Modelling the freezing response of baker’s yeast prestressed cells: a statistical approach

Abstract

Aims: To study the effect of prestress conditions on the freezing and thawing (FT) response of two baker’s yeast strains and the use of statistical analysis to optimize resistance to freezing. Methods and Results: Tolerance to FT of industrial strains of Saccharomyces cerevisiae was associated to their osmosensitivity and growth phase. Pretreatments with sublethal stresses [40°C, 0·5 mol l−1 NaCl, 1·0 mol l−1 sorbitol or 5% (v/v) ethanol] increased freeze tolerance. Temperature or hyperosmotic prestresses increased trehalose contents, nevertheless no clear correlation was found with improved FT tolerance. Plackett–Burman design and response surface methodology were applied to improve freeze tolerance of the more osmotolerant strain. Optimal prestress conditions found were: 0·779 mol l−1 NaCl, 0·693% (v/v) ethanol and 32·15°C. Conclusions: Ethanol, saline, osmotic or heat prestresses increased freezing tolerance of two phenotypically distinct baker’s yeast strains. A relationship among prestresses, survival and trehalose content was not clear. It was possible to statistically find optimal combined prestress conditions to increase FT tolerance of the osmotolerant strain. Significance and Impact of the Study: Statistically designed combination of prestress conditions that can be applied during the production of baker’s yeast could represent a useful tool to increase baker’s yeast FT resistance.

Improved robustness of an ethanologenic yeast strain through adaptive evolution in acetic acid is associated with its enzymatic antioxidant ability

“…Then, cells were washed three times with distilled water, centrifuged at 5000 g for 10 min and resuspended in 0·1 mol l −1 potassium phosphate buffer (pH 6·0) before being subjected to the following stress conditions: ethanol (10% v v −1 , 1 h), aliphatic acid (5 g l −1 acetic acid, 6 h, or 20 mmol l −1 formic acid, 30 min), temperature (42°C, 2 h), osmotic shock (3 mol l −1 sorbitol, 3 h), slow freeze‐thawing—two cycles for 24 h (Kronberg et al . ), saline treatment (1·5 mol l −1 NaCl, 4 h), phenolic acid (15 mmol l −1 gallic acid, 4 h) and oxidative stress (5 mmol l −1 H 2 O 2 , 1 h). After treatments, stressors were removed by washing with 0·1 mol l −1 potassium phosphate buffer (pH 6·0) and/or by ending the experiment in a water bath at 25°C.…”

Adaptive evolution of baker's yeast in a dough‐like environment enhances freeze and salinity tolerance

“…, 1988) or oxidative stress (Hermes‐Lima and Storey, 1993) appear to play important roles. Consequently, diverse strategies, including activation of cross‐protection mechanisms (Kronberg et al. , 2007) or pre‐loading of yeast cells with freeze‐protective molecules such as trehalose (Hirasawa et al.…”

“…Freezing is a complex and multifaceted stress, in which different stressors, such as osmotic (Wolfe and Bryant, 1999), mechanical (Morris et al, 1988) or oxidative stress (Hermes-Lima and Storey, 1993) appear to play important roles. Consequently, diverse strategies, including activation of cross-protection mechanisms (Kronberg et al, 2007) or pre-loading of yeast cells with freeze-protective molecules such as trehalose (Hirasawa et al, 2001) or glycerol (Myers and Attfield, 1999), have been proposed to increase freeze resistance of yeast cells in baking applications. However, physiological conditioning approaches do not solve the lack of intrinsic freeze resistance of yeast cells and their effects are rapidly lost at the onset of fermentation (Tanghe et al, 2003).…”