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Screening, identification and characterisation of bacteriocins produced by the wine isolated LABNdlovu, Joseph Buyani 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Lactic acid bacteria (LAB) play a vital role in reducing wine acidity and also contributing to its
aroma and flavour. However, they can also be responsible for many wine spoilage problems that
compromise the quality and value of wine. While Oenococcus oeni contributes positive characteristics to
the sensory properties of wine, certain species of the genera, Lactobacillus and Pediococcus can affect the
wholesomeness of wine by producing undesirable compounds, such as biogenic amines and ethyl
carbamate.
Chemical preservatives like sulphur dioxide (SO2) are used to prevent the growth of spoilage
micro-organisms during the winemaking process. SO2 also acts as a reducing agent and maintains the
benefits of antioxidant properties of the polyphenols of wine. However, there is a worldwide demand to
reduce SO2 levels due to the increasing health related risks and other factors.
All these considerations have increased the interest in research to look for new preservation
strategies, and LAB-produced bacteriocins seem to be a potential alternative that has been explored in the
last decade. Various types of bacteriocins have been identified and characterized. However, there are few
reports on bacteriocins produced by LAB of oenological origin or on bacteriocins present in the finished
wine.
The present study screened 155 LAB isolates from the IWBT culture collection for bacteriocin
production. The isolates originated from South African red wines undergoing spontenous malolactic
fermentation (MLF). Eight strains (5%) were identified to be producers, as evidenced by strong inhibition
zones formed against sensitive organisms on agar plates. The producers demonstrated a broad spectrum of
antimicrobial activity by inhibiting Lactobacillus spp., Leuconostoc mesenteroides, Listeria
monocytogenes and Pediococcus pentosaceus strains. Some of these bacterial genera are important in
winemaking since they are potential wine spoilage bacteria. Hence these strains and/or the bacteriocins
they produce could possibly find application in the food fermentation industry. The physiological results, biochemical tests and sugar fermentation profiles all gave the same
results for the seven isolates, which were indicative of enterococci. The identification through 16S rRNA
gene sequencing revealed that the seven tested isolates were all Enterococccus faecium. RAPD-PCR
fingerprinting gave the same profile for the seven strains confirming that they were all identical on
genetic level. Determining the molecular weight using SDS-PAGE showed the peptides to be below
4.6 kDa in size. PCR amplification of the enterocin P gene, sequencing and BLAST search results
confirmed that all eight strains contained the enterocin P gene from Ent. faecium.
The enterocin tested in this study was heat stable at 100°C (30 min), but lost 50% of its activity at
121°C (15 min). Factors such as bacteriocin production and heat resistance are among many that enable
enterococci to be dominant in fermented products such as dairy foods or meat. Therefore, enterococci
producing bacteriocins have potential applications in various foods and fermented products. The pH tests
showed enterocin to be active over a broad pH range (2-10). Enterocin activity over a wide pH range make them potentially more suitable as natural preservatives of foods and fermented products where
products are acidified or pH decreases due to natural LAB present. They also have potential applications
in oenological process where pH levels are as low as 3 and 4.
Proteolytic enzyme treatments with lysozyme, lipase, lyticase and catalase could not inhibit
enterocin activity. This indicated that their antimicrobial activity was independent of lipid or carbohydrate
moieties or hydrogen peroxide. α-Chymotrypsin and proteinase K inactivated enterocin, which indicated
that the compound was proteinaceous in nature.
Bacteriocin production tested in two of the isolates, #16.3 and 128.1, coincided with the
exponential growth phase which occurred after 6 hours of incubation at 30°C, which was an indication of
primary metabolite kinetics. The highest production of 400 AU/ml was observed after eight hours and
was maintained for several hours (46 hours) in the stationery phase. The bactericidal effect of the cell free
supernatants from #16.3 and 128.1 against the sensitive culture of Lactobacillus pentosus DSM 20314
was clearly demonstrated by complete inhibition of growth for most of the experimental period, while the
control increased exponentially throughout the experiment.
In conclusion, this study has confirmed the isolation and identification of Ent. faecium strains
from wine, a genus that is rarely found in the wine environment. Although one can speculate on the origin
of this bacterium in the wine e.g. human handling and contaminated water, these bacterial isolates
produced enterocin P which have antimicrobial action against wine-related LAB genera and therefore
have a potential role in wine spoilage control. / AFRIKAANSE OPSOMMING: Melksuurbakterieë (MSB) speel ‘n belangrike rol in die redusering van die suurgehalte van wyn
en dra ook by tot die aroma en smaak daarvan. Hulle kan egter ook verantwoordelik wees vir vele
wynbederfprobleme wat die gehalte en waarde van wyn negatief beïnvloed. Hoewel Oenococcus oeni
positiewe karaktertrekke aan die sensoriese eienskappe van wyn verleen, kan sekere spesies van die
genus, Lactobacillus en Pediococcus, die heilsaamheid van wyn beïnvloed deur ongewenste verbindings,
soos biogeniese amienes en etielkarbamaat, te produseer.
Chemiese preserveermiddels, soos swaweldioksied (SO₂), word gebruik om die groei van
bederfmikro-organismes tydens die wynbereidingsproses te voorkom. SO₂ fungeer ook as ‘n
reduseermiddel en onderhou die voordele van die antioksidant eienskappe van die poli-fenole van wyn.
Daar is egter ‘n wêreldwye vraag na die redusering van SO₂-vlakke as gevolg van die toename in
gesondheidsverwante risiko’s en ander faktore.
Al hierdie oorwegings het belangstelling in die navorsing van nuwe preserveringstrategieë laat
toeneem en MSB-geproduseerde bakteriosiene lyk na ‘n potensiële alternatief wat in die laaste dekade
ondersoek word. Verskeie tipes bakteriosiene is geïdentifiseer en getipeer. Daar is egter nog weinig
gerapporteer oor bakteriosiene wat deur MSB van wynkundige oorsprong geproduseer is of oor
bakteriosiene wat in afgeronde wyn teenwoordig is.
Die huidige studie het 155 MSB isolate van die Instituut vir Wynbiotegnologie se
kultuurversameling vir bakteriosien-produsering gegradeer. Agt stamme (5%) is as produseerders
geïdentifiseer, soos gestaaf is deur sterk inhibisiesones wat teen sensitiewe organismes op agarplate
gevorm het. Die produseerders het ‘n breë spektrum van antimikrobiese aktiwiteit by inhiberende
Lactobacillus spp., Leuconostoc mesenteroides, Listeria monocytogenes en Pediococcus pentosaceus
stamme gedemonstreer. Sommige van hierdie bakteriese genera is belangrik in wynbereiding, omdat dit
potensiële wynbederfbakterieë is. Hierdie isolate en/of die bakteriosiene wat dit produseer, kan dus moontlik toepassing in die voedselfermentasiebedryf vind.
Die fisiologiese resultate, biochemiese toetse en suikerfermentasieprofiele het almal dieselfde
resultate vir die sewe isolate, wat indikatief van enterococci was, gelewer. Die identifisering deur 16S
rRNA-basispaaropeenvolging het onthul dat die sewe getoetste isolate almal Enterococccus faecium was.
RAPD-PKR-vingerafdrukke het dieselfde profiel vir die sewe rasse gelewer, wat bevestig dat die
rasse almal identies op genetiese vlak was. Deur die molekulêre gewig vas te stel deur middel van SDSPAGE,
het dit getoon dat die peptiede kleiner as 4.6 kDa in grootte is. PKR-amplifikasie van die
enterosien-P geen, die bepaling van basispaaropeenvolging en BLAST-soekresultate het bevestig dat al
agt rasse die enterosien-Pgeen van Ent. faecium bevat.
Die enterosien wat in hierdie studie getoets is, was hitte-stabiel teen 100°C (30 min), maar het
50% van sy aktiwiteit teen 121°C (15 min) verloor. Faktore soos bakteriosienproduksie en
hittebestandheid, is van die vele faktore wat enterococci in staat stel om dominant in gefermenteerde produkte, soos suiwelprodukte of vleis te wees. Enterococci wat bakteriosiene produseer het dus
potensiële toepassings in verskeie kossoorte en gefermenteerde produkte. Die pH-toetse het getoon dat
enterosien-P oor ‘n breë pH spektrum (2-10) aktief was. Enterosienaktiwiteit oor ‘n wye pH spektrum
maak dit potensieel meer geskik as natuurlike preserveermiddels vir kossoorte en gefermenteerde
produkte waar produkte versuur word of die pH afneem as gevolg van natuurlike MSB wat teenwoordig
is. Dit het ook potensiële toepassings in enologiese prosessering waar pH-vlakke so laag as 3 en 4 is.
Proteolitiese ensiembehandelings met lisosiem, lipase, litikase en katalase kon nie
enterosienaktiwiteit inhibeer nie. Daar is getoon dat hul antimikrobiese aktiwiteit onafhanklik was van
lipiede, koolhidraatdele óf waterstofperoksied. α-Chymotripsien en proteïenase-K het enterosien onaktief
gemaak, wat getoon het dat die samestelling proteïenagtig van nature is.
Bakteriosienproduksie wat in twee van die stamme #16.3 en 128.1 getoets is, het ooreengestem
met die eksponensiële groeifase wat na 6 ure van inkubasie teen 30°C plaasgevind het, en wat ‘n
aanduiding is van primêre metabolitiese kinetika. Die hoogste produksie van 400 AU/ml is na agt ure
waargeneem en is vir etlike ure (46 uur) in die stasionêre fase gehandhaaf. Die bakterie-dodende effek
van die selvrye supernatant van #16.3 en 128.1 teenoor die sensitiewe kultuur van Lactobacillus pentosus
DSM 20314 is duidelik gedemonstreer deur totale inhibisie van groei vir die grootste deel van die
eksperimentele periode, terwyl die kontrole eksponensieel deur die hele eksperiment toegeneem het.
Hierdie studie het dus die isolering en identifisering van Ent. faecium-stamme, ‘n genus wat baie
selde gevind word in ‘n wynomgewing, vanuit wyn bevestig. Alhoewel daar gespekuleer kan word oor
die oorsprong van hierdie bakterie in wyn bv. menslike hantering en besmette water, het hierdie rasse wel
enterosien geproduseer en daarom die potensiaal om ‘n rol te speel in beheer teen verskeie bederf-MSB-genera. / TIA, NRF and THRIP
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Mode of action studies of defensin peptides from native South African Brassicaceae speciesBarkhuizen, Helmien 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Plant defensin peptides have become promising and attractive candidates to be used as
antifungal agents in agricultural biotechnology. These peptides have a broad spectrum
antifungal activity and play a vital role in the innate immune system of plants. Plant diseases
caused by fungi are a major contributor to the decrease in the quality and safety of agricultural
products. Due to the dangerous effects and negative environmental impact of pesticides, an
effective, safe, natural and durable method to control crop pathogens has therefore become one
of the major concerns in modern agriculture. Although these peptides are promising and
attractive candidates, their precise mechanism of action is to date still unknown. Several
common observations have been made. These include the antagonistic effect of cations on the
activity of plant defensins. It is of vital importance to understand the underlying mechanism of
the cation-antagonistic effect on the antifungal potency of defensin peptides in order to evaluate
the possible contribution to defence reactions against microorganisms in planta.
