Food Tests Lab Report

Food Test 1: Test for Glucose – with Benedicts solution Benedicts solution is used to test for simple sugars, such as glucose. It is a clear blue solution of sodium and copper salts. In presence of simple sugars, the blue solution changes color to either green, yellow or brick-red, depending on the amount of sugar.

Method

1. Mix smalls amount of each food sample (i. e. , Egg lumen, cylindrical piece of potato tuber, bread crump and crisps) in different test tubes with distilled water to make a liquid test.Take another test tube with glucose

   solution to act as a control so as to compare the difference in color after the completion of the experiment.

2. Label each of the test tubes with a marker for the substance.

3. Add 10 drops of Benedict’s solution to each test tube.

4. Carefully heat the test tubes by suspending in a hot water bath using a 500 ml beaker at about 40-50 degrees Celsius for five minutes.

5. Note any color change.

Positive test for Glucose: If sugar is present solution will turn from blue to green, yellow, or brick-red, depending on sugar concentration. A green precipitate means a little glucose was present. A red precipitate means glucose is present in vast amounts.

Food Test 2: Test for Starch – with Iodine solution. Iodine solution is used to identify the presence of starch- a complex carbohydrate. Iodine solution (potassium iodide solution) reacts with amylase – a type of starch – whereby a blue-black polyiodide complex is formed.

Method

1. Mix smalls amount of each food samples (i. e. , Egg lumen, cylindrical piece of potato tuber, bread crump and crisps) in different test tubes with distilled water to make a liquid test.Take another test tube with starch solution to act as a control to compare the difference in color after the completion of the experiment.
2. Label each test tube with a marker for the substance.
3. Add 5 drops of iodine reagent solution to each test tube.
4. Note any color change.

Positive Test for Starch: The brick-red solution of iodine turns to blue-black.

Food Test 3: Test for Protein – with Biuret solution is used to identify the presence of protein. More accurately, it detects the presence of peptide bonds. Peptide bonds form a violet chelate complex with copper (II) ions present in the Biuret Reagent.

Method

1. Mix smalls amount of each food samples (i. e. , Egg lumen, cylindrical piece of potato tuber, bread crump and crisps) in different test tubes with distilled water to make a liquid test. Take another test tube with protein solution to act as a control to compare the difference in color after the completion of the experiment.
2. Label each test tube with a marker for the substance.
3. Add 5 drops of Biuret reagent solution to each test tube. Shake gently to mix.
4. Note any color change. Positive test for proteins: the solution will turn from blue to pink/purple.

Food Test 4: Test for Lipids – the ethanol emulsion test.

Ethanol determines the presence of lipids – i. e. , fats and oils. The solubilities of lipid in ethanol and water are exploited in this test since lipids are soluble in ethanol but not in water. So, if lipids are present a milky/cloudy white suspension is formed.

Method

1. Add all different food samples (i. e. , Egg lumen, cylindrical piece of potato tuber, bread crump and crisps) in different test tubes. Also, take another test tube with Vegetable oil to act as a control to compare the difference in emulsion of the lipids after the completion of the experiment.
2. Label each test tube with a marker for the substance.
3. Add 5cm3 of ethanol to each test tube. Shake the sample with ethanol.
4. Pour some cold water into this mixture in the test tube.
5. Note whether the different solutions become cloudy to prove the presence of lipid Positive test for lipid: The solution changes into a cloudy-white emulsion due to the suspension formed.

Conclusion and Evaluation (CE)

• Conclusion

This test reveals the hidden fats, sugars, proteins and starch in food items. Compounds such as sugars and fats are present in living things. Though the food samples being tested had more than one compound present i. . , egg lumen contains starch, proteins and lipids; Potato tuber contains starch, glucose and lipids; Bread contains starch, glucose and slight lipids; and crisps contain starch, glucose and lipids. Hence, different food samples have different compounds present.

• Evaluation

Limitations

1. The time the test tubes were kept in the water bath was not accurate.
2. The volume of food samples differ in each test tube for the same test.

Improvements 

1. By using a stop watch for more accurate timing.
2. Set a fixed volume of food samples in each test tube.