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The assessment of fructophilic phenotypes of wine-relevant yeast
Thesis (MSc)--Stellenbosch University, 2025.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867614139721973760 |
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| access_status_str | Open Access |
| author | Africa, Jesse |
| author2 | Bauer, Florian Franz |
| author_browse | Africa, Jesse Bauer, Florian Franz |
| author_facet | Bauer, Florian Franz Africa, Jesse |
| author_sort | Africa, Jesse |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132099 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:47:17.937Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132099 The assessment of fructophilic phenotypes of wine-relevant yeast Africa, Jesse Bauer, Florian Franz Setati, Mathabatha Evodia Fairbairn, Samantha Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture & Oenology & Institute for Wine Biotechnology. Wine -- Composition Wine and wine making -- South Africa Saccharomyces cerevisiae -- Biotechnology Phenotype Saccharomyces cerevisiae -- Effect of stress on Fructose Fermented beverages UCTD Thesis (MSc)--Stellenbosch University, 2025. Africa, J. 2025. The assessment of fructophilic phenotypes of wine-relevant yeast. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/fe527473-7668-4d9b-8802-12b7b2a755b4 ENGLISH ABSTRACT: Saccharomyces cerevisiae is the most efficient yeast species for most alcoholic fermentations, including in wine and beer, and can ferment grape juice, which contains up to 300g of hexose to dryness (less than 5 g of hexose / l). Within the grape juice matrix, the total sugar consists almost exclusively of close to equimolar amounts of glucose and fructose. While both sugars are consumed concomitantly by S. cerevisiae, this yeast shows some preference for glucose, creating a discrepancy in sugar utilization as alcoholic fermentation proceeds, and an excess of fructose towards the end of the process. Data suggest that a glucose on fructose ratio (G/F) below 0.2, coupled with other factors including nutrient availability and changes in the environment (pH, oxygen levels, increasing ethanol etc.) can directly contribute to sluggish fermentation behaviour and premature fermentation arrest. To address this problem, non-Saccharomyces yeast species that naturally occur in grape juice have been investigated for their hexose preference throughout fermentation. This research hypothesized that some fructophilic yeast strains or species may be able to eliminate sugar discrepancy and reduce the risk of stuck fermentations when co-inoculated with S. cerevisiae strains. The aim of this study was to individually screen strains of wine-relevant species isolated from South African grapes and pressed grape juices, including strains from the species S. cerevisiae, Hanseniaspora vineae, Torulaspora delbrueckii, Starmerella bacillaris and Metschnikowia pulcherimma, for favourable G/F ratios in synthetic grape juice. Promising strains were further evaluated in co-inoculations using an industry-relevant sequential inoculation strategy. The data show that all non-Sacchromyces species showed strain dependent differences in the G/F ratios during fermentation with some species showing a wide phenotypic range. Interestingly, the S. cerevisiae strains that showed a better G/F ratio (i.e. more similar consumption of glucose and fructose) during fermentation were generally fermenting at a slower rate, suggesting that these strains were not so much improved in fructose utilisation, but consumed glucose slower than other strains. This includes the two S. cerevisiae strains that are currently commercialised for their more fructophilic nature. These strains also show an ability to more efficiently restart stuck fermentation, a phenotype not assessed in this project. The sequential inoculation of promising non-Saccharomyces and S. cerevisiae strains sometimes showed transgressive phenotypes, i.e. G/F ratios significantly different from the individual ratios recorded for the two inoculated strains. These data suggest that the interaction between the two species leads to modifications in glycolytic metabolic flux. Specific pairings of S. cerevisiae and S. bacillaris show improved G/F ratios throughout fermentation and will be tested in real grape must in future. Future studies will evaluate the transcriptional responses and metabolic fluxes in the best performing co-inoculations to optimize the fermentation process. AFRIKAANSE OPSOMMING: Saccharomyces cerevisiae is die mees doeltreffende gis spesie vir meeste alkoholiese fermentasies, insluitend wyn en bier, en kan druiwesap