Barfoed’s Test: Objective, Principle, Reagents, Procedure and Result
Objective:
- to detect reducing sugar
- to distinguish monosaccharides from reducing disaccharides
Principle of Barfoed’s test:
Barfoed’s test is used for distinguishing monosaccharides from reducing disaccharides. Monosaccharides usually react in about 1-2 minute while the reducing disaccharides take much longer time between 7-12 minutes to react with the reagent. Brick red color is obtained in this test which is due to formation of cuprous oxide.
Reagents for Barfoed’s test:
- test solution: 5 % Glucose, 5 % Sucrose, 5 % Maltose, 5 % Lactose, 5 % Starch
- Barfoed’s reagent: cupric acetate in 1% acetic acid
- Water bath
- Dry test tubes
- Pipettes
Procedure of Barfoed’s test:
- Take 1ml of test sample in dry test tube.
- Take 1ml of distilled water in another tube as control.
- Add 2ml of Barfoed’s reagent to all the tubes.
- Keep in boiling water bath.
- Look for the development of brick red precipitate.
- Note the time taken to develop the color.
Result interpretation of Barfoed’s test:
- Positive Barfoed’s test: development of brick red color ppt within 3-5 minutes
- Negative Barfoed’s test: absence of red color
** reducing disaccharides also give positive barfoed test on prolong heating