Thesis (PhD)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Wine is the result of a variety of biochemical reactions and microbial interactions which contribute
to the organoleptic properties of wine. Wine aroma and flavour encapsulate the sensory
experience of wine and could ultimately determine wine quality and consequently influence
consumer acceptance and preference of a product. A thorough understanding of potential factors
influencing wine aroma and flavour is therefore needed in order to exploit such factors. The aim of
this study was to evaluate the influence of commercial malolactic fermentation (MLF) starter
cultures on wine composition, aroma and flavour and the potential impact on consumer preference
of experimentally produced red wines.
An analytical platform was established to capture the compositional changes induced by
different MLF bacteria in experimentally produced red wines. A fast gas chromatography flame
ionisation detection (GC-FID) method was developed to determine 39 wine volatile compounds in
less than 15 minutes per sample. A 3-fold reduction in analysis time was achieved in comparison
to a conventional GC-FID method (40 minutes). Analytes quantified comprise a large boiling point
and polarity range which illustrates the robustness of the method. A method was also developed
for the direct quantification of carbonyl compounds including diacetyl, acetoin, 2,3-pentanedione
and certain aldehydes using headspace solid phase microextraction coupled to gas
chromatography mass spectrometry (HS-SPME GC-MS). Both analytical methods showed
satisfactory linearity, repeatability and limits of quantification.
The contribution of four commercial Oenococcus oeni malolactic fermentation (MLF) starter
cultures to the volatile composition, organic acid content and infrared spectral properties of
experimentally produced South African red wines, showed significant strain-specific variations in
the organic acid profiles, especially for the production of citric acid and lactic acid during MLF.
Subsequently, concentrations of compounds related to citric acid metabolism, namely ethyl lactate,
acetic acid, diacetyl and acetoin, were influenced accordingly. Bacterial metabolic activity
increased the concentration of higher alcohols, fatty acids and esters, with a larger increase
observed in ethyl esters compared to acetate esters. A strain-specific tendency to reduce total
aldehyde concentrations was found at the completion of MLF, however, further investigation is
needed to clarify this observation. Infrared spectral fingerprints were used to characterise the
different bacteria and in addition, the prediction of MLF related compounds, diacetyl, acetoin and
2,3-pentanedione, from mid-infrared spectra was explored by partial least squares (PLS) models.
Quantitative descriptive analysis (QDA) results depicted significant differences between wines
fermented with different starter cultures, in terms of sensory attributes including buttery, fruity, nutty
and yoghurt/buttermilk aroma as well as smoothness and mouth-feel attributes. Consumer
preference testing results indicate that sensory differences imparted by different MLF bacteria
could influence consumer-liking. Preference mapping revealed interesting relationships between
sensory attributes and consumer-liking, that can be used for preliminary interpretative purposes.
In conclusion, this study illustrated the potential impact of bacterial strains on wine aroma and
flavour, resulting sensory properties and consumer preference through an integrative approach
combining compositional, spectral, sensory and consumer data. The results presented in this study
are of significance to the wine industry since they illustrate and reiterate the potential of different
MLF starter cultures as an additional tool to contribute to wine aroma and flavour, and potentially
influencing consumer preference and product liking. / AFRIKAANSE OPSOMMING: Wyn is die resultaat van ‘n verskeidenheid biochemiese reaksies en mikrobiologiese interaksies
wat tot die organoleptiese eienskappe van die finale produk bydra. Wynaroma en geur vang die
sensoriese ervaring van wyn vas en dit kan dus wynkwaliteit bepaal en gevolglik
verbruikersaanvaarding asook voorkeur van ‘n produk beïnvloed. Die potensiële faktore wat
wynaroma en geur kan beïnvloed moet dus vir hierdie rede deeglik bestudeer word ten einde sulke
faktore ten volle te benut. Die doel van hierdie studie was om die invloed van kommersiële
applemelksuurgisting (AMG) aanvangskulture op wynsamestelling, die gevolglike aroma en geur
eienskappe en die potensiële impak op verbruikersvoorkeure te ondersoek.
