Aroma diacetyl

CgHgO, diacetyl [431-03-8], and benzaldehyde [100-52-7], C H O, are aroma chemicals used by the food industry (53). 

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... 

Aliphatic carbonyl compounds, such as diacetyl, which has a butter-like odour, also may contribute to the aromas derived from the MaiUard reaction, and many of the Strecker aldehydes also have characteristic aromas (Table 12.1). 

Cultured buttermilk is manufactured by fermenting whole milk, reconstituted nonfat dry milk, partly skimmed milk, or skim milk with lactic acid bacteria. Most commercial cultured buttermilk is made from skim milk. Mixed strains of lactic streptococci are used to produce lactic acid and leuconostocs for development of the characteristic diacetyl flavor and aroma. Buttermilk is similar to skim milk in composition, except that it contains about 0.9% total acid expressed as lactic acid. The percentage of lactose normally found in skim milk is reduced in proportion to the percentage of lactic acid in the buttermilk. According to White (1978), the fat content of buttermilk usually varies from 1 to 1.8%, sometimes in the form of small flakes or granules to simulate churned buttermilk, the by-product of butter churning. Usually 0.1% salt is added. 

Pack, M. Y., Vedamuthu, E. R., Sandine, W. E. Elliker, P. R. and Leesment, H. 1968. Effect of temperature on growth and diacetyl production by aroma bacteria in single-and mixed-strain lactic cultures. J. Dairy Sci. 51, 339-344. 

Godshall et al. (57) have concluded that typical molasses aroma is composed of two fractions. One is a sweet component that can arise from compounds such as diacetyl and other aldehydes while the other is a strong grassy or green note which they attribute to... 

The experiments have been completed by additional reaction of xylose, fructose and some characteristic sugar degradation products like cyclotene, Furaneol and diacetyl and by thermal decomposition of Ama-dori rearrangement products. It is well knwon that sugars can react with suitable amino compounds very easily. In the course of these reactions sugars are mostly decomposed and brown melanoidins are formed. By-products of these melanoidins are many volatile compounds of characteristic aroma properties. They are also responsible for the well known aromas of heated food like meat, coffee and bread. 

Also acetic acid may arise from a reaction of this type. Most important compounds of this pathway are pyruvic aldehyde, diacetyl, hydro-oxyacetone and hydroxydiacetyl which can easily react with amino acids. The Strecker degradation is a reaction where the amino acid is de-carboxylated and loses its amino group. Reaction products are the Strecker aldehyde and - as an intermediate - an aminoketone which forms a pyrazine by dimerization. This pathway is considered to be most important for the origin of pyrazines in thermal aromas. However, only limited knowledge is available about the fate of the Strecker aldehydes. As we will demonstrate they are very reactive. 

Rothe (5, , 1 5) calculated the aroma values of some volatiles identified in the crumb of wheat bread and the crust of rye bread. The data listed in Table I indicate that ethanol, isobutanal, iso-pentanal, diacetyl and isopentanol contribute with high aroma values to the aroma of the wheat bread crumb. During baking of rye bread, the two Strecker aldehydes, isobutanal and isopentanal, increased so much in the crust that they showed the highest aroma values of the volatiles investigated. 

While the wine contains several g/L of L-malic acid before MLR, it usually only contains between 200 mg/L and 300 mg/L of citric acid. Although the citric acid is only present in low concentrations, it is of considerable importance. On the one hand, its metabolic pathway leads to production of acetic acid, in other words, it increases the volatile acidity of the wine. However, the most important enological significance associated with fermentation of citrate is the production of diacetyl and other acetonic compounds, which affect the wine aroma. 

