Characterization of antioxidant and antimicrobial compounds of cinnamon and ginger essential oils

Abstract

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.