Acetoin production

Hillman JD, Andrews SW and Dzuback AL (1987) Acetoin production by wild-type strains and a lactate dehydrogenase-deficient mutant of Streptococcus mutans. Infect Immun 55, 1399-1402. 

Cogan, T. M., O Dowd, M. and Mellerick, D. 1981. Effect of pH and sugar on acetoin production from citrate by Leuconostoc lactis. AppL Environ. Microbiol. 41, 1-8. 

Schut, G.J., Vaccaro, B.J., Basen, M., Kelly, R.M., and Adams, M.W.W. (2016) Temperature-dependent acetoin production by Pyrococcus furiosus is catalyzed by a biosynthetic acetolactate synthase and its deletion improves ethanol production. Metab. Eng., 34, 71-79. 

Acetate induces the three enzymes and activates acetolactate synthase. In a study comparing wildtype Enterobacter aerogenes and mutants deficient in 2,3-BD and acetoin production, during the highest phase of 2,3-BD production, the three enzymes of the pathway constituted approximately 2.5 % of the protein in the cell. Butanediol production also appears to play a role in regulating the NADH/NAD ratio (Johansen et al. 1975). 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

On the other hand, as mentioned in the preceding subsection, a preparative-scale enzymic synthesis of 1-deoxy-D-r/ireo-pentulose can be achieved, according to Reaction 1, in the presence of an extract of B. pumilus. Obviously, this raises the question of the relevance of Eq. 1 to the production of the pentulose in microorganisms. Acetoin in Reaction 1 could be replaced by 3-hydroxy-3-methyl-2-butanone (then the by-product is acetone). More interestingly, it can be also replaced by pyruvate, then the pentulose is synthesized according to Reaction 3 ... 

A model developed by Leksawasdi et al. [11,12] for the enzymatic production of PAC (P) from benzaldehyde (B) and pyruvate (A) in an aqueous phase system is based on equations given in Figure 2. The model also includes the production of by-products acetaldehyde (Q) and acetoin (R). The rate of deactivation of PDC (E) was shown to exhibit a first order dependency on benzaldehyde concentration and exposure time as well as an initial time lag [8]. Following detailed kinetic studies, the model including the equation for enzyme deactivation was shown to provide acceptable fitting of the kinetic data for the ranges 50-150 mM benzaldehyde, 60-180 mM pyruvate and 1.1-3.4 U mf PDC carboligase activity [10]. 

Based on the model described in the previous section, an optimization strategy has been developed for substrate feeding with maximum PAC production as its objective fimction. A molar ratio of pyruvate benzaldehyde of 1.2 1 was maintained in the feed as some of the pyruvate is converted also to by-products acetaldehyde and acetoin. 

From the simulation results in Figure 4, a maximum PAC concentration of 740 mM was predicted at 81 h together with by-products acetoin (55 mM) and acetaldehyde (10 mM). The activity of PDC decreased rapidly throughout the biotransformation with only 5% residual activity when feeding was terminated. 

It is possible that product inhibition by PAC or by-product inhibition by acetoin or acetaldehyde may play a more important role than benzaldehyde in influencing PAC production in this aqueous phase system. 

The B. licheniformis JF-2 strain produces a very effective surfactant under conditions typical of oil reservoirs. The partially purified biosurfactant from JF-2 was shown to be the most active microbial surfactant found, and it gave an interfacial tension against decane of 0.016 mN/m. An optimal production of the surfactant was obtained in cultures grown in the presence of 5% NaCl at a temperature of 45° C and pH of 7. TTie major endproducts of fermentation were lactic acid and acetic acid, with smaller amounts of formic acid and acetoin. The growth and biosurfactant formation were also observed in anaerobic cultures supplemented with a suitable electron acceptor, such as NaNO3[1106]. 

