Protective effects of commercial propolis ethanolic extracts on maize seeds contaminated with Aspergillus flavus, Aspergillus parasiticus or Fusarium verticillioides

Maize is one of the most important cereals in the world, and its fungal contamination with Aspergillus and Fusarium is a big challenge to food security. Due to the well-known antimicrobial properties of propolis, commercial ethanolic extracts of propolis (EEP) have the potential as a suitable natural alternative to protect seeds. In the present study, samples of EEP were used to protect maize seeds from A. flavus, A. parasiticus or F. verticillioides infection. The preliminary selection of EEP was based on an antibiogram-like susceptibility test and total polyphenol content based on gallic acid equivalents (GAE). In vitro cytotoxicity and in-situ efficacy assays were done with two EEP rendered as most effective and readily available. Conidia cytotoxicity assay was based on the resazurin reduction method. Efficacy experiments were done by treating maize seeds with 1% and 2% dilutions of each of the most effective EEP, respectively, followed by fungal conidia inoculation with 10 mu L of a 1x10(4) conidia suspension of either A. flavus, A. parasiticus or F. verticillioides. The most effective treatments (Br and Ra) had total polyphenol content between 418 and 582 mg GAE/100 mL and showed adequate inhibition of fungal growth. Regarding cytotoxicity, 50% dilutions of EEP (Br and Ra) had cytotoxicity percentages ranging from 38- 57% and 24-34%, respectively. In the experiments of the effectiveness on seeds, significant differences (p < 0.05) were observed for most treatments when compared to the control and among them (p < 0.05). Hence propolis may represent a strategy to prevent fungal contamination of maize seeds.