Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Spoilage, be it due to microbial actions, chemical reactions or both, poses a serious
threat to the food and beverage industries. Not only can spoilage lead to great
economic losses, but it can also cause industries to lose their competitive edge in the
economic and consumer market. Considering all the modern technologies and the
range of preservation techniques that are available, it is surprising that spoilage is still
an economic problem. Wine spoilage due to unpalatable bitterness, and the role of
lactic acid bacteria (LAB) in causing this bitterness, have received much attention
over the years, but no definite understanding has yet emerged.
The first objective of this study was to isolate, enumerate and identify the LAB
from three red grape varieties, viz. Pinotage, Merlot and Cabernet Sauvignon. The
LAB populations on the grapes of all three varieties ranged from 102 to 104 cfu/ml
during the 2001 and 2002 harvest seasons. The Cabernet Sauvignon grapes had
slightly higher numbers than the Pinotage and Merlot. The LAB population in the
Cabernet Sauvignon, Pinotage and Merlot wines after completion of the alcoholic
fermentation ranged from 102 to 105 cfu/ml, while during 2002 the numbers in wine
undergoing malolactic fermentation (MLF) ranged from 104 to 108 cfu/ml. The
isolated LAB were divided into the three metabolic groups, with 59% belonging to the
facultatively heterofermentative group, 26% to the obligately heterofermentative
group and 15% to the obligately homofermentative group. The isolates were
identified by means of species-specific primers as Leuconostoc mesenteroides (4),
Oenococcus oeni (28), Lactobacillus brevis (15), Lb. hilgardii (15), Lb. plantarum
(98), Lb. pentosus (12), Lb. paraplantarum (3), Lb. paracasei (28),
Pediococcus acidilactici (2) and Pediococcus spp. (35). The most predominant
species isolated was Lb. plantarum, followed by Pediococcus spp. The results
suggest that Pinotage carries a more diverse LAB population in comparison to Merlot
and Cabernet Sauvignon.
The second objective of this study was to determine the presence of the glycerol
dehydratase gene in the LAB strains by using the G01 and G02 primers. Twenty-six
strains tested positive, namely Lb. plantarum (15), Lb. pentosus (1), Lb. hilgardii (5),
Lb. paracasei (2), Lb. brevis (2) and a Pediococcus spp. (1). Interestingly, 62% of
these strains were isolated from Pinotage. The strains all had the ability to degrade
glycerol by more than 90%, and no significant differences were observed between
the species. The GO-possessing strains exhibited varying degrees of inhibition
towards Gram-positive and Gram-negative bacteria, and the results suggest that this
inhibition activity may be similar to that of reuterin, which is produced by Lb. reuteri.
This study can form the foundation for unravelling the causes of bitterness in red
wines. Combining the results of this study with analytical, sensory and molecular
data may very well provide the industry with valuable tools with which to combat the
occurrence of bitterness. / AFRIKAANSE OPSOMMING: Bederf as gevolg van mikrobiese aksies, chemiese reaksies of beide, hou 'n groot
bedreiging vir die voedsel- en drankbedrywe in. Nie net kan bederf lei tot groot
ekonomiese verliese nie, maar dit kan ook veroorsaak dat bedrywe hul
kompeterende voordeel in die ekonomiese en verbruikersmarkte verloor. As die
moderne tegnologie en die reeks preserveringstegnieke wat beskikbaar is, in ag
geneem word, is dit verbasend dat bederf steeds 'n ekonomiese probleem is.
Wynbederf as gevolg van oormatige bitterheid en die rol van melksuurbakterieë
(MSB) in die ontwikkeling van hierdie bitterheid het oor die jare heen baie aandag
geniet, maar geen definitiewe verklaring is nog daarvoor gevind nie.
Die eerste doelwit van hierdie studie was om MSB vanaf drie rooidruifvariëteite,
nl. Pinotage, Merlot en Cabernet Sauvignon, te isoleer, te kwantifiseer en te
identifiseer. Die MSB-populasies op die druiwe van al drie variëteite het gedurende
die 2001- en 2002-parsseisoene tussen 102 en 104 kvu/ml gevarieer. Die Cabernet
Sauvignon-druiwe het effens hoër getalle as die Pinotage- en Merlot-druiwe gehad.
Die MSB-populasies in die Cabernet Sauvignon-, Pinotage- en Merlot-wyne aan die
einde van die alkoholiese fermentasie het tussen 102 en 1055 kvu/ml gevarieer.
Gedurende 2002 het die MSB-getalle in die wyne waarin appelmelksuurgisting
(AMG) aan die gang was tussen 104 en 108 kvu/ml gevarieer. Die geïsoleerde MSB
was onderverdeel in die drie metaboliese groepe, met 59% wat behoort aan die
fakultatiewe, heterofermentatiewe groep, 26% aan die obligate, heterofermentatiewe
groep en 15% aan die obligate, homofermentatiewe groep. Die isolate is
geïdentifiseer as Leuconostoc mesenteroides (4), Oenococcus oeni (28),
Lactobacillus brevis (15), Lactobacillus hi/gardii (15, Lactobacillus p/antarum (98),
Lactobacillus pentosus (12), Lactobacillus parap/antarum (3), Lactobacillus paracasei
(28), Pediococcus acidi/actici (2) en Pediococcus spp. (35) deur middel van spes iespesifieke
inleiers. Die mees algemeen geïsoleerde spesies was Lb. p/antarum,
gevolg deur Pediococcus spp. Die resultate impliseer dat Pinotage 'n meer
uiteenlopende MSB-populasie in vergelyking met Merlot en Cabernet Sauvignon dra.
Die tweede doelwit van hierdie studie was om die teenwoordigheid van die
gliseroldehidratase-geen in die MSB-isolate deur middel van die GD1- en GD2-
inleiers te bepaal. Ses-en-twintig isolate was positief, nl. Lb. p/antarum (15), Lb.
pentosus (1), Lb. hi/gard;; (5), Lb. paracasei (2), Lb. brevis (2) en 'n Pediococcus spp.
(1). 'n Interessante resultaat was dat 62% van hierdie isolate vanaf Pinotage
geïsoleer is. Die isolate was almal in staat om meer as 90% van die gliserol te
gebruik en geen noemenswaardige verskille is tussen die isolate waargeneem nie.
Die GD-bevattende isolate het verskillende grade van inhibisie teenoor Grampositiewe
en Gram-negatiewe bakterieë getoon, en die resultate impliseer dat hierdie
inhiberende aktiwiteit dieselfde is as dié van reuterin wat deur Lb. reuteri
geproduseer word. Hierdie studie kan dus die basis vorm vir die ontrafeling van die oorsake van
bitterheid in rooiwyne. Deur die resultate van hierdie studie met analitiese,
sensoriese en molekulêre data te kombineer, kan die wynbedryf voorsien word van
waardevolle metodes om die voorkoms van bitterheid mee te bekamp.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53271 |
| Date | 03 1900 |
| Creators | Krieling, Shannon Janine |
| Contributors | Du Toit, M., Pretorius, I. S., 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 | 72 pages : illustrations |
| Rights | Stellenbosch University |
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