Agriculture Reference
In-Depth Information
was reported that Acetobacter strains are able to synthesize methylbutyric acid.
Besides its industrial relevance as a fl avor, this acid can be a valuable precursor of
common fl avor esters (Vandamme and Soetart 2002).
11.2.4
Other compounds
Terpenes
Terpenes are the most abundant group in nature responsible for the characteristic
odors of essential oils and are a preferable substrate for bioconversion studies
(Janssens et al. 1992). In studies involving de novo synthesis, terpenes are present
only in a few works.
Drawert and Barton (1978) related the use by Kluyveromyces lactis in the
production of citronellol, linalool and geraniol. Bluemke and Schrader (2001)
reported a production of citronellol and geraniol by Ceratocystis moniliformis in
a fi ve-liter bioreactor.
Sulfur compounds
Methional is important for the typical taste of cheeses, especially cheddar
(Spinnler et al. 2002). Another example is methylthioacetate, which has been used
in baked goods, imitation dairy, chewing gum, meat products, condiments,
relishes, non-alcoholic beverages, frozen dairy, snack foods, soft candy, hard
candy and soups (Burdock and Fenaroli 2010) and lager beer at a concentration
between 4 and 31 ppb (Spinnler et al. 2002). Strains of Hanseniaspora uvarum,
Hanseniaspora guilliermondii and Saccharomyces cerevisiae are capable of
producing sulfur compounds such as methional and 2-methyltetrahydrothiophen-
3-one, 2-mercaptoethanol, cis -2-methyltetrahydro-thiophen-3-ol, trans -2-
methyltetrahydro-thiophen-3-ol and 3-mercapto-1-propanol (Moreira et al. 2005,
2008). Other volatile thiols, in particular 4-mercapto-4-methylpentan-2-one,
3-mercaptohexan-1-ol and 3-mercaptohexyl acetate, are some of the most potent
aroma compounds of wine. At optimal concentrations in wine, these compounds
impart fl avors of passionfruit, grapefruit, gooseberry, blackcurrant, lychee and
guava (Swiegers et al. 2007).
￿ ￿ ￿ ￿ ￿
Pyrazines
Tetramethylpyrazine has a musty, fermented, coffee odor and is present in several
cheeses (Swiss, camembert, gruyère), roasted peanuts, soy products, beans,
mushroom, cocoa and coffee products. This compound has an aroma threshold
varying from 1 to 10 ppm and is of great industrial importance in beverages,
baked goods, meat products and frozen dairy products (Burdock and Fenaroli
2010). A few microorganisms are also able to produce this pyrazine, e.g. Bacillus
subtilis grown on a sucrose asparagine medium (Kosuge and Kamiya 1962). The
same compound was also evidenced during the fermentation of cocoa beans
by the action of microorganisms (Reineccius et al. 1972). One strain of
Corynebacterium glutamicum was able to produce 3 g L −1 of tetramethypyrazine
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