At low levels (5 mg/L), diacetyl is considered to add complexity to wine aroma since it can impart positive nutty or caramel characteristics, although at levels above 5 mg/L it can resuit in spoilage, creating an intense buttery or butterscotch flavour, and is perceived as a flaw. Microbial formation of diacetyl is a dynamic process and its concentration in wine depends on several factors bacterial strain, pH, wine contact with lees, SO2 content (Martineau and Henick-Kling 1995 Nielsen and Richelieu 1999). The sensory threshold for the compound can vary depending on the levels of certain wine components, such as sulfur dioxide. It can also be produced as a metabolite of citric acid when all the malic acid has been used up. However, diacetyl rarely taints wine to levels where it becomes undrinkable. 

The most significant ketone produced by yeast is diacetyl (2,3-butanedione), a vicinal diketone, although malolactic fermentation is a more important source, when it is used in wine production. Having a sensory threshold of 0.2-2.9 mg/L, according to the type of wine, it is characterised by a nutty , toasty or buttery aroma depending on concentration (Martineau et al. 1995). Dry white wines tend to contain lower concentrations (0.1-2.3 mg/L) than red wines (0-7.5 mg/L) (Bartowsky et al. 2002 Martineau et al. 1995). Acetoin, which produces a buttery flavour, is formed by partial reduction of diacetyl, and is itself reduced to 2,3-butanediol. Acetoin is usually present at concentrations (<80 mg/L) much lower than its sensory threshold of 150 mg/L (Romano and Suzzi 1996). 

Bartowsky, E. J., Francis, 1. L., Bellon, J. R., Henschke, P. A. (2002) Is buttery aroma perception in wines predictable from diacetyl concentration Australian Journal of Grape and Wine Research, 8, 180-185. 

Acetals are equilibrium products between aldehydes and alcohols. As discussed by Williams and Strauss (30) acetals generally have less intense aromas than the corresponding alcohols and aldehydes. 1,1,3-Triethoxypropane and diethoxybutan-2-one (derived from acrolein and diacetyl, respectively) are common acetals in the heads fractions from continuous stills acetals from other aldehydes including acetaldehyde, propanal, isobutanal, and isovaleraldeyde are also common (30). The equilibrium between the aldehyde and the acetal is highly dependent on alcohol concentration and pH, again m ng accurate quantitation of either the aldehyde or the acetal dependent on the analytical conditions (e.g., sample dilution, solvent extraction, etc.) (30). 

By using aroma extract dilution analysis (AEDA) of the volatile fractions of fresh and stored butter oil, Widder et al. (29) determined diacetyl, butanoic acid, 8-octalactone, skatole, 8-decalactone, cw-6-dodeceno-8-decalactone, l-octen-3-one, and l-hexen-3-one as potent contributors to the flavor of butter oil. The concentration of l-octen-3-one, trani-2-nonenal, and i-l,5-octadien-3-one increased during the storage of the butter oil at room temperature. 

Table 5 shows the sensory evaluation by Schieberle et al. (30) of the different kinds of butter, namely, Irish sour cream (ISC), cultured butter (CB), sour cream (SC), sweet cream (SwC), and farmer sour cream (ESC). It revealed ISC butter and ESC butter with the highest overall odor intensities. Table 5 shows that 19 odor-active compounds were detected by aroma extract dilution analysis (AEDA) in a distillate of the ISC butter. The highest flavor dilution (ED) factors have been found for 5-decalactone, skatole, i-6-dodeceno-y-lactone, and diacetyl followed by trany-2-nonenal, cw,c -3,6-nonadienal, c/i-2-nonenal, and l-octen-3-one. 

There are several ways of making cultured butter from sweet cream. Pasilac-Danish Turnkey Dairies, Ltd. developed the IBC method (Figure 10) (81). The main principles of the IBC method are as follows. After sweet cream churning and buttermilk drainage, a starter culture mixture is worked into the butter, which produces both the required lowering of butter pH and, because of the diacetyl content of the starter culture mixture, the required aroma. The starter mixture consists of two types of starter culture (1) Lactococcus lactis and (2) L. cremoris and L. lactis ssp. diace-tylactis. With respect to production costs, the experience with this method shows that, for the manufacture of mildly cultured butter, the direct costs are only about one-third of the costs of other methods (81). 

