3-Hydroxy-2-Butanone Acetoin

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). 

The intermediary cofactor bound acetyl anion equivalent can be transferred to an aldehyde acceptor, e.g. to acetaldehyde already produced during regular catalytic reaction in which optically active 3-hydroxy-2-butanone (acetoin, an important aroma constituent) is formed. Interestingly, PDCs from different sources differ in stereoselectivity [443] acetoin (I )-143 is obtained using brewer s yeast PDC (ee 28-54%) [444,445] while the enantiomeric (S)-143 is produced preferentially by PDC from wheat germ (ee 16-34%) [446] or from Z. mobilis (ee 24-29%) [445], When glyoxylate 14 (instead of 2) is subjected to decarboxylation in the presence of acetaldehyde, optically active lactaldehyde... 

Bertrand, 1994 Allen, 1995) decanal and ( )-2-nonenal, on the other hand, are associated with sawdust or plank odour (Chatonnet and Dubourdieu, 1996 1998). The principal carbonyl compound formed in MLF is 2,3-butanedione (diacetyl), whose level can improve, or affect, the wine with its butter-like or fat note (Davis et al., 1985). Diacetyl and 3-hydroxy-2-butanone (acetoin, the reduced form of diacetyl) are produced by pyruvate metabolism of yeasts and lactic bacteria, and their levels may increase two or three fold with MLF depending on the lactic bacteria strain involved (Davis et al., 1985 Martineau and Henick-Kling, 1995 Radler, 1962 Fornachon and Lloyd, 1965 Rankine et al., 1969 Mascarenhas, 1984). For diacetyl in wine sensory thresholds ranging from 0.2mg/L (in Cbardonnay) to 0.9mg/L (Pinot noir), and 2.8 mg/L (Cabernet Sauvignon wine), are reported (Martineau et al., 1995). 

Hydroxy-2-butanone (acetoin) [513-86-0] M 88.1, b 144-145", [m 100-105" dimer]. Wash acetoin with EtOH until colourless, then with diethyl ether or acetone to remove biacetyl. Dry it in air by suction and dry further in a vacuum desiccator. [Beilstein 1IV 3991.]... 

Diacetyl Diacetyl (butanedione, CH3COCOCH3) can be industrially obtained by oxidation of 2-butanone using a copper catalyst at 300 °C, by dehydrogenation of 2,3-butanediol over a copper or silver catalyst in the presence of air, or with 3-hydroxy-2-butanone (acetoin) as a by-product [144]. On the other hand, this compound is naturally produced by LAB conferring a strong buttery aroma to many fermented dairy products (butter, buttermilk, and cheese). Diacetyl is synthesized by oxidative decarboxylation of the intermediate product a-acetolactate [55]. The most important diacetyl-producing LAB species have been shown to be Lc. lactis, Lactobacillus spp.. Strep, thermophilus, and Leuc. mesenteroides [65] ... 

A vast number of carbonyl compoimds could be formed by a-keto acids decarboxylation. Nevertheless, as they are reduced by yeasts and/ or by the presence of SO2, they exist in wines at levels which are not easily detectable. The compounds susceptible of influencing wine aroma are basically acetaldehyde, 3-hydroxy-2-butanone (acetoin) and 2,3-butanedione (diacetyl) (Bayonove et al, 1998). 

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. 

In general, pyruvate decarboxylase (EC 4.1.1.1) catalyzes the decarboxylation of a 2-oxocar-boxylic acid to give the corresponding aldehyde6. Using pyruvic acid, the intermediately formed enzyme-substrate complex can add an acetyl unit to acetaldehyde already present in the reaction mixture, to give optically active acetoin (l-hydroxy-2-butanone)4 26. Although the formation of... 

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 ... 

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. 

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. 

Hydrophobic amino acid containing 0-aminoacyl sugars, biuemess, 159,160r 3-Hydroxy-2-butanone, See Acetoin... 

Acetoin FEMA No. 2008 Acetyl Methyl Carbinol Dimethylketol 3-Hydroxy-2-butanone Monomer 88.n/c4H802/ CH3CH(OH)COCH3 Monomer colorless to pale yel liq/ buttery Monomer m—ale, prop glycol, water ins—veg oils/ 148° ... 

Acetoin (= 3-Hydroxy-2-butanone) (aliphatic ketone) Vitis mmjera (Vitaceae) (wine) OD-R (fatty, pleasant, wet)... 

Diacetyl (2,3-butanedione) is the principal desirable flavor component of butter (198) but gives an offensive flavor to beer (199, 200), frozen orange juice (201, 202), and wine (203), It is produced by yeast (202, 204) and bacteria (203, 204, 205, 206) and degraded by irreversible reduction to acetoin (3-hydroxy-2-butanone, acetyl methylcarbinol) with... 

An interesting end product, tetramethylpyrazine was also presented in the reaction mixture (27.3% of peak area of the total volatiles). Previous study of the model reaction of 2,3-butanedione and ammonium acetate did not yield any tetramethylpyrazine. It is probably due to the reducing environment provided by H2S which reduced 2,3-butanedione to 3-hydroxy-2-butanone. This explained that both 3-hydroxy-2-butanone and 3-mercapto-2-butanone were found in the reaction mixture. This study also supported the mechanism proposed by Elmore and Mottram 10) who observed that, during the reactions of hydroxyketones with aldehydes and ammonium sulfide, the formation of thiazoles was discouraged due to reducing environment provided by H2S derived from ammonium sulfide. It is also interesting to note that con aring to previous a-hydroxyketone series tetramethylpyrazine was present at trace levels whereas in the a-dicarbonyl series it was the major product under comparable tenq)erature conditions. The reason for this observed phenomenon is not obvious. It is possible that in the reaction system of acetoin and ammonium sulfide, the... 

Butanone, 1-phenyI-2-Butanone, 3,3-dimethyl-2-Butanone, 3,4-dihydroxy-H3C-CO-CHOH-CH2OH 2-Butanone, 3-hydroxy- acetoin H3C-CO-CHOH-CH3... 

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