Antimycotic Effects of 11 Essential Oil Components and Their Combinations on 13 Food Spoilage Yeasts and Molds

Abstract

Food safety is important to reduce food spoilage microorganisms and foodborne pathogens. However, food safety is challenging, as customers' demand for natural preservatives is increasing. Essential oils (EOs) and their components (EOCs) are alternative antibacterial and antimycotic food additives. In this study, the minimal inhibitory concentrations (MIC) of 11 different EOCs against 13 food spoilage molds and yeasts were investigated via the microdilution method. Cinnamaldehyde (CA) revealed the lowest MIC for all tested strains and all EOCs (32.81-328.1 µg ml^-1). However, CA is organoleptic and was therefore combined with other EOCs via the checkerboard method. Overall, 27 out of 91 combinations showed a synergistic effect, and both respective EOC concentrations could be reduced by maintaining MIC. Thereby, the combination with citral or citronellal showed promising results. The concentration-dependent effect of CA was studied in further detail on Saccharomyces cerevisiae, with CA causing delayed growth-kinetics and reduced total cell numbers. In addition, flow cytometric measurements combined with live-dead staining indicate the fungicidal effect of CA, due to decreasing total cell numbers and increasing relative amount of propidium iodide-positive cells. In this study, we demonstrated that CA is a potent candidate for the use as a natural preservative against food-relevant mold and yeasts showing fungistatic and fungicidal effects. Therefore, CA and EOC combinations with respective lower EOC concentrations reduce organoleptic reservations, which ease their application in the food industry.

Keywords: antifungal; checkerboard method; cinnamaldehyde; essential oil; fractional inhibitory concentration; growth kinetics.

Figure 1

Effect of 0.125 minimal inhibitory concentration (MIC; 0.02 µL mL⁻¹) of cinnamaldehyde (CA); 0.25 MIC CA (0.03 µL mL⁻¹); 0.5 MIC CA (0.06 µL mL⁻¹); 1 MIC CA (0.125 µL mL⁻¹); or 2 MIC CA (0.25 µL mL⁻¹) compared to negative control without cells and positive control without treatment with CA on the growth of S. cerevisiae over time. Error bars (only negative error bars are shown) indicate standard error of independent biological triplicate measurements (n = 3). Different letters beside curves indicate significant differences (p < 0.05) between different treatments according to one-way analysis of variance.

Figure 2

Total cell number (a) and relative amount of PI positive of S. cerevisiae cells (b) after 48 h of growth with cinnamaldehyde (CA). Positive control treated without CA; 0.125 minimal inhibitory concentration (MIC) CA (0.02 µL mL⁻¹); 0.25 MIC CA (0.03 µL mL⁻¹); 0.5 MIC (0.06 µL mL⁻¹) CA; 1 MIC CA (0.125 µL mL⁻¹); or 2 MIC CA (0.25 µL mL⁻¹). Dashed line (a) denotes inoculum concentration. Error bars indicate standard error of six independent replicates (n = 6). Different letters above bars indicate significant differences (p < 0.05), according to one-way analysis of variance.