Effects of zinc chelating nutrients on Aflatoxin production in Aspergillus flavus

Aflatoxins are carcinogenic metabolites produced by Aspergillus and Penicillium spp. Aflatoxin contamination of food is a serious health hazard. Some metal ions (such as Zn2+) affect Aspergillus growth and aflatoxin biosynthesis. Presence of zinc in the growth medium incites aflatoxin production. This study investigates the effect of zinc binding amino acids and peptides on aflatoxin synthesis in indigenous toxigenic Aspergillus species isolated from agro-ecological zones in Northern Iran. Zinc (II) chelating nutrients (such as Histidine (His), Cysteine (Cys), Histidine-Cysteine (His-Cys), and triple peptide (Asn-Cys-Ser) were added to the growth medium of toxigenic Aspergillus isolates and incubated at temperature range of 25–40 °C. Aflatoxin production on different culture media was tested using ELISA. Addition of cysteine to Sabouraud dextrose broth (SDB) medium significantly reduced aflatoxin production, which could be related to its zinc chelating property. Aflatoxin production was drastically restrained at high concentration of His, especially in combination with Cys, at high pH values and incubation temperature (pH = 7.5, temperature = 40 °C). Aflatoxin production was low in presence of triple peptide (Asn-Cys-Ser) at concentration of 500 mg/L. From the application perspective, natural zinc chelators can be used as harmless aflatoxin-production inhibitors.