Synthetic colorants extraction

Fig. 1 TLC and visible absorption spectra of synthetic colors extracted from a pickled vegetable under TLC/scanning densitometry. (A) Standards of tartrazine (Y-4), orange I (Or-I), and orange RN (Or-RN). (B) Standard of orange H (Or-II). (C) Extract of the sample. TLC/scanning densitometric conditions. Plate RP-18 (E. Merck). Solvent system methyl ethyl ketone-methanol-5 % sodium sulfate (1 1 1). Apparatus Shimadzu CS-9000. Wavelength scanning range 370 700 nm. Slit size 0.4 X 0.4 mm. Measuring mode reflecting absorption.

Gonzales, M., Gallego, M., and Valcarcel, M., Liquid chromatographic determination of natural and synthetic colorants in lyophilized foods using an automatic sohd-phase extraction system, J. Agric. Food Chem., 51, 2121, 2003. 

A sequential analysis protocol includes three steps (1) extraction in water or other appropriate solvent for the colorant, (2) purification or concentration of the colorant, and (3) separation coupled with detection of the target molecule. Different methods of extracting synthetic colorants from foods have been developed using organic solvents followed by SPE protocols using as adsorption support RP-C18, amino materials, or Amberlite XAD-2. Eor qualitative evaluations, the easiest option for separating colorant molecules from unwanted ingredients found in an extract is SPE on polyamide or wool. 

Relevant Methods for Extracting, Separating, and Identifying Synthetic Colorants... 

The identification of synthetic colorants (pure or mixtures) in foods is usually carried out using spectrophotometry but the resolution of complex mixtures in food requires a previous separation of extract components by SPE and chromatographic techifiques. Dual wavelength, solid phase, and derivative spectrophotometric methods combined with chemometric approaches have been used. ... 

All these methods give similar results but their sensitivities and resolutions are different. For example, UV-Vis spectrophotometry gives good results if a single colorant or mixture of colorants (with different absorption spectra) were previously separated by SPE, ion pair formation, and a good previous extraction. Due to their added-value capability, HPLC and CE became the ideal techniques for the analysis of multicomponent mixtures of natural and synthetic colorants found in drinks. To make correct evaluations in complex dye mixtures, a chemometric multicomponent analysis (PLS, nonlinear regression) is necessary to discriminate colorant contributions from other food constituents (sugars, phenolics, etc.). 

We have observed a decreasing interest in the development of new synthetic colorants, while increased efforts are directed toward the discovery of new natural pigments and the development of extractions and formulations of natural colorants. ... 

The food industry, following scientific and technological developments and market demands, takes into account consumer wishes to have more naturally colored foods and adapts its methodologies to safer ways of producing food. In recent decades, we experienced a shift from exclusive use of certifiable synthetic colorants to exempt colorants and to natural complex extracts. 

Considering the concerns of consumers for synthetic colorants and interest in natural formulas, many food manufacturers seek alternative healthy solutions to replace colorants, even the regulated ones from positive lists (like p-carotene), with colored fruit and vegetable extracts to be used as functional food ingredients or nutraceuticals (food supplements). ... 

In recent decades, the synthetic colorant market has dechned, to the benefit of the natural-oriented market and consumers. Excluding FD C Red 40 and Red 28, the synthetic colorants are now as well accepted as they were. In addition to the decreasing enthusiasm for chemicals in food, the high costs of toxicological studies also inhibit the development and approval of new synthetic colorants. The existing technologies used for the extraction, concentration, and purification of natural plant pigments to be used as food colorants still produce lower yields and the final products are still expensive. 

For some foods, incomplete extraction of color is obtained, probably due to the high binding affinity of dyes to the bulk of the food matrix, especially to proteins, lipids, and carbohydrates (156,161,162). This problem can be overcome by the use of selected solvents or enzymes to digest the food prior to extraction. Petroleum ether can be used to extract lipids (163). Acetone can be used to remove lipids and coagulate protein (164). Enzymes, such as amyloglucosidase (165,166), papain (167), lipase, pectinase, cellulase, and phospholipase, added to the sample and incubated under optimum pH and temperature conditions release synthetic colors bound to or associated with the food matrix. Furthermore, enzyme digestion can solubilize some foods, enabling analysis to be continued (156). 

