Biochemistry

On the basis of alcoholic fermentation bread is baked, beer, wine and alcohol is made. Along with lactic fermentation, it is used in the technology of producing some lactic acid drinks (koumiss, kefir), as well as in pickling vegetables. Spontaneous alcoholic fermentation in fruit juices, syrups, compotes, preserves causes their spoilage - fermentation. The causative agents ofalcoholic fermentation include yeast (wine, beer, bakery, top and bottom fermentation) and some mycelial fungi, however, this produces much less alcohol (5-7%). Yeast enzymes ferment D-glucose, D-fructose, D-mannose, D-galactose, all monosaccharides, and some pentoses. Ethanol and CO2 are the main products of alcoholic fermentation, glycerol, acetic and succinic acids are side products, fusel oils - are mixtures of higher alcohols (isoamyl, isobutyl, amyl, propyl, etc.). Alcoholic fermentation for yeast is the process of obtaining energy under anaerobic conditions. Therefore, alcoholic fermentation takes place in oxygen-free conditions. Fermentation proceeds in two stages: the first — oxidative — involves the conversion of glucose to pyruvic acid with the formation of two reduced NADH 2 molecules — an intermediate hydrogen acceptor: C 6 H 12 O 6 -> 2CH3COCOOH + 2NAD H 2 Glucose pyruvic acid reduced form of NAD (NADH 2 ) And in the second stage — reduction — NAD H 2 transfers hydrogen to the final acceptor, which turns into the main end-product of fermentation. Yeast has the enzyme of pyruvate deca-boxylase, which catalyzes the decarboxylation reaction of pyruvic acid with the elimination of CO 2 and the formation of acetaldehyde: 2CH3COCOOH — > 2CH3CHO + 2CO 2 pyruvic acid acetaldehyde Carbon dioxide is the end product of alcoholic fermentation. An acetaldehyde plays the role of the final acceptor of hydrogen, reacting with NADH 2 with the participation of the enzyme alcohol dehydrogenase is reduced to ethyl alcohol, and NADH 2 is oxidized to NAD. 2CH3CHO + NAD-H 2 -> 2CH 3 CH 2 OH + 2NAD acetaldehyde ethanol 237