Fermentation fusel alcohols

Since (A) does not contain any other functional group in addition to the formyl group, one may predict that suitable reaction conditions could be found for all conversions into (A). Many other alternative target molecules can, of course, be formulated. The reduction of (H), for example, may require introduction of a protecting group, e.g. acetal formation. The industrial synthesis of (A) is based upon the oxidation of (E) since 3-methylbutanol (isoamyl alcohol) is a cheap distillation product from alcoholic fermentation ( fusel oils ). The second step of our simple antithetic analysis — systematic disconnection — will now be exemplified with all target molecules of the scheme above. For the sake of brevity we shall omit the syn-thons and indicate only the reagents and reaction conditions. 

Fusel Oil. Fusel oil is an inclusive term for heavier, pungent tasting alcohols produced during fermentation. Fusel oils are composed of a mixture of / -propyl, isobutyl, and isoamyl alcohols. 

Synonyms AI3-15288 C-07328 EINECS 204-663-5 FEMA No. 2057 Fermentation amyl alcohol Fusel oil IP3 l-Hydroxy-3-methylbutane Isoamylol Isobutyl carbinol Isopentanol Isopentyl alcohol Methyl-3-butan-l-ol 2-Methyl-4-butanol 2-Methylbutan-4-ol 3-Methylbutanol 3-Methylbutan-l-ol 3-Methyl-l-butanol NSC 1029 Primary isoamyl alcohol Primary isobutyl alcohol UN 1105. 

ISOAMYL ALCOHOL Fermentation amyl alcohol, Fusel oil, Isopentyl alcohol, 3-MethyH-butanol Combustible Liquid 1 2 0... 

Higher Alcohols. The most abundant, volatile minor products of alcoholic fermentation are the higher alcohols or fusel alcohols. The most important are isoamyl (3-methyl-l-butanol), d-active amyl (2-methyl-l-butanol), isobutyl (2-methy 1-1-propanol), and n-propyl (1-propanol) alcohols. It is now recognized (4, 5, 6, 7) that these higher alcohols are formed by decarboxylation of particular a-keto acids to yield the corresponding aldehydes, and these in turn are reduced to the alcohols in a manner analogous to the formation of ethyl alcohol from pyruvic acid. 

The desirable properties of distilling wines include wines a) made from white varieties by fermentation of separated juice clarified as much as practicable, b) fermented without addition of sulfur dioxide, c) fermented with strains of yeast which form comparatively low amounts of fusel alcohols at temperatures below 75°F, and d) distilled as soon as possible after fermentation. 

Deamination 17 Examples of deamination and decarboxylation include conversion of amino acids to fusel oil (leucine to isoamyl alcohol, isoleucine to amyl alcohol, and phenylalanine to phenyl ethanol). Fusel oil formation is a normal function of all yeast fermentations (in alcoholic beverages, levels range from trace to 2200 parts per million). Deamination Glutamic acid to gamma-OH-butyric acid (S. cerevisiae). 

The third and fourth influential factors on wine aroma chemistry arise from the problems caused by the matrix on both the isolation and preconcentration of molecules and on the sensory assessment of the role played by the impact odorants. The presence of major volatiles, such as ethanol and fusel alcohols, complicates the isolation of the other wine odorants, particularly of those present at low levels. This has a marked influence on the way in which the extracts for screening and for further qualitative or quantitative studies should be prepared. On the other hand, ethanol and the major fermentation volatiles have also a deep influence on the way in which the odor chemicals are released and perceived. 

Esters. Esters are extremely important aroma compounds and there are many reports that esters are biosynthetic products of bacterial action. Thus, the fruity flavor defect sometimes found in cheddar cheese is due to the presence of esters, principally ethyl butyrate and ethyl caproate (25). Similar esters can be found in beer in which both fusel alcohols and the short chain fatty acids, acetic and butyric, are also present. These materials can undergo esterification, which in this case is mediated by the enzyme alcohol acetyltransferase present in the yeast used for beer fermentation (26). There are a number of esters present in wine which are metabolically produced by the yeast. Of these,... 

