44 research outputs found
Evolution of phenolic composition during barrel and bottle aging
[EN] During red wine ageing, phenolic compounds undergo several reactions that have an impact on wine colour and mouthfeel properties. The evolution of phenolic content is affected during wine ageing. The aimof this study was to investigate the phenolic content and evolution of 82 commercial red wines subjected to barrel and bottle ageing. The phenolic content evolution of wines that underwent an ageing period of 12 months in commercial 225 litre barrels, followed by 12 months in the bottle, was monitored. While the total phenolic content remained stable, the anthocyanin fraction was affected the most, which led to substantial changes in the colour properties of the wines. Differences were found during both ageingregimes, indicating certain phenolic reactions being favoured or compromised under different ageing conditions, with an impact on wine colour properties. This paper provides the first large-scale study on the phenolic evolution of commercial red wine during ageing.Aleixandre Tudo, J.; Du Toit, W. (2020). Evolution of phenolic composition during barrel and bottle aging. South African journal of enology and viticulture. 41(2):233-237. https://doi.org/10.21548/41-2-4128S23323741
The Role of UV-Visible Spectroscopy for Phenolic Compounds Quantification in Winemaking
Phenolic compounds are bioactive substances present in a large number of food products including wine. The importance of these compounds in wine is due to their large effect on the organoleptic attributes of wine. Phenolic compounds play a crucial role in the colour as well as mouthfeel properties of wines. UV-visible spectroscopy appears as a suitable technique for the evaluation of phenolic compounds’ properties and content. The ability of the phenolic ring to absorb UV light and the fact that some of the phenolic substances are coloured compounds, i.e. show absorption features in the visible region, make UV-visible spectroscopy a suitable technique to investigate and quantify grape and wine phenolic compounds. A number of analytical techniques are currently used for phenolic quantification. These include both simpler approaches (spectrophotometric determinations) as well as more complex methodologies such liquid chromatography analysis. Moreover, a number of spectroscopy applications have also been recently reported and are becoming popular within the wine industry. This chapter reviews information on the UV-visible spectral properties of phenolic compounds, changes occurring during wine ageing and also discusses the current UV-visible based analytical techniques used for the quantification of phenolic compounds in grapes and wine
White Wine Phenolics: Current Methods of Analysis
[EN] White wine phenolic analyses are less common in the literature than analyses of red wine phenolics. Analytical techniques for white wine phenolic analyses using spectrophotometric, chromatographic, spectroscopic, and electrochemical methods are reported. The interest of research in this area combined with the advances in technology aimed at the winemaking industry are promoting the establishment of novel approaches for identifying, quantifying, and classifying phenolic compounds in white wine. This review article provides an overview of the current research into white wine phenolics through a critical discussion of the analytical methods employed.The authors gratefully acknowledge Winetech South Africa for funding and support under grant number JT-NP07.Clarke, S.; Bosman, G.; Du Toit, W.; Aleixandre Tudo, J. (2023). White Wine Phenolics: Current Methods of Analysis. Journal of the Science of Food and Agriculture. 103(1):7-25. https://doi.org/10.1002/jsfa.12120725103
Partial least squares calibrations and batch statistical process control to monitor phenolic extraction in red wine fermentation under different maceration conditions
[EN] The extraction of phenolic compounds during maceration is of utmost importance in red winemaking. However, the monitoring of phenolic extraction is often hampered by analytical and statistical constraints. The aim of this study was to monitor phenolic extraction kinetics with the use of PLS phenolic calibrations and batch statistical process control. Eight batches of Cabernet Sauvignon and Shiraz grapes during alcoholic fermentation under different maceration conditions (pressing at 1/3rd, 2/3rd and end of fermentation) and punch down regimes (low vs. high frequency) were evaluated in the study. Cabernet Sauvignon appeared to be a more suitable cultivar for longer maceration conditions with increased tannin extraction observed. Similar trends were observed for punch down for both cultivars. The use of PLS calibrations and batch level modelling provided an enhanced interpretation and understanding of phenolic extraction during red wine fermentationsFourie, E.; Aleixandre Tudo, J.; Mihnea, M.; Du Toit, W. (2020). Partial least squares calibrations and batch statistical process control to monitor phenolic extraction in red wine fermentation under different maceration conditions. Food Control. 115:1-10. https://doi.org/10.1016/j.foodcont.2020.107303S11011
Bibliometric analysis of publications by South African viticulture and oenology research centres
We analysed the production, impact factor of, and scientific collaboration involved in viticulture and oenology articles associated with South African research centres published in international journals during the period 1990¿2009. The articles under scrutiny were obtained from the Science Citation Index database, accessed via the Web of Knowledge platform. The search strategy employed specific viticulture and oenology terms and was restricted to the field `topic¿. The results showed that 406 articles were published during the review period, with the most number of publications being in the South African Journal of Enology and Viticulture (n = 34), American Journal of Enology and Viticulture (n = 16) and Journal of Agricultural and Food Chemistry (n = 16). The articles were published by 851 authors from 236 institutions. The collaboration rate was 3.7 authors per article, having grown over the two decades examined. The most productive institutions (i.e. those receiving a greater number of citations) were Stellenbosch University (219 published articles and 2592 citations) and the Agricultural Research Council (49 published articles and 454 citations), both from South Africa. Graphical representation of co-authorship networks identified 18 groups of authors and a single network of institutions whose core is Stellenbosch University. In conclusion, we have identified a significant growth in South African viticulture and oenology research in recent years, with a high degree of internationalisation and a constant level of domestic collaboration.Aleixandre-Benavent, R.; Aleixandre Tudo, J.; González Alcaide, G.; Ferrer Sapena, A.; Aleixandre Benavent, JL.; Du Toit, W. (2012). Bibliometric analysis of publications by South African viticulture and oenology research centres. SOUTH AFRICAN JOURNAL OF SCIENCE. 