Spelling suggestions: "subject:"line anda wide making - microbiology"" "subject:"line anda wide making - microbiologyc""
21 |
Comparative 'omic' profiling of industrial wine yeast strainsRossouw, Debra 12 1900 (has links)
Thesis (PhD(Agric) Viticulture and Oenology. Wine Biotechnology))--University of Stellenbosch, 2009. / The main goal of this project was to elucidate the underlying genetic factors responsible for the
different fermentation phenotypes and physiological adaptations of industrial wine yeast strains. To
address this problem an ‘omic’ approach was pursued: Five industrial wine yeast strains, namely
VIN13, EC1118, BM45, 285 and DV10, were subjected to transcriptional, proteomic and exometabolomic
profiling during alcoholic fermentation in simulated wine-making conditions. The aim
was to evaluate and integrate the various layers of data in order to obtain a clearer picture of the
genetic regulation and metabolism of wine yeast strains under anaerobic fermentative conditions.
The five strains were also characterized in terms of their adhesion/flocculation phenotypes,
tolerance to various stresses and survival under conditions of nutrient starvation.
Transcriptional profiles for the entire yeast genome were obtained for three crucial stages during
fermentation, namely the exponential growth phase (day 2), early stationary phase (day 5) and late
stationary phase (day 14). Analysis of changes in gene expression profiles during the course of
fermentation provided valuable insights into the genetic changes that occur as the yeast adapt to
changing conditions during fermentation. Comparison of differentially expressed transcripts
between strains also enabled the identification of genetic factors responsible for differences in the
metabolism of these strains, and paved the way for genetic engineering of strains with directed
modifications in key areas. In particular, the integration of exo-metabolite profiles and gene
expression data for the strains enabled the construction of statistical models with a strong predictive
capability which was validated experimentally.
Proteomic analysis enabled correlations to be made between relative transcript abundance and
protein levels for approximately 450 gene and protein pairs per analysis. The alignment of
transcriptome and proteome data was very accurate for interstrain comparisons. For intrastrain
comparisons, there was almost no correlation between trends in protein and transcript levels, except
in certain functional categories such as metabolism. The data also provide interesting insights into
molecular evolutionary mechanisms that underlie the phenotypic diversity of wine yeast strains.
Overall, the systems biology approach to the study of yeast metabolism during alcoholic
fermentation opened up new avenues for hypothesis-driven research and targeted engineering
strategies for the genetic enhancement/ modification of wine yeast for commercial applications.
|
22 |
Kinetic modelling of wine fermentations : why does yeast prefer glucose to fructoseMocke, Leanie 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In the present-day competitive global market, wine industries are constantly
aiming to improve the wine-making process,including the role of yeast. The
most commonly used wine yeast is Saccharomyces cerevisiae, which is able to
produce high quality wines, but problem fermentations do sometimes arise.
The occurrence of stuck and sluggish fermentations pose a serious problem
leading to loss of productivity and quality. Although the precise mechanism
leading to stuck fermentations is unknown, they are often correlated with
high fructose to glucose ratios in the wine-must. S. cerevisiae is a glucophylic
yeast, indicating its preference for consuming glucose over fructose. Both these
hexose sugars are present in unfermented wine must, mostly in equal concentrations.
As fermentation progresses, glucose is consumed at a faster rate than
fructose, leading to an increase in the fructose to glucose ratio. Yeast are left
with the undesirable fructose at the later stages of fermentation, when the
environmental stresses on the yeast can lead to stuck or sluggish fermentation.
This residual fructose can lead to undesirable sweetness, as fructose is
about twice as sweet as glucose. Even with the extensive research into yeast
metabolism, there is as yet no definitive explanation as to why yeasts ferment
glucose faster than fructose.
This study aimed to investigate the mechanism responsible for the faster consumption
of glucose over fructose of a commercially used wine yeast strain
S. cerevisiae VIN 13. The first two steps of sugar metabolism, uptake and
phosphorylation, were investigated as the possible sites of discrepancy in fermentation
rates. Enzyme rates and affinities for both glucose and fructose as substrates for the relevant enzymes were experimentally determined. These
kinetic parameter values were used to improve an existing model of yeast glycolytic
pathway to model wine fermentations. The feasibility of constructing
and validating a kinetic model of wine fermentations were investigated, by
comparing model predicted fluxes with experimentally determined fluxes.
Another aspect of this study was an investigation into the effect of hexose
sugar type on fermentation profiles. Wine fermentations were done with only
one hexose sugar as carbon source to determine if it has an effect on the flux
through metabolism.
This work succeeded in the construction of a kinetic model that distinguished
between glucose and fructose as carbon source. The glucose was consumed
faster than fructose, with control lying in the hexose transport step. It was
also established that fermentation prfiles of fermentations with only one sugar
was the same for both one sugar type fermentations. Fermentation with either
glucose or fructose as the sole carbohydrate source had the same specfic
production and consumption rates as normal fermentations with both sugars.
