Thesis (PhDAgric (Viticulture and Oenology. Wine Biotechnology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Stuck alcoholic fermentations are a major enological problem for the international
winemaking industry. Incomplete wine fermentations are frequently characterized by high
residual fructose concentrations and the near-absence of residual glucose, a fact that is due to
the glucophilic character of the wine yeast Saccharomyces cerevisiae. Wines with high contents
of post fermentation sugar are very susceptible for microbial spoilage since residual fructose
and/or glucose can be metabolized by bacteria and yeast to undesired by-products such as
volatile acid and off-flavours, resulting in wine spoilage and considerable economic losses. It
has been reported that stuck fermentations are usually caused by several synergistically acting
inhibition factors, and the glucose to fructose ratio (GFR) is thought to play an important role in
this context. This study is aimed at contributing towards a better understanding of this industrial
problem, and at finding industrially applicable solutions.
In a first part, this study describes the isolation of two appropriate strains of the
fructophilic yeast Zygosaccharomyces bailii from the natural microflora of grapevine, followed by
trials in small scale test fermentations using stuck industrial fermentations as model media.
These experiments were expanded to also investigate large scale industrial fermentations. As a
result, a strategy for the treatment of stuck fermentations was developed and successfully
applied in several wineries with fermentation problems. This methodology represents an entirely
novel and industrially applicable solution to high residual fructose levels.
In a second part, the data contributes to elucidating the molecular nature of the
fructophilic phenotype of Z. bailii by characterizing some of the genes and proteins that may be
responsible for the fructophilic character. In particular, the investigation focused on the first two
steps of hexose metabolism, the transport of sugar into the cell by permeases and sugar
phosphorylation by hexokinases, which combined are thought to be primarily responsible for
sugar preference.
One result of this study was Fructoferm W3©, a dry yeast product which is commercially
available. Fructoferm W3 was awarded with the innovation medal for enological products at
Intervitis/Interfructa, Stuttgart, Germany in 2007. / AFRIKAANSE OPSOMMING: Die voorkoms van steek alkoholiese fermentasies is ‘n ernstige problem in die internasionale
wyn industrie. Onvolledige fermentasies word dikwels gekenmerk deur hoë residuele fruktose
konsentrasies en die veitlike afwesigheid van residuele glukose. Die kenmerke kan meestal
toegeskryf word aan die glukofilliese kakakter van die wyngis Saccharomyces cerevisiae. Wyne
met ‘n hoë suiker inhoud na die afloop van fermentasie is vatbaar vir mikrobiese bederf
aangesien residuele fruktose en/of glukose gemetaboliseer kan word deur bakterië en gis om
ongewenste byprodukte soos vlugtige sure en bygeure te vorm wat kan lei tot wyn bederf en
aansienlike ekonomies verlies. Dit is vasgestel dat steek fermentasies gewoonlik veroorsaak
word deur verskeie sinergisties werkende inhibisie faktore, waartoe die glukose/fruktose
verhouding ‘n noemenswaardiege bydrae lewer. Die mikpunt van hierdie studie was om ‘n
bydrae te lewer tot die begrip van steek fermentasies en die daarstelling van moontlike
industriële oplossings.
Die eerste deel van die werk beskryf die isolasie van twee rasse van die gis
Zygosaccharomyces baillie uit die natuurlike wingerd mikroflora, gevolg deur steekproewe in die
vorm van kelinskaalse fermentasies met steek industriële fermentasies gebruik as model media.
Hierdie ekserimente is vervolgens uitgebrei om grootskaalse industriële steek fermentasies te
bestudeer. Die uitkoms van hierdie werk het gelei tot die ontwikkeling van ‘n strategie vir die
behandeling van steek fermentasies wat susksesvol toegepas is in verskeie wynmakerye. Die
metodiek bring ‘n nuwe en industrieel toepasbare oplossing vir hoë residuele fruktose vlakke.
Die data aangebied in die tweede afdeling dra by tot die verheldering van die molekulêre natuur
van die fruktofilliese fenotipe van Z. baillie deur die tipering van gene en protiëne wat moontlik
verantwoordelik is vir die fruktofilliese karakter van die gis. Die ondersoek het spesifiek op die
eerste twee stappe van heksose metabolisme, naamlik die invoer van suiker in die sel deur
permeases en suiker fosforilering deur heksokinases, gekonsentreer. Die kombinasie van die
twee prosesse is vermoedelik verantwoordelik vir die regulering van suiker voorkeur.
‘n Gevolg van die studie was die ontwikkeling van ‘n droë gisproduk, Fructferm W3©, wat
kommersieel beskikbaar gestel is. Fructoferm W3 is in 2007 toegeken met die innovasie
medalje vir wynkundige produkte by Intervittis/Interfructa in Stuttgart, Duitsland.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4013 |
| Date | 03 1900 |
| Creators | Sutterlin, Klaus A. (Klaus Alfred) |
| Contributors | Bauer, Florian, Gafner, Jurg, University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 186 p. : ill. |
| Rights | University of Stellenbosch |
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