Evaluating the impace of yeast co-operation on individual yeast metabolism and wine consumption
University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology
Du Toit, M
Bauer, F F
Jolly, N P
The dynamics of the microbial populations during winemaking has been studied for several decades. Traditional microbiology techniques together with the more recent aid of molecular techniques, has shown that the microbial diversity of grape juice is by far the greatest and diminishes throughout the vinification progress. Saccharomyces cerevisiae has long been identified as the main contributor to alcoholic fermentation. Indeed, this species quickly out competes the other yeasts. These non-Saccharomyces yeasts have hence been regarded as either detrimental or unnecessary to the production of high quality wines, because of their metabolisms leading to unwanted compounds (acetic acid, ethyl acetate, acetaldehyde, etc.) or their slow and limited fermentative capabilities respectively. The strains selected to be used as starter cultures therefore all belonged to the species Saccharomyces sensu stricto. The main selection criterion was initially their high fermentation performance in terms of efficiency and therefore of time while other criteria such as their ability to out compete the other species and strains and to confer positive sensorial attributes to wine were later considered as equality important.
It was always believed that non-Saccharomyces yeasts, metabolically active in the first stages of fermentation, played a non-negligible role on wine composition. Furthermore, the strong fermentative abilities and/or the extracellular enzymatic activities of some of these species could be exploited to generate more complex wines. In recent years, the following species have received greater attention from the wine industry: Starmerella bombicola (formerly known as Candida stellata), Lachancea thermotolerans (formerly known as Kluyveromyces thermotolerans), Torulaspora delbrueckii and Metschnikowia pulcherrima. The first three species indeed display relatively strong fermentative abilities with peculiar primary metabolisms. , S. bombicola is fructophilic and produces more glycerol and succinic acid and T. delbrueckii less acetic acid than Saccharomyces cerevisiae. M. pulcherrima, known for secreting several enzymes active under winemaking conditions, has been shown to produce wines of enhanced quality when co-inoculated with Saccharomyces cerevisiae, in comparison to the same wines produced by a pure Saccharomyces cerevisiae culture. Pure inoculation of non-Saccharomyces species in grape juice is likely to lead to stuck fermentations and/or to the formation of undesired compounds. Multi-starter cultures are therefore strongly envisaged and, in some cases, already available on the market.
If the impact of these non-Saccharomyces yeasts on the organoleptic quality of wines has been assessed, the interactions between the different yeast species, when co-inoculated, have never been assessed on a molecular level. In particular, the impact of the presence of non-Saccharomyces yeast, inoculated at high cell density, on S. cerevisiae has not been investigated. This study aims at unravelling how the presence of another species in high cell density impacts on the metabolism of Saccharomyces cerevisiae and ultimately on wine composition. This will allow predicting the outcome of a mixed fermentation, depending on grape juice composition, on the interacting species/strains and on the cell density at inoculation time. Other parameters, such as oxygen and nitrogen availability, will also be considered.
To achieve this goal, a membrane bioreactor will be used. The equipment allows separating the two species studied while the medium diffuses freely between the two compartments through the membrane. The equipment is available at the INP-ENSIACET, Toulouse, France and collaboration with Prof Taillandier is therefore proposed that during the first year of this project, a student will be sent to the INP-ENSIACET to be trained using the equipment. Thereafter, the equipment could be purchased and the remainder of the project carried out at the IWBT.
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Divol, B, Mains, A O, Mostert, T T and Bauer, F F. 2013. Specific wine yeast interactions revealed by metabolomic and proteomic approaches. Paper presented at the 18th Conference of the South African Society for Microbiology. 24-27 November, Warmbaths, South Africa.
Divol, B, Mains, A O and Bauer, F F. 2013. Multispecies yeast starter cultures and their impact on fermentation kinetics and outcomes. Paper presented at the 35th South African Society for Enology and Viticulture Conference. 13-15 November, Somerset West, South Africa.
De Kock, M C, Bauer, F F and Divol, B. 2014. Response to osmotic stress in mixed culture of Saccharomyces and non-Saccharomyces yeasts under enological conditions. Paper presented at the 36th South African Society for Enology and Viticulture Conference. 12-14 November, Somerset West, South Africa.
Luyt, N, Bauer, F F, Beaufort, S, Fernandez-Lopez, C L, Brandam, C, Divol, B and Taillandier, P. 2015. Comparison of direct and indirect contact during interactions between Saccharomyces and non Saccharomyces yeasts. Paper presented at the Oeno 2015: 10th Symposium of Oenology at Bordeaux, 29 June – 1 July 2015.
Divol, B, Bauer, F F. 2015. Wynmakers kan die aromatiese profiel van wyn met behuip van verskeie gisspesies in die beginnerkulture verander, WineLand, Mnth Nov (p. 115-118)