108(5-6):74-84. https://doi.org/10.4102/sajs.v108i5/6.661S74841085-
The crust and upper mantle structure of central and West Antarctica from Bayesian inversion of Rayleigh Wave and receiver functions
Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 123 (2018): 7824-7849, doi:10.1029/2017JB015346.We construct a new seismic model for central and West Antarctica by jointly inverting Rayleigh wave phase and group velocities along with P wave receiver functions. Ambient noise tomography exploiting data from more than 200 seismic stations deployed over the past 18 years is used to construct Rayleigh wave phase and group velocity dispersion maps. Comparison between the ambient noise phase velocity maps with those constructed using teleseismic earthquakes confirms the accuracy of both results. These maps, together with P receiver function waveforms, are used to construct a new 3‐D shear velocity (Vs) model for the crust and uppermost mantle using a Bayesian Monte Carlo algorithm. The new 3‐D seismic model shows the dichotomy of the tectonically active West Antarctica (WANT) and the stable and ancient East Antarctica (EANT). In WANT, the model exhibits a slow uppermost mantle along the Transantarctic Mountains (TAMs) front, interpreted as the thermal effect from Cenozoic rifting. Beneath the southern TAMs, the slow uppermost mantle extends horizontally beneath the traditionally recognized EANT, hypothesized to be associated with lithospheric delamination. Thin crust and lithosphere observed along the Amundsen Sea coast and extending into the interior suggest involvement of these areas in Cenozoic rifting. EANT, with its relatively thick and cold crust and lithosphere marked by high Vs, displays a slower Vs anomaly beneath the Gamburtsev Subglacial Mountains in the uppermost mantle, which we hypothesize may be the signature of a compositionally anomalous body, perhaps remnant from a continental collision.National Science Foundation Grant Numbers: PLR‐1142518, PLR‐1246712, PLR 1246151, PLR‐1246416, PLR‐1744883, PLR‐ 17448832019-03-2
Sources of acetic and other fatty acids and their role in sluggish and stuck red wine fermentations
Thesis (MScAgric)--University of Stellenbosch, 2000.ENGLISH ABSTRACT: The quality of wine is influenced by numerous factors. These factors include the quality of
the grapes, winemaking techniques and quality control throughout the winemaking
process. It is thus very important that any process leading to the lowering of the quality of
the wine be prevented. Evidence in the wine industry shows that bacterial spoilage is still
very much a common problem in many wineries. The spoilage of wine by bacteria can
lead to amongst other problems, elevated volatile acidity levels, of which only a certain
concentration limit in wine is permitted. Usually more than 90% of the volatile acidity of
wine consists of acetic acid. Different yeast strains, heterofermentative lactic acid bacteria
and acetic acid bacteria (which can all be spoilage microorganisms) can produce acetic
acid in high concentrations. It is thus important to be able to prevent the formation of this
acid by controling the unwanted growth of these spoilage microorganisms. Acetic acid and
other medium chain fatty acids, octanoic- and decanoic acid, can also lead to stuck or
sluggish fermentations. A stuck or sluggish fermentation can also lead to wine spoilage,
due to sugar remaining in the fermentation which can be utilized by spoilage
microorganisms. Acetic- and other fatty acids enter the yeast cell by passive diffussion
and releases its proton in the cytoplasm, thereby acidifying the cytoplasm and inhibiting
some enzymes. These acids can also work synergistically with ethanol and its inhibitory
effect is also dependent on the temperature. Yeast strains can also differ in their
resistance to acetic and other medium chain fatty acids and these acids can also influence
the growth of lactic acid bacteria.
How acetic acid bacteria influence the winemaking process and the used measures to
keep these bacteria from spoiling wine have been the subject of very little attention in the
past. This was due to the belief that the anaerobic conditions prevailing in wine and the
use of sulfur dioxide are enough to control these bacteria, since acetic acid bacteria were
always described as being strictly aerobic microorganisms. Recently, some evidence
showed that acetic acid bacteria can survive and even overcome the limits that the
winemaking process places on its growth. These bacteria are also known to inhibit the
yeasts growth and fermentation ability due to the production of acetic acid and other
factors. A research programme on the origin of volatile acidity in South African wines had
been initiated at the Department of Viticulture and Enology and at the Institute for Wine
Biotechnology at the University of Stellenbosch after increases in volatile acidity in
different South African wines had been reported. This spurred us to investigate the
occurrence of acetic acid bacteria in South African red wine fermentations, which forms
part of this study, and to identify the dominant acetic acid bacterial strains. The sulfur
dioxide resistance of five representative strains were also determined, as well as the effect
of metabolites which were produced by these bacteria on yeast growth and fermentation
ability.
