Phytochemical Characterization and Concentration-dependent Antimicrobial Activity of Kaempferia galanga L. Rhizome Essential Oil

Abstract

Kaempferia galanga L. (Zingiberaceae) is an aromatic rhizomatous medicinal plant whose essential oil is characterised by marked geographical and chemotypic variation. The present study characterised the rhizome essential oil of K. galanga collected from Marngar, Ri-Bhoi district, Meghalaya, northeastern India, and evaluated its in vitro antimicrobial activity against selected bacterial and fungal microorganisms. Hydrodistillation of 1 kg fresh rhizomes yielded approximately 4 g of pale-yellow essential oil, corresponding to 0.40% (w/w) on a fresh-weight basis. GC-MS analysis was performed on a Thermo Scientific ISQ-7000 system. The instrument report recorded a 41.99-min run, 1.00 µL injection volume, and 29 integrated chromatographic peaks accounting for 100% of total peak area. Library searching produced strong matches for ethyl p-methoxycinnamate (EPMC) at 12.541 min (22.36%; SI/RSI 908/930) and 13.891 min (5.19%; SI/RSI 942/946). Other abundant tentative first-hit assignments included p-mentha-1(7),8-dien-2-ol (13.56%), 1-octadecanesulphonyl chloride (8.87%), epicurzerenone (7.44%), an oxygenated sesquiterpenoid-like furanone (6.91%), camphene (6.80%), α-terpineol (6.58%) and β-acorenol (6.05%). Because several assignments showed only moderate spectral similarity or were chemically unusual, all library-based identities are treated as tentative pending retention-index and authentic-standard confirmation. The essential oil showed a clear concentration-dependent inhibitory response against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Aspergillus fumigatus and Nigrospora sphaerica. At 1000 µg mL⁻¹, inhibition ranged from 89.70 ± 0.92% for P. aeruginosa to 97.30 ± 0.58% for A. fumigatus. One-way ANOVA showed a significant effect of concentration for every microorganism (P<0.001), while PCA indicated that the common concentration gradient accounted for most multivariate variation (PC1=99.65%). The findings establish a location-specific chemical and antimicrobial profile for K. galanga from Meghalaya and support further confirmation of its major volatile constituents and standardised antimicrobial testing.