Decontamination of aflatoxin B1 and mycocinogenic activity evaluation by using yeasts belonging to the complex Meyerozyma guilliermondii

Abstract

This study pursued understanding the modes of action by which yeast isolates belonging to the complex Meyerozyma guilliermondii affect AFB1 production by Aspergillus flavus. Isolates Y16 and Y25 were not able to produce killer toxins. However, whole cells and some cellular constituents were able to reduce AFB1 concentrations in different evaluated conditions. Cell-free supernatant of isolates decreased AFB1 levels in liquid medium. For this reason, the effect on ground maize grains was studied. The characterization of the cell-free supernatants and the optimization of the biological decontamination activity of the toxin were tested. The experimental design showed that the best conditions for the cellfree supernatant of yeast Y16 to produce a significant reduction of AFB1 were 39° C, pH 8 and the presence of Mg+. The cell-free supernatant of yeast Y25 was effective at 28° C, pH 5 and presence of Mg+. These results made us suppose a possible enzymatic effect in the reduction of AFB1. To determine whether the effect of the cell-free supernatant of the yeasts on the accumulation of AFB1 was attributable to a protein activity, they were subjected to heat inactivation and proteinase k treatment. No changes on the reduction of the toxin levels were detected. The toxin reduction doesn’t correspond to an enzymatic effect. The cell-free supernatant from the two yeast isolates added to ground maize grains were able to reduce the levels of AFB1 when the toxin was already present in the substrate. Characterization of cell-free supernatants and optimization of the biological decontamination activity of the toxin are necessary steps in the process of selecting a treatment applicable to stored maize.