Construction of detailed kinetic models can aid in the metabolic and cellular
engineering of novel yeast strains. By identifying the importance of hexose
transport, and thus the glucophilic character of the yeast, in flux control, yeast
transporters can be targeted for strain improvement. This may in turn lead to
more effective fermentation practices for controlling problem fermentations, or
to the development of novel strains that utilizes fructose in the same manner as
glucose, and in so doing lower the risk of stuck or sluggish wine fermentation. / AFRIKAANSE OPSOMMING: In die hedendaagse kompeterende wynmark is wynmakers aanhoudend besig
om die wynmaak proses te verbeter en dit sluit die verbetering van wyngis
in. Die mees algemeenste gebruikte wyngis is Saccharomyces cerevisiae, omdat
dit wyn van gehalte produseer, maar probleem fermentasies kom wel voor.
Die verskynsel van vasval of stadige fermentasies kan lei tot die verlies van
produksie en kwaliteit. Die oorsaak van probleem fermentasies is gewoontlik
veelvoudig, maar die verhouding van glukose tot fruktose in die wyn-mos kan
ongunstig raak om fermentasies te onderhou. S. cerevisiae is 'n glukofiliese
gis, wat sy voorkeur om glukose bo fruktose te gebruik beskryf. Albei hierdie
heksose suikers is teenwoordig in ongefermenteerde wyn-mos, meestal in gelyke
hoeveelhede. Soos fermentasies vorder word glukose vinniger verbruik as
fruktose wat lei tot 'n toename in die fruktose tot glukose verhouding. Die gis
moet dus die fruktose in die later stadium van fermentasie gebruik wanneer
die omgewings druk op die gis kan lei tot probleem fermentasies. Die oorblywende
fruktose kan lei tot ongewenste soetheid aangesien fruktose twee keer
soeter is as glukose. Selfs met die ekstensiewe navorsing met betrekking tot
gis metabolisme is daar nog nie 'n verduideliking hoekom gis glukose vinniger
as fruktose gebruik nie.
Hierdie studie het beoog om die meganisme wat lei tot die vinniger verbruik
van glukose oor fruktose te ondersoek vir 'n kommersieël gebruikte gis S. cerevisiae VIN 13. Die eerste twee stappe van suiker metabolisme, suiker opname
en fosforilasie, was ondersoek as die moontlike punt van die verskil in fermentasie
tempo. Ensiem snelhede en affiniteite vir beide glukose en fruktose as substrate vir die ensieme van belang was eksperimenteel bepaal. Hierdie
waardes is gebruik om 'n bestaande model van gis glikolise aan te pas vir wyn
fermentasies. Die uitvoerbaarheid van saamstel en valideer van 'n kinetiese
model van wyn fermentasies was ondersoek, deur model voorspelde fluksie
waardes met eksperimentele fluksie waardes te vergelyk.
'n Ander aspek van die studie was die ondersoek van die effek van heksose
suiker tipe op fermentasie profiel. Wyn fermentasies is gedoen met slegs een
heksose suiker as koolstof bron om te bepaal of dit 'n invloed het op die fluksie
deur metabolisme.
Hierdie werk het daarin geslaag om 'n kinetiese model saamtestel wat onderskei
tussen glukose en fruktose as koolstof bron. Die glukose is vinniger verbruik as
fruktose, met beheer gesetel in die heksose opname stap. Dit was ook vasgestel
dat fermentasie profiele van fermentasies met slegs een suiker nie verskil het
vir fermentasies met slegs fruktose of glukose. Fermentasies met slegs een
suiker het dieselfde spesifieke produksie en konsumpsie tempo gehad as die
normale fermentasie met albei suikers. Die konstruksie van 'n gedetailleerde
kinetiese model kan gebruik word in die metaboliese en sellulêre ontwikkeling
van nuwe gisstamme. Deur die ontdekking van die belangrikheid van heksose
opname in fluksie beheer, wat lei tot die glukofiliese karakter van gis, kan gis
opname geteiken word vir gis ontwikkeling. Dit mag om die beurt lei tot meer
effektiewe fermentasie praktyk in die beheer van probleem fermentasies, of die
ontwikkeling van nuwe stamme wat fruktose in dieselfde manier as glukose
benut, en sodoende die risiko van vasval of stadige wyn fermentasies verlaag. / National Research Foundation / Post-graduate Merit Bursary
|
23 |
n Studie van die mikro-organimes geassosieerd met die blomme en rypwordende korrels van 'n aantal druiwevarieteiteDu Plessis, L. de W. (Ludwig de Wet) 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 1959. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming
|
24 |
Acolein in wine : bacterial origin and analytical detectionBauer, Rolene 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT:
Wine quality is compromised by the presence of 3-hydroxypropionaldehyde (3-HPA)
due to spontaneous conversion into acrolein under wine making conditions. Acrolein
is highly toxic and is presence has been correlated with the development of
bitterness in wine. Lactic acid bacterial strains isolated from South African red wine,
Lactobacillus pentosus and Lactobacillus brevis, are implicated in accumulating 3-
HPA during anaerobic glycerol fermentation. The environmental conditions leading
to its accumulation are elucidated. In aqueous solution 3-HPA undergoes reversible
dimerization and hydration, resulting in an equilibrium state between different
derivatives. Interconversion between 3-HPA derivatives and acrolein is a complex
and highly dynamic process driven by hydration and dehydration reactions. Acrolein
is furthermore highly reactive and its steady-state concentration in complex systems
very low. As a result analytical detection and quantification in solution is problematic.
