Diacetyl formation

Genetic manipulation or cloning offers many possibiUties and perhaps there will be yeast strains especially designed for special beers, ie, types, which are usehil because of low diacetyl formation, high—low ester formation, and insensitivity to pressure or high fermentation temperatures or extracellular enzymatic abiUties (P-glucanases). 

Scheme 23.5 Metabolic pathways of lactic acid bacteria leading from pyruvate to a-acetolactate and acetoin and chemical diacetyl formation. ALS a-acetolactate synthase, ALDB a-acetolactate decarboxylase, DDH diacetyl dehydrogenase. (Adapted from [72])...

Unfortunately diacetyl formation is still not well understood. Acetoin formation occurs either by nonspecific interaction of acetaldehyde with the a-hydroxyethyl thiamine pyrophosphate intermediate in pyruvate decarboxylation (209) or by decarboxylation of a-acetolactate (210), which in turn arises either from interaction of pyruvate with a-hydroxyethyl thiamine pyrophosphate (211) or as a specific intermediate in valine biosynthesis (212, 213). Diacetyl does not appear to be formed directly from acetoin (208, 214). It is formed from a-acetolactate, in absence of cells, by O2 oxidation (215), and even under N2 (216), although an oxidation must occur. It is also formed from acetyl CoA (217, 218), probably by interaction with a-hydroxyethyl thiamine pyrophosphate [cf. stimulation by acetyl CoA addition to a solution of pyruvate and pyruvate decarboxylase (2i5)]. It is not known whether this involves a specific enzyme or is a mere side reaction. 

The results plotted at Figure 1 seem to be useful for elucidation of the reaction pathway. In the course of butadione formation two hydrogen molecules of 2,3-butanediol must be eliminated. The elimination can proceed either simultaneously or step by step via consecutive elimination of hydrogen molecules and intermediate formation of acetoin. One can see that conversion of the latter into diacetyl proceeds faster and at lower temperature as compared to the conversion of butanediol. By increasing the temperature and conversion of butanediol the curve of acetoin formation passes maximum and the curve of diacetyl formation has an induction period. Thus, one can believe that the conversion proceeds mainly via consecutive elimination of hydrogen molecules and intermediate formation of acetoin ... 

Figure 7.1. Overview of the biochemical routes leading to glycerol, pyruvate, and ethanol. Furthermore, valine biosynthesis and diacetyl formation are shown, which may be bypassed by introduction of a heterologous a-acetolactate decarboxylase that directly converts a-acetolactate to acetoin. GPDl and GPD2, glycerol dehydrogenases 1 and 2 ADHl, alcohol dehydrogenase 1 ILV2, acetolactate synthetase ID/5, acetolactate reductoisomerase [Refs in 502].

Curie, M., Stuer-Lauridsen, B., Renault, R, Nilsson, D. (1999). A general method for selection of a-acetolactate decarboxylase-deficient Lactococcus lactis mutants to improve diacetyl formation. Applied and Environmental Microbiology, 65, 1202-1206. 

Increases fermentation efficiency by reducing diacetyl formation. 

The diacetyl monoxime condenses readily with hydroxylamine hydrochloride or sulphate with the formation of dimethylglyoxime (diacetyl dioxime) ... 

Pentafluorophenyl acetate is a highly selective acetylating reagent, useful for acetylations at hydroxyl and amino groups under mild conditions When applied to the acetylation of amino alcohols, it gives selective formation of H acetyl derivatives at room temperature and M,0 diacetylated products under moderate heating in the presence of triethylamine [149]... 

X0 to hydroxy compounds. Lower temperatures favor ketone formation and sterically hindered carbonyls, such as 2-thienyl t-butyl ketone, are not reduced. The sensitivity of desulfurization to steric factors is evident by the failure to desulfurize 2,5-di-i-butyl-3-acetylthiophene. The carbonyl groups of both aldehydes and ketones can be protected by acetal formation, as particularly cyclic acetals are stable during desulfurization in methanol at room temperature. " The free aldehydes give primary alcohols on desulfurization. Another method to obtain only keto compounds is to oxidize the mixtures of ketone and secondary alcohol with CrOs after the desulfurization. - Through the desulfurization of 5,5 -diacetyl-2,2, 5, 2"-terthienyl (228), 2,15-hexadecandione (229) has been obtained, which... 

