To study the biochemical tests for starch, sucrose, glucose, fat and protein.

                                                                                                                                         (Biochemistry)

Principle:  Presence of the substances can be ascertained using some confirmatory tests.

Materials required: 5 test tubes, test tube holder, starch solution, glucose solution, sucrose solution, vegetable oil, protein solution, iodine solution, Fehling’s solutions A and B, paper, Sudan III, benzene, , Biuret solution, Xanthoproteic reagent, spirit lamp

 Procedure:  

STARCH

Sr no.	Test	Observation	Inference
1.	Iodine Test: Take about 2 ml of the sample solution in a test tube and add one or two drops of iodine solution in it.	Solution turns blue.	Starch is present.

Result: The given sample solution is starch.

 

 SUCROSE

Sr no.	Test	Observation	Inference
1.	Iodine Test: Take about 2 ml of the sample solution in a test tube and add one or two drops of iodine solution in it.	No blue colour.	Starch is absent.
2.	Fehling’s Test: Take about 2 ml of the sample solution in a test tube; and add some amount Fehling’s solution A and B (in equal amount) Heat the mixture of the test tube.	Red precipitate is not formed.	Monosaccharide (Glucose, fructose) is absent.
3.	Fehling’s Test: Take about 2 ml of the sample solution in a test tube; and add 2 or 3 drops of dil HCl. Stir it. Heat the mixture in a test tube. Now add some amount of Fehling’s solution A and B (in equal amount). Heat the mixture of the test tube.	Red coloured precipitate is formed.	Monosaccharide (Glucose or fructose) is present.  (On adding dil HCl, Sucrose hydrolyses into glucose and fructose.)

Result: The given sample solution is sucrose.

 

GLUCOSE

Sr no.	Test	Observation	Inference
1.	Iodine Test: Take about 2 ml of the sample solution in a test tube and add one or two drops of iodine solution in it.	No blue colour.	Starch is absent.
2.	Fehling’s Test: Take about 2 ml of the sample solution in a test tube; and add some amount of Fehling’s solution A and B (in equal amount) Heat the mixture of the test tube.	Red coloured precipitate is formed.	Monosaccharide (Glucose, fructose) is present.   Presence of glucose is confirmed.
3.	Benedict’s  Test: Take about 2 ml of the sample solution and add some amount of Benedict’s solution. Stir it. Heat the mixture of the test tube.	Red coloured precipitate is formed.	Presence of glucose is reconfirmed.

Result: The given sample solution is glucose. 

 

 

FAT

Sr no.	Test	Observation	Inference
1.	Paper Test: Put a drop of the sample on a paper.	Translucent area is formed on the paper. Or Some area is translucent.	Fat is confirmed. Or Some fat is present in the solution.
2.	Solubility Test: Take 2 ml of the sample in a test tube; and add 2 ml of water in it. Stir it.	Sample floats on water. Two layers are formed.	Fat is possible.
	Take 2 ml of the sample in a test tube; and add some benzene (or chloroform or ether) in it.	Sample is soluble in benzene (or chloroform or ether).	Fat is possible.
3.	Sudan III Test: Take 2 ml of the sample in a test tube; and add a little Sudan III in it. Stir it.	Pink droplets appear.	Fat is confirmed.

Result: The given sample is fat. 

 

PROTEIN

 

Sr no.	Test	Observation	Inference
1.	Biuret Test: Take 2 ml of the sample solution in a test tube; and add some Biuret solution. Stir it.	Blue-violet colour appears.	Presence of protein is confirmed.
2.	Xanthoproteic Test: Take 2 ml of the sample solution in a test tube; and add Xanthoproteic reagent in it. Stir it. Heat the mixture.	Yellow precipitate is formed.	Presence of protein is reconfirmed.

Result: The given sample solution has protein in it.