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

The present investigation reports on the chemical composition of three commercial citrus fruit essential oils (orange [Citrus sinensis], lemon [Citrus lemon] and Mandarin [Citrus reticulata]) from Spain, and examines their antimicrobial activity against spoiling and pathogenic microorganisms, as well as possible synergistic lethal effects in combination with mild heat. Gas chromatography-mass spectrometry analysis allowed for the identification of 65 compounds as main volatile constituents. Limonene was the major component in the three essential oils (59-85%). Preliminary results obtained by using the disc agar diffusion technique indicated mandarin EO as the best growth inhibitor and discarded orange and lemon essential oils. The evaluation of the bacteriostatic and bactericide effect confirmed the broadest spectrum of action to be that of the mandarin essential oil. However, low concentrations of the three essential oils (0.2 μl/ml) in combination with a mild heat treatment (54 °C/10 min) showed synergistic lethal effects, inactivating more than 5 log cycles of bacterial cells, and demonstrating their potential in the design of successful combined treatments for food preservation.