Adsorption of Zearalenone by β-d-Glucans in the Saccharomyces cerevisiae Cell Wall

Cell walls of yeasts and bacteria are able to complex with mycotoxins and limit their bioavailability in the digestive tract when these yeasts and bacteria are given as feed additives to animals. To identify the component(s) of the yeast cell wall and the chemical interaction(s) involved in complex formation with zearalenone, four strains of Saccharomyces cerevisiae differing in their cell wall glucan and mannan content were tested. Laboratory strains wt292, fks1, and mnn9 were compared with industrial S. cerevisiae strain sc1026. The complex-forming capacity of the yeast cell walls was determined in vitro by modelling the plots of amount of toxin bound versus amount of toxin added using Hill's model. A cooperative relationship between toxin and adsorbent was shown, and a correlation between the amount of β-d-glucans in cell walls and complex-forming efficacy was revealed (R2 = 0.889). Cell walls of strains wt292 and mnn9, which have higher levels of β-d-glucans, were able to complex larger amounts of zearalenone, with higher association constants and higher affinity rates than those of the fks1 and sc1026 strains. The high chitin content in strains mnn9 and fks1 increased the alkali insolubility of β-d-glucans from isolated cell walls and decreased the flexibility of these cell walls, which restricted access of zearalenone to the chemical sites of the β-d-glucans involved in complex formation. The strains with high chitin content thus had a lower complex-forming capacity than expected based on their β-d-glucans content. Cooperativity and the three-dimensional structure of β-d-glucans indicate that weak noncovalent bonds are involved in the complex-forming mechanisms associated with zearalenone. The chemical interactions between β-d-glucans and zearalenone are therefore more of an adsorption type than a binding type.