Air drying optimization of Saccharomyces cerevisiae through its water-glycerol dehydration properties

This study describes the different stages of optimization in an original drying process for yeasts, which allows the retrieval of dried samples of Saccharomyces cerevisiae CBS 1171 with maximum viability.

The process involves the addition of wheat flour to yeast pellets, followed by mixing and then air-drying in a fluidized bed dryer. The sensitivity to the osmotic stress was first studied in a water-glycerol solution and the observed results were then applied to the drying process. This study have shown that the yeast was quite resistant to osmotic stress and pointed out the existence of zones of sensitivity where viability dramatically decrease as function of final osmotic pressure and temperature of the treatment. Thus, for dehydration until low osmotic pressure (133 MPa, i.e. a(w) = 0.38) results have shown that viability was better when temperature of the treatment was less than 8 degrees C or higher than 25 degrees C. Moreover, kinetic of dehydration was found to greatly influence cells recovery.

These observations allowed the choice of parameters of dehydration of yeasts with an original drying process which involve the mix of the yeasts with wheat flour and then drying in a fluidized bed.

This process dried rapidly the yeasts to less than 220 MPa (aw < or = 0.2) with whole cell recovery and good fermentative capabilities.