Antifungal and sensorial properties of spices have been recognized for years. The antifungal compounds are products of the plant's secondary metabolism, and the action of those compounds could be used to inhibit the growth of spoilage and pathogenic microorganisms in food. Mexican oregano (Lippia berlandieri) grows wildly in the desert zone of Mexico and is usually added to regional foods. The goal of this study was to evaluate the antifungal activity of Mexican oregano versus food-contaminant fungi. Fungi were isolated from spoiled fruit and vegetables and identified according to morphological characteristics. The antifungal activity of oregano was evaluated by radial growth measurement on potato dextrose agar added with dried oregano (0.25 to 4.0%). The essential oil antifungal activity of oregano was also evaluated by the diffusion well test. Twenty-one fungal strains were isolated, which included Penicillium, Geotrichum, Aspergillus, and Bipolaris. In seven of the 21 strains, no inhibitory effect was observed at either concentration of oregano. An increase in growth at the lower or higher concentrations of oregano, when compared to the control, was observed in two fungal strains; in 12 strains, a strong inhibitory effect of oregano was evident. The oregano essential oil was inhibitory to all fungal strains, but there were differences in the extent of the effect. Although the antifungal effect of oregano is strongly established, there was a differential effect with the fungal strains studied. Besides pathogenic fungi and bacteria, microbial spoilage flora should be considered when the addition of spices for food preservation is proposed.
The antimicrobial activity of oregano has been attributed mainly to the presence of volatile compounds found in its essential oil (EO), mainly carvacrol and thymol. The search for antimicrobial activity of oregano EO with different concentrations of thymol and carvacrol, can lead to products with a wider range of applications. The aim of this work was to describe the in vitro antifungal effect of Mexican oregano (Lippia berlandieri Schauer) EO fractions on the growth of Aspergillus, Penicillium, and Rhizopus sp. The Mexican oregano EO fractions studied had different concentrations of carvacrol, which decreased from fraction 1 to 5 (81% to 23%), while thymol content increased from 3% to 64%. Fungal inhibition was evaluated on a wheat flour-based medium with EO fractions concentrations ranging from 50 to 200 mg/kg. Radial growth curves were fitted using the modified Gompertz model (R(2)(adj) = 0.989 ± 0.01). No significant differences (P > 0.05) were found with the different composition of the Mexican oregano EO fractions; nevertheless, fraction concentration presented significant (P < 0.05) mold inhibition as concentration increased. Rhizopus sp. (Rh18) showed a linear reduction on specific growth rate, on the maximum mold growth at the stationary phase, and an increase in the lag time as the concentration of the oregano EO increased; mold growth inhibition were achieved at 150 mg/kg in fractions 1 to 4, and at 100 mg/kg for fraction 5. Aspergillus sp. (As6) and Penicillium sp. (Pe36) were inhibited at 150 and 200 mg/kg, respectively. Results obtained suggest that Mexican oregano EO (Lippia berlandieri Schauer) compounds could be used as antimicrobial agents to prevent fungal growth in bakery products.
Spices acting as antimicrobial agents can be used in combination with other factors to assure food safety. The aim of this work was to evaluate the effect of Mexican oregano (Lippia berlandieri Schauer) essential oil (EO) fractions on the growth of Aspergillus spp. using a bread model media. Fungal growth was evaluated on a wheat flour-based medium with controlled Aw (0.925, 0.950) and with five Mexican oregano EO fractions with different concentrations of thymol and carvacrol (50-200 mg/kg). Fungal growth (modified Gompertz equation) was affected by Aw values and the concentration of Mexican oregano EO fractions. Differences on thymol and carvacrol had no significant effect on the fungal growth kinetic parameters. Low Aw (0.925) and fractions with high concentration of carvacrol (1 and 2) at 100 mg/kg showed fungicidal activity. Combined methods for food preservation can include Mexican oregano EO, where Aspergillus spp. fungal growth can be inhibited. PRACTICAL APPLICATIONSIncorporation of herbs and essential oils to food products can be considered as a good form to increase shelf life of the product, but usually data on antimicrobial and/or antioxidant capacity are performed under laboratory-controlled conditions. The development of predictive models that consider the effect of the food components on the effectiveness of natural antimicrobials can lead to a better understanding of the best conditions for their addition to food products. The present work describes the effect of water activity and wheat components on the antifungal activity of Mexican oregano essential oil. The composition of the essential oil and its concentration were tested in combination with water activity, and it was observed that those factors greatly affected the biological activity of the essential oil.
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