Natural flavourings from biotechnology for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 238

in a fi ve-day fermentation from amino acids (e.g. leucine, isoleucine and valine)
(Demain et al. 1967).
Several pyrazines such as 2,5-dimethylpyrazine (characteristic earthy potato-
like odor), 2,6-dimethylpyrazine (nutty and coffee-like odor) and trimethylpyrazine
were produced by strains of Bacillus cereus . Trimethylpyrazine has a baked potato
or roasted nut aroma and is of great commercial importance (Burdock and Fenaroli
2010). The concentrations of these pyrazines did not reach more than 4 mg L −1
and the production depended on the temperature and the culture medium
(Demyttenaere et al. 2002; Feron and Waché 2006).

11.3 Production of natural fl avors by biotransformation
Biotransformations comprise single reactions catalyzed enzymatically and
resulting in a product structurally similar to the substrate molecule. In some
cases, the precursors employed can be considered inexpensive and readily
available, such as fatty or amino acids, and can be converted to more highly
valued fl avors (Krings and Berger 1998). The main substrates used in
biotransformation processes are described below and some examples of the
processes employed to obtain aroma compounds by biotransformation are detailed
in Table 11.2 .

11.3.1 Monoterpene alcohols
α -Terpineol is one of the most commercially important monoterpene alcohols for
the fl avor industry. Its annual consumption is estimated to be approximately
9.2 tons, which represents an individual intake of 17.2 μ g/kg/day in the US. It has
a lilac odor and sweet smell reminiscent of peach, with an aroma threshold of
280-350 ppb. The reported food usages for α -terpineol, usually in a range of
10-20 ppm, include baked goods, chewing gum, condiments, dairy products,
candies and beverages (Burdock and Fenaroli 2010). It is also applied for the
formulation of soaps and cosmetics (Surburg and Panten 2006). Although it
occurs in a large number of essential oils such as Cupressaceae, Pinaceae, lavandin
and many other leaves, herbs and fl owers, and may be produced by fractional
distillation of pine oils, this alcohol is commonly synthesized by acid hydration of
α -pinene or turpentine followed by partial dehydration (Surburg and Panten 2006;
Burdock and Fenaroli 2010). However, one of the most recent tendencies is the
production of natural α -terpineol by the biotransformation of limonene, α -pinene
or β -pinene (Bicas et al. 2008). One of the most viable processes described so far
yields almost 130 g L −1 using limonene as substrate in a biphasic medium (Bicas
et al. 2010b).
Carveol, together with carvone (Fig. 11.2), is another important fl avor
compound. It has a spearmint-like odor used in baked goods, chewing gums,
frozen dairy, gelatin, puddings, beverages and candies, in a concentration close to
220 ppm. Its annual consumption is around 1.2 tons, representing an individual

￿ ￿ ￿ ￿ ￿