Thesis (PhD (Food Science))--University of Stellenbosch, 2006. / The aim of the study was to provide the South African wine industry with guidelines for the production of
Pinotage wines with optimal total antioxidant capacity (TAC), while retaining sensory quality. The contribution of
individual phenolic compounds to the wine TAC is important in this regard. The wine TAC was measured with
the 2,2 -azino-di(3-ethylbenzo-thiazoline-sulphonic acid radical cation) (ABTS +) scavenging assay. The
contributions of individual phenolic compounds to the wine TAC were calculated from their content in the wines
and the Trolox equivalent antioxidant capacity (TEAC) of pure phenolic standards. The effects of climate region,
vine structure, enological techniques (pre-fermentation maceration, juice/skin mixing, addition of commercial
tannins, extended maceration) and maturation (oak barrels, alternative oak products, oxygenation) on the phenolic
composition, TAC and sensory quality of Pinotage wines were also investigated.
The TEAC values of quercetin-3-galactoside, isorhamnetin and peonidin-3-glucoside were reported for the
first time. TEAC values observed for most compounds were much lower than those reported previously, although
TEAC values for gallic acid, caftaric acid, caffeic acid and kaempferol were consistent with some previous
reports. Caftaric acid and malvidin-3-glucoside were the largest contributors to the wine TAC. The contents of
monomeric phenolic compounds and procyanidin B1, however, only explained a small amount (between 11 and
24%) of the wine TAC, with the remaining TAC attributed to oligomeric and polymeric phenolic compounds and
other unknown compounds. Some synergy between different monomeric phenolic compounds was also
demonstrated.
All the viticultural and enological factors investigated affected the phenolic composition of Pinotage wines,
while the wine TAC was only affected by some treatments. Changes in wine TAC could not always be explained
by changes in phenolic composition as the contribution of oligomeric, polymeric and unknown compounds could
not be assessed, but could play a large role. Differences in wine colour were also difficult to explain due to the
large number of factors involved and the dark wine colour, which made objective measurements difficult. The
concentration of vitisin A, an orange-red pyranoanthocyanin, was increased consistently as a result of prefermentation
maceration treatments and affected the wine colour of oxygenated wines. Increased wine TAC was
observed when cultivating Pinotage grapes on bush vines and in cooler climatic regions, compared to cultivation
on trellised vines in warmer climatic regions. All the climatic regions and vine structure treatments, however,
resulted in wines with good sensory quality. In terms of enological techniques, pumping-over, as opposed to
punching-down and rotor treatments, is not recommended as a juice/skin mixing technique, due to reduced wine
TAC, colour and sensory quality. Pre-fermentation maceration, addition of commercial tannin preparations, and
oak maturation using traditional and alternative treatments, resulted in improved sensory quality, but with no
change in wine TAC. However, optimisation of the tannin addition protocol may result in increased wine TAC if
additions are made after fermentation or higher dosages are used. Oxygenation of Pinotage wine needs further
investigation to optimise the protocol, as improvements to the wine colour and fullness were observed for some
treatments, but loss of sensory quality and TAC were observed in most cases.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1300 |
| Date | 12 1900 |
| Creators | De Beer, Dalene |
| Contributors | Joubert, E., Marais, J., Manley, M., University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science. |
| Publisher | Stellenbosch: University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 5458697 bytes, application/pdf |
| Rights | University of Stellenbosch |
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