190 Applications and Occurrences of Heterocycles in Everyday Life
A number of heterocycles have been identifi ed, such as the simple pyrrole, pyrraline, but also in cross-linking by imi-
dazoles and more complex systems, exemplifi ed by pentosidine (which is derived by cyclisation involving the sugar
residue). Pentosidine-type cross-linking is signifi cant, but free pentosidine (which is fl uorescent) is used as a conven-
ient marker for AGE formation.
Pentosidine, as its name implies, is mainly derived from pentoses, such as ribose, although it can form from glucose
and fructose.
Natural and synthetic food colours
Natural food colours include the large general class of anthocyanins and fl avonoids (see pages 165–166), and also
substances specifi c to small groups of plants, such as betanin, the red substance in beetroot. This, being natural,
requires no safety testing and is used as a colour additive in other foods, in preference to synthetic dyes. Many syn-
thetic dyes permitted in foods are azo dyes, including the heterocycle tartrazine, but development of new synthetic
food dyes is now much more diffi cult and expensive, due to the requirement for rigorous safety testing, almost like
that required for new drugs.
Flavours and fragrances (F&F)
Flavours and fragrances are very closely linked commercially and suppliers generally sell components for use in both
areas. There is often crossover between applications. The fi nal products, particularly fragrances, are usually complex
blends of components. Whilst most F&F constituents are aliphatic or carbocyclic, a large number of heterocycles are