This study highlights the roles played by natural chemical derivatives and shows that
the acrolein dimer can be used as a marker for indicating the presence of acrolein in
wines. Solid-phase microextraction (SPME) coupled to gas chromatograph mass
spectrometry (GC-MS) was validated as a technique for direct detection of the
acrolein dimer in wine. The potential of a recently introduced sorptive extractive
technique with a sample enrichment probe (SEP) was also investigated. The SPME
technique simplifies the detection process and allows for rapid sampling of the
acrolein marker, while SEP is more sensitive. / AFRIKAANSE OPSOMMING:
Die teenwoodigheid van 3-hidroksiepropioonaldehied (3-HPA) in wyn het ‘n
negatiewe invloed op kwaliteit as gevolg van die moontlike omskakeling na akroleien
tydens die wynmaak prosses. Akroleien is hoog toksies en is moontlik betrokke by
die ontwikkeling van ‘n bitter komponent in wyn. Hierdie studie wys dat stamme van
die melksuurbakteriëe Lactobacillus pentosus en Lactobacillus brevis, geisoleer uit
Suid-Afrikaanse wyn, 3-HPA tydens anaerobiese alkoholiese fermentasie kan opbou.
Kondisies wat ontwikkeling beinvloed is bestudeer. 3-HPA ondergaan omkeerbare
dimerisasie en hidrasie in oplossing en het ‘n ewewig tussen veskillende derivate tot
gevolg. Omkakeling tussen 3-HPA derivate en akroleien is ‘n komplekse en hoogs
dinamiese prosses wat gedryf word deur hidrasie en dehidrasie reaksies. Akroleien
is verder hoogs reaktief en die ewewigskonsentrasie van hierdie aldehied in
komplekse omgewings is laag. Analitiese waarneming en kwantifisering is gevolglik
problematies. Hierdie studie lig die rol wat natuurlike chemise derivate speel duidelik
uit en wys dat die akroleien dimeer as ‘n merker gebruik kan word om die
teenwoodigeid van akoleien in wyn te staaf. Soliede-fase mikro-ekstraksie (SPME)
gekoppel aan gas chromatografie massa spektroskopie (GC-MS) is gevalideer as ‘n
tegniek vir die direkte waarneming van die akroleien dimeer in wyn. Die potensiaal
van ‘n nuwe ekstraksie tegniek, gebasseer op ‘n peiler wat vir die monster verreik
(SEP), was ook ondersoek. Die SPME tegniek is vinnig en vergemaklik analiese,
terwyl SEP meer sensitief is.
|
25 |
Expression of the Aspergillus niger glucose oxidase gene in Saccharomyces cerevisiaeMalherbe, Daniel Francois 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2002. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: The winemaking process constitutes a unique ecological niche that involves the interaction
of yeasts, lactic acid bacteria and acetic acid bacteria. Saccharomyces cerevisiae has
established its importance as a wine yeast and also proven itself as a reliable starter
culture organism. Its primary role is to convert the grape sugar into alcohol and, secondly,
its metabolic activities result in the production of higher alcohols, fatty acids and esters,
which are important flavour and aroma compounds that are essential for consistent and
predictable wine quality. There is a growing consumer demand for wine containing lower
levels of alcohol and chemical preservatives.
Glucose oxidase (GOX) has received considerable research interest regarding its
potential application in the wine industry to reduce alcohol levels and as a biocontrol
agent. Several physical processes are used for the removal or reduction of alcohol in wine
and some of them are sometimes used in combination. These processes tend to involve
expensive equipment and can be intensive from a processing point of view. An alternative
approach was introduced with the concept of treating grape must with GOX to reduce the
glucose content of the must, and therefore produce a wine with a reduced alcohol content
after fermentation. Due to the demanding nature of modern winemaking practices and
sophisticated wine markets, there is an ever-growing quest for specialised wine yeast
strains possessing a wide range of optimised, improved or novel oenological properties.
