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 HCl) 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 HCl 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.

Formulations for protecting the probiotic Saccharomyces boulardii from degradation in acidic condition.

Saccharomyces boulardii is a nonpathogenic yeast with proven health benefits, some of them depending on its viability. However, the living yeast is sensitive to environmental conditions and its viability is less than 1% in the faeces after oral administration. Therefore, we assessed the survival conditions of S. boulardii in aqueous suspension and in its freeze-dried form and we formulated microspheres with the former and tablets with the latter in order to preserve the viability of the probiotic. While the viability of the yeast in aqueous suspension could be maintained for one year at -20 degrees C and +5 degrees C, increasing the temperature led to almost total mortality within 14 d at +40 degrees C and 4 d at +60 degrees C. The viability of the freeze-dried yeast was preserved for one year at +25 degrees C without moisture. With 75% relative humidity, the mortality was significant at 28 d at +25 degrees C and almost total within 1 d at +60 degrees C. In vitro, whereas less than 1% of non-encapsulated or non-tabletted S. boulardii survived after 120 min at pH 1.1, both formulations in microspheres and direct compression enabled to protect the yeast from degradation in HCl and to release it viable at pH 6.8. However, despite a similar release profile from both dosage forms, the compression led to a significant decrease in the viability of the freeze-dried yeast. In conclusion, although both formulations are efficient in protecting S. boulardii in acidic condition, microspheres provide a higher entrapment efficiency and a faster release of the viable probiotic in intestinal condition than matrix tablets.