Multispecies interactions in a simplified wine yeast consortium

Nutt, John (2018-03)

Thesis (MScAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Over the last two decades various studies have evaluated the impact of non-Saccharomyces (NS) yeasts on alcoholic fermentation of wine, the chemical imprint they leave in the wine and how this affects wine quality. These NS yeasts are either present naturally in the grape must or inoculated together with Saccharomyces cerevisiae, but little is known about how these NS interact with each other and with S. cerevisiae and how these interactions might influence the presences of other yeast during fermentation and ultimately affect the contribution of each yeast to the wine. In recent years, several strains of the species, Torulaspora delbrueckii, Pichia kluyveri, Metschnikowia pulcherrima and Lachancea thermotolerans have been commercialized. The availability of such commercial preparations allows winemakers to perform mixed-culture fermentations through different inoculation strategies. Research has evaluated co-inoculations and sequential inoculations between NS and S. cerevisiae, but grape must is a complex ecosystem with a large variety of indigenous yeasts that partake during fermentation. Understanding how various yeasts interact within such a larger matrix is challenging, but will make an essential contribution to sound decision making in wineries. This study was designed to better understand how NS yeasts perform individually and how their behaviour might differ in the presence of one or more other yeasts and what effect this might have on the final wine. Three commercial NS yeasts strains and one S. cerevisiae yeast strain were used to determine how these yeasts interact and how these interactions might alter the chemical composition of wine. Fifteen inoculations scenarios, including mono-culture, co-culture and combinations of three and ultimately a consortium containing all four yeasts were performed. Fermentations were carried out in synthetic grape juice at both 15°C and 25°C. The data showed significant variations in the cell densities of all species through-out fermentation depending on the nature of the co-inoculated species and the environmental conditions. These changes in population dynamics also had a clear impact on the concentration of and types of aromatic compounds produced. Chenin blanc wines made with the consortium of all four yeasts, S. cerevisiae and spontaneous fermentations, showed distinct chemical profiles. However, no correlation was found, regarding population dynamics or aroma profiles of the wines, between the synthetic wine and the Chenin blanc wines both derived from the consortium inoculation. This study provides the foundation for future work on understanding how multiple species (more than two yeasts) interact within fermentations and how this will affect wine quality. It also provides a better understanding of how one yeast can suppress the presence of other yeasts and how different temperatures might affect the presence of each yeasts and how this might influence the interactions between the yeasts.

AFRIKAANSE OPSOMMING: Gedurende die afgelope twee dekades was daar menigde studies gedoen om die impak van Nie-Saccharomyces (NS) giste te evalueer gedurende alkoholiese gisting van wyn, die chemiese impak wat hulle het op die wyn en hoe dit die wynkwaliteit beïnvloed. Hierdie NS giste kom of natuurlik voor op die druiwe, of word geïnokuleer tesame met Saccharomyces cerevisiae, maar daar is egter min informasie betreffende hoe hierdie NS giste in mekaar se teenwoordigheid reageer, asook in die teenwoordigheid van S. cerevisiae, en hoe hierdie interaksies die teenwoordigheid van mekaar sal beïnvloed en watter invloed dit op die wyn sal hê. In die afgelope paar jaar was daar menigde stamme van die spesies, Torulaspora delbrueckii, Pichia kluyveri, Metschnikowia pulcherrima en Lachancea thermotolerans ontwikkel vir kommersiële gebruik. Die beskikbaarheid van hierdie NS giste laat wynmakers toe om gemengde-kultuur fermentasies te doen met verskillende inokulasie strategië. Daar is egter baie navorsing beskikbaar rakende mede-inokulasie en gesaamtlike-inokulasie van NS met S. cerevisiae, maar druiwe mos is ‘n komplekse medium met ‘n groot verskeidenheid natuurlike giste teenwoordig wat ook deelneem aan die fermentasie van wyn. Dit is egter belangrik om te verstaan hoe verskeie hoeveelhede giste interaksie voer in mekaar se teenwoordigheid en kan veral moeilik wees in sulke groot matrikse, maar sal 'n baie groot bydrae lewer to wynmaak strategië. Hierdie studie is dus ontwikkel om beter te verstaan hoe NS individueel fermenteer en hoe hulle moontlik anders kan fermenteer in die teenwoordigheid van meer giste en watter effek dit op die finale wyn mag hê. Drie kommersieel beskikbare giste en een S. cerevisiae gis was gebruik in hierdie studie om die interaksies te bepaal tussen die giste en te bepaal watter impak die interaksies moontlik kan hê op die chemiese samestelling van die finale wyn. Vyftien inokulasie strategië, insluitende enkel- en dubbel inokulasies, kombinasies van drie asook al vier tesame, was bestudeer. Die fermentasies was gedoen by beide 15ºC en 25ºC. Die data het ‘n groot verskil in sel-konsentrasies van al die giste gewys asook in al die fermentasies en was afhanklik van die kombinasie gebruik en die omgewingsomstandighede teenwoordig. Die verskille in sel konsentrasies het ook tot duidelike verskille gelei in die konsentrasies van aromatiese komponente wat geproduseer was. Chenin blanc wyne was gemaak met die gebruik van die kombinasie wat al vier giste ingesluit het, S. cerevisiae en spontane gisting. Die wyne het almal verskillende chemiese samestellings tot gevolg gehad. Daar was egter geen verhouding gevind tussen die resultate van die populasie samestellings en chemiese profile van die sintetiese wyn medium en die regte wyn medium nie. Die studie verskaf dus die basis vir toekomstige werk rakende die kennis van hoe verskeie giste (meer as twee) reageer in die teenwoordigheid van mekaar in fermentasies en hoe dit die wynkwaliteit sal beïnvloed. Dit verskaf ook informasie om beter te verstaan hoe die teenwoordigheid van een gis die teenwoordigheid van ander giste kan beïnvloed en hoe verskillende temperature die interaksies moontlik kan beïnvloed tuseen die giste.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103538
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