant), and oleic acid (antitumor). Conclusion: The present study demonstrates potential of Z. nimmonii rhizomes as a rich source of secondary metabolites which can be exploited toward developing anti-infective formulations and free radical quenchers.