Natural pigments quantitation

Neutralization indicators, or acid-base indicators or pH indicators, are auxiliary reagents added to the titrand solution in order to detect the equivalence point in acid-base titrations. They can also be used for an accurate quantitative measure of the pH. Tournesol, a natural pigment extracted from some blue-green lichens, was the first pH indicator to be used (1850). Phenolphthalein and methyl orange were introduced somewhat later (1877 and 1878, respectively). Undeniably, the chief interests in the use of acid-base indicators are their low cost and ease of handling. However, they give rise to less precise and less accurate endpoints than some instrumental methods. 

The pH differential method was described as a fast and convenient assay for the quantitation of monomeric anthocyanins by Giusti (2001). It was approved by the Association of OfQcial Analytical Chemists (AOAC) in 2005 as a standard method to evaluate total monomeric anthocyanin pigment content in fruit juices, beverages, natural colorants, and wines. The degradation index is the ratio between total and monomeric anthocyanins (Table 6.3.1). The content of total anthocyanins can be obtained by the single pH method and the monomeric anthocyanin by the pH differential method. ... 

Lipoproteins. The lipid moiety of the lipoproteins is quite variable, both qualitatively and quantitatively Mucoproteins are carbohydrate in nature Chromoproteins are pigments... 

For almost any experiment that involves a light microscope, quantitative data to test a hypothesis may be obtained by microphotometry. Add a photometer and a few accessories to a light microscope, and it may be possible to quantify a cytochemical reaction product, measure the spectrum of a pigment, quantify natural or induced fluorescence, quantify birefringence, or map and analyze an image. But manually collecting thousands of numbers is unbelievably tedious. The solution is obvious. Use a personal computer (PC) to collect the numbers. 

Numerous CE separations have been published for synthetic colours, sweeteners and preservatives (Frazier et al., 2000a Sadecka and Polonsky, 2000 Frazier et al., 2000b). A rapid CZE separation with diode array detection for six common synthetic food dyes in beverages, jellies and symps was described by Perez-Urquiza and Beltran (2000). Kuo et al. (1998) separated eight colours within 10 minutes using a pH 9.5 borax-NaOH buffer containing 5 mM /3-cyclodextrin. This latter method was suitable for separation of synthetic food colours in ice-cream bars and fmit soda drinks with very limited sample preparation. However the procedure was not validated for quantitative analysis. A review of natural colours and pigments analysis was made by Watanabe and Terabe (2000). Da Costa et al. (2000) reviewed the analysis of anthocyanin colours by CE and HPLC but concluded that the latter technique is more robust and applicable to complex sample types. Caramel type IV in soft drinks was identified and quantified by CE (Royle et al., 1998). 

Because of their high separation capacity, short analysis time, low reagent consumption and simplicity, various electrophoretic methods have found application in the separation and quantitative determination of anthocyanins in various complex matrices [267].The different techniques used for the measurement of anthocyanins in beverages [268], the application of capillary electrophoresis (CE) for the analysis of natural food pigments [269], the use of CE for the determination of anthocyanins in foods [270] and in medicinal plants [271] have been previously reviewed. 

Since arucadiol and miltirone both have an aromatic "B" ring, enone 64 served as a common intermediate for both of these quinone pigments. The aromatization of 64 was readily achieved using 2,3-dicyano-5,6-dichloro-l,4-quinone (DDQ) (Equation 5.2). With substrate 65 in hand, only demethylation of the ethers was required to complete a synthesis of arucadiol (58). This transformation was accomplished in nearly quantitative yield using boron tribromide. Our synthetic arcudiol was spectrally identical with the natural material. 

The analysis of the natural carotenoid pigments found in orange juice, for example, is extremely complex and should be left to an expert laboratory. However, the quantitative analysis of added /3-carotene and/or /3-apo-8 -carotenal to an orange drink or dilutable is much easier as pure standards are commercially available and these compounds can be readily separated using HPLC. 

Although there are a number of important food components which are naturally fluorescent (e.g., cereal brans, lignified materials such as pea, soy and cotton fiber, and even proteins and pigments), detection of many food components requires application of specific fluorochromes or diachromes. Therefore, quantitative analysis using microscopic imaging also requires judicious use of sensitive dyes or stains suitable for visualization and rapid measurement. The dyes must be stable, non-toxic to liing cells, easily and inexpensively... 

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