Page 90 - Medicinal Plants 02-06-06-101_First year_PharmD (1)

Lactic acid fermentation (Figure 26)

➢ NADH transfers its electrons directly to pyruvate, generating lactate
as a by-product. Lactate, which is just the deprotonated form of lactic
acid, gives the process its name.

➢ Lactic acid can be fermented to propionic acid by bacteria (used in
the manufacture of food products such as yogurt and Swiss cheese)

➢ Note that muscle cells also carry out lactic acid fermentation, when
they have too little oxygen for aerobic respiration to continue as due
to vigorous exercise.

Alcoholic fermentation

➢ Under anaerobic conditions in higher plants, the pyruvic acid formed
during glycolysis is usually converted into carbon dioxide and ethyl
alcohol.

➢ NADH donates its electrons to pyruvate, producing ethanol in a two
step process (Figure 27):
1. Carboxyl group is removed from pyruvate and released as carbon
dioxide, producing a two-carbon molecule called acetaldehyde.
2. NADH passes its electrons to acetaldehyde, regenerating NAD+
and forming ethanol.

➢ Alcohol fermentation by yeast produces the ethanol found in alcoholic
drinks like beer and wine.

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