Our results indicate that acetic acid bacteria can occur in high concentrations in the
fresh must and during alcoholic fermentation. In the 1998 harvesting season acetic acid
bacteria occurred at 106-107 cfu per ml in the fresh must. In 1999 these numbers were
104-105 cfu/ml. Acetic acid bacteria numbers decreased in 1998 to 102-103 cfulml during
fermentation. The survival of these bacteria in 1999 correlated with the pH of the must, as well as sulfur dioxide dosages in the must. In must with a low pH and higher sulfur dioxide
the number of acetic acid bacterial numbers decreased more drastically than in the high
pH, low sulfur dioxide musts. This was also true for acetic acid bacterial counts during
cold soaking of musts, with the number of acetic acid bacteria increasing during the cold
soaking period in musts with a high pH. In musts with a low pH and higher S02 dosages
acetic acid bacterial counts did not, however, increase during cold soaking.
Gluconobacter oxydans dominated in the fresh must with Acetobacter liquefaciens and
especially Acetobacter pasteurianus dominating during the fermentation. Different
biochemical and physiological tests revealed that 52% of the 115 isolates tested belong to
A. pasteurianus. The high occurrence of A. liquefaciens with A. pasteurianus during
fermentation showed that the dominant acetic acid bacterial species in South Africa
differed from reports from other wine producing countries. The sulfur dioxide resistance of
the acetic acid bacteria tested also differed in white grape juice, with a molecular sulfur
dioxide concentration of 0.64 mg/I being necessary to eliminate all the acetic acid bacterial
strains tested. The A. hansenii strain was found to be the most resistant to sulfur dioxide
and G. oxydans the least resistant. The latter strain was eliminated by only 0.05 mg/I
molecular sulfur dioxide, while A. hansenii was only eliminated by 0.64 mg/I molecular
sulfur dioxide. The A. pasteurianus, A. liquefaciens and A. aceti strains tested displayed
varying degrees of resistance to sulfur dioxide. The volatile acidity produced by these
bacteria profoundly influenced the growth and fermentation ability of yeast, which led to
slow/stuck fermentation. The A. hansenii and A. pasteurianus strains produced the most
volatile acidity in grape juice, with up to 4.02 g/I for A. hansenii within 4 days, which led to
a stuck alcoholic fermentation. This was, however, prevented by inhibiting or eliminating
the acetic acid bacteria with sufficient sulfur dioxide additions prior to yeast inoculation.
Compounds produced by acetic acid bacteria can also influence wine quality. Certain
organic acids were produced and metabolized by acetic acid bacteria, as well as acetoin.
We could not, however, detect any other fatty acids that are inhibitory to yeast (produced
by these bacteria).
This study clearly showed that acetic acid bacteria could occur during fermentation
and that certain winemaking techniques, like the maintenance of a low pH in the must and
sulfur dioxide additions can influence the growth and survival of acetic acid bacteria.
Acetic acid bacteria also influence both the winemaking process by inhibiting yeast as well
as the quality of the wine by producing acetic acid and/or other compounds. This study
also shed some light on the occurrence of acetic acid bacterial species in the South
African context and could be important in assisting the winemaker, as well as the scientific
reseacher, in finding ways to inhibit acetic acid bacteria in the ongoing battle against these
spoilage microorganisms of wine.AFRIKAANSE OPSOMMING: Wynkwaliteit word deur verskillende faktore beinvloed. Dit sluit die druifkwaliteit, wynmaak
tegnieke en kwaliteitsbeheer deur die wynmaakproses in. Enige prosesse en faktore wat
tot die verlaging in wynkwaliteit kan lei moet dus ten alle koste voorkom word. Die bederf
van wyn deur bakterieë kan en is 'n algemene probleem in enige kelder. Bakteriese
bederf kan, onder andere, lei tot verhoogte vlugtige suurheid, waarvan 'n sekere
konsentrasie limiet in wyn toegelaat word. Asynsuur maak gewoonlik 90% van die
vlugtige suurheid uit. Asynsuur kan deur verskillende gisrasse, heterofermantatiewe
melksuurbakterieë en asynsuurbakterieë (wat almal wyn kan bederf) gevorm word. Die
vorming van asynsuur in wyn kan dus voorkom word deur die ongewenste groei van dié
organismes te voorkom. Asynsuur en ander medium ketting vetsure, soos oktanoë- en
dekanoësuur, kan ook tot slepende of gestaakte gistings lei. Suiker wat in die wyn
agterbly wat In slepende/gestaakte fermentasie ondergaan kan deur bederf bakterieë
gebruik word om die wyn te bederf. Ongedissosieerde asynsuur en ander vetsure dring
die gissel binne deur passiewe diffussie en stel 'n proton vry in die sitoplasma wat
sitoplasma versuur en sekere ensieme inhibeer. Hierdie sure werk ook sinergisties met
etanol en hul inhiberede effek is ook temperatuur afhanklik. Gisrasse verskil in hul
weerstandbiedendheid teen asynsuur- en ander mediumketting vetsure en dié vetsure kan
ook melksuurbakterieë se groei beïnvloed.
