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Beiträge zur Wirtschaftsgeschichte Zürichs im MittelalterGeilinger, Eduard. January 1900 (has links)
Thesis--Universität Zürich. / Vita. "Erscheint als Heft 2, Band 19 der Schweizer Studien zur Geschichtswissenschaft." Bibliography: p. 104-106.
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Determinants of producers' choice of wine grape cultivars in the South African wine industry /Musango, Josephine Kaviti. January 2005 (has links)
Thesis (MSc(Agric))--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.
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A study of the interaction between vine vigour, crop level and harvest dates and their effects on grape and wine characteristics /Quixley, Pieter C. January 2007 (has links)
Thesis (MAgric)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.
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Formation of mousy off-flavour in wine by lactic acid bacteriaCostello, Peter James. January 1998 (has links) (PDF)
Bibliography: leaves 200-214. Three structurally related compounds, 2-acetyltetrahydropyridine (ACTPY), 2-ethyltetrahydropyridine (ETPY) and N-heterocycle, 2-acetyl-1-pyrroline (ACPY), were quantified and found to be unique components of mousy wines. 35 lactic acid bacteria (LAB) were screened for the ability to produce mousy off-flavour. In addition to Lactobacillus brevis and L. cellobiosus, a diversity of LAB species, particularly heterofermentative Lactobacillus spp. and Oenococcus oeni exhibited this ability in a range of ethanolic and wine-based media. The substrates and metabolism of mousy compound formation by LAB were also investigated. A pathway for the formation of ACPY and ACTPY by heterofermentative LAB was proposed.
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The evaluation of bacteriocins and enzymes for biopreservation of wineDu Toit, Corina 03 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The winemaking process involves a number of microorganisms, each with its own role.
Yeasts are responsible for the alcoholic fermentation, the lactic acid bacteria (LAB) are
Gram-positive bacteria associated with must and wine and perform the malolactic
fermentation (MLF), while the acetic acid bacteria (AAB) are Gram-negative bacteria
converting ethanol to acetic acid. These microorganisms are present in the cellar and
fermentation tanks and can be seen either as beneficial or as wine spoilage
microorganisms because, under certain circumstances, they affect the wine quality if they
should grow in the wine or must.
Strict measures need to be implemented in the cellar during the winemaking process
to ensure microbiological stability. This can be achieved through good microbiological
practices and, additionally, chemical preservatives. Sulphur dioxide (S02) is widely used
as the primary preservative in winemaking. However, consumer resistance has been
building up against the use of chemical preservatives, due to the possible health risks and
a decrease in nutritional value and sensorial quality of certain foods and beverages.
Biopreservation as an alternative to the traditionally-used chemical preservation is a
new approach and has been attracting much attention. This implies the use of the natural
microflora and/or their antibacterial products, such as bacteriocins and bacteriolytic
enzymes (e.g. lysozyme). Bacteriocins from LAB are proteins or protein complexes,
produced by Gram-positive bacteria, with antibacterial activity against closely-related
Gram-positive species. Lysozyme occurs in substances such as hen egg white and has
lytic activity against Gram-positive bacteria. '
The bacteriocins nisin, of the class I lantibiotics, and pediocin PA-1 and leucocin BTA
11a, of the class lIa Listeria-active bacteriocins, have been investigated for the
biopreservation of wine. Nisin, however, is the only bacteriocin that has been approved for
use as a preservative, while pediocin is likely to follow in approval. Lysozyme has been
approved for use in winemaking by the Office International de la Vigne et du Vin (OIV).
The main objectives of this study were to determine whether these substances
showed any antimicrobial action against wine-associated microorganisms, namely LAB,
AAB and yeasts. The stability and suitability of the bacteriocins and lysozyme as
antimicrobials in wine was researched, especially when used in combination. Possible
synergistic or antagonistic interactions between the bacteriocins were also investigated by
means of the microtitre broth dilution method and scanning electron microscopy, as well as
at what concentration and combinations the bacteriocins were most effective against
increasing LAB concentrations.
