Ammonia, reaction with reducing sugars

Caramel in this context means a brown colour that is produced either traditionally by heating sugar or as a very intense product that is made by heating carbohydrate, usually glucose syrup, with ammonia. Caramel colour is the product of the Maillard reaction, i.e. the reaction of a reducing sugar with an amino group. Chemically the colour is a melanoidin - these substances are extremely stable and can be used in any type of confectionery. 

A further quantity of the same substance was prepared by these workers and purified by repeated precipitation with lead acetate and ammonia. The product had [q ]d + 67.7° which changed to —10° after hydrolysis with dilute sulfuric acid for four hours. The amount of reducing sugar present was 75.6%. Mannose, D-arabinose and an unidentified sugar acid were obtained from the hydrolyzate. The substance did not produce a skin reaction, nor did it stimulate antibody formation. It reacted with immune serum in high dilution (1 2,000,000) in the precipitin test. It was claimed that this product was closely related to the polysaccharide isolated by Laidlaw and Dudley. ... 

Pyridine has found some use as a catalyst for the transformation— especially in applications to ketose synthesis. The base has usually been employed as both catalyst and solvent (in anhydrous form). Under these conditions, it appears to act sluggishly—a conclusion which, since anhydrous pyridine solutions of a reducing sugar contain no acid except the sugar itself, is in accord with the idea that the transformation requires an acid as well as a base for its catalysis. The possibility of increasing the reaction rates by incorporating an appropriate acid catalyst, such as phenol, into these pyridine mixtures should be explored. Other nitrogenous bases which have been reported as catalysts for the transformation are ammonia, quinoline, and quinaldinc. ... 

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