Hoe asynsuurbakterieë wyn bederf en die aksies wat geneem kan word om dit te
verhoed is in die verlede nie baie ondrsoek nie. Dit is hoofsaaklik daaraan toe te skryf dat
geglo is dat die anaerobiese kondisies in wyn en die gebruik van swaweidioksied die groei
van asynsuurbakterieë, wat altyd beskryf is as streng aerobe mikroorganismes, kan
beheer. Daar is onlangs aangetoon dat asynsuurbakterieë kan oorleef in wyn en selfs die
ongunstige kondisies daarin kan oorkom. Hierdie bakterieë is ook in staat om gisgroei en
fermentasie vermoë te inhibeer deur die produksie van asynsuur en ander faktore. In
Navorsingsprogram om die oorsprong van verhoogde vlugtige suurheid in Suid-Afrikaanse
wyne te bepaal is deur die Departement Wingerd- en Wynkunde en die Instituut vir
Wynbiotegnologie van die Universiteit van Stellenbosch geinisieer. Dit het ons
aangemoedig om die voorkoms van asynsuurbakterieë in Suid-Afrikaanse rooiwyngistings,
wat deel vorm van hierdie ondersoek, en ook die dominante asynsuurbakterie rasse te
identifiseer. Die swaweidioksied bestandheid van vyf verteenwoordegende rasse en die
effek wat metaboliete wat deur dié bakterieë geproduseer is op gisgroei en
gisitingsvermoë is bepaal.
Ons resultate bewys dat asynsuurbakterieë teen hoë getalle in vars mos en
gedurende alkoholiese gisting kan voorkom. Asynsuurbakterieë het gedurende die 1998
seisoen teen 106-107 kve/ml en in 1999 teen 104-105 kve/ml in die vars mos voorgekom.
Gedurende fermentasie het hierdie getalle in die 1998 seisoen gedaal na 102-103 kve/ml.
Die oorlewing van hierdie bakterieë het gedurende die 1999 seisoen gekorrelleer met die
pH en swaweidioksied konsentrasies van die mos. In die lae pH, hoë swaweidioksied
moste het asynsuurbakterie getalle vinniger en meer dramaties gedaal as in die hoë pH,
lae swaweidioksied moste. Asynsuurbakterie getalle het dieselfde tendens getoon in
moste gedurende dopkontak by lae temperature. In moste met 'n hoë pH het asynsuurbakterie getalle toegeneem gedurende koue dopkontak, terwyl dit nie gebeur het
nie in moste met 'n lae pH en hoë swaweidioksied konsentrasies.
In die vars mos het Gluconobacter oxydans en gedurende die fermentasie
Acetobacter liquefaciens en veral Acetobacter pasteurianus oorheers. Verskillende
biochemiese en fisiologiese toetse het bepaal dat 52% van die 115 isolate A. pasteurianus
is. Die hoë voorkoms van A. liquefaciens saam met A. pasteurianus gedurende gisting
bewys dat die voorkoms en dominansie van asynsuurbakterieë in Suid- Afrika verskil van
ander wynproduserende lande. Die swaweidioksied weerstandbiedendheid van die
asynsuurbakterieë wat getoets het, het ook verskil, met 0.64 mg/I molekulêre swaweIdioksied
nodig om hul almal te elimineer in wit druiwesap. Die A. hansenii en G. oxydans
rasse was die mees weerstandbiedend en sensitiefste onderskeidelik ten opsigte van
swaweidioksied. Slegs 0.05 mg/I molekulêre swaweidioksied was voldoende om G.
oxydans te elimineer, terwyl A. hansenii deur 0.64 mg/I molekulêre swaweidioksied
geëlimineer is. Die A. pasteurianus, A. liquefaciens en A. aceti rasse het verskillende
swaweidioksied weerstandbiedendheid getoon. Die vlugtige suurheid wat deur dié
bakterieë geproduseer is het die groei en gistingvermoë van gis drasties beinvloed, wat tot
slepende/gestaakte fermentasies gelei het. Die A. hansenii en A. pasteurianus rasse het
die meeste vlugtige suurheid geproduseer, met tot 4.02 g/I geproduseer deur A. hansenii
na vier dae se groei, wat tot 'n gestaakte fermentasie gelei het. Dit is egter voorkom deur
die asynsuurbakterieë te elimineer deur genoegsame swaweidioksied toevoegings tot die
mos voor gisinokulasie te doen. Verbindings wat deur asynsuurbakterieë geproduseer
word kan ook wynkwaliteit beinvloed. Sekere anorganiese sure is deur hierdie bakterieë
geproduseer, terwyl ander gemetaboliseer is. Asetoïen is geproduseer deur die getoetse
asynsuurbakterieë. Ons kon egter nie ander vetsure wat gis inhibeer opspoor nie.
(Geproduseer deur die bakterieë).
