Antifungal activity of a food-grade dilution-stable microemulsion against<i>Aspergillus niger</i>

Abstract

AIMS: To study the antifungal activities of a prepared food-grade dilution-stable microemulsion against Aspergillus niger. METHODS AND RESULTS: Results from the antifungal activity on solid medium by agar dilution method showed that the microemulsion caused complete growth inhibition at 2000 ppm, and at 1000 ppm, showed 55% growth inhibition after 4 days of incubation and a delay of conidiation by 1 day compared with controls. Results from the antifungal activity in liquid medium by broth dilution method showed that the growth of A. niger was completely inhibited when a liquid medium containing 10(6) spores per ml was treated with 500 ppm of microemulsion, which was determined by minimum fungicidal concentration. Study of fungicidal kinetics showed that more than 99% of viable spores were killed within 15 min. These antifungal activities were confirmed by scanning electron microscopy, light microscopy and increased Ca(+2), K(+) and Mg(+2) leakages. CONCLUSIONS: The results suggest that the prepared microemulsions are effective antifungal systems with excellent growth inhibition and sporicidal activities, and indicate that their antifungal activity may be to the result of the disruption and dysfunction of A. niger cell walls and biological membranes. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests the potential use of food-grade dilution-stable microemulsions for antifungal use in the food and pharmaceutical industries.