Viability and thermal stability of a strain of Saccharomyces cerevisiae freeze-dried in different sugar and polymer matrices

Abstract

The viability and thermal stability of a freeze-dried yeast strain were studied in relation to some physical properties of the matrices in which the cells were freeze-dried. Samples of inoculum with solutions of the matrix components [polyvinylpyrrolidone (PVP), maltose, trehalose, maltodextrins, or mixtures of maltodextrin and trehalose] and controls without matrices were freeze-dried and then equilibrated at several relative humidities. Viability was determined before and after freeze-drying and after heat treatment (100 min at 70 degrees C). Freeze-drying with trehalose, PVP, maltose or 1.8-kDa maltodextrin, and mixtures of maltodextrin/trehalose increased viability in comparison with controls. The 3.6-kDa maltodextrin was ineffective at protecting the cells during freeze-drying. The glass transition temperature (Tg), which depends on moisture content, was indicated as a possible factor to determine the stability of labile materials. Protective effects of the excipients during thermal treatment were analysed in relation to the physical changes (collapse or structural shrinkage) which were dependent on the Tg of the systems. The presence of a certain amount of amorphous disaccharides during freeze-drying and heating was found to be a critical factor for ensuring cell viability, which was protected even in rubbery (above Tg) matrices.

Trehalose synthesis is induced upon exposure of Escherichia coli to cold and is essential for viability at low temperatures

“…Another possible protective role for trehalose at 4°C may be in stabilizing cell membranes, whose fluidity decreases during temperature downshift. It is noteworthy that exogenous trehalose helps protect a variety of organisms against freezing (17,52), and that the maximal protection is seen when trehalose is present on both sides of the cell membrane (16,17). Possibly trehalose enhances viability at low temperatures by multiple mechanisms, including ones distinct from those proposed above.…”

Microencapsulation of curcumin in cells of Saccharomyces cerevisiae

“…As mentioned above, T m depends on the moisture content of the system and on the phospholipids' composition/ structure (Laroche & Gervais, 2003). An independent measurement of the moisture content of our freeze-dried yeast cells by the ovendrying method (Lodato, Segovia de Huergo, & Buera, 1999) gave 3.2 ± 0.2% w/w water on dry basis, similar to that of Normand et al (2005) (3.8 ± 0.2% w/w). Therefore, the observed differences considering T m of empty cells are due to the different strain of S. cerevisiae used, to different growth conditions of cells (aeration, temperature, growth medium) or in the stage of growth phase where yeast cells were harvested.…”

Effect of protective agents on the viability of Lactococcus lactis subjected to freeze-thawing and freeze-drying

“…The combined damage caused by freeze-drying can be attributed to two primary causes: changes in the physical state of the membrane lipids and protein damage or proteind enaturation [ 6,11]. As wateri sr emoved from theb iomembrane,t he headgroups of thel ipidsa re broughtc losert ogethera nd this results in increased van der Waals interaction between the acyl chains.…”

“…To protect bacteria from these negative effects, protective agents are commonly addedpriortofreezing or freeze-drying [6,7,8,9,10,11,12,13,14,15,16,17]. However, the protection afforded by agivenadditive depends on the species of microorganism.…”