Evaluation of chemical constituents and antioxidant and antimicrobial properties of the essential oils of two citrus species

The aim of this study was to extract and identify the volatile constituents of the essential oils of two species of citrus named Clementine and Mandarin and to investigate their antioxidant and antimicrobial potential. The compounds of the essential oils prepared by steam distillation were identified by gas chromatography-mass spectrometry (GC/MS). The antioxidant abilities of the essential oils were evaluated by ABTS and DPPH assays. The antimicrobial activities of the essential oils were investigated using the disc diffusion method against three Gram-positive (Staphylococcus aureus, Bacillus ceruse, and Bacillus subtilis) and two Gram-negative (Escherichia coli and Salmonella typhi) bacteria, a yeast (Candida albicans) and a fungus (Aspergillus niger) in comparison with the synthetic antibiotics.The GC/MS results revealed that both essential oils were rich in hydrogenated monoterpens and limonene was the main compound in both essential oils. The highest percentage of DPPH and ABTS free radical scavenging was shown about 34.38% and 48.44%, respectively for Clementine essential oil and for Mandarin essential oil was 67.53% and 96.44%, respectively, at 900 ppm. The results showed that both essential oils inhibited the growth of the studied microorganisms and increasing the essential oil concentration, increased the zone of inhibition. The highest diameter of inhibition zone was observed in Candida albicans in both essential oils. The lowest inhibition zone for Clementine and Mandarin essential oils was also observed in Escherichia coli and Aspergillus niger, respectively. In general, the antifungal effect of both essential oils was more than their antibacterial effect. In conclusion, citrus peel essential oil could be suggested as a natural antioxidant and antimicrobial substance for use in food products.