Читать книгу Handbook of Enology: Volume 1 - Pascal Ribéreau-Gayon - Страница 52

In the presence of sulfite (Neuberg, 1946), the fermentation of glucose by yeasts produces equivalent quantities of glycerol, carbon dioxide, and acetaldehyde in its bisulfite form. This glyceropyruvic fermentation takes place in the following manner. Since the sulfite‐bound acetaldehyde cannot be reduced into ethanol, dihydroxyacetone phosphate becomes the terminal acceptor of electrons from the oxidation of glyceraldehyde 3‐phosphate, which is then reduced to glycerol 3‐phosphate. The latter is dephosphorylated into glycerol. This mechanism was used for the industrial production of glycerol. In this fermentation, only two molecules of ATP are produced for every molecule of hexose degraded. ATP is required to activate the glucose in the first step of glycolysis (Figure 2.5). Glyceropyruvicfermentation, whose net gain in ATP is nil, does not furnish biologically assimilable energy for yeasts.

Glyceropyruvic fermentation does not occur solely in a highly sulfited environment. At the beginning of alcoholic fermentation of grape must, the inoculum consists of yeasts initially grown in the presence of oxygen. Their PDC and alcohol dehydrogenase are weakly expressed. As a result, acetaldehyde accumulation is limited. The reoxidation of NADH therefore does not involve acetaldehyde, but rather dihydroxyacetone. Glycerol, pyruvate, and some secondary fermentation products are formed. These secondary products are pyruvate derivatives—including, but not limited to, succinate and diacetyl.