Isothiocyanate profile and selective antibacterial activity of root, stem, and leaf extracts derived from Raphanus sativus L.

Acetone and hexane extracts derived from the root, stem, and leaf of Raphanus sativus were investigated for their antibacterial activity against foodborne and resistant pathogens, such as Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Salmonella typhimurium, Enterobacter aerogenes, Enterobacter cloacae, and Escherichia coli. Total and individual isothiocyanate (ITC) components and their relationship with the antibacterial activity of R. sativus were also evaluated. Both acetone and hexane fractions of root, stem, and leaf exhibited selective antibacterial activity against the organisms tested. Antibacterial activity was strongest in the acetone fraction of root with larger zone of inhibition and lower minimum inhibitory concentration. The results obtained were comparable to that seen with standard antibiotics. Of the different parts of R. sativus studied, root tended to be more active than the stem and leaf extracts in inhibiting the bacterial growth. Gas chromatographic analysis revealed the presence of variable amounts of five different ITCs such as allyl isothiocyanate (AITC), phenyl isothiocyanate (PITC), benzyl isothiocyanate (BITC), phenethyl isothiocyanate, and 4-(methylthio)-3-butenyl isothiocyanate (MTBITC) in different parts of the plant. The low linear correlation between the total ITC content and antibacterial activity implied that bacterial growth inhibitory ability of R. sativus was not dependent on the total ITC content. However, the antibacterial activity of R. sativus was well correlated with AITC, PITC, and BITC for all organisms except for Enteroc. faecalis, whose inhibitory effect was more related to MTBITC.