Hierdie studie bewys dat asynsuurbakterieë gedurende alkoholiese fermentasie kan
voorkom en dat sekere wynmaaktegnieke, soos die verkryging van moste met 'n lae pH en
genoegsame swaweidioksied toevoegings die groei en oorlewing van asynsuurbakterieë
kan beivloed. Asynsuurbakterieë kan ook beide die wynmaakproses, deur giste te
inhibeer, en die wynkwaliteit beivloed deur die produksie van asynsuur en/of ander
verbindings. Hierdie studie het ook kennis oor die voorkoms van asynsuurbakterieë in
Suid-Afrikaanse moste verbeter en kan ook as 'n nuttige hulpmiddel dien vir die wynmaker
en navorser in die stryd om hierdie bederf organismes van wyn te elimineer
Sources of acetic and other fatty acids and their role in sluggish and stuck red wine fermentations
Thesis (MScAgric)--University of Stellenbosch, 2000.ENGLISH ABSTRACT: The quality of wine is influenced by numerous factors. These factors include the quality of
the grapes, winemaking techniques and quality control throughout the winemaking
process. It is thus very important that any process leading to the lowering of the quality of
the wine be prevented. Evidence in the wine industry shows that bacterial spoilage is still
very much a common problem in many wineries. The spoilage of wine by bacteria can
lead to amongst other problems, elevated volatile acidity levels, of which only a certain
concentration limit in wine is permitted. Usually more than 90% of the volatile acidity of
wine consists of acetic acid. Different yeast strains, heterofermentative lactic acid bacteria
and acetic acid bacteria (which can all be spoilage microorganisms) can produce acetic
acid in high concentrations. It is thus important to be able to prevent the formation of this
acid by controling the unwanted growth of these spoilage microorganisms. Acetic acid and
other medium chain fatty acids, octanoic- and decanoic acid, can also lead to stuck or
sluggish fermentations. A stuck or sluggish fermentation can also lead to wine spoilage,
due to sugar remaining in the fermentation which can be utilized by spoilage
microorganisms. Acetic- and other fatty acids enter the yeast cell by passive diffussion
and releases its proton in the cytoplasm, thereby acidifying the cytoplasm and inhibiting
some enzymes. These acids can also work synergistically with ethanol and its inhibitory
effect is also dependent on the temperature. Yeast strains can also differ in their
resistance to acetic and other medium chain fatty acids and these acids can also influence
the growth of lactic acid bacteria.
How acetic acid bacteria influence the winemaking process and the used measures to
keep these bacteria from spoiling wine have been the subject of very little attention in the
past. This was due to the belief that the anaerobic conditions prevailing in wine and the
use of sulfur dioxide are enough to control these bacteria, since acetic acid bacteria were
always described as being strictly aerobic microorganisms. Recently, some evidence
showed that acetic acid bacteria can survive and even overcome the limits that the
winemaking process places on its growth. These bacteria are also known to inhibit the
yeasts growth and fermentation ability due to the production of acetic acid and other
factors. A research programme on the origin of volatile acidity in South African wines had
been initiated at the Department of Viticulture and Enology and at the Institute for Wine
Biotechnology at the University of Stellenbosch after increases in volatile acidity in
different South African wines had been reported. This spurred us to investigate the
occurrence of acetic acid bacteria in South African red wine fermentations, which forms
part of this study, and to identify the dominant acetic acid bacterial strains. The sulfur
dioxide resistance of five representative strains were also determined, as well as the effect
of metabolites which were produced by these bacteria on yeast growth and fermentation
ability.
Our results indicate that acetic acid bacteria can occur in high concentrations in the
fresh must and during alcoholic fermentation. In the 1998 harvesting season acetic acid
bacteria occurred at 106-107 cfu per ml in the fresh must. In 1999 these numbers were
104-105 cfu/ml. Acetic acid bacteria numbers decreased in 1998 to 102-103 cfulml during
fermentation. The survival of these bacteria in 1999 correlated with the pH of the must, as well as sulfur dioxide dosages in the must. In must with a low pH and higher sulfur dioxide
the number of acetic acid bacterial numbers decreased more drastically than in the high
pH, low sulfur dioxide musts. This was also true for acetic acid bacterial counts during
cold soaking of musts, with the number of acetic acid bacteria increasing during the cold
soaking period in musts with a high pH. In musts with a low pH and higher S02 dosages
acetic acid bacterial counts did not, however, increase during cold soaking.
Gluconobacter oxydans dominated in the fresh must with Acetobacter liquefaciens and
especially Acetobacter pasteurianus dominating during the fermentation. Different
biochemical and physiological tests revealed that 52% of the 115 isolates tested belong to
A. pasteurianus. The high occurrence of A. liquefaciens with A. pasteurianus during
fermentation showed that the dominant acetic acid bacterial species in South Africa
differed from reports from other wine producing countries. The sulfur dioxide resistance of
the acetic acid bacteria tested also differed in white grape juice, with a molecular sulfur
dioxide concentration of 0.64 mg/I being necessary to eliminate all the acetic acid bacterial
strains tested. The A. hansenii strain was found to be the most resistant to sulfur dioxide
and G. oxydans the least resistant. The latter strain was eliminated by only 0.05 mg/I
molecular sulfur dioxide, while A. hansenii was only eliminated by 0.64 mg/I molecular
sulfur dioxide. The A. pasteurianus, A. liquefaciens and A. aceti strains tested displayed
varying degrees of resistance to sulfur dioxide. The volatile acidity produced by these
bacteria profoundly influenced the growth and fermentation ability of yeast, which led to
slow/stuck fermentation. The A. hansenii and A. pasteurianus strains produced the most
volatile acidity in grape juice, with up to 4.02 g/I for A. hansenii within 4 days, which led to
a stuck alcoholic fermentation. This was, however, prevented by inhibiting or eliminating
the acetic acid bacteria with sufficient sulfur dioxide additions prior to yeast inoculation.
