Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT:
The present study was initiated by the wine industry of South Africa to overcome the
lack of available information on the flavor and aroma of South African wines. The
aim was to develop new analytical methods and improve existing ones for the analysis
of volatile compounds in the South African wines. Initially a new analytical method
based on stir bar sorptive extraction (SBSE) in the headspace mode for the analysis of
37 pre-selected volatile compounds was developed and validated. Consequently, the
method was improved by making important modifications and increasing the number
of compounds analyzed to 39. This method was successfully applied to a large
number of Pinotage wines of vintages 2005 and 2006. The quantitative data of these
wines were subjected to chemometric analysis in order to investigate possible co-
/variances. A clear distinction was observed between the two vintages, where the
2005 wines were more characterized by wood-related compounds and the 2006 wines
by the fermentation compounds. The developed method was further applied to other
cultivars of vintage 2005, including two white (Sauvignon Blanc and Chardonnay)
and three red (Shiraz, Cabernet Sauvignon and Merlot) cultivars. In a similar fashion,
the quantitative data of the six cultivars of vintage of 2005 were analysed by
chemometric methods. Significant differences were observed between the two white
cultivars and among the four red cultivars. It was shown that among these cultivars,
the major role-players were the wood and fermentation related volatiles. A striking
observation was the confirmation of the unique character of the Pinotage wines
compared to the other red cultivars, mainly influenced by the high level of isoamyl
acetate and low level of isoamyl alcohol, the former being categorized as a varietal
compound for Pinotage expressed by a fruity (banana) odor.
In addition, advanced chromatographic technology in the form of comprehensive twodimensional
gas chromatography (GC × GC) coupled to time-of-flight mass
spectrometry (TOFMS) was investigated for the detailed analysis of volatile
compounds in young South African wines. This work focused primarily on Pinotage
wines. In the first instance, solid phase micro extraction (SPME) in the headspace
mode in combination with GC × GC-TOFMS was used. Due to the high resolution
and large peak capacity of GC × GC, more than 200 compounds previously reported
as wine components were identified. These compounds were dominated by the highly volatile and less polar compounds, mainly due to the characteristics of SPME. In an
attempt to further extend these results, another selective extraction method, solid
phase extraction (SPE) was used in combination with GC × GC-TOFMS analysis.
Using this technique, more than 275 compounds, most of them unidentified using the
previous method, were detected. These groups of compounds include volatile phenols,
lactones as well as mostly aromatic esters and norisoprenoids, which can potentially
influence the aroma and flavor of wine. The techniques developed as part of this study
have extended our knowledge of the volatile composition of South African wines. / AFRIKAANSE OPSOMMING:
Hierdie studie is geïnisieer deur die wyn industrie van Suid-Afrika om die tekort aan
beskikbare inligting aangaande wyn aroma van Suid-Afrikaanse wyne te oorkom. Die
doel was om nuwe analitiese metodes te ontwikkel en die huidige metodes te verbeter
vir die analise van vlugtige verbindings in Suid-Afrikaanse wyne. Oorspronklik is ʼn
nuwe analitiese metode ontwikkel en gevalideer gebaseer is op ‘stir bar sorptive
extraction’ (SBSE) in die gas fase vir die analise van 37 vooraf geselekteerde vlugtige
verbindings. Die metode is verbeter deur belangrike modifikasies aan te bring en die
hoeveelheid verbindings wat analiseer word te vermeerder na 39. Hierdie metode is
suksesvol aangewend op ʼn groot hoeveelheid Pinotage wyne van oesjare 2005 en
2006. Die kwantitatiewe data van hierdie wyne is onderwerp aan verskillende
chemometriese analises om moontlike ko-/variasies te ondersoek. ʼn Duidelike
onderskeid is opgemerk tussen die twee oesjare, waar die 2005 wyne gekarakteriseer
is deur hout-verwante verbindings en die 2006 wyne weer meer deur fermentasie
verbindings. Die verbeterde metode is verder aangewend vir analiese van ander
kultivars van oesjare 2005, wat twee wit (Sauvignon Blanc en Chardonnay) en drie
rooies (Shiraz, Cabernet Sauvignon en Merlot) ingesluit het. Die kwantitatiewe data
van die ses kultivars van oesjaar 2005 is op ʼn soortgelyke wyse geanaliseer deur
verskillende chemometriese metodes te gebruik. Beduidende verskille is opgemerk
tussen die twee wit kultivars en tussen die vier rooi kultivars. Die hoof rolspelers
tussen die ses kultivars was weereens die verbindings wat ʼn hout en fermentasie aard
het. Die unieke karakter van die Pinotage wyne in vergelyking met die ander rooi
kultivars was opvallend. Hierdie wyn word gekarakteriseer deur hoë vlakke van
isoamiel asetaat en lae vlakke van isoamiel alkohol, waar eersgenoemde gekatogiseer
word as ʼn verbinding wat ʼn vrugte (piesang) geur in Pinotage uitdruk.
Verder is gevorderde chromatografiese tegnologie in die vorm van ‘comprehensive
two-dimentional gas chromatography’ (GC x GC) gekoppel met ‘time-of-flight mass
spectroscopy’ (TOFMS) ondersoek vir die analiese van vlugtige verbindings in jong
Suid-Afrikaanse wyne. Hierdie werk het hoofsaaklik op Pinotage wyne gefokus.
Eerstens is ‘solid phase micro extraction’ (SPME) in die gas fase gekombineer met
GC x GC-TOFMS. As gevolg van die hoë resolusie en groot piek kapasiteit van GC x
GC is meer as 200 verbindings wat voorheen gerapporteer is as wyn komponente geïdentifiseer. Hierdie verbindings is gedomineer deur hoë vlugtige polêre
verbindings, hoofsaaklik as gevolg van die karaktersitieke van SPME..In ʼn poging om
die metode verder te verbeter is ʼn selektiewe ekstraksie metode naamlik ‘solid phase
extraction’ (SPE) in kombinasie met GC x GC-TOFMS gebruik. Met hierdie tegniek
is meer as 275 verbindings geïdentifiseer, waarvan die meeste nie met die vorige
metode waargeneem is nie. Hierdie verbindings sluit vlugtige fenole, laktone en
meestal aromatiese esters en norisoprenoïdes in, wat moontlik die reuk en smaak van
wyn kan beïnvloed. Die metodes ontwikkel gedurende die studie het nuwe informasie
verskaf aangaande die vlugtige komponente teenwoordig in Suid Afrikaanse wyne.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1129 |
| Date | 12 1900 |
| Creators | Weldegergis, Berhane Tekle |
| Contributors | Crouch, A. M., De Villiers, A., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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