Purpose: To evaluate the antimicrobial activity of carvacrol and cinnamaldehyde against Salmonella Tennessee in a low water activity model over 72h at 25°C.
Methods: Model solutions at aw 1.0, 0.7, 0.5 and 0.3 were made using glycerol and sterile deionized H2O, with 5% (w/v) sucrose. Carvacrol and cinnamaldehyde stocks were made in 95% ethanol and added to each aw solution either individually to achieve final concentrations of 0, 125, 250 and 500 ppm or together with each compound at 125 or 250 ppm. All solutions were inoculated with stationary phase S. Tennessee K4643 and incubated up to 72h at 25°C. Samples were taken every 24h, serially diluted, and plated on tryptic soy agar. Each experiment was performed in triplicate.
Results: Reduced aw (0.7, 0.5 and 0.3) alone decreased the viable population over time with greater reduction at lower aw. With antimicrobials, greater inactivation was seen at higher aw. At aw 1.0 and 0.7, a >7 log CFU/ml reduction in population was observed within 24h with 500 ppm carvacrol. Cinnamaldehyde was more effective than carvacrol at aw 0.5 and 0.3 (2.7-2.9 vs. 0.39-1.97 log reduction). When combined, possible synergistic effects of the two were observed at aw 1.0 and 0.7 but not at lower aw.
Significance: Both essential oil components have the potential to be used in reduced aw foods. Cinnamaldehyde was more effective than carvacrol at aw < 0.5. The combination of the two caused greater inhibition than would have been expected with the compounds used alone at higher aw but possible antagonistic effects were observed at lower aw.