Pre-storage treatments for suppressing of aflatoxins production in wheat grains

Wheat grains were collected from various locations in six governorates of Egypt and subjected to isolation trials. The isolated fungi were identified as Aspergillus spp. followed by Alternaria spp., Fusarium spp., Rhizopus spp. and other unidentified fungi, in that respective order. All isolated A. flavus strains (16 isolates) were screened for their ability to produce aflatoxins (AFs) on synthetic medium under long (365 nm wavelength) UV irradiation to determine their mycotoxin production capabilities. Data revealed that seven toxigenic isolates of A. flavus exhibited high fluorescent color. A preliminary test using TLC technique detected high production of aflatoxins by A. flavus isolates 2, 3, 4 and 6. The concentrations of AFs produced by positive A. flavus strains were determined using high-performance liquid chromatography (HPLC), to confirm high production of AFs by the 4 isolates. The A. flavus strain with the highest AFs production was selected for further studies. In laboratory conditions, the inhibitory effects of various organic acids, salts and essential oils were evaluated against the linear growth of A. flavus. Results indicated complete inhibition (100%) of fungal growth at 1.0% concentrations of malic acid, potassium sorbate, thyme and carnation oils. The production of aflatoxins in stored wheat grains treated with different concentrations of essential oils, organic acids and salts was studied over 45-day period. Untreated stored wheat grains showed high concentrations of AFG₁, AFG₂, AFB₁ and AFB₂ produced by A. flavus compared to grains treated with essential oils (thyme and carnation), malic acid and potassium sorbate. It was observed that all types of produced AFs gradually decreased with increasing concentrations of oil, acid or salt reaching their minimum levels at the highest concentration used (8%). The data demonstrated that the lowest aflatoxin production was recorded in grains treated with 8% potassium sorbate.