The first and main objective of this study was to genetically engineer wine yeasts to
produce wine with a reduced alcohol content. In order to do this, the structural glucose
oxidase (gox) gene of Aspergillus niger was cloned into an integration vector (Ylp5)
containing the yeast mating pheromone a-factor secretion signal (MFa1 s) and the
phosphoglycerate kinase 1 gene promoter and terminator (PGK1PT). This PGK1p-MFa1sgox-
PGKh gene cassette (designated GOX1) was introduced into a laboratory strain of
S. cerevisiae (~1278). Results obtained indicated the production of biologically active
glucose oxidase and showed that it is secreted into the culture medium. This would mean
that the enzyme will convert the glucose to gluconic acid in the medium before the yeast
cells are able to metabolise the glucose to ethanol. Microvinifications performed with
Chardonnay grapes showed that the laboratory yeast starter cultures transformed with
GOX1 were indeed able to reduce the total amount of alcohol in the finished product.
The second objective of this study involved the potential application of GOX as a
biocontrol agent. Screening was performed for wine spoilage microorganisms, such as
acetic acid bacteria and lactic acid bacteria, using plate assays. The wine spoilage
microorganisms tested formed different sized inhibition zones, indicating varying degrees
of inhibition. The inhibition of some of the wine spoilage microorganisms was confirmed
under a scanning electron microscope. The total collapse of the bacterial cell wáll could be
seen and might be explained by the fact that a final product of the GOX enzymatic reaction
is hydrogen peroxide (H202). The produced H202 leads to hyperbaric oxygen toxicity, a
result of the peroxidation of the membrane lipid, and a strong oxidising effect on the
bacterial cell, which is the cause of the destruction of basic molecular structures, such as
nucleic acids and cell proteins.
In this exciting age of molecular yeast genetics and modern biotechnology, this
study could pave the way for the development of wine yeast starter culture strains for the
production of wine with a lower alcohol content and reduced levels of chemical preservatives, such as sulphur dioxide. The use of genetically modified organisms (GMOs)
within the wine industry is a limiting factor at present and credible means must be found to
effectively address the concerns of traditionalists within the wine industry and the negative
overreaction by some consumer groups. There is a vast potential benefit to the wine
consumer and industry alike and the first recombinant wine products therefore should
unmistakably demonstrate safe products free of potentially harmful compounds, and have
organoleptic, hygienic and economic advantages for both the wine producer and
consumer. / AFRIKAANSE OPSOMMING: Die wynmaakproses behels 'n ekologiese interaksie tussen gis, asynsuurbakterieë en
melksuurbakterieë. Saccharomyces cerevisiae het homself alreeds bewys as 'n belangrike
en betroubare inisiëringsgis in wyn. Die hoofdoel van die gis is om druifsuikers na etanol
om te skakel. Tweedens lei die gis se metaboliese aktiwiteite tot die produksie van hoër
alkohole, vetsure en esters, wat tot die konsekwente voorspelbare smaak en
aromaverbindings in herhaalbare kwaliteit wyn bydra. Daar is 'n toenemende aanvraag na
wyne met 'n laer alkoholinhoud en minder preserveermiddels.
Glukoseoksidase (GOX) het heelwat navorsing in die wynindustrie uitgelok omdat dit
gebruik kan word om die alkoholinhoud in wyn te verlaag, asook as 'n biologiese
beheermiddel kan funksioneer. Daar is reeds sekere fisiese prosesse wat gebruik kan
word om die alkohol in wyn te verwyder of te verminder. Sommige van hierdie prosesse
word soms in kombinasie gebruik. Die nadeel is egter dat hierdie prosesse baie duur en
intensief is, veral ten opsigte van prosessering. 'n Alternatief om die alkoholinhoud van
wyn te verlaag, het egter na vore gekom toe daar voorgestel is om die mos met GOX te
behandel. As gevolg van die veeleisende aard van moderne wynmaakpraktyke en
gesofistikeerde wynmarkte, is daar 'n nimmereindigende soektog na meer
gespesialiseerde wyngisrasse wat 'n wye reeks van geoptimiseerde en verbeterde, en
selfs unieke, wynkundige einskappe bevat.
Die hoofdoelwit van hierdie navorsingsprojek behels die genetiese manipulasie van 'n
gisras sodat dit in staat is om wyn met 'n laer alkoholinhoud te produseer. Om hierdie doel
te verwesentlik, is die strukturele glukoseoksidasegeen (gox) van Aspergillus niger in 'n
integreringsvektor gekloneer. Transkripsie-inisiëring en -terminering is deur
fosfogliseraatkinase-1-promotor en -termineerder (PGK1PT) bewerkstellig. Die a-spesifieke
gisferomoon-a-faktor (MFa1 s) is gebruik om die uitskeiding van GOX uit die gis te
bewerkstellig. Saam vorm bogenoemde die PGK1p-MFals-gox-PGKh-geenkasset, wat
as GOX1 bekend is. GOX1 is na 'n labaratoriumras van S. cerevisiae (:E1278)
getransformeer. Resultate dui aan dat biologies aktiewe GOX geproduseer en uitgeskei
word. Dit beteken dat van die glukose in die medium reeds na glukoonsuur omgesit sal
word voordat die gis dit kan begin benut en alkohol produseer. Kleinskaalse
wynmaakprosesse wat met Chardonnay-druiwe en GOX-produserende labaratoriumgis
uitgevoer is, het inderdaad tot laer alkoholpersentasies gelei.
