Inhibitory Effect of Flower-Shaped Zinc Oxide Nanostructures on the Growth and Aflatoxin Production of a Highly Toxigenic Strain of Aspergillus flavus Link

Abstract

Flower-shaped zinc oxide (ZnO) nanostructures were prepared via a simple aqueous precipitation strategy at room temperature. The as-grown nanostructures were characterized by UV⁻vis spectroscopy, UV⁻vis diffuse reflectance spectroscopy (DRS), spectrofluorometry, Fourier transform infrared (FTIR) spectroscopy with attenuated total reflection (ATR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). The antifungal and anti-aflatoxigenic activities of the ZnO nanostructures were further investigated using a highly toxigenic strain of Aspergillus flavus Link under in vitro and in situ conditions. The results showed that the A. flavus isolate was inhibited to various extents by different concentrations of ZnO nanostructures, but the best inhibitions occurred at 1.25, 2.5, and 5 mM in the culture media. At these concentrations, suppression of aflatoxin biosynthesis (99.7%) was also observed. Moreover, a reasonable reduction in the aflatoxin content (69%) was observed in maize grains treated with the lowest ZnO concentration that exhibited the strongest inhibitory activity in the liquid media. SEM micrographs clearly indicate multiple degenerative alterations in fungal morphology after treatment with ZnO such as damage of the tubular filaments, loss of hyphae shape, as well as hyphae rupture. These results suggest that flower-shaped ZnO nanostructures exhibit strong antifungal and anti-aflatoxigenic activity with potential applications in the agro-food system.

Keywords: Aspergillus flavus; ZnO nanostructures; anti-aflatoxigenic activity; antifungal.

Figure 1

UV–vis absorption spectrum of synthesized flower-shaped zinc oxide (ZnO) nanostructures.

Figure 2

UV–vis diffuse reflectance spectrum of synthesized flower-shaped ZnO nanostructures. The inset shows their corresponding Kubelka-Munk transformed reflectance spectrum.

Figure 3

Room temperature fluorescence spectrum of synthesized flower-shaped ZnO nanostructures.

Figure 4

Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) spectrum of synthesized flower-shaped ZnO nanostructures.

Figure 5

Representative X-ray diffraction pattern of synthesized flower-shaped ZnO nanostructures.

Figure 6

(a) Field emission scanning electron microscopy (FESEM) image of synthesized flower-shaped ZnO nanostructures; and (b) a high magnification image of a single flower.

Figure 7

Effect of nanostructured ZnO on mycelial growth of Aspergillus flavus in culture media. Mean values ± standard error of three independent experiments. Bars not sharing a common superscript differ significantly (Dunnett < 0.05).

Figure 8

Effect of nanostructured ZnO on aflatoxin production in culture media. Boxes and whiskers not sharing a common superscript differ significantly (Dunnett < 0.05).

Figure 9

Scanning electron microscopy of Aspergillus flavus mycelium: (a–c) without treatment; (d–f) with nanostructured ZnO treatment at 1.25 mM. Profiles c,f are enlargements of b,e, respectively.

Figure 9

Scanning electron microscopy of Aspergillus flavus mycelium: (a–c) without treatment; (d–f) with nanostructured ZnO treatment at 1.25 mM. Profiles c,f are enlargements of b,e, respectively.