Acetaldehyde, production, yeast

Effect of Yeast on Fermentation. North Coast enologists recognize the important effects yeast strains have on the management of the fermentation, its evenness and completion, and the wine composition. Rankine (23) reviewed the different effects of yeast strain on wine composition and noted especially the relationship of yeast strain to sulfur dioxide, hydrogen sulfide, and acetaldehyde production. 

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. 

Romano, P, Suzzi, G., Turbanti, L., Polsinelli, M. (1994) Acetaldehyde production in Saccha-romyces cerevisiae wine yeasts. FEMS Microbiology Letters, 118, 213-218. 

Yeast (qv) metabolize maltose and glucose sugars via the Embden-Meyerhof pathway to pymvate, and via acetaldehyde to ethanol. AH distiUers yeast strains can be expected to produce 6% (v/v) ethanol from a mash containing 11% (w/v) starch. Ethanol concentration up to 18% can be tolerated by some yeasts. Secondary products (congeners) arise during fermentation and are retained in the distiUation of whiskey. These include aldehydes, esters, and higher alcohols (fusel oHs). NaturaHy occurring lactic acid bacteria may simultaneously ferment within the mash and contribute to the whiskey flavor profile. 

Other organisms are equipped to produce ethanol, by employing a thiamine diphosphate-dependent decarboxylation of pyruvate to acetaldehyde (see Section 15.8) and NAD+ is regenerated by reducing the acetaldehyde to ethanol. This is a characteristic of baker s yeast, and forms the essential process for both bread making (production of CO2) and the brewing industry (formation of ethanol). 

Efficient Production of DR5P from Clucose and Acetaldehyde by Coupling of the Alcoholic Fermentation System of Baker s Yeast and Deoxyriboaldolase-Expressing . coli... 

Scheme 9.5 Multi-step enzymatic process for 2 -deoxyribo-nucleoside production from glucose, acetaldehyde and a nucleobase through glycolysis, reverse reactions of 2 -deoxy-ribonucleoside degradation and ATP regeneration by the yeast glycolytic pathway recycling the phosphate generated by nucleoside phosphorylase.

Reactions of anthocyanins and flavanols take place much faster in the presence of acetaldehyde that is present in wine as a result of yeast metabolism and can also be produced through ethanol oxidation, especially in the presence of phenolic compounds, or introduced by addition of spirit in Port wine technology. The third mechanism proposed involves nucleophilic addition of the flavanol onto protonated acetaldehyde, followed by protonation and dehydration of the resulting adduct and nucleophilic addition of a second flavonoid onto the carbocation thus formed. The resulting products are anthocyanin flavanol adducts in which the flavonoid units are linked in C6 or C8 position through a methyl-methine bond, often incorrectly called ethyl-link in the literature. 

A patented process for the production of green notes applying bakers yeast for in situ reduction of enzymatically produced aldehydes [67, 68] has been called into question regarding the effective production of (Z)-3-hexenol. According to Gatfield s report [69] the isomerisation of (Z)-3-hexenol to (E)-2-hexenal is a very fast process. The latter undergoes facile conversion to hexanol. Beside this, baker s yeast can add activated acetaldehyde to ( )-2-hexenal, forming 4-octen-2,3-diol. 

Rankine (6, 38) believes that the differences in the secondary products formed in wines during fermentation by various yeasts are quantitative rather than qualitative, and careful selection of pure yeast strains can eliminate wine disorders caused by large amounts of undesirable by-products such as hydrogen sulfide, mercaptans, acetaldehyde, acetic acid, ethyl acetate, higher alcohols, etc. 

Acetaldehyde. In routine winery operation acetaldehyde is seldom measured. However, in the production of sherry, either by the film yeast or submerged culture processes, regular acetaldehyde determination is necessary. 

To limit this possibility, Torulaspora delbrueckii, in mixed or sequential culture with S. cerevisiae, has been proposed for fermentation (Bely et al., 2008 Ciani et ah, 2006 Lafon-Lafourcade et ah, 1981 Renault et ah, 2009). Although this yeast generates little alcohol, its application in mixed starter cultures is promising. It may also reduce the accumulation of other undesirable by-products, such as acetaldehyde, ethyl acetate, and acetoin. 

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