Characterisation of wine yeasts for varietal red wine production by using chemical, sensory and metabolomic tools

Williams, Michell Teresa (2018-03)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Modern day wine making includes direct inoculation of active dried yeast (ADY), primarily Saccharomyces cerevisiae, into relatively ‘neutral’ flavoured grape must. Subsequently, wine yeast strains influence wine quality through de novo synthesis or by converting odourless aroma precursors present in red grape must into aroma active compounds, which contribute to the varietal aromas and flavours ranging from ‘strawberry’, ‘raspberry’, ‘blackcurrant’, ‘plum’, ‘caramel’, ‘herbaceous and/or vegetative’, to ‘spicy’, and even ‘peppery’. Furthermore, yeast proteins produced and secreted during alcoholic fermentation were shown to have oenological importance, since they are critical during the release of some aroma compounds e.g. volatile thiols. Thus, it is important to select yeast starter cultures with the ability to enhance and complement varietal aromas and flavours. Therefore, this master’s study was undertaken with the aim of investigating the influence of a naturally isolated wine yeast strain i.e. ARC Nvbij 6 (S. cerevisiae) on typical red wine quality by utilising chemical, sensory, proteomic and metabolomics characterisation tools. Shiraz, Merlot and Cabernet Sauvignon winemaking trials were initiated during the 2016 and 2017 vintages with the inclusion of two commercial reference strains i.e WE372 (Anchor Oenologies, South Africa) and MERIT (Chr. Hansen, Denmark). The yeast strain ARC Nvbij 6 was shown to consistently produce Shiraz, Merlot, and Cabernet Sauvignon during the 2016 and 2017 vintages, equal and in some instances better than both commercial references. It is noteworthy that all wines produced with ARC Nvbij 6 also had a negative association with undesirable volatile acidity (VA) and acetic acid, which are known to impart unpleasant off-odours, thereby masking the sought-after varietal aromas and flavours. Furthermore, descriptive sensory evaluations showed that the ARC Nvbij 6 strain, for the most part, produced Shiraz, Merlot, and Cabernet Sauvignon wines with sought-after aromas and flavours. Gas chromatography (GC) also showed the ARC Nvbij 6 strain to be a better ‘3-mercaptohexan-1-ol (3MH) to 3-mercaptohexyl acetate (3MHA) converter’, as both commercial references also failed to convert 3MH to 3MHA during one vintage in two cultivars. In terms of aroma compounds i.e. esters (associated with fruity nuances), both commercial references mostly produced Shiraz, Merlot and Cabernet Sauvignon wines with higher ester concentrations than the ARC Nvbij 6 strain. Nonetheless, ARC Nvbij 6 consistently produced less of the undesirable compounds that are associated with wine off-odours, which can influence the wine sensory quality negatively. Furthermore, sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed that all yeast strains differentially expressed proteins within given molecular weights. It can be envisaged that peptide mass fingerprinting (PMF) in conjunction with matrix-assisted laser desorption ionization with time of flight mass spectrometry (MALDI -TOF MS) will be deployed to characterise specific yeast-derived proteins that were regulated and draw conclusions with regard to how they are associated with aroma compounds. Thus, proteomic tools may be used to select promising wine yeast strains with sought-after traits in terms of wine quality. The use of multiple omics approaches is also encouraged, as proteome does affect metabolome, which in turn determine wine chemical and sensory quality. Overall, the ARC Nvbij 6 strain proved that it has a commercial role to play in the production of varietal red wines, especially Shiraz, based on chemical and sensory attributes of all red wines included in this study.

