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

Abstract

Aims: 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. Methods and Results: 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 ¼ 0AE38) results have shown that viability was better when temperature of the treatment was less than 8°C or higher than 25°C. Moreover, kinetic of dehydration was found to greatly influence cells recovery. Conclusions: 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. Significance and Impact of the Study: This process dried rapidly the yeasts to less than 220 MPa (aw £ 0AE2) with whole cell recovery and good fermentative capabilities.

Towards a maximal cell survival in convective thermal drying processes

“…This observation was later confirmed when the investigation was extended to food environment (Laroche, Fine, & Gervais, 2005). On the other hand, Mille et al (2005) suggested that after severe dehydration (which resulted in a reduced initial a w prior to drying), the drying temperature exhibited even greater importance to the maintenance of cell viability during the drying process. At the range of 8-25°C, microbial cells were mostly sensitive to the osmotic pressure arisen from dehydration during drying.…”

“…As to date, some studies have shown promising results, with a cell survival ratio higher than 80% after being convectively dried Mille et al, 2005;Oliveira et al, 2007;Reddy et al, 2009). Vacuum drying of Saccharomyces cerevisiae under optimized conditions was reported to result in a higher viability than freeze drying (Cerrutti, de Huergo, Galvagno, Schebor, & del Pilar Buera, 2000).…”

“…Reconstituted skim milk is another reputed carrier (or encapsulating agent) for spray drying process (Ananta, Volkert, & Knorr, 2005;Gardiner et al, 2000;Lian, Hsiao, & Chou, 2002). (4) Compared to spray drying, other drying processes with lower drying temperature and milder processing conditions allow enhanced survival of microorganisms (Bayrock & Ingledew, 1997a;Cerrutti et al, 2000;Mille et al, 2005;Tsaousi et al, 2008). (5) In spray drying process, the use of a higher outlet temperature, which is usually accompanied with lower final moisture content, gives increased death ratio of microorganisms (Boza, Barbin, & Scamparini, 2004;Elizondo & Labuza, 1974;Fu & Etzel, 1995;Johnson & Etzel, 1993).…”

“…To date, a number of drying approaches have been investigated for their feasibility as an alternative to the freeze drying process, with the aim of obtaining highly viable and long-term maintained microbial culture in the dry form. These approaches include spray drying (Corcoran, Ross, Fitzgerald, & Stanton, 2004;Gardiner et al, 2000;Reddy, Madhu, & Prapulla, 2009;Teixeira, Castro, Malcata, & Kirby, 1995), fluidized bed drying (Bayrock & Ingledew, 1997a;Mille, Girard, Beney, & Gervais, 2005;Strasser, Neureiter, Geppl, Braun, & Danner, 2009), vacuum drying (Santivarangkna, Kulozik, & Foerst, 2006;Tymczyszyn, del Rosario Diaz, Gomez-Zavaglia, & Disalvo, 2007a), thermal convective air-drying in an oven Friesen, Hill, Pugsley, Holloway, & Zimmerman, 2005;, tunnel drying (Alpas, Ozilgen, Bozoglu, & Katnas, 1996) and spouted-bed drying (Oliveira et al, 2007). The strains involved and some results obtained in these studies are summarized in Table 2.…”

Desiccation Tolerance of Adult Stem Cells in the Presence of Trehalose and Glycerol

“…Desiccation studies on E. coli and B. thuringiensis have supported the postulation that an increase in tolerance to drying appears to result from an ability of the sugars to lower the phase transition temperature of the membrane [11,12]. Sugars like trehalose and sucrose have also been shown to protect not only the membranes but also intracellular proteins during bacterial drying [13][14][15][16]. Desiccation tolerance of different cell types ranging from microbial pathogens of humans [17] to several varieties of plant species such as rice (Oryza sativa), wild rice (Zizania palustris) [18] and soybean [19] have also been studied and shown to be related to the production of saccharides in response to an external environmental stress.…”