Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The quality of wine is influenced and determined by various factors, one of which includes the
process of malolactic fermentation (MLF). MLF plays an integral role in the flavour and sensory
profile of most red wines as well as some white wines like Chardonnay. This process is conducted
by lactic acid bacteria (LAB), specifically of the genera Oenococcus, Lactobacillus, Pediococcus
and Leuconostoc. Of these, Oenococcus oeni is best adapted to survive in the harsh wine
environment.
MLF is defined as the conversion of L-malic acid to L-lactic acid and carbon dioxide. The
conversion of the dicarboxylic malic acid to the monocarboxylic lactic acid results in a decrease in
acidity and an increase in pH, to give a softer mouthfeel and more favourable flavour profile. A
further reason for conducting MLF in wine includes the improvement of microbial stability due to
the removal of malic acid as a possible substrate for microorganisms. Recently, research focus has
shifted to the ability of MLF and LAB to alter the aroma profile of wine via the production and/or
modification of certain aroma compounds.
In order for wine LAB to conduct MLF, they need to be able to survive the harsh and
challenging wine environment. Conditions in South African wines are particularly challenging due
to the long, hot ripening seasons resulting in high sugar concentrations which give high ethanol
concentrations. Some LAB also struggle to adapt to an environment with high pH and low malic
acid concentrations. These factors, combined with the use of sulphur dioxide, cause LAB to
struggle in conducting and completing successful MLF. Many of the commercial starter cultures
that are currently available contain LAB that have not been isolated from South African wine and
are therefore not optimal for use under these challenging wine conditions. Oenococcus oeni is also
the single LAB culture present in all commercially available starter cultures.
The overriding goal of this study was to create a MLF starter culture containing a mixture of
LAB cultures, namely O. oeni and Lactobacillus plantarum, which can successfully convert malic
acid to lactic acid, ensure microbial stability, but also make a positive contribution to the wine
aroma profile. Lactobacillus plantarum has previously been considered for possible use in a
commercial starter culture. The LAB isolates used in this study were selected from the Institute for
Wine Biotechnology culture collection as well as isolated from spontaneous MLF.
The first objective was to characterise these LAB strains for important traits and for possible
use as a MLF starter culture. A total of 23 strains were identified as O. oeni and 19 strains as
Lb. plantarum. The identified strains were screened in a synthetic wine medium for their ability to
convert malic acid to lactic acid. Based on the LAB strain performance in the synthetic wine
medium, seven strains of both O. oeni and Lb. plantarum were selected. These 14 strains were
screened for the presence of genes encoding for enzymes responsible for biogenic amine
production and were found to contain none of the genes associated with the formation of
histamine, tyramine or putrescine. The LAB strains were genetically screened for enzymes associated with aroma modification by LAB during MLF. The enzymes of interest that were
screened for included β-glucosidase, esterase, protease and phenolic acid decarboxylase (PAD).
The Lb. plantarum strains were found to possess more diverse enzymatic profiles related to aroma
than O. oeni. The biggest differences were observed for the presence of β-glucosidase and PAD.
The second objective was to perform small-scale fermentations with the individual LAB
isolates. The individual isolates were evaluated in Pinotage and based on these results; three
strains of each O. oeni and Lb. plantarum were selected for evaluation in mixed culture
fermentations. The mixed cultures were evaluated in Pinotage, Shiraz and Cabernet Sauvignon in
the 2008 vintage. As a third objective, the wines were also analytically and sensorially evaluated to
investigate the changes in the aroma profile that could be attributed to the presence of the mixed
LAB isolates. Based on the fermentation data as well as data pertaining to the aroma modification,
three mixed cultures were selected for evaluation in the 2009 vintage in Pinotage, Cabernet
Sauvignon and Chardonnay. The mixed cultures were able to successfully complete MLF in
fermentation periods comparable to that of a commercial culture used as control. The different LAB
cultures had distinct and diverse effects on the wine aroma profile. The O. oeni strain played a
larger role in the ester concentration present after MLF, while the Lb. plantarum strain had a larger
effect on the higher alcohol and volatile fatty acid concentration upon completion of MLF.
The results generated by this novel study clearly indicate the potential of a mixed LAB starter
culture for conducting MLF. The mixed cultures successfully completed MLF and made a positive
contribution to the wine aroma profile. / AFRIKAANSE OPSOMMING: Die kwaliteit van wyn word beïnvloed en bepaal deur verskeie faktore en wynbereidings prosesse,
wat die proses van appelmelksuurgisting (AMG) insluit. AMG speel ’n integrale rol in die
sensoriese profiel van meeste rooiwyne, sowel as sommige witwyne soos Chardonnay.
AMG word gedefinieër as die omskakeling van L-appelsuur na L-melksuur en koolstofdioksied.
Hierdie omskakeling kan toegeskryf word aan die teenwoordigheid van melksuurbakterieë (MSB),
spesifiek spesies van die genera Oenococcus, Lactobacillus, Pediococcus en Leuconostoc. Vanuit
hierdie wyn MSB, is Oenococcus oeni die spesies wat die beste aanpas en oorleef onder
stresvolle wyn kondisies. Die omskakeling van appelsuur, ’n dikarboksielsuur, na melksuur, ’n
monokarboksielsuur, lei tot ‘n vermindering in suurheid en ’n verhoging in pH. Hierdie vermindering
in suurheid gee ’n sagter en meer geronde mondgevoel aan die wyn en dra by tot ‘n meer
aangename geurprofiel. ’n Verdere rede vir AMG in wyn is om mikrobiese stabiliteit te verseker
deurdat appelsuur verwyder word as ’n moontlike koolstof substraat vir mikroörganismes. Onlangs
het navorsing begin fokus op AMG en die vermoë van MSB om die aroma profiel van wyn te
beïnvloed deur die produksie/modifisering van sekere aroma komponente.
