Natural flavourings from biotechnology for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 243

or from m -cresol from petrochemical origin (van der Schaft 2007). In terms of
biotechnological processes involving menthol, the references are limited. It
may be a precursor in biotransformation processes (see Bicas et al. 2009 for
references) and can also be prepared by the biotransformation of menthyl acetate
by plant cell and organ cultures (Scragg 2007). Fungal biotransformation of
citronellol to menthol has also been reported (see Noma and Asakawa 2010 for
references).
Verbenol (Fig. 11.2) is a bicyclic monoterpene alcohol with a fresh pine,
ozone odor (Burdock and Fenaroli 2010), also described as having camphor
and mint fl avor notes (Rottava et al. 2010b). It has been used (concentration
of ~1 ppm) in baked goods, beverages, frozen dairy, gelatine, pudding and
candies, but its annual consumption is estimated to be less than 1 kg. Verbenol is
found, for example, in spearmint oil, juniper berry, myrtle and mango and may be
prepared by chemical synthesis from (−)- α -pinene (Burdock and Fenarioli 2010).
Microbial biotransformations of α -pinene to verbenol as the major product have
also been reported. The microorganisms capable of performing such a conversion
were a hybrid (protoplast fusion) from Aspergillus niger and Penicillium digitatum
(Rao et al. 2003), Pseudomonas putida (Divyashree et al. 2006), Serratia
marcescens (Wright et al. 1986) and unidentifi ed microbial strains (Rottava et al.
2010b).
Another bicyclic monoterpene alcohol, myrtenol (Fig. 11.2), has a
camphoraceous, minty, medicinal, woody odor, with an aroma threshold of 7 ppb.
Its reported usages are confection, frosting, gelatin, pudding, milk products and
beverages, commonly in a concentration of 5 ppm (Burdock and Fenaroli 2010).
Myrtenol is also present in non-food products, where it is used as an ingredient in
decorative cosmetics, fi ne fragrances, shampoos, soaps, household cleaners and
detergents. However, its use worldwide is less than 0.1 tonnes per year (Bhatia
et al. 2008). Many berries, citrus fruits and herbs contain myrtenol. The synthesis
of myrtenol is usually performed with α -pinene, SeO 2 and ethanol (Burdock
and Fenaroli 2010). The biotransformation of α - and β -pinenes with Bacillus
pallidus yields myrtenol in low quantities, together with other major products
(Savithiry et al. 1998).

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11.3.2 Terpene ketones
Carvone (Fig. 11.2) is a very important monoterpene ketone for the fl avor industry.
S -(+)-Carvone is the main component of caraway oil and dill, with an odor
resembling these herbs. The other isomer ( R -(−)-carvone) occurs at high
concentrations (70-80%) in spearmint oil and is also the major component
responsible for its aroma. The aroma threshold for carvone is in the range of
6.7-820 ppb, for S -(+)-carvone and 2.7-600 ppb for the R -(−)-isomer. They have
a high annual consumption (almost 90 tons), with reported uses in many products
(food, beverages and oral hygiene products) in a usual range of 30-200 ppm
(Surburg and Panten 2006; Burdock and Fenaroli 2010). Several applications
have been reported for carvone. Its use as a fragrance and fl avor, potato sprouting