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Sensor technology to assess grape bunch temperature variability in Vitis vinifera L. cv. ShirazMoffat, Tessa 03 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The microclimate environment around the bunch is complex. The spatial distribution of leaves as well as bunch position and morphology impact on the path of direct radiation received by the berries. Canopy microclimate is largely determined by the meteorological conditions (air temperature, solar radiation, wind speed and direction, relative humidity, and precipitation) as well as management practices (trellis/training system, canopy height, vine spacing, row orientation, canopy management practices, irrigation and soil variability and management). The fact that the grapevine continuously responds to its environment, adds to the complexity and dynamic nature of the microclimate that the bunches experience. Field studies involving the effect of the natural bunch environment (i.e. light and temperature conditions) on berry composition, are therefore a challenge, due to the difficulties in quantifying meteorological elements such as temperature and light, which can be hugely variable.
There are different sensors available to assess bunch and berry temperature and it can be deployed in different ways within the grapevine canopy, but the difficulty remains in studying the variability that exists within a bunch. This study investigated the value of available sensor technology to measure bunch/berry temperature as well as the spatial and temporal variability on a bunch. Differences in temperature on an intra-berry level were assessed whereas the impact of canopy configuration and bunch orientation on the different sensor levels was also investigated. The contribution of macro- and mesoclimate on bunch and berry temperature was addressed by measuring at two locations (Robertson and Stellenbosch). The potential long term differences in temperature within a bunch with regard to thermal accumulation are discussed. Issues around sensor placement and some technical difficulties related to the sensors are discussed. The results indicated how the effects of mesoclimate were transferred through to the different sensors. A dominating effect of the sea breeze in Stellenbosch was found. Canopy configuration/architecture affected the light regime in the canopy, consequently impacting on bunch temperature variability, specifically in Stellenbosch where a "Ballerina" trellising system was used. Bunch orientation resulted in differences in the temporal variability of bunch/berry temperature and little variability was observed in temperature within the berry. Temperatures of berries situated at the back of the bunch were judged more optimal compared to exposed berries. Direct radiation caused extreme temperatures in exposed berries, which may be detrimental to berry composition and wine quality. This emphasized the importance of the canopy (trellis/training system and management practices) in protecting the bunch from extreme conditions. The large on-bunch spatial variability, observed from measurements with the thermal imager, demonstrated the importance of sensor placement in quantifying the bunch temperature regime; this is also relevant for the future development of berry temperature modelling. Thermal accumulation through the season also illustrated the variability that existed within a bunch, suggesting a potential long term effect on the berry composition. This study proved, in conditions similar to those that may prevail in the South African wine industry, that sensor type and positioning need to be carefully considered in any viticultural/oenological study where bunch microclimate and grape temperatures are assessed. / AFRIKAANSE OPSOMMING: Die mikroklimaat omgewing rondom die tros is kompleks. Die ruimtelike verspreiding van blare sowel as trosposisie en -morfologie het 'n impak op die pad waarlangs direkte straling ontvang word deur die korrels. Lowermikroklimaat word grootliks bepaal deur die meteorologiese kondisies (lugtemperatuur, sonstraling, windspoed en -rigting, relatiewe humiditeit en reënval) sowel as bestuurspraktyke (prieel/opleistelsel, lowerhoogte, wingerdstokspasiëring, ry-oriëntasie, lowerbestuurspraktyke, besproeiing asook grondvariasie en bestuur). Die feit dat die wingerdstok voortdurend reageer op sy omgewing dra by tot die kompleksiteit en dinamiese aard van die mikroklimaat wat die trosse ervaar. Veldstudies gemoeid met die effek van die natuurlike trosomgewing (d.w.s. lig- en temperatuurkondisies) op korrelsamestelling is daarom 'n uitdaging. Die rede hiervoor is dat dit problematies is om meteorologiese elemente soos temperatuur en lig, wat baie veranderlik kan wees, te kwantifiseer.
Verskillende sensors is beskikbaar waarmee tros- en korreltemperatuur bepaal kan word en dit kan op verskillende wyses binne die wingerdstoklower aangewend word. Die bestudering van die variasie wat bestaan binne 'n tros is egter steeds problematies. Hierdie studie het die waarde ondersoek van die beskikbare sensortegnologie vir die meting van tros/korreltemperatuur en die ruimtelike en tydsvariasie op 'n tros. Verskille in temperatuur op 'n intra-korrelvlak is bepaal terwyl die impak van lowerkonfigurasie en trosoriëntasie op die verskillende sensorvlakke ook ondersoek is. Die bydrae van makro- en mesoklimaat tot tros- en korreltemperatuur is ondersoek deur te meet by twee verskillende liggings (Robertson en Stellenbosch). Die potensiële langtermyn verskille in temperatuur binne-in 'n tros met betrekking tot temperatuur akkumulasie word bespreek. Kwessies rakende sensorplasing en sommige tegniese probleme wat verband hou met sensors word bespreek. Die resultate het aangedui hoedat die effekte van mesoklimaat oorgedra is na die verskillende sensors. 'n Dominerende effek van die seebries is waargeneem in Stellenbosch. Lowerkonfigurasie/argitektuur het die ligregime in die lower beïnvloed en gevolglik 'n invloed gehad op die trostemperatuur veranderlikheid. Dit was veral die geval in Stellenbosch waar 'n "Ballerina" opleistelsel gebruik is. Trosoriëntasie het gelei tot verskille in tydsvariasie van tros/ korreltemperatuur en min variasie is waargeneem in temperatuur binne die korrel. Temperature van korrels wat voorkom aan die agterkant van die tros is beoordeel as meer optimaal vergeleke met blootgestelde korrels. Direkte straling het uiterste temperature in blootgestelde korrels veroorsaak wat nadelig kan wees vir korrelsamestelling en wynkwaliteit. Hierdeur is die belang van die lower (prieel/opleistelsel en bestuurspraktyke) om die tros te beskerm teen uiterste kondisies beklemtoon. Die groot ruimtelike variasie op 'n tros, soos waargeneem in metings met die termiese kamera, het die belangrikheid van sensorplasing in die kwantifisering van die trostemperatuur regime beklemtoon. Dit is ook relevant vir die toekomstige ontwikkeling van korreltemperatuur modellering. Termiese akkumulasie gedurende die seisoen is ook geïllustreer deur die veranderlikheid wat voorkom binne 'n tros, wat dui op 'n potensiële langtermyn effek op die korrelsamestelling. Hierdie studie het bewys, in kondisies wat algemeen voorkom in die Suid-Afrikaanse wynbedryf, dat sensortipe en -plasing sorgvuldig in ag geneem moet word in enige wingerd/wynkundige studie waar trosmikroklimaat en druiftemperature bepaal word. / Winetech and the National Research Foundation for their financial support of the project
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Channelling metabolic flux away from ethanol production by modification of gene expression under wine fermentation conditionsHeyns, Eva Hutton 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: There is a global demand for technologies to reduce ethanol levels in wine without
compromising wine quality. While several chemical and physical methods have been developed
to reduce ethanol in finished wine, the target of an industrially applicable biological solution has
thus far not been met. Most attempted biological strategies have focused on developing new
strains of the main fermentative organism, the yeast Saccharomyces cerevisiae. Gene
modification approaches have primarily focused on partially redirecting yeast carbon
metabolism away from ethanol production towards glycerol production. These techniques have
met with some moderate success, thus the focus of the current study was to re-direct carbon
flux towards trehalose production by moderate over-expression of the TPS1 gene. This gene
encodes trehalose-6-phosphate synthase, which converts glucose 6-phosphate and UDPglucose
to α,α-trehalose 6-phosphate. Previous data have shown that the overproduction of
trehalose restricts hexokinase activity reducing the amount of glucose that enters glycolysis.
