Natural colorants

Natural colorants, both of dyes or pigments, can be derived from natural sources all over the world, including from plants, animals and microorganisms such as bacteria that extract the colorant of various materials. Most natural colorants faU into six general classes which include (21)  

Examples of tetrapyrroles include porphyrins and porphyrin derivatives and more specifically, chlorophylls, heme pigments and bilins. Examples of tetra-terpenoids or carotenoids include carotenes and xanthophylls. Examples of quinines include benzo-quinones, anthraquinones and naphthiquinones. Examples of oxygen-containing heterocyclic compounds such as flavonoids include anthocyanins and flavonols. Examples of nitrogen-containing heterocyclic compounds include indigoids and indole derivatives, such as betalaines and eumelanins, and substituted pyrimidines such as pterins and purines. 

Finally, examples of metallo-proteins, such as oligomeric proteins, include iron-based proteins such as haemerythrin and myohemery-thrin, which exhibit color in an oxygenated state. Other examples of natural colorants are lipofuscins and fungal pigments (21). Specific examples of dyes from natural resources are summarized in Table 3.11. 

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The three classes of PE, designated as A, B, and C, specify the color, amount, and type of antioxidants and other additives. Class A refers to naturally colored PE, Class B includes white or black polymer, and Class C covers weather-resistant black polymer containing no less than 2% carbon black. Typical characteristics of resins used for film manufacture, injection mol ding, and blow mol ding are given in Table 5. 

ISO 4660, Bubber, Bjaw Natural—Color Index Test, International Organization for Standardization, Geneva, Switzerland, 1991. 

Other Color Order Systems. The Natural Color System (24), abbreviated NCS, developed ia Sweden is an outgrowth of the Hesselgren Color Adas, and uses the opponent color approach. Here colors are described on the basis of their resemblances to the basic color pairs red-green and blue-yeUow, and the amounts of black and white present, all evaluated as percentages. Consider a color that has 10% whiteness, 50% blackness, 20% yellowness, and 20% redness note that the sum is 100%. The overall NCS designation of this color is 50, 40, Y50R iadicating ia sequence the blackness, the chromaticness (20 + 20), and the hue (50% on the way from yellow to red the sequence used is Y, R, G, B, Y). 

Most staple foods such as meat, white bread, potatoes and other vegetables, and most fmits are not artificially colored siace their natural appearance is perfecdy acceptable. Foods are usually colored because they have no natural color of their own, because their natural color was destroyed or drastically altered as a result of processiag or storage, or because their color varies greatly with the season of the year or their geographic origin. Thus, colorants are added to foods to make them appear the way the customer wants and expects them to appear. 

Other products having natural color that varies enough to make standardization of their color desirable include the shells of certain kinds of nuts, the skins of red and sweet potatoes, and ripe oHves. 

N. Dkiesen, FoodTechnol, 40 (May 1975). Toxicology and Regulation of Natural Colors. Some thoughts on international regulation. 

Flavones. These compounds are the most widely distributed natural coloring matter formerly used as dyestuffs. The term flavone was first suggested in 1895 (69), and is indicative of their yellow color ijlavus, Latin for yellow). They have lost their commercial value as dyes since the advent of synthetic dyes in 1856. 

Lohschmidt sche Zahl. Lohschmidt number. Lokal, n, locality, place tavern shop, -farbe, /. natural color, -geschmack, m, local taste, lokalisieren, v.t. localize. 

Methods are described for determining the extent to which original natural color is preserved in processing and subsequent storage of foods. Color differences may be evaluated indirectly in terms of some physical characteristic of the sample or extracted fraction thereof that is largely responsible for the color characteristics. For evaluation more directly in terms of what the observer actually sees, color differences are measured by reflectance spectrophotometry and photoelectric colorimetry and expressed as differences in psychophysical indexes such as luminous reflectance and chromaticity. The reflectance spectro-photometric method provides time-constant records in research investigation on foods, while photoelectric colorimeters and reflectometers may prove useful in industrial color applications. Psychophysical notation may be converted by standard methods to the colorimetrically more descriptive terms of Munsell hue, value, and chroma. Here color charts are useful for a direct evaluation of results. 

When testing for a tannin reserve or tannin index, the presence of natural color aids detection. Testing for tannin is simple and relatively accurate using either a permanganate reduction test (development of permanent purple color) or lignin/tannic acid polymer test (tungstate blue color). 

Besides artificial colors, many natural colors are used in foods. Some of these are ... 

Delgado-Vargas, F. and Paredes-Lopez, O., Natural Colorants for Food and Nutra-ceutical Uses, CRC Press, Boca Raton, FL, 2003, chap. 2. 

Chaudhry, Y., Carotenoids natural food colors and health benefits. Symposium 12 Interaction of Natural Colors with Other Ingredients, July 19, 2003, GNT USA Inc., Tarrytown, NY. 

As for anthocyanins, betalains are found in vacuoles and cytosols of plant cells. From the various natural sources of betalains, beetroot (Beta vulgaris) and prickly pear cactus (Opuntia ficus indica) are the only edible sources of these compounds. In the food industry, betalains are less commonly used as natural colorants from plant sources than anthocyanins and carotenoids, probably related to their more restricted distribution in nature. To date, red beetroot is the only betalain source exploited for use as a natural food coloring agent. The major betalain in red beetroot is betanin (or betanidin 5-0-P-glucoside). Prickly pear fruits contain mainly (purple-red) betanin and (yellow-orange) indicaxanthin and the color of these fruits is directly related to the betanin-to-indicaxanthin ratio (99 to 1, 1 to 8, and 2 to 1, respectively in white, yellow, and red fruits)." ... 

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