Thesis (MSc)--Stellenbosch University, 2007. / ENGLISH ABSTRACT: With ever increasing pressure on wine producers to lower the financial costs involved in
winemaking to be able to compete in the market, all while maintaining a high level of wine
quality, the focus on maintaining control over all aspects of the winemaking process are
greatly emphasized.
Malolactic fermentation (MLF) is one of the important processes in red wine production.
The advantages of this process, when performed successfully, is widely known and
accepted. One way to gain control over MLF is the use of MLF starter cultures. Starter
cultures usually consist of Oenococcus oeni that has been isolated from grapes or wines
and is in most cases available in a freeze-dried form ready for direct inoculation into the
wine when MLF is desired. Starter cultures are induced into wine and usually ensure the
immediate onset as well as a fast and clean execution of the process. Starter cultures
used in South Africa are in most cases isolated from cooler viticultural regions in the
Northern hemisphere. The constitution of wines from cooler viticultural regions, differ from
those in South Africa, which has a warm climate. The most important difference is the acid
content of the wines which is lower in South African must/wines and results into a higher
pH. The three most important changes that develop in wine during MLF are a decrease in
acidity due to the conversion of malic acid to the less harsh lactic acid, enhanced flavour
and aroma of wine and an increase in the microbiological stability of wine. The decrease
in acidity is very important for wines produced for grapes grown in cool viticulture regions.
In South Africa though, the climate is warm and higher pH’s are present in the musts and
wines and the de-acidification due to MLF is not the main aim but rather the
microbiological stabilisation. One of the compounds that could be produced by lactic acid
bacteria (LAB) is biogenic amines (BA’s). These compounds can be hazardous to human
health. This thesis focussed on the performance of MLF starter cultures in high pH South
African red wines.
The first objective of the study was to stretch MLF starter cultures in high pH red wines
of South Africa. Stretching means to use less than the prescribed dosage or the re-use of
starter cultures. The difference in MLF rate, the influence of the natural occurring LAB and
the levels of biogenic amines formed during MLF were determined for the different
stretching treatments. The results showed that different rates in malic acid degradation
were experienced between the treatments, but in all cases MLF fermentation was completed. Biogenic amines were formed at various levels and the influence of the natural
occurring LAB also played a role.
The second objective of the study was the evaluation of the effect of a wine isolated
LAB (Lactobacillus) and an acetic acid bacteria (AAB), inoculated with a MLF starter
culture had on MLF at different wine pH’s. It was found that especially in the case where
the Lactobacillus was inoculated in combination with the MLF starter culture a possible
stimulatory effect was experienced with regards to malic acid degradation rate. Biogenic
amine concentration was measured at the end of MLF and it was found that no histamine
and tyramine were formed in any of the treatments, while the putrescine and cadaverine
levels were found to be at approximately similar levels for the different treatments.
The third objective was to evaluate the possible influence of commercial tannin
additions and a pectolytic enzyme on rate of MLF and phenolic composition of high pH red
wine. The commercial tannins had possible inhibitory as well as stimulatory effects on the
rate of malic acid degradation especially during the initial stages of MLF, with the highest
dosage having the significant effect. The BA results showed difference in the levels
produced due to tannin additions as well as strain differences could exist. The phenolic
content showed a decrease in colour density, total red pigments, total phenolics and
anthocyanins between AF and MLF.
The fourth objective was to evaluate inoculation time of MLF starter cultures. The
results showed that the fastest AF/MLF time was with simultaneous inoculation of the
yeast and MLF starter cultures. It was also for this treatment where no histamine or
tyramine was detected at the end of MLF compared to the other inoculation strategies
(before the end of AF and after AF).
This study generated a large amount of novel data which made a valuable contribution
with regards to MLF in high pH red wines of South Africa. / AFRIKAANSE OPSOMMING: Die druk om wyne van hoë gehalte teen lae insetkoste te lewer om deel te bly van ’n
kompeterende mark, plaas die fokus weer sterk op onder andere die beheer van alle
aspekte van die wynmaak proses.
Appelmelksuurgisting (AMG) is een van die belangrikste prosesse van rooiwyn produksie.