Die tweede doelwit van die navorsingsprojek was om te bepaal of GOX die potensiaal
as biologiese beheermiddel het. Daar is ondersoek ingestel na sekere
wynbederfsorganismes soos asynsuur- en melksuurbakterieë en die inhibisie van die
organismes is op agarplate gemonitor. Verskillende grade van inhibisie, soos die grootte
van die inhibisiesone, was sigbaar vir die verskillende wynbederfsorganismes wat getoets
is. Die inhibiese van sekere wynbederfsorganismes is ook met behulp van 'n
skandeerelektronmikroskoop bevestig. Die totale ineenstorting van die bakteriële selwand
was sigbaar en kan verklaar word deur die teenwoordigheid van waterstofperoksied
(H202). Laasgenoemde is 'n byproduk van die laaste metaboliese reaksie en staan as 'n
antimikrobiese middel bekend. Die byproduk (H202) gee aanleiding tot hiperbariese
suurstoftoksisiteit, 'n gevolg van die peroksidasie van membraanlipiede en 'n sterk
oksiderende effek t.o.v. die bakteriële selwand. Dit lei tot die vernietiging van die basiese
molekulêre strukture, soos die nukleïensure en selproteïene.
Tydens hierdie opwindende era van molekulêre gisgenetika en biotegnologie kan
hierdie navorsing die fondament lê vir die ontwikkeling van 'n wyngiskultuur wat in staat is
om wyn met 'n laer alkoholinhoud te produseer. Die gebruik van geneties gemanupileerde
organismes (GMO's) in die wynbedryf is egter nog 'n beperkende faktor. 'n
Geloofwaardige manier moet dus gevind word om die bekommernisse van tradisionaliste,
asook die negatiewe oorreaksies van sommige verbruikers, aan te spreek en hok te slaan.
Daar is groot potensiaal en voordele vir beide die verbruiker en industrie. Dit is dus
belangrik dat die eerste rekombinante wynprodukte wat die mark betree, veilig en vry van
potensieel skadelike verbindings is, asook organoleptiese, higiëniese en ekonomiese
voordele toon te opsigte van beide die wynprodusent en gebruiker.
|
26 |
An investigation into lactic acid bacteria as a possible cause of bitterness in wineKrieling, Shannon Janine 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Spoilage, be it due to microbial actions, chemical reactions or both, poses a serious
threat to the food and beverage industries. Not only can spoilage lead to great
economic losses, but it can also cause industries to lose their competitive edge in the
economic and consumer market. Considering all the modern technologies and the
range of preservation techniques that are available, it is surprising that spoilage is still
an economic problem. Wine spoilage due to unpalatable bitterness, and the role of
lactic acid bacteria (LAB) in causing this bitterness, have received much attention
over the years, but no definite understanding has yet emerged.
The first objective of this study was to isolate, enumerate and identify the LAB
from three red grape varieties, viz. Pinotage, Merlot and Cabernet Sauvignon. The
LAB populations on the grapes of all three varieties ranged from 102 to 104 cfu/ml
during the 2001 and 2002 harvest seasons. The Cabernet Sauvignon grapes had
slightly higher numbers than the Pinotage and Merlot. The LAB population in the
Cabernet Sauvignon, Pinotage and Merlot wines after completion of the alcoholic
fermentation ranged from 102 to 105 cfu/ml, while during 2002 the numbers in wine
undergoing malolactic fermentation (MLF) ranged from 104 to 108 cfu/ml. The
isolated LAB were divided into the three metabolic groups, with 59% belonging to the
facultatively heterofermentative group, 26% to the obligately heterofermentative
group and 15% to the obligately homofermentative group. The isolates were
identified by means of species-specific primers as Leuconostoc mesenteroides (4),
Oenococcus oeni (28), Lactobacillus brevis (15), Lb. hilgardii (15), Lb. plantarum
(98), Lb. pentosus (12), Lb. paraplantarum (3), Lb. paracasei (28),
Pediococcus acidilactici (2) and Pediococcus spp. (35). The most predominant
species isolated was Lb. plantarum, followed by Pediococcus spp. The results
suggest that Pinotage carries a more diverse LAB population in comparison to Merlot
and Cabernet Sauvignon.