Tetramethylethylene behaves in the AlCIs-catalyzed diacetylation as 155 (Aik = iso-Pr)affording2,6-dimethyl-4-isopropylpyrylium. Although the olefin acylation had been investigated by many chemists beginning with Kondakov (cf. Nenitzescu and Balaban and Balaban and Nenitzescu ), the formation of pyrylium salts had escaped notice because they are water-soluble and had been discarded after hydrolysis of the reaction mixture. Only in the study of the ZnCla-catalyzed acetylation of diisobutene had a crystalline product been observed by Byrns and Doumani its reaction... 

Methane, ethene, ethane, propene, acetaldehyde, methyl formate, butene, acetone, furan, dimethyl sulfide, isoprene, isobu-tyraldehyde, diacetyl, methylfuran, and isovaleraldehyde... 

The chlorination of methyl chloroformate in sunlight was first reported by Hentschel, but without a detailed description of either the procedure or the results. The first step of the present procedure for the preparation of trichloromethyl chloroformate utilizes an ultraviolet light source and affords a simple and reproducible way to obtain this reagent. Although trichloromethyl chloroformate may also be synthesized by photochemical chlorination of methyl formate,the volatility of methyl formate causes losses during the reaction and increases the hazard of forming an explosive mixture of its vapor and chlorine gas. The preparation of trichloromethyl chloroformate by chlorination of methyl chloroformate in the dark with diacetyl peroxide as initiator has been reported. However, the procedure consists of several steps, and the overall yield is rather low. 

Methyl formate Formic acid, methyl ester (8,9) (107-31-3) Acetyl peroxide (8) Peroxide, diacetyl (9) (110-22-5)... 

The diazaphosphetidinones (9 R = OMe or NMej) gave stable phos-phoranes (10) with benzil at - 70 °C, but the adduct of (9 R = NMcz) with diacetyl could not be isolated although there was n.m.r. evidence for its formation. ... 

Several of the lower molecular weight aliphatic compounds, in a mixture, are part of the roasted coffee aroma. A nine-compound mixture with roasted coffee aroma contained isopentane, n-hexane, acetaldehyde, dimethyl sulfide, propanal, isobutanal, isopentanal, methanol, and 2-methylfuran.20 In addition, the freshness of aroma and taste has been correlated with 2-methylpropanal and diacetyl. When the concentration of these falls off, so does the taste.21 Other aliphatic compounds that are steadily lost from ground roasted coffee, unless it is vacuum packaged, include methyl formate, methyl acetate, methyl thioacetate, and acetone.22 The concentrations in roast coffee for four compounds whose contribution to the fresh flavor have long been known are dimethyl sulfide (4 ppm), methyl formate (12 ppm), isobutanal (20 ppm), and diacetyl (40 ppm). The taste thresholds are 0.1, 0.5, 0.5, and 1.0 ppm, respectively, in the brew made with 5 g coffee per 100 ml water.15... 

Oxidation of 2,3-dimethylquinoxaline (from phenylenediamine and diacetyl) with either peracids or hydrogen peroxide in acetic acid gives the 1,4-dioxide (162). Treatment of this bis-N-oxide with selenium dioxide leads to oxidation of one of the methyl groups to the methyl carbinol and formation of... 

Following a published procedure [1], octene was treated with a solution of perox-yacetic acid in acetic acid for 8 h to form the epoxide, but the reaction mixture was then allowed to stand uncooled overnight. Next morning, when a 3pl sample was injected into a heated GLC injection port, the syringe shattered. This was attributed to formation of diacetyl peroxide during the overnight standing, and its subsequent explosion in the heated port [2],... 

Application of fluorine to aqueous sodium acetate solution causes an explosion, involving formation of diacetyl peroxide. 

The crude products of ozonolysis at — 30°C of the chloroalkene tended to decompose explosively on warming to ambient temperature, particularly in absence of solvents. The products included the individually explosive compounds acetyl 1,1,-dichloroethyl peroxide, 3,6-dichloro-3,6-dimethyl-2,3,5,6-tetraoxane and diacetyl peroxide [1], Ozonolysis in ethyl formate saturated with hydrogen chloride gives a high yield of 1,1-dichloroethyl hydroperoxide as a further unstable intermediate product [2],... 

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