Name: ________________________________________
Identifying Nutrient Indicators
Purpose: You have just started a job as a food-quality tester. Your task will be to develop a procedure to test
foods for sugar, starch, protein and lipids. The testing procedure will be used by dietitians who will analyze foods
to create nutritional menus for hospital patients. Your first assignment is to demonstrate proficiency using
standard tests for nutrients in foods.
Background: Substances or compounds that supply your body with energy and the building blocks of macromolecules are called nutrients. The food you eat contains nutrition important to your body. Sugars and starches
make up a group of organic compounds called Carbohydrates, which are important in supplying your body with
energy. Some starches provide your body with indigestible fiber, or roughage, which aids digestion. Organic
compounds called proteins are important for growth and repair. Lipids are organic compounds that can supply as
much as four times the amount of energy as carbohydrates or proteins.
You can perform qualitative tests to identify the presence of organic compounds in food using Indicators, chemical
substances that react in a certain way when a particular substance is present. A standard is a positive test for a
known substance. Unknown substances can be tested and compared with the standard for positive identification
of the substance.
Procedure:
Put on safety goggles.
GLUCOSE TEST
1. Add 5 drops of Benedict’s solution to each of 5 test tubes.
2. Label and line up the 5 test tubes.
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To test tube 1, add 20 drops of glucose
To test tube 2, add 20 drops of starch
To test tube 3, add 20 drops of lipid solution
To test tube 4, add 20 drops of protein solution
To test tube 5, add 20 drops of water
3. Heat the tubes in a hot water bath for five minutes
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In which test tube do you see a reaction? ____________________
What color change occurs when Benedict's solution is heated in the presence of this substance?
__________________
4. Pour the contents of each test tube down the drain while the water is running and thoroughly clean each of the
test tubes
IODINE TEST
5. Label the tests tubes 1-5.
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6.
To test tube 1, add 20 drops of glucose
To test tube 2, add 20 drops of starch
To test tube 3, add 20 drops of lipid solution
To test tube 4, add 20 drops of protein solution
To test tube 5, add 20 drops of water
Add 2 drops of iodine solution to each test tube.
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In which test tube do you see a reaction? ____________________
What color occurs when iodine solution is in the presence of this substance? __________
7. Pour the contents of each test tube down the drain while the water is running and thoroughly clean each of the
test tubes
BIURET TEST
8.
Label the tests tubes 1-5.
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To test tube 1, add 20 drops of glucose
To test tube 2, add 20 drops of starch
To test tube 3, add 20 drops of lipid solution
To test tube 4, add 20 drops of protein solution
To test tube 5, add 20 drops of water
9. Add 3 drops of Biuret solution to each test tube.
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10.
In which test tube do you see a reaction? ____________________
What color occurs when Biuret solution is in the presence of this substance? ________
Pour the contents of each test tube down the drain while the water is running and thoroughly clean each of
the test tubes
SUDAN IV
11.
Label the tests tubes 1-5.
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To test tube 1, add 20 drops of glucose
To test tube 2, add 20 drops of starch
To test tube 3, add 20 drops of lipid solution
To test tube 4, add 20 drops of protein solution
To test tube 5, add 20 drops of water
12. Add 3 drops of Sudan IV and 10 drops of water to each test tube. Shake gently to mix.
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In which test tube do you see a reaction? ____________________
In which of the layers is the Sudan IV dye found? ____________________________ What do these results tell you
about the polarity of Sudan IV molecule? Explain. __________________________________________________________________
_____________________________________________________________________________________________
13.
Pour the contents of each test tube down the drain while the water is running and thoroughly clean each of
the test tubes
ANALYSIS QUESTIONS
1) Use your data to fill in the following data. Tell what indicator tests for each macromolecule and
describe what a positive test looks like for that macromolecule when the indicator is used.
Remember, the indicators we used were
-Benedict’s solution
-Iodine solution
-Sudan IV
-Biuret’s solution
Macromolecule
Sugar