Dissertation (PhD)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The conversion of sugar into ethanol and carbon dioxide is a process that has been
intertwined with human culture and long as civilized man has existed. This fermentation
process has been dominated by the micro-organism Saccharomyces cerevisiae and from
providing ancient seafaring explorers of a non perishable beverage to equipping bakers
with a raising agent to turn flour into bread; this organism with its fermentative potential,
has formed an essential part of most societies.
In more recent times, many industries still rely on this basic principle. The
complexities and efficiencies of the conversion of sugar into its various fermentative byproducts
have been studied and optimised extensively to meet the specific demands of
industries. Depending on the raw material used as starting point, the major beneficiaries of
the useful characteristics have been alcoholic beverage producers (wine, beer, and
whiskey amongst others), bakers (bread leavening) and biofuel producers.
One of the obstacles in fermentation optimisation is the sugar consumption
preferences displayed by the organism used. S. cerevisiae can consume a wide variety of
sugars. Depending on the complexities of its structures, it shows a preference for the
simpler saccharides. The fermentation of certain more complex sugars is delayed and runs
the risk of being left residually after fermentation. Many of the crops utilised in
fermentation-based products contain large amounts of starch. During the starch
degradation process many different forms of sugars are made available for fermentation.
Improved fermentation of starch and its dextrin products would benefit the brewing,
whiskey, and biofuel industries. Most strains of Saccharomyces ferment glucose and
maltose, and partially ferment maltotriose, but are unable to utilise the larger dextrin
products of starch. This utilisation pattern is partly attributed to the ability of yeast cells to
transport the aforementioned mono-, di- and trisaccharides into the cytosol. The
inefficiency of maltotriose transport has been identified as the main cause for residual
maltotriose. The maltotriose transporting efficiency also varies between different
Saccharomyces strains.
By advancing the understanding of maltotriose transport in yeast, efforts can be
made to minimise incomplete fermentation. This aim can be reached by investigating the
existing transporters in the yeast cell membrane that show affinity for maltotriose. This
study focuses on optimising maltotriose transport through the comparison of the alpha
glucoside transporter obtained from different strains of Saccharomyces. Through specific
genetic manipulations the areas important for maltotriose transport could be identified and
characterised.
This study offers prospects for the development of yeast strains with improved maltose
and maltotriose uptake capabilities that, in turn, could increase the overall fermentation
efficiencies in the beer, whiskey, and biofuel industries. / AFRIKAANSE OPSOMMING: Die transformasie van suiker na etanol en koolstof dioksied is so oud soos die beskawing self, en dit is van die vroegste tye af onlosmaaklik met die mens se kultuur verbind. Hierdie fermentasie-proses word gedomineer deur die Saccharomyces cerevisiae mikroorganisme. Hierdie organisme het antieke seevaarders voorsien van ‘n nie-bederfbare drankie en van ouds af aan bakkers ‘n rysmiddel verskaf waarmee meel in brood verander kon word. As gevolg van hierdie fermenteringspotensiaal het hierdie organisme ‘n onmisbare rol in meeste beskawings gespeel. Baie industrieë is steeds op hierdie basiese beginsel gebou. Die kompleksiteite en effektiwiteit van die transformasie van suiker na sy verskeie gefermeenteerde neweprodukte is breedvoerig bestudeer en geoptimiseer om aan die spesifieke behoeftes van verskeie industrieë te voeldoen. Afhangend van die grondstowwe wat as beginpunt gebruik is, is die primêre begunstigdes van die fermentasie proses die alkoholiese drankprodusente (onder andere die wyn-, bier- en whiskey produsente), bakkers en biobrandstofprodusente. Die suikerverbruik-voorkeur van die organisme wat die fermentering fasiliteer is een van die struikelblokke in die optimisering van die proses. S. cerevisiae kan ‘n wye spektrum van suikers verbruik maar dit toon ‘n voorkeur vir die eenvoudiger suikers. Die fermentasie van sekere van die meer komplekse suikers is vertraag en loop die risiko om agtergelaat te word na fermentasie. Vele van die gewasse wat in die gefermenteerde produkte gebruik word bevat groot hoeveelhede stysel. Vele soorte suikers word gedurende die afbreek van die stysel beskikbaar gestel vir fermentasie. Die brouers-, whiskey- en biobrandstof industrieë sal almal voordeel trek uit die verbeterde fermentasie van stysel en sy gepaardgaande dekstrin produkte. Meeste Saccharomyces gisrasse fermenteer glucose en maltose; maltotriose word gedeeltelik gefermenteer, maar die meer komplekse dekstrien produkte gevind in stysel word nie gefermenteer nie. Hierdie verbruikerspatroon kan gedeeltelik toegeskryf word aan die vermoë van gisselle om die bogenoemde mono-, di- and trisaccharides in die sitosol op te neem. Die oneffektiwiteit van maltotriose transport is identifiseer as die hoofoorsaak van post-fermentatiewe, oortollige maltotriose. Die effektiwiteit van maltotriose transport verskil ook tussen verskillende Saccharomyces rasse. Pogings om onvolledige fermentasie te veminder kan bevorder word deur die kennis rondom maltotriose transport in gis uit te bou. Hierdie oogmerk kan bereik word deur die bestaande transporters in die gissel se membraan wat ‘n affiniteit vir maltotriose toon te ondersoek. Hierdie studie fokus op die optimisering van maltotriose transport deur die vergelyking van die alpha glucoside transporter (AGT1) wat van verskillende Saccharomyces rasse afkomstig is. Die areas wat relevant is tot maltotriose transport kon deur spesifieke genetiese manipulasies identifiseer en gekarakteriseer word. Hierdie studie bevorder die vooruitsig op die ontwikkeling van gisrasse met verbeterde
maltose en maltotriose transport vermoëns wat op sy beurt weer kan aanleiding gee tot die
verbeterde fermentasie effektiwiteit in die bier, whiskey en biobrandstof industrieë.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21760 |
| Date | 12 1900 |
| Creators | Smit, Annel |
| Contributors | Cordero Otero, Ricardo R., Pretorius, Isak S., Du Toit, Maret, 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 | Unknown |
| Type | Thesis |
| Format | vii, iv, 104 leaves : ill. |
| Rights | Stellenbosch University |
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