Nevertheless, preliminary TPS1 over-expression studies using multiple copy plasmids have
shown some promise, but also indicated significant negative impact on the general fermentation
behaviour of strains. In order to reduce such negative impacts of excessive trehalose
production, a new strategy consisting in increasing the expression of TPS1 only during specific
growth phases and by a relatively minor degree was investigated. Our study employed a lowcopy
number episomal vector to drive moderate over-expression of the TPS1 gene in the widely
used industrial strain VIN13 at different stages during fermentation. The fermentations were
performed in synthetic must with sugar levels representative of those found in real grape must.
This, as well as the use of an industrial yeast strain, makes it easier to relate our results to real
winemaking conditions. A reduction in fermentation capacity was observed for all transformed
strains and controls. Expression profiles suggest that the DUT1 promoter certainly results in
increased TPS1 expression (up to 40%) during early exponential growth phase compared to the
wild type strain (VIN13). TPS1 expression under the control of the GIP2 promoter region
showed increased expression levels during early stationary phase (up to 60%). Chemical
analysis of the yeast and the must at the end after fermentation showed an increase in
trehalose production =in line with the expression data of TPS1. Importantly, glycerol production
was also slightly increased, but without affecting acetic acid levels for the transformed strains.
Although ethanol yield is not significantly lower in the DUT1-TPDS1 strain, s statistically
significantly lower ethanol yield is observed for over-expression under the GIP2 promotor.
Increasing trehalose production during stationary phase appears therefore to be a more
promising approach at lowering ethanol yield and redirecting flux away from ethanol production.
This controlled, growth phase specific over expression suggests a unique approach of lowering
ethanol yield while not impacting on the redox balance. / AFRIKAANSE OPSOMMING: Wêreldwyd is daar ‘n aanvraag na tegnologie wat die etanol vlakke in wyn kan verminder
sonder om wyngehalte te benadeel. Terwyl verskeie chemiese en fisiese metodes ontwikkel is
om etanol in die finale wynproduk te verminder, is die soeke na 'n industrieel gebaseerde
biologiese oplossing tot dusver nie gevind nie. Meeste biologiese strategieë fokus op die
ontwikkeling van nuwe rasse van die primêre fermentatiewe organisme, naamlik
Saccharomyces cerevisiae. Geen modifikasie benaderings het hoofsaaklik gefokus op die
gedeeltelike kanalisering van koolstof metabolisme weg van etanol produksie na gliserol
produksie. Hierdie benadering is net matiglik suksesvol, dus is ons huidige fokus om koolstof te
kanaliseer na trehalose produksie deur gematigde oor-uitdrukking van die TPS1 geen. Hierdie
geen kodeer vir trehalose-6-fosfaat sintase, wat glukose-6-fosfaat en UDP-glukose omskakel na
α, α-trehalose-6-fosfaat. Vorige data het getoon dat die oorproduksie van trehalose hexokinase
aktiwiteit beperk en die hoeveelheid glukose wat glikolise binne gaan. Voorlopige TPS1 ooruitdrukking
studies met behulp van multi-kopie plasmiede toon matige sukses, maar het ook ‘n
negatiewe impak op die algemene fermentasie kapasiteit van die gis. Ten einde so 'n negatiewe
impak van oormatige trehalose produksie te oorkom, is 'n nuwe strategie gevolg wat bestaan uit
die verhoogde uitdrukking van die TPS1 geen slegs gedurende spesifieke groei fases met baie
lae vlakke van oor-uitdrukking. Ons studie gebruik 'n lae-kopie episomale vektor met matige
oor-uitdrukking van die TPS1 geen in die industriële ras VIN13 op verskillende stadiums tydens
fermentasie. Die fermentasie is uitgevoer in sintetiese mos met suiker vlakke
verteenwoordigend van dié van werklike wyn mos. Hierdie, sowel as die gebruik van 'n
industriële gisras, maak dit makliker om ons resultate te vergelyk met regte wyn fermentasie
kondisies. Verlaagde fermentasie kapasiteit is waargeneem vir alle getransformeerde stamme
en hul kontroles. Geen uitdrukkings profiele dui op verhoogde TPS1 uitdrukking (tot 40%) onder
beheer van die DUT1 promotor gedurende die vroeë eksponensiële groeifase wanneer vergelyk
word met die wilde tiepe (VIN13). TPS1 uitdrukking onder die beheer van die GIP2 promotor het
verhoogde uitdrukking van tot 60% gedurende die vroeë stasionêre fase. Chemiese analise van
die gis aan die einde van fermentasie dui op ‘n toename in trehalose produksie wat korreleer
met die uitdrukking profiele van TPS1. Gliserol produksie is ook effens verhoog, maar sonder ‘n
toename in asynsuur vlakke vir die getransformeerde rasse. Alhoewel etanol opbrengs nie
aansienlik laer vir die DUT1-TPS1 ras is nie, is etanol opbrengs vir die oor-uitdrukking onder
beheer van die GIP2 promotor wel laer. Toenemende trehalose produksie gedurende
stasionêre fase blyk dus 'n meer belowende benadering op die verlaging van etanol opbrengs
en her-kanaliseering weg van etanol produksie. Hierdie benadering met die fokus op groeifase
spesifieke oor-uitdrukking dui op 'n unieke strategie vir die verlaging van etanol opbrengs
sonder om die redoks balans te beinvloed. / The NRF, IWBT and Stellenbosch University for funding
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Site and vintage response of malic and tartaric acid in Vitis vinifera L. cv’s Cabernet Sauvignon and Sauvignon blancCoetzee, Zelmari 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Acids are one of the major components that originate largely from the berry, that are found in
wine, and that influence the sensory perception. The presence of organic acids in adequate
concentrations in the grape berry, of which tartaric- and malic acid are the main organic acids
present, is important as this determines the potential of a must to produce a good and stable
wine.
The effect of temperature on the organic acid content of the must is widely discussed with
higher temperatures in general being associated with lower quantities of organic acids present
in the juice, and lower temperatures during ripening associated with higher quantities,
specifically in the case of malic acid.
Due to the topographical diversity of the Stellenbosch Wine of Origin district and the closeness
of the ocean and the occurrence of sea breezes, the mesoclimate differs greatly over short
distances. Sixteen sites, consisting of eight Sauvignon Blanc and Cabernet Sauvignon sites
respectively, were selected from a broader terroir study site network. Three vintages with
complete climatic datasets were selected for vintage comparisons. Climate in the study area
was monitored on differing scales, and data from a weather station network, as well as from
mesoclimatic dataloggers within the sites were available.
The available data was firstly compared to determine the variability of the data, not only
between the two climatic scales, but also between the sites. Different climate classification
indices and parameters available in literature were thereafter compared and evaluated for the
best representation in this area. The Huglin index was found to be a better representation
regarding the thermal climatic indices. Due to the great differences between temperatures noted
for the mesoclimatic loggers and the nearest automatic weather station, the use of mesoclimatic
logger data was preferred, and is advised in future studies where this scale of data is available.
Malic and tartaric acid has a definite synthesis period up until véraison, after which the content
of tartaric acid remains constant in the berry and the content of malic acid decreases until
harvest due to mainly respiration. The temperature data was therefore separated in a synthesis
period from flowering to véraison, and a ripening period from véraison to harvest.
In this study, clear differences were firstly seen in the climate as expected, not only between
sites per vintage, but in addition between vintages and between vintages per site. The
phenological differences between the sites could be largely attributed to the differences in
temperature as phenology and temperature was found to be highly correlated in this study.
Differences in the ripening parameters were noticed in addition to the contents of the organic
acids between sites, although no definite contribution of temperature was shown to affect the
contents of these compounds at either véraison or harvest. These differences may be attributed
to other factors such as the soil water content and the canopy architecture. In addition, these
factors all contribute in differing percentages to the differences found in the contents per site.
