Natural flavourings from biotechnology for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 245

11.3.3 Terpene aldehydes and acids
Perillyl aldehyde (Fig. 11.2) is a monocyclic monoterpene aldehyde with a carbon
skeleton similar to its reduced counterpart, perillyl alcohol. Perillyl aldehyde has
a threshold value of 30-62 ppb and a powerful fatty-spicy, oily, herbaceous odor.
It is used in beverages, baked goods, frozen dairy, puddings, candies, etc. at a
concentration of 2-10 ppm, corresponding to an annual consumption of ~25 kg.
The natural sources of perillyl aldehyde are the essential oils of fruits (e.g. citrus,
guava), berries (e.g. bilberries, blackberry), herbs and others (e.g. gingergrass,
lavender, spearmint, caraway seed) (Burdock and Fenaroli 2010). In
biotransoformation processes, perillyl aldehyde may be prepared from limonene
using Mortierella minutissima (Trytek et al. 2009), but it is usually an intermediate
for the production of perillic acid (Speelmans et al. 1998) and thus it accumulates
only in minor amounts. In fact, high production of perillic acid from limonene, via
perillyl aldehyde, has been achieved with Pseudomonas putida (Mirata et al.
2009). However, the precursors perillyl aldehyde and perillyl alcohol are the
industrially more interesting targets (Speelmans et al. 1998).
The sesquiterpene aldehyde, α -sinensal, has a potent sweet orange aroma, with
a very low odor threshold (<0.1 ppb). It is present in different citrus oils and may
be prepared from the biotransformation of farnesene, but the yields obtained were
too low (Krings et al. 2006; Schrader 2007). One alternative may be the use of
trans -nerolidol as starting product (Hrdlicka et al. 2004).

11.3.4 Monoterpene ethers
One of the most interesting monoterpene ethers for the fl avor and fragrance
industries is rose oxide. This compound occurs in two isomeric forms ( cis and
trans ), which are found in small amounts in the oils of rose (Bulgarian) and
geranium. Rose oxide has a powerful distinctive geranium note and is used in
perfume compositions for the formulation of rose, geranium and all many other
fl oral fragrances. Baked goods, dairy products, puddings and candies also contain
1-3 ppm of citral (Surburg and Panten 2006; Burdock and Fenaroli 2010). Rose
oxide is usually prepared from citronellol through a photosensitized oxidation
with singlet oxygen or by means of microbial processes (Bicas et al. 2009). The
biotransformation of citronellol to rose oxide is also performed by Aspergillus
niger (Demyttenaere et al. 2004) and Penicillium sp. (Maróstica and Pastore
2006), but the reported yields were low for this aroma compound.
The oxidation of linalool may produce linalool oxide, another important ether
aroma compound, with a sweet woody, earthy-fl ower, bergamot-like odor, found
in many fruits, coffee, hop, lavender and other natural sources. Its reported aroma
threshold is about 320 ppb and it is used in perfumery to confer, for example,
lavender notes (Surburg and Panten 2006; Burdock and Fenaroli 2010). Linalool
furanoid and pyranoid oxides may be prepared by the oxidation of linalool
( Demyttenaere et al. 2001). The highest productivity was reported for Corynespora
cassiicola (Mirata et al. 2008).

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