AFRIKAANSE OPSOMMING: Moderne wynmaak behels direkte inenting van ‘neutral’ gegeurde druiwemos met aftief gedroogde gis (AGG), hoofsaaklik Saccharomyces cerevisiae. Gevolglik, affekteer bovermelde gisras wyn kwaliteit deur de novo sintese of omskakeling van geurlose aroma verbindings afkomstig vanaf druiwe na vlugtige aromatiese verbindings wat bydra tot kultivar aroma and geure, onder andere, ‘aarbei’, ‘framboos’, ‘swartbessie’, ‘pruim’, ‘karamel’, ‘kruidagtig/vegetatief’, ‘speserye’, en selfs ‘pepper’. Gis-geproduseerde en uitgeskeide proteïene tydens alkoholiese fermentasie is van oenologiese belang, siende dat dit ‘n rol speel tydens vrystelling van sommige aroma verbindings byvoorbeeld vlugtige tiole. Die seleksie van gis suursel kulture met die vermoë om kultivar aromas en geure uit te lig is dus belangrik. Op grond hiervan is ‘n meesters studie onderneem met die doel om die effek van ‘n natuurlik geïsoleerde wyngis naamlik ARC Nvbij 6 (S. cerevisiae) op tipiese rooiwyn kwaliteit te ondersoek met behulp van chemiese, sensoriese, proteïen en metaboliet evaluasies. Gevolglik is Shiraz, Merlot en Cabernet Sauvignon wynmaak proewe tydens 2016 en 2017 oesjare geinisieër, met die insluiting van twee kommersiële verwyssings gisrasse naamlik WE372 (Anchor Oenologies, South Africa) en MERIT (Chr. Hansen, Denmark). Die gisras ARC Nvbij 6 het konsekwent Shiraz, Merlot en Cabernet Sauvignon wyne gelyk en soms beter in kwaliteit as beide verwyssings giste geproduseer gedurende beide oesjare (2016 en 2017). Dit is opmerklik dat die ARC Nvbij 6 gisras rooiwyne produseer het wat `n negatiewe assosiasie met ongewenste vlugtige suur (VS) sowel as asynsuur getoon het. Beide verbindings dra by tot onsmaaklike afgeure, wat op hul beurt gesogte kultivar aromas en geure oordonder. Beskrywende sensoriese evaluerings het ook getoon dat ARC Nvbij 6 Shiraz, Merlot en Cabernet Sauvignon wyne produseer het met gesogte kultivar aromas en geure. Verdermeer het gas chromatografiese (GC) analise ook gewys dat die gis ‘n doeltreffender ‘3-merkaptoheksanol (3MH) na 3-merkaptohexyl asetaat (3MHA)’ omskakkelaar is in vergelyking met beide kommersiële verwyssings giste. Laasgenoemde giste het wel Shiraz, Merlot en Cabernet Sauvignon wyne produseer met hoër ester (word geassosieer met vrugtige geure) vlakke as wat ARC Nvbij 6 geproduseer het. Die gisras ARC Nvbij 6 het nogtans konsekwent aansienlik minder ongewenste verbindings wat rooiwyn sensoriese kwaliteit negatief kan beïnvloed geproduseer. Natrium dodecyl sulfaat poli-akrielamied gel elektroforese (SDS-PAGE) het ook getoon dat alle giste proteïne met gegewe molekulere gewigte differensieël uitgedruk het. Daar word ook onderneem om spesifieke gereguleerde gis proteïene te karakteriseer met behulp van peptied massa vingermerking (PMF) en matriks-geassesteerde desorpsie ionisasie met tyd van vlug massa spektrometrie (MALDI-TOF). Daarvolgens kan gevolgtrekkings gemaak word of bovermelde proteïne enigsins ‘n assosiasie het met aroma verbindings. Dit wil blyk asof proteïn analitiese metodes ‘n rol kan speel tydens die seleksie van belowende wyngisrasse met gesogte kenmerke in terme van wynkwaliteit. Die gebruik van veelvuldige ‘omics’ benaderings word ook aanbeveel, siende dat proteïen uitdrukking metaboliet produksie en vrystelling affekteer, wat op hul beurt wyn chemiese en sensoriese kwalieit bepaal. Oor die algemeen wys die studie dat ARC Nvbij 6 ‘n kommersiële rol het om te speel vir die produksie van eiesoortige rooiwyn, veral Shiraz op grond van chemiese en sensoriese eienskappe van alle rooiwyn kultivars wat in hierdie studie ingelsuit is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103370
This item appears in the following collections: