Saccharomyces cerevisiae ethanol formation

Fig. 1. Redox metabolism in Saccharomyces cerevisiae during anaerobic growth on glucose. The ethanol yield is lowered by the production of biomass and glycerol. The glycerol flux, x, can be decreased, and the ethanol yield thereby increased if the stoichiometric coefficient a for biomass formation is reduced, e.g., by having nitrogen assimilation via an NADH-depen-dent glutamate dehydrogenase [10]...

The natural formation and excretion of low levels of sulfite, sulfides and thiols is a general feature of the ethanol fermentation by Saccharomyces cerevisiae under... 

Sato and Yoshizawa [119] modeled the production of ethanol, a catabolic end product, during SSF of Saccharomyces cerevisiae. The rate of ethanol production was assumed to be directly proportional to the rate of carbon dioxide formation, which had both growth and non-growth associated terms as shown in Eq. (18). The non-growth associated term represented maintenance metabolism and the non-growth associated rate constant was assiuned to decrease exponentially as the ethanol concentration increased, in order to describe the inhibitory effect of ethanol on its own production. 

Cao, L., Zhang, A., Kong, Q., Xu, X., Josine, T. L., Chen, X. (2007). Over-expression of GLTl in IpslAgpdA mutant for optimum ethanol formation hy Saccharomyces cerevisiae. Biomolecular Engineering, 24(6), 638. 

Ester formation is associated with yeast growth in the early phase of fermentation. Acetate esters are produced via the reaction between an alcohol and acetyl Co-A, which is catalysed by the enzyme alcohol acetyl transferases (ATFl and ATF2). Ethanol, branched-chain alcohols and 2-phenylethanol are the common moieties of acetate esters. Ethyl esters of medium-chain fatty adds are formed through the reaction between ethanol and respective fatty acyl Co-A, which is catalysed by the enzyme alcohol acyl transferases. Saccharomyces cerevisiae strains also produce esterases that hydrolyse esters, and thus the final concentration of esters in beers is the net balance between ester synthesis and hydrolysis. Strains of brewing yeasts produce predominantly ethyl esters of fatty acids, particularly ethyl octanoate, with relatively little formation of acetate esters. Ester production in beer is regulated by a number of factors such as yeast strain, temperature, hydrostatic pressure, wort composition, sugar type and concentration, type and amount of yeast-assimilable nitrogen, aeration, and unsaturated fatty acids (Hiralal, Olaniran, PiUay, 2014 Pires et al., 2014). 

The enzymatic activity and ethanol formation abilities of Fusarium oxysporum makes it ideal for a simultaneous saccharification and biological conversion process [82]. Birch wood containing high xylose content, was used for the simultaneous saccharification and biological conversion test [82]. The birch chips were steam-treated at 185 °C for 30 min. Cellulase from Trichoderma reesei and either Saccharomyces cerevisiae or Fusarium oxysporum were used for the simultaneous saccharification and biological conversion process. Rates of hydrolysis and bioconversion were studied by varying the amount of T. reesei cellulase, since the... 

M. (1990) Ethanol formation in adhO mutants reveals the existence of a novel acetaldehyde-reducing activity in Saccharomyces cerevisiae. J. Bacteriol, 172, 3909-3917. 

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