It was found that nisin, pediocin and leucocin were effective to varying degrees
against a test panel of LAB type and reference strains, as well as wine isolates. Nisin
repeatedly had the highest level of inhibition against all the LAB tested, followed by
pediocin and leucocin. There was no inhibition of the wine-associated AAB and yeasts
tested. Pediocin stability was evaluated in simulated wine must and proved to be stable for
at least 20 days, without being affected by the sulphur or alcohol content. A low pH,
however, led to a more rapid decrease in activity. The same was found for nisin and
leucocin in other studies. Combinations of bacteriocins at increasing concentrations were evaluated against
increasing concentrations of a LAB wine isolate. When used in pairs (namely, nisinleucocin,
nisin-pediocin and pediocin-Ieucocin), the combinations were most effective
against lower concentrations of bacteria, namely 102 and 104 cfu/ml. At lower
concentrations, the pairs of bacteriocins were much less effective against the higher
bacterial concentrations of 106 and 108 cfu/ml. Leucocin-pediocin combinations were the
least effective, while nisin-Ieucocin combinations were marginally more effective than the
nisin-pediocin combinations. The most pronounced effect was observed when all three the
bacteriocins were used together. Combinations of bacteriocins had no inhibitory effect
against AAB. Pediocin and lysozyme was used in combination against the same wine
isolate, but no conclusive conclusions could be drawn in this experiment. __
Scanning electron microscopy was used to investigate any disturbances in cell
morphology when bacteriocins were added to LAB. The above-mentioned LAB was
subjected to bacteriocins used singularly and also in combinations of equal amounts of
bacteriocins. The action of the bacteriocins led to major disturbances in cell morphology.
Once again, the combination of leucocin-pediocin was the least effective, even less so
than when the single bacteriocins were used. The nisin-pediocin and nisin-Ieucocin
combinations seemed to be more effective in causing cell disturbances and perturbations.
The microtitre broth dilution methodwas used to further characterise the nature of the
interaction of the pairs of bacteriocins. This test showed clearly that the bacteriocins had
definite interactions. By adding one bacteriocin to varying concentrations of another
bacteriocin, the inhibitory action of the second bacteriocin was affected, either increasing
or decreasing its effectiveness. The most important factor to consider seems to be the
ratio at which the bacteriocins should be used together, leading either to synergism or
antagonism, and this also implies a very complex interaction.
This project indicated that it is indeed possible to use both bacteriocins and lysozyme
in "Vine preservation, both being stable in wine environments and effective against LAB
without affecting the yeast fermentation. Bacteriocins could also be used in combination, to
broaden the inhibition spectrum, as well as possibly increasing the inhibitory potential of
the individual antimicrobials. The underlying interactions in such combinations should be
carefully researched, however, when considering using combinations of antimicrobials in
food and beverage products. Further attention can also be given to finding
biopreservatives against the Gram-negative AAB, as well as to research the interaction of
the pairs of bacteriocins over time. Another point to consider would be the engineering of
yeasts or bacteria to produce these antibacterial substances in situ as part of their
metabolism. / AFRIKAANSE OPSOMMING: Daar is 'n verskeidenheid mikroorganismes in die wynrnaakproses betrokke, elkeen met sy
eie rol. Giste is vir die alkoholiese fermentasie verantwoordelik, die Gram-positiewe
melksuurbakterieë (MSB) wat in mos en wyn voorkom, is vir die appelmelksuurgisting
(AMG) verantwoordelik, terwyl die Gram-negatiewe asynsuurbakterieë (ASB) etanol in
asynsuur omskakel. Hierdie mikroorganismes is in die wynkelder en fermentasietenke
teenwoordig en kan as óf gunstig óf ongunstig beskou word, afhangende van die
toestande waaronder hulle groei en hoe die wyn daardeur beïnvloed word.