To this end we set out to characterize the effect of cations in the form of biological salts,
NaCl, KCl, MgCl2 and CaCl2 on the structural stability and activity in terms of growth inhibition,
morphological effects and permeabilization. In order to perform these characterization
experiments, a production method resulting in a greater yield and involving simple and rapid
purification methods was required. Heliophila coronopifolia peptides have previously been
produced in a bacterial system, however the purification methods were tedious resulting in poor
yields. Pichia pastoris was selected as production system as several other plant defensins have
been successfully produced in this eukaryotic system. Hc-AFP1 and Hc-AFP3 was successfully
produced using the Pichia production system and rendered active peptides. Hc-AFP2 and Hc-
AFP4 was, however, not produced correctly, due to a post-translational modification event
leading to the cyclization of the N-terminal glutamine to generate pyroglutamic acid. This
modification negatively influenced the activity of these peptides. An active Hc-AFP2 could be
produced by replacing the production buffer with a reduced ionic buffer.
The effect of divalent and monovalent cations on the secondary structure of Hc-AFP1 was
evaluated by circular dichroism spectroscopy. These cations induced a conformational change
in the secondary structure of Hc-AFP1, with NaCl and MgCl2 inducing a more defined secondary
structure and KCl and CaCl2 inducing a less defined secondary structure. Monovalent cations
caused a slight reduction in the growth inhibition activity of Hc-AFP1 on Botrytis cinerea,
however, characteristic hyperbranching and other morphogentic effects were still visible.
Divalent cations had a greater antagonistic effect on the activity of Hc-AFP1, completely
abolishing the growth inhibitory activity of the peptide, but the induced morphological effects on
hyphae remained present. The activity of Hc-AFP1 to permeabilize B. cinerea hyphae was not
influenced by the addition of cations, however it was in fact increased to up to 10-fold. However,
since the growth inhibition activity of Hc-AFP1 was reduced in the presence of the biological
salts indicates that permeabilization is not the sole activity responsible for growth inhibition
caused by Hc-AFP1. This peptide probably has an alternative/primary target and more complex
MOA. This is the first known report of the investigation of the influence of cations on the
structure of plant defensin peptides. It is clear that cations induce a secondary structural
conformational change in Hc-AFP1. This may be linked to the antagonism on the activity of this
peptide. This study provides significant progress towards the structure-function analysis of plant
defensins. / AFRIKAANSE OPSOMMING: Plantdefensinpeptiede word beskou as belowende en aantreklike kandidate vir gebruik as
swammiddles in agribiotegnologie. Hierdie peptiede beskik oor breë spektrum antifungiese
aktiwiteit en speel ‘n essensiële rol in die ingebore immuunsisteem van plante. Plant siektes wat
deur swamme veroorsaak word dra betekenisvol by tot die afname in die kwaliteit en veiligheid
van landbouprodukte. As gevolg van die skadelike effekte en negatiewe omgewingsimpak van
plaagdoders, het effektiewe, veilige, natuurlike en duursame metodes om gewaspatogene te
beheer, van die belangrikste vraagstukke van moderne landbou geword. Alhoewel hierdie
peptiede belowende en aantreklike kandidate is vir die toepassing, is hulle presiese meganisme
van aksie tot vandag toe steeds onbekend. Verskeie algemene waarnemings is egter al
gemaak. Dit sluit die antagonistiese effek van katione op die aktiwiteit van
plantdefensinpeptiede in. Dit is kernbelangrik om die onderliggende meganisme van die
katioon-antagonistiese effek op die antifungiese effektiwiteit te verstaan om die moontlike
bydrae van die peptiede tot die verdedigingsreaksies teen mikro-organismes in planta te
evalueer.
Met die doel voor oë het ons gemik om die effek van katione, spesifiek in die vorm van die
biologiese soute NaCl, KCl, MgCl2 en CaCl2, op die strukturele stabiliteit en aktiwiteit in terme
van groei inhibisie, morfologiese effekte en permeabilisasie te karakteriseer. Om uiteindelik
hierdie karakterisasie eksperimente uit te voer was dit nodig om ‘n metode met ‘n groter
opbrengs en wat vinnige suiwering van die peptied ondersteun, te optimiseer. Heliophila
coronopifolia peptiede was voorheen in ‘n bakteriese sisteem geproduseer, maar die
suiweringsmetodes was tydsaam en het gelei tot ‘n swak opbrengs. Pichia pastoris is dus
geselekteer as die produksie sisteem aangesien verskeie ander plantdefensinpeptiede al
suksesvol geproduseer is in hierdie eukariotiese sisteem. Hc-AFP1 and Hc-AFP3 is suksesvol
vervaardig in die Pichia sisteem en het aktiewiteit getoon. Hc-AFP2 and Hc-AFP4 kon egter nie
korrek vervaardig word nie as gevolg van ‘n na-vertalingsverandering wat gelei het tot die
siklisering van die N-terminale glutamien, om piroglutamiensuur te lewer. Hierdie verandering
het die aktiwiteit van die peptied negatief beinvloed. ‘n Aktiewe Hc-AFP2 kon wel vervaardig
word deur die produksiebuffer te vervang met ‘n lae-ionise buffer.
Die effek van divalente en monovalente katione op die sekondêre struktuur van Hc-AFP1 is
ge-evalueer deur van sirkulêre dikroisme spektroskopie gebruik te maak. Hierdie katione het ‘n
vouingsverandering in die sekondêre struktuur van Hc-AFP1 geïnduseer, NaCl and MgCl2 het ‘n
meer gedefinieërde sekondêre struktuur induseer, terwyl KCl and CaCl2 ‘n minder gedefinieërde
sekondêre struktuur geinduseer het. Monovalente katione het ‘n effense vermindering in die
groei-inhibisie aktiwiteit van Hc-AFP1 op Botrytis cinerea veroorsaak, alhoewel kenmerkende
hife-oorvertakking en ander morfologiese effekte nogsteeds sigbaar was. Divalente katione het
‘n sterker antagonistiese effek gehad op die aktiwiteit van Hc-AFP1, waar dit totaal en al die
groei-inhibisie aktiwiteit van die peptied vernietig het, alhoewel die geïnduseerde morfologiese
effekte op die hiffes steeds sigbaar was . Die aktiwiteit van Hc-AFP1 om B. cinerea hyphae te
permeabiliseer is nie negatief beinvloed deur die byvoeging van katione nie, tewens dit het die
aktiwiteit tot 10-voudig verhoog. Aangesien die groei-inhibisie aktiwiteit van Hc-AFP1 nie
verminder is in die teenwoordigheid van die biologiese soute nie, dui dit aan dat permeabilisasie
nie die enigste aktiwiteit is wat die groei inhibisie veroorsaak het nie. Die peptied het dus
moontlik ‘n alternatiewe of primêre teiken en ‘n meer komplekse meganisme van aksie. Dit is
die eerste verslag wat die invloed van katione op die struktuur van plantdefensinpeptiede
ondersoek het. Dit is duidelik dat katione ‘n sekondêre strukturele vouingsverandering in Hc-AFP1 induseer. Hierdie verandering mag dalk bydra tot die antagonistiese uitwerking op die
aktiwiteit van hierdie peptied. Hierdie studie het betekensisvolle vordering gemaak met die
analise van die struktuur-funksie interaksie van plantdefensinpeptiede. / The National Research Foundation (NRF), Institute of Wine Biotechnology (IWBT),
THRIP and Winetech for financial assistance.
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Development of infrared spectroscopic methods to assess table grape qualityDaniels, Andries Jerrick 03 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The two white seedless table grape cultivars, Regal Seedless and Thompson Seedless fulfil a
very important role in securing foreign income not only for the South African table grape
industry, but the South African economy as a whole. These two cultivars, however, are like so
many other white table grape cultivars, also prone to browning, especially netlike browning on
Regal Seedless and internal browning on Thompson Seedless grapes. This leads to huge
financial losses every year, since there is no established way to assess at harvest, during
storage or during packaging, whether the grapes will eventually turn brown. In other words,
there is no well-known protocol of assessing the browning risk of a particular batch of grapes
prior to export. Numerous studies have been undertaken to determine the exact cause of
browning and how it should be managed, but to date, no chemical or physical parameter has
been firmly associated with the phenomenon.
The overall aim of this study was thus to find an alternative way to deal with the problem by
investigating the potential of near infrared (NIR) spectroscopy as a fast, non-destructive
measurement technique to determine the browning potential of whole white seedless table
grapes. A secondary aim was the determination of optimal ripeness of table grapes. In this way
harvest maturity and quality indicative parameters namely total soluble solids (TSS), titratable
acidity (TA), pH, glucose and fructose, also associated with the browning phenomenon, was
quantified using models based on infrared spectra.
Three different techniques (a) Fourier transform Near Infrared (FT-NIR), (b) Fourier
transform – Mid Infrared (FT-MIR) and (c) Fourier transform – Mid Infrared Attenuated Total
Reflectance (FT-MIR ATR) spectroscopy were investigated to determine these parameters. This
was done so that a platform of different technologies would be available to the table grape
industry.
The grapes used in this study were harvested over two years (2008 and 2009) and were
sourced from two different commercial vineyards in the Hex River valley, Western Cape, South
Africa. Different crop loads (the total amount of bunches on the vines per hectare) were left for
Regal Seedless (75 000, 50 000 and 35 000) and for Thompson Seedless (75 000 and 50 000).
Three rows were used for Regal Seedless and two rows for Thompson Seedless. Each row had
six sections which each represented a repetition for each crop load. In 2008 these cultivars
were harvested early at 16°Brix, at optimum ripeness (18°Brix) and late at 20°Brix. In 2009 they
were harvested twice at the optimum ripeness level.
Berries from harvested bunches were crushed and the juice was used to determine the
reference values for the different parameters in the laboratory according to their specific
methods. The obtained juice was also scanned on the three different instruments. Different
software (OPUS 6.5 for the FT-NIR and FT-MIR ATR instruments and Unscrambler version 9.2
for the FT-MIR instrument) as well as different spectral pre-processing techniques were also
evaluated before construction of the models for all the instruments.
Partial least squares (PLS) regression was used for the construction of the different
calibration models. Different regression statistics, that included the root mean square error for
prediction (RMSEP); the coefficient of determination (R2); the residual prediction deviation
(RPD) and the bias were used to evaluate the performance of the developed calibration models.
