Antifungal Effect of Starch Edible Films Containing Mexican Oregano (Lippia berlandieri Schauer) Essential Oil and Different pH Values

Introduction: In recent years Rhizopus and Aspergillus became the main genres that cause postharvest decay, major economic losses, and food spoilage in various horticultural products. Recently fungal resistance is developed to chemical products and the use of higher concentrations, increases the risk of high levels of toxic residues. An alternative to this is the use of plant extracts like essential oils (EOs) is believed to be safer to consumers and the environment. In this sense, edible films can incorporate these extracts to provide microbiological stability and reduce the risk of microbial growth on food surfaces.

Purpose: The aim of this study was to evaluate the antifungal effect on Rhizopus and Aspergillus spp. of starch edible films containing Mexican oregano (Lippia berlandieri Schauer) EO and different pH values.

Methods: Starch edible films were formulated with Mexican oregano EO concentrations of 0.00, 0.25, 0.50, 0.75, 1.00, or 2.00%, each concentration at pH values of 5, 6, or 7. Mold radial growth was evaluated inoculating spores in 2 ways: edible films were placed over inoculated agar, Film/Inoculum mode (F/I), or the edible films were first placed in the agar and then films were inoculated, Inoculum/Film mode (I/F). Radial growth curves were described by the Gompertz modified equation.

Results: There was significant difference (P < 0.05) in growth parameters between the 2 modes of inoculation. Starch edible films exhibited better antifungal effectiveness at pH 6 (MIC 0.50%) for Aspergillus, pH 5 (MIC value of 0.25%) for Rhizopus. The modified Gompertz model adequately described growth curves. A significant (P < 0.05) change of Gompertz parameters was observed among essential oil concentrations, increasing the lag phase and decreasing radial growth rates as oil concentration increased. 

Significance: Starch edible films, with acid pH values, added with Mexican oregano essential oil are effective con control fungal growth of Rhizopus and Aspergillus spp.