The use of polyamide is advantageous because it separates natural from synthetic coloring material, removes sugars, acids, and flavoring materials, and concentrates dilute solutions of colors (156,167). However, the use of polyamide is not applicable to chocolate brown FB, chocolate brown HT, or indigotine, because the two chocolate browns are not completely eluted from the column and indigotine decomposes during extraction (157). 

Tetrabutylammonium phosphate was used for the extraction of dyes from grape beverages. Sample containing TBA was passed through a Sep-Pak Cl 8 cartridge. The synthetic colors were retained on the column while most natural colors were not. The cartridge is washed with water and the synthetic colors are eluted with methanol water, 1 1 v/v (159). 

Confirmation of the identity of synthetic colors can be obtained by subjecting the purified extracts to UV-V1S spectrophotometric examination. As an aid to identification, Wadds (225) and Young (190) have reproduced the UV-VIS absorption spectra in neutral, acidic, and alkaline media of 16 commonly used synthetic colors. 

The synthetic color industry dates back to the accidental discovery of the first synthetic organic dye (mauve) in 1856. Sir William Henry Perkin, in an unsuccessful attempt to synthesize quinine, succeeded in obtaining a violet dye by the oxidation of aniline. This led other scientists to experiment and discover many new colors with superior properties to the natural pigments and extracts. The use of these new and different colors in foods, drugs, and cosmetics began almost immediately because of their tinctorial value, stability, and the many shades in which they were available. 

Only for dietary supplements or processed food samples, extraction of anthoeyanins followed by solid phase purification with subsequent analysis by HPLC with UVA/ IS detection is performed as first level analysis. The matrix in those samples is complex and may include synthetic colorants in accordance with applicable food legislation, hence simple UVA IS analysis would yield most certainly erroneousness results. At this stage of analysis a decision is necessary on whether or not HPLC/MS analysis has to be performed. HPLC/ MS is powerful for the confirmation of anthocyanin structures but seldom useful for quantification as the calibration is complicated and robustness is low. 

Valcarcel and co-workers proposed in 2003 an automatic system for the determination of riboflavin in lyophilized food products using a solid-phase extraction process that included columns filled with cotton or silica C18 for the sequential retention of synthetic colorants and natural colorants, respectively (Gonzalez et al. 2003). In this case riboflavin was assessed as an authorized natural colorant for total estimation of this class of compounds. The analytical characteristics of this methodology are summarized in Table 18.3. 

As early as 2500 bce m India indigo was used to dye cloth a deep blue The early Phoenicians discovered that a purple dye of great value Tyrian purple could be extracted from a Mediterranean sea snail The beauty of the color and its scarcity made purple the color of royalty The availability of dyestuffs underwent an abrupt change m 1856 when William Henry Perkin an 18 year old student accidentally discovered a simple way to prepare a deep purple dye which he called mauveme from extracts of coal tar This led to a search for other synthetic dyes and forged a permanent link between industry and chemical research... 

Qumones are colored p benzoqumone for example is yellow Many occur natu rally and have been used as dyes Alizarin is a red pigment extracted from the roots of the madder plant Its preparation from anthracene a coal tar derivative m 1868 was a significant step m the development of the synthetic dyestuff industry... 

Animals that do not readily accept pelleted feeds may be enticed to do so if the feed carries an odor that induces ingestion. Color development is an important consideration in aquarium species and some animals produced for human food. External coloration is desired in aquarium species. Pink flesh in cultured salmon is desired by much of the consuming pubHc. Coloration, whether external or of the flesh, can be achieved by incorporating ingredients that contain pigments or by adding extracts or synthetic compounds. One class of additives that imparts color is the carotenoids. 

The most popular natural antioxidants on the market are rosemary extracts and tocopherols. Natural antioxidants have several drawbacks which limit use. Tocopherols are not as effective ia vegetable fats and oils as they are ia animal fats. Herb extracts often impart undesirable colors or flavors ia the products where used. In addition, natural antioxidants cost considerably more than synthetic ones. Despite this, the pubHc s uncertainty of the safety of synthetic antioxidants continues to fuel the demand for natural ones (21). 

Hair coloring preparations have been in use since the ancient Egyptians, and recorded recipes exist in many cultures. These followed the traditional apphcation of plant extracts or metallic dyes, both of which still are used. In the latter part of the nineteenth century, synthetic organic compounds were discovered which eventually led to modem hair coloring. 

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