The Effect of Preconditioning Cells under Osmotic Stress on High Alcohol Production

This paper focuses on the research into the influence of salt on physiology of the yeast, Saccharomyces cerevisiae. Specifically, the work focused on how NaCl affected the growth, viability and fermentation performance of this yeast in laboratoryscale experiments. One of the main findings of the research presented involved the influence of salt “preconditioning” of yeasts which represents a method of pre-culturing of cells in the presence of salt in an attempt to improve subsequent fermentation performance. Such an approach resulted in preconditioned yeasts having an improved capability to ferment high-sugar containing media (up to 60% w/v of glucose) with increased cell viability and with increased levels of produced ethanol (higher than 20% in vol.). Salt-preconditioning was most likely influencing the stress-tolerance of yeasts by inducing the synthesis of key metabolites such as trehalose and glycerol which act to improve cells’ ability to withstand osmostress and ethanol toxicity. The industrial-scale trials using salt-preconditioned yeasts verified the benefit of the physiological engineering approach to practical fermentations. Overall, this research has demonstrated that a relatively simple method designed to adapt yeast cells physiologically – by salt-preconditioning – can have distinct advantages for alcohol fermentation processes.