Compounds produced by acetic acid bacteria can also influence wine quality. Certain
organic acids were produced and metabolized by acetic acid bacteria, as well as acetoin.
We could not, however, detect any other fatty acids that are inhibitory to yeast (produced
by these bacteria).
This study clearly showed that acetic acid bacteria could occur during fermentation
and that certain winemaking techniques, like the maintenance of a low pH in the must and
sulfur dioxide additions can influence the growth and survival of acetic acid bacteria.
Acetic acid bacteria also influence both the winemaking process by inhibiting yeast as well
as the quality of the wine by producing acetic acid and/or other compounds. This study
also shed some light on the occurrence of acetic acid bacterial species in the South
African context and could be important in assisting the winemaker, as well as the scientific
reseacher, in finding ways to inhibit acetic acid bacteria in the ongoing battle against these
spoilage microorganisms of wine.AFRIKAANSE OPSOMMING: Wynkwaliteit word deur verskillende faktore beinvloed. Dit sluit die druifkwaliteit, wynmaak
tegnieke en kwaliteitsbeheer deur die wynmaakproses in. Enige prosesse en faktore wat
tot die verlaging in wynkwaliteit kan lei moet dus ten alle koste voorkom word. Die bederf
van wyn deur bakterieë kan en is 'n algemene probleem in enige kelder. Bakteriese
bederf kan, onder andere, lei tot verhoogte vlugtige suurheid, waarvan 'n sekere
konsentrasie limiet in wyn toegelaat word. Asynsuur maak gewoonlik 90% van die
vlugtige suurheid uit. Asynsuur kan deur verskillende gisrasse, heterofermantatiewe
melksuurbakterieë en asynsuurbakterieë (wat almal wyn kan bederf) gevorm word. Die
vorming van asynsuur in wyn kan dus voorkom word deur die ongewenste groei van dié
organismes te voorkom. Asynsuur en ander medium ketting vetsure, soos oktanoë- en
dekanoësuur, kan ook tot slepende of gestaakte gistings lei. Suiker wat in die wyn
agterbly wat In slepende/gestaakte fermentasie ondergaan kan deur bederf bakterieë
gebruik word om die wyn te bederf. Ongedissosieerde asynsuur en ander vetsure dring
die gissel binne deur passiewe diffussie en stel 'n proton vry in die sitoplasma wat
sitoplasma versuur en sekere ensieme inhibeer. Hierdie sure werk ook sinergisties met
etanol en hul inhiberede effek is ook temperatuur afhanklik. Gisrasse verskil in hul
weerstandbiedendheid teen asynsuur- en ander mediumketting vetsure en dié vetsure kan
ook melksuurbakterieë se groei beïnvloed.
Hoe asynsuurbakterieë wyn bederf en die aksies wat geneem kan word om dit te
verhoed is in die verlede nie baie ondrsoek nie. Dit is hoofsaaklik daaraan toe te skryf dat
geglo is dat die anaerobiese kondisies in wyn en die gebruik van swaweidioksied die groei
van asynsuurbakterieë, wat altyd beskryf is as streng aerobe mikroorganismes, kan
beheer. Daar is onlangs aangetoon dat asynsuurbakterieë kan oorleef in wyn en selfs die
ongunstige kondisies daarin kan oorkom. Hierdie bakterieë is ook in staat om gisgroei en
fermentasie vermoë te inhibeer deur die produksie van asynsuur en ander faktore. In
Navorsingsprogram om die oorsprong van verhoogde vlugtige suurheid in Suid-Afrikaanse
wyne te bepaal is deur die Departement Wingerd- en Wynkunde en die Instituut vir
Wynbiotegnologie van die Universiteit van Stellenbosch geinisieer. Dit het ons
aangemoedig om die voorkoms van asynsuurbakterieë in Suid-Afrikaanse rooiwyngistings,
wat deel vorm van hierdie ondersoek, en ook die dominante asynsuurbakterie rasse te
identifiseer. Die swaweidioksied bestandheid van vyf verteenwoordegende rasse en die
effek wat metaboliete wat deur dié bakterieë geproduseer is op gisgroei en
gisitingsvermoë is bepaal.
Ons resultate bewys dat asynsuurbakterieë teen hoë getalle in vars mos en
gedurende alkoholiese gisting kan voorkom. Asynsuurbakterieë het gedurende die 1998
seisoen teen 106-107 kve/ml en in 1999 teen 104-105 kve/ml in die vars mos voorgekom.
Gedurende fermentasie het hierdie getalle in die 1998 seisoen gedaal na 102-103 kve/ml.
Die oorlewing van hierdie bakterieë het gedurende die 1999 seisoen gekorrelleer met die
pH en swaweidioksied konsentrasies van die mos. In die lae pH, hoë swaweidioksied
moste het asynsuurbakterie getalle vinniger en meer dramaties gedaal as in die hoë pH,
lae swaweidioksied moste. Asynsuurbakterie getalle het dieselfde tendens getoon in
moste gedurende dopkontak by lae temperature. In moste met 'n hoë pH het asynsuurbakterie getalle toegeneem gedurende koue dopkontak, terwyl dit nie gebeur het
nie in moste met 'n lae pH en hoë swaweidioksied konsentrasies.
