Thesis (MSc)--Stellenbosch University, 2015. / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/98050 |
| Date | 12 1900 |
| Creators | De Koker, Simone |
| Contributors | Divol, Benoit, Bauer, Florian, Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 85 pages : illustrations |
| Rights | Stellenbosch University |
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