Carbohydrates, color reactions properties

Diazonium ions react rapidly with histidyl, lysyl, and tyrosyl residues to form mono- and di-azo derivatives, and much more slowly with arginyl, cysteinyl, and tryptophanyl residues.18 The lack of specificity of the reaction can create problems in interpreting results, particularly if critical residues are modified. The azo-proteins formed may be readily purified, and are intensely colored this property may permit quantitation of the extent of the reaction by measurement of the absorbance. Not uncommonly, however, the products of the reaction are of a dark-brownish color that interferes with many of the standard assays for protein and carbohydrate. 

Colored smoke mixtures also contain either sulfur or a carbohydrate as the fuel, and a volatile organic dye that sublimes from the reaction mixture to produce the colored smoke. These compositions contain a large excess of potential fuel, and their explosive properties are greatly diminished as a result. Smoke mixtures react with low flame temperatures (500°C or less)... 

In many projects involving a transformation or isolation of carbohydrates, it is important to quantify the amount of product obtained. It is sometimes difficult to measure the content of a specific component in a mixture. The process can be laborious with instrumentation such as HPLC or GC, especially if the sample contains major impurities of different natures. Fortunately, knowledge of the properties of the desired product can suggest a specific method of analysis, several of which involve colorimetric analysis. With colorimetric analyses, a selective chemical transformation will produce color. The absorbance or transmittance of the colored sample is directly correlated with the presence of a certain functional group or product in the mixture. Various reactions that produce color are known to be selective for certain types of carbohydrates. 

Caramel is unintentionally generated in burnt carbohydrate foods (rice, oatmeal, cornmeal, etc.) and molasses (Kowkabany et al., 1953) it is the source of maple flavor and color in the concentration of maple sap to maple syrup (Stinson and Willits, 1965). In industrial manufacturing, the intended application is taken into account, because reaction conditions help determine the properties of the pyrolysate, e.g., its tinctorial value, water solubility, and alcohol stability. Tinctorial value refers to the absorbance at 560 nm of a 0.1-wt/vol% solution in a 1-cm cell. Tinctorial strength increases with acidity, temperature, and duration of heating. Caramel manufactured above pH 6.3 is biologically unstable and much below pH 3.1, it is a resin. 

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