In die vars mos het Gluconobacter oxydans en gedurende die fermentasie
Acetobacter liquefaciens en veral Acetobacter pasteurianus oorheers. Verskillende
biochemiese en fisiologiese toetse het bepaal dat 52% van die 115 isolate A. pasteurianus
is. Die hoë voorkoms van A. liquefaciens saam met A. pasteurianus gedurende gisting
bewys dat die voorkoms en dominansie van asynsuurbakterieë in Suid- Afrika verskil van
ander wynproduserende lande. Die swaweidioksied weerstandbiedendheid van die
asynsuurbakterieë wat getoets het, het ook verskil, met 0.64 mg/I molekulêre swaweIdioksied
nodig om hul almal te elimineer in wit druiwesap. Die A. hansenii en G. oxydans
rasse was die mees weerstandbiedend en sensitiefste onderskeidelik ten opsigte van
swaweidioksied. Slegs 0.05 mg/I molekulêre swaweidioksied was voldoende om G.
oxydans te elimineer, terwyl A. hansenii deur 0.64 mg/I molekulêre swaweidioksied
geëlimineer is. Die A. pasteurianus, A. liquefaciens en A. aceti rasse het verskillende
swaweidioksied weerstandbiedendheid getoon. Die vlugtige suurheid wat deur dié
bakterieë geproduseer is het die groei en gistingvermoë van gis drasties beinvloed, wat tot
slepende/gestaakte fermentasies gelei het. Die A. hansenii en A. pasteurianus rasse het
die meeste vlugtige suurheid geproduseer, met tot 4.02 g/I geproduseer deur A. hansenii
na vier dae se groei, wat tot 'n gestaakte fermentasie gelei het. Dit is egter voorkom deur
die asynsuurbakterieë te elimineer deur genoegsame swaweidioksied toevoegings tot die
mos voor gisinokulasie te doen. Verbindings wat deur asynsuurbakterieë geproduseer
word kan ook wynkwaliteit beinvloed. Sekere anorganiese sure is deur hierdie bakterieë
geproduseer, terwyl ander gemetaboliseer is. Asetoïen is geproduseer deur die getoetse
asynsuurbakterieë. Ons kon egter nie ander vetsure wat gis inhibeer opspoor nie.
(Geproduseer deur die bakterieë).
Hierdie studie bewys dat asynsuurbakterieë gedurende alkoholiese fermentasie kan
voorkom en dat sekere wynmaaktegnieke, soos die verkryging van moste met 'n lae pH en
genoegsame swaweidioksied toevoegings die groei en oorlewing van asynsuurbakterieë
kan beivloed. Asynsuurbakterieë kan ook beide die wynmaakproses, deur giste te
inhibeer, en die wynkwaliteit beivloed deur die produksie van asynsuur en/of ander
verbindings. Hierdie studie het ook kennis oor die voorkoms van asynsuurbakterieë in
Suid-Afrikaanse moste verbeter en kan ook as 'n nuttige hulpmiddel dien vir die wynmaker
en navorser in die stryd om hierdie bederf organismes van wyn te elimineer
The renin-angiotensin-aldosterone-system and left ventricular mass in young black and white adults: the African-PREDICT study
M Health Sciences (Cardiovascular Physiology), North-West University, Potchefstroom CampusMotivation. The renin-angiotensin system (RAS) is a central regulatory component implicated in sodium and water homeostasis that affects blood volume and pressure. Dysregulation of this system results in increased blood pressure (BP) and may contribute to the development of left ventricular hypertrophy (LVH). In addition to the RAS and BP, factors such as increased age, sex, black ethnicity and a low socio-economic status (SES) also contribute to left ventricular remodelling. In the South African context low SES may be even more important as it affects 55.5% of the population with a large proportion (63.4%) of them being young and unemployed. It is therefore important to investigate RAS-related increases in left ventricular mass (LVM) along with the possible influence low SES may have in young South Africans. Aim. This study investigated the relationship between LVMi (index) and the RAS components in young (20-30 years) healthy participants of the African-PREDICT study while taking factors such as SES, ethnicity and sex into consideration. Methods. This study used cross-sectional data from 1 186 black and white men and women divided into low and high SES groups. Demographic data including age, sex, ethnicity, skill level (classified according to the South African Standard Classification of Occupation (SASCO), education and income were collected using various questionnaires. Socio-economic status was calculated using a point system adapted from the Kuppuswamy's Socioeconomic Status Scale. Anthropometric measurements and physical activity were measured. Cardiovascular measurements included clinic BP, 24h ambulatory BP, total peripheral resistance and echocardiography which were used to determine LVM - normalised for body surface area to derive LVMi. The RAS Fingerprint® was measured with an ultra-pressure-liquid chromatography tandem-mass spectrometry (LC-MS/MS) method. A wide range of other biochemical markers considered as cardiovascular disease risk markers were also analysed. Results. Aligned with the aim of this study it was determined whether LVMi is associated with components of the RAS. LVMi associated inversely and independently with plasma renin activity (ꞵ=-0.168; P=0.017), angiotensin I (ꞵ=-0.155; P=0.028) and angiotensin II (ꞵ=-0.172; P=0.015), only in black women with low SES. No associations were evident between LVMi and components of the RAS in black women with high SES, or white women, black or white men, independent of SES. Conclusion. This finding suggests that multiple factors may play a role in the development of increased LVM, including suppressed RAS, raised BP, female sex, black ethnicity and a low socio-economic environment.Master
The effect of oxygen on the composition and microbiology of red wine
