Fining must or wine with proteins of animal origin such as out of egg or milk is a traditional treatment. On the other hand proteins of milk or egg can cause intolerances and allergies in some people. Traces of these proteins out of egg or milk may remain in the wine after fining and can cause such health problems. Treatment of must or wine with egg or milk products has thus to be declared towards the consumer in the European Union (regulation (EC) No 579/2012) since 2012. Therefore alternative sources of proteins were looked for.The objective of the studies of this doctoral thesis was to obtain protein extracts by yeast autolysis that could be used for fining treatments of musts and wines.Mutants of a yeast strain of the species Saccharomyces cerevisiae were created by mutagenesis induced by UV-radiation. These mutants showed reduced viability and autolysis when exposed to stressors such as elevated temperature or change in osmotic pressure. A methodology was established at laboratory scale to produce protein extracts out of selected mutants which were forced to autolyse by stress conditions. Upscaling of the protein extraction process to industrial conditions was possible.The yeast protein extracts could successfully clarify red wines and had a clarification capacity and kinetic as well as an influence on wine colour comparable or similar to the traditional fining agent gelatine. The sensory quality of the red wines was maintained after fining with yeast protein extracts and no aroma impressions typical of other yeast extracts used in the food industry such as cheesy or meaty notes were detected in the wines. A partial characterization of proteins, glycoproteins and sugars (after acid hydrolysis) of the yeast protein extract was also performed. The quantitative analysis of proteins by two methods gave differing results. Therefore, no simple conclusion about the relation between protein concentration and clarification behaviour (onset of visible flocculation and speed of sedimentation) could be drawn. A qualitative analysis of molecular masses by SDS-PAGE (electrophoresis on polyacrylamide gels after unfolding of proteins with SDS (sodium dodecyl sulphate)) showed that proteins were in a mass range at the end of the developing process of the industrial extract comparable to extract produced at the laboratory. However, no direct relation between the profile of molecular masses of the protein extracts and their clarification performance and influence on wine colour could be stated. All yeast protein extracts contained mannoproteins and mannose was detected in them after acid hydrolysisYeast protein extracts are now permitted for fining of must and wine in the European Union (regulation (EC) No 144/2013) and offer an alternative for wine professionals.
Verknüpfung zu Publikationen oder weiteren Datensätzen
