Seliwanoff’s Test for Glucose and Fructose

In this seliwanoff’s test for glucose and fructose post we have briefly explained about seliwanoff’s test’s principle, requirements, seliwanoff’s test procedure and results.

Seliwanoff's Test for Glucose and Fructose

Any material that is or might be used to make food dangerous, substandard, misbranded, or contains extraneous content is referred to as a “adulterant.” If the quality of food is diminished or changed by the addition of harmful ingredients or the removal of healthy substances, it is considered adulterated.

Lactose is the most frequent sugar found in milk. In comparison to the protein amount, milk has a higher fat content. Table sugar like sucrose is added to the milk to increase the carbohydrate content of the milk and thus the density of milk will be increased. As a result, water can now be added to milk and the lactometer test will not detect it. Sucrose is not found in milk, and its presence indicates that the milk has been adulterated. The following method can be used to determine the presence of sucrose in milk.

Principle

To discriminate between aldoses and ketoses, Seliwanoff’s test is performed. When ketoses are treated with concentrated Acid, they dehydrate more quickly, yielding furfural derivatives, and when they are condensed with resorcinol, they yield cherry red complex.

Requirements

Materials

Milk sample

Resorcinol Solution (0.5%)

Distilled Water

Water bath

Pipettes

Dry test tubes

Reagents

Resorcinol Solution (0.5%): Weigh 0.5 g of resorcinol in about 40 ml of distilled water. Add 35 ml of concentrated HCl (12 N) to it and make up the volume to 100 ml using distilled water in seliwanoff’s test.

Seliwanoff's Test Procedure

1. In a seliwanoff’s test tube, pour 1 mL of milk. Mix with 1 mL of Resorcinol Solution. Place the tube in a 5 minute boiling water bath.

2. Remove the tube and examine the color. The presence of sucrose, or a ketose sugar, is indicated by a rich red color. Pure milk samples do not produce this red tint, and the sample remains white in nature.

Result

Seliwanoff’s Test for Cane sugar

The creation of the cherry red colored complex gives a good result, indicating the presence of ketones in the milk sample. The absence of such colour or the appearance of such colour after a long time shows a negative result, indicating that the seliwanoff’s test sample does not contain ketones.

Limitations

1. The limit of detection (LOD) is usually defined as the lowest quantity or concentration of a component, Seliwanoff’s test for Milk Adulteration limit is 0.1 percent.

2. A high concentration of glucose or another sugar may interfere with seliwanoff’s test reagent by creating similar coloured molecules.

3. Long-term boiling can convert glucose to fructose by the catalytic action of acid, resulting in the formation of cherry red-complex and a false-positive result in seliwanoff’s test.

Further Readings

Reference