Colourings synthetic carotenoids

The majority of the permitted colourants discussed in this account are natural products with the exception of the four synthetic carotenoids. The only semi-synthetic materials used appear to be copper chlorophyllin and caramel. Although in all the natural materials discussed in this whole account mixtures are undoubtedly present, the composition of caramel (E150, Cl natural brown 10) must be even more complex, probably justifying the expression describing it as a composition of matter. ... 

Food products, which undergo undesirable colour changes in the presence of enzymes and oxygen, are sterilised to achieve the inactivation of enzymes, and stored in an inert atmosphere or in the presence of antioxidants. In cases where it is impossible to prevent the degradation of carotenoids (e.g. during the storage of flour or the manufacture of pasta, losses of carotenoids can reach 30-60%), the material can be coloured using synthetic carotenoids. 

There is as yet no agreed international list of permitted food colours. Thus a food dye that is permitted in one country may be considered unacceptable in another. The synthetic food colorants permitted in the European Union are listed in Table 1.8 [60]. All were originally introduced as acid dyes for wool many years ago. Furthermore, more than thirty colorants of natural origin are permitted in most countries. The natural carotenoid dyes are of outstanding importance for colouring edible fats and oils. These yellow to red methine dye structures occur in many families of plants and animals, including vegetables, berries,... 

The discussion above has addressed the assessment of a product s colour or perceived colour in basic terms. In the next two sections, methods to determine which coloured compounds are present in a product will be addressed. For the purpose of this chapter, the section on synthetic dyes will cover the analysis of the water-soluble dyes, or so-called coal tar dyes, and the section on natural pigments will cover the anthocyanin pigments, such as grape skin extracts, and the carotenoid-based materials, even if they are of synthetic origin. 

Identification and Assignment of Structure The identity of a synthetic product is often established by comparison of its absorption curve with that of the natural product or another standard sample. The absorption curves of synthetic and natural vitamin A2 are shown in Figure 7.1. The identification pf coloured substances is easier since colour can almost always be correlated with the presence of certain types of chromo-phoric groups. Thus, visible absorption spectra are employed for the detection and identification of the natural pigments (e.g. carotenoids, anthocyanins md porphyrins), dyes and other colouring matters. Hie absorption spectra of these colouring principles will be discussed separately in Chapter 12. 

As with many natural products for pharmaceutical or medicinal use, extraction of permitted natural food colourants takes priority over synthesis except in the instance of the carotenoids. In this class a remarkable synthetic activity makes the three important compounds p-carotene, apocarotenal, and canthaxanthin commercially available. 

Although only three carotenoids are commercially synthsised for use as permitted food colourants, namely p-carotene, apocarotenal and canthaxanthin, the availability of nature-identical counterparts of the natural products has always attracted interest. For the study of biological properties and for chromatographic studies access to synthetic versions is highly desirable. In the course of the isolation of the natural product its total synthesis finally always remained historically as a target. Such chemical work had invariably been carried out well before the introduction of the permitted range concept focussed attention on certain natural products... 

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