Antibacterial effects of castor oil on foodborne pathogens: comparative evaluation of the components

For centuries, antimicrobial compounds derived from plants, have been used for medicinal treatment. The aim of this study was to evaluate the antibacterial activity of castor seed oil extracted from Mashhad and Isfahan varieties on Staphylococcus aureus, Escherichia coli and Listeria inocula. The sensitivity of the indicator bacteria was evaluated using disc diffusion technique and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were tested by broth micro-dilution assays. Oil from castor seeds was extract by Soxhlet method and the extracted oils were analyzed by a gas chromatograph connected to a mass spectrometer (GC/MS). According to the results of various dilutions of the extracts, MIC for castor oils ranged 12.5-25%, except for the Isfahan variety that was estimated at 6.25-12.5% for E. coli. The two varieties of castor oils showed the MBC activity on the indicator organisms at the original (100%) concentration. Based on GC/MS data, ricinoleic acid (1.307%), genetistic acid (0.597%) and palmitic acid (1.947%) were detected in oil extracted from Isfahan variety; meanwhile these compounds did not found in Mashhad variety. According to the results, the two castor varieties had antibacterial impact on E. coli. In addition, the overall antimicrobial activity of Isfahan variety was higher than Mashhad type. It seems that the presence of phenolic compounds as well as camphoric and unsaturated fatty acids is the major reason for the higher antibacterial effect of Isfahan variety on E. coli. Considering the inhibitory impact of castor oil, it can be used as a natural preservative in food industry.