Chemical composition of commercial citrus fruit essential oils and evaluation of their antimicrobial activity acting alone or in combined processes

Identification and Quantification of the Antimicrobial Components of a Citrus Essential Oil Vapor

The anti-bacterial components of a citrus essential oil vapor were identified as linalool, citral and β-pinene using a bioautography method and quantified by GC-MS. Essential oil vapor release, monitored in real-time with Atmospheric Pressure Chemical Ionization – MS (APCI-MS), showed differences in the vapor release profile of limonene, β-pinene and linalool over 24 hours, while Solid Phase Micro-extraction (SPME) GC-MS demonstrated changes in composition of the vapor at 35°C. Fourteen isolates were tested in vitro for their susceptibility to the EO vapor and to linalool, citral and β-pinene vapors, both separately and in a mixture containing the three components in the amounts at which they occur in the EO vapor. All eleven Gram-positive strains tested were susceptible to the EO vapor, linalool, citral and β-pinene vapors separately and the mixture with zones of inhibition of 4.34 cm, 5.32 cm, 5.58 cm, 4.86 cm and 4.68 cm, respectively. Of the three Gram-negative strains tested, Pseudomonas aeruginosa 10145 was resistant to all the vapors. When bacteria inoculated onto stainless steel surfaces were exposed to either the EO vapor or a linalool/citral/β-pinene vapor mixture there was no significant difference in reduction for the Gram-positive isolates, while the Gram-negative isolates were resistant to both EO vapor and the linalool/citral/β-pinene mixture.