Vir MSB om AMG te kan deurvoer, moet hulle kan oorleef in die stresvolle wynomgewing.
Wyntoestande in Suid-Afrika is veral uitdagend vir die oorlewing van mikroörganismes as gevolg
van lang, warm somers wat lei tot ’n matriks met ’n hoë suikerkonsentrasie en wyn met ’n hoë
etanolkonsentrasie. ‘n Omgewing met ‘n hoë pH en lae appelsuur konsentrasie, kan ook bydrae tot
stresvolle kondisies vir MSB. Hierdie parameters, tesame met die gebruik van swaweldioksied,
maak dit moeilik vir MSB om AMG te inisieer en te voltooi. Sommige van die kommersiële
aanvangskulture wat tans beskikbaar is, bevat nie MSB wat onder Suid-Afrikaanse wyntoestande
geïsoleer is nie en daarom is dit nie altyd optimaal vir gebruik nie. Oenococcus oeni is ook die
enkele MSB kultuur wat in alle kommersiële kulture gebruik word.
Die hoofdoelwit van hierdie studie was om ’n potensiële kommersiële aanvangskultuur te
ontwikkel wat ‘n mengsel van MSB bevat. Hierdie aanvangskultuur moet AMG suksesvol kan
voltooi, mikrobiologiese stabiliteit bevorder en steeds die wynaroma positief kan beïnvloed.
Bakterierasse van O. oeni en Lb. plantarum is geselekteer vir gebruik in hierdie studie.
Lactobacillus plantarum het reeds in vorige studies potensiaal getoon as ‘n moontlike
aanvangskultuur. Die MSB isolate vir hierdie studie is geselekteer uit die Instituut vir
Wynbiotegnologie se kultuurversameling en geïsoleer uit spontane AMG fermentasies.
Die eerste doelwit was om hierdie MSB isolate te karakteriseer vir belangrike eienskappe en
die moontlike gebruik as ’n kommersiële AMG aanvangskultuur. ‘n Totaal van 23 O. oeni en 19
Lb. plantarum isolate is geïdentifiseer. Hierdie isolate is in ’n sintetiese wynmedium geëvalueer vir
hul vermoë om appelsuur na melksuur om te skakel. Op grond van hul reaksie in die sintetiese
wynmedium, is sewe isolate van elk van die O. oeni en Lb. plantarum geselekteer. Hierdie 14
isolate is ondersoek vir die teenwoordigheid van die gene wat kodeer vir biogeenamien produksie en daar is gevind dat geen van die isolate enige van die biogeenamien gene wat ondersoek is,
naamlik histamien, tiramien en putresien besit nie. Die MSB isolate is geneties ondersoek vir die
teenwoordigheid van dié gene wat kodeer vir ensieme wat die aromaprofiel tydens AMG
beïnvloed. Dié ensieme sluit β-glukosidase, esterase, protease, fenoliese suurdekarboksilase en
sitraatliase in. Daar is gevind dat die Lb. plantarum isolate meer diverse ensiemprofiele as O. oeni
besit. Die grootste verskille in die ensiemprofiele kan toegeskryf word aan die teenwoordigheid van
β-glukosidase en fenoliese suurdekarboksilase.
Die tweede doelwit was om kleinskaalse AMG fermentasies met die individuele MSB isolate
uit te voer. Die individuele isolate is in Pinotage geëvalueer. Volgens hierdie resultate is drie isolate
van elk van die O. oeni en Lb. plantarum geselekteer om in gemengde kulture getoets te word. Die
gemengde kulture is in Pinotage, Shiraz en Cabernet Sauvignon in 2008 geëvalueer. As ’n derde
doelwit is hierdie wyne ook analities en sensories geëvalueer om die veranderinge in die
aromaprofiele as gevolg van die teenwoordigheid van die MSB te ondersoek. Op grond van die
fermentasiedata, sowel as die data oor die aromaveranderinge, is drie gemengde kulture
geselekteer vir evaluering in Pinotage, Cabernet Sauvignon en Chardonnay in 2009. Die
gemengde kulture kon AMG suksesvol voltooi met fermentasietempo’s wat vergelykbaar was met
dié van ‘n kommersiële AMG kultuur wat as kontrole gebruik is. Die verskillende MSB kulture het
spesifieke en uiteenlopende uitwerkings op die wynaroma gehad. Die O. oeni isolaat in die
gemengde kultuur blyk ‘n belangriker rol te speel in die esterkonsentrasie na AMG, terwyl die
Lb. plantarum isolaat ’n groter effek het op die hoër alkohol en vlugtige vetsuurinhoud na AMG.
Die resultate wat deur hierdie unieke studie gegenereer is, gee ’n aanduiding van die
potensiaal van ’n gemengde MSB aanvangskultuur vir AMG. Die gemengde kulture kon AMG
suksesvol voltooi en ‘n positiewe bydrae tot die aromaprofiel van die wyn lewer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4362 |
| Date | 03 1900 |
| Creators | Lerm, Elda |
| Contributors | Du Toit, Maret, Engelbrecht, Lynn, University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 151 p. : ill. |
| Rights | University of Stellenbosch |
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