Yeast metabolites

This mechanism can be extrapolated to other enolizable precursors potentially present in wine, including yeast metabolites such as a-ketoglutatic acid and 2-hydroxybutan-2-one, but also to acetone, which can react with anthocyanins during solvent extraction proced-ures. The resulting products are pyranoanthocyanins as presented in Figure 5.11, with Rs = CH2-COOH, R4 = COOH R3 = H, R4 = CHOH CH3 R3 = H, R4 = CH3. 

Benabdeljalil, C. et al.. Evidence of new pigments resulting from reaction between anthocyanins and yeast metabolites. Set Aliment, 20, 203, 2000. 

The fermentation usually is complete within 30 or 40 days. During this period additional anthocyanins are extracted from pomace and the color stabilizes due to polymerization between the anthocyanins and tannins. Winemakers call this process pomace "maturation". Moreover, due to the increasing alcohol concentration, many other metabolites are extracted from the pomace. In addition, yeast metabolites contribute to the aromatic complexity of the wine. 

Pulcherriminic acid (H 6), 1, 5-dihydroxy-3, 6-diisobutyl-2(l//)-pyrazinone 4-oxide, a Candida sp yeast metabolite, initially as an Fe complex (pul-cherrimin) [957-86-8],... 

These various reactions involving yeast metabolites and non-pigmented phenolics are also believed to lead to changes that affect the astringency of tannins (Eglinton et al. 2005). Sensory evaluation of wines made with two Saccharomyces yeast which differed in acetaldehyde production led to differences in mouth-feel attributes associated with tannins, namely grainy, silky, velvet, drying and pucker. 

These last works were highly significant since, In spite of the abundance of volatiles formed by yeast during fermentation, these non-terpene compounds did not vary systematically among the varieties Furthermore, the yeast metabolites did not mask the distinguishing aroma properties of the grape monoterpenes. 

While the identity of the relevant yeast metabolites in the fermented medium sampled at day 2 needs to be clarified, previously published data have provided some evidence about the role of acetaldehyde-mediated condensation of catechin with MSG (13-20). We therefore aimed to extend these model studies and to confirm chemical formation of pigmented polymers from condensed tannins, which are commercially used in red winemaking, and anthocyanins. The model reactions were conducted with vatying concentrations of acetaldehyde and SO2 as shown in Table 2 and analysed by HPLC after 2, 4 and 7 days. After 7 days visible precipitation of unidentified material started to occur in presence of acetaldehyde and the reactions were discontinued. 

The third group of wine pigments corresponds to pyranoanthocyanins (fig. 3c) formed, as described in die anthocyanin reactivity section, by reaction of genuine anthocyanins with yeast metabolites released during fermentation (d)... 

Finally, the relative amounts of anthocyanin-flavanol pigments and anthocyanin-anthocyanin pigments obviously depend on the anthocyanin to flavanol ratio. However, the kinetics of anthocyanin polymerization and flavanol-anthocyanin reactions as well as the quantities of the resulting pigments in wine remain to be established. Consequently, the importance of these processes with respect to other anthocyanin reactions (hydration and subsequent degradation, cycloadditon with yeast metabolites) and the impact of resulting polymeric anthocyanins on wine quality are speculative. 

Although acetaldehyde is also a major yeast metabolite, it can be... 

In this reaction, a fourth ring was formed, which was considered to be responsible for their higher stability than the original anthocyanins (20). The components which reacted with anthocyanins include 4-vinylphenol, hydroxycinnamic acids, acetone, and several yeast metabolites such as acetaldehyde and pyruvic acid (20-28). 

A mechanism for cycloaddition on anthocyanins involving various yeast metabolites was demonstrated by Cameira dos Santos et al. (1996). This consists of a cycloaddition between a flavylium and compounds with a polarized double bond. The new pigments formed are generally orange, stable and insensitive to variations in both pH and sulfur dioxide. 

Fermenting must is a reducing medium, so no oxidation can occm, but reactions with yeast metabolites may give the color an orange tinge. Direct A+ T reactions also produce colorless compounds that react when the wine is... 

Hein, E.M. and Hayen, H. (2012) Comparative lipidomic profiling of S. cerevisiae and four other hemiascomycetous yeasts. Metabolites 2, 254-267. 

The behavioral activity of the compounds isolated from the yeasts was tested in laboratory bioassays on pedestrian male and female D. frontalis (446, 448). In this bioassay procedure, a standard attractant mixture of frontalin trani-verbenol loblolly turpentine (1 1 12), referred to subsequently as the triplicate standard, was used. None of the yeast metabolites exhibited any activity alone. The two acetate esters were found to enhance the attractiveness, mainly of males, to the triplicate standard, especially at low concentrations of triplicate standard and ester. 2-Phenyl-ethanol decreased the response of females to the triplicate standard. More recent results on the inhibitory effect of 2-phenylethanol on the response of females has shown that a concentration of triplicate standard that gives a response of 50—60% can be substantially decreased by the addition of 2-phenylethanol at concentrations up to 10 times lower than that of the triplicate standard (Brand, unpublished data). 

Brand, J. M., J. Schultz, S. J. Barras, L. J. Edson, T. L. Payne, and R. L. Hedden Bark beetle pheromones enhancement of Dendroctonus frontalis (Coleoptera Scolytidae) aggregation pheromone by yeast metabolites in laboratory bioassays. J. Chem. Ecol. 3,651—666 (1977). 

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