It was found though that temperature can be used as an indicator of the organic acid content in
the grape berry, considering that the temperature data is available on a mesoclimatic scale,
separated in a synthesis and period of degradation, and the number of hours within the
temperature thresholds are determined. Differences seen in the organic acid contents can
however not only be attributed to the differences in topography and the temperature as
discussed in this study. / AFRIKAANSE OPSOMMING: Sure is belangrike druifkomponente wat grootliks hul oorsprong in die korrel het, in die wyn
voorkom, en die sensoriese persepsie van die wyn beïnvloed. Die voorkoms van organiese
sure in genoegsame konsentrasies in die korrel, waarvan wynsteensuur en appelsuur die hoof
organiese sure is, is belangrik aangesien dit die potensiaal van die sap om ʼn goeie en stabiele
wyn te produseer, bepaal.
Hoe temperatuur die inhoud van organiese sure in die druiwesap affekteer is gereeld onder
bespreking, met hoër temperature in die algemeen geassosieer met ʼn laer inhoud van
organiese sure, terwyl laer temperature geassosieer word met ʼn hoër inhoud van organiese
sure in die sap, veral in die geval van appelsuur.
As gevolg van die topografiese diversiteit van die Stellenbosch Wyn van Oorsprong distrik,
asook die nabyheid van die oseaan met die gepaardgaande voorkoms van die seebries,
verander die mesoklimaat aansienlik oor klein afstande in hierdie area. Vir die studie was
sestien wingerde, wat bestaan het uit agt Sauvignon Blanc en agt Cabernet Sauvignon
wingerde, geselekteer vanuit ʼn groter terroir studie. Verder was drie seisoene, met volledige
klimaatsdatastelle, geselekteer vir die vergelyking van data tussen die seisoene.
Klimaat was op verskillende skale binne die studie area gemonitor en data van ʼn weerstasie
netwerk, sowel as van mesoklimaat dataversamelaars binne die wingerde, was beskikbaar. Die
beskikbare datastelle was vergelyk, asook geëvalueer, om die mees verteenwoordigende
datastel vir die area te bepaal. Met die oorweging van die termiese indekse was daar gevind dat
die Huglin indeks beter verteenwoordigend van die area was. Verder, as gevolg van die groot
verskille wat gevind is tussen die temperature gemeet met die mesoklimaat dataversamelaars
en die naaste outomatiese weerstasie, was daar besluit dat die gebruik van die mesoklimaat
data verkies is en is dit ook aan te beveel vir die gebruik in toekomstige navorsing indien die
tipe data beskikbaar is.
Wynsteen- en appelsuur het beide ʼn definitiewe sintese periode tot en met véraison, waarna die
hoeveelheid wynsteensuur in die korrel relatief konstant bly en die hoeveelheid appelsuur
afneem hoofsaaklik as gevolg van respirasie. Die temperatuur data was dus verdeel in ‘n
periode van sintese vanaf blom tot en met véraison, en ʼn rypwordingsperiode vanaf véraison tot
en met oes.
In hierdie studie was daar eerstens groot verskille waargeneem in die klimaat soos wat daar
verwag is. Hierdie verskille was nie net waargeneem as tussen die seisoene nie, maar ook
tussen die wingerde binne ʼn seisoen. Die fenologiese veskille tussen die wingerde wat ook
waargeneem is, kon hoofsaaklik aan die verskille in die temperatuur toegeskryf word en ʼn goeie
korrelasie tussen temperatuur en fenologie is opgemerk.
Merkwaardige verskille in die rypwordingsparameters, asook in die inhoud van die organiese
sure, was waargeneem, alhoewel die bydrae van temperatuur op die inhoud van hierdie
komponente by véraison of oes nie as definitief getoon is nie. Dit kan toegeskryf word aan die
bydrae van ander faktore, soos byvoorbeeld die grondwaterinhoud en die lowerargitektuur, op
die inhoud van hierdie komponente. Die addisionele faktore dra egter in verskillende
persentasies by tot die verskille waargeneem tussen die wingerde.
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The impact of amino acids on growth performance and major volatile compound formation by industrial wine yeastMcKinnon, Alexander 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Nitrogen composition of grape must is highly variable and impacts on the health of the
fermenting yeast population as well as the formation of aroma and flavour compounds in wine.
Insufficient yeast assimilable nitrogen (YAN), mostly consisting of amino acids and ammonium,
can lead to stuck or sluggish fermentations as well as the formation of undesirable compounds
such as H2S. Furthermore, it is well established that the total concentration of YAN and the
specific amino acid composition have a significant impact on the final aroma and flavour of
wines. However, the impact of individual amino acids and of specific amino acid compositions
on fermentation kinetics and on the production of aroma and flavour impact compounds under
winemaking conditions is not well understood.
The first goal of this study was to evaluate the effect of single amino acids on growth
kinetics and major volatile production of two industrial wine yeast strains under conditions
resembling wine fermentations. To facilitate these fermentation conditions while also allowing
for easy reproducibility and manipulation of the initial components, a synthetic grape media was
utilized. Biomass formation, exponential growth rate, lag phase, and fermentation duration were
utilized to evaluate the efficiency of single amino acids.
The data show that previously observed trends in laboratory strains mostly apply to these
conditions and strains. In general, the efficiency of amino acids to be used as nitrogen sources
and the production of major volatiles due to their presence followed the same patterns for both
industrial yeast strains. However, the production of the secondary metabolites butanol,
propanol, acetic acid, and ethyl acetate were found to be produced in different final
concentrations dependent upon the yeast strain.
The branched-chained and aromatic amino acids (BCAAs) treatments were observed to
have the most dramatic effects on major volatile production. Investigating the relationships
between the initial concentration of the BCAAs and the final concentrations of major volatile
compounds, it was found that the production of fusel alcohols and fusel acids due to the
degradation of BCAAs by S. cerevisiae could be predicted from the initial concentration of
BCAAs. While under simple nitrogen conditions the production of several other secondary metabolites such as butanol, propionic acid, valeric acid, decanoic acid and 2-phenylethyl
acetate were found to be correlated to the initial concentration of BCAAs in the media.
Future studies should focus on the validation of these trends in aroma production in real
grape musts under various fermentation temperatures for a number of industrial wine yeast
strains. / AFRIKAANSE OPSOMMING: Die stikstof samestelling van druiwemos is hoogs veranderlik en impakteer op die
kerngesondheid van die fermenterende gis populasie asook die produksie van aroma- en
geurverbindings in wyn. Onvoldoende assimileerbare stikstof (ook genoem “yeast assimilable
nitrogen” (YAN)), wat meestal bestaan uit aminosure en ammonium, kan aanleiding gee tot
steek- of slepende fermentasies, asook die vorming van ongewensde verbindings soos H2S. Dit
is alombekend dat die totale konsentrasie van YAN en dan ook die spesifieke aminosuur
samestelling ‘n noemenswaardige impak op die finale aroma en smaak van wyn het. Die
invloed van individuele am inosure en spesifieke aminosuur samestellings op die fermentasie
kinetika, asook die produksie van verbindings met ‘n impak op die wyn aroma en smaak, word
egter nie deeglik verstaan nie.
Die eerste doelwit van die studie was om twee industriële gisrasse te gebruik om die effek
van enkel aminosure op die groei-kinetika en produksie van die vername vlugtige verbindings
onder wynmaak toestande te bepaal. Kunsmatige, gedefinieerde druiwermosmedium is gebruik
om wynmaak toestande te simuleer en ook herhaalbaarheid en manipulering van die
aanvanklike samestelling van die medium te verseker.
