This thesis concerns research into the influence of salt on physiology of the yeast, Saccharomyces cerevisiae
. Specifically, the work focused on how sodium chloride affected the growth, viability and fermentation performance in industrial (winemaking) strains of this yeast in both laboratory-scale and industrial-scale experiments. Comparative fermentations were also conducted with selected non-Saccharomyces
yeasts that are of relevance in enology. One of the main findings of the research presented involved the influence of salt "preconditioning” of yeasts which represents a method of pre-culturing 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 with increased cell viability and with elevated levels of produced ethanol. 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 winemaking fermentations. Benefits were also observed in a specialized fermentation system (WITY produced by the first letters of the words Wine, Immobilization, Tower, and Yeast) that utilized immobilized yeast. Overall, this research has demonstrated that a relatively simple method designed to physiologically adapt yeast cells - by salt-preconditioning - can have distinct advantages for alcohol fermentation processes.
|Date of Award||May 2009|
|Supervisor||Graeme Walker (Supervisor)|