Carotenoid dyes structure

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,... 

Maybe this is not the right place to say it, but these problems should not discourage you from trying normal-phase systems out. The selectivity of these systems is often much greater than that of reversed phases, especially if the solutes have the same polarity with small structural differences such as carotenoids, dyes, isomers and phospholipids. Remember polar groups on the surface might make some trouble but they often have a positive contribution to the selectivity. 

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. 

Association of molecules changes their As as has been proven for metal complexes, charge transfer complexes, Lewis acids, etc. In any case, complex formation can be followed by the variation of the CD. Molecular association is the first step to an aggregation and, furthermore, is the presupposition for supramolecular structures. Compounds with inter-molecular exciton interaction, e.g., carotenoids or cyanine dyes, have been successfully analyzed. The spontaneous association to chiral associates from achiral compounds, e.g., cyanines, have been proven and analyzed with the help of ECD spectroscopy. In this context, the successful CD analyses with Langmuir-Blodgett films as well as the analyses of membranes have to be mentioned where suprastruc-tural chirality can also emerge from achiral monomers. 

Chromatophores were prepared from cells of Rhodopseudomonas sphaeroides green mutant as described in S. Itoh (1982). Absorption changes of carotenoids and merocyanine dye (NK2274, see Fig. 1 for the structural formulae) were measured with Hitachi 557 dual wavelength spectrophotometer or with a split beam flash spectrophotometer constructed in the Institute. A merocyanine dye was purchased from Nippon Kanko Shikiso Laboratory, Okayama. 

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