Thesis (PhD(Agric) (Viticulture and Oenology))--University of Stellenbosch, 2006.The winemaking process involves different complex chemical and biochemical
reactions, which include those of oxygen (O2). Oxygen can come into contact with the
wine through various winemaking procedures and can be used by the winemaker to
enhance the quality of red wine. In wine, the main substrates for oxidation are
phenolic molecules, which form quinones. These can influence the sensory
characteristics of the wine. O2 can be used in fresh must to remove oxidisable
phenolic molecules through a process called hyper-oxidation and can also be added
to fermenting must to enhance the fermentation performance of yeast. Controlled O2
additions during ageing can lead to the wine’s colour being increased and the
astringency of the wine decreased. This is due to the formation of acetaldehyde from
the oxidation of ethanol, which induces the polymerisation of tannin and anthocyanin
molecules. The addition of too much O2 to wine can, however, lead to unwanted
over-oxidation, with certain off-odours being formed. It can also enhance the growth
of unwanted spoilage microorganisms, such as Brettanomyces and acetic acid
bacteria. Although research on O2 in wine was started many years ago, many
questions still remain. These include the general effect of O2 on the sensory and
phenolic profile of red wine especially and the microbiology of wine during ageing. An
effective way of measuring oxidation, especially in red wine must also be developed.
In the first part of this study, the effects of O2 and sulfur dioxide (SO2) additions
on a strain of Brettanomyces bruxellensis (also known as Dekkera bruxellensis) and
Acetobacter pasteurianus were investigated. Epifluorescence microscopy and plating
revealed that the A. pasteurianus strain went into a viable but non-culturable state in
the wine after prolonged storage under relative anaerobic conditions. This state,
however, could be negated with successive increases in culturability by the addition
of O2, as would happen during the transfer of wine when air is introduced. The A.
pasteurianus strain was also relatively resistant to SO2, but the B. bruxellensis strain
was more sensitive to SO2. A short exposure time to molecular SO2 drastically
decreased the culturability of the B. bruxellensis strain, but bound SO2 had no effect
on the culturability or viability of either of the two types of microorganisms. Oxygen
addition to the B. bruxellensis strain also led to a drastic increase in viability and
culturability. It is thus clear that SO2 and O2 management in the cellar is of critical
importance for the winemaker to produce wines that have not been spoiled by
Brettanomyces or acetic acid bacteria. This study should contribute to the
understanding of the factors responsible for the growth and survival of
Brettanomyces and acetic acid bacteria in wine, but it should be kept in mind that
only one strain of each microorganism was used. This should be expanded in future
to include more strains that occur in wine.
The second part of this study investigated the effect of micro-oxygenation on four
different South African red wines. It was found that the micro-oxygenation led to an
increase in the colour density and SO2 resistant pigments of the two wines in which micro-oxygenation was started just after the completion of malolactic fermentation. In
one of these wines, a tasting panel preferred the micro-oxygenation treated wines to
the control. In the other two red wines, in which the micro-oxygenation was started
seven months after the completion of malolactic fermentation, very little colour
increase was observed. One of these two wines was also matured in an oak barrel,
where the change in phenolic composition was on par with the treated wines. A
prolonged period of micro-oxygenation, however, led to this wine obtaining an
oxidised, over-aged character. Micro-oxygenation and maturation in an oak barrel
also enhanced the survival of acetic acid bacteria and Brettanomyces in this wine.
Micro-oxygenation can hence be used by the wine producer on young red wines to
enhance the quality of the wine, but should be applied with care in older red wines.
Future research into micro-oxygenation should focus on whether it can simulate an
oak barrel. More research into the effect of micro-oxygenation on the sensory profile
of the wine is needed.
As mentioned, the addition of O2 can lead to oxidative degradation of wine. The
brown colour in wine is often used as an indication of oxidation, but oxidative aromas
can be perceived before a drastic increase in the brown colour has been observed in
red wine.
The third part of this study was to assess the possible use of Fourier Transform
Infrared Spectroscopy (FTIR) to measure the progression of oxidation in Pinotage red
wines. Three wines were used in this study and clear separation between the control
and aerated wines was observed by using Principle Component Analysis (PCA).
Sensory analysis of these wines confirmed this observation, with a reduction
especially in berry fruit and coffee characters and an increase first in potato skin and
then acetaldehyde aroma characters as the oxidation progressed. PCA analysis also
revealed that in certain wines the visible spectrum of light did not indicate the
progression of oxidation as sensitively as with the use of FTIR. This also correlated
with the inability of the panel to observe a drastic colour change. FTIR should be
further investigated as a possible means of monitoring oxidation in wine and this
study should be expanded to wines made from other cultivars as well