Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The use of non-Saccharomyces yeasts together with Saccharomyces cerevisiae in mixed
starter cultures has become an accepted oenological tool to enhance the organoleptic
properties of wine. Recent studies have indeed demonstrated the positive contribution that non-
Saccharomyces yeasts may have on the bouquet of wine. These mixed starter cultures are
characterized by high inoculation levels of individual strains into the must, and each strain in
turn is characterized by its own specific metabolic activity. These factors lead to a multitude of
interactions occurring between the individual populations within the must. The fundamental
mechanisms which drive these interactions are still largely unknown, but several studies have
been conducted in order to investigate the metabolic outcome of these interactions. In this
study, we endeavour to further characterize the interactions which occur between four individual
non-Saccharomyces yeast strains in mixed culture fermentation with S. cerevisiae. Metschnikowia pulcherrima IWBT Y1337, Lachancea thermotolerans IWBT Y1240, Issatchenkia
orientalis Y1161 and Torulaspora delbrueckii CRBO LO544 were used in mixed culture
fermentations with a commercial strain of S. cerevisiae at an inoculation ratio of 10:1 (non-Saccharomyces: S. cerevisiae). The biomass evolution and fermentation kinetics of both
participating species were affected by the high cell density of the other, with neither population
reaching the maximal density attained by the pure culture fermentation. The final wine
composition of each individual mixed fermentation showed clear differences, from the pure
cultured S. cerevisiae and from each other, based on the concentrations of the major volatile
compounds found in the wine. Upon further characterization of these specific mixed culture
fermentations, it was found that each individual combination of non-Saccharomyces and S.
cerevisiae produced similar increases and decreases of certain major volatile compounds as
demonstrated by previous authors, using the same combination of non-Saccharomyces species
together with S. cerevisiae. From a winemaking perspective, the use of these non-
Saccharomyces yeast strains in combination with S. cerevisiae could be a useful strategy to
diversify the chemical composition of wine, by increasing the concentration of certain desirable
volatile compounds and by modulating the concentration of undesirable metabolites.
Furthermore, this research serves as a foundation for further elucidation of the interactions
which drive these metabolic outcomes in response to the high cell density of two yeast
populations in mixed culture fermentations.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96062 |
| Date | 12 1900 |
| Creators | Mains, Arlene Olive |
| Contributors | Bauer, Florian F., Divol, Benoit, Stellenbosch University. Faculty of AgriSciences. Dept. of Institute for Wine Biotechnology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 72 p. : ill. |
| Rights | Stellenbosch University |
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