Natural products colouring

Yolk colour plays a role in consumer acceptance, but the preferred colour varies in different countries. Yolk colour has no relation to nutrient content, flavour or freshness, but is often enhanced in conventional production systems by addition of synthetic pigments to the animal feed. In organic production, synthetic yolk pigments are prohibited and this normally results in paler yolks, but may also lead to greater variability in yolk colour intensity. In many European countries paler yolk colour is perceived by consumers as being associated with less natural production systems, an issue that clearly needs to be addressed by improved consumer information. 

Synthetic MIO is used in primers as well as in topcoat paints the natural MIO was too coarse for use in undercoats. Weathering tests with different paint binders indicated that the performance of the synthetic product was as good or better than, that of the natural product (Carter and Laundon, 1990). The aspect ratio of MIO produced by hydro-thermal synthesis can be altered by doping with Al, Mn or Si, thus enabling a more lustrous material with a reddish-brown colour to be produced this material is suitable for decorative as well as for purely protective purposes (Pfaflfand Reynders, 1999). 

The flavonoids, the derivatives of 1,3-diphenylpropane, are a large group of natural products, which are widespread in higher plants hut also found in some lower plants, including algae. Most flavonoids are yellow compounds, and contrihute to the yellow colour of the flowers and fruits, where they are usually present as glycosides. 

Heterocyclic colouring matters have been in use since prehistoric times through such natural products as indigo (1) (76MI11200), its 6,6 -dibromo derivative (Tyrian Purple), extracted from the shell of the Mediterranean mollusc, Murex brandaris (74MI11200), and logwood or haematin (2). Haematin is extracted in its leuco or colourless form, haematoxylin,... 

Turpentine is an oleo-resin exuded from the trunks of certain conifers (so-called Scio turpentine is obtained from one of the Terebinthaceae, Pistada terebinthus L.) and consists essentially of resin acids, neutral resins, volatile oil and small proportions of various other substances (succinic acid, bitter principles, colouring matters, water). Distillation of turpentine and rectification of the distillate gives oil oj turpentine, the residue being colophony. By dry distillation of the latter resin oils are obtained. The present chapter deals with the natural product, i.e. turpentine, and with the products obtained from it. 

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... 

Chemically, carotenoids have conjugated double bonds which render them liable to oxidation. However, this tendency to oxidation can be reduced by adding antioxidants to the product. In the sort of product where natural colours are used, suitable antioxidants are tocopherols or ascorbic acid. Chemical antioxidants such as butylated hydroxytoluene might be suitable technically but would not fit the image of an all natural product. To create a more favourable image, ascorbic acid could be declared as vitamin C rather than as an antioxidant. As oxidation can be started by exposure to light, unsuitable storage conditions are best avoided. 

No colour is obtained with other natural products,... 

Colours and some of the other agents added to food, however, have less obvious benefit for the consumer and are probably more important for the manufacturer. Enhancing the attractiveness of food, for example, increases its saleability, which would appear to be the main reason for the use of some additives such as colouring agents. Often we as consumers prefer to have attractively coloured food, but recently many consumers have begun to question the unnecessary use of additives in food and to demand additive-free food or the use of natural additives. While this may satisfy those who believe that natural substances are intrinsically safe, the fact is that natural products can be just as toxic as synthetic ones (see pp. 145-58, 240-57). Therefore each natural food additive also needs to be assessed for safety. For example, a tin of custard powder may claim to contain no artificial colours but contains annatto as colouring, which while it may be of natural origin has been associated with adverse effects (see below). 

Technical name means a name that is generally used in commerce, regulations and codes to identify a substance or mixture, other than the lUPAC or CAS name, and that is recognized by the scientific community. Examples of technical names include those used for complex mixtures (e.g., petroleum fractions or natural products), pesticides (e.g., ISO or ANSI systems), dyestuffs (Colour Index system) and minerals ... 

Recently, 6-hydroxydihydrosanguinarine (34) has been reported as a new alkaloid isolated from Dactylicapnos torulosa Hook f et Thoms. [125,126]. The compound is described as an amorphous solid of yellow colour, however, the substance e diibits major discrepancies in ipectral data with the structure given [127]. 6-Hydroxydihydrochelerythrine has allegedly been isolated from Toddalia aculeata Pers. in the form of its acetic acid ester [128], However, its H NMR data are not in agreement with those previously published for this compound [129]. Universally, 6-hydroxydihydroderivatrves (pseudobases) are unstable semiaminoacetals with basic character which cannot occur in acidic plant tissues at all and could not be isolated as natural products especially after 5% HCl has been used in the isolation procedure cf. 125,128]. 

The number of colouring-matters included in the present chapter is unfortunately very large most of them are natural products obtained from plant and animal sources. As these natural dyestuffs are very numerous, only those are described which are of interest from a technical or scientific point of view. 

Application of natural aqueous smoke flavourings to meat is done in large part for the purpose of producing smoked colour. Smoke solutions are applied to the surface of meat where smoked product colour is desired. The carbonyls are known to be the initiators of a brown smoked colour. While aqueous smoke solutions are innately a reddish brown colour, virtually none of this colour is imparted to the product through a staining effect. Rather, carbonyls first react with amines to produce Schiff bases which eventually end up as mealnoidins through complex, multiple-step reactions which are driven by heat and dehydration. 

Often natural products in particular are subject to colour fluctuations, which are not necessarily related to taste. 

The mordant dyes are capable of combining with metallic ovides to form insoluble coloured lakes. Many of the old natural dyes siurli as. Mizarin, Logwood, Weld, and rustic were dyed on libres which had ]ire iously been impregnated, or mordanted, with hydroxides of chromium, tin, or aluminium. Some of these natural products v ere replaced by their synthetic equivalents and, after the structure of Alizarin had been determined, the range was increased by the addition of many analogous substances derived from anthraquinone. 

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