Physicochemical differences in dehydrated Saccharomyces boulardii yeast asa function of the dehydration process

Measurements of the masses of incorporated water and of the heats of hydrat ion have been performed at 310 K, under air atmosphere saturated with water vapour, on three differently dehydrated samples of the Saccharomyces boula rdiiyeast in order to evaluate differences in physicochemical properties re lated to the following dehydration processes: cryodesiccation (or lyophiliz ation) and thermodesiccation (spray drying and in-fluidized-bed heating). Thermogravimetric (TG) experiments have shown that the lyophilized yeast co ntains less residual water than heat-treated yeasts and that it incorporate s more water and more rapidly. Isothermal water sorption of a spherical yea st cell has been represented by a two-parameter equation able to take accou nt of a maximum of the hydration rate when this is taken as a function of t ime. On the other hand, isothermal DSC experiments have shown that hydratio n-heat values are higher for the heat-treated yeasts than for the lyophiliz ed one. The TG and DSC results have been shown to be consistent with the id ea that the physicochemical properties of a dehydrated yeast are related to cell-wall behaviour during desiccation.