Evaluating the effect of different winemaking techniques on ethanol production

[摘要] Over the years, different techniques have been used to legally reduce the ethanol content ofwines. Several physical processes are available for producing wines with less alcohol. Despitetheir efficacy, these treatments have a capital and operational cost influence. They can alsoaffect the concentration of other wine components. On the other hand, vast amount of researchhas been conducted through genetic modification of wine yeast strains in order to reduce theethanol yield of Saccharomyces cerevisiae by diverting sugar metabolism towards various byproducts.However, genetically modified yeasts are not currently accepted in most wineindustries worldwide, including South Africa. Therefore, other approaches need to beenvisaged.Commercial enzymes are commonly added during winemaking. Most enzymes essential forvinification naturally occur in grapes, but are inefficient under pH and sulphur levels associatedwith winemaking. Enzymes of fungal origin are resistant to such conditions. The most widelyused commercial enzymes include pectinases, hemicellulases, glucanases and glycosidases.With the exception of glucanases, produced by Trichoderma harzianium, all the other enzymesare 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 beforefermentation 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 thebaking industry. Glucose oxidase catalyses the oxidation of glucose to gluconic acid andhydrogen peroxide in the presence of molecular oxygen.Gluzyme was initially used in synthetic grape must where different enzyme concentrationsand factors influencing its activity were investigated for its use in winemaking. The resultsshowed that up to 0.5% v/v less alcohol were obtained using an enzyme concentration of 20 kUcompared to the control. This reduction in alcohol was increased to 1 and 1.3% v/v alcohol atpH 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 treatedwines after fermentation contained 0.68% v/v less alcohol than the control samples at 30 kUenzyme. Colour and volatile flavour compounds of treated wine did not differ significantly fromthe untreated samples. Lower free anthocyanin and total phenol concentrations in treated thancontrol samples were observed, possibly due to the hydrogen peroxide oxidation which couldhave led to polymerisation.The present study has clearly demonstrated that Gluzyme may be used in winemaking toproduce reduced-alcohol wine without affecting its colour and aroma compounds. The enzymein its current form is however, not ideal for winemaking; other forms such as liquid or powderform 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 studyingthe effects of Gluzyme in various grape must in semi-industrial scale. A tasting panel shouldalso evaluate its impact on the organoleptic properties and the overall quality of the resulting wines.

[发布机构] Stellenbosch University