Ethanol metabolic processes

Once the product specifications have been fixed, some decisions need to be made regarding the reaction path. There are sometimes different paths to the same product. For example, suppose ethanol is to be manufactured. Ethylene could be used as a raw material and reacted with water to produce ethanol. An alternative would be to start with methanol as a raw material and react it with synthesis gas (a mixture of carbon monoxide and hydrogen) to produce the same product. These two paths employ chemical reactor technology. A third path could employ a biochemical reaction (or fermentation) that exploits the metabolic processes of microorganisms in a biochemical reactor. Ethanol could therefore also be manufactured by fermentation of a carbohydrate. 

Horse liver alcohol dehydrogenase, HLADH, (also abbreviated as ADH or LADH) is the most extensively studied oxido-reductase. It plays a central role in ethanol metabolism and has been one of the main tools for understanding the mechanism of this process.15 it was crystaliized from horse liver in 1948 by Bonnichen and Wassen and is commercially available. Three isozymes EE, ES and SS are formed by dimeric combination of two different, E or S (E "ethanol-active" and S "steroid active"), protein chains. 16 The EE- isozyme of HLADH has been used in organic synthesis. 

In the literature, the major VOCs found in the breath of healthy persons are isoprene (10-600 pph ), acetone (1-2000 ppbv), ethanol (10-1000 ppbv) and methanol (150-200 ppbv). All are products of the standard metabolic processes in the human body [7]. 

See also LDH Isoenzymes, Pyruvate/Lactate/Ethanol Metabolism, Anaerobic Process for Generating Metabolic Energy, Lactic Acid Fermentation, Ethanol Metabolism and Gluconeogenesis... 

Fermentation itself can be stopped when the desired alcohol content is reached, either by removal of yeast (filtration, centrifugation) or by their deactivation (pasteurization). A further possibility is to create fermentation conditions, which suppress yeast metabolism (Narziss, Miedaner, Kem, Leibhard, 1992). The most practical tool to suppress yeast metabolism is low temperature. This method is called the cold contact process (CCP) , which ensures very slow ethanol prodnction while other metabolic processes, snch as formation of higher alcohols and esters or reduction of carbonyls, may exhibit moderate activities (Perpete Collin, 1999). After interrupting the fermentation at an alcohol content less than 0.5% voL, the AFB is usually matured for at least 10 days at 0-1 °C to enrich flavour and improve the colloidal stability. Then the product is filtered, carbonated, stabilized and sterilized (Branyik, Silva, et al., 2012 Burberg Zamkow, 2009). 

Concepts of mechanism and rate-limiting steps apply as well, as can be illustrated with a simplified view of the metabolic processing of ethanol ... 

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