Om mikrobiologiese stabiliteit in wyn te verseker, moet daar streng higiëniese
maatreëls in die kelder toegepas word en word daar ook van addisionele chemiese
preserveermiddels gebruik gemaak. Swaweidioksied (S02) word tans algemeen as
pnmere preserveermiddel in die wynbedryf gebruik. Weens die moontlike
gesondheidsrisiko's wat S02 mag inhou en die moontlike verlaging van die
voedingswaarde en sensoriese gehalte waarmee dit in sommige voedsel- en
drankprodukte geassosieer word, bou daar tans verbruikersweerstand teen die gebruik
daarvan as chemiese preserveermiddelop.
Biopreservering is 'n alternatief tot hedendaagse chemiese preservering en het reeds
baie belangstelling ontlok. Hierdie metode impliseer die gebruik van die natuurlike
mikroflora en/of die antimikrobiese produkte van hierdie rnikroërqanisrnes, soos
bakteriosiene en bakteriolitiese ensieme (bv. lisosiem). Bakteriosiene van MSB is
proteïene of proteïenkomplekse met antimikrobiese aktiwiteit teen naby-verwante Grampositiewe
spesies. Lisosiem kom in produkte soos hoendereierwit voor en het litiese
aktiwiteit teen Gram-positiewe bakterieë.
Die bakteriosiene nisien, wat tot die klas I lantibiotiese bakteriosiene behoort, en
pediosien PA-1 en leukosien B-TA11a, wat tot die klas lIa Listeria-aktiewe bakteriosiene
behoort, is as moontlike biopreserveringsagense in wyn ondersoek. Nisien is egter tot op
hede die enigste bakteriosien wat amptelik vir gebruik as 'n preserveermiddel in voedsel
goedgekeur is, terwyl pediosien moontlik sal volg. Lisosiem is vir gebruik in wynmaak deur
die Office International de la Vigne et du Vin (OIV) goedgekeur.
Die hoofdoelwitte van hierdie studie was om te bepaal of die bogenoemde stowwe
antimikrobiese werking teen wyngeassosieerde mikroorganismes het, soos die
ongewenste MSB, ASB en giste. Die stabiliteit en geskiktheid van dié bakteriosiene en
lisosiem as antimikrobiese middels in wyn is ook ondersoek, veral wanneer hulle in
kombinasie vir preservering gebruik is. 'n Mikrotiterverdunningsboeljon-metode en
skanderingselektronmikroskopie is gebruik om moontlike sinergistiese en antagonistiese
interaksies tussen bogenoemde bakteriosienpare te ondersoek. Terselfdertyd is die
effektiefste konsentrasies en kombinasies van bakteriosiene teen stygende MSB-getalle
bepaal.
Daar is bevind dat nisien, pediosien en leukosien in verskillende mates teen 'n
toetspaneel van MSB tipe- en verwysingsrasse, asook MSB-wynisolate, effektief is. Nisien
was herhaaldelik die effektiefste teen dié MSB, gevolg deur pediosien en dan leukosien.
Die bakteriosiene was nie teen die wyngeassosieerde ASB of giste wat getoets is, effektief
nie. Daar is ook bewys dat pediosien vir tot 20 dae stabiel in 'n gesimuleerde wynomgewing
was, sonder dat die alkohol- of die swaweldioksiedkonsentrasie 'n invloed op die aktiwiteit gehad het nie. 'n Lae pH het geblyk om die grootste invloed op die afname in
aktiwiteit te hê. Hierdie bevindinge ten opsigte van pediosien het die resultate van nisien
en leukosien in ander, soortgelyke ondersoeke, bevestig.
Die werking van toenemende konsentrasies van bakteriosienkombinasies (as pare
van nisien-Ieukosien, nisien-pediosien, leukosien-pediosien, en al drie saam as nisienpediosien-
Ieukosien) teen toenemende getalle van In wyngeïsoleerde MSB is geëvalueer.
