Disaccharides

Disaccharides are carbohydrates composed of two monosaccharide units linked together through a glycosidic bond. They are sweet in taste. These molecules serve as a fundamental energy source in living organisms, and on hydrolyzes yield simple sugars that can readily be absorbed and utilized by the body of living organisms. One of the most common disaccharides is sucrose(also called table sugar), formed by linking glucose and fructose. Lactose(also called milk sugar), another important disaccharide, consists of glucose and galactose and is primarily found in milk. Maltose, composed of two glucose units, arises from the breakdown of starch during digestion.

Barfoed’s Test for Disaccharides

The Barfoed’s Test is a chemical test used to distinguish between monosaccharides and disaccharides based on their ability to form copper(I) oxide upon heating in the presence of an acidic copper(II) acetate solution (Barfoed’s reagent). Here’s how the Barfoed’s Test works specifically for detecting disaccharides:

Principle:

Barfoed’s reagent consists of a solution of copper(II) acetate in acetic acid. Disaccharides, such as maltose, can hydrolyze under acidic conditions to release reducing monosaccharides (e.g., glucose). These reducing monosaccharides can react with the copper(II) ions in Barfoed’s reagent to form a red precipitate of copper(I) oxide upon heating.

Requirements:

Reagent

• Barfoed’s reagent()

• sample

Material required

• Pipettes
• Test tube
• Test tube holder

Equipment

• Vortex

• Water bath

Procedure:

• Take 1 ml of the sample(disaccharides) in a clean and dry test tube.
• Take control of 1 ml of distilled water in another test tube.
• Add 2-3 drops of Barfoed’s reagent in both test tubes.

• And mix it well in the vortex after the addition of barfoed’s reagent

• Keep the test tubes in a water bath for 2 minutes.

• As the monosaccharides hydrolyze into simple sugars( monosaccharides) give positive results if the sample is disaccharides.
• Note the change in color in both test tubes.
• Note the time of appearance of color in a sample test tube.

Results:

• If a reddish-brown precipitate forms within a few minutes of heating, it indicates the presence of reducing sugars, typically derived from disaccharides like maltose.
• Disaccharides that can hydrolyze under acidic conditions (e.g., maltose) will yield a positive result due to the release of reducing monosaccharides (e.g., glucose) that react with the Barfoed’s reagent

Advantages:

• Barfoed’s Test is relatively simple and quick to perform.
• It provides a qualitative indication of the presence of disaccharides that can hydrolyze to form reducing sugars.
• It gives positive results for monosaccharides if it is reducing in nature.

Limitations:

• It primarily detects disaccharides that hydrolyze to release reducing sugars. Non-reducing disaccharides (e.g., sucrose) will not give a positive result unless they are hydrolyzed first.
• The qualitative test may not provide precise quantitative measurements without calibration against standards.

Summary

Barfoed’s Test is a useful method for detecting disaccharides that can hydrolyze to release reducing sugars under acidic conditions. It provides a straightforward indication of the presence of such carbohydrates based on the formation of a reddish-brown precipitate of copper(I) oxide upon heating with Barfoed’s reagent.

FAQ