Calibration models which are fit for screening purposes were obtained on the FT-NIR and FTMIR
ATR instruments for TSS (11.40 - 21.80°Brix) (R2 = 85.92%, RMSEP = 0.71 °Brix RPD =
2.67 and bias = 0.03°Brix), pH (2.94 - 3.9) (R2 = 85.00%, RMSEP = 0.08 RPD = 2.59 and bias =
-0.01) and TA (4.3 - 13.1 g/L), (R2 = 90.77%, RMSEP = 0.48 g/L RPD = 3.30 and bias = -0.03
g/L). Models for fructose (46.70 – 176.82 g/L) (R2 = 74.66%, RMSEP = 9.28 g/L RPD = 2.00 and
bias = 1.10 g/L) and glucose (20.36 – 386.67 g/L) (R2 = 70.71%, RMSEP = 11.10 g/L RPD = 1.87 and bias = 1.64 g/L) were obtained with the FT-NIR and FT-MIR ATR instruments that
were in some instances fit for screening purposes and in some instances unsuitable for
quantification purposes. The FT-MIR instrument gave models for all the parameters that were
not yet suitable for quantification purposes.
Combined spectral ranges used for calibration were often similar for some parameters,
namely 12 493 - 5 446.2 for TSS and pH, 6 101.9 - 5 446.2 for TSS, TA and fructose and
4 601.5 - 4 246.7 for pH and fructose on the FT-NIR instrument, 2 993.2 - 2 322.3 for pH, TA
and glucose and 1 654.3 - 649.4 for pH and glucose on the FT-MIR ATR instrument and
sometimes they were adjacent (3 996.6 - 3 661.2, 3 663.5 - 3 327.7 and 3 327.2 - 2 322.3 for
TSS and glucose, 1 988.3 - 1 652.8 and 1 654.3 - 649.4 for TSS, pH and TA. Other times they
were overlapping (1 654.3 - 649.4 and 1 318.8 - 649.4) for pH, TA and fructose on the FT-MIR
ATR instrument. This is a very good sign for transfer of this technology to a handheld device,
where adjacent and/ or overlapping wavenumbers are crucial. Instruments which have to
determine different parameters over large spectral ranges are not only impractical, because the
instrument has to be big, but because it is also very expensive.
Another advantage of implementing especially FT-NIR spectroscopy as a fast, accurate and
inexpensive technique for determining harvest maturity and quality parameters is because no
sample preparation is necessary and very little waste (few single berries tested) is produced.
This is a pre-requisite which is highly recommended in the green era that we are currently living
in and will do so for aeons to come. A platform of technologies has now been made available
through this study for the determination of the respective parameters in future table grape
samples by just taking their spectra on one of the instruments. Indeed something that has not
been possible or available for the South African table grape industry before. Berries for the browning experiments were scanned on a FT-NIR instrument immediately
after harvest (before cold storage) and again after cold storage. Before cold storage they were
scanned on each side of the berry and after cold storage they were scanned twice on a brown
spot if browning was present and twice on a clear spot, irrespective of whether browning was
present or not. Inspection of the berries for the incidence of browning after cold storage
revealed that Regal Seedless had a higher incidence of browning (68% in 2008 and 66% in
2009) than Thompson Seedless (21% in 2008 and 25% in 2009). Regal Seedless was also
more prone to external browning, specifically netlike browning, whereas Thompson Seedless
was more prone to internal browning, despite the different phenotypes of browning that were
present on both.
Principal component analysis (PCA) done on the spectra obtained before and after cold
storage revealed that NIR can capture the changes related to cold storage with the first principal
components explaining almost 100% of the variation in the spectra. Classification models also
build using PCA was based on spectra of berries that remained clear before and after cold
storage and those that turned brown after cold storage. Classification models of berries based
on spectra obtained after cold storage (browning present) had a better total accuracy (94% for
training- and 87% for test datasets), than the classification models based on spectra obtained
before cold storage (79% for training- and 64% for test datasets). The implication of this is that
the current models will be able to classify berries in terms of those which have turned brown
already and those that remained clear better after cold storage than before cold storage, which
is the critical stage where we want to actually know whether the berries will turn brown or not.
The potential, however, to use NIR spectroscopy to detect browning before harvest already on
white seedless grapes is still present, since all these models were built using the whole NIR
spectrum. No variable selection was thus done and all the different browning phenotypes were
also used together. Further analysis of the data will thus be based on using variable selection techniques like particle swarm optimization (PSO) to select certain wavelengths strongly
associated with the browning phenomenon and only on the main types of browning (netlike on
Regal Seedless and internal browning on Thompson Seedless). This study has major
implications for the table grape industry, since it is the first time that the possibility to predict
browning with other methods than visual inspection, especially before cold storage, is shown. / AFRIKAANSE OPSOMMING: Die twee wit pitlose tafeldruif kultivars, Regal Seedless en Thompson Seedless onderskeidelik,
speel 'n baie belangrike rol in die verkryging van buitelandse inkomste, nie net vir die Suid-
Afrikaanse tafeldruif industrie nie, maar ook vir die Suid-Afrikaanse ekonomie as 'n geheel.
Hierdie twee kultivars is egter, soos baie ander wit kultivars, ook geneig tot verbruining. Dit is
veral netagtige verbruining op Regal Seedless en interne verbruining op Thompson Seedless
wat pertinent is. Hierdie belangrike kwaliteitsprobleme lei jaarliks tot groot finansiële verliese,
aangesien daar huidiglik geen gevestigde prosedure is om voor oes, tydens opberging of
tydens verpakking te bepaal of die druiwe uiteindelik gaan verbruin nie. Met ander woorde, daar
is geen gevestigde protokol vir die beoordeling van die verbruinings risiko van 'n bepaalde
groep druiwe voor dit uitgevoer word nie. Talle studies is alreeds onderneem om vas te stel wat
die presiese oorsaak van hierdie verskynsel is en hoe dit bestuur moet word, maar geen enkele
aspek wat bestudeer is kon tot op hede, herhaaldelik ge-assosieer word met die presiese
oorsaak van verbruining nie.
Die oorkoepelende doel van hierdie studie was dus om 'n alternatiewe manier te kry om
hierdie probleem aan te spreek. ‘n Ondersoek na die potensiaal van naby infrarooi (NIR)
spektroskopie as 'n vinnige en nie-vernietigende metings tegniek om die verbruinings potensiaal
van ‘n wit pitlose tafeldruifkorrel wat nog heel is te bepaal, is onderneem. 'n Sekondêre doel
was om die bepaling van optimale rypheid van tafeldruiwe te onderosek. Op hierdie manier is
oesrypheid, en die kwaliteitsfaktore, naamlik totale oplosbare vastestowwe (TOVS), titreerbare
suur (TS), pH, glukose en fruktose, wat ook gekoppel word aan die voorkoms van verbruining,
deur middel van infrarooi (IR) spektroskopie modelle gekwantifiseer. Drie verskillende infrarooi
metodes naamlik (a) die Fourier transform naby infrarooi (FT-NIR), (b) Fourier transform - Mid
Infrarooi (FT-MIR) en (c) Fourier transform - Mid Infrarooi Verswakte Totale Refleksie (FT-MIR
VTR) spektroskopie is gebruik om die aspekte te bepaal. Dis gedoen sodat 'n platform van
tegnologie beskikbaar sou wees vir die tafeldruif industrie. Die druiwe wat in hierdie studie gebruik is, is oor twee jaar (2008 en 2009) en van twee
verskillende kommersiële wingerde in die Hexriviervallei, Wes-Kaap, Suid-Afrika ge-oes.
Verskillende oesladings (die totale aantal trosse op die wingerdstokke per hektaar) is vir Regal
Seedless (75 000, 50 000 en 35 000) en Thompson Seedless (75 000 en 50 000) gelaat. Daar
is drie rye gebruik Regal Seedless en twee vir Thompson Seedless. Elke ry het ses vakkies
gehad wat dan verteenwoordigend was van ‘n herhaling vir elke oeslading. In 2008 is hierdie
kultivars by vroeë rypwording (16°Brix), by optimale rypheid (18°Brix) en by laat rypheid
(20°Brix) geoes. In 2009 is dit twee keer by die optimale rypheidsgraad geoes. Vir die bepaling
van oesrypheid, en die kwaliteitsapekte is verskillende sagteware (OPUS 6.5 op die FT-NIR en
FT-MIR VTR instrumente en Unscrambler weergawe 9.2 vir die FT-MIR instrument) sowel as
verskillende spektrale voor-verwerking tegnieke ëvalueer voor die konstruksie van die kalibrasie
modelle op die verskillende instrumente.
Parsiële kleinste kwadraat (PKK) regressie is gebruik vir die opstel van kalibrasiemodelle
vir die bepaling van laasgenoemde aspekte. Verskillende statistieke gegewens is gebruik om
die kalibrasie modelle te evalueer, naamlik die bepalingskoëffisiënt (R2), die vierkantswortelgemiddelde-
kwadraat fout vir voorspelling (VGKV), relatiewe voorspellingsafwyking (RVA) en
sydigheid. Kalibrasie modelle wat geskik is vir keuring is verkry op die FT-NIR en FT-MIR VTR
instrumente vir TOVS (11.40 – 21.80°Brix) (R2 = 85.92%, VGKV = 0.71°Brix, RVA = 2.67 en
sydigheid = 0.03°Brix), pH (2.94 – 3.9) (R2 = 85.00%, VGKV = 0.08 g/L, RVA = 2.59 en
sydigheid = -0.01 g/L), en TS (4.3 – 13.1 g/L), (R2 = 90.77%, VGKV = 0.48 g/L RVA = 3.30 en
sydigheid = -0.03 g/L). Modelle vir fruktose (46.70-176.82 g/L) (R2 = 74.66%, VGKV = 9.28 g/L
RVA = 2.00 en sydigheid = 1.10 g/L) en glukose (20.36 – 386.67 g/L) (R2 = 70.71%, VGKV = 11.10 g/L RVA = 1.87 en sydigheid = 1.64 g/L) is verkry met die FT-NIR en FT-MIR VTR
instrumente wat in sommige gevalle gepas was vir keuringsdoeleindes en in sommige gevalle
nie geskik was vir kwantifiserings doeleindes nie. Die FT-MIR-instrument het modelle vir al die
aspekte gegee wat nog nie vir kwantifiserings doeleindes of vir keuringsdoeleindes geskik was
nie.
Gekombineerde spektrale reekse is gebruik vir die kalibrasies wat dikwels soortgelyk was
vir sommige aspekte naamlik 12 493 - 5 446.2 vir TOVS en pH, 6 101.9 - 5 446,2 vir TOVS, TS
en fruktose en 4 601.5 - 4 246.7 vir pH en fruktose op die FT-NIR instrument, 2 993.2 - 2 322.3
vir pH, TA en glukose en 1 654.3 – 649.4 vir pH en glukose op die FT-MIR VTR instrument.
