Thesis (MSc Food Sc (Food Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This study focussed on the sensory effects of the main volatile compounds produced by
Brettanomyces yeast causing spoilage in wine. This research firstly aimed to determine the
detection thresholds of eight Brett-related spoilage compounds in wine. The second aim was to
determine the sensory effect of the four most important Brett-related compounds when present
individually in wine. The third aim was to determine the sensory effects of these four compounds
when present in wine in a range of combinations, and to further investigate their effect on
consumer liking. Finally, this project aimed to investigate the incidence of these compounds in a
small range of South African wines.
The sensory detection thresholds of 4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol, 4-
vinylphenol, 4-vinylguaiacol, isovaleric acid, isobutyric acid and acetic acid were determined.
Apart from 4-ethylcatechol, these values generally agreed well with recent literature where
values determined in wine are available. However, the discrepancies highlighted the importance
of the effect of the medium (wine) when determining sensory detection thresholds. The use of
the median as alternative calculation method was also investigated, and it was found that this
method gives more insightful results than the standard American Society of Testing Materials
(ASTM E679-04) method.
Four compounds, namely 4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol and isovaleric acid
were profiled individually in wine using a trained sensory panel. It was found that all four
compounds caused a suppression of the natural berry-like character in the wine, which induced
a sick-sweet character. 4-ethylphenol contributed Elastoplast™ and leather aromas in the wine,
both of which are commonly associated with Brettanomyces taint. 4-ethylguaiacol added a
medicinal aroma to the wine, and 4-ethylcatechol and isovaleric acid were responsible for
savoury and pungent aromas, respectively.
4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol and isovaleric acid were also profiled in
combination according to the central composite design. Several univariate and multivariate
methods were applied to the dataset obtained. PARAFAC, a multiway method not widely
utilized regarding sensory data, was applied to the data, the results of which were
complementary to those obtained during univariate and multivariate analyses. It was found that
there is a great deal of interaction between the four compounds profiled in terms of sensory
effects. The most notable was the Elastoplast™ attribute, the intensity of which was affected by
all four compounds. The pungent attribute was also affected by the 4-ethylphenol concentration. Consumer analysis revealed that some of the samples spiked with Brettanomyces-spoilage
compounds were preferred to the unspiked (control sample). However, no further relationship
could be found between consumer liking and either chemical composition or sensory profile. It is
therefore speculated that consumer liking of Brettanomyces infected wine is driven by more
complex sensory or socio-demographic factors.
Finally, the concentration of 4-ethylphenol, 4-ethylguaiacol, 4-ethylcatechol, 4-vinylphenol, 4-
vinylguaiacol, isovaleric acid, isobutyric acid and acetic acid was determined in a small set of
South African wines, selected to contain a high proportion of wines spoiled by Brettanomyces.
Significant correlations were found between 4-ethylphenol and 4-ethylguaiacol, as well as 4-
ethylphenol and isovaleric acid. However, no correlation could be found between 4-ethylphenol
and 4-ethylcatechol. It is speculated that this lack of relationship is due to the different precursor
profiles present in the analysed wines. This study paved the way for future investigations on the
sensory effects of Brettanomyces spoilage in Pinotage red wine. / AFRIKAANSE OPSOMMING: Hierdie studie het gefokus op die sensoriese invloed van die belangrikste vlugtige komponente
wat deur die Brettanomyces gis geproduseer word en bederf veroorsaak in wyn. Eerstens is
gefokus op die bepaling van die deteksiedrempelwaardes van agt Brett-verwante bederwende
komponente. Die tweede doelwit was om die sensoriese invloed van vier van die mees
belangrike Brett-komponente te bepaal wanneer hulle individueel in wyn voorkom. Die derde
doelwit was om die sensoriese invloed van hierdie vier komponente te bepaal wanneer hulle in
verskillende kombinasies in wyn voorkom, asook die effek daarvan op verbruikervoorkeur.
Laastens is gepoog om die voorkoms van hierdie komponente in ‘n klein seleksie van Suid-
Afrikaanse wyne te bepaal.
