Influence of sub-lethal antioxidant doses, water potential and temperature on growth, sclerotia, aflatoxins and aflD (=nor-1) expression by Aspergillus flavus RCP08108

Effects of interacting conditions of sub-lethal levels of antioxidants, water potential ( ) and temperature were evaluated on growth, sclerotial characteristics, aflatoxin B1 (AFB1) production and aflD (=nor-1) gene expression by Aspergillus flavus strain RCP08108. These studies were carried out on peanut meal extract agar osmotically modified to -2.8,-7.1, -9.9 and -16.0 MPa and incubated at 28 and 20 oC. The food grade antioxidants added were butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) at (1 + 1 mM - M1) and (5 + 5 mM - M2). To relate the aflD expression after toxigenic A. flavus grew under interacting stress conditions, real-time PCR was used. Antioxidant mixtures caused a higher and significant (p < 0.001) reduction in growth rate. The major impact on size and volume sclerotia was produced by ; followed by antioxidant mixtures. High AFB1 levels were observed in response to the M1 applied at -7.1 MPa. Induction of the aflD gene was observed in response to the M1 treatment at -2.8, -7.1 and -9.9 MPa; but significant decreases of AFB1 production and aflD transcripts were observed; when the fungus grew in the presence of the M2 treatment. These results showed that it is necessary to apply food-grade antioxidants into the peanut storage system at levels higher than 5 mM. This is an important tool to avoid sub-lethal antioxidant doses that can lead to fungal growth, increase resistance structures, and stimulate aflD gene expression and AFB1 accumulation in this substrate.