Advances in Food Mycology

Mixtures of Natural and Synthetic Antifungal Agents 281
conclude that synergistic antifungal combinations of these agents must
include: 1/12 MIC < phenolic concentrations < 1/6 MIC. Comparing
binary and ternary mixture results, it can be observed that a considerable
reduction of potassium sorbate concentration from 150-250 ppm
to 32-68 ppm is possible. Maintaining a potassium sorbate concentration
near 100 ppm, allows a considerable reduction in phenolic antimicrobial
concentrations in the inhibitory ternary mixtures. Figure 4
presents a representation of FIC of potassium sorbate-thymol-eugenol
inhibitory combinations that inhibit A. flavus, this 3-D isobologram as
well as FIC Index illustrate the synergistic combinations.
Ternary mixtures where vanillin is included (Tables 13, 15 and 16)
have in common that growth was observed in those combinations
where synergism was expected. However, some ternary combinations
presented an additive result (FIC Index = 1). Observing binary results of
those mixtures that include vanillin, synergism was anticipated in
ternary mixtures but the results cannot be predicted, as can be seen in
Tables 13, 15 and 16. Monzón et al. (2001) reported that individual or
binary antimicrobial agents that exhibit synergistic results do not
necessary generate similar outcomes in ternary antimicrobial mixtures.
1.00
0.87
FIC Eugenol
0.73
0.60
0.47
0.33
0.20
0.07
1
0.87
0.73
0.60
0.47
0.33
0.20
0.07
1
0.8
0.6
0.4
0.2
0
FIC Thymol
FIC KS
Figure 4. Fractional inhibitory concentration (FIC) isobologram for potassium
sorbate (KS), eugenol and thymol combinations to inhibit Aspergillus flavus in potato
dextrose agar (a w 0.99 and pH 3.5) after 30 days incubation at 25°C.