PRACTICAL 2: FOOD TEST

Objective:

1. To test the presence of starch, reducing sugars, non-reducing sugars, proteins and lipids in food samples.

Hypothesis: Food sample A contains starch, food sample B contains non-reducing sugar (sucrose), food sample C contains protein, food sample D contains reducing sugar (glucose), food sample E contains lipid

Variables:

a) Manipulated: Types of food samplesb) Responding: Changes colour of food samplesc) Fixed: Volume of the reagent used Literature review:

400 B.C. -- Hippocrates, the "Father of Medicine", said to his students, "Let thy food be thy medicine and thy medicine be thy food". He also saidA wise man should consider that health is the greatest of human blessings.Materials and apparatus:

Iodine solution, Benedict solution, sodium hydrogen carbonate solution, 20% sodium hydroxide solution, hydrochloric acid, 1% copper (II) sulphate solution and food samples (unknown to students)

(A-raisin/dates solution, B-pounded groundnut, C-milk, D-honey syrup, and E- mayonnaise) the food samples can varies.

Test tubes, test-tube holders, beakers, Bunsen burner, dropper, wire gauze, tripod stand, white tile and filter paper.

Procedure:

1. Five samples of food labelled A, B.C, D and E is prepared.

2. Food tests are carried out to determine presence of starch, reducing sugars, non-reducing sugars, proteins and lipids in these food samples.Results:

Food

sampleTest forProcedureObservationInference

AStarch1. Pour 2ml of sample A into a test tube2. Add three drops of iodine solution to the food sample

3. Observe what happens

4. Repeat steps 1 to 3 with other food samples.A blue black colour formed on the solutionThis is because starch is present in the solution.

BNon-reducing sugar1. Pour 2 ml of sample B into a boiling tube. Then add a few drops of dilute hydrochloric acid2. Heat the mixture in a water bath for about five minutes

3. Remove the boiling tube from water bath and cool the mixture under a running tap.

4. Neutralise the acid by adding sodium hydrogen carbonate solution until the effervescence stops.

5. Then, conduct Benedicts test on the mixture.

6. Observe any colour change in the mixture.

7. Repeat steps 1 to 6 using other food samples. Solution remains clear This is because non-reducing sugar (sucrose) is present in the solution.

CProtein, 1. Pour 2ml of sample C into a test tube.2. Add 20% sodium hydroxide solution in excess to the food sample and shake well.

3. Slowly, add a few drops of 1% copper (II) sulphate solution to the mixture.

4. Shake well and allow the mixture to stand.

5. Observe any colour change in the mixture.

6. Repeat steps 1 to 5 using other food samples. A blue or lilac purple form in the solution.This is because protein is present in the solution.

DReducing sugar1. Pour about 2ml of sample D into a test tube.2. Add about 1ml of Benedicts solution to the food sample

3. Shake the mixture. Then, heat the test tube by placing it in water bath until the mixture is brought to a boil.

4. Observe any colour change that takes place.

5. Repeat steps 1 to 4 using other food samples.A brown or red precipitate is formed in the solution This is because reducing sugar (glucose) is present in the solution

ELipids1. Rub a small amount of each food sample on a piece of filter paper. 2. Dry the filter paper. You may use a hairdryer.

3. Hold the filter paper against the light. Record your observations. A cloudy white emulsion is formed on the filter paper.This is because lipids are present in the food sample.

Discussion:

1. When a reducing sugar is heated with Benedicts solution, the reducing sugar reduces the blue copper (II) sulphate in Benedicts solution to form a red precipitate of copper (I) oxide.

2. A brick-red precipitate indicates that a large amount of reducing sugar is present while an orange or green precipitate indicates the presence of a lesser amount of reducing sugar. If the original pale blue colour of the solution remains, this indicates that reducing sugar is not present.3. The different food samples are first heated with dilute hydrochloric acid to hydrolyse the non-reducing sugar (sucrose) to its constituent monosaccharides (glucose and fructose) which are reducing sugars.

4. The mixture of food sample and hydrochloric acid is first neutralised by adding sodium hydrogen carbonate powder before adding Benedicts solution.

5. If the food sample provided is solid, the food needs to be cut into very small piece or ground before adding a little water to provide a more concentrated solution for testing.

Conclusion:

The hypothesis is accepted. Food sample A contains starch, food sample B contains non-reducing sugar, food sample C contains protein, food sample D contains reducing sugar and food sample E contains lipids. PRACTICAL 2: FOOD TEST

Objective:

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Hypothesis:

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Literature review:

400 B.C. -- Hippocrates, the "Father of Medicine", said to his students, "Let thy food be thy medicine and thy medicine be thy food". He also saidA wise man should consider that health is the greatest of human blessings.Materials and apparatus:

.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................Procedure:

1. Five samples of food labelled A, B.C, D and E is prepared.

2. Food tests are carried out to determine presence of starch, reducing sugars, non-reducing sugars, proteins and lipids in these food samples.

Results:

Food

sampleTest forProcedureObservationInference

AStarch1. Pour 2ml of sample A into a test tube

2. Add three drops of iodine solution to the food sample

3. Observe what happens

4. Repeat steps 1 to 3 with other food samples.

BNon-reducing sugar1. Pour 2 ml of sample B into a boiling tube. Then add a few drops of dilute hydrochloric acid

2. Heat the mixture in a water bath for about five minutes

3. Remove the boiling tube from water bath and cool the mixture under a running tap.

4. Neutralise the acid by adding sodium hydrogen carbonate solution until the effervescence stops.

5. Then, conduct Benedicts test on the mixture.

6. Observe any colour change in the mixture.

7. Repeat steps 1 to 6 using other food samples.

CProtein, 1. Pour 2ml of sample C into a test tube.

2. Add 20% sodium hydroxide solution in excess to the food sample and shake well.

3. Slowly, add a few drops of 1% copper (II) sulphate solution to the mixture.

4. Shake well and allow the mixture to stand.

5. Observe any colour change in the mixture.

6. Repeat steps 1 to 5 using other food samples.

DReducing sugar1. Pour about 2ml of sample D into a test tube.

2. Add about 1ml of Benedicts solution to the food sample

3. Shake the mixture. Then, heat the test tube by placing it in water bath until the mixture is brought to a boil.

4. Observe any colour change that takes place.

5. Repeat steps 1 to 4 using other food samples.

ELipids1. Rub a small amount of each food sample on a piece of filter paper.

2. Dry the filter paper. You may use a hairdryer.

3. Hold the filter paper against the light. Record your observations.

Discussion:

1. When a reducing sugar is heated with Benedicts solution, the reducing sugar reduces the blue copper (II) sulphate in Benedicts solution to form a red precipitate of copper (I) oxide.

2. A brick-red precipitate indicates that a large amount of reducing sugar is present while an orange or green precipitate indicates the presence of a lesser amount of reducing sugar. If the original pale blue colour of the solution remains, this indicates that reducing sugar is not present.

3. The different food samples are first heated with dilute hydrochloric acid to hydrolyse the non-reducing sugar (sucrose) to its constituent monosaccharides (glucose and fructose) which are reducing sugars.

4. The mixture of food sample and hydrochloric acid is first neutralised by adding sodium hydrogen carbonate powder before adding Benedicts solution.

5. If the food sample provided is solid, the food needs to be cut into very small piece or ground before adding a little water to provide a more concentrated solution for testing.

Conclusion:

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