On account of their two conjugated C=0 double bonds, both diacetyl and 2,3-pentanedione are intensely yellow compounds, and both are strong flavors. At a level of up to 2 mg/kg, diacetyl is the principal flavor and colorant of butter, and for this reason it is added to margarine to give it the taste and look of butter. Diacetyl is also used as a flavor in ice cream and baked goods. By contrast, 2,3-pentanedione is used as aroma in alcoholic and nonalcoholic beverages. 

Main components Up to 0.8% essential oil in the fresh herb, which is partly lost during drying. Phthalide derivatives as well as diacetyl are aroma carriers [48]. The monoterpene fraction represents app. 95% of the herb oil and contains mainly limonene, myrcene and Z-ocimene [49], The essential oil produced from the fruits (they contain up to 2.5% oil) is considered more valuable (see also [50] for the corresponding oleoresins). 

In addition to diacetyl, O. oeni produces esters, flavor compounds also important for wine flavor and aroma. Esters are primarily produced by Saccharomyces during alcoholic fermentation (Mason and Dufour, 2000 Nykanen, 1986 Nykanen and Nykanen, 1977 Soles et al., 1982), although evidence shows that esters such as ethyl acetate, ethyl lactate, ethyl hexano-ate, and ethyl octanoate can be synthesized by O. oeni (De Revel et al., 1999 Delaquis-Pascal et al., 2000 Edwards and Peterson, 1994 Maicas et al., 1999 Tracey and Britz, 1989). For example, Edwards and Peterson (1994) reported that strains of O. oeni synthesized relatively large amounts of ethyl lactate (183-1280 /ig/L) during growth in microbiological medium. In agreement, Maicas et al. (1999) reported that 50 mg/L of ethyl lactate was produced in wines fermented with O. oeni, as well as isoamyl acetate and ethyl caproate, compounds important for a pleasant fruity note in wine (Gil et al., 1996 Mason and Dufour, 2000 Nykanen, 1986). 

Growth of Pediococcus species in wine has been considered undesirable because of the production of off-aromas and off-flavors. Pediococci are capable of producing excessive acetoin and diacetyl, which can give undesirable aromas... 

The mutant which was blocked in the synthesis of branched chain amino acids produced very low levels of methoxy pyrazines. Cultures of this mutant did generate a new N peak and produced a strong butter-like aroma. TVo compounds were identified in these cultures as 2,3,5,6-tetramethy1 pyrazine and diacetyl. The synthesis of tetramethylpyrazine by a Corynebacterium glutamicum that was also metabolically blocked in the branched chain amino acid pathway has previously been reported (24). 

Low Molecular Weight Carbonyl Compounds. In the dairy field, a major product made this way is starter distillate. The main component is diaceyl which is a very important aroma compound responsible for the characteristic buttery flavor of fermented dairy products such as sour cream or buttermilk. The dairy industry relies upon fermentation by lactic streptococci for the production of diacetyl in cultured products. Starter distillate is a natural product rich in diacetyl which is produced by distilling such lactic cultures. The key intermediate in the biosynthesis of diacetyl is aL-acetolactic acid which is decarboxylated to form diacetyl (Figure 3). The starting material of the biosynthetic pathway is citrate which is a natural component of milk. 

Although more than 280 compounds have been identified in the volatile fiction of wheat bread, only a small number is responsible for the flavor notes in the crust and the crumb. Schieberle and Grosch (73) used aroma extract dilution analysis (AEDA) to select 32 odorants in wheat. Among the odorants, 2-acetyl-pyrroline (roasly, bread crust-like) was the most potent aroma, followed by E-2-nonenal (green, tallowy), 3-methylbutanal (malty, nutty), diacetyl (buttery) and Z-2-nonenal (green, fiitty). 

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