Butter, Diacetyl

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. 

Many substances identical to natural compounds are used to impart a butter-like flavour and taste to margarine. Most such flavour mixtures are composed on the basis of analytical data on butter. Diacetyl, fatty acids and ketones are the most important components. 

Traditionally, butter was made by allowing cream to separate from the milk by standing the milk in shallow pans. The cream is then churned to produce a water in oil emulsion. Typically butter contains 15% of water. Butter is normally made either sweet cream or lactic, also known as cultured, and with or without added salt. Lactic butter is made by adding a culture, usually a mixture of Streptococcus cremoris, S. diacetylactis and Betacoccus cremoris. The culture produces lactic acid as well as various flavouring compounds, e.g. diacetyl, which is commonly present at around 3 ppm. As well as any flavour effect the lactic acid inhibits any undesirable microbiological activity in the aqueous phase of the butter. Sweet cream butter has no such culture added but 1.5 to 3% of salt is normally added. This inhibits microbiological problems by reducing the water activity of the aqueous phase. It is perfectly possible to make salted lactic butter or unsalted sweet cream butter if required. In the UK most butter is sweet cream while in continental Europe most butter is lactic. 

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). 

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). 

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. 

In a similar study on butter flavor [28] we recently showed that a mixture of diacetyl, 8-decalactone and butanoic acid dissolved in sunflower oil in the same concentrations occurring in a cultured butter, closely matched the flavor of the butter itself. 

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... 

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). 

Flavors. Most of the flavors used in shortenings are butterlike. Diacetyl was the major butter flavor used in fat and oil products until improved analytical techniques identified other flavor components in butter. Today, the U.S. FDA regulations allow safe compounds that impart a suitable flavor to the finished product (16). The choice of a particular flavor or blend of flavors depends on the expertise and the taste preference of the product developer. 

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). 

There is some experience concerning other milk and plant fats which may be fermented by micro-organisms only on a laboratory scale. Examples are butter flavours (generation of diacetyl and acetoin) by suitable bacteria cultures which are derived from milk (Streptococcus diacetylactis and Leuconostoc citrovorum). Today, buttery flavours are especially important for dietetic foods, like fat reduced butter or for the fortification of plant fats (margarine). 

CIC Vanillin, the main component in vanilla flavour is the basic key ingredient for the creamy, sweet character. All other volatile flavouring compounds have been identified only in small traces. Among them 2-methoxy phenol and 2-methoxy-4-vinyl phenol are responsible for the phenolic, smoky odour. 4-Methoxy benzalde-hyde, 3,4-methylene-dioxy-benzaldehyde, methyl benzoate and methyl ciimamate impart the warm, powdery, aromatic floral character. Vitispirane adds a fruity, floral topnote. Natural vanilla extract blends very well with other flavourings and it has been modified in different directions ethyl vanillin is used to increase the sweet, creamy vanillin aspect. Tonka beans and coumarin add a full, dried hay, slightly caramel-like custard aspect, supported by the butter notes of diacetyl and 4-hydroxy-decanolide. 

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). 

Schmalfuss and Barthmeyer (1929), still unaware of the results of the analytical work of Reichstein and Staudinger, studied the presence of diacetyl in foods. They noticed the caramel and buttery note of this compound that results from the oxidation of acetylmethylcarbinol (3-hydroxy-2-butanone) and quantified its presence in butter, tobacco, coffee, cocoa, beer and honey. 

The cream used for butter may be fresh ( pH 6.6) or ripened (fermented pH 4.6), yielding sweet-cream and ripened cream (lactic) butter, respectively. Sweet-cream butter is most common in English-speaking countries but ripened cream butter is more popular elsewhere. Traditionally, the cream for ripened cream butter was fermented by the natural microflora, which was variable. Product quality and consistency were improved by the introduction in the 1880s of cultures (starters) of selected lactic acid bacteria, which produce lactic acid from lactose and diacetyl (the principal flavour component in ripened cream butter) from citric acid, A flavour concentrate, containing lactic acid and diacetyl, is now frequently used in the manufacture of ripened cream butter, to facilitate production schedules and improve consistency. 

Acetoin has a slight milky odor and is present at concentrations on the order of 10 mg/1. Diacetyl has a pleasant odor of butter and hazelnuts which may be perceptible at low concentrations (2 mg/1). 

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