Browsing by Author "Styger, G."

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    Genetic analysis of the metabolic pathways responsible for aroma metabolite production by Saccharomyces cerevisiae.
    (SPRINGER, 233 SPRING STREET, NEW YORK, USA, NY, 10013, 2013) Styger, G.; Jacobson, D.; Prior, B. A.; Bauer, Florian
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    The effect of increased branched-chain amino acid transaminase activity in yeast on the production of higher alcohols and on the flavour profiles of wine and distillates
    (2006) Lilly, M.; Bauer, Florian; Styger, G.; Lambrechts, M. G.; Pretorius, I. S.
    In Saccharomyces cerevisiae, branched-chain amino acid transaminases (BCAAT ases) are encoded by the BAT1 and BAT2 genes. BCAATases catalyse the transfer of amino groups between those amino acids and α-keto-acids, α-Keto-acids are precursors for the biosynthesis of higher alcohols, which significantly influence the aroma and flavour of yeast-derived fermentation products. The objective of this study was to investigate the influence of BAT-gene expression on general yeast physiology, on aroma and flavour compound formation and on the sensory characteristics of wines and distillates. For this purpose, the genes were overexpressed and deleted in a laboratory strain, BY4742, and overexpressed in an industrial wine yeast strain, VIN13. The data show that, with the exception of a slow growth phenotype observed for the BAT1 deletion strain, the fermentation behaviour of the strains was unaffected by the modifications. The chemical and sensory analysis of fermentation products revealed a strong correction between BAT gene expression and the formation of many aroma compounds. The data suggest that the adjustment of BAT gene expression could play an important role in assisting winemakers in their endeavour to produce wines with specific flavour profiles. © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved.
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    Wine flavor and aroma
    (2011) Styger, G.; Prior, B.; Bauer, Florian
    The perception of wine flavor and aroma is the result of a multitude of interactions between a large number of chemical compounds and sensory receptors. Compounds interact and combine and show synergistic (i.e., the presence of one compound enhances the perception of another) and antagonistic (a compound suppresses the perception of another) interactions. The chemical profile of a wine is derived from the grape, the fermentation microflora (in particular the yeast Saccharomyces cerevisiae), secondary microbial fermentations that may occur, and the aging and storage conditions. Grape composition depends on the varietal and clonal genotype of the vine and on the interaction of the genotype and its phenotype with many environmental factors which, in wine terms, are usually grouped under the concept of "terroir" (macro, meso and microclimate, soil, topography). The microflora, and in particular the yeast responsible for fermentation, contributes to wine aroma by several mechanisms: firstly by utilizing grape juice constituents and biotransforming them into aroma- or flavor-impacting components, secondly by producing enzymes that transform neutral grape compounds into flavor-active compounds, and lastly by the de novo synthesis of many flavor-active primary (e.g., ethanol, glycerol, acetic acid, and acetaldehyde) and secondary metabolites (e.g., esters, higher alcohols, fatty acids). This review aims to present an overview of the formation of wine flavor and aroma-active components, including the varietal precursor molecules present in grapes and the chemical compounds produced during alcoholic fermentation by yeast, including compounds directly related to ethanol production or secondary metabolites. The contribution of malolactic fermentation, ageing, and maturation on the aroma and flavor of wine is also discussed. © 2011 Society for Industrial Microbiology.