Nitrogen utilisation of selected non-Saccharomyces yeasts and the impact on volatile compound production

De Koker, Simone (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: During fermentation, nitrogenous compounds serve as nutrients for the yeasts, which enable their growth, functioning and maintenance of the yeasts cells. From a winemaking perspective, a certain amount of nitrogen is required for the yeasts in order to avoid sluggish or stuck fermentation. Moreover, nitrogen metabolism leads to the production of aroma compounds such as higher alcohols, fatty acids and esters which contribute positively to overall sensory characteristics of wine. Nitrogen metabolism (uptake of ammonium and amino acids) have been extensively studied in Saccharomyces cerevisiae. Nonetheless, the fairly great variances observed between strains in terms of preference for certain nitrogen sources and metabolism thereof are not so well understood. Additionally, these mechanisms nitrogen metabolism of non- Saccharomyces yeasts are even vaguer and simply assumed to be globally similar to those of S. cerevisiae. This study aimed to investigate the uptake of nitrogen compounds (ammonium and individual amino acids) by selected non-Saccharomyces yeasts (Lachancea thermotolerans IWBT Y1240, Torulaspora delbrueckii Biodiva TD291, Pichia kluyveri FrootZen, Metschnikowia pulcherrima IWBT Y1123 and Metschnikowia pulcherrima Flavia) to assess the impact of fermentation kinetics and the production of aroma compounds during sequential fermentations with S. cerevisiae under different initial YAN concentrations, with 300 mg/L, 150 mg/L and 75 mg/L, respectively). Fermentations were performed in a synthetic grape juice medium with pure and sequential fermentations. The data showed that the assimilation of nitrogen compounds were species specific. For example, L. thermotolerans preferred alpha amino nitrogen above ammonia, where the opposite hold true for T. delbrueckii. Notable differences could also be identified for the uptake of certain single amino acids. Irrespective of the initial YAN concentrations during sequential fermentations, the yeasts only assimilated about half of the initial YAN. The non-Saccharomyces yeasts did not influence fermentation performance during sequential fermentations. However, a low initial YAN (75 mg/L) had a strong influence on the fermentation kinetics and aroma compound production. The higher uptake (compare to S. cerevisiae) of specific single amino acids by non-Saccharomyces yeasts (especially L. thermotolerans), can be tentatively correlated with certain aroma compounds produced at the end of fermentation. The results also revealed that agitation could impact overall fermentation performance and aroma compound production. This study contributes to an improved understanding of how different initial nitrogen concentrations affect growth, fermentation performances and aroma compound production of wine-related yeasts under fermentative conditions. Moreover, the uptake of single amino acids by selected non-Saccharomyces yeasts had also been identified, which is a good starting point to better understand non- Saccharomyces yeasts nitrogen requirements which may be used for the optimization of nitrogen source addition, during alcoholic fermentation, when used in mixed fermentations in order to ensure a complete alcoholic fermentation. To the best of our knowledge, the uptake of single amino acids and YAN consumption by selected non-Saccharomyces yeasts under fermentation conditions tested, have never been studied before.

AFRIKAANSE OPSOMMING: Tydens wynfermentasies dien talle stikstof komponente as voedingstowwe vir wyngis wat hul groei, funksie en onderhoud bevorder. Van `n wynmaak perspektief word daar `n sekere hoeveelheid stikstof benodig deur die wyngis om te verhoed dat slepende of onvolledige fermentasies plaasvind. Verder lei stikstofmetabolisme na die produksie van aroma verbindings, soos hoër alkohole, vlugtige vetsure en esters wat positief bydra tot die sensoriese karaktereienskappe van wyn. Die stikstofmetabolisme (opneem ammonium en aminosure) is deeglik nagevors in die wyngis Saccharomyces cerevisiae, maar die klein variasies waargeneem tussen die gisras in terme van die voorkeur van sekere stikstof komponente is egter nog onduidelik. Daarbenewens is die stikstofmetabolisme nog meer onbekend in nie- Saccharomyces wyngis en word dit oor die algemeen aanvaar dat die werking van die stikstofmetabolisme dieselfde is as in S. cerevisiae. Hierdie studie het gestreef om die opneem van stikstof komponente (ammonium en aminosure) te ondersoek van uitverkiesde nie-Saccharomyes gis (Lachancea thermotolerans IWBT Y1240, Torulaspora delbrueckii Biodiva TD291, Pichia kluyveri FrootZen, Metschnikowia pulcherrima IWBT Y1123 and Metschnikowia pulcherrima Flavia) deur te bepaal wat die impak is op die groei-kinetika en op die produksie van aroma komponente gedurende gemengde kultuur fermentasies met S. cerevisae onder verskillende aanvangs assimileerbare stikstof (300 mg/L, 150 mg/L en 75 mg/L). Fermentasies is in sintetiese druiwemos uitgevoer vir beide enkel en gemengde kultuur fermentasies. Die resultate demonstreer dat die assimilasie van stikstof ras spesifiek was. Byvoorbeeld, L. thermotolerans verkies alfa amino stikstof bo ammonium waar die teenoorgestelde waar is vir T. delbrueckii. Beduidende verskille is ook waargeneem vir die opneem van sekere individuele aminosure. Die wyngis het steeds net die helfte van die assimileerbare stikstof opgeneem gedurende gemengde kultuur fermentasies ongeag die aanvangsstikstof konsentrasies. Die nie-Saccharomyces gis het nie die fermentasie kinetika beïnvloed tydens gemengde kultuur fermentasies nie. Daar was egter ook waargeneem dat `n lae assimileerbare stikstof (75 mg/L) `n negatiewe invloed op die fermentasie kinetika sowel as aroma produksie gehad het. Die hoër opname (vergelyking met S. cerevisiae) van sekere aminosure deur nie-Saccharomyces gis, kan tydelik gekoppel word aan die produksie van spesifieke aroma verbindings aan die einde van fermentasies. Die resultate het ook gewys dat die toepassing van skud `n impak het op die fermentasie kinetika sowel as die produksie van aroma komponente. Die studie dra by om beter te verstaan van hoe verskillende aanvangsstikstof die groei, fermentasie kinetika en aroma produksie beïnvloed onder fermentasie kondisies. Die opneem van sekere aminosure deur nie-Saccharomyces gis word ook beskryf, wat `n goeie beginpunt is om beter te vertaan wat die stikstof vereistes vir die geselekteerde wyngis is, wat gebruik kan word vir die optimisering van stikstofaanvullings, sodat die risiko van probleemfermentasies verlaag sal word. So ver as wat ons kennis strek is die opneem van aminosure en die gebruik van assimileerbare stikstof deur nie-Saccharomyces wyngis onder fermentasie kondisies nog nie ondersoek nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98050
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