Carbohydrate Classification and Tests

Carbohydrate Classification

• Carbohydrates are aliphatic organic compounds that do not contain acidic groups.
• Classified into three categories: monosaccharides, disaccharides and polysaccharides.
• Monosaccharides are simple sugars like glucose and fructose.
• Disaccharides are made up of two monosaccharide units, such as lactose, maltose and sucrose.
• Disaccharides can be categorized as reducing or non-reducing sugars.
• Polysaccharides are complex carbohydrates formed by many monosaccharide units, like starch.

Molish Test

• A general test for carbohydrates.
• A violet ring forms at the interface of two liquids when α-naphthol and concentrated sulfuric acid are added to a carbohydrate solution.
• The violet color spreads throughout the solution after shaking.

Iodine Test

• Detects the presence of starch.
• A blue solution indicates a positive test for starch.
• A pale yellow solution indicates a negative test for starch.

Fehling's Test

• Detects the presence of reducing sugars.
• A brown or reddish-brown solution after boiling indicates a reducing sugar.
• No color change indicates a non-reducing sugar.

Tollen's Test

• Tests for reducing sugars.
• A silver or grey precipitate forms when the solution is heated in a water bath, indicating a reducing sugar.
• No precipitate indicates sucrose.

Osazone Test

• Differentiates between monosaccharides and disaccharides.
• Yellow crystals formed while heating indicate monosaccharides (e.g., glucose, fructose).
• Yellow crystals formed after heating indicate disaccharides (e.g., lactose, maltose).

Rapid Furfural Test

• Differentiates between glucose and fructose.
• A violet color appearing during boiling indicates fructose.
• A violet color appearing after boiling for two minutes indicates glucose.

Furfural Test

• Differentiates between glucose and fructose.
• A yellow color on aniline acetate paper inserted at the top of the tube indicates glucose.
• No change in color indicates the presence of fructose.