The effect of some species of yeasts on reduction of aflatoxin B1 of Aspergillus flavus in simulated model of human stomach

AFB1 is a highly carcinogenic secondary metabolite of some species of Aspergillus. Recently, use of microorganisms has been increased to reduce the absorption of mycotoxins in gastrointestinal tract. So, in this study the effect of the three yeasts Saccharomyces cerevisiae, Pichia fermentans, and Rhodotorula mucilaginosa on reduction of AFB1 in a simulated model of human stomach was investigated.

At first, A. flavus was isolated and then were purified. Then, AFB1 was produced in PDB media and presence of AFB1 was determined by blue fluorescence radiation under UV light. Toxin was extracted using the method of solvation in chloroform and injected into HPLC and the final concentration was 49 ng/ml. The simulated stomach was contaminated with 0.1 ml samples of AFB1 of three concentrations: 0.25 ng/ml and 0.50 ng/ml from standard AFB1 and also 49 ng/ml from the A. flavus under study. Then the yeasts were added and the mixture was incubated. After sampling at 0 and 120 minutes, the samples were centrifuged. The supernatants were separated to determine the concentration of residual toxin by direct competitive ELISA method. The experiment was conducted in a completely randomized design with a factorial experiment. The three factors included yeast (four levels: three yeasts and non-yeast treatments), concentration (four levels: 0, 0.25, 0.50 and 0.49 ng/ml) and time (two levels: 0 and 120 min). The whole experiment was carried out 3 times.

The results showed that all three yeasts had the ability to reduce the toxin in the stomach compared to the control treatment (without yeast), but the effect of R.mucilaginosa was more significant than the other two. The lowest toxin concentration in supernatant was observed at 0.25 ng/ml. Over time, toxin concentration in supernatant decreased. The interaction of yeasts and toxin concentration showed that in comparison with the control, at each three concentrations, all three yeasts could reduce toxin concentration. The minimum toxin concentration in supernatant was obtained at 0.25 ng/ml in the presence of R.mucilaginosa. The results of interaction of yeast×time showed that after both 0 and 120 minutes, all three yeasts were able to reduce the toxin and the minimum toxin concentration was observed after 120 minutes for R.mucilaginosa. The results of interaction of time and toxin concentration in the model showed that at 0.25 ng/ml toxin concentration was at the lowest level after 120 minutes. The results of interaction of yeast×time×toxin concentration showed that the lowest toxin concentration was related to R.mucilaginosa after 120 minutes at 0.25 ng/ml. To conclude, the results of this study showed that all three yeasts had the ability to reduce AFB1 in the simulated model of human stomach, but R.mucilaginosa can be introduced as the most efficient isolate in biocontrol of AFB1.