Natural flavourings from biotechnology for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 246

11.3.5 Carotenoid-derived aroma compounds
Many biological effects are attributed to the presence of carotenoids. One of them
is the metabolism of carotenoids to retinoids (Krinsky 1994), which is the main
dietary source of vitamin A. More recently, the protective effects of β -carotene
and other carotenoids against serious disorders such as cancer, heart disease and
degenerative eye disease have been recognized, and have stimulated intensive
research into the role of carotenoids as antioxidants and as regulators of the
immune response system (Ziegler 1991; Zorn et al. 2003).
Apart from their biological importance, the carotenoids are important precursors
of a variety of compounds: the C 20 -retinoids, the C 15 -phytohormones, and the C 9 - to
C 13 -aromas (see Fig. 11.3). Among the last type, C 13 -carotenoid-derived compounds
(norterpenoids/norisoprenoids) such as ionones and damascones constitute an
essential aroma compound in tea, grapes, roses, tobacco and wine (Rodriguez-
Bustamante and Sanchez 2007), and are formed via enzymatic oxidation and
photo-oxidation of the various carotenoids found in plants, fl owers and fruits
(Enzell 1985; Wu et al. 1999; Winterhalter and Rouseff 2001). Although carotenoid-
derived aroma compounds are ubiquitous constituents in plant-derived aromas,
very little is known about their biogeneration (Winterhalter and Rouseff 2001).
The occurrence of norisoprenoids in natural sources is restricted to trace amounts
and extraction has turned out to be tedious and costly (Zorn et al. 2003). In this
sense, the bioproduction of volatile compounds derived from carotenoids is attracting
more attention from the fl avor and fragrance industries because it represents a
feasible alternative to chemical synthesis and offers the production of enantiomerically
pure molecules, which can be labeled as 'natural'. To date, biotransformation of
carotenoids has been reported using integer cells (plant-cultured cells, fungi, bacteria
and yeasts) and pure enzymes (see Bicas et al. 2009 for references).

Norisoprenoids
As discussed above, the norisoprenoids are important fl avor compounds derived
from carotenoids. These compounds have not only been detected in leaf products
such as tobacco, tea and mate, but also in many essential oils, fruits (grapes,
passionfruit, starfruit, quince, apple, nectarine, tomato, melon) and spices (saffron,
red pepper), as well as additional sources such as wine, rum, coffee, oak wood,
honey and seaweeds (Winterhalter and Rouseff 2001).
In general three steps are required to generate an aroma compound from the
parent carotenoid: (i) the initial dioxygenase cleavage; (ii) subsequent enzymatic
transformations of the initial cleavage product giving rise to polar intermediates
(aroma precursors); and (iii) acid-catalyzed conversions of the non-volatile
precursors into the aroma-active form (Krings and Berger 1998).

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α- and β -ionone
The C 13 ketones α - and β -ionone are cyclic terpenoid derivatives that occur in many
essential oils. α - and β -ionone have violet-like odor, however the latter has a more
fruity and woody aroma. They naturally occur in the distillate of the fl owers of
Boronia megatisma Nees and in a few other essences, while some references suggest