Determination of antibacterial and synergic effects of carvacrol, thymol and cuminaldehyde against Escherichia coli and investigation of their effects on the microbiological shelf life of meat

In this study, the antimicrobial effects of thymol, carvacrol and cuminaldehyde, which have the potential to be used as natural antimicrobials in foods, against Escherichia coli ATCC 25922 were investigated in vitro by determining the minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) by macrodilution method. Also, the synergistic effects of antimicrobials in double and triple combinations were determined by calculating the Fractional Inhibition Concentration (FIC) index using the checkerboard method. Antimicrobials alone, in double and triple combination, were added at MIC values to the raw ground beef pre-inoculated with Escherichia coli ATCC 25922 and the number of microorganisms was determined on the 1st, 7th and 14th days under refrigerator conditions. The MIC values of thymol, carvacrol and cuminaldehyde alone on E.coli ATCC 25922 bacteria were found to be 150ppm, 300ppm and 300ppm, respectively. MBK values have the same result as MIC values. Since MBK/MIC ratio is < 4, it was determined that thymol, carvacrol and cuminaldehyde showed bactericidal properties (it can kill 99.99%) against E.coli ATCC 25922. FIC values in duble combinations; 0.625 for carvacrol-cuminaldehyde, 0.625 for thymol-carvacrol and 1 for thymol-cuminaldehyde. According to these results, it was concluded that carvacrol-cuminaldehyde and thymol-carvacrol dual combinations showed a synergistic effect (FIC<1), but thymol-cuminaldehyde combinations did not have any effect on increasing or decreasing the effects of each other (FIC=1). The FIC value of thymol-carvacrol-cuminaldehyde triple combination was found to be 0.75 and it was found to have a synergistic effect. In the shelf life study on ground beef, it was determined that the MIC values of antimicrobials were not sufficient in the food environment and higher doses were needed. Keywords: E.coli, Carvacrol, Thymol, Cuminldehyde, Synergistic Effect, Natural Antimicrobials