Die voordele van AMG, in die geval van die suksesvolle implementering daarvan is
vandag bekend en word geredelik aanvaar. Een van die metodes om beheer te verkry oor
the proses van AMG is deur die gebruik van AMG aanvangskulture. AMG
aanvangskulture bestaan uit Oenococcus oeni wat geïsoleer word vanaf druiwe of
mos/wyn en is in meeste gevalle beskikbaar in ’n gevries-droogte vorm wat direk in wyn
geïnokuleer kan word. Aanvangskulture word in wyn geïnduseer om die onverpose
aanvang van AMG te bewerkstellig asook om ’n vinnige en skoon deurvoering van die
proses te verseker. Die aanvangskulture wat in Suid-Afrika vir hierdie doeleinde gebruik
word is in meeste van die gevalle verkry uit koue wingerdbou gebiede in die Noordelike
Halfrond. Die samestelling van druiwe van koue wingerdbou gebiede en dié van
Suid-Afrikaanse warm wingerdbou gebiede verskil. Die belangrikste verskil word ervaar in
die suur inhoud, wat laer is in Suid-Afrikaanse druiwe en dus lei tot ‘n hoër pH inhoud. Die
drie mees belangrikste veranderinge wat gedurende AMG in wyn plaasvind is die
vermindering van die suur, as gevolg van die omskakeling van appelsuur na melksuur, die
verbetering van die aroma en geur van wyn en die verbeterde mikrobiologiese stabiliteit.
Die afname in suur is veral belangrik in wyne van koue wingerbou gebiede omdat die
suur-inhoud daarvan soveel hoër is. In Suid-Afrika kan hierdie verlaging in suur egter lei
tot ’n verdere verhoging in die pH wat plat wyne en uiteindelik ’n verlaging in die kwaliteit
van wyn tot gevolg kan hê. Biogene amiene (BA) is verbinding wat melksuurbakterieë
(MSB) kan vorm gedurende AMG en kan ernstige implikasies hê vir die mens se
gesondheid.
Hierdie tesis fokus op die evaluering van AMG aanvangskulture in hoë pH rooi wyne
van Suid-Afrika.
Die eerste doelwit gedurende hierdie studie was om AMG kulture te rek en die invloed
daarvan in hoë pH rooiwyn te evalueer ten opsigte van the tempo van AMG, die rol van die
natuurlike MSB te bestudeer asook om die vlak van biogene amiene te bepaal vir die
verskillende behandelings. Die resultate het aan die lig gebring dat die rek van kulture verskille in die tempo van appelsuur afbraak tot gevolg het, maar dat AMG in alle gevalle
wel suksesvol deurgevoer kon word. Die BA’e wat gevorm is, was teenwoordig in
verskillende hoeveelhede.
Die tweede doelwit was om die effekt van die gesamentlike inokulasie van ’n wyn
geisoleerde MSB (Lactobacillus) asook ’n asynsuurbakterie (ASB) met ’n kommersiële
AMG aanvangskultuur op AMG te evalueer. Hierdie eksperiment is uitgevoer by
verskillende pH’s. Daar is gevind dat veral in die kombinasie inokulasie met die
Lactobacillus, die tempo van appelsuur afbraak moontlik gestimuleer was. Geen
histamien of tiramien is tydens AMG gevorm in hierdie eksperiment gevorm nie, terwyl
putresien en kadaverien teenwoordig was teen ongeveer gelyke vlakke vir die
behandelings.
Die derde doelwit was om die moontlike invloed van kommersiële tannien toevoegings
en die toevoeging van ’n pektolitiese ensiem te evalueer ten opsigte van AMG tempo die
fenoliese samestelling van rooiwyn te bestudeer. Verskillende kommersiële tanniene het
’n moontlike sowel as inhiberende uitwerking gehad, veral gedurende die aanvanklike
stadium AMG. Die grootste verskille is waargeneem in die behandelings waar die hoogste
dosisse tannien bygevoeg is. Die BA resultate toon dat verkillende vlakke geproduseer
was en dat hierdie verskille onstaan het as gevolg van verskille in tannien dosisse sowel
as aanvangskulture. Die fenoliese inhoud het ’n afname in kleur intensiteit, totale rooi
pigmente, totale fenole en antosianiene getoon vir die periode vanaf AF tot die einde van
AMG.
Die vierde doelwit was om the tyd van inokulasie van AMG aanvangskulture te
bestudeer. Die resultate het getoon dat die vinningste tydperk van AF/AMG was
ondervind in die geval waar die gis aanvangskulture gelyktydig met die AMG
aanvangskulture geïnokuleer was. Geen histamine en tyramine het ook in hierdie
behandeling ontwikkel nie, terwyl daar wel vlakke teenwoordig was in die ander
behandelings (inokulasie net voor die einde van AF en na afloop van AF).
Tydens hierdie studie is ’n groot hoeveelheid nuwe data geskep wat ‘n groot bydrae
ten opsigte van AMG in hoë pH rooi wyne vanaf Suid-Afrika kan lewer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21913 |
| Date | 03 1900 |
| Creators | Van der Merwe, Hanneli |
| Contributors | Du Toit, M., Du Toit, W. J., 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 | 111 leaves : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0034 seconds