In a subsequent report, however, the thiazolopapains were shown to be competent in catalyzing a carbon-carbon bond-forming reaction of the acetoin condensation type (Fig. 14) [50]. The reaction of the papain derivatives with 6-oxo-heptanal was assayed at neutral pH (Fig. 14). The course of the reaction was monitored by HPLC and the products analyzed by H NMR. In the case of the... 

Several products were also detected in base-degraded D-fructose solution acetoin (3-hydroxy-2-butanone 62), l-hydroxy-2-butanone, and 4-hydroxy-2-butanone. Three benzoquinones were found in the product mixture after sucrose had been heated at 110° in 5% NaOH these were 2-methylbenzoquinone, 2,3,5-trimethylbenzoquinone, and 2,5-dimethyl-benzoquinone (2,5-dimethyl-2,5-cyclohexadiene-l,4-dione 61). Compound 62 is of considerable interest, as 62 and butanedione (biacetyl 60) are involved in the formation of 61 and 2,5-dimethyl-l,4-benzenediol (63) by a reduction-oxidation pathway. This mechanism, shown in Scheme 10, will be discussed in a following section, as it has been proposed from results obtained from cellulose. 

Cultor Ltd. (Finland) and Tuchenhagen(Germany) have developed a process, where yeast cells are adsorbed on the surface of the carrier developed for glucose isomerase (Spezyme, Table 6.1). The high volumetric productivity of the immobilized yeast cells make a conversion of dr-acetolactate to acetoin possible with only a few hours residence time in the packed bed columns. 

The mechanism of this reaction is obscure. One suggested mechanism, analogous to the vapor phase reaction, involves concerted decarboxylation of the pyruvic acid to yield a triplet hydroxy carbene which can either dimerize or attack another molecule of pyruvic acid to yield the observed product.91 Dimerization seems to be the less likely process since the carbene can rearrange to acetaldehyde or react with water. Further, this mechanism predicts that acetoin will be formed when pyruvic acid is irradiated in any solvent that does not possess readily abstractable hydrogen atoms, such as benzene, a solvent in which no reaction is observed. One possible explanation of this discrepancy is that the solvation of the pyruvic acid is extremely different in benzene and in water. However, the specific role that the water plays in the reaction has not been determined. 

Reaction of Acetoin (3-Hydroxy-2-butanone) with Ammonia. Aqueous solution of ammonium hydroxyde (20%, 100 ml) was added to acetoin (17.6 g, 0.2 mol) and the reaction mixture was stirred for 30 min at 50°C and then for 6 h at room temperature. The precipitated product was filtered off, the filtrate was neutralized with 10% hydrochloric acid, and extracted with ether (continuous overnight extraction). The extract was washed with water, dried over anhydrous sodium sulfate, and concentrated on a spinning-band distillation apparatus. The residual solution was then analyzed by GC and GC-MS. 

Reaction of Acetoin with Ammonia. Space limitations do not allow us to discuss the remaining reactions in detail. Among other products, the reaction of acetoin with ammonia gives pyrazines (this work, cf. also ref. 54). 

Reactions of Acetoin and Aldehydes with Ammonium Sulfide. This reaction leads to the various substituted oxazolines, thiazolin-es, and Imidazolines. Additional heterocyclic systems identified in this reaction include thiophenes and pyrazines. All these products are important aroma compounds in the food industry. 

Hydroxy-2-butanone (acetoin) is a characteristic constituent of butter flavour used for flavouring margarine and can be obtained as a by-product of molasses-based and lactic acid fermentations [49, 71]. The closely related 2,3-butanedione (diacetyl) has a much lower organoleptic threshold than acetoin and is an important strongly butter-like flavour compound in butter and other dairy products [72] in buttermilk, for instance, the diacetyl concentration is only about 2-4 mg [73]. a-Acetolactate (a-AL) is an intermediate of lactic acid bacteria mainly produced from pyruvate by a-acetolactate synthase. In most lactic acid bacteria, a-AL is decarboxylated to the metabolic end product acetoin by a-AL decarboxylase (ALDB) [71] (Scheme 23.5). 

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