Qualitative tests for carbohydrates
There are several rapid tests available to characterize whether there is sugar or a carbohydrate in a given sample. These assays are relied on chemical reactions of carbohydrate’s functional groups: hydroxyl and carbonyl group. For hydroxyl group, the concentrated acid (i.e., sulfuric acid or hydrochloric acid) is used in the assays to produce furfural and its derivatives. Such products can then react with phenol compounds (e.g., naphthol, resorcinol and orcinol) and yield a distinct colorful product (see Figure 2.1). In addition, the free carbon atom (position 1) of the carbonyl group (as an aldose or ketose) has the reducing property and is able to reduce Cu2+, Ag+, and Fe(CN)63-. The sugars with such a property are called “reducing sugars”.