The second objective of this study was to determine the presence of the glycerol
dehydratase gene in the LAB strains by using the G01 and G02 primers. Twenty-six
strains tested positive, namely Lb. plantarum (15), Lb. pentosus (1), Lb. hilgardii (5),
Lb. paracasei (2), Lb. brevis (2) and a Pediococcus spp. (1). Interestingly, 62% of
these strains were isolated from Pinotage. The strains all had the ability to degrade
glycerol by more than 90%, and no significant differences were observed between
the species. The GO-possessing strains exhibited varying degrees of inhibition
towards Gram-positive and Gram-negative bacteria, and the results suggest that this
inhibition activity may be similar to that of reuterin, which is produced by Lb. reuteri.
This study can form the foundation for unravelling the causes of bitterness in red
wines. Combining the results of this study with analytical, sensory and molecular
data may very well provide the industry with valuable tools with which to combat the
occurrence of bitterness. / AFRIKAANSE OPSOMMING: Bederf as gevolg van mikrobiese aksies, chemiese reaksies of beide, hou 'n groot
bedreiging vir die voedsel- en drankbedrywe in. Nie net kan bederf lei tot groot
ekonomiese verliese nie, maar dit kan ook veroorsaak dat bedrywe hul
kompeterende voordeel in die ekonomiese en verbruikersmarkte verloor. As die
moderne tegnologie en die reeks preserveringstegnieke wat beskikbaar is, in ag
geneem word, is dit verbasend dat bederf steeds 'n ekonomiese probleem is.
Wynbederf as gevolg van oormatige bitterheid en die rol van melksuurbakterieë
(MSB) in die ontwikkeling van hierdie bitterheid het oor die jare heen baie aandag
geniet, maar geen definitiewe verklaring is nog daarvoor gevind nie.
Die eerste doelwit van hierdie studie was om MSB vanaf drie rooidruifvariëteite,
nl. Pinotage, Merlot en Cabernet Sauvignon, te isoleer, te kwantifiseer en te
identifiseer. Die MSB-populasies op die druiwe van al drie variëteite het gedurende
die 2001- en 2002-parsseisoene tussen 102 en 104 kvu/ml gevarieer. Die Cabernet
Sauvignon-druiwe het effens hoër getalle as die Pinotage- en Merlot-druiwe gehad.
Die MSB-populasies in die Cabernet Sauvignon-, Pinotage- en Merlot-wyne aan die
einde van die alkoholiese fermentasie het tussen 102 en 1055 kvu/ml gevarieer.
Gedurende 2002 het die MSB-getalle in die wyne waarin appelmelksuurgisting
(AMG) aan die gang was tussen 104 en 108 kvu/ml gevarieer. Die geïsoleerde MSB
was onderverdeel in die drie metaboliese groepe, met 59% wat behoort aan die
fakultatiewe, heterofermentatiewe groep, 26% aan die obligate, heterofermentatiewe
groep en 15% aan die obligate, homofermentatiewe groep. Die isolate is
geïdentifiseer as Leuconostoc mesenteroides (4), Oenococcus oeni (28),
Lactobacillus brevis (15), Lactobacillus hi/gardii (15, Lactobacillus p/antarum (98),
Lactobacillus pentosus (12), Lactobacillus parap/antarum (3), Lactobacillus paracasei
(28), Pediococcus acidi/actici (2) en Pediococcus spp. (35) deur middel van spes iespesifieke
inleiers. Die mees algemeen geïsoleerde spesies was Lb. p/antarum,
gevolg deur Pediococcus spp. Die resultate impliseer dat Pinotage 'n meer
uiteenlopende MSB-populasie in vergelyking met Merlot en Cabernet Sauvignon dra.
Die tweede doelwit van hierdie studie was om die teenwoordigheid van die
gliseroldehidratase-geen in die MSB-isolate deur middel van die GD1- en GD2-
inleiers te bepaal. Ses-en-twintig isolate was positief, nl. Lb. p/antarum (15), Lb.
pentosus (1), Lb. hi/gard;; (5), Lb. paracasei (2), Lb. brevis (2) en 'n Pediococcus spp.
(1). 'n Interessante resultaat was dat 62% van hierdie isolate vanaf Pinotage
geïsoleer is. Die isolate was almal in staat om meer as 90% van die gliserol te
gebruik en geen noemenswaardige verskille is tussen die isolate waargeneem nie.