Die sensoriese deteksiedrempelwaardes vir 4-etielfenol, 4-etielguaiacol, 4-etielcatechol, 4-
vinielfenol, 4-vinielguaiacol, isovaleraatsuur, isobuteraatsuur en asynsuur is bepaal. Met die
uitsondering van 4-etielcatechol het die waardes oor die algemeen goed ooreengestem met
waardes wat onlangs in die wetenskaplike literatuur gepubliseer is. Die uitsonderings het egter
die belangrikheid van die medium (wyn) gedurende die bepaling van sensoriese
deteksiedrempelwaardes uitgelig. Die gebruik van die mediaan as ‘n alternatiewe
berekeningsmetode is ook ondersoek en daar is gevind dat hierdie metode meer insiggewende
resultate lewer as die standaard American Society of Testing Materials (ASTM E679-04)
metode.
Vier komponente naamlik 4-etielfenol, 4-etielguaiacol, 4-etielcatechol en isovaleraatsuur is
individueel in wyn geprofileer met behulp van ‘n opgeleide sensoriese paneel. Daar is gevind
dat al vier die komponente die natuurlike bessiekarakter in die wyn onderdruk terwyl dit
aanleiding gee tot ‘n onnatuurlike soet karakter. 4-etielfenol is gekenmerk aan Elastoplast™ en
leeragtige aromas in die wyn en beide van hulle word algemeen geassosieer met
Brettanomyces bederf. 4-etielguaiacol het ‘n medisinale aroma tot die wyn toegevoeg en 4-
etielcatechol en isovaleraatsuur het respektiewelik souterige (“savoury”) en sterk (“pungent”)
aromas tot gevolg gehad.
4-etielfenol, 4-etielguaiacol, 4-etielcatechol en isovaleraatsuur is ook in verskeie kombinasies
geprofileer volgens die sentrale saamgestelde ontwerp (“central composite design”). Verskeie
enkelveranderlike en meerveranderlike statistiese analisemetodes is ook op die datastel
uitgevoer. PARAFAC, ‘n meerrigtingsmetode wat nie normaalweg vir sensoriese analise data
gebruik word nie, is ook uitgevoer op die data en die resultate was komplimentêr tot die van die
enkelveranderlike en meerveranderlike analisemetodes. Daar is gevind dat, met betrekking tot sensoriese effekte, daar noemenswaardige interaksie tussen die vier komponente plaasvind.
Die mees opmerklike hiervan was die Elastoplast™ aroma, waarvan die intensiteit deur al vier
die ander komponente geaffekteer is. Verder is die sterk (“pungent”) aroma beïnvloed deur die
4-etielfenol konsentrasie.
Verbruikersvoorkeur-analise het aangedui dat sommige van die monsters waarby
Brettanomyces bederwende komponente gevoeg is, verkies word bó die kontrole-wyn. Daar
kon egter geen verdere verband gevind word tussen die verbruiker se voorkeur en, nog die
chemise komposisie of sensoriese profiele, van die wyn nie. Daar kan dus gespekuleer word
dat verbruiker voorkeur van Brettanomyces bederfde wyn gedryf word deur meer komplekse en
sosio-demografiese faktore.
Laastens is die konsentrasies van 4-etielfenol, 4-etielguaiacol, 4-etielcatechol, 4-vinielfenol, 4-
vinielguaiacol, isovaleraatsuur, isobuteraatsuur en asynsuur in ‘n seleksie van Suid-Afrikaanse
wyne bepaal. Dié wyne is spesifiek so gekies sodat ‘n aansienlike aantal van hulle met
Brettanomyces bederf was. Betekenisvolle korrelasies is gevind tussen 4-etielfenol and 4-
etielguaiacol, sowel as 4-etielfenol en isovaleraatsuur. Daar is egter geen korrelasie tussen 4-
etielfenol and 4-etielcatechol gevind nie. Daar word vermoed dat hierdie gebrek aan korrelasie
te wyte is aan die voorloperkomponent profiele teenwoordig in die wyne. Hierdie studie het die
weg gebaan vir verdere ondersoeke na die sensoriese effekte van Brettanomyces bederf in
Pinotage rooi wyn.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4141 |
| Date | 03 1900 |
| Creators | Botha, Janita J |
| Contributors | Muller, M., Tredoux, A. G. J., De Villiers, A. J., Du Toit, W. J., University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 150 p. : ill. |
| Rights | University of Stellenbosch |
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