Natural flavourings from biotechnology for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 244

inhibitor, antimicrobial agent, building block, biochemical environmental
indicator and in medical applications increases the interest in this ketone (de
Carvalho and da Fonseca 2006). Carvone was traditionally isolated by fractional
distillation of caraway or spearmint oils, but the chemical synthesis from limonene
has been the preferred method (Surburg and Panten 2006). The use of the nitrosyl
chloride method for obtaining this ketone is one of the most commonly used
procedures, although the biotechnological techniques are becoming important
(Bicas et al. 2009). The biotransformation of limonene to carvone has already
been described for Rhodococcus opacus (de Carvalho and da Fonseca 2003).
Carveol has also been used as a substrate using the bacteria Rhodococcus globerus
(Duetz et al. 2001) or R. erythropolis (de Carvalho et al. 2005) as biocatalysts.
Concentrations up to 150 g L −1 have been achieved in small-scale column
reactors.
Menthone is another important monocyclic monoterpene ketone. With a
characteristic mint-like odor and an annual consumption of ca. 23 tonnes in the
US, it is used for synthetic peppermint oils and bases and is also applied in
chewing gums, gelatine and baked goods. (−)-Menthone can be obtained by
distillation of dementholized cornmint oil or by oxidation of (−)-menthol (Surburg
and Panten 2006; Burdock and Fenaroli 2010). Regarding biotechnological
processes, (−)-menthone may be prepared by the biotransformation of
(+)-neomenthol using plant cells (Scragg 2007). As for menthol, microbial
processes involving menthone are also limited (Noma and Asakawa 2010).
Verbenone (Fig. 11.2) is a bicyclic monoterpene ketone representing the
impact compound of rosemary oil (Schrader 2007), where it is usually present in
trace amounts, from 0-0.4 to 0.7-2.5%, depending on the source (Surburg and
Panten 2006). This compound is currently obtained from pine and eucalyptus and
has a market value of USD 3000 per kg (Agrawal and Joseph 2000). In
biotransformation processes, this ketone is formed as the major product when
using Aspergillus niger (Agrawal and Joseph 2000) or the yeast Hormonema sp.
(Van Dyk et al. 1998). However, in the latter case, high amounts of verbenol are
also produced.
The ketone nootkatone is the only sesquiterpene ketone described in this
chapter owing to its high demand for the fragrance, food, cosmetics and
pharmaceutical industries (Fraatz et al. 2009). It is present in the oils of citrus
fruits (bergamot, lemon, lime, orange and tangerine), especially in grapefruit peel
and juice, where nootkatone is one of the characteristic components of the aroma.
The aroma threshold for nootkatone is 170-800 ppb and its taste characteristics
(grapefruit, citrus, orange and bitter) are observed for concentrations above
20 ppm. Its estimated annual consumption is around 83 kg and it is used for
fl avoring beverages. The synthesis of nootkatone is performed by oxidation of
valencene (Surburg and Panten 2006; Burdock and Fenaroli 2010). This might be
performed by microorganisms or their enzymes in biotransformation processes.
One of the highest yields was described from the basidiomycete Pleurotus sapidus
(Fraatz et al. 2009).

￿ ￿ ￿ ￿ ￿