Food dyes, reduction

Azoreductase Reductive deavage of azo compounds Food dyes, sulfasalazine... 

Dubin P, Wright KL (1975) Reduction of azo food dyes in cultures of Proteus vulgaris. Xenobiotica 5 563-571... 

As for food dyes, many of these are azo compounds, which implies the possibility of reduction, e.g., by the action of certain bacteria. The loss of color, in these cases, is an indication of spoilage. Bisulfite is also able to reduce azo dyes (Wedzicha and Rumbelow, 1981). 

Scheline RR, Nygaard RT, Longberg B (1970) Enzymatic reduction of azo dye, Acid Yellow, by extracts of Streptococcus faecalis, isolated from rat intestine. Food Cosmet Toxicol 8 55-58... 

Rafii F, Moore JD, Ruseler-van Embden JGH, Cemiglia CE (1995) Bacterial reduction of azo dyes used in foods, drugs and cosmetics. Microecol Ther 25 147-156... 

One consequence of the uptake of some contaminants is a reduction in the ability of lysosomes to retain the dye Neutral Red. As a consequence, the Neutral Red retention time has been developed as an index of lysosomal membrane fragility and thus of toxicity. The test has been used on the digestive cells involved with intracellular digestion of endocytosed food following administration of organic contaminants, such as polycyclic aromatic hydrocarbons [71]. The phenomenon has been reported many times after exposure to... 

Azo-based dyes, known to be carcinogenic, contain easily hydrolyzed azo bonds. In the GI tract, these bonds are cleaved to yield the free aromatic amine(s) [20]. Azo reduction may also take place in the liver of humans and other mammals by reductase enzymes, but it is likely that hydrolysis in the GI tract is predominant [21]. The resultant aromatic amines are easily absorbed in the intestines. It was found that inclusion of sulfonate moieties on the aromatic amine feedstocks mitigates the toxicity, as illustrated with the azo dye Brilliant Black BN (Cl Food Black 1) in Figure 13.6. The sulfonate moieties are highly ionized in the GI tract and at environmental pHs (5-9), and their reduction products cannot penetrate the GI endothelial membranes following oral exposure. Consequently, the chemicals are poorly absorbed, and any portion that is absorbed is rapidly excreted in the urine [22, 23]. 

Reduction of the azo dye piontosil to produce the antibacterial drug sulfanilamide (Fig. 4.38) is a well-known example of azo reduction. This reaction is catalyzed by cytochromes P-450 and is also carried out by the reductases in the gut bacteria. The reduction of azo groups in food coloring dyes such as amaranth is catalyzed by several enzymes, including cytochromes P-450, NADPH cytochrome P-450 reductase, and DT-diaphorase, a cytosolic enzyme. 

Comminution also may be used to examine the stability of dispersed phases such as oil droplets. Depending on the viscosity of the product one simply mixes it or breaks it up in a solvent (usually water but, for example, use fresh soybean oil for chocolate), a buffer or the appropriate dyes (below). For instance, we mix easily dispersible foods (cream cheese, ice cream mix or tablespreads) with dyes on slides in a ratio of about 1 1 before examination. Where the dye is a diachrome (that is, highly colored) or is fluorescent in the absence of the substrate (for example, Acridine Orange) some attempt must be made to remove excess, uncomplexed dye molecules which might confound the interpretation. This can be done by reduction of the dye concentration or by making the preparation thinner. The advantage of these simple techniques is that a battery of microchemical tests to identify protein, lipid and carbohydrate can be completed on multiple samples in a very short time period. 

Other colourants in use are sunset yellow (Eiio), another synthetic azo dye, and caramel. Caramel colours are manufactured from sugars and are very widely used. This food colour has caused some concern due to effects in experimental animals, for example the reduction in the number of white blood cells in rats. This may be due to the effects of contaminants at the high doses given which may be enhanced by a reduced intake of vitamin B6 in the diet. Annatto and beta carotene are naturally occurring colourants, but in one study 26 per cent of patients with chronic urticaria were shown to react to annatto. 

---