fermenteer wat tot 300g heksose bevat totdat dit droog is (minder as 5 g heksose / l). Binne die druiwesapmatriks bestaan die totale suiker inhoud byna uitsluitlik uit ekwimolêre hoeveelhede van glukose en fruktose. Alhoewel beide suikers gelyktydig deur S. cerevisiae verbruik word, toon hierdie gis 'n voorkeur vir glukose, wat 'n teenstrydigheid veroorsaak in suikerverbruik soos die alkoholiese fermentasie voortgaan, en 'n oorskot van ongebruikte fruktose teen die einde van die proses. Data dui aan dat 'n glukose-teenoor-fruktose verhouding (G/F) van minder as 0.2, tesame met ander faktore soos voedingstofbeskikbaarheid en veranderinge in die omgewing (pH, suurstofvlakke, toenemende etanol, ens.) direk kan bydra tot traag fermentasiegedrag en die voortydige staking van fermentasies. Om hierdie probleem aan te spreek, is nie-Saccharomyces gis spesies wat natuurlik in druiwesap voorkom, ondersoek vir hul heksose voorkeur tydens fermentasie. Hierdie navorsing het die hipotese gestel dat sommige fruktofiliese gisrasse of spesies in staat mag wees om ‘n suiker teenstrydigheid te verwyder en die risiko van gestaakte fermentasies te verminder wanneer dit saam met S. cerevisiae rasse geïnokuleer word. Die doel van hierdie studie was om individuele gisrasse van wyn-relevante spesies wat uit Suid-Afrikaanse druiwe en geparsde druiwesap geïsoleer is, insluitend rasse van die spesies S. cerevisiae, Hanseniaspora vineae, Torulaspora delbrueckii, Starmerella bacillaris en Metschnikowia pulcherimma, te toets vir gunstige G/F verhoudings in sintetiese druiwesap. Belowende gisrasse is hierna verder geëvalueer in co-inokulasies deur gebruik te maak van 'n bedryf-relevante gesamentlike inokulasie strategie. Die data dui aan dat alle nie-Saccharomyces spesies rasse-afhanklike verskille in die G/F verhoudings tydens fermentasie getoon het, met sommige spesies wat 'n wye fenotipiese reeks vertoon. Van besondere belang was die feit dat die S. cerevisiae rasse wat 'n beter G/F verhouding (d.w.s. meer soortgelyke verbruik van glukose en fruktose) tydens fermentasie vertoon het oor die algemeen stadiger gefermenteer het. Hierdie verskynsel dui daarop aan dat hierdie rasse nie noodwendig verbeter is in fruktoseverbruik nie, maar eintlik glukose stadiger verbruik as ander rasse. Dit sluit die twee S. cerevisiae rasse in wat tans vir hul meer fruktofiliese aard kommersieel bemark word. Hierdie rasse toon ook 'n vermoë om gestaakte fermentasies meer doeltreffend te hervat, 'n fenotipe wat nie in hierdie projek beoordeel is nie. Die gesamentlike inokulasie van belowende nie-Saccharomyces en S. cerevisiae gisrasse het soms ‘n verandering in fenotipe getoon, d.w.s. G/F verhoudings tydens ko-inokulasie het beduidend verskil met die individuele verhoudings wat vir die twee geïnokuleerde rasse opgeteken is. Hierdie data dui aan dat die interaksie tussen die twee spesies gelei het tot modifikasies in die glikolitiese metaboliese vloei van die fermentasies. Spesifieke pare van S. cerevisiae en S. bacillaris het verbeterde G/F verhoudings regdeur fermentasie vertoon en sal in druiwesap in die toekoms getoets word. Toekomstige studies sal die transkripsionele veranderinge en metaboliese vloei in die beste presterende co- inokulasies evalueer om die fermentasieproses te optimiseer. Masters 2025-05-23T12:17:38Z 2025-05-23T12:17:38Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132099 en Stellenbosch University 112 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Wine -- Composition Wine and wine making -- South Africa Saccharomyces cerevisiae -- Biotechnology Phenotype Saccharomyces cerevisiae -- Effect of stress on Fructose Fermented beverages UCTD Africa, Jesse The assessment of fructophilic phenotypes of wine-relevant yeast |
| title | The assessment of fructophilic phenotypes of wine-relevant yeast |
| title_full | The assessment of fructophilic phenotypes of wine-relevant yeast |
| title_fullStr | The assessment of fructophilic phenotypes of wine-relevant yeast |
| title_full_unstemmed | The assessment of fructophilic phenotypes of wine-relevant yeast |
| title_short | The assessment of fructophilic phenotypes of wine-relevant yeast |
| title_sort | assessment of fructophilic phenotypes of wine relevant yeast |
| topic | Wine -- Composition Wine and wine making -- South Africa Saccharomyces cerevisiae -- Biotechnology Phenotype Saccharomyces cerevisiae -- Effect of stress on Fructose Fermented beverages UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132099 |
| work_keys_str_mv | AT africajesse theassessmentoffructophilicphenotypesofwinerelevantyeast AT africajesse assessmentoffructophilicphenotypesofwinerelevantyeast |