Screening for antifungal activity of some essential oils against common spoilage fungi of bakery products

The antifungal effect of 20 essential oils against the most important moulds in terms of spoilage of bakery products (Eurotium spp., Aspergillus spp. and Penicillium spp.) was investigated. Suitable solutions of essential oils were added directly to an agar culture medium (containing 2% wheat flour) to obtain a final concentration in the range between 0 to 1,000 ppm. Antifungal activity was tested at different water activity (a(w)) and pH conditions, and the fungal growth was followed by measuring the colony diameter during the incubation period. Only cinnamon leaf, rosemary, thyme, bay and clove essential oils exhibited some antifungal activity against all isolates. The antifungal activity depended on aw and pH levels. In general, a stronger inhibition was observed as the water availability increased, moreover, in some cases at 0.80a(w) they favoured fungal growth. The interaction between essential oil concentration and pH depended mainly on the essential oil. Rosemary, thyme and bay were more effective at pH 5, loosing their activity as pH increased, while only cinnamon leaf was more effective near neutrality. These findings strengthen the possibility of using plant essential oils as an alternative to chemicals to preserve bakery products.