Die GD-bevattende isolate het verskillende grade van inhibisie teenoor Grampositiewe
en Gram-negatiewe bakterieë getoon, en die resultate impliseer dat hierdie
inhiberende aktiwiteit dieselfde is as dié van reuterin wat deur Lb. reuteri
geproduseer word. Hierdie studie kan dus die basis vorm vir die ontrafeling van die oorsake van
bitterheid in rooiwyne. Deur die resultate van hierdie studie met analitiese,
sensoriese en molekulêre data te kombineer, kan die wynbedryf voorsien word van
waardevolle metodes om die voorkoms van bitterheid mee te bekamp.
|
27 |
Monitoring the spreading of commercial wine yeasts in the vineyardMuller, Christo A. 12 1900 (has links)
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.
|
28 |
Screening, isolation and characterisation of antimicrobial/antifungal peptides produced by lactic acid bacteria isolated from wineMorgan, Joanne 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2003. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: Winemaking is an age-old tradition that dates back to as early as 6000 BC. In our
modern era there are several insects and microorganisms that pose a threat to the
grapevine, the environment and the final wine product. Farmers and winemakers are
becoming aware of the threat and the fight against disease, spoilage and/or
pathogenic microorganisms is on the rise. Currently, the natural environment is being
altered through rural developments, pollution and disaster, which in turn is
responsible for altering the natural micro flora. The result is a harsh battle between
man and microorganism. The weapon used often against microorganisms is chemical
preservatives, such as sulphur dioxide. These chemical preservatives change the
nutritional value, quality and wholesomeness of the wine. Chemical preservatives
suppress the quality of the wine with a reduction in wine consumption by the
consumers.
Until the 18th century, wine was regarded as a safe drink and prescribed by
doctors. In the zo" century alcohol consumption became the focus point of some
health campaigners. Medical science restored the good name of wine in the 1990s
when it came to light that moderate red wine consumption may aid in preventing
heart disease and assist in stress management. The only drawback that lowers
consumption levels is the use of chemical preservatives.
It is of utmost importance to place the focus on health issues and the development
of natural preservation methods that are environmentally friendly and contributes to
the overall wholesomeness of the wine. Due to these demands, the scientific
community placed the focus of research projects on the development and
enhancement of biopreservation methods, in order to minimise chemical preservation
use.
One of the most promising biocontrol agents is bacteriocins. These proteinaceous
molecules produced by various lactic acid bacteria exert antimicrobial activity towards
closely related organism. Research has shown that bacteriocins may aid in the
prevention of wine-spoilage and enhance natural preservation techniques.
Most of the research on biopreservation in food and beverages has been
performed on the bacteriocins of LAB. No evidence could be found that indicated
bacteriocin production by wine isolated LAB in South Africa. This study is therefore,
of utmost importance and is considered to be novel pioneering work for the South
African wine industry.
The main objective of this study was to screen wine isolated LAB for the
production of antimicrobial and/or antifungal compounds. This was followed by the
isolation and characterisation of the produced bacteriocins. This study forms part of a
greater project that focuses on wine preservation, under the auspices of the Institute
for Wine Biotechnology.The research results in this study indicated the production of bacteriocins by
wine isolated LAB of South African origin. It was found that numerous isolates
exerted antimicrobial activity towards other wine associated LAB. The most
predominant species that gave the highest activity was Lactobacillus brevis and
Lactobacillus paracasei. Experimental results indicated that the bacteriocins
produced by these two species were thermo-stable and active over a wide pH range,
including the temperatures and pH values that reign in the South African wine
environment. The antimicrobial activity was lost after treatment with proteolytic
enzymes, such as proteinase K and lysozyme. The size, production and growth
kinetic curves of the bacteriocins under investigation showed similar results that are
comparable to other findings in the literature. Antifungal activity was detected against
Botryfis cinerea that indicated limited inhibitory activity towards spore germination,
but had no effect on hyphal growth.
This study provides novel information regarding bacteriocin production by LAB
isolated from the South African wine industry. The results indicate the suitability of
these bacteriocins as possible biopreservatives in the wine environment. The
proposed results obtained in this study will aid in the development of bacteriocinproducing,
tailored made wine yeast or LAB that may in future, play vital roles in the
winemaking process. / AFRIKAANSE OPSOMMING: Wynmaak is 'n eeu oue tradisie wat terugdateer tot so vroeg soos 6000 jaar v.C. In
ons moderne eeu is daar verskeie insekte en mikro-organismes wat In bedreiging vir
die wingerdstok, asook die omgewing en die finale wynproduk inhou. Boere en
wynmakers word al hoe meer bewus van hierdie bedreiging, terwyl die stryd teen
siektes, bederf en/of patogene mikro-organismes ook aan die toeneem is. Tans word
die natuurlike omgewing deur landelike ontwikkeling, besoedeling en natuurlike
rampe verander, wat op sy beurt weer verantwoordelik is vir die verandering van
mikroflora. Die gevolg is 'n harde stryd tussen die mens en mikro-organismes. Die
wapen wat gereeld ingespan word in die stryd teen mikro-organismes, is chemiese
preserveermiddels, soos swaweidioksied. Hierdie chemiese preserveermiddels
verander die voedingswaarde, kwaliteit en die voedsaamheid van die wyn. Dit
onderdruk ook die gehalte van wyn, wat meebring dat minder wyn deur die verbruiker
gedrink word.
