Antimicrobial activity of cold pressed citrus seeds oils, some citrus flavonoids and phenolic acids

This study aims at determining the antimicrobial activity of cold pressed lemon, orange, and grapefruit seed oils, and to compare their activities with some antibiotic disks, flavonoid and phenolic acid standards. These oils had inhibition zones ranging from 6.62 to 11.00 mm against fifteen tested pathogenic bacteria. Only lemon seed oils and orange seed oil showed some inhibition against Candida utilis yeast. None of the oils had measurable inhibition zone against Micrococcus luteus ATCC 4698. Although most oils showed no growth inhibition even at a 100% concentration, Escherichia coli ATCC 25922 and Salmonella Enteriditis ATCC 13076 inhibited at 100% oil concentrations. Cold pressed and solvent extracted lemon seed oils inhibited growth of Staphylococcus aureus RSKK 1009 at 2% level, and cold pressed and microwave treated-cold pressed orange seed oil inhibited growth of Klebsiella pneumonia ATCC 700603 at 16 and 50%, respectively. The antibiotic disks ampicillin, sulbactam, piperacillin, tobramycin, mezlocillin, amoxicillin and cycloheximide presented 3-4 fold larger inhibition zones (10.24 - 47.00 mm) than the oil samples. Similarly, flavonoid standards naringin, naringenin, hesperidin, neohesperidin, catechin and kaempherol; and phenolic acids gallic, syringic, tr-ferulic, rosmarinic, tr-2-hydroxycinnamic and chlorogenic acids had inhibition zones like the seed oil samples. Hence citrus seed oils pose moderate levels of antimicrobial activity and could be used as antimicrobial aids.