Die studie het vorige tendense wat opgemerk is in die evaluasie van laboratorium rasse
onder soortgelyke toestande bevestig. Die doeltreffendheid waarmee aminosure oor die
algemeen gebruik word as stikstofbron, asook die produksie van die vernaamste vlugtige
verbindings wat gekoppel is aan hulle teenwoordigheid, het ‘n vergelykbare patroon vir beide
rasse gevolg. Die sekondêre metaboliete butanol, propanol, asetaat en etiel-asetaat is egter wel
in verskillende eindkonsentrasies geproduseer deur die verskillende gisrasse. Die vertakte-ketting en aromatiese aminosuur (“branched-chained and aromatic amino
acids” (BCAAs)) behandelings het die mees dramatiese effek op die produksie van die
vernaamste vlugtige komponente gehad. Ondersoek na die verwantskap tussen die
aanvanklike konsentraies van die BCAAs en die finale konsentrasies van dié verbindings het
aangedui dat die produksie van hoër alkohole en sure, as gevolg van die afbraak van BCAAs
deur S. cerevisiae, met behulp van die aanvanklike konsentrasie van die BCAAs voorspel kon
word. Terselfdertyd is gevind dat onder eenvoudige stikstoftoestande, verskeie ander sekondêre metaboliete soos butanol, propionaat, valeriaat, dekanoësuur en 2-fenieletielasetaat,
gekorreleer kan word met die aanvanklike BCAAs in die media.
Verdere studies moet poog om hierdie tendense ten opsigte van aromaproduksie te bevestig en
wel deur gebruik te maak van ware druiwemos, verskeie fermentasietemperature, asook ’n
verskeidenheid van wyngisrasse.
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Metabolic, genetic and physiological responses to SO2 exposure and nutrient-limiting conditions in Brettanomyces bruxellensisLouw, Marli 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Brettanomyces bruxellensis has become of increasing interest over the past few decades yet this complex red wine spoilage yeast is still poorly understood and strain variance also leads to the contradictory results reported in literature. This yeast is responsible for the production of phenolic compounds, associated with off-flavours that render wine unpalatable. Sulphur dioxide (SO2) is the most commonly used antioxidant and antimicrobial preservative instrumental in the control of spoilage yeasts such as B. bruxellensis. However, its diploid/triploid genome is enriched for genes that provide the yeast a fortuitous advantage, under conditions permissive for growth, with genotype-dependent SO2 tolerance phenotypes observed among numerous strains. This study investigates the metabolic, physiological and genetic responses associated with SO2 exposure. It also explores the environmental cues responsible for the onset of non-SO2 induced morphological characteristics. These morphological characteristics were investigated using fluorescent probes and microscopy in the presence of SO2 and in the absence thereof, in YPD media. Pseudohyphae formation was observed to be a highly strain dependent feature and less pronounced in the presence of 0.6 mg/L molecular SO2. This study also reports on the metabolic response observed over a 3-week period, following exposure to SO2, in a synthetic wine medium. The following metabolites were consistently monitored during the course of the experiment: acetic acid, acetaldehyde, D-glucose and D-fructose. Utilization of sugars was retarded in the presence of SO2 for up to 10 days in the presence of 1.2 mg/L molecular SO2 and overproduction of acetaldehyde was prominent, with a peak at day 10. The study further highlights the expression profiles observed for the SSU1 gene (referring to SO2 tolerance) and the PAD gene (referring to production of volatile compounds) under SO2 induced conditions in SWM, using qRT-PCR. The co-involvement of increased acetaldehyde production and elevated gene expression were indicative of B. bruxellensis yeast adapting to the presence of molecular SO2, allowing survival of this fascinating yeast. Sequencing of the SSU1 and PAD genes suggests the probable existence of different alleles of these genes that could explicate SO2 tolerance and phenolic compound production associated differences among strains of this species. / AFRIKAANSE OPSOMMING: Hoewel Brettanomyces bruxellensis oor die afgelope paar dekades toenemende belangstelling gewek het, word hierdie komplekse rooiwynbederfgis steeds swak verstaan en lei rasvariasie ook tot teenstrydige resultate in die literatuur. Hierdie gis is verantwoordelik vir die produksie van fenoliese verbindings, wat geassosieer word met afgeure, wat die wyn onsmaaklik laat. Swaweldioksied (SO2) is die algemeenste preserveermiddel wat, weens antioksidant- en antimikrobiese eienskappe, instrumenteel in die beheer van bederforganismes, soos B. bruxellensis, gebruik word. Nogtans is die diploïede/triploïede genoom vir gene verryk, wat die gis ‘n toevallige voordeel bied tydens ongunstige toestande, met genotipe-afhanklike SO2 weerstandbiedende fenotipes wat onder verskeie rasse waargeneem word. Hierdie studie ondersoek die metaboliese, fisologiese en genetiese reaksies tydens SO2-blootstelling. Dit bestudeer verder die omgewingsleidrade wat vir die aanvang van die nie-SO2 geassosiseerde morfologiese eienskappe verantwoordelik is. Hierdie morfologiese eienskappe is ondersoek met behulp van fluoresserende bakens en mikroskopie in die teenwoordigheid van molekulêre SO2 en, in die afwesigheid daarvan, in YPD-medium. Pseudohyphae-vorming is as ʼn baie rasspesifieke eienskap waargeneem en is minder prominent in die teenwoordigheid van molekulêre SO2. Hierdie studie rappoteer ook oor die metaboliese reaksies waargeneem oor ‘n 3-weke tydperk, na blootstelling aan SO2, in ‘n sintetiese wynmedium. Die volgende metaboliete was voordurend gemonitor tydens die verloop van die eksperiment: asynsuur, asetaldehied, D-glukose en D-fruktose. Benutting van die suikers is in die teenwoordigheid van SO2 vertraag en oorproduksie van asetaldehied is prominent waargeneem. Hierdie studie beklemtoon verder die uitdrukkingsprofiele vir die SSU1-geen (verwys na SO2-weerstandbiedendheid) en die PAD-geen (verwys na die produksie van vlugtige verbindings) in SO2-geïnduseerde toestande in SWM, met behulp van qRT-PCR. Die gesamentlike invloed van beide verhoogde asetaldehied produksie en verhoogde uitdrukking van gene, was beduidend van B. bruxellensis-gis wat aanpas in die teenwoordigheid van molekulêre SO2, wat die oorlewing van hierdie fassinerende gis verseker. Volgordebepaling van die SSU1- en PAD-geen dui daarop dat daar waarskynlik meer as een verskillende alleel vir dié gene bestaan, wat die SO2-verdraagsaamheid en produksie van fenoliese verbindings, wat tans tussen verskeie spesies teenwoordig is, kan verduidelik.
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Sensory characterisation of several red cultivar (Vitis vinifera L.) wines, using berry sugar accumulation as a physiological indicator and sequential harvestNell, Marissa 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The global wine industry has shifted to a more adopted ‘consumer-preference’ production. Modern wine consumers are more knowledgeable and cultivated in their understanding of wine quality, value and style. The quality of red wines mainly depends on grape composition, the wine making process and the ability of tasters to recognise sensory attributes. The harvest date/stage has an influence on the grape composition, thus making the decision on when to harvest an important factor in the production of quality wines or different wine styles.
The traditional indicators used in the wine industry to determine time of harvest are more related to the perception of taste and mouthfeel and give little indication of the style of wine in terms of aromatic profile. A new physiological indicator using berry sugar accumulation for the purpose of sequential harvest is proposed to assist the winemaker in producing wines with possible different sensory profiles. This indicator can be used in association with the classical indicators of ripening to affect the diversity of wine styles from a single vineyard or a group of vineyards. The wines could thus have different potential aroma profiles, depending on when the grapes were harvested.