Tot en met die agtiende eeu is wyn deur dokters as 'n veilige drankie voorgeskryf.
In die twintigste eeu het alkoholverbruik die fokuspunt van gesondheidskamvegters
geword. In die 1990's het die mediese wetenskap wyn se goeie naam in ere herstel
toe dit aan die lig gekom het dat In matige verbruik van rooiwyn moontlik hartsiektes
kan voorkom en help om stres te beheer. Die enigste nadelige faktor wat
verbruikersvlakke verlaag, is die gebruik van chemiese preserveermiddels.
Dit is uiters noodsaaklik om die fokus op gesondheidskwessies te plaas en die
ontwikkeling van natuurlike preserveermetodes wat omgewingsvriendelik is en tot die
algehele voedsaamheid van wyn bydra. As gevolg van hierdie eise het
wetenskaplikes die fokus geplaas op navorsingsprojekte vir die ontwikkeling en
verbetering van biopreserveringsmetodes met die doelom die gebruik van chemiese
preserveermiddels te verminder.
Een van die belowendste biokontrolemiddels is bakteriosiene. Hierdie
proteïenagtige molekule word deur verskeie melksuurbakterieë vervaardig en oefen
anti-mikrobiese aktiwiteit teenoor nabyverwante organismes uit. Navorsing het
getoon dat bakteriosiene moontlik kan help in die voorkoming van wynbederf en
natuurlike preserveertegnieke kan verbeter.
Die meeste van die navorsing op biopreservering in voedsel en drank is op die
bakteriosiene van melksuurbakterieë uitgevoer. Geen bewys kon gevind word in Suid
Afrika wat bakteriosienproduksie deur wyn-geïsoleerde melksuurbakterieë aangedui
het nie. Hierdie studie is daarom baie belangrik en word as baanbreker werk vir die
Suid Afrikaanse wynbedryf beskou.
Die hoofdoel van hierdie studie was om wyn-geïsoleerde melksuurbakterieë vir die
produksie van anti-mikrobiese en/of anti-fungiese substanse te toets. Dit is gevolg
deur die isolasie en karakterisering van die geproduseerde bakteriosiene. Hierdie
studie maak deel uit van 'n groter projek wat fokus op wynpreservering en wat onder
leiding van die Instituut van Wynbiotegnologie uitgevoer word.
Navorsingsresultate van hierdie studie dui op die produksie van bakteriosiene deur
wyn-geïsoleerde melksuurbakterieë van Suid Afrikaanse oorsrong.
Daar is gevind dat verskeie isolate anti-mikrobiese aktiwiteit teenoor ander
wynverwante malksuurbakterieë uitgeoefen het. Die oorheersende spesie wat die
hoogste aktiwiteit getoon het, was Lactobacillus brevis en Lactobacillus paracasei.
Eksperimentele uitslae dui daarop dat die bakteriosiene wat deur hierdie twee
spesies geproduseer word, termostabiel en aktief is oor 'n wye pH reeks, insluitende
die temperature en pH-waardes wat in die Suid Afrikaanse wynomgewing voorkom.
Die anti-mikrobiese aktiwiteit het verlore gegaan na behandeling met proteolitiese
ensieme soos proteïnase K. Die groote, produksie en groeikinetika kurwes van die
bakteriosiene wat ondersoek is, toon vergelykbare resultate met ander bevindings in
die literatuur. Anti-fungiese aktiwiteit is opgemerk teen Botrytis cinerea, wat beperkte
inhiberende aktiwiteit ten opsigte van spoorontkieming aangedui het, maar geen
effek op hifegroei gehad nie.
Hierdie studie verskaf nuwe inligting aangaande bakteriosienproduksie deur
melksuurbakterieë wat van die Suid Afrikaanse wynomgewing geïsoleer is. Die
resultate dui op die geskiktheid van hierdie bakteriosiene as moontlike
biopreserveermiddels in die wynbedryf. Die voorgestelde resultate deur hierdie studie
verkry sal help in die ontwikkeling van bakteriosien produserende, spesifiek
vervaardigse wyngis of melksuurbakterieë, wat in die toekoms 'n baie belangrike rol
in die wynmaakproses sal speel.
|
29 |
n Fisiologiese studie van vier Suid-Afrikaanse gisrasse met betrekking tot vlugtige suur- en alkoholvormingVan Zyl, J. A. January 1954 (has links)
Thesis (MScAgric)--Stellenbosch University, 1954. / No Abstract Available
|
30 |
Die invloed van melksuurvormende bakteriee op die kwaliteit en samestelling van droe rooiwynSnyman, J. P. (Jacobus Petrus) 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 1978. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming
|
Page generated in 0.1325 seconds