Abstract
Aspergillus flavus is a frequent contaminant of maize grain. We isolated this fungus, determined the colony morphology and species (by internal transcribed spacer sequencing) and measured the aflatoxin content. The selected A. flavus fungi were placed into two groups, toxigenic and atoxigenic; both appeared similar morphologically, except that the atoxigenic group lacked sclerotia. An essential oil fumigation test with clove and cinnamon oils as antifungal products was performed on fungal conidial discs and fungal colonies in Petri plates. Cinnamon oil at 2.5 to 5.0 μL/plate markedly inhibited the mycelial growth from conidial discs of both strains, whereas clove oil showed less activity. The oils had different effects on fungal mycelia. The higher clove fumigation doses of 10.0 to 20.0 μL/plate controlled fungal growth, while cinnamon oil caused less inhibition. Compared with atoxigenic groups, toxigenic A. flavus responded stably. Within abnormal A. flavus hyphae, the essential oils degenerated the hyphal morphology, resulting in exfoliated flakes and shrinkage, which were related to fungal membrane injury and collapse of vacuoles and phialide. The treatments, especially those with cinnamon oil, increased the electroconductivity, which suggested a weak mycelium membrane structure. Moreover, the treatments with essential oils reduced the ergosterol content in mycelia and the aflatoxin accumulation in the culture broth. The fumigations with clove and cinnamon oils inhibited the development of both conidia and colonies of A. flavus in dose-dependent manners.
Highlights
Maize (Zea mays L.) is an important food crop produced by smallholder farmers
An essential oil fumigation test with clove and cinnamon oils as antifungal products was performed on fungal conidial discs and fungal colonies in Petri plates
Within abnormal A. flavus hyphae, the essential oils degenerated the hyphal morphology, resulting in exfoliated flakes and shrinkage, which were related to fungal membrane injury and collapse of vacuoles and phialide
Summary
Maize (Zea mays L.) is an important food crop produced by smallholder farmers. The crop provides household food security through income generation. Harvested grain may contain storage fungi that cause spoilage during storage. The grain losses caused by storage fungi pose a significant constraint on household food security. Most of the postharvest processing in the food and feed industry focuses on the contaminants of storage fungi such as Aspergillus sp., Penicillium sp. Fungi produce aflatoxin B1 and aflatoxin B23-6 They can reduce the quality of human and animal health[7]. Controlling the moisture content helps to reduce the growth of spoilage fungi such as Aspergillus sp., Penicillium sp., Fusarium sp., and other postharvest fungi[8]. Fresh harvested grains with a moisture content of 23% were dried until they reached a lower limit of 13% before storage in a cabin. Delays in the dry grain process caused an increase in fungal contamination[9]
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