It is possible to test the presence or absence of biologically important compounds like lipids, proteins, disaccharides, and monosaccharides using an indicator. An indicator changes color in the presence of a particular molecule. In this analysis, five food tests were carried out to test for the presence of carbohydrates, proteins and fats in foods.
Materials Used
Starch 1%
Glucose 1%
Sucrose 1%
Maltose 1%
Albumen 1%
Ethanol 95%
Hydrochloric acid 1M
Sodium hydroxide 1M
Benedict’s Solution
Biuret solution
Iodine solution
Test tubes
Test tube rack
Water bath set at 80-1000C
Disposable pipettes
Procedure
Part 1 – Benedict’s solution on glucose, maltose, and sucrose solutions
A plastic pipette was used to transfer approximately 2ml of the solution under test into a clean test tube.
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2ml of distilled water was then added to each test tube and 2 ml Benedict’s solution.
The test tubes were then heated using a water bath to approximately 800C for 5 minutes.
Test 2: Non-Reducing Sugar Test on the Glucose, Maltose, and Sucrose Solutions
A pipette was used to transfer approximately 2 ml of the solution under test into a clean test tube.
1 ml of hydrochloric acid was then carefully added to each test tube, and the test tube is the placed in a water bath and heated to 1000C for 5 minutes.
Upon cooling of the solution, 1 ml of sodium hydroxide was added to neutralize the HCL.
2 ml Benedict’s solution was then added.
The test tubes were heated to approximately 800C using a water bath for 5 minutes.
Test 3: Starch Test on the Glucose, and Starch Solutions
A pipette was used to transfer approximately 2 ml of the solution under test into a clean test tube.
2-3 drops of iodine solution was then added.
Test 4: Biuret Test on Proteins, Glucose, and Albumen Solutions
A pipette was used to transfer approximately 2 ml of the solution under test into a clean test tube.
2 ml of Biuret reagent was then added.
The content of the test tube are then shaken gently to mix them.
The test tube is then observed for any color change by looking it underneath a white sheet of paper.
Test 5: Emulsion Test for Fats
The food sample is added to 2 ml ethanol and the mixture is shaken well. If the sample is solid, 3-5 ml of ethanol is added to the powdered material and the mixture is mixed thoroughly.
The solution is left to settle for 2 minutes to allow the food to dissolve in the ethanol.
Any clear liquid is then emptied into a test tube containing 2 ml of distilled H20.
Observation is then made for a milky-white emulsion.
Observation
Test One and Two
There were different color changes observed in the test tubes: Green, yellow, orange, and brick red.
Test 3: Iodine Test
One of the test tube turned black upon the addition of iodine, and the other one turned yellow.
Test 4: Biuret Test
One test tube turned purple while the other one turned light blue upon the addition of the Biuret reagent.
Test 5: Emulsion Test
Three test tubes are involved:
One test tube turned red after 5 minutes of heating.
One test tube turned brown after 5 minutes of heating.
One test tube did not change color after 5 minutes of heating.
Discussion
Test One and Two
The different colors observed can be interpreted as follows:
Green – Trace amounts of reducing sugars present.
Yellow – Low amounts of reducing sugars present.
Orange – Moderate amounts of reducing sugars present.
Brick red – High amounts of reducing sugars present.
Test 3: Iodine Test
The test tube that turned black was an indication of the presence of starch while the one that turned yellow was an indication of the presence of glucose.
Test 4: Biuret Test
The purple color was an indication of the presence of albumen and the light blue color indicated the presence of glucose
Test 5: Emulsion Test
Three test tubes are involved:
The red color indicates the presence of glucose, the brown color indicates the presence of maltose, and the test tube that did not change color indicates the presence of sucrose.
Bibliography
Chang, S.K. and Zhang, Y., 2017. Protein analysis. In Food analysis (pp. 315-331). Springer, Cham.
Pomeranz, Y. ed., 2013. Food analysis: theory and practice . Springer Science & Business Media.
