Optimization of Grapevine Leafroll Detection on White Cultivars by Sentinel Canes

Project Number
IWBT 01-14

Project title
Expression of a glucose oxidase gene in yeast for the production of wine with reduced levels of alcohol

Project leader
Van Rensburg, P

University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology

Team members
Du Toit, M A
Muller, C A
Cordero Otero, R R
Malherbe, D F
Kriel, J H

Project description
The development of a recombinant wine yeast strain that would be able to reduce the levels of alcohol in wine and also has the possibility to reduce the risk of microbial spoilage and oxidation in wine.

In recent years there has been increased international interest and indeed increased consumer demand for reduced-alcohol, low-alcohol and de-alcoholised wines. In South Africa’s warm climate grapes have to be harvested earlier than usual otherwise the sugar concentration will be too high and with concomitant excessively high levels of alcohol in the final product. Because the grapes are harvested earlier not all of their flavour and aroma components have developed. Commercial interest has also been stimulated by the potential for savings in taxes on the reduced alcohol content in these classes of wines.

Several processes have been applied for the removal or reduction of alcohol in wine, often in combination, including thermal, distillation, membranes, extraction, adsorption, centrifugation, freeze concentration, and partial fermentation. An alternative approach was introduced with the concept of treating grape juice from mature fruit with glucose oxidase (GOX) to reduce the glucose content of the juice, which after fermentation produces wine with a reduced alcohol content. Glucose oxidase is therefore of considerable industrial importance. It is also widely applied for the determination of glucose in body fluids and in removing residual glucose or oxygen from foods and beverages. It has also been advocated as a mechanism for improving wine sensory balance and for use in wine stability. Furthermore it is believed that glucose oxidase resulted products also possess the ability to suppress or inhibit the growth of certain microorganisms. The glucose oxidase system has been used safely and effectively since the 1950’s in the food and beverage industries. In general it has been used to improve shelf life and to maintain flavour and colour stability. Foods subject to deterioration in the presence of glucose (Maillard reaction) are protected by the enzymatic oxidation of glucose. When oxidation is the causative agent of deterioration (colour fading, rancidity, flavour instability etc.) glucose oxidase provides protection by catalytically exhausting the oxygen present.

Glucose oxidase metabolises glucose into gluconic acid. Thus not all the glucose is metabolised into alcohol. The possible effect of glucose oxidase enzyme on wine quality parameters was investigated using descriptive analysis of wine appearance and flavour attributes. The relative intensities of mouth-feel attributes and length of flavour were also evaluated. The results of the effect of the glucose oxidase enzyme were encouraging. Wine yeast, transformed with heterologous glucose oxidase gene, would secrete the enzyme during fermentation into the grape must and will enable the winemaker to produce wine, from must containing a higher sugar concentration, with a 1 to 2% lower alcohol concentration. This wine yeast also has the possibility to be used to reduce the risk of microbial spoilage and oxidation.

Malherbe, D F, Du Toit, M, Cordero Otero, R R, Pretorius, I S and Van Rensburg, P. 2004. Low-alcohol yeasts that are able to bio-preserve wine. Paper presented at the 13th Congress of the South African Society for Microbiology. 2-5 April, Stellenbosch, South Africa.

Malherbe, D F, Du Toit, M, Cordero Otero, R R, Pretorius, I S and Van Rensburg, P. 2004. Developing low-alcohol yeasts that are also able to bio-preserve wine. Paper presented at 12th Australian Wine Industry Technical Conference. 24-29 July, 2004, Melbourne, Victoria.

Malherbe, D F, Du Toit, M, Cordero Otero, R R, Pretorius, I S and Van Rensburg, P. 2004. Low-alcohol yeasts that are able to bio-preserve wine. Paper presented at the 19th International Symposium Food Micro 2004. 12-16 September, Portoroza, Slovenia.

Van Rensburg, P, Pretorius, I S. 2000. Enzymes in winemaking: Harnessing natural catalysts for efficient biotransformations – review, South African Journal of Enology and Viticulture, v. 21 Special issue (p. 52-73)


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