Thesis (MSc)--Stellenbosch University, 2003. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: Traditionally, wine has been produced by the spontaneous fermentation of grape
juice by yeast that originate from the grapes and winery equipment. Research has
shown that the population composition and dynamics of these yeasts and other
microorganisms are very complex. Kloeckera and its anamorph, Hanseniaspora,
dominate the yeast population found on the surfaces of grapes, although prevailing
Saccharomyces cerevisiae strains complete the fermentation process.
The yeast S. cerevisiae is an important factor contributing to the quality of wines
and, therefore, the improvement of wine yeasts receives considerable attention
worldwide. Apart from classical yeast breeding studies, genetic engineering and
recombinant DNA techniques are increasingly being used in strain development
research programmes. These techniques might enable the wine yeasts to produce
heterologous enzymes that degrade polysaccharides, convert malic acid to lactic
acid, increase glycerol production, release roam and flavour compounds, secrete
antimicrobial peptides, etc. The release of recombinant yeast strains (genetically
modified organisms, GMOs) is subject to statutory approval. Therefore, it is important
to answer several questions prior to the use of such genetically improved yeast in the
commercial production of wine. For example, will recombinant yeast strains be able
to multiply and spread in nature, and will this GMO be able to out-compete the
natural microflora because of its newly acquired genetic traits. Since existing
commercial wine yeasts are used in the abovementioned strain development
research, it is essential to determine already at this early stage to what extent these
wine yeast strains survive and spread in nature and to what extent they influence the
fermentations of the following vintages.
This study is divided into two sections. The aim of the first section is to sample a
representative number of yeast strains from various vineyards in different
climatological areas, mainly in the Western Cape, South Africa. These yeast strains
were identified mainly by electrophoretic karyotyping (contour-clamped homogenous
electric field electrophoresis; CHEF).
The second part of the study summarises the results obtained when Fourier
transform infrared (FT-NIR) spectroscopy was used to differentiate commercial wine
yeast strains. Sets of data, containing the spectra of the mostly used commercial
wine yeast strains, were constructed and used as a reference library. The spectra of
the isolated yeast strains were then compared to the reference dataset with specific
FT-NIR computer software using mathematical calculations.
In conclusion, the two methods used in conjunction with one another proved that
the commercial wine yeast strains do not easily disperse from the cellar into the
vineyard. The commercial wine yeast strains are also more likely to be found near
the cellar and the places where the grape skins are dumped. Therefore, should a
recombinant yeast strain be used in winemaking, it would not be dispersed into the
vineyard. It therefore appears that the commercial use of genetically improved yeast does not pose a high risk in terms of dominance of the indigenous microbial
population in the environment / AFRIKAANSE OPSOMMING: Wyn is tradisioneel gemaak deur die natuurlike gisting van druiwesap deur giste wat
op die druiwe en keldertoerusting voorkom. Navorsing het getoon dat die
samestelling en dinamika van die gispopulasie en ander mikro-organismes baie
kompleks is. Kloeckera en sy anamorf, Hanseniaspora, domineer die inheemse
gispopulasie op druiwedoppe, terwyl Saccharomyces cerevisiae in baie klein getalle
op die druiwedoppe voorkom, maar later die fermentasie oorheers en uiteindelik
voltooi.
Die gis S. cerevisiae speel 'n baie belangrike rol in die kwaliteit van wyn en
daarom geniet die verbetering van wyngiste wêreldwyd besondere aandag.
Benewens die klassieke gistelingstudies, word genetiese manipuleringstegnieke
toenemnd in navorsingsprojekte gebruik wat daarop gefokus is om wyngisrasse te
verbeter. Hierdie tegnieke mag die giste in staat stelom heteroloë ensieme te
produseer wat polisakkariedes afbreek, appelmelksuur afbreek, gliserolproduksie
verhoog, smaak- en geurkomponente vrystel, antimikrobiese peptiede afskei, ens.
Voordat sulke geneties gemanipuleerde giste het egter in kommersiële wynproduksie
gebruik sal kan word, is daar heelwat wetlike vereistes waaraan voldoen sal moet
word en vrae wat vooraf beantwoord sal moet word. Byvoorbeeld, sal die
rekombinante giste in staat wees om vinniger te vermeerder as gevolg van die nuwe
genetiese eienskappe en sodoende die natuurlike populasies onderdruk? Omdat
kommersiële wyngiste in bogenoemde gisverbeteringprogramme gebruik word, is dit
noodsaaklik om nou reeds die verspreiding van die kommersiële giste te monitor en
te bepaal hoe geredelik hulle in die natuur kan versprei en oorleef, en hoe hulle
wynfermentasies van die daaropvolgende jare beïnvloed.
Die studie is in twee gedeeltes verdeel. Die doel van die eerste gedeelte was om
'n verteenwoordigende aantal gisrasse uit die wingerde van 'n aantal wynplase in
verskillende klimaatstreke te isoleer, spesifiek in die Wes-Kaap, Suid-Afrika. Die
gisrasse was grotendeels deur elektroforetiese kariotipering (kontoer-geklampte
homogene elektriese veld; CHEF) geïdentifiseer.
Die tweede deel van die navorsing was gefokus op die onderskeiding tussen die
mees gebruikte kommersiële wyngiste met 'Fourier-Transform Near Infrared' (FTNIR)
spektroskopie. Eerstens is 'n stel data, bestaande uit die spektrum data oor die
kommersiële wyngiste opgestel om as 'n verwysingsbiblioteek te dien. Tweedens is
die spektrum van data oor die geïsoleerde giste onder presies dieselfde toestande
met die verwysingsbiblioteek vergelyk. Dié tegniek maak dit moontlik om tussen die
kommersiële wyngiste te onderskei.
As die twee metodes saam gebruik word vir identifikasie, kan die afleiding
gemaak word dat kommersiële wyngiste nie maklik vanaf die kelder na die wingerd
versprei nie. Die kommersiële wyngiste is ook meestal naby die kelder en die
dopstortingsterreine gevind. Sou 'n rekombinante gisras dus gebruik word om wyn te maak, sal dit nie maklik versprei nie. Die kommersiële gebruik van geneties
gemanipuleerde wyngiste behoort dus nie In groot omgewingsrisiko in te hou nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53505 |
| Date | 12 1900 |
| Creators | Muller, Christo A. |
| Contributors | Pretorius, I. S., Lambrechts, M. G., Van Rensburg, P., Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 78 pages : illustrations |
| Rights | Stellenbosch University |
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