Antifungal Activity of Selected Natural Preservatives against Aspergillus westerdijkiae and Penicillium verrucosum and the Interactions of These Preservatives with Food Components.

The present study examined the influence of primary food components on the antifungal activity of the essential oil of Origanum vulgare, carvacrol, thymol, eugenol, and trans-cinnamaldehyde against Penicillium verrucosum and Aspergillus westerdijkiae. The MIC was determined in food model media enriched with proteins (1, 5, or 10%), carbohydrates (1, 4, or 6%), or oil (1, 5, or 10%). Proteins increased the antifungal activity of O. vulgare essential oil, carvacrol, thymol, and eugenol, whereas the effect of trans-cinnamaldehyde decreased with increasing protein content. The presence of carbohydrates diminished the inhibitory effect of the natural preservatives on A. westerdijkiae; for P. verrucosum, their inhibitory effect increased with carbohydrates. Only the antifungal activity of trans-cinnamaldehyde did not depend on the carbohydrate content. The presence of oil had the strongest influence. At a concentration of 1% oil, the antifungal activity decreased significantly, and at 10% oil, almost no inhibition was observed. To investigate the effect of the antifungal agents on the morphology of the target molds, they were grown on malt extract agar containing carvacrol and trans-cinnamaldehyde and were examined by scanning electron microscopy. The hyphae, conidiophores, vesicles, and phialides were severely altered and deformed, and spore formation was clearly suppressed.

Effects of selected natural preservatives on the mycelial growth and ochratoxin A production of the food-related moulds Aspergillus westerdijkiae and Penicillium verrucosum.

The present study examines the influence of the natural preservatives carvacrol, eugenol, trans-cinnamaldehyde and the essential oil (EO) Origanum vulgare on ochratoxin A (OTA) production and the mycelial growth of two food-related moulds, Penicillium verrucosum and Aspergillus westerdijkiae, by broth macro-dilution assay for 21 days. With the addition of ½ minimum inhibitory concentration (MIC) carvacrol, eugenol and O. vulgare EO, the mycelial dry weight of both moulds decreased significantly over the whole incubation period of 7, 14 and 21 days. Trans-cinnamaldehyde slightly stimulated the growth of A. westerdijkiae and P. verrucosum at 14 and 21 days of incubation. Growth inhibition did not accompany inhibition of OTA production. Although the growth of both moulds was inhibited after the addition of ½ MIC carvacrol, eugenol and O. vulgare EO, the OTA production of the strong mycotoxin producer A. westerdijkiae was stimulated. Only trans-cinnamaldehyde inhibited the production of OTA with the addition of ½ MIC. P. verrucosum produced significantly less OTA than A. westerdijkiae, and its mycotoxin production was almost completely inhibited by the addition of ½ MIC of the natural preservatives.

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.