Wanneer die bakteriosiene in pare gebruik is, was die kombinasies die effektiefste teen
laer MSB selgetalle (102 en 104 kfe/ml), terwyl dit baie minder effektief teen hoër selgetalle
(106 en 108 kfe/ml) was, veral wanneer lae bakteriosienkonsentrasies gebruik is. Die
nisien-Ieukosien kombinasiewas tot 'n geringe mate meer effektief as die nisien-pediosien
kombinasie. Die leukosien-pediosien kombinasie het die laagste effektiwiteit van.al die
pare bakteriosiene wat gebruik is, getoon. Die sterkste werking is waargeneem toe al drie
die bakteriosiene saam teen bogenoemde MSB gebruik is. Die bakteriosien kombinasies
het geen effek teen ASB gehad nie. Pediosien en lisosiem is ook in kombinasie teen
dieselfde wynisolaat gebruik, maar geen oortuigende afleidings kon van hierdie
eksperiment gemaak word nie.
Skanderingselektronmikroskopie is gebruik om enige morfologiese verandering in die
MSB-wynisolaat waar te neem wanneer bakteriosiene daarby gevoeg is. Dieselfde
wynisolaat is weer gebruik en bakteriosiene is by die bakterieë gevoeg, enkelvoudig asook
in kombinasies (soos voorheen gebruik) teen gelyke hoeveelhede. Die werking van die
bakteriosien het gelei na merkbare veranderinge in selmorfologie, en die kombinasie van
pediosien-Ieukosien was weereens die minste effektief.
Die mikrotiterverdunningsboeljon-metode is gebruik om die aard van die
bakteriosieninteraksies verder te karakteriseer. Die toetse het duidelik aangedui dat die
bakteriosiene op mekaar reageer. Deur een bakteriosien tot variërende konsentrasies van
'n ander bakteriosien te voeg, is die inhibitoriese werking van die tweede bakteriosien
geaffekteer deurdat die effektiwiteit daarvan toegeneem of afgeneem het. Dit het ook
geblyk dat die belangrikste faktor wat hier in ag geneem moet word die verhouding is
waarteen die bakteriosiene met mekaar gebruik word, aangesien dit tot óf sinergisme óf
antagonisme kan lei. Dft dui op 'n baie komplekse interaksie.
Die resultate van hierdie projek het dus daarop gedui dat dit inderdaad moontlik is
om beide bakteriosien en lisosiem in wynpreservering te gebruik, aangesien beide nie net
stabiel in 'n wynomgewing is nie, maar ook effektief is teen MSB sonder dat die
gisfermentasies geaffekteer word. Bakteriosiene kan ook in kombinasie gebruik word om
die inhibisie spektrum te verbreed, en om ook moontlik die inhibisiepotensiaal van die
individuele peptiede te verhoog. Onderliggende interaksies by sulke kombinasies moet
egter sorgvuldig ondersoek word wanneer daar oorweeg word om kombinasies van hierdie
antimikrobiese middels in voedsel- en drankprodukte te gebruik. Verder moet daar ook
aandag geskenk word om biopreserveermiddels te vind wat ook teen die Gram-negatiewe
ASB effektief is, asook aan die aard van die verloop van interaksies van pare van
bakteriosiene oor tyd. Nog 'n punt om te oorweeg is die manipulasie van giste of bakterieë
omdie antimikrobiese peptiede in situ, as deel van hulle metabolisme, te produseer.
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The influence of leaf, cluster, and berry thinning, and leaf position and shading on yield, juice composition and vine vigor of hybrid grapes /Kaps, Martin L. January 1985 (has links)
No description available.
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Effect of oak aging treatments on the phenolic composition and sensory quality of Seyval blanc wines /Wilker, Karl Lawrence January 1986 (has links)
No description available.
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Pomace wines ; their composition and detectionEoff, John R. January 1916 (has links)
Master of Science
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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.
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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.
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