Identifying genes that impact on aroma profiles produced by Saccharomyces cerevisiae and the production of higher alcohols

Abstract

During alcoholic fermentation, many volatile aroma compounds are formed by Saccharomyces cerevisiae, including esters, fatty acids, and higher alcohols. While the metabolic network that leads to the formation of these compounds is reasonably well mapped, surprisingly little is known about specific enzymes involved in specific reactions, the regulation of the network, and the physiological roles of individual pathways within the network. Furthermore, different yeast strains tend to produce significantly different aroma profiles. These differences are of tremendous biotechnological interest, since producers of alcoholic beverages such as wine and beer are searching for means to diversify and improve their product range. Various factors such as the redox, energy, and nutritional balance of a cell have previously been suggested to directly or indirectly affect and regulate the network. To gain a better understanding of the regulations and physiological role of this network, we screened a subset of the EUROSCARF strain deletion library for genes that, when deleted, would impact most significantly on the aroma profile produced under fermentative conditions. The 10 genes whose deletion impacted most significantly on higher alcohol production were selected and further characterized to assess their mode of action within or on this metabolic network. This is the first description of a large-scale screening approach using aroma production as the primary selection criteria, and the data suggest that many of the identified genes indeed play central and direct roles within the aroma production network of S. cerevisiae.

Effect of Skin Contact Before and During Alcoholic Fermentation on the Chemical and Sensory Profile of South African Chenin Blanc White Wines

“…Moreover, the most important flavour and aroma compounds formed from amino acids are higher alcohols and their associated esters and volatile acids. The presence of skins during fermentation could have favoured the availability of different aromaprecursor amino acids, therefore influencing the wine's final volatile composition (Styger et al, 2011). In addition, the presence in skin contact wines of higher available assimilable nitrogen levels could influence yeast CO 2 production, which also might cause an important volatilisation with CO 2 evolution during fermentation (Dennis et al, 2012).…”

Metabolic engineering of Corynebacterium crenatium for enhancing production of higher alcohols

“…1. Previous studies have shown that metabolic perturbation derived from mutation of genes associated with the biosynthesis and degradation pathways of leucine, isoleucine, and valine in yeast can improve C4~C5 higher alcohol yield based on these two pathways242526. Mutating acetohydroxyacid synthase (AHAS) gene responsible for transforming pyruvic acid into α-acetolactic acid can reduce the generation of the diacetyl, thereby improving the production of higher alcohols.…”

Flavour-active wine yeasts

“…Sensory analysis confirmed that the overexpression of BAT1 and BAT2 had an impact on aroma profiles of wines and distillates (Lilly et al 2006b). The perturbation of the BAT genes not only affects the concentrations of metabolites directly linked to these genes, but also other aroma metabolites not directly related to higher alcohols, highlighting the complexities of the interconnections within such complex metabolic networks (Lilly et al 2006b; Styger et al 2011a). BAT2 seems to have a more prominent role than BAT1 in the Ehrlich pathway.…”

“…To date, five proteins have been implicated in α-keto decarboxylation: the pyruvate decarboxylases Pdc1p, Pdcp5 , and Pdc6p; the phenylpyruvate decarboxylase Aro10p; and the probable carboxylase Thi3p (Styger et al 2011a), which plays a role as a regulatory protein of the enzymes involved in thiamine biosynthesis (Mojzita and Hohmann 2006; Nosaka et al 2005). …”