Co-expression of aroma liberating enzymes in a wine yeast strain

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dc.contributor.advisor Van Rensburg, P.
dc.contributor.advisor Zietsman, Anscha
dc.contributor.author De Klerk, Daniel
dc.contributor.other University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
dc.date.accessioned 2009-02-23T09:24:14Z en_ZA
dc.date.accessioned 2010-06-01T08:35:41Z
dc.date.available 2009-02-23T09:24:14Z en_ZA
dc.date.available 2010-06-01T08:35:41Z
dc.date.issued 2009-03
dc.identifier.uri http://hdl.handle.net/10019.1/1888
dc.description Thesis (Msc (Viticulture and Oenology. Institute for Wine Biotechnology))--University of Stellenbosch, 2009.
dc.description.abstract Monoterpenes are important aroma compounds in certain grape varieties such as Muscat, Gewürztraminer and Riesling and are present as either odourless, glycosidically bound complexes or as free aromatic monoterpenes. These complexes occur as monoglucosides or, when present as diglycosides, most commonly as 6-O-α-L-arabinofuranosyl-β-D-glucopyranosides of mainly linalool, geraniol, nerol and citronellol. The release of monoterpenes from non-volatile glycosidically bound precursors occurs either by acid hydrolysis or enzymatic hydrolysis. High temperature acid hydrolysis causes a rearrangement of the monoterpene aglycones and a decrease in the aroma and changes in the aromatic characteristics of monoterpenes and is therefore not suitable. Enzymatic hydrolysis does not modify the monoterpene aglycones and can be an efficent method to release potentially volatile monoterpenes. α-L-arabinofuranosidase and β-glucosidase are important enzymes responsible for the liberation of monoterpene alcohols from their glycosides. Glycosidases from Vitis vinifera and Saccharomyces cerevisiae are severely inhibited by winemaking conditions and this leads to unutilized aroma potential, while commercial preparations of aroma liberating enzymes are crude extracts that often have unwanted and unpredictable side effects. It is therefore of interest to investigate alternative measures to release glycosidically bound monoterpenes to increase the floral aroma of wine without side activities that impact negatively on wine. Heterologous α-L-arabinofuranosidases and β-glucosidases have previously been expressed in S. cerevisiae and these studies have evaluated and found increased glycosidic activities against both natural and synthetic substrates. In this study, we expressed the Aspergillus awamori α-L-arabinofuranosidase (AwAbfB) in combination with either the β-glucosidases Bgl2 from Saccharomycopsis fibuligera or the BglA from Aspergillus kawachii in the industrial yeast strain S. cerevisiae VIN13 to facilitate the sequential enzymatic hydrolysis of monoterpene diglycosides. Enzyme assays and GC-FID (Gas Chromatography with a Flame Ionization Detector) results show a significant increase in the amount of free monoterpene concentrations under winemaking conditions in the strain co-expressing the AwAbfB and the Bgl2. The increases in free monoterpene levels obtained were similar to those obtained with a commercial enzyme preparation, LAFAZYM AROM. Sensorial evaluation confirmed the improvement in the wine aroma profile, particularly the floral character. This yeast strain permits a single culture fermentation which improves the sensorial quality and complexity of wine. Further investigations on the factors influencing the stability and reactivity of monoterpenes during alcoholic fermentation are needed. en
dc.language.iso en
dc.publisher Stellenbosch : University of Stellenbosch
dc.subject Dissertations -- Wine biotechnology en
dc.subject Theses -- Wine biotechnology en
dc.subject.lcsh Enzymes -- Industrial applications en
dc.subject.lcsh Wine -- Flavor and odor en
dc.subject.lcsh Wine and wine making -- Microbiology en
dc.subject.lcsh Monoterpenes en
dc.subject.lcsh Saccharomyces cerevisae en
dc.title Co-expression of aroma liberating enzymes in a wine yeast strain en
dc.type Thesis
dc.rights.holder University of Stellenbosch


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