Andersyds, was dit aangrensend (3 996.6 - 3 661.2, 3 663.5 - 3 327.7 en 3 327.2 - 2 322.3) vir
TOVS en glukose, 1 988.3 - 1 652.8, 1 654.3 – 649.4 vir TOVS, pH en TS en ander tye was dit
weer oorvleuelend 1 654.3 – 649.4 en 1 318.8 – 649.4 vir pH, TS en fruktose op die FT-MIR
VTR instrument. Dit is 'n baie goeie teken vir die oordrag van hierdie tegnologie na ‘n
handgedraagde instrument, waar aanliggende en/of oorvleuelende golfnommers noodsaaklik is.
Instrumente wat verskillende aspekte oor groot spektrale reekse moet bepaal is nie net
onprakties, omdat die instrument groot moet wees nie, maar dit is ook baie duur.
Nog 'n voordeel van die implementering van veral FT-NIR spektroskopie as 'n vinnige,
akkurate en goedkoop tegniek vir die bepaling van oesrypheid, en die kwaliteit aspekte van
druiwe is omdat daar geen monster voorbereiding nodig is nie en baie min afval (paar enkele
korrels word gemonster) geproduseer word. 'n Voorvereiste wat sterk aanbeveel kom in die
groen era waarin ons tans leef en nog vir eeue van nou af gaan doen. ‘n Platform van
tegnologie is nou beskikbaar gestel deur middel van hierdie studie vir die bepaling van die
onderskeie aspekte in toekomstige tafeldruif monsters deur net op een van die instrumente
hulle spektra te neem. Inderdaad iets wat nie voorheen moontlik of beskikbaar was vir die Suid-
Afrikaanse tafeldruif industrie nie. Korrels vir die verbruiningseksperimente is geskandeer direk na oes (voor koelopberging)
en weer na koelopberging. Dit was voor koelopberging op elke kant van die korrel skandeer en
na koelopberging was dit twee maal skandeer op 'n bruin vlek indien verbruining teenwoordig
was en twee keer op 'n helder plek, ongeag of verbruining teenwoordig was of nie. Inspeksie
van die korrels vir die voorkoms van verbruining na koelopberging het aan die lig gebring dat
Regal Seedless 'n hoër voorkoms van verbruining (68% in 2008 en 66% in 2009) as Thompson
Seedless (21% in 2008 en 25% in 2009) gehad het. Regal Seedless was ook meer geneig om
eksterne verbruining, spesifiek netagtige verbruining te vertoon, terwyl Thompson Seedless
meer geneig was om interne verbruining te vertoon, ten spyte van die verskillende fenotipes van
verbruining wat teenwoordig was op beide kultivars.
Hoofkomponente analise (HKA) is op die spektra gedoen voor en na koelopberging en
naby infrarooi spektroskopie het aan die lig gebring dat die veranderinge wat verband hou met
koelopberging met die eerste hoofkomponent (HK) verduidelik kan word met byna 100% van
die variasie in die spektra wat daarin vasgevang is. Klassifikasiemodelle is ook deur die gebruik
van HKA gebou en was gebaseer op die spektra van korrels wat vekry is voor en na
koelopberging asook die wat verkry is nadat korrels verbruin het na koelopberging.
Klassifikasiemodelle van korrels wat gebaseer was op spektra na koelopberging (verbruining
teenwoordig) het 'n beter algehele akkuraatheid (94% vir opleidingsdata en 87% vir toetsdata),
getoon as die klassifikasiemodelle wat gebaseer was op spektra van korrels voor koelopberging
(79% vir opleidings data en 64% vir toetsdata). Die implikasie hiervan is dat die huidige modelle
in staat sal wees om korrels beter te klassifiseer in terme van diegene wat alreeds verbruin het
en die wat nie verbruin het na koelopberging as daardie voor koelopberging, wat juis die kritieke
stadium is waar ons wil weet of die korrels wel gaan verbruin of nie. Daar is wel potensiaal wat verder ontgin kan word, aangesien al hierdie modelle gebou is deur gebruik te maak van die
hele NIR spektrum. Geen veranderlike seleksie is dus gedoen nie en al die verskillende
verbruiningsfenotipes is ook saam gebruik in die opstel van die modelle. Verdere analise van
die data sal dus gebaseer word op die gebruik van veranderlike seleksie tegnieke soos deeltjie
swerm optimisasie (DSO) wat sekere golflengtes kies wat sterk verband hou met die verbruining
verskynsel en slegs die belangrikste tipes van verbruining (netagtig op Regal Seedless en
interne verbruining op Thompson Seedless) sal gebruik word. Hierdie studie het 'n baie
belangrike implikasie vir die tafeldruifbedryf, want dit is die eerste keer dat die moontlikheid om
verbruining te voorspel met ander metodes as visuele inspeksie, veral voor koelopberging,
getoon word. / The Postharvest and Innovation Programme, for financing this study
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A case study of source-sink relationships using shoot girdling and berry classification (Vitis vinifera L. cv. Cabernet Sauvignon)Joubert, Chandre 03 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The relationships between leaf and fruit represent a fundamental concept in perennial plants. This concept allows to understand and to manage, with regard to farming, the balance of a vine, which is important in terms of fruit quality (i.e. fruit composition), mainly when it comes to producing wines of different categories and styles. The understanding of vine structure, physiology and vine functioning ultimately allows for appropriate recommendations to be given with regard to farming procedures. These include the adaptation of the canopy architecture to achieve a certain yield per vine, the determination of an appropriate fruit microclimate as well as the prediction of harvest dates. One of the central notions of vine balance involves the relationship between the source and the sink organs. The definition of source-sink relationships incorporates several concepts, including the ability of a source tissue to produce carbohydrates through photosynthesis, the transport of these carbohydrates to various plant organs-tissues via appropriate transport channels, and the assimilation and storage of the carbohydrates in the sink organs. In past years, a number of simple ratios have been created to incorporate the relationship between source and sink organs and thereby define vine balance in order to aid in practical management decisions (choice of a training system, irrigation, canopy manipulation etc.). However, vine functioning is very complex and cannot be defined accurately by simple, static ratios. More integrated and dynamic physiological indicators of vine balance and functioning are needed in order to understand the complex communication between organs and ultimately improve on farming practices. In order to achieve this, a better grasp of source-sink relationships, including the signalisation between organs and the functioning of the transport tissues is required. A two year experiment was proposed to study the interaction between source and sink organs using a combination of both primary shoot girdling methods and berry classification according to size. Girdling removes the bark and phloem tissue, thereby interrupting carbon import as well as water flow to the bunch to a certain degree. The aim of the study was to demonstrate the complexity of vine functioning by investigating the dynamics of berry sugar and water accumulation (used as physiological indicators) and the influence thereof on berry fresh mass evolution. Furthermore, the use of berry sugar loading was proposed as an improved physiological indicator of vine balance as it is directly linked to source and sink functioning. Sugar production and the dynamics of berry sugar accumulation rely on photosynthesis which in turn is dependent on stomatal conductance and therefore also incorporates the effects of external abiotic factors (temperature, light and water). It furthermore gives a direct indication of sink functioning as it shows the progressive accumulation of sugar throughout the ripening period and the possible consequences on berry volume evolution. A primary shoot which bore two bunches was used to represent a biological replicate. The lower bunches were girdled above and below in order to completely isolate them from any carbohydrate import. These bunches, along with the upper ungirdled bunches and two control bunches from another shoot were sampled. The berries from these bunches were classified according to diameter, thereby providing the unique opportunity to study berries of the same volume/size. Measurements were done to determine the fresh and dry masses of the sampled berries, as well as to analyse the concomitant sugar concentrations.
It was found that girdling clearly had an effect on berry sugar dynamics and the method was improved in the second year of the trial. Girdling in interaction with berry classification according to diameter demonstrated that berries from the same size could have different sugar concentrations. It further showed that, to a certain degree, a relationship exists between the first rapid phase of sugar accumulation and the post véraison increase in berry fresh mass, until the plateau of fruit sugar accumulation, which generally occurs around a sugar concentration of 20 Brix. Additionally, and more importantly, it was found that vine functioning and the balance between the source and the sink organs may be controlled to a certain degree. There is a strong degree of compensation within a vine which results from signalling between and within organs. When taking the results of this study into consideration, it becomes clear that the classical ratios used to quantify the complex relationships between the fruit and the leaves may not be completely adequate to do so. The current way of looking at source-sink relationships and thereby determining whether a vine is balanced or not is over-simplified and there are numerous limitations involved in this approach. The vine is far more complex and various aspects must be taken into consideration before any claims can be made concerning source-sink relationships and consequently leaf to fruit balance. / AFRIKAANSE OPSOMMING: Die verhoudings tussen blaar en vrug verteenwoordig ‘n fundamentele konsep in meerjarige plante. Begrip van hierdie konsep maak dit moontlik om in boerdery die balans van ‘n wingerdstok te verstaan en bestuur. Hierdie wingerdbalans is belangrik in terme van vrugkwaliteit (d.w.s. vrugsamestelling), hoofsaaklik met betrekking tot die produksie van wyne van verskillende kategorieë en style. Begrip van die wingerdstok se struktuur, fisiologie en funksionering maak dit moontlik om gepaste aanbevelings te maak rakende boerdery prosedures. Dit sluit in die aanpassing van die lower argitektuur om ‘n sekere opbrengs per wingerdstok te verkry, die vasstel van ‘n geskikte vrug mikroklimaat asook die voorspelling van oesdatums. Een van die sentrale denkwyses rondom wingerdstok funksionering behels die die bron-vragpunt verhouding. Die definisie van bron-vragpunt verhoudings inkorporeer verskeie konsepte, insluitende die vermoë van ‘n bronweefsel om koolhidrate te produseer deur fotosintese, die vervoer van hierdie koolhidrate na verskeie plantorgaan weefsels via die gepaste vervoerkanale asook die opname en berging van hierdie koolhidrate in die vragpunt organe. In die verlede is ‘n aantal eenvoudige verhoudings geskep om die verband tussen die bron en vragpunt organe te beskryf en sodoende die wingerdstokbalans te definieer met die doel om ondersteuning te bied in praktiese bestuursbesluite (die keuse van opleistelsel, besproeiing, lowermanipulasie, ens.). Wingerdstok funksionering is egter baie kompleks en kan nie akkuraat gedefinieer word deur eenvoudige, statiese verhoudings nie. Meer geïntegreerde en dinamiese fisiologiese aanwysers van wingerdstokbalans en funksionering is nodig om die komplekse kommunikasie tussen organe te verstaan en uiteindelik boerdery praktyke te verbeter. Om dit te bereik is ‘n beter begrip van bron-vragpunt verhoudings asook die seinoordrag tussen organe en die werking van die vervoerweefsels nodig. ‘n Twee jaar lange eksperiment is voorgestel om die interaksie tussen bron- en benuttingsorgane te ondersoek deur gebruik te maak van beide die primêre loot ringelering metode en korrel klassifikasie volgens grootte. Ringelering verwyder die bas en floëem weefsel en onderbreek sodoende koolstof invoer sowel as watertoevoer na die tros tot ‘n sekere mate. Die doel van die studie was om die kompleksiteit van wingerdstok funksionering aan te toon deur die dinamika van suiker en water akkumulasie in die korrel te ondersoek asook die invloed daarvan op korrel vars massa ontwikkeling. Verder is die gebruik van korrel suikerlading voorgestel as ‘n beter fisiologiese aanduiding van wingerdstok funksionering aangesien dit direk geassosieer is met bron-vragpunt funksionering. Suikerproduksie en die dinamika van suiker akkumulasie in die korrel berus op fotosintese wat weer afhanklik is van stomatale geleiding en daarom ook die effek van eksterne abiotiese faktore (temperatuur, lig en water) inkorporeer. Dit gee verder ‘n direkte aanduiding van die funksionering van die vragpunt organe omdat dit die progressiewe akkumulasie van suiker gedurende die rypwordingsperiode aantoon, asook die moontlike gevolge op korrelvolume ontwikkeling.
‘n Primêre loot wat twee trosse dra is gebruik om ‘n biologiese herhaling te verteenwoordig. Die laer trosse is bo en onder geringeleer om hulle heeltemal te isoleer van enige koolhidraat invoer. Hierdie trosse, tesame met boonste ongeringeleerde trosse en twee kontrole trosse vanaf ‘n ander loot is gemonster. Die korrels van hierdie trosse is geklassifiseer volgens hulle deursnee, om sodoende die unieke moontlikheid daar te stel om korrels van dieselfde volume/ grootte te bestudeer. Metings is gedoen om die vars en droë massas van die gemonsterde korrels te bepaal, asook om die gepaardgaande suikerkonsentrasies te analiseer.
Daar is gevind dat ringelering duidelik ‘n effek gehad het op korrelsuiker dinamika en die metode is verbeter in die tweede jaar van die proef. Ringelering in wisselwerking met korrel klassifikasie volgens korrel deursnee het aangetoon dat korrels met dieselfde grootte verskillende suikerkonsentrasies kon hê. Dit het verder aangedui dat daar, tot ‘n sekere mate, ‘n verhouding bestaan tussen die vinnige fase van suiker akkumulasie en die na-véraison toename in korrel vars massa, totdat die plato in suiker akkumulasie bereik word, gewoonlik rondom ‘n suikerkonsentrasie van 20 Brix. Daarbenewens, en van groter belang, is gevind dat wingerdstok funksionering en die balans tussen die bron en vragpunt organe onder ‘n mate van beheer is. Daar is ‘n sterk mate van kompensasie binne ‘n wingerdstok wat die gevolg is van seinoordrag tussen en binne organe in die wingerdstok. Wanneer die resultate van hierdie studie in aanmerking geneem word, word dit duidelik dat die klassieke verhoudings, wat gebruik word om wingerdstok funksionering en balans mee te bepaal, moontlik nie beduidend betekenisvol is nie. Die wyse waarop bron-vragpunt verhoudings tans beskou word is, tot ‘n mate, ‘n oorvereenvoudiging en daar is heelwat beperkinge betrokke by hierdie benadering. Die wingerd is baie meer kompleks en verskeie aspekte moet in aanmerking geneem word voordat enige bewering gemaak kan word rakende bron-vragpunt verhoudings. / The University of Stellenbosch and Winetech for financial support
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Maltotriose transport in yeastSmit, Annel 12 1900 (has links)
Dissertation (PhD)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The conversion of sugar into ethanol and carbon dioxide is a process that has been
intertwined with human culture and long as civilized man has existed. This fermentation
process has been dominated by the micro-organism Saccharomyces cerevisiae and from
providing ancient seafaring explorers of a non perishable beverage to equipping bakers
with a raising agent to turn flour into bread; this organism with its fermentative potential,
has formed an essential part of most societies.
In more recent times, many industries still rely on this basic principle. The
complexities and efficiencies of the conversion of sugar into its various fermentative byproducts
have been studied and optimised extensively to meet the specific demands of
industries. Depending on the raw material used as starting point, the major beneficiaries of
the useful characteristics have been alcoholic beverage producers (wine, beer, and
whiskey amongst others), bakers (bread leavening) and biofuel producers.
One of the obstacles in fermentation optimisation is the sugar consumption
preferences displayed by the organism used. S. cerevisiae can consume a wide variety of
sugars. Depending on the complexities of its structures, it shows a preference for the
simpler saccharides. The fermentation of certain more complex sugars is delayed and runs
the risk of being left residually after fermentation. Many of the crops utilised in
fermentation-based products contain large amounts of starch. During the starch
degradation process many different forms of sugars are made available for fermentation.
Improved fermentation of starch and its dextrin products would benefit the brewing,
whiskey, and biofuel industries. Most strains of Saccharomyces ferment glucose and
maltose, and partially ferment maltotriose, but are unable to utilise the larger dextrin
products of starch. This utilisation pattern is partly attributed to the ability of yeast cells to
transport the aforementioned mono-, di- and trisaccharides into the cytosol. The
inefficiency of maltotriose transport has been identified as the main cause for residual
maltotriose. The maltotriose transporting efficiency also varies between different
Saccharomyces strains.
By advancing the understanding of maltotriose transport in yeast, efforts can be
made to minimise incomplete fermentation. This aim can be reached by investigating the
existing transporters in the yeast cell membrane that show affinity for maltotriose. This
study focuses on optimising maltotriose transport through the comparison of the alpha
glucoside transporter obtained from different strains of Saccharomyces. Through specific
genetic manipulations the areas important for maltotriose transport could be identified and
characterised.
This study offers prospects for the development of yeast strains with improved maltose
and maltotriose uptake capabilities that, in turn, could increase the overall fermentation
efficiencies in the beer, whiskey, and biofuel industries. / AFRIKAANSE OPSOMMING: Die transformasie van suiker na etanol en koolstof dioksied is so oud soos die beskawing self, en dit is van die vroegste tye af onlosmaaklik met die mens se kultuur verbind. Hierdie fermentasie-proses word gedomineer deur die Saccharomyces cerevisiae mikroorganisme. Hierdie organisme het antieke seevaarders voorsien van ‘n nie-bederfbare drankie en van ouds af aan bakkers ‘n rysmiddel verskaf waarmee meel in brood verander kon word. As gevolg van hierdie fermenteringspotensiaal het hierdie organisme ‘n onmisbare rol in meeste beskawings gespeel. Baie industrieë is steeds op hierdie basiese beginsel gebou. Die kompleksiteite en effektiwiteit van die transformasie van suiker na sy verskeie gefermeenteerde neweprodukte is breedvoerig bestudeer en geoptimiseer om aan die spesifieke behoeftes van verskeie industrieë te voeldoen. Afhangend van die grondstowwe wat as beginpunt gebruik is, is die primêre begunstigdes van die fermentasie proses die alkoholiese drankprodusente (onder andere die wyn-, bier- en whiskey produsente), bakkers en biobrandstofprodusente. Die suikerverbruik-voorkeur van die organisme wat die fermentering fasiliteer is een van die struikelblokke in die optimisering van die proses. S. cerevisiae kan ‘n wye spektrum van suikers verbruik maar dit toon ‘n voorkeur vir die eenvoudiger suikers. Die fermentasie van sekere van die meer komplekse suikers is vertraag en loop die risiko om agtergelaat te word na fermentasie. Vele van die gewasse wat in die gefermenteerde produkte gebruik word bevat groot hoeveelhede stysel. Vele soorte suikers word gedurende die afbreek van die stysel beskikbaar gestel vir fermentasie. Die brouers-, whiskey- en biobrandstof industrieë sal almal voordeel trek uit die verbeterde fermentasie van stysel en sy gepaardgaande dekstrin produkte. Meeste Saccharomyces gisrasse fermenteer glucose en maltose; maltotriose word gedeeltelik gefermenteer, maar die meer komplekse dekstrien produkte gevind in stysel word nie gefermenteer nie. Hierdie verbruikerspatroon kan gedeeltelik toegeskryf word aan die vermoë van gisselle om die bogenoemde mono-, di- and trisaccharides in die sitosol op te neem. Die oneffektiwiteit van maltotriose transport is identifiseer as die hoofoorsaak van post-fermentatiewe, oortollige maltotriose. Die effektiwiteit van maltotriose transport verskil ook tussen verskillende Saccharomyces rasse. Pogings om onvolledige fermentasie te veminder kan bevorder word deur die kennis rondom maltotriose transport in gis uit te bou. Hierdie oogmerk kan bereik word deur die bestaande transporters in die gissel se membraan wat ‘n affiniteit vir maltotriose toon te ondersoek. Hierdie studie fokus op die optimisering van maltotriose transport deur die vergelyking van die alpha glucoside transporter (AGT1) wat van verskillende Saccharomyces rasse afkomstig is. Die areas wat relevant is tot maltotriose transport kon deur spesifieke genetiese manipulasies identifiseer en gekarakteriseer word. Hierdie studie bevorder die vooruitsig op die ontwikkeling van gisrasse met verbeterde
maltose en maltotriose transport vermoëns wat op sy beurt weer kan aanleiding gee tot die
verbeterde fermentasie effektiwiteit in die bier, whiskey en biobrandstof industrieë.
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Mannoprotein production and wine haze reduction by wine yeast strainsNdlovu, Thulile 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Wine protein haze formation is a major challenge for wine makers, and several wine clarifying agents such as bentonite are used in the industry to protect wine from this occurrence. However, clarifying agents may have an undesirable impact on wine quality. Yeast mannoproteins have been shown to possess haze-protective properties, while also positively impacting on the sensorial properties of the product. However, while such mannoproteins are released into the wine during the wine making process, the amounts are low and therefore of limited oenological significance. However, and although commercial wine yeast strains display significant genotypic and phenotypic diversity, no broader assessment of haze protective activity and of mannoproteins release by different wine yeast strains has been undertaken.
In this study, several yeast strains were screened for their impact on wine haze formation in Chardonnay must and in a grape juice model system. The data show that strains of the species Saccharomyces paradoxus possess better haze protective properties than the common Saccharomyces cerevisiae wine yeast strains. Differences in the nature of the proteins released by these two species were investigated, and indicated that several mannoproteins were released at significantly higher levels by S. paradoxus, and that some of these proteins might indeed contribute to the haze-protective activity. A further exploration of yeast cell wall properties indicated that the cell walls of haze-protective S. paradoxus strains contained higher levels of chitin than non-haze protective strains. Grape chitinases are likely to be primarily responsible for wine haze formation, and the data clearly demonstrate that these enzymes are able to bind to the yeast cell walls, and that strains with higher amounts of chitin in the cell wall will bind more chitinases. This finding suggests that the haze-protective nature of the strains is at least in part linked to the chitin levels of the strains.
Furthermore, the impact of some genetic modifications in two wine strains (namely S. cerevisiae VIN13 and S. paradoxus RO88) suggests that several proteins contribute to wine haze protection. However, none of the mannoprotein-encoding flocculation genes, FLO1, FLO5, and FLO11 showed any impact on this property.
Further studies are required to assess the full impact of the S. paradoxus strains on haze protection. In particular, the possible use of such strains as starter cultures or the use of S. paradoxus yeast hulls as clarifying agent needs to be further explored. / AFRIKAANSE OPSOMMING: Wyn proteïen-waas vorming is 'n groot uitdaging vir wynmakers en verskeie wyn verhelderings agente soos bentoniet word in die wynbedryf gebruik om wyn te beskerm teen die vorming van waas. Hierdie verheldering agente het egter 'n ongewenste impak op wynkwaliteit. Gis mannoproteïene is uitgewys as proteïene met moontlike waas-beskermende eienskappe wat ook 'n positiewe uitwerking op die sensoriese eienskappe van die produk het. Al word hierdie mannoproteïene egter vrygestel in die wyn tydens die wynmaak proses, is die hoeveelhede oor die algemeen te laag om van wynkundige belang te wees. Verder, ten spyte van die beduidende genotipiese en fenotipiese diversiteit van kommersiële wyngisrasse is daar nog geen breër assessering van die waas beskermende aktiwiteit van mannoproteïene, vrygestel deur verskillende rasse, tot dusver onderneem nie.
In hierdie studie is verskeie gisrasse gekeur vir hul impak op wyn waas-vorming in Chardonnay mos en ook in 'n model druiwesap. Die data wys dat rasse van die spesie Saccharomyces paradoxus besit beter waas beskermende eienskappe as die algemene Saccharomyces cerevisiae wyngisrasse. Verskille in die aard van die proteïene wat vrygestel is deur hierdie twee spesies is ondersoek, en dit is aangedui aangedui dat verskeie mannoproteins vrygestel aan aansienlik hoër vlakke deur S. Paradoxus. Dit is ook aangedui dat sommige van hierdie proteïene wel bydra tot die waas-beskermende aktiwiteit.
'n Verdere verkenning van gis selwand eienskappe het aangedui dat die selwande van waas-beskermende rasse van S. paradoxus hoër vlakke chitien as nie-waas beskermende stamme bevat. Druiwe chitinases is waarskynlik hoofsaaklik verantwoordelik vir wyn waas vorming, en die data toon duidelik dat hierdie ensieme in staat is om te bind aan die gis selwande, en dat die stamme met hoër vlakke chitien in die selwand meer chitinases sal bind. Hierdie bevinding dui daarop dat die waas-beskermende aard van die stamme ten minste gedeeltelik gekoppel is aan die chitien vlakke van die stamme. Die impak van sekere genetiese modifikasies in twee verskillende gisrasse, naamlik die S. cerevisiae ras VIN13 en die S. paradoxus ras RO88, dui verder daarop dat verskeie proteïene dra by tot die beskerming teen wyn waas. Geeneen van die mannoprotein-koderende flokkulasie gene, FLO1, FLO5 en FLO11 het egter 'n impak op hierdie eienskap nie.
Verdere studies is nodig om die volle impak van die S. paradoxus rasse op waas beskerming te assesseer. In die besonder, die moontlike gebruik van sulke rasse as 'n inkolasie kultuur of die gebruik van S. paradoxus gis doppe as verheldering agent moet verder ondersoek word.
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Investigating the impact of sulphur dioxide on Brettanomyces bruxellensis at a molecular and cellular levelDuckitt, Edward 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The yeast Brettanomyces was isolated from beer in 1904 and associated with wine thereafter. A
sporulating form, Dekkera, was discovered later. Brettanomyces bruxellensis produces high
levels of volatile phenol off-flavours in wine. Sulphur dioxide (SO2) is the most widely used
chemical preservative in wine. Yeasts have several mechanisms to cope with the SO2, namely
Ssu1p, a membrane bound SO2 transporter; sulphite reduction, sulphite oxidation and
acetaldehyde production. In unfavourable environmental conditions, certain yeasts can enter a
viable-but-non-culturable (VBNC) state which is characterised by reduced metabolic rate,
inability to reproduce on solid media and a reduction of cell size. VBNC can be triggered by
chemical stress such as high SO2 levels. The objectives of this study were to examine the SO2
tolerance of B. bruxellensis and Saccharomyces cerevisiae, to quantify their rates of SO2
accumulation and efflux, determine the effect of SO2 on their energy metabolism and investigate
if B. bruxellensis possesses an orthologue to S. cerevisiae SSU1.
In this study, the identity of a number of Brettanomyces/Dekkera strains was confirmed using
5.8S rDNA-ITS RFLP analysis and DNA sequencing. Sporulation assays were used to confirm
whether these strains belonged to the Dekkera or Brettanomyces genus. A method to
accurately quantify SO2 in laboratory conditions was optimised. Molecular SO2 tolerance was
tested by spotting fresh yeast cultures on media with SO2 and/or ethanol. Tolerance to SO2
and/or ethanol showed highly strain dependent results with S. cerevisiae showing the highest
tolerance levels while B. bruxellensis tolerated SO2 and ethanol poorly but certain strains grew
well with only SO2. The SO2 accumulation and efflux rates of 3 S. cerevisiae strains and 3 B.
bruxellensis strains were determined. It was shown that the S. cerevisiae strains followed the
same trends as previously found in literature whereas B. bruxellensis strains showed similar
trends but displayed highly variable strain-dependent results. B. bruxellensis CB63 and S. cerevisiae VIN13 were investigated for their response to SO2 in two
different media, TA and SWM, over a 48-hour and 32-day period respectively. Acetic acid,
acetaldehyde, D-glucose, D-fructose (only in SWM) and ethanol (only in TA) were regularly
monitored over the time course of each experiment. SO2 had the greatest impact on
B. bruxellensis with decreased rates of glucose consumption and ethanol production as well as
increased acetic acid. Acetaldehyde peaked shortly after SO2 addition with the subsequent
restarting of sugar consumption for certain samples. This suggests that sufficient acetaldehyde
was produced to bind free SO2 to reduce SO2 stress. Volatile phenols were quantified for day 32
of the SWM experiment. An increase of 4-ethyl guaiacol was correlated to higher molecular SO2
levels. SO2 negatively affected both yeasts energy metabolism, forcing the yeasts metabolism
to adapt to ensure survival.
In general, SO2 was shown to have a negative impact on all aspects of a yeasts growth and
metabolism and that SO2 tolerance is highly strain dependent and a far more complicated
characteristic than currently understood. / AFRIKAANSE OPSOMMING: Die gis Brettanomyces is in 1904 uit bier geïsoleer en daarna met wyn geassosieer. 'n
sporulerende vorm, Dekkera, is later ontdek. Brettanomyces bruxellensis produseer hoë vlakke
van vlugtige fenol afgeure in wyn. Swaweldioksied (SO2) is die mees gebruikte chemiese
preserveermiddel in wyn. Giste het verskeie meganismes om SO2 te hanteer, naamlik Ssu1p, 'n
membraan-gebonde SO2 transporter, sulfietvermindering, sulfiet-oksidasie en
asetaldehiedproduksie. In ongunstige omgewingstoestande kan sekere giste 'n lewensvatbare,
maar nie-kultiveerbare (LMNK)-toestand aanneem wat gekenmerk word deur verlaagde
metaboliese tempo, onvermoë om voort te plant op soliede media en 'n vermindering van die
selgrootte. LMNK kan veroorsaak word deur chemiese stres, soos hoë SO2-vlak. Die doelwitte
van hierdie studie was om die SO2 -bestandheid van B. bruxellensis en Saccharomyces
cerevisiae te ondersoek, hul spoed van SO2 -opneming/akkumulasie en -uitskeiding te
kwantifiseer, die invloed van SO2 op energiemetabolisme te bepaal en te ondersoek of B.
bruxellensis oor ‘n soortgelyke geen as die S. cerevisiae SSU1 beskik.
In hierdie studie is die identiteit van 'n aantal Brettanomyces/Dekkera-stamme bevestig deur
5.8S rDNA-ITS RFLP-analise en DNA-opeenvolging te gebruik. Sporulasietoetse is gebruik om
te bevestig of hierdie stamme aan die genus Dekkera of Brettanomyces behoort. 'n Metode om
SO2 onder laboratoriumtoestande akkuraat te kwantifiseer, is geoptimiseer. Molekulêre SO2-
bestandheid is getoets deur vars giskulture op media met SO2 en/of etanol te groei.
Bestandheid teen SO2 en/of etanol het stam-afhanklike resultate getoon, S. cerevisiae wat die
hoogste toleransievlakke getoon het, terwyl B. bruxellensis SO2 en etanol swak tolereer, maar
sekere stamme het goed gegroei met slegs SO2. Die SO2-akkumulasie en -uitskeidingtempo
van 3 S. cerevisiae-rasse en 3 B. bruxellensis-stamme is bepaal. Daar is gevind dat die S.
cerevisiae-rasse dieselfde tendens soos voorheen in die literatuur beskryf, gevolg het, terwyl B.
bruxellensis-stamme soortgelyke tendense getoon het,maar hoogs veranderlike stamafhanklike
resultate vertoon. B. bruxellensis CB63 en S. cerevisiae VIN13 is ondersoek vir hul reaksie tot SO2 in twee
verskillende media, TA en SWM, oor 'n tydperk van 48-uur en 32-dae onderskeidelik. Asynsuur,
asetaldehied, D-glukose, D-fruktose (slegs in SWM) en etanol (slegs in TA) is gereeld
gemoniteer oor die verloop van elke eksperiment. SO2 het die grootste impak op B. bruxellensis
met ‘n verlaagde tempo van glukoseverbruik en etanolproduksie, sowel as verhoogde asynsuur.
‘n Asetaldehiedhoogtepunt is bereik kort na die SO2-byvoeging met die daaropvolgende
hervatting van suiker wat vir sekere monsters gebruik is. Dit dui daarop dat voldoende
asetaldehied geproduseer is om vry SO2 te bind om SO2-stres te verminder. Vlugtige fenole is
op dag 32 van die SWM-eksperiment gekwantifiseer. 'n Toename van 4-etiel-guajakol korreleer
met hoër molekulêre SO2-vlakke. SO2 het beide giste se energiemetabolisme negatief
beïnvloed, wat die gis dwing om sy metabolisme aan te pas om oorlewing te verseker. Oor die algemeen het SO2 'n negatiewe impak op alle aspekte van giste se groei en
metabolisme, en SO2-bestandheid is hoogs stam–afhanklik. Dit is ook 'n baie meer
ingewikkelde kenmerk as wat tans verstaan word.
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Volatile metabolic profiling of SA Chenin blanc fresh and fruity and rich and ripe wine styles : development of analytical methods for flavour compounds (aroma and flavour) and application of chemometrics for resolution of complex analytical measurementsLawrence, Nina 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: The aroma and flavour of wine are important aspects that form the basis for consumers’
organoleptic experience of wine. Therefore, an understanding of the chemical
composition of wine aroma is of major importance, to establish possible links between
wine chemistry, sensory attributes and consumer preference for a product. For this
purpose analytical chemistry and multivariate techniques are indispensable tools for the
metabolic profiling of wine.