The main aim of this study was to assess the effect of performing sequential harvest using a physiological indicator on red wine’s sensory composition. This was done to study the possible relation between harvest time (e.g. fruit composition evolution) and the wine styles/sensory attributes across the different harvest times, thereby possibly increasing the diversity of wine styles. A theoretical berry sugar loading concept was compiled and displays a phase of rapid sugar loading starting at véraison followed by a plateau phase. Depending on whether grapes were harvested in the beginning, mid or end of the plateau phase of fruit sugar accumulation the wines could have different potential aroma profiles. Three main stages: fresh fruit (FF), neutral (N) or pre ripe and mature fruit (MF) has been previously proposed using the sugar loading concept and in terms of harvesting dates.
Cabernet Sauvignon and Merlot grapes form Eikendal Vineyards, Stellenbosch were used to make wines according to sequential harvest. Four harvest stages were considered, pre fresh fruit (Pre FF), fresh fruit (FF), mature fruit (MF) and over ripe (OR). The wines were tasted and analysed using two different sensory techniques. In both Merlot and Cabernet Sauvignon wines, the PreFF and OR stages could be more easily discriminated than the two harvest stages in-between, FF and MF. The results suggested that the wines made from the FF and MF stages could not be distinguished from each other in general when the attribute citation frequency method or sorting tasks were performed. However, a trend could be observed for both Cabernet Sauvignon and Merlot wines in terms of aroma attributes with attributes changing from green to ripe fruit during ripening using expert tasters. Relevant research should be engaged to refine sequential harvest in order to obtain more diverse wine styles from a single site or a group of vineyards. / AFRIKAANSE OPSOMMING: Die wêreldwye wynbedryf het ’n verskuiwing ondergaan na ’n verbruikersvoorkeurbenadering in produksie. Wynverbruikers is deesdae beter ingelig en meer ontwikkeld ten opsigte van hulle kennis van wyngehalte, wynstyl, asook die waarde van wyn. Die gehalte van rooiwyn hang hoofsaaklik af van die druifsamestelling, die wynmaakproses en die vermoë van proewers om sensoriese eienskappe te herken. Aangesien die oesdatum/-fase ’n invloed het op druifsamestelling, is die besluit oor wanneer daar geoes moet word ’n belangrike faktor in die vervaardiging van gehaltewyne of verskillende wynstyle.
Die tradisionele aanwysers wat in die wynbedryf gebruik word om oestyd te bepaal, hou verband met die waarneming van smaak en mondgevoel en gee weinig aanduiding van die wynstyl op grond van die aromatiese profiel. ’n Nuwe fisiologiese aanwyser wat gebruik maak van suikerakkumulasie in die druiwekorrel in opeenvolgende oeste, het ten doel om die wynmaker te help om wyne met verskeie moontlike sensoriese profiele te vervaardig. Hierdie aanwyser kan saam met die klassieke aanwysers van rypwording gebruik word om ’n verskeidenheid wynstyle uit een wingerd of wingerdgroep te vervaardig. Die wyne kan dus potensieel oor verskillende aromatiese profiele beskik, afhangend van wanneer die druiwe geoes is.
Die hoofdoel van die studie was om die invloed van opeenvolgende oes te toets deur ’n fisiologiese aanwyser op rooiwyn se sensoriese samestelling toe te pas. Dit word gedoen deur die moontlike verhouding tussen die oestyd (bv. ontwikkeling van vrugsamestelling) en die wynstyle of wyn se sensoriese kenmerke op verskillende oestye te bestudeer ten einde die verskeidenheid wynstyle potensieel te vermeerder. ’n Teoretiese konsep van druifsuikeropname is saamgestel wat dui op ’n fase van vinnige suikeropname wat by véraison begin, gevolg deur ’n plato-fase. Wyn kan oor verskillende moontlike aromatiese profiele beskik, afhangend daarvan of die druiwe aan die begin, middel of einde van die plato-fase van suikeropname geoes is. Drie hooffases is al voorheen voorgestel deur gebruik te maak van die konsep van suikeropname volgens oesdatum, te wete vars vrugte (VV) (“fresh fruit”, FF), neutraal (N) (“neutral”, N) of voor ryp (“pre ripe”), en ryp vrugte (RF) (“mature fruit”, MF).
Cabernet Sauvignon- en Merlot-druiwe van Eikendal, Stellenbosch, se wingerde is gebruik om wyn volgens opeenvolgende oes te maak. Vier oesfases is oorweeg, te wete voor vars vrugte (VVV) (“pre fresh fruit”, Pre FF), vars vrugte (VV) (“fresh fruit”, FF), ryp vrugte (RV) (“mature fruit”, MF), en oorryp (OR) (“over ripe”, OR). Die wyn is geproe en geanaliseer deur gebruik te maak van twee verskille sensoriese tegnieke. In die geval van beide die Merlot- en Cabernet Sauvignon-wyn kon die VVV- en OR-fases makliker onderskei word as die twee tussenin-fases, VV en RV. Resultate dui daarop dat wyn wat van die VV- en RV-fases gemaak is, oor die algemeen nie van mekaar onderskei kan word wanneer die frekwensie van kenmerkaanhaling-metode en sorteringstaak uitgevoer word nie. ’n Tendens kon egter waargeneem word vir Cabernet Sauvignon- én Merlot-wyn ten opsigte van aromatiese kenmerke, deurdat kenmerke gedurende rypwording van groen na ryp vrugte verander het indien ekspertproewers gebruik is. Verdere navorsing moet gedoen word om opeenvolgende oes te verfyn ten einde ’n wyer verskeidenheid wynstyle van ’n enkele area of wingerdgroep te verkry.
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Application of modern analytical techniques and chemometric methods to the chemical characterisation of South African wines : determination of non-volatilesDe Villiers, A. J. (Andre Joubert) 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The present study deals in the first instance with the improvement of current analytical
techniques for the analysis of the non-volatile content of wines. An improved sample
preparation method, using solid phase extraction (SPE), was initially developed for the
analysis of organic acids, sugars and phenolic compounds. Consequently, modem
analytical methodologies were assessed to obtain optimal techniques for the separation of
various non-volatile compounds. A capillary electrophoresis (CE) method, demonstrably
more reliable than currently used high performance liquid chromatography (HPLC) and CE
methods, is proposed for the analysis of organic acids. HPLC with refractive index (RI) or
evaporative light scattering detection (ELSD) proved more suitable than CE for the analysis
of sugars in dry wines. Liquid-chromatography-mass spectroscopy (LC-MS) offered
superior sensitivity and resolution compared to the relatively new technique of CE-MS for
the analysis of wine phenolics. LC-MS was further applied for the efficient and sensitive
analysis of non-coloured phenolics and anthocyanins in wine. Negative- and positive
electrospray ionisation, respectively, were used in conjunction with an ion-trap mass
analyzer, for the identification of 34 phenolics and 31 anthocyanins in red wine samples.
Complementary CE and LC methods were developed to allow the identification of artificial
dyes in red wines, added illegally to improve their colour. Also, the application of stir bar
sorptive extraction (SBSE) with liquid desorption and micellar electrokinetic
chromatography (MEKC) for the analysis of bitter acids in beer is reported.
