Defining the chemical features of wine perception

Fairbairn, Samantha (2018-03)

Thesis (PhDAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: All wines evoke a product recognition, regardless of quality and cultivar, but what is the origin of this feature? The prevalence of this wine concept suggests that its formation occurs independent of the varietal, and ageing-related aromas, and is therefore potentially a function of yeast metabolism. Yeast utilise the nutrients present in grape must to produce biomass, and metabolites which ultimately signify the conversion of grape juice to wine. Consequently, the nutrient composition is highly influential on the aromatic outcomes of alcoholic fermentation. Synthetic grape must is widely used to evaluate all facets of the fermentation process but there remains much to learn. In this study, the impact of two nutrients, namely, amino acids and anaerobic factors, were evaluated with regard to their impact on yeast growth and aroma production under fermentative conditions. This work also examines the extent to which yeast de novo metabolism, both primary and secondary metabolism, contributes to the formation of the wine-like feature. In a single amino acid context, a linear relationship was apparent between the amino acid concentration and the production of their associated volatile products. This relationship was evaluated in more complex amino acid mixtures and as expected, this linear relationship was lost. Nonetheless, a significant degree of responsiveness between the amino acid and its catabolites remained. The impact of sterol (plant or yeast derived) or unsaturated fatty acid treatments, individually, as well as in combinations, were compared for their contributions to biomass formation and aroma production. Sterols had a greater impact on biomass development, as the fermentations treated with only unsaturated fatty acids displayed a poorer response. Moreover, they differently impacted aroma production. The unsaturated fatty acid lowered the production of acetate esters, medium chain fatty acids and their esters, whereas sterol supplementation generally bolstered the production of all compounds measured. This work highlights the importance of anaerobic factor management during winemaking. Although these nutrients certainly impact wine aroma, this study also sought to examine the degree to which these nutrients contribute to wine (product) recognition. Using a novel fermentation-based approach, Saccharomyces cerevisiae converted a synthetic grape must into a wine-like product. These synthetic products underwent sensory evaluations to rate the product’s resemblance to wine as well as to describe the aroma. This sensory data was used as a decision-making tool to decide upon treatments to be studied in subsequent fermentations. Ultimately, a wine-like character was created by altering the anaerobic factor composition of a synthetic grape must. The use of this synthetic grape must would allow for the more meaningful sensory characterisation of these synthetic products, in addition to providing a wine-like matrix used to evaluate the sensory implications of wine odorants.

AFRIKAANSE OPSOMMING: Alle wyne kan as 'n wynproduk herken word, ongeag die kwaliteit en kultivar, maar wat is die oorsprong van hierdie kenmerk? Die voorkoms van hierdie wynkonsep dui daarop dat die vorming daarvan onafhanklik van die variëteit en verouderingsverwante aromas is, en daarom moontlik 'n funksie van gismetabolisme is. Gis gebruik die voedingstowwe wat in druiwe mos teenwoordig is om biomassa en metaboliete te produseer, wat uiteindelik die omskakeling van druiwesap na wyn aandui. Gevolglik het die nutrient-samestelling ‘n groot invloed op die aromatiese resultaat van alkoholiese fermentasie. Sintetiese druiwe mos word algemeen gebruik om alle fasette van die fermentasieproses te evalueer, maar daar is nog baie om te leer. In hierdie studie is die impak van twee voedingstowwe, naamlik aminosure en anaërobiese faktore, op gisgroei en aroma produksie onder fermentatiewe toestande geëvalueer. Hierdie werk ondersoek ook die mate waartoe gis de novo metabolisme, beide primêre en sekondêre metabolisme, bydrae tot die vorming van die wynagtige kenmerk. In 'n enkel aminosuur konteks, was daar 'n oënskynlike lineêre verhouding tussen die aminosuurkonsentrasie en die vorming van hul verwante vlugtige produkte. Hierdie verhouding is in meer komplekse aminosuurmengsels geëvalueer en soos verwag, is hierdie lineêre verhouding verloor. Nietemin het 'n beduidende mate van die verhouding tussen die aminosuur en die verwante kataboliete behoue gebly. Die impak van sterole (plant of gis verwant) of onversadigde vetsuur, individueel, sowel as in kombinasie, is vergelyk vir hul bydraes met betrekking tot die vorming van biomassa en aroma produksie. Sterole het 'n groter impak op die vorming van biomassa gehad, aangesien die fermentasies wat slegs met die onversadigde vetsuur behandel was tot 'n swakker reaksie gelei het. Verder is die aroma produksie verskillend beïnvloed; die onversadigde vetsuur het die produksie van asetaat esters, mediumkettingvetsure en hul esters verlaag, terwyl die sterol aanvullings oor die algemeen die produksie van alle verbindings wat gemeet is bevorder het. Hierdie werk beklemtoon die belangrikheid van die bestuur van anaërobiese faktore tydens wynmaak. Alhoewel hierdie voedingstowwe beslis wynaroma beïnvloed, het hierdie studie ook probeer om die mate waartoe hierdie voedingstowwe bydrae tot wyn (produk) herkenning te ondersoek. Met behulp van 'n nuwe fermentasie-gebaseerde benadering, het Saccharomyces cerevisiae 'n sintetiese druiwe mos in 'n wynagtige produk omskep. Hierdie sintetiese produkte is sensories geëvalueer om die produkte se ooreenkoms met wyn te bepaal, asook om die aroma te beskryf. Die sensoriese data het as 'n besluitnemende instrument gedien om te besluit watter behandelings in die daaropvolgende fermentasies bestudeer moet word. Uiteindelik is 'n wynagtige karakter geskep deur die samestelling van die anaërobiese faktore van 'n sintetiese druiwe mos te verander. Die gebruik van hierdie sintetiese druiwe mos sal ‘n meer betekenisvolle sintuiglike karakterisering van hierdie sintetiese produkte moontlik maak, asook om 'n wynagtige matriks te bied wat gebruik kan word om die sensoriese implikasies van wyn aromas te evalueer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103704
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