Chenin blanc is one of the most important South African export white wine varieties.
However, despite its importance, very limited profiling of Chenin blanc aroma
compounds has been done and information is restricted to isolated and dated reports on
a few chemical compounds only. Therefore, the overall aim of this study was to obtain
an in-depth view of the volatile chemical profile of this cultivar.
The first task was to perform targeted volatile metabolic profiling of the three dry and offdry
Chenin blanc styles, fresh and fruity, rich and ripe unwooded and rich and ripe
wooded. To this end, a new, simple and robust liquid-liquid extraction technique using
dichloromethane was developed and validated for extraction of analytes prior to gas
chromatography flame ionization detection (GC-FID) analysis, to quantify 57 analytes in
one rapid analytical procedure. This method was applied to profile 48 Chenin blanc
wines. Very successful discrimination between the three styles, using the quantified
volatile compounds, was obtained with two multivariate methods. These were partial
least squares regression-discriminant analysis, (PLS-DA), as well linear-DA, using best
subset selection for identifying the most important variables. According to the
classification models, a higher content of maturation derived, malolactic fermentation
derived and wood derived compounds were predominantly characteristic of the wooded
wines. Higher content of some terpenes and ethyl esters were predominantly
associated with the rich and ripe unwooded style Chenin blanc wines, while the fresh
and fruity style were generally characterized by high levels of acetate esters.
Secondly, untargeted analysis of 21 wines was done with gas chromatography mass
spectrometry (GC-MS). Mathematical chromatography, using PARAllel FACtor analysis
(PARAFAC and PARAFAC2), was applied to the GC-MS data for resolution of the complex chromatographic results by multi-way modeling, and to derive unbiased
multivariate classification models of the three styles. This approach provided excellent
style differentiation, without the arduous task of analysis of numerous standards and
setting up of calibration curves, required by the targeted approach described above.
Additionally, the data generated during this study will form part of the current South
African wine aroma database, which does not contain any data regarding Chenin blanc
at present. / AFRIKAANSE OPSOMMING: Die aroma en geur van wyn is belangrike aspekte aangesien dit die basis vorm van die
wynverbruiker se organoleptiese ervaring van die produk. Derhalwe, is ‘n deeglike
kennis van die chemiese samestelling van wynaroma baie belangrik, ten einde die
korrelasies tussen wynchemie, sensoriese eienskappe en verbruikersvoorkeure te
bepaal. Vir hierdie doel, is die insameling van analitiese chemiese data, tesame met
multi-veranderlike tegnieke om relevante inligting uit die data te onttrek, onmisbaar vir
die metaboliese profilering van wyn.
Chenin blanc is huidiglik een van Suid-Afrika se belangrikste uitvoer wit wynvariëteite.
Ten spyte hiervan, is daar tot hede egter baie min profilering van Chenin blanc se
aromakomponente gedoen en die beskikbare inligting is beperk tot geïsoleerde en
verouderde navorsingsbevindinge. In die lig van bogenoemde, is die oorkoepelende
motivering vir hierdie studie dus om die vlugtige chemiese komponente se profiel in
Chenin blanc wyn, in diepte te bepaal.
Die eerste taak was die geteikende bepaling van die metaboliese profiel van drie droë
of halfdroë Chenin blanc wynstyle, nl. vars en vrugtig, ryk en ryp ongehout, asook ryk
en ryp gehout. Om dit te bereik, is ‘n nuwe eenvoudige en robuuste vloeistof-vloeistof
ekstraksieprosedure met dichlorometaan ontwikkel, wat analise met gaschromatografie
– vlamionisasie deteksie (GC-FID) voorafgaan, om die konsentrasies van 57
komponente in een vinnige analise te bepaal. Hierdie metode is gebruik om 48 Chenin
blanc wyne te profileer. Deur gebruik te maak van multi-veranderlike data analitiese
tegnieke, is die gekwantifiseerde vlugtige komponente data gebruik in diskriminant
analise. Baie suksesvolle onderskeid tussen die drie style, is verkry deur gebruik te
maak van twee multi-veranderlike metodes, naamlik: parsiële kleinste kwadrate
regressie, diskriminant analise, asook liniêre diskriminant analise. Vir laasgenoemde
analise, is die seleksie van die mees belangrike veranderlikes met beste sub-groep
regressie bepaal.
Volgens hierdie klassifikasie modelle is ‘n hoër inhoud van veroudering-,
appelmelksuurgisting- en houtverwante aroma komponente baie kenmerkend in die houtbehandelde wyne. Hoër vlakke van sommige terpene en etiel esters was
kenmerkend met betrekking tot ryk en ryp ongehoute Chenin blanc style, terwyl die vars
en vrugtige style meer gekenmerk was met hoë vlakke van asetaat esters.
Tweedens is ‘n seleksie van 21 wyne geanaliseer deur gebruik te maak van
gaschromatografie – massa spektrometrie (GC-MS) in ‘n ongeteikende metaboliese
profileringsbenadering. Wiskundige chromatografiese metodes, spesifiek, parallelle
faktor analise (PARAllel FACtor analysis (PARAFAC and PARAFAC2)), was voorts
gebruik om komplekse chromatogramme te prosesseer met wiskundige, multi-vlak
modellering. Met hierdie nie-selektiewe benadering, is ook suksesvolle
klassifikasiemodelle gegenereer vir die diskriminasie tussen die drie verskillende
Chenin blanc style. Die voordeel van die ongeteikende GC-MS analise, gekoppel met
die data hanterings- en prosesseringsprotokols in hierdie studie gebruik, is dat die
arbeidsintensiewe taak om kalibrasiekurwes op te stel vir elke individuele komponent,
soos wat vereis word in die geteikende benadering, nie nodig is nie.
Die data wat ingewin is gedurende hierdie studie, sal ook bygevoeg word tot ‘n
bestaande Suid-Afrikaanse aroma databasis, wat tans geen data aangaande Chenin
blanc wyn bevat nie.
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The evaluation of malolactic fermentation starter cultures under South African winemaking conditionsVan der Merwe, Hanneli 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2007. / ENGLISH ABSTRACT: With ever increasing pressure on wine producers to lower the financial costs involved in
winemaking to be able to compete in the market, all while maintaining a high level of wine
quality, the focus on maintaining control over all aspects of the winemaking process are
greatly emphasized.
Malolactic fermentation (MLF) is one of the important processes in red wine production.
The advantages of this process, when performed successfully, is widely known and
accepted. One way to gain control over MLF is the use of MLF starter cultures. Starter
cultures usually consist of Oenococcus oeni that has been isolated from grapes or wines
and is in most cases available in a freeze-dried form ready for direct inoculation into the
wine when MLF is desired. Starter cultures are induced into wine and usually ensure the
immediate onset as well as a fast and clean execution of the process. Starter cultures
used in South Africa are in most cases isolated from cooler viticultural regions in the
Northern hemisphere. The constitution of wines from cooler viticultural regions, differ from
those in South Africa, which has a warm climate. The most important difference is the acid
content of the wines which is lower in South African must/wines and results into a higher
pH. The three most important changes that develop in wine during MLF are a decrease in
acidity due to the conversion of malic acid to the less harsh lactic acid, enhanced flavour
and aroma of wine and an increase in the microbiological stability of wine. The decrease
in acidity is very important for wines produced for grapes grown in cool viticulture regions.
In South Africa though, the climate is warm and higher pH’s are present in the musts and
wines and the de-acidification due to MLF is not the main aim but rather the
microbiological stabilisation. One of the compounds that could be produced by lactic acid
bacteria (LAB) is biogenic amines (BA’s). These compounds can be hazardous to human
health. This thesis focussed on the performance of MLF starter cultures in high pH South
African red wines.
The first objective of the study was to stretch MLF starter cultures in high pH red wines
of South Africa. Stretching means to use less than the prescribed dosage or the re-use of
starter cultures. The difference in MLF rate, the influence of the natural occurring LAB and
the levels of biogenic amines formed during MLF were determined for the different
stretching treatments. The results showed that different rates in malic acid degradation
were experienced between the treatments, but in all cases MLF fermentation was completed. Biogenic amines were formed at various levels and the influence of the natural
occurring LAB also played a role.
The second objective of the study was the evaluation of the effect of a wine isolated
LAB (Lactobacillus) and an acetic acid bacteria (AAB), inoculated with a MLF starter
culture had on MLF at different wine pH’s. It was found that especially in the case where
the Lactobacillus was inoculated in combination with the MLF starter culture a possible
stimulatory effect was experienced with regards to malic acid degradation rate. Biogenic
amine concentration was measured at the end of MLF and it was found that no histamine
and tyramine were formed in any of the treatments, while the putrescine and cadaverine
levels were found to be at approximately similar levels for the different treatments.
The third objective was to evaluate the possible influence of commercial tannin
additions and a pectolytic enzyme on rate of MLF and phenolic composition of high pH red
wine. The commercial tannins had possible inhibitory as well as stimulatory effects on the
rate of malic acid degradation especially during the initial stages of MLF, with the highest
dosage having the significant effect. The BA results showed difference in the levels
produced due to tannin additions as well as strain differences could exist. The phenolic
content showed a decrease in colour density, total red pigments, total phenolics and
anthocyanins between AF and MLF.
The fourth objective was to evaluate inoculation time of MLF starter cultures. The
results showed that the fastest AF/MLF time was with simultaneous inoculation of the
yeast and MLF starter cultures. It was also for this treatment where no histamine or
tyramine was detected at the end of MLF compared to the other inoculation strategies
(before the end of AF and after AF).
This study generated a large amount of novel data which made a valuable contribution
with regards to MLF in high pH red wines of South Africa. / AFRIKAANSE OPSOMMING: Die druk om wyne van hoë gehalte teen lae insetkoste te lewer om deel te bly van ’n
kompeterende mark, plaas die fokus weer sterk op onder andere die beheer van alle
aspekte van die wynmaak proses.
Appelmelksuurgisting (AMG) is een van die belangrikste prosesse van rooiwyn produksie.
Die voordele van AMG, in die geval van die suksesvolle implementering daarvan is
vandag bekend en word geredelik aanvaar. Een van die metodes om beheer te verkry oor
the proses van AMG is deur die gebruik van AMG aanvangskulture. AMG
aanvangskulture bestaan uit Oenococcus oeni wat geïsoleer word vanaf druiwe of
mos/wyn en is in meeste gevalle beskikbaar in ’n gevries-droogte vorm wat direk in wyn
geïnokuleer kan word. Aanvangskulture word in wyn geïnduseer om die onverpose
aanvang van AMG te bewerkstellig asook om ’n vinnige en skoon deurvoering van die
proses te verseker. Die aanvangskulture wat in Suid-Afrika vir hierdie doeleinde gebruik
word is in meeste van die gevalle verkry uit koue wingerdbou gebiede in die Noordelike
Halfrond. Die samestelling van druiwe van koue wingerdbou gebiede en dié van
Suid-Afrikaanse warm wingerdbou gebiede verskil. Die belangrikste verskil word ervaar in
die suur inhoud, wat laer is in Suid-Afrikaanse druiwe en dus lei tot ‘n hoër pH inhoud. Die
drie mees belangrikste veranderinge wat gedurende AMG in wyn plaasvind is die
vermindering van die suur, as gevolg van die omskakeling van appelsuur na melksuur, die
verbetering van die aroma en geur van wyn en die verbeterde mikrobiologiese stabiliteit.
Die afname in suur is veral belangrik in wyne van koue wingerbou gebiede omdat die
suur-inhoud daarvan soveel hoër is. In Suid-Afrika kan hierdie verlaging in suur egter lei
tot ’n verdere verhoging in die pH wat plat wyne en uiteindelik ’n verlaging in die kwaliteit
van wyn tot gevolg kan hê. Biogene amiene (BA) is verbinding wat melksuurbakterieë
(MSB) kan vorm gedurende AMG en kan ernstige implikasies hê vir die mens se
gesondheid.
Hierdie tesis fokus op die evaluering van AMG aanvangskulture in hoë pH rooi wyne
van Suid-Afrika.
Die eerste doelwit gedurende hierdie studie was om AMG kulture te rek en die invloed
daarvan in hoë pH rooiwyn te evalueer ten opsigte van the tempo van AMG, die rol van die
natuurlike MSB te bestudeer asook om die vlak van biogene amiene te bepaal vir die
verskillende behandelings. Die resultate het aan die lig gebring dat die rek van kulture verskille in die tempo van appelsuur afbraak tot gevolg het, maar dat AMG in alle gevalle
wel suksesvol deurgevoer kon word. Die BA’e wat gevorm is, was teenwoordig in
verskillende hoeveelhede.
Die tweede doelwit was om die effekt van die gesamentlike inokulasie van ’n wyn
geisoleerde MSB (Lactobacillus) asook ’n asynsuurbakterie (ASB) met ’n kommersiële
AMG aanvangskultuur op AMG te evalueer. Hierdie eksperiment is uitgevoer by
verskillende pH’s. Daar is gevind dat veral in die kombinasie inokulasie met die
Lactobacillus, die tempo van appelsuur afbraak moontlik gestimuleer was. Geen
histamien of tiramien is tydens AMG gevorm in hierdie eksperiment gevorm nie, terwyl
putresien en kadaverien teenwoordig was teen ongeveer gelyke vlakke vir die
behandelings.
Die derde doelwit was om die moontlike invloed van kommersiële tannien toevoegings
en die toevoeging van ’n pektolitiese ensiem te evalueer ten opsigte van AMG tempo die
fenoliese samestelling van rooiwyn te bestudeer. Verskillende kommersiële tanniene het
’n moontlike sowel as inhiberende uitwerking gehad, veral gedurende die aanvanklike
stadium AMG. Die grootste verskille is waargeneem in die behandelings waar die hoogste
dosisse tannien bygevoeg is. Die BA resultate toon dat verkillende vlakke geproduseer
was en dat hierdie verskille onstaan het as gevolg van verskille in tannien dosisse sowel
as aanvangskulture. Die fenoliese inhoud het ’n afname in kleur intensiteit, totale rooi
pigmente, totale fenole en antosianiene getoon vir die periode vanaf AF tot die einde van
AMG.
Die vierde doelwit was om the tyd van inokulasie van AMG aanvangskulture te
bestudeer. Die resultate het getoon dat die vinningste tydperk van AF/AMG was
ondervind in die geval waar die gis aanvangskulture gelyktydig met die AMG
aanvangskulture geïnokuleer was. Geen histamine en tyramine het ook in hierdie
behandeling ontwikkel nie, terwyl daar wel vlakke teenwoordig was in die ander
behandelings (inokulasie net voor die einde van AF en na afloop van AF).
Tydens hierdie studie is ’n groot hoeveelheid nuwe data geskep wat ‘n groot bydrae
ten opsigte van AMG in hoë pH rooi wyne vanaf Suid-Afrika kan lewer.
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Characterization of Chenin Blanc wines produced by natural fermentation and skin contact : focus on application of rapid sensory profiling methodsWeightman, Jayne 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Producers of South African (SA) dry and semi-dry Chenin blanc table wines are currently
experimenting with winemaking techniques to modulate the flavours of the predominantly fruity
styles of this genre. An important stage during wine style development is sensory profiling
paired with consumer acceptance testing, before wine is produced on industrial scale. With
those aforementioned goals in mind, this study was conducted in partnership with two
commercial SA wine cellars.
The main focus of the study was an investigation into the treatment effects of two winemaking
techniques, respectively grape skin contact and natural fermentation, on the sensory profiles of
experimentally produced Chenin blanc wines. Results obtained with descriptive sensory
analysis (DA) of the wines were compared to those obtained by two rapid sensory profiling
methods, namely projective mapping (PM) and frequency of attribute citation (FC). A consumer
preference study was also done on the wines. In order to understand the treatment effects
better, the dominant non-Saccharomyces yeasts that were present during the natural
fermentations were identified using polymerase chain reaction (PCR), while the major volatile
chemical compounds were identified with chromatography and mass spectrometry.
The sensory and chemical profiles of the naturally fermented wines were significantly different
from those of the inoculated wines. PCR analysis identified some of the yeasts present during
alcoholic fermentation. In comparison to the inoculated fermented wines, the naturally
fermented wines were generally perceived to have more intense and riper tropical fruity aromas,
with enhanced sweetness and reduced intensities of sourness, bitterness and astringency.
The wines fermented on the skins (FoS) had lower ester and volatile thiol concentrations than
the control wines (with no skin contact) and limited skin contact wines. Sensory attributes linked
to the FoS wines included aromas of dried fruit, dried grass and a vegetative character, with an
increased sour and bitter taste and astringent mouthfeel. In contrast, the wines that were
produced with limited skin contact (12 hours) retained their tropical fruity aromas better than the
FoS wines. Limited skin contact seemed to have had a less harsh effect on the taste and
mouthfeel than the FoS wines. A consumer study was done to establish a Generation Y
consumer group’s (18-35 years) preference for the different treated wines. Overall, the naturally
fermented wines, which were described as having a strong tropical fruit character, were
preferred. The FoS wines were generally disliked by the consumers. Results obtained from the three sensory analysis methods, respectively DA, PM and FC, were
similar, thereby confirming the suitability of the rapid methods PM and FC, to extract qualitative
information from the sensory profiling of white wine.
The results of this study made a significant contribution towards validation of rapid sensory
methods for wine evaluation, which are particularly valuable in the context of sustainability and
technology transfer to research and industry alike. The knowledge gained on the chemical
profiles of SA Chenin blanc is novel and this is one of the first reports on the volatile thiol
content of SA Chenin blanc wine. / AFRIKAANSE OPSOMMING: Produsente van Suid-Afrikaanse (SA) droë en semi-droë Chenin blanc tafelwyne
eksperimenteer tans met wynmaaktegnieke om die oorwegend vrugtige style van hierdie genre
te varieer. ‘n Belangrike fase van wynstylontwikkeling is sensoriese profilering van die produkte
met gepaardgaande verbruikersaanvaardingstoetse, voordat die wyne op industriële skaal
geproduseer word. Met dié bogenoemde doelwitte in gedagte, was hierdie studie in
vennootskap met twee kommersiële SA wynkelders gedoen.
Die hooffokus van die studie was om die invloed van twee wynmaaktegnieke, onderskeidelik
druifdopkontak en natuurlike fermentasie, op die sensoriese profiele van eksperimenteel
geproduseerde Chenin blanc wyne te ondersoek. Resultate wat met beskrywende sensoriese
analise (DA) van die wyne verkry is, is vergelyk met dié wat deur twee vinniger sensoriese
profileringsmetodes metodes, naamlik projektiewe kartering (PM) en frekwensie van
kenmerkaanhaling (FC) verkry is. 'n Verbruikervoorkeurstudie is ook op die wyne gedoen. Ten
einde die behandelingseffekte beter te verstaan, is die dominante nie-Saccharomyces giste wat
teenwoordig was tydens die natuurlike fermentasie geïdentifiseer met behulp van die
polimerasekettingreaksie (PCR), terwyl die vernaamste vlugtige chemiese verbindings
geïdentifiseer is met chromatografie en massaspektrometrie.
Die sensoriese en chemiese profiele van die natuurlike gefermenteerde wyne was beduidend
anders as dié van die geiinokuleerde wyne. PCR analise het sommige giste wat teenwoordig
was tydens alkoholies fermentasie geïdentifiseer. In vergelyking met die geiinokuleerde wyne,
het die natuurlik gefermenteerde wyne intenser en ryper tropiese vrugtige aromas getoon, met
‘n verhoogde perspesie van soetheid en laer intensiteite van suurheid, bitterheid en vrankheid. Die wyne wat berei is deur fermentasie op die druifdoppe (FoS) het laer konsentrasies van
esters en vlugtige swawelverbinding gehad, as die kontrole wyne (geen dopkontak) en beperkte
dopkontak wyne. Sensoriese eienskappe gekoppel aan die FoS wyne was geasssosieer met
gedroogde vrugte, gedroogde gras en 'n vegetatiewe aroma, met gepaardgaande verhoogde
suur en bitter smaakpersepsies en ‘n frank mondgevoel. In teenstelling, het die wyne wat
geproduseer is met 'n beperkte dopkontak (12 uur) hul tropiese vrugtige aroma beter behou as
die FoS wyne. Beperkte dopkontak het ook ‘n minder negatiewe uitwerking op die
smaakpersepies van bitterheid en vrankheid gehad. ‘n Verbruikerstudie is gedoen om 'n groep
jong Generasie Y verbruikers (18-35 jaar) se voorkeure vir die verskillende behandelings te
bepaal. Oor die algemeen is die natuurlike gefermenteerde wyne, wat beskryf is met 'n sterk
tropiese vrugtekarakter verkies, terwyl die groep nie van die FoS wyne gehou het nie. Resultate wat verkry is met drie sensoriese analise metodes, onderskeidelik DA, PM en FC,
was soortgelyk en die geskiktheid van die vinniger metodes, PM en FC, om kwalitatiewe
inligting van witwyn se sensoriese eienskappe te verkry, is bevestig.
Die resultate verkry met hierdie studie maak ‘n beduidende bydrae tot die validering van
vinniger sensoriese metodes vir wynevaluering, wat veral waardevol is in die konteks van
volhoubaarheid en tegnologieoordrag na navorsing en die industrie.
Die nuwe kennis wat in hierdie studie gegenereer is met die chemiese profilering van SA
Chenin blanc wyn is baie waardevol en hierdie is een van die eerste narvorsingsprojekte oor die
inhoud van vlugtige swawelverbings in SA Chenin blanc wyn.
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