Ethanol microbial synthesis

The production of ethanol alone is not economically feasible without continued subsidies but a plant becomes profitable if it produces ethanol and furfural as co-products (10). The technology development in the Latvian State Institute of Wood Chemistry (LSIWC) provides an excellent possibility for producing both furfural and ethanol. As a result, the problem of the complete utilization of the deciduous wood polysaccharide complex yielding furfural and fermentable sugars to be used subsequently for the production of bioethanol and other microbial synthesis products has been solved. Residual lignin could be used as a calorific fuel. 

These techniques, in which mutant strains are selected for their ability to overproduce metabolites, represent an important advance in the industrial development of microbial synthesis. Their use to improve amino-acid manufacture was not new they had already been used to improve the titres of antibiotics but the nature of the changes introduced into the metabolism of the mutated organisms could not be interpreted in the way that was possible for amino-acid synthesis. What is, perhaps, also apparent is that the technique of interfering with the metabolic pathway between aspartate and lysine is, in principle, no different from the use of sulphite to inhibit the synthesis of ethanol (section 6.2.1.2). In one case C. glutamicum overproduces lysine, while in the other S. cerevisiae will produce glycerol. 

Grbin et al. 2007). ATHP reduction may lead to EHTP. As ethanol is a precursor, mousy off-flavour occurs after alcoholic fermentation, preferably after lactic acid bacteria activity. It seems that the formation of mousiness may be induced by oxidation but it is not clear if the effect is on the microorganisms or in any chemical reaction stimulated by the redox potential. Other agents claimed to affect its production (high pH, low sulphite, residual sugar content) (Lay 2004 Snowdon et al. 2006 Romano et al. 2007) are also stimulators of microbial activity and so the true mechanisms are not yet clarified, but the non-enzymatic chemical synthesis has been ruled out in D. anomala (Grbin et al. 2007). 

Ethanol is the key reactant in Eq. (1), and also in Eq. (2) because it is readily converted to acetaldehyde. The process based on Eq. 1 was developed in Russia and the process based on Eq. 2 was developed in the United States. The yield of butadiene for the Russian process is about 30-35%. It is about 70% if mixtures of ethanol and acetaldehyde are employed as in the U.S. process. Equation (3) represents a process that involves 2,3-butylene glycol, a product from the microbial conversion of biomass. The process is carried out in two sequential steps via the glycol diacetate in overall yields to butadiene of about 80%. The process of Eq. (4) starts with a biomass derivative, the cyclic ether tetrahydrofuran, and can be carried out at high yields. When this process was first operated on a large scale in Germany, acetylene and formaldehyde were the raw materials for the synthesis of intermediate tetrahydrofuran. It is manufactured today from biomass feedstocks by thermochemical conversion, as will be discussed later. 

Microbes use enzymes as catalysts to obtain the desired or beneficial reaction and typically under mild conditions. The brewing of beer and fermentation of fruit and vegetable mass high in starches to produce consumable ethanol are the oldest and most familiar examples of using microbial action to achieve a desired end. But now much more has been demonstrated, from the production of essential human hormones to the synthesis of specialty chemicals. 

The synthesis of the leading candidate compound 47 in an anticancer program [79,80] required (S)-2-chloro-l-(3-chlorophenyl)ethanol 48 (Figure 16.13) as an intermediate. Other possible candidate compounds used analogs of the (S)-alcohol. From microbial screening of reduction of ketone 49 to the (S)-alcohol 48, two cultures, namely, Hansenula polymorpha SC13824 (73.8% EE) and Rhodococcus globerulus... 

The chiral intermediates (S)-l-(2 -bromo-4 -fluorophenyl)ethanol 76 and (S)-methyl 4-(2 -acetyl-5 -fluorophenyl)-butanol 77 are potential intermediates for the synthesis of several potential anti-Alzheimer s drugs, such as 78 [97,98], The chiral intermediate (S)-l-(2 -bromo-4 -fluoro phenyl)ethanol 76 (Eigure 16.19A) was prepared by the enantioselective microbial reduction of 2-bromo-4-fluoro acetophenone 79 [99]. Organisms from genuses Candida, Hansenula, Pichia, Rhodotorula, Saccharomyces, and Sphingomonas and baker s yeast reduced 79 to 76 in more than 90% yield and 99% EE. 

Occasionally the synthesis of a microbial product, for example that of ethanol from glucose, is catalysed by non-viable cells (section 6.2.1.1). Then the process is properly catalytic because the Saccharomyces cerevisiae cells do not change, for a time at least. However there are some industrially important reactions in which micro-organisms are first grown to a high biomass and are then added to a substrate which is almost quantitatively converted to a product. These are effectively catalytic processes in which one or a few enzymes in the organism transform an added substrate into a useful product. These transformations are divorced from cell growth, in contrast to syntheses such as those in which carbohydrates are converted into citric acid or complex feedstocks into secondary metabolites. 

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