Acetaldehyde yeast

Ethanol results from the decarboxylation of pyruvate and the reduction of acetaldehyde. Yeasts and other organisms that produce ethanol use a two-step reaction sequence. First, pyruvate decarboxylase releases CO2 to make acetaldehyde. Then alcohol dehydrogenase transfers a pair of electrons from NADH to the acetaldehyde, resulting in ethanol. 

In this thiamine pyrophosphate-mediated process, ben2aldehyde (29), added to fermenting yeast, reacts with acetaldehyde (qv) (30), generated from glucose by the biocatalyst, to yield (R)-l-phen5l-l-hydroxy-2-propanone (31). The en2ymatically induced chiral center of (31) helps in the asymmetric reductive (chemical) condensation with methylamine to yield (lR,23)-ephedrine [299-42-3] (32). Substituted ben2aldehyde derivatives react in the same manner (80). 

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. 

Biological catalysts are called enzymes. Nearly every step of the breakdown of a complex molecule to a series of smaller ones, within living cells, is catalyzed by specific enzymes. For instance, when acetaldehyde is reduced in yeast... 

DuPont has developed a process for the manufacture of glyoxylic acid by aerobic oxidation of glycolic acid (Fig. 2.33) mediated by whole cells of a recombinant methylotrophic yeast (Gavagnan et al, 1995). The glycolic acid raw material is readily available from the acid-catalysed carbonylation of formaldehyde. Traditionally, glyoxylic acid was produced by nitric acid oxidation of acetaldehyde or glyoxal, processes with high E factors, and more recently by ozonolysis of maleic anhydride. 

Figure 30. A medium complexity model of yeast glycolysis [342], The model consists of nine metabolites and nine reactions. The main regulatory step is the phosphofructokinase (PFK), combined with the hexokinase (HK) reaction into a single reaction vi. As in the minimal model, we only consider the inhibition by its substrate ATP, although PFK is known to have several effectors. External glucose (Glc ) and ethanol (EtOH) are assumed to be constant. Additional abbreviations Glucose (Glc), fructose 1,6 biphosphate (FBP), pool of triosephosphates (TP), 1,3 biphosphogly cerate (BPG), and the pool of pyruvate and acetaldehyde (Pyr).

C. J. Dickenson and F. M. Dickinson, A study of pH and temperature dependence of the reaction of yeast alcohol dehydrogenase with ethanol, acetaldehyde and butyraldehyde, Biochem. J., 147, 303-311 (1975). 

The question of how glycolytic oscillations synchronize in a population of yeast cells is of great current interest [51]. It has long been known that the oscillations disappear in a yeast suspension when the cell density decreases below a critical value. Acetaldehyde appears to act as synchronizing factor in such suspensions [52], and the way it allows cells to synchronize is being... 

P. Richard, B. M. Bakker, B. Teusink, K. Van Dam, H. V. Westerhoff, Acetaldehyde mediates the synchronization of sustained glycolytic oscillations in populations of yeast cells. Eur. 

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 9.3 DR5P synthesis from glucose and acetaldehyde by baker s yeast and deoxyriboaldolase-expressing E. 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.

Animal tissues are capable of carboligatically joining propionaldehyde and acetaldehyde to synthesize the homolog of acetylmethylcarbinol, propionylmethylcarbinol, CHs-CHOH-CO-CHs-CHj. Yeast attacks the corresponding diketone, acetylpropionyl, CHs-CO-CO-CHs-CHs, and yields two stereoisomeric glycols with the formula CHs-CHOH-CHOH--CH2-CH. At first the dextrorotatory form is present in excess. Just... 

Experiments made with yeast that had been killed by boiling showed that even in the presence of sugar such yeast is unable to reduce thio-acetaldehyde to ethyl mercaptan. 

Conversely, NADH is one of the important natural reductants, and in yeast cells, for example, it reduces acetaldehyde to ethanol ... 

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. 

Structure/ Reaction of grape anthocyanin 3-glucosides with acetaldehyde yielded the corresponding series of pyranoanthocyanins that were also formed after yeast fermentation of a synthetic must containing anthocyanins/ ... 

Another example is the commercialized formation of R-phenylacetylcarbinol (R-PAC) from benzaldehyde and pyravate by fermenting brewer s yeast (see chapter 4.16 Neuberg Hirsch, 1921). Pymvate decarboxylase is responsible for the formation of an activated acetaldehyde from the decarboxylation of pyravate and the condensation of this activated acetaldehyde with benzaldehyde. Nowadays, about 1000 tons per aimum (tpa) R-PAC is produced this way. 

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. 

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