Butanol occurs in fusel oil and as a by-product of the fermentation of alcoholic beverages such as beer or wine. It is present in beef fat, chicken broth, and nonflltered cigarette smoke (Sherman 1979). 

Alcohol solutions, 3.3 Denatured alcohol, 3 Fermentation amyl alcohol Fusel oil,... 

Fusel oil (8013-75-0) is a mixture of the eight possible isomers of amyl alcohol and smaller amounts of other alcohols resulting from the fermentation of certain carbohydrates including grains and potatoes, hence fermentation amyl alcohol (123-51-3) which is principally 3-methyl-l-butanol. Fusel oil is a widely used solvent. 

The flavor of fermented foods depends highly on the metabolic activity of the cnltnre nsed. Especially, the amino acid and the lipid metabolism in yeasts have a cmcial contribution to flavor, because they are linked to the production of flavor-active compounds snch as esters, alcohols, carbonyl compounds, fatty acids, and nonvolatile components. " The increased ester and decreased fusel alcohol (mainly amyl alcohols) formation that has been observed dnring fermentations nsing immobilized cells, or the improved ratios of esters to higher alcohols, especially at low tanpera-tures, is considered to have a great impact on beverage quality and technology. 

Apart from the particular properties of yeast strains, the principal factors leading to elevated levels of fusel alcohols in brewery fermentations are (/) elevated levels of amino acids in wort, (ii) anaerobic conditions, (///) high temperatures, (zv) continuous agitation, (v) large amount of yeast growth, and (vi) high ethanol concentration [66],... 

Fatty acids and alcohols are products of yeast metabolism but the uncatalysed rate of chemical reaction between these substances is 1000 times too slow to account for ester formation in fermentation. Pantothenic acid (a precursor of coenzyme A) stimulates ester production [79] and factors which influence acetyl CoA metabolism affect ethyl acetate synthes s [77]. The biosynthesis of esters in yeast was therefore proposed to occur by the alcoholysis of acyl CoA compounds [77]. The alcohols involved in these reactions are ethanol and the fusel alcohols. The acyl CoA molecules used may be derived in one of several ways ... 

The use of elevated temperatures for fermentation has been advocated by many workers. Providing that there is no bacterial or wild yeast contamination, acceptable beers can be produced at comparatively high temperatures, say 20 C (68°F) for bottom yeasts and ITQ (81 °F) for top yeasts. The quality of these beers is different however from those fe mented at normal temperatures in connection with lower pH, bitterness, shelf-life, foam stability, and ease of filtration. Ester and fusel alcohol contents are higher [6]. Fermentation temperatures of around 25°C (77°F) are used for the manufacture of certain Trappist beers [19]. 

Fig, 19,3 The course of a typical traditional bottom-fermentation. SG, t, pH, fa and e refer to specific gravity of the wort, temperature (°C), pH of the wort, fusel alcohol content (jig/ml), and ester content (iig/ml). 

Since S. cerevisiae is the workhorse in industrial ethanol fermentations and has the natural capacity to secrete fusel alcohols as by-products (reviewed in Hazelwood et ah, 2008), this organism is supposed to be an attractive host for the production of higher alcohols. Furthermore, S. cerevisiae tolerates up to 20% ethanol and also shows a comparatively high tolerance against butanol (Knoshaug and Zhang, 2009 Chen et ah, 2011). 

Fusel oil formation varies with yeast strain, temperature of fermentation, pH, nutritional status, suspended solids level, and oxygen concentration of juice/must. Under oxidative conditions as would occur before the onset of alcoholic fermentation, or in cases of stuck fermentation, Pichia, Hansenula, and Candida may produce substantial quantities of fusel alcohols from fermentable sugars. The fusel alcohol, 2-phenylethanol (arising from 2-phenylalanine), has the unmistakable odor of roses and is also... 

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