Fermentation, Metabolic Flux and Biomass Formation: Balancing the Major Products of Fermentative Metabolism to Reduce Ethanol and Volatile Acidity Formation

Project Number
IWBT Y 11-04

Project title
Fermentation, metabolic flux and biomass formation: Balancing the major products of fermentative metabolism to reduce ethanol and volatile acidity formation

Project leader
Bauer, F F

University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology

Team members
Fairbairn, S

Project description
The project proposes the development of tools to control the flux towards the quantitatively most important carbon compounds produced during fermentation, including ethanol, glycerol, acetic and succinic acid, ethyl acetate and storage carbohydrates, as well as biomass. Excessive levels of ethanol, as well as frequent problems regarding the control of volatile acidity, continue to present major challenges to the South African and global wine industry. Previous attempts to rebalance the carbon metabolic flux away from ethanol towards other products (without using tools of genetic modification) and without increasing acetic acid and / or volatile acidity formation have largely failed. Our data suggest that the main reason for this failure the past assumption that carbon metabolite production is primarily a function of the intrinsic genetic properties of an individual yeast strains. As a consequence, projects focused on and attempted to generate strains with lower ethanol yields by modifying the genetic blueprint of individual strains through breeding, selection or genetic modification. Our data suggests that this is in fact the wrong strategy, since individual yeast strains may be low producers in one condition, and turn to become high ethanol or volatile acidity producers in another. Different yeast strains respond differently to environmental circumstances and to differences in grape must composition, and ethanol yield is only partly a result of intrinsic genetic properties of yeast strains.

The project will address the question of ethanol yield holistically by investigating relevant molecular regulatory circuits and their response to those environmental parameters that can be controlled during the winemaking process. The project will identify specific yeast strains that can be used to reduce ethanol yields in specific musts and result in specific guidelines on how to reduce ethanol and the yield of other unwanted by-products of carbon metabolism, in particular of acetic acid, from high sugar grape musts.

Rossouw, D, Heyns, E H, Setati, M E, Bosch, S, Bauer, F F. 2013. Adjustment of trehalose metabolism in wine Saccharomyces cerevisiae strains to modify ethanol yields, Applied and Environmental Microbiology, Mnth Sep v. 79 (17) (p. 5197-5207)

Rossouw, D, Bauer, F F. 2016. Exploring the phenotypic space of non-Saccharomyces wine yeast biodiversity. Food Microbiology, Mnth May v. 55 (p. 32-46)

Bauer, F F, Rossouw, D, Franken, J. 2013. Finding novel carbon sinks in S. cerevisiae, IN: Proceedings of the 1st International Symposium on Alcohol Level Reduction in Wine. 6 September 2013, Bordeaux, France. (p. 38-48)


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