Fermentation, glyceropyruvic

Although the production of ethanol is the most important pathway to regenerate NAD+, there is an alternative pathway for this purpose. This pathway, called glyceropyruvic fermentation, generates glycerol as its final product (Prior and Hohmann 1996). Figure 1.5 shows the biochemical mechanism of glyceropyruvic fermentation. 

Regulation Between Alcoholic Fermentation and Glyceropyruvic Fermentation Glycerol Accumulation... 

Temperature influences fermentation kinetics. The alcohol yield is generally lower at elevated temperatures, in which case some of the alcohol may be entrained with the intense release of carbon dioxide. Additionally, most of the secondary products of glyceropyruvic fermentation are found in greater concentrations. Fatty acids, higher alcohols and their esters are the most affected their formation is at its maximum at about 20°C and then progressively diminishes. Low fermentation... 

Glycerol is one of the principal components of wine, both in its concentration (5-8 g/1) and in its contribution to taste. Yeasts form glycerol by glyceropyruvic fermentation at the beginning of fermentation. The degradation of glycerol harms wine quality, partly because of the decrease in its concentration and partly because of the resulting products of the metabolism. 

Alcoholic fermentation is the principal source of ethanal in wine. It is an intermediary product in the formation of ethanol from sugars. Its accumulation is linked to the intensity of the glyceropyruvic fermentation. It principally depends on the level of aeration, but the highest values are obtained when yeast activity occurs in the presence of free SO2. The formation of sulfurous aldehydic acid is a means of protection for the yeasts against this antiseptic. Consequently, the level of grape sulflting controls the ethanal and ethanal bound to SO2 concentration. 

The yield of the transformation of sugar to alcohol is difficult to determine. It seems to be similar to the alcoholic yield of yeasts—18.5 g of sugar per 1% percent volume of ethanol. Various secondary products are simultaneously formed 1.45-2.42 g of glycerol, 21-46 mg of ethanal, approximately 300 mg of succinic acid and 40-60 mg of acetic acid per Uter. The presence of all of these compounds indicates the existence of a mechanism similar to yeast-based alcoholic fermentation. Yet in this case, the glyceropyruvic fermentation portion would be greater, since the average glycerol/ethanol ratio x 100 is 18-20% instead of 8%. 

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