Influence of pH conditions on the viability of Saccharomyces boulardii yeast

Saccharomyces boulardii is a probiotic with proven health benefits. However its survival is challenged by gastrointestinal transit, and a ratio between 1 and 3% of living yeast is recovered in the feces after oral administration. The aim of the study was to determine to what extent the yeast was sensitive to gastrointestinal pH conditions. Therefore we explored the survival of different concentrations of S. boulardii in conditions mimicking the stomach pH (pH 1.1 0.1 N HCI) and the intestinal pH (pH 6.8 phosphate buffer) in vitro. The probiotic being commercialized as a freeze-dried powder obtained from an aqueous suspension, both forms were evaluated. In phosphate buffer pH 6.8, the viability remained stable for both forms of S. boulardii for 6 h. In HCI pH 1.1, viability of both forms (200 mg L-1) significantly decreased from 5 min. Observation under scanning/transmission electron microscopy showed morphological damages and rupture of the yeast wall. Threshold value from which S. boulardii viability was unaltered was pH 4. At the highest concentration of 200 g L-1, the initial pH value of 1.1 rose to 3.2, exerting a protective effect. In conclusion, although the yeast in aqueous suspension was less sensitive than the freeze-dried yeast to acidic conditions, a gastric protection for improvement of oral bioavailability of viable S. boulardii appears necessary.