Diacetyl, lactic acid

Citrobacter Brewing liquor, fermenting wort Parsnip, sulphury DMS, diacetyl, lactic acid, acetaldehyde... 

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. 

Acetaldehyde and acetoin can be excreted in substantial amounts by lactic acid bacteria, in addition to diacetyl and methylglyoxal. For example, acetoin excretion has been studied in Streptococcus mutans (Hillman et al., 1987). Acetaldehyde (Nordbo, 1971) and methylglyoxal (Armstrong, 1964) stain teeth in vitro. 

Diacetyl as well as acetylmethylcarbinol are reduced to 2,3-butylene glycol (see p. 86) by lactic acid bacilli and streptococci. ... 

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). 

Scheme 23.5 Metabolic pathways of lactic acid bacteria leading from pyruvate to a-acetolactate and acetoin and chemical diacetyl formation. ALS a-acetolactate synthase, ALDB a-acetolactate decarboxylase, DDH diacetyl dehydrogenase. (Adapted from [72])...

The highly flavorable compound diacetyl is an important by-product of lactic acid bacterial fermentation. The mechanism of its formation has recently been unraveled (35). Diacetyl (measured as diacetyl rather than as diacetyl plus acetoin) is present in higher concentrations in wines with malo-lactic fermentation (cf. Ref. 36). At approximately threshold levels, this compound might contribute favorably to the flavor of wine (7) since increased complexity has been shown to enhance the quality of wine (37). 

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. 

Richter, R. L., Brank, W. S., Dill, C. W. and Watts, C. A. 1979. Ascorbic acid stimulation of diacetyl production in mixed-strain lactic acid cultures. J. Food Prot. 42, 294-296. 

The structure of the osazone was established by synthesis. 1,3-Diacetyl-4-desoxy-D-glycerotetrulose (XLI) was synthesized from acetyl-i/-lactyl chloride prepared from L-(dea lactic acid, through 3-acetyl-l-diazo-l,4-didesoxy-L-glycerotetrulose following the general procedure of Wolfrom, Waisbrot and Brown for the synthesis of ketoses. When this diacetyl derivative was hydrolyzed with dilute ammonia and the hydrolyzate was treated with acetic acid and phenylhydrazine, a phenylosazone (XLII) was isolated which was identical with that obtained from streptobiosamine. Its optical rotation was determined in pyridine solution. The preparation of the phenylosazone from streptobiosamine was well reproducible, with yields of 25-30 % of the theoretical in terms of chromatographed material. 

PGE Polyglycerol Esters of fatty acids DATEM Diacetyl Tartaric Esters of Mono-digiycerides GLP Glycerol Lacto Palmitate (Lactic acid esters)... 

Lactic acid bacteria and bifidobacteria are preferred as protective and probiotic cultures, and have been used since the beginning of history as starter cultures. They have a long history of being safely used and consumed. LAB are widely used for fermentation of milk, meat, and vegetable foods. In fermentation of dairy products, lactose is metabolized to lactic acid. Other metabolic products, hydrogen peroxide, diacetyl, and bacteriocins may also play inhibitory roles and contribute to improving the organoleptic attributes of these foods, as well as their preservation (Messens and De Vuyst, 2002). 

Lactic Acid Streptococci, Lactobacilli, Leuconostoc sp Sharp, buttery, fresh Acetaldehyde, Diacetyl, Acetoin, Lactic Acid... 

The so-called starter distillates used by the dairy industry are now produced on a commercial scale from lactic acid cultures. These distillates in which 70% of the substrate is converted to diacetyl have been patented(67) and are used to impart a buttery taste to edible oils. They are manufactured by the steam distillation of cultures of bacteria grown on a medium of skim milk fortified with 0.1% citric acid. Organisms used are Streptococcus lactis. S. cremoris. S. lactis subsp. diacetvlactis. Leuconostoc citrovorum and L dextranicum. Diacetyl comprises 80-90% of the flavor compounds in the aqueous distillate but is present at only 10-100 ppm. 

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. 

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