Essential oils obtained from the bark of Cinnamomum zeylanicum (cinnamon) and the rhizomes of Zingiber officinale (ginger) were characterized by analytical TLC and GC/MS, and their antimicrobial and antioxidant compounds were detected by TLC-bio-autography assays. Essential oil of cinnamon bark (CEO) was found to be a unique aromatic monoterpene-rich natural source, with trans-cinnamaldehyde (45.62%) as the major constituents. Ginger oil (GEO) was characterized by high content of sesquiterpene hydrocarbons, including β-sesquiphellandrene (27.16%), caryophyllene (15.29%), zingiberene (13.97%), α-farnesene (10.52%) and ar-curcumin (6.62%). CEO and GEO oils showed significant inhibitory activity against selected strains of bacteria and pathogenic fungi, with MIC values ranging from 20 to 120 µg/ml depending upon the microbial species. Cinnamaldehyde (CA) and eugenol in cinnamon bark oil and β-sesquiphellandrene, caryophyllene and zingiberene in ginger rhizome oil were identified as the most active antibacterial components, with the aid of bioautography on TLC and GC-MS. Also, both oil exhibited appreciable in vitro antioxidant activity as assessed by 2, 2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and β-carotene bleaching methods, compared to α-tocopherol, BHT and BHA. Guided isolation through TLC-autography using 0.05% DPPH and β-carotene/linoleic acid as a detection reagent led to identified CA and eugenol as main active antioxidant compounds in CEO. The significant antimicrobial and antioxidant activities of both oils suggest that it could serve as a source of compounds with preservative phenomenon.
Key words: Antimicrobial, bioautographic assay, antioxidant, essential oils, ginger, cinnamon.
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