In the second part of the thesis, the analytical results obtained for South African red and
white wines were evaluated. Following comparison of the results with literature reports,
several pattern recognition techniques were employed. A classification function obtained by
linear discriminant analysis (LDA) was used to classify both red and white wines according
to variety, based on their chemical composition. This classification is achieved independent
of the factors of wine age or geographical origin, making it useful for authenticity
evaluation. / AFRIKAANSE OPSOMMING: Hierdie studie het as primêre doel die verbetering van bestaande analitiese metodes vir die
analise van nie-vlugtige komponente in wyn. In die lig hiervan, is eerstens 'n toepaslike
monster-voorbereidingstegniek, gebasseer op soliede fase ekstraksie (SPE), ontwikkel vir
die gelyktydige analise van organise sure, suikers en fenoliese komponente vanuit die wyn
matriks. Vervolgens is moderne analitiese rtietodes ondersoek en gepastde
skeidingstegnieke is ontwikkel vir die verskillende chemiese wyn-komponente. Kappillêre
elektroforese (CE) en hoë-druk vloeistof-chromatografie (HPLC) in kombinasie met
verskeie deteksie-metodes is vergelyk. Hieruit is 'n verbeterde CE metode vir die analise
van organise sure is ontwikkel, terwyl HPLC in kombinasie met refraksie-indeks- en
verdampings lig verstrooiings deteksie (ELSD) die beste resultate lewer vir die analise van
suikers in droë wyne. Die toepasbaarheid van vloeistof-chromatografie met massa
spektrometriese deteksie (LC-MS) vir die analise van fenoliese komponente is
gedemonstreer, terwyl CE-MS onvoldoende resolusie en sensitiwiteit toon vir die analises.
LC-MS is vervolgens ook gebruik vir die identifikasie van 34 fenoliese verbindings en 31
antosianiede in rooi wyn. Komplementêre HPLC en CE metodes is ontwikkel vir die
identifikasie van onwettige sintetiese kleurstowwe in' rooi wyn. 'n Addisionele monstervoorbereidingsstap,
roerstaaf sorptiewe ekstraksie (SBSE), is saam met vloeistof-desorpsie
en misellêre elektrokinetiese chromatografie (MEKC) gebruik vir die analise van hops
bitter sure in bier.
In die tweede deel van die tesis word die resultate verkry m.b.v. bg. tegnieke vir die analise
van Suid-Afrikaanse rooi- en wit wyne, bespreek. Die resultate is vergelyk met waardes uit
die literatuur, en verskeie statistiese metodes is gebruik om die data te ondersoek. Met
behulp van chemometriese metodes is 'n klassifikasie funksie verkry wat die klassifikasie
van Suid-Afrikaanse wyne volgens druifsoort, gebasseer op die chemiese samestelling van
die wyne, toelaat. Die klassifikasie is moontlik, onafhanklik van die ouderdom of
geografiese oorsprong van die wyne.
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Applicatins of liquid chromatography-tandem mass spectrometry to wine analysis : targeted analysis and compound identificationAlberts, P. 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The wine industry is an important sector of agriculture and wine analysis forms the basis of
assessing compliance of its commodities with regulatory standards and research in this field.
Liquid chromatography (LC) is extensively used for the determination of a wide range of nonvolatile
wine components, but conventional detectors impose performance limitations on the
technique that prevents its application to sophisticated analytical problems. In particular,
conventional detectors for LC often lack the sensitivity and specificity for the determination of
many wine compounds, especially trace level analytes, and furthermore, do not possess
spectral capabilities for compound identification or structure elucidation. The hyphenation of
mass spectrometry (MS) to LC has led to the introduction of a range of detectors that confers
high levels of sensitivity and selectivity to the technique. In addition, a wide variety of MS
architectures are available that are inherently suited for targeted analysis or structure
elucidation studies.
In this dissertation, the potential benefits of liquid chromatography – tandem quadrupole mass
spectrometry (LC-MS/MS) to solve analytical problems relevant to the wine industry are
explored. LC-MS/MS is a particularly versatile analytical technique because both mass
analysers can be operated in full-spectrum mode or selected-ion monitoring, which, together
with optional fragmentation, gives rise to four modes of operation that may be used for highly
specific and sensitive targeted analysis or spectral investigations. In multiple reaction monitoring (MRM) mode, both analysers are set at single ion frequencies
specific for the compound under investigation and one or more of its product fragments,
respectively. MRM mode is ideally suited for trace level analysis in complex mixtures, even in
cases where the target components are not resolved from interferences. In this study, MRM
detection was used to solve challenges relevant to the wine industry for the selective
quantitation of target analytes that could not be analysed by conventional LC methods. The
application of this approach for the analysis of natamycin, ethyl carbamate (EC) and 3-alkyl-2-
methoxypyrazines (MPs) in wine is demonstrated.
Natamycin is an antimicrobial preservative that is not permitted in wine in the European Union.
A rapid and sensitive method for the determination of natamycin was developed, and has been used since 2009 to regulate this vitally important sector of the South African wine export
industry.
EC is a natural carcinogen that occurs at trace level amounts in alcoholic products. It also has
the potential to accumulate in wines and can occur in very high concentrations in some fruit
brandies. The determination of EC is complicated by its physicochemical properties, and
available analytical methods suffer from drawbacks such as the requirement for elaborate
extraction procedures and high solvent consumption. A novel method for the determination of
EC in wines, fortified wines and spirits is described and it was applied to perform an audit of the
South African industry as well as to investigate factors responsible for its accumulation in
alcoholic beverages. This work forms an integral part of the food safety mandate of the State
and it ensures that export products comply with international norms for trade.
MPs are ultra-trace-level aroma compounds that contribute to the varietal character of
Sauvignon blanc wines. Their analytical determination is challenging due to their low levels of
occurrence. The loading capacity of LC combined with the sensitivity and resolving power of MS
was exploited to analyse concentrated extracts, in order to achieve very low limits of detection.
The performance of the LC-MS/MS method enabled the quantitation of these compounds at
their natural levels of occurrence, including the first quantitation and spectral confirmation of 3-
ethyl-2-methoxypyrazine in wine. Extensive data pertaining to South African Sauvignon blanc
wines are reported and statistical analysis is performed, reporting the correlation of variables
such as vintage and origin as well as wine parameters such as malic acid with wine MPs. Furthermore, the application of LC-MS/MS for structural elucidation and screening of target
classes of analytes was demonstrated for the analysis of red wine anthocyanins. The
anthocyanidin-glycosides are responsible for the colour of red grapes and wine, contribute to
the sensory properties of wine, and are also of interest due to their beneficial biological
properties. Their determination is complicated by their large numbers and structural diversity,
further exacerbated by diverse reactions during wine ageing as well as the lack of reference
standards for most members of this class of compounds. Tandem MS in scan mode was used
for the highly selective detection of glycosylated anthocyanins and derivatives, exploiting the
predictable elimination of the sugar moiety in neutral loss mode. Concurrent survey scan
experiments were used to unambiguously identify neutral loss detected compounds. The
method therefore follows a simplified and structured approach for unambiguous peak identification based on elution order and mass spectral information to impart a high level of
certainty in compound identification.
In summary, the work presented in this dissertation demonstrates that LC-MS/MS is a versatile
and powerful analytical approach for the analysis of diverse compounds of relevance to the wine
industry. The sensitivity and specificity of MRM mode, and the selectivity and spectral
capabilities of neutral loss and survey scan modes of MS/MS detection, is amply demonstrated
by the applications presented in the dissertation. / AFRIKAANSE OPSOMMING: Die wynbedryf is ‘n belangrike komponent van landbou en wyn-analise vorm ‘n integrale deel
van gehalteversekering ten opsigte van toepaslike wetlike standaarde. Wyn-analise is ook
belangrik in navorsing oor die samestelling van wyn. Vloeistofchromatografie word dikwels
aangewend vir die bepaling van ‘n wye verskeidenheid nie-vlugtige wynkomponente, maar
konvensionele detektors plaas beperkinge op die aanwending van die tegniek tot
gesofistikeerde analitiese toepassings. Meer spesifiek, konvensionele detektors vir
vloeistofchromatografie beskik nie oor die sensitiwiteit en selektiwiteit vir die bepaling van baie
wynkomponente nie, veral in die geval van spoorvlakanalise, en beskik boonop ook nie oor
spektrale vermoëns vir identifikasie van komponente en struktuurbepaling nie. Die koppeling
van vloeistofchromatografie met massaspektrometrie het ‘n reeks detektors tot die tegniek
toegevoeg wat hoë vlakke van sensitiwiteit en selektiwiteit bied. Verder bied die verskeidenheid
van massaspektrometrie-konfigurasies ook instrumente wat inherent geskik is vir geteikende
analise of struktuurbepaling, afhangende van die doel van die ondersoek.
