Alkali Extraction of β-d-Glucans from Saccharomyces cerevisiae Cell Wall and Study of Their Adsorptive Properties toward Zearalenone

The isolated cell wall of Saccharomyces cerevisiae has some capacity to adsorb zearalenone (affinity near 30%) and reduce the bioavailability of toxins in the digestive tract. The adsorption process was quantified in vitro, and the data obtained when plotted with Hill's equation indicated a cooperative process. The model showed that the adsorption capacity was related to the yeast cell wall composition. This work focused on the role of various β-d-glucan types in the efficacy of zearalenone adsorption by yeast cell wall and sought to elucidate some of the adsorption mechanisms. Zearalenone was mixed at 37 °C with a constant quantity of alkali-soluble or alkali-insoluble β-d-glucans isolated from yeast cell walls, and the amount of adsorbed zearalenone was measured. Given that the alkali solubility of β-d-glucans is a determining factor for their three-dimensional conformation and that the alkali-insoluble fraction had a greater affinity (up to 50%) than the alkali-soluble fraction (∼16%), it was concluded that the three-dimensional structure strongly influences the adsorption process. The alkali insolubility of β-d-glucans led to the formation of single and/or triple helices, which have been identified as the most favorable structures for zearalenone adsorption efficacy. The β(1,3)-d-glucan and β(1,6)-d-glucan compositions of the two alkali-extracted fractions and their involvement in the adsorption process are discussed. Keywords: Zearalenone; mycotoxins; yeast cell wall; alkali-soluble β-d-glucans; alkali-insoluble β-d-glucans; adsorption; cooperativity; detoxification