GC-FID studies on the levels of allyl isothiocyanate in mustard oil combined with menthol/thymol and its antimicrobial investigation

The excessive use of antimicrobials and rapid resistance to antibiotics is a major concern for health care providers. Hence there is a need to develop effective antimicrobials. Natural sources are considered as the potential source of antimicrobial agents. The study aimed to decrease the pungency or irritancy effects of the allyl isothiocyanate (AITC) contents present in the mustard oil after mixing it with natural phytochemicals such as menthol/thymol and to evaluate its effects as potential antimicrobials.

The mustard oil was mixed with menthol, stirred for 12h and with thymol stirred for 7 days in the presence of triethylamine. The components were analysed for decrease in the allyl isothiocyanate contents by gas chromatography-flame ionisation detector (GC-FID).

The results showed 40% and 60% decrease in the allyl isothiocyanate content in mustard oil when mixed with menthol and thymol, respectively. In vitro antimicrobial experiments demonstrated that the tested bacterial species were highly susceptible to the mustard oil mixed with thymol or menthol as compared to the neat mustard oil except Klebsiella aerogenes. Mustard oil mixed with menthol (4.5 mg menthol/ 0.3 mL of mustard oil) exhibited the most potent antimicrobial activity as shown by zone of inhibition (in diameter). The most susceptible species was Bacillus subtilis (2 cm zone of inhibition as compared to neat mustard oil 1.2 cm). The study highlights the potential of mustard oil mixed with thymol or menthol as potential antimicrobials.