Purpose: The objective of this study was to quantitate the influence of a food protein, lipid and carbohydrate on the antimicrobial efficacy of cinnamaldehyde and eugenol. The model food components were sodium caseinate, soybean oil and potato starch.
Methods: Initially, the minimum inhibitory concentration (MIC) of cinnamaldehyde and eugenol against Escherichia coli (EC) BA-1882 and Listeria monocytogenes (LM) Scott A were determined at 37°C and 32°C, respectively, by the microbroth dilution method. Then, growth curves were performed at the MICs of the essential oils in tryptic soy broth (EC) or TSB plus yeast extract (LM). Food components were added at 0, 1% and 5% (w/v). Incubation was: EC: 37°C, 24h; LM: 32°C, 48h.
Results: The MICs for EC and LM, respectively, of cinnamaldehyde were 250 and 150 ppm and of eugenol 500 and 550 ppm. For EC, cinnamaldehyde antimicrobial activity was reduced significantly by 1% soybean oil and eliminated by 5% oil. In contrast, 1% caseinate and starch had little effect on activity. For eugenol, the negative effect was more pronounced with 1% of all significantly reducing activity. For LM, results were similar for soybean oil but caseinate and starch had much less of an effect on antimicrobial activity, even at 5%.
Significance: These results indicate that food components reduce, but do not always eliminate, antimicrobial activity. Food components had less of an effect on cinnamaldehyde than eugenol. Thus, cinnamaldehyde has potential for activity in foods with higher protein, higher starch or moderate to low lipid content. Eugenol has much less potential to be incorporated into foods without a significant loss of antimicrobial activity.