Antifungal activity of selected natural preservatives against the foodborne molds Penicillium verrucosum and Aspergillus westerdijkiae.

The present study examines the inhibitory effect of the essential oil (EO) of Origanum vulgare, its active components carvacrol and thymol, and a few active components of other EOs, namely, eugenol, trans-cinnamaldehyde and 1,8-cineole, against Penicillium verrucosum CBS 302.48, Aspergillus westerdijkiae CBS 112803 and Aspergillus westerdijkiae CBS 112804. Therefore, the minimum inhibitory concentration (MIC) was determined by broth macrodilution of each antifungal agent. Regarding their antifungal activity, the following ranking in order of decreasing inhibitory action is: trans-cinnamaldehyde > carvacrol = thymol > O. vulgare EO > eugenol > 1,8-cineole. The combined effects of the natural preservatives were studied by checkerboard assay. The results are based on the fractional inhibitory concentration indices (FICIs), which are interpreted as 'synergy', 'no interaction' or 'antagonism'. The indices ranging from 0.8 to 1.3 and thus show no interaction. In addition, the dependence of the natural inhibitors on different pH values (pH 7.0, 5.6, 4.5 and 3.5) and water activity (0.99, 0.92, 0.90 and 0.87 aw) was investigated. All tested natural preservatives are tolerant to the different examined milieu conditions, with the lowest MICs recorded at pH 3.5 and 0.87 aw.