‘n Analitiese platform is gevestig om die veranderings in samestelling veroorsaak deur
verskillende AMG bakterieë in eksperimenteel bereide rooi wyne vas te vang. ‘n Vinnige gas
chromatografiese vlam geïoniseerde deteksie (GC-FID) metode is ontwikkel vir die meting van 39
vlugtige komponente in minder as 15 minute per wynmonster. In vergelyking met ‘n konvensionele
GC-FID metode (40 minute) is ’n 3-voudige vermindering in analise tyd behaal. Gekwantifiseerde
komponente bestaan uit ‘n wye kookpunt- en polariteitsreeks wat die robustheid van die metode
illustreer. ‘n Metode vir die direkte kwantifisering van karboniel komponente, insluitende diasetiel,
asetoïen, 2,3-pentanedioon en verskeie aldehiede is ontwikkel met die gebruik van dampfase
soliede fase mikroekstraksie gekoppel aan gas chromatografie massa spektrometrie (HS-SPME
GC-MS). Albei analitiese metodes besit voldoende lineariteit, herhaalbaarheid en lae deteksie
limiete.
Die bydrae van vier kommersiële Oenococcus oeni AMG aanvangskulture tot die vlugtige
samestelling, organiese suurinhoud en infrarooi spektrale eienskappe van Suid-Afrikaanse rooiwyn
het beduidende ras spesifieke variasies in die organiese suur profiele, spesifiek vir die produksie
van sitroensuur en melksuur gedurende AMG, vertoon. Gevolglik is die konsentrasies van
komponente verwant aan sitroensuur metabolisme, naamlik etiellaktaat, asynsuur, diasetiel en
asetoïen, dien ooreenkomstig beïnvloed. Bakteriese metaboliese aktiwiteit het ‘n toename tot
gevolg gehad in die hoër alkohole, vetsure en algemene ester konsentrasies met ‘n groter
toename in etiel-esters in vergelyking met asetaat-esters. ‘n Ras-spesifieke tendens om die totale
aldehiedkonsentrasie te verminder na afloop van AMG, is waargeneem alhoewel verdere
ondersoek in hierdie area nodig is. Infrarooi spektrale patrone is gebruik om verskillende bakterieë
te karakteriseer asook om die voorspelling van spesifieke AMG verwante komponente soos
diasetiel, asetoïen en 2,3-pentanedioon met die gebruik van mid-infrarooi spektrala parsiële
kleinste kwadraat verskille (PLS) modelle te ondersoek.
Kwantitiewe beskrywende sensoriese analise illustreer beduidende verskille tussen wyne wat
gefermenteer is met verskillende aanvangskulture in terme van geure soos botteragtigheid,
vrugtigheid, neutagtigheid, joghurt/karringmelkgeur, asook gladheid en mondgevoel eienskappe.
Verbruikersvoorkeur resultate illustreer die groot invloed wat sensoriese verskille veroorsaak deur
verskillende AMG bakterieë op verbruikersvoorkeure kan hê. Voorkeur kartering het interessante
verhoudings tussen sensoriese eienskappe en verbruikersvoorkeure uitgelig.
Hierdie studie illustreer die impak van bakteriese rasse op wynaroma en geur en
verbruikersvoorkeure deur ‘n geïntegreerde benadering waarin samestellende, spektrale,
sensoriese en verbruikersdata gekombineer is. Die resultate van hierdie studie is van belang vir
die wynindustrie deurdat dit die potensiële bydrae van verskillende AMG kulture tot wynaroma en
geur asook die potensiaal om verbruikersvoorkeure te beïnvloed, illustreer en beklemtoon.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6587 |
| Date | 03 1900 |
| Creators | Malherbe, Sulette |
| Contributors | Nieuwoudt, H. H., Du Toit, M., Tredoux, A. J. G., Naes, T., 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 | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 121 p. : ill. |
| Rights | University of Stellenbosch |
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