Thesis (MscAgric (Viticulture and Oenology))--Stellenbosch University, 2008. / Over the years, different techniques have been used to legally reduce the ethanol content of
wines. Several physical processes are available for producing wines with less alcohol. Despite
their efficacy, these treatments have a capital and operational cost influence. They can also
affect the concentration of other wine components. On the other hand, vast amount of research
has been conducted through genetic modification of wine yeast strains in order to reduce the
ethanol yield of Saccharomyces cerevisiae by diverting sugar metabolism towards various byproducts.
However, genetically modified yeasts are not currently accepted in most wine
industries worldwide, including South Africa. Therefore, other approaches need to be
envisaged.
Commercial enzymes are commonly added during winemaking. Most enzymes essential for
vinification naturally occur in grapes, but are inefficient under pH and sulphur levels associated
with winemaking. Enzymes of fungal origin are resistant to such conditions. The most widely
used commercial enzymes include pectinases, hemicellulases, glucanases and glycosidases.
With the exception of glucanases, produced by Trichoderma harzianium, all the other enzymes
are produced by Aspergillus niger.
In this study, the possibility of using Gluzyme Mono® 10.000 BG (Gluzyme) (Novozymes,
South Africa) to reduce the glucose content of synthetic grape must and grape must before
fermentation in order to produce wine with a reduced alcohol content was investigated.
Gluzyme is a glucose oxidase preparation from Aspergillus oryzae, currently being used in the
baking industry. Glucose oxidase catalyses the oxidation of glucose to gluconic acid and
hydrogen peroxide in the presence of molecular oxygen.
Gluzyme was initially used in synthetic grape must where different enzyme concentrations
and factors influencing its activity were investigated for its use in winemaking. The results
showed that up to 0.5% v/v less alcohol were obtained using an enzyme concentration of 20 kU
compared to the control. This reduction in alcohol was increased to 1 and 1.3% v/v alcohol at
pH 3.5 and pH 5.5 respectively in aerated synthetic grape must using 30 kU enzyme.
Secondly, Gluzyme trials were carried out using Pinotage grape must. Gluzyme treated
wines after fermentation contained 0.68% v/v less alcohol than the control samples at 30 kU
enzyme. Colour and volatile flavour compounds of treated wine did not differ significantly from
the untreated samples. Lower free anthocyanin and total phenol concentrations in treated than
control samples were observed, possibly due to the hydrogen peroxide oxidation which could
have led to polymerisation.
The present study has clearly demonstrated that Gluzyme may be used in winemaking to
produce reduced-alcohol wine without affecting its colour and aroma compounds. The enzyme
in its current form is however, not ideal for winemaking; other forms such as liquid or powder
form should be considered if the enzyme is to be used under winemaking conditions.
Future work should focus on evaluating the potential new form of the enzyme and studying
the effects of Gluzyme in various grape must in semi-industrial scale. A tasting panel should
also evaluate its impact on the organoleptic properties and the overall quality of the resulting wines.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2493 |
| Date | 12 1900 |
| Creators | Biyela, Busisiwe Nokukhanya E. |
| Contributors | Divol, Benoit T., Du Toit, Wessel J., Van Rensburg, Pierre, Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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