Diacetyl butter aroma

Diacetyl, butane-2,3-dione CH3-CO-CO-CH3, a diketone produced as a byproduct of carbohydrate degradation, m.p. -3°C, b.p. 88.8 °C.D. is a component of butter aroma, and has been found in many biological materials. It is produced by dehydrogenation from acetoin, the decarboxylation product of pyruvate. In microorganisms D. is also produced by reaction of active acetaldehyde with acetyl-CoA. Little is known about the further metabolism of D.It is used as an aroma carrier in the food industry. 

The chemical transformations of wine by malolactic fermentation are much more complex in reality. Malolactic fermentation also produces ethyl lactate, the formation of which conffibutes to the sensation of body in wine (Henick-Kling, 1992). Additionally, other secondary products have been identified, the most important being diacetyl, produced by bacteria (a few milligrams per liter), that belongs to a complex pool of production and degradation mechanisms. At moderate concentrations, this secondary product contributes to aromatic complexity, but above 4 mg/1 the characteristic butter aroma of this substance dominates. 

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. 

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. 

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). 

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] ... 

Some species of the LAB group such as Leuconostoc mesenteroides subsp. cremoris, Leuconostoc mesenteroides subsp. dextranicum, and Lactococcus lactis subsp. lactis biovar diacetylactis, are known for their capability to produce diacetyl (2,3-butanedione) from citrate, and this metabolism appears especially relevant in the field of dairy products (Figure 13.4). Actually, selected strains belonging to the above species are currently added as starter cultures to those products, e.g., butter, in which diacetyl imparts the distinctive and peculiar aroma. Nevertheless, in particular conditions where there is a pyruvate surplus in the medium (e.g., in the presence of an alternative source of pyruvate than the fermented carbohydrate, such as citrate in milk or in the presence of an alternative electron acceptor available for NAD+ regeneration) (Axelsson, 2(X)9, pp. 1-72), even other LAB such as lactobacilli and pediococci can produce diacetyl by the scanted pyruvate (Figure 13.5). Thus, in addition to butter and dairy products, diacetyl can be present in other fermented foods and feeds, such as wine and ensilage (Jay, 1982). 

Diacetyl Chemical compound with an intense aroma of butter produced by yeast during fermentation. 

Citrate is present in milk, fruit, and vegetables. It can be co-metabolized with sugars by citrateutilizing LAB. Citrate utilization results in an excess of pyruvate, which is thus converted to diacetyl (2,3-butanedione), acetoin (2-hydroxy-3-butanone), and 2,3-butanediol to equilibrate the redox balance of cellular metabolism (Collins 1972 Bartowsky and Henschke 2004). Some LAB can also synthesize 2,3-pentanedione from pyruvate and threonine (Ott et al. 2000). Diacetyl and 2,3-pentanedione are associated with a buttery aroma, which positively contributes to the flavor of a range of fermented dairy products such as butter (MalUa et al. 2008), yogurt (Routray and Mishra 2011), and cheese (Curioni and Bosset 2002). Diacetyl also contributes to wine style, while it is responsible for flavor defects in beer. Diacetyl is widely produced by LAB, including species of the Lactococcus, Streptococcus, Leuconostoc, Lactobacillus, Pediococcus, and Oenococcus genera. 

The most aroma-active compounds in fresh sour cream butter were elucidated as the character impact compound diacetyl, with supporting roles from 5-decalactone, (Z)-6-dodeceno-y-lactone, and butyric acid (81). 

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