Evaluating the vitamin requirements of wine-related yeasts and the resultant impact on population dynamics and fermentation kinetics

Julies, Jerobiam Marvin (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Within the vineyard environment, grape berries serve as a habitat to various microorganisms including bacteria, filamentous fungi and yeasts, of which some play distinct roles in winemaking. Studies on yeast species other than Saccharomyces cerevisiae, commonly referred to as non-Saccharomyces (NS) yeasts in oenology, have evaluated the ability of these yeast to modulate the sensory profile of wine. In the early stages of spontaneous fermentation when the ethanol concentrations are low, the NS yeast population increases, but is progressively replaced by S. cerevisiae, which is better adapted to the environmental conditions associated with fermenting grape juice. The overall sensory profile of wine is in part a result of the metabolite production of yeasts, and the extent of the contribution of each species will depend on the total metabolic activity of each species. Metabolic activity is directly related to the availability of nutrients such as carbon, nitrogen, vitamins and trace elements. These nutrients are indeed converted to biomass and other metabolites, many of which are aroma and flavour active by-products. Only limited information regarding the nutrient requirements of wine-related yeasts other than S. cerevisiae has been published. Several studies have explored the carbon and nitrogen requirements of some NS species, but the vitamin requirements of many biotechnologically relevant species remains to be determined. Vitamins are organic compounds, mostly of a complex chemical nature, and serve as cofactors in metabolic reactions. Vitamins occur in small quantities in grapes and grape juice, but some data suggest that they may in some cases be limiting for yeast growth in this environment, affecting metabolism and ultimately impact the final wine. This knowledge gap motivates the current study, which focuses on the growth and fermentation kinetics of different NS yeasts when presented with varying concentrations of the relevant vitamins: biotin, pantothenate, inositol, thiamine and pyridoxine. In a first section, a high-throughput microtiter plate assay was optimised to allow for the rapid screening of the vitamin requirements of NS yeasts. The results of this assay showed differences in the vitamin requirements amongst the different yeasts. The statistically most significant vitamin-dependent yeast phenotypes from the screen were selected for further investigation. These included the dependence of Viniflora® P. kluyveri Frootzen ™ on biotin and thiamine and of Viniflora ® L. thermotolerans Concerto ™ on inositol. The data obtained from this study provide a better understanding of the vitamin requirements of NS yeasts and how these requirements can potentially enhance the growth performance of NS yeasts. The data suggest that targeted nutrient additions may lead to a better modulation of the overall sensory profile of wine.

AFRIKAANSE OPSOMMING: In ‘n wingerdomgewing dien druiwebessies as 'n habitat vir verskeie mikroörganismes, insluitend bakterieë, filamentiese swamme en giste, wat almal verskillende rolle speel in wynmaak. Studies oor gis spesies behalwe Saccharomyces cerevisiae, wat algemeen bekend staan as nie-Saccharomyces (NS) giste in wynkunde, het die vermoë van hierdie giste geëvalueer om die sensoriese profiel van wyn te moduleer. In die vroeë stadiums van spontane fermentasie wanneer die etanolkonsentrasies laag is, is daar ‘n toename in die NS-gispopulasie wat geleidelik vervang deur S. cerevisiae, wat beter aangepas is by die omgewingstoestande wat geassosieer word met die fermentasie van druiwesap. Aangesien die algemene sensoriese profiel van wyn gedeeltelik afhanklik is van die metabolietproduksie deur giste, sal die omvang van die bydrae van elke betrokke spesie afhang van die totale metaboliese aktiwiteit van elke spesie. Die metaboliese aktiwiteit is gedeeltelik afhanglik van die beskikbaarheid van voedingstowwe soos koolstof, stikstof, vitamiene en spoorelemente. Hierdie voedingstowwe word omskep in biomassa en neweprodukte deur middel van metaboliese aktiwiteit. Beperkte inligting aangaande die voedingsvereistes van NS giste is gepubliseer. Terwyl verskeie studies die koolstof- en stikstofvereistes van sommige NS spesies ondersoek het, is die vitamien-behoeftes van hierdie giste onbepaald. Vitamiene is organiese verbindings wat van 'n komplekse chemiese aard is en hoofsaaklik dien as kofaktore in metaboliese reaksies. Vitamiene kom in klein hoeveelhede in druiwe voor en kan moontlik vir gisgroei beperk word, wat metabolisme beïnvloed en uiteindelik die finale wyn beïnvloed. Dus, het hierdie studie fundamenteel gefokus op die groei- en fermentasie kinetika van verskillende NS-giste wanneer dit aangebied word met wisselende konsentrasies van die mees relevante vitamiene vir giste: biotien, pantotenaat, inositol, tiamien en piridoksien. In 'n eerste afdeling is 'n hoë-deurlaat mikrotiter plaat toets geoptimaliseer om voorsiening te maak vir die vinnige bepaling van die vitamienbehoeftes van NS-giste. Die resultate van hierdie toets het verskille getoon in die vitamienbehoeftes onder die verskillende giste. Sommige van die statisties mees betekenisvolle vitamien-afhanklike gis fenotipes van die toets was gekies vir verdere ondersoek: die afhanklikheid van P. kluyveri Frootzen van biotien en tiamien sowel as dié van L. thermotolerans Concerto aangaande inositol. Die data verkry uit hierdie studie het 'n beter begrip aangaande die vitamienbehoeftes van NS-giste aangebied en hoe hierdie vereistes die groeiprestasie van NS-gis kan verbeter. Die data dui daarop dat geteikende voedingtoevoegings kan lei tot 'n beter modulasie van die algehele sensoriese profiel van wyn.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105764
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