In hierdie dissertasie word die voordele ondersoek wat verbonde is aan die aanwending van
vloeistofchromatografie – tandem kwadrupool massaspektrometrie om relevante analitiese
vraagstukke in die wynbedryf op te los. Hiedie tegniek is besonder toepaslik aangesien beide
massa-analiseerders in geselekteerde-ioon modus of in volle skandering gebruik kan word.
Tesame met opsionele fragmentasie, gee hierdie uitleg aanleiding tot vier funksionaliteite wat vir
hoogs sensitiewe geteikende analise of spektrale onledings gebruik kan word. Eerstens word beide massa analiseerders vir enkel-ioon frekwensies opgestel, spesifiek tot die
teikenkomponent en een of meer van sy produkfragmente, wat verkry word deur komponentspesifieke
fragmentasie. Hierdie modus is by uitstek geskik vir spoorvlakontleding van
komplekse monsters, selfs wanneer die teikenkomponente nie chromatografies van die matriks
geskei is nie. In hierdie studie is die tegniek aangewend vir die hoogs sensitiewe bepaling van
spoorvlak komponente wat nie met konvensionele detektors gemeet kon word nie. Die
aanwending van hierdie tegniek word gedemonstreer vir die spoorvlakbepaling van natamycin,
etielkarbamaat en 3-alkiel-2-metoksiepierasiene in wyn.
Natamycin is ‘n antimikrobiese preserveermiddel wat ontoelaatbaar is in wyn in die Europese
Unie. ‘n Vinnige en sensitiewe metode vir die bepaling van natamycin is ontwikkel, en word reeds sedert 2009 aangewend om hierdie uiters belangrike sektor van die Suid-Afrikaanse wyn
uitvoerbedryf te reguleer.
Etielkarbamaat is ‘n karsinogeen wat natuurlik voorkom in spoorhoeveelhede in alkoholiese
produkte. Dit kan ook onder sekere omstandighede akkumuleer in wyn en in hoë konsentrasies
voorkom in vrugtebrandewyne. Die bepaling van etielkarbamaat word bemoeilik deur sy
chemiese eienskappe, en gevolglik word analitiese metodes gekenmerk deur uitgebreide,
arbeidsintensiewe monstervoorbereiding en die gebruik van groot hoeveelhede, meestal giftige,
oplosmiddels. ‘n Nuwe metode vir die bepaling van etielkarbamaat in wyn, gefortifiseerde wyn
en spiritualië word beskryf en word aangewend om die faktore vir vorming daarvan te
ondersoek. Die metode word aangewend om die Suid-Afrikaanse bedryf te ouditeer in terme
van die voedselveiligheid mandaat van die Staat, en om te verseker dat uitvoere voldoen aan
standaarde vir internasionale handel. Metoksiepierasiene is vlugtige, ultraspoorvlak wynaromakomponente wat verantwoordelik is vir
die kenmerkede kultivarkarakter van Sauvignon blanc wyne. Hul analitiese bepaling word
bemoeilik deur hulle lae konsentrasies in wyn. Die ladingskapasiteit van vloeistofchromatografie
tesame met die sensitiwiteit en selektiwiteit van massaspektrometrie was benut om hoogs
gekonsentreerde ekstrakte te ontleed. Baie hoë vlakke van sensitiwiteit word sodoende verkry.
Die verrigting van die metode was voldoende om hierdie komponente teen hulle natuurlike
konsentrasies te kwantifiseer, insluitende die eerste kwantifisering en spektrale bevestiging van
3-etiel-2-metoksiepierasien. Omvattende data van die vlakke van hierdie komponente in Suid-
Afrikaanse Sauvignon blanc wyne word getoon en statistiese ontleding is gedoen om
korrelasies tussen veranderlikes soos oorsprong en oesjaar sowel as basiese wyn
veranderlikes soos byvoorbeeld appelsuur, met metoksiepierasienvlakke te ondersoek.
Verder was die toepassing van vloeistofchromatografie – tandem massaspektrometrie tot
struktuurbepaling en skandering vir groepe van komponente gedemonstreer vir die ontleding
van rooiwyn antosianiene. Die antosianien-glukosiede is verantwoordelik vir die kleur van rooi
druiwe en wyn, dra by tot die sensoriese eienskappe daarvan, en is ook relevant as gevolg van
die voordelige biologiese eienskappe daarvan. Die bepaling van hierdie komponente word
gekompliseer deur hulle groot getalle en strukturele diversiteit, verder bemoeilik deur die wye
verskeidenheid van reaksies wat hulle ondergaan tydens veroudering. Daar is ook ‘n gebrek
aan beskikbaarheid van standaarde vir die meeste van die lede van hierdie klas van komponente. Tandem massaspektrometrie was in skanderingsmodus gebruik vir hoogs
selektiewe deteksie van die antosianien-glukosiede deur die voorspelbare eliminasie van die
suiker komponent in neutrale verliesskandering te benut. Gelyktydige skanderings van die
komponente wat met neutraleverliesskandering waargeneem word, is gebruik vir
ondubbelsinnige komponent identifikasie. Die metode volg daarom ‘n eenvoudige en
gestruktureerde benadering vir piek identifikasie wat gebaseer is op chromatografiese orde,
sowel as massaspektrale inligting, om ‘n hoë vlak van sekerheid aan die identifikasie van
komponente te verleen.
Samevattend, word daar getoon deur die werk wat in hierdie dissertasie uiteengesit is dat
vloeistofchromatografie – tandem massaspektrometrie ‘n veelsydige en kragtige tegniek bied vir
chemiese analise relevant tot die wynbedryf. Die sensitiwiteit, selektiwiteit en spektrale
vermoëns van die tegniek word duidelik deur toepassings in die dissertasie getoon.
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Antioxidant capacity of Pinotage wine as affected by viticultural and enological practicesDe Beer, Dalene 12 1900 (has links)
Thesis (PhD (Food Science))--University of Stellenbosch, 2006. / The aim of the study was to provide the South African wine industry with guidelines for the production of
Pinotage wines with optimal total antioxidant capacity (TAC), while retaining sensory quality. The contribution of
individual phenolic compounds to the wine TAC is important in this regard. The wine TAC was measured with
the 2,2 -azino-di(3-ethylbenzo-thiazoline-sulphonic acid radical cation) (ABTS +) scavenging assay. The
contributions of individual phenolic compounds to the wine TAC were calculated from their content in the wines
and the Trolox equivalent antioxidant capacity (TEAC) of pure phenolic standards. The effects of climate region,
vine structure, enological techniques (pre-fermentation maceration, juice/skin mixing, addition of commercial
tannins, extended maceration) and maturation (oak barrels, alternative oak products, oxygenation) on the phenolic
composition, TAC and sensory quality of Pinotage wines were also investigated.
The TEAC values of quercetin-3-galactoside, isorhamnetin and peonidin-3-glucoside were reported for the
first time. TEAC values observed for most compounds were much lower than those reported previously, although
TEAC values for gallic acid, caftaric acid, caffeic acid and kaempferol were consistent with some previous
reports. Caftaric acid and malvidin-3-glucoside were the largest contributors to the wine TAC. The contents of
monomeric phenolic compounds and procyanidin B1, however, only explained a small amount (between 11 and
24%) of the wine TAC, with the remaining TAC attributed to oligomeric and polymeric phenolic compounds and
other unknown compounds. Some synergy between different monomeric phenolic compounds was also
demonstrated.
All the viticultural and enological factors investigated affected the phenolic composition of Pinotage wines,
while the wine TAC was only affected by some treatments. Changes in wine TAC could not always be explained
by changes in phenolic composition as the contribution of oligomeric, polymeric and unknown compounds could
not be assessed, but could play a large role. Differences in wine colour were also difficult to explain due to the
large number of factors involved and the dark wine colour, which made objective measurements difficult. The
concentration of vitisin A, an orange-red pyranoanthocyanin, was increased consistently as a result of prefermentation
maceration treatments and affected the wine colour of oxygenated wines. Increased wine TAC was
observed when cultivating Pinotage grapes on bush vines and in cooler climatic regions, compared to cultivation
on trellised vines in warmer climatic regions. All the climatic regions and vine structure treatments, however,
resulted in wines with good sensory quality. In terms of enological techniques, pumping-over, as opposed to
punching-down and rotor treatments, is not recommended as a juice/skin mixing technique, due to reduced wine
TAC, colour and sensory quality. Pre-fermentation maceration, addition of commercial tannin preparations, and
oak maturation using traditional and alternative treatments, resulted in improved sensory quality, but with no
change in wine TAC. However, optimisation of the tannin addition protocol may result in increased wine TAC if
additions are made after fermentation or higher dosages are used. Oxygenation of Pinotage wine needs further
investigation to optimise the protocol, as improvements to the wine colour and fullness were observed for some
treatments, but loss of sensory quality and TAC were observed in most cases.
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Strategies for the control of malolactic fermentation : characterisation of Pediocin PD-1 and the gene for the malolactic enzyme from Pediococcus damnosus NCFB 1832Bauer, Rolene 12 1900 (has links)
Dissertation (PhD Agric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Malolactic fermentation (MLF) is conducted by lactic acid bacteria (LAB) and entails
the decarboxylation of L-malate to L-Iactate through a reaction catalysed by the
malolactic enzyme (MLE). The consequence of this conversion is a decrease in total
acidity. MLF plays a part in microbial stabilisation and due to the metabolic activity of
the bacteria the organoleptic profile of the wine is modified. In some wines MLF is
considered as spoilage, especially in warm viticultural regions with grapes containing
less malic acid. In addition to undesirable organoleptic changes, MLF can alter wine
colour, and biogenic amines may be produced. To induce MLF we provided
s. cerevisiae with the enzymatic activities required for MLF, which is then conducted
by the yeast during alcoholic fermentation. The malolactic enzyme-encoding gene
(mieD) was cloned from Pediococcus damnosus NCFB 1832, characterised and
expressed in S. cerevisiae. The activity of this enzyme was compared to two other
malolactic genes, mieS from Lactococcus lactis MG1363 and mleA from Oenococcus
oeni La11, expressed in the same yeast strain. All three recombinant strains of
S. cerevisiae converted L-malate to L-Iactate in synthetic grape must, reaching
L-malate concentrations of below 0.3 gIL within 3 days. However, a lower conversion
rate and a significant lower final L-Iactate level were observed with the yeast
expressing mieD. In order to inhibit MLF, we show that the growth of O. oeni, the
main organism responsible for MLF, could be safely repressed with a ribosomaly
synthesised antimicrobial peptide, pediocin PD-1, produced by P. damnosus NCFB
1832, without effecting yeast growth. Pediocin PD-1 is stable in wine at 4°C-100°C,
and ethanol or S02 does not affect its activity. The peptide was purified to
homogeneity and sequence analysis suggests that the peptide is a member of the
lantibiotic family of bacteriocins. The molecular mass was estimated by mass
spectroscopy to be 2866.7 ± 0.4 Da. Pediocin PD-1 forms pores in sensitive cells, as
indicated by the efflux of K+ from O. oeni, combined with inhibition of cell wall
biosynthesis, leading to cell lysis. Loss of cell K+was reduced at low temperatures,
presumably as a result of the increased ordering of the lipid hydrocarbon chains in
the cytoplasmic membrane. Although pediocin PD-1 is active over a broad pH range,
optimal activity was recorded at pH 5.0. The petide is, however, more stable
between pH 2.0 and 5.0, with the best stability observed between pH 3.0 and 4.0.
Pediocin PD-1 provides a safer biological alternative than chemical preservatives
such as S02. / AFRIKAANSE OPSOMMING: Appelmelksuurgisting (AMG) word deur sekere melksuurbakterieë (MSB) uitgevoer
en verwys na die dekarboksilering van L-malaat na L-Iaktaat, 'n reaksie gekataliseer
deur die appelmelksuurensiem (AME). AMG verlaag die suurvlakke in wyn, speel 'n
rol in mikrobiologiese stabiliteit, en verander die organoleptiese profiel van die wyn.
In sommige wyne word AMG beskou as bederf, veral in warm wynbou streke met
minder malaat in druiwe. AMG kan ongewenste organoleptiese veranderinge teweeg
bring, die wyn se kleur beinvloed, en tot die produksie van biogene amiene lei. Vir
die bevordering van AMG het ons S. eerevisiae met die ensiematiese aktiwiteit
benodig vir AMG voorsien wat dan veilig deur die gis tydens alkoholiese fermentasie
uitgevoer word. 'n AME-koderende geen (mIeD) is uit Pedioeoeeus damnosus NCFB
1832 gekloneer, gekarakteriseer en in S. Cerevisiae uitgedruk. Die aktiwiteit van die
ensiem is vervolgens vergelyk met die aktiwitet van twee ander AME gene, mIeS van
Laetoeoeeus laetis MG1363 en mleA van Oenoeoeeus oeni Lal1, uitgedruk in
dieselfde gisras. AI drie rekombinante gisrasse het L-malaat binne die bestek van
drie dae na L-Iaktaat omgeskakel en die finale L-malaat vlakke was minder as 0.3
gIL. Die tempo van omkakeling was egter laer in die gis wat die mIeD geen uitdruk en
die finale L-Iaktaat vlakke was veel laer. Om AMG te inhibeer is die groei van O.
oeni, die organisme hoofsaaklik verantwoordelik vir AMG, onderdruk deur die
byvoeging van 'n ribosomaal gesintetiseerde antimikrobiese peptied, pediocin PD-1,
geproduseer deur P. damnosus NCFB 1832. Gisgroei is nie geaffekteer nie.
Pediocin PD-1 is stabiel in wyn by temperature wat wissel tussen 4°C en 100°C, en
die aktiwiteit van die peptied word nie geaffekteer deur ethanol of S02 nie. Die
peptied is gesuiwer volgens In eenvoudige metode wat amoniumsulfaat-presipitasie
en katioon uitruilings-ehromatografie insluit. Aminosuur volgorde bepaling van
gesuiwerde peptied dui daarop dat pediocin PD-1 tot die lantibiotiese familie van
bakteriosiene behoort. Die molekulêre massa van die peptied, soos bepaal deur
massa spektroskopie, is 2866.7 ± 0.4 Da. Pediocin PD-1 vorm porieë in
selmembrane van sensitiewe selle soos aangedui deur die uitvloei van K+vanuit O.
oeni selle. Die peptied kombineer hierdie aksie met die inhibisie van selwand
biosintese wat lei tot sel lise. Verlies van sellulêre K+verminder by laer temperature,
waarskynlik as gevolg van verandering in die lipied- en protein inhoud van die
sitoplasmiese membraan. Alhoewel die peptied aktief is oor 'n breë pH grens, is die
antimikrobiese aksie optimaal by pH 5.0. Die peptied is meer stabiel tussen pH 2.0
en 5.0 en toon die beste stabiliteit tussen pH 3.0 en 4.0. Peiocin PD-1 is 'n veilige
biologiese alternatief vir chemiese preserveermiddels soos S02.
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