Thesis (MSc (Wine Biotechnology))--University of Stellenbosch, 2011. / Includes bibliography. / ENGLISH ABSTRACT: The varietal character of Sauvignon blanc wine is mostly defined by the balance between
tropical and green vegetative flavour nuances. Grape derived methoxypyrazines are the main
aroma contributors towards green vegetative flavours. Methoxypyrazines are heat and light
sensitive. Due to warm climatic conditions in South Africa, methoxypyrazine levels decrease
during grape ripening.
The addition of food flavourings to Sauvignon blanc wine, a practice known as spiking, has
occurred in the past to improve the green character of the wines. Adding flavourings to wine and
selling the wine as natural certified wine is illegal in South Africa. Currently, adulterated
Sauvignon blanc wines are identified using gas chromatography–mass spectrometry (GC-MS)
and liquid chromatography–mass spectrometry (LC-MS) methods to quantify methoxypyrazines
and compare levels to an established database. Although of high sensitivity, GC-MS and LCMS methods are costly and time consuming, therefore not optimal for routine screening of
wines. Hence the need for the development of a fast and cost effective method for routine
screening of large amounts of wines to identify adulteration.
Small scale vinification practices were used to prepare experimental Sauvignon blanc wine.
Flavourings were added to Sauvignon blanc grape juice before fermentation, during the
preparation of experimental spiked wines. Control wines, containing no flavouring, were also
prepared. Commercial wines were spiked after fermentation and bottling. Each wine was only
spiked with a single flavouring. The flavourings added were the juice of homogenised fresh
green peppers and commercially available flavourings for wine. The following commercial
flavourings were used: green pepper, asparagus, grassy and tropical.
The above mentioned wines were analyzed using Fourier transform infrared (FT-IR)
spectroscopy, GC-MS, LC-MS and descriptive sensory analysis. The FT-IR techniques used
were Fourier transform mid infrared (FT-MIR) transmission, FT-MIR attenuated reflection and
Fourier transform near infrared (FT-NIR) reflection spectroscopy. The data was interpreted
using the following multivariate statistical techniques: principal component analysis (PCA),
partial least squares discrimination (PLS-D) and conformity testing.
Multivariate models constructed from FT-MIR and FT-NIR data were able to discriminate
between spiked and control wines. Sensory analysis results clearly showed differences between
non-spiked wines and spiked wines with 3-isobutyl-2-methoxypyrazine concentrations 10 times
higher than naturally occurring in wine. Differences between control and spiked wines with
concentrations of 3-isobutyl-2-methoxypyrazine similar to concentrations naturally occurring in
wines could not be detected to prove adulteration conducting sensory analysis. However,
differences between control and spiked wines with levels of 3-isobutyl-2-methoxypyrazine
similar to levels naturally occurring in wines could be detected using FT-IR data in conjunction
with multivariate statistics.
This study showed that, FT-IR spectroscopy in conjunction with multivariate statistical methods
can be a possibility for the screening and identification of wines suspected of adulteration in
terms of added flavourings. Descriptive sensory analysis also proved to be a potentially useful
tool. However screening and training of potential panel members are time consuming. / AFRIKAANSE OPSOMMING: Die variëteitskarakter van Sauvignon blanc wyn word grotendeels gedefinieer deur die balans
tussen tropiese en groen vegetatiewe aromas. Metoksipirasiene is die hoof aroma verbindings
wat verantwoordelik is vir groen vegetatiewe aromas. Metoksipirasien is hitte- en ligsensitief.
Warm klimaatsomstandighede in Suid-Afrika het tot gevolg dat metoksipirasien konsentrasies
daal tydens druif rypwording.
Sauvignon blanc wyne is in die verlede vervals deur middel van die byvoeging van vars groen
soetrissies om die groen vegetatiewe karaktereienskappe van die wyne te bevorder. Die
byvoeging van geurmiddels of plantekstrakte by wyn en verkoop van daardie wyn as
gesertifiseerde natuurlike wyn is onwettig in Suid-Afrika. Tans word vervalsde wyne met behulp
van gaschromatografie-massaspektrometrie (GC-MS) en vloeistofchromatografie-massaspektrometrie (LC-MS) opgespoor. Kwantifisering van metoksiepirasien konsentrasies in wyne
en druiwesappe word vergelyk met konsentrasies in ‘n bestaande databasis. Alhoewel GC-MS
en LC-MS hoë sensitiwiteitsmetodes is, is dit duur en tydrowende metodes, dus nie optimaal vir
roetine sifting nie. Dus word ‘n koste- en tydseffektiewe roetine metode benodig om vervalsing
van wyne op te spoor.
Eksperimentele wyne is op klein skaal berei. Geurmiddels is voor fermentasie by die druiwesap
gevoeg. Kontrole wyne waarby geen geurmiddels gevoeg is nie, is ook berei. Kommersiële
wyne is gegeur na fermentasie en bottelering. Elke wyn is met ‘n enkele geurmiddel gegeur.
Gehomogeniseerde vars groen soetrissie asook kommersieel beskikbare geursels vir wyn is
gebruik. Die volgende kommersiële geursels is gebruik: groen soetrissie, aspersie, gras en
tropiese geursel.
Die volgende analitiese tegnieke is gebruik vir analisering van bogenoemde wyne: Fourier
transformasie infrarooi (FT-IR) spektroskopie, GC-MS, LC-MS en beskrywende sensoriese
analise. Die spesifieke FT-IR tegnieke wat gebruik is, is: Fourier transformasie mid-infrarooi
(FT-MIR) transmissie, FT-MIR verswakte weerskaatsing en Fourier transformasie naby-infrarooi
(FT-NIR) reflektansie. Die volgende multiveranderlike statistiese tegnieke is gebruik ter
interpretasie van data: hoof komponent analise (PCA), parsiële kleinste kwadraat diskriminant
analise (PLS-D) en gelykvormigheidstoetsing.
Multiveranderlike modelle, bereken met behulp van FT-MIR en FT-NIR data, kon diskrimineer
tussen gegeurde en kontrole wyne. Resultate wat verkry is tydens sensoriese analises het
duidelike verskille uitgewys tussen gegeurde en kontrole wyne met betrekking tot 3-isobutiel-2-
metoksipirasien konsetrasies waar 3-isobutiel-2-metoksipirasien konsentrasies 10 keer hoër
was as wat natuurlik voorkom in wyn. Geen beduidende verskille kon waargeneem word in
gevalle waar wyne vervals is met laer konsentrasies van geurmiddels deur sensoriese data te
ontleed nie. Nietemin, statisitiese verskille tussen kontrole en vervalsde wyne kon waargeneem
word vir lae-konsentrasie-geurmiddel vervalsde wyne deur FT-IR data met behulp van
multiveranderlike statisitiese metodes te ontleed.
Hierdie studie het gewys dat FT-IR in kombinasie met multiveranderlike statistiese tegnieke
spesifiek hoof komponent analise (PCA) en parsiële kleinste kwadraat diskriminant analise
(PLS-D) asook gelykvormigheidstoetsing bruikbare tegnieke is om te onderskei tussen kontrole
(egte natuurlike) en vervalsde wyne ten opsigte van die byvoeging van geurmiddels.
Beskrywende sensoriese analise kan ook nuttig gebruik word, alhoewel keuring en opleiding
van paneellede tydrowend is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6594 |
| Date | 03 1900 |
| Creators | Treurnicht, Jeanne |
| Contributors | Nieuwoudt, H. H., Van Rensburg, P., University of Stellenbosch. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 69 p. : ill. |
| Rights | University of Stellenbosch |
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