Colour components

RPLC separation with spectrophotometric detection is often applied to the identification of the anthraquinone colour components of cochineal, lac dye and madder. [28,40,41,50 53] In particular the latter, containing many colourants, is the object of many research studies. Due to the large number of anthraquinones isolated from plants of the Rubiaceae family, their unambiguous identification solely by UV-Vis detection is not always possible,... 

Figure 13.2 Structures of colour components present in plants of the Rubiaceae family. A, 6 O f3 D xylopyrosyl D glycosyl...

HPLC ESI MS is also a useful tool in the analysis of non-anthraquinone red dyestuffs. The use of this technique allows the identification of carthamin as the main colour component of safflower.[34] Ten species of the genus Alkanna are extracted with hexane, and dissolved in water-methanol solution after evaporation. [47] Ammonium formate buffer (pH 3.0) was used as the mobile phase modifier. In the preparations, alkannin and many hydroxynaphthoquinones (alkannin derivatives) were identified by comparison of retention times, as mass spectra (in the NI mode) for all compounds consisted only of quasi-molecular peaks. 

Analysis of dyed fibres allows identification of real colouring components of natural dyestuffs taking part in the dyeing process. Wool threads dyed with madder (Rubia tinc-torum) as well as Our Lady s bedstraw (Galium verum), were studied by HPLC DAD ESI MS" (SIM mode).[8] Chromatograms of the extracts from wool dyed with madder... 

Indigo is considered as one of the most important dyes. Its preparations are usually analysed by HPLC with UV-Vis [46,60] or APCI MS detection. [61,62] Separation of the colouring components of indigo extracted with DMSO is usually performed with the use of a Cl 8 column. Spectrophotometric detection of blue indigotin is performed at 617 nm, red indirubin at 540 nm, and brown isoindigo at 365 and 490 nm. As mobile phases, mixtures of methanol or acetonitrile and water with the addition of TFA or formic acid are used to ensure compatibility with the requirements of the APCI source. 

A strong curry is generally dark red-brown in colour, whereas a milder curry, such as biryani, is paler in hue. And the difference in the intensity of the curry stain arises from the varying concentration of the coloured components in the curry sauce. As an example, we will discuss the red and spicy tasting compound capsaicin (I), which is the cause of both the hotness of a chilli and contributes to its red colour. 

In the blood pigment, haemoglobin, the coloured component which is separated as haemin in the manner described above is combined with a complicated protein component known as globin. According to Hans Fischer, haemin has the composition C31H3204N4FeCl. This compound in the form of the so-called Teichmann crystals serves for the microscopic detection of blood. 

Carrots with an overlay of the structure of the coloured component. 

Rubrafusarin (170), a colouring component of the fungus Fusarium culmorum, was shown to be a linear naphthopyranone rather than a xanthone by X-ray crystallography and various spectroscopic techniques (62AX451,62AX1060). 

Although there are a number of food colours suitable for use in soft drinks, it should be appreciated that the contribution of any one of these cannot be entirely predictable. In any soft drink formulation, the colour component, as with all other ingredients, has to be carefully selected for its performance in the presence of certain acids, flavourings, antioxidants and even preservatives. It is essential, therefore, at all stages of development that meaningful storage trials are completed to ascertain the real contribution from colour in the newly finished beverage. 

Clearly, Class III and IV caramels are close to melanoidins produced by the Maillard reaction, but detailed structures for the coloured components cannot be given for any of these commercial caramels. 

In order to separate or to estimate the various constituents, the chromatogram, after development, is pushed out of the glass tube and the various zones are cut with a knife at the boundaries. The coloured components are dissolved separately in suitable solvents. This process of recovery of constituents from the chromatogram is known as elution. Since 1930 column chromatography has been used extensively in the separation and purification of plant pigments and other natural products. It is now frequently used in a number of laboratory processes for purification of several other compounds as well. The substance to be purified need not be necessarily coloured. However, a... 

To facilitate easy detection and improved separation, spacer components have been inserted between the members of the displacement train. The so-called Test Substance II (Camag, Muttenz, Switzerland) has numerous coloured components e.g., the Sudan Black components are members of the displacement train optimised for the ecdysteroids, semisynthetic morphine derivatives, and various phenylalkylamines. The various Sudan Black components were inserted between the components to be separated, if both the component and the ecdysteroids (or morphine derivatives or phenylalkylamines) were displaced. Black lines and white spots were observed, showing sharp separation and easy observation. In the case of the study of metabolism, the use of spacers facilitated the differentiation of poorly separated metabolites. 

In practice, various combinations of colourants are often used. If the mutual oxidation-reduction reactions can take place, the resulting colour is not a linear combination of the effects of the individual colouring components. Moreover, the colour intensity may be affected by non-colouring components. For example, the effect of T1O2 on the colouring by Fe, Cu, and Ce is explained by its... 

Colour is vitally important as a part of vision (in sensory terms the colour component of the characteristic vision). There are physiological as well as psychological reasons for this. But it would be too complicated to embark on an explanation here. At all events, it is permissible to allow colour to be an influence when an aroma is being tested, unless the colour itself is being tested. 

This class owes its name to the fact that the dyes ionize and the coloured component always constitutes the cation. For this reason there is now a tendency to refer to them as the cationic dyes. The dye bases usually have a general formula of the type rX SnHj which is capable of salt formation... 

Beer s law generally holds good over a wide range of concentration if the structure of the coloured non-electrolyte in the dissolved state does not change with concentration. Small amount of electrolytes, which do not react chemically with the coloured components, do not usually affect the light absorption, large amounts of electrolytes may result in a shift of the maximum absorption and may also change the value of extinction coefficient. Discrepancies are normally observed when the coloured solute ionises, dissociates or associates in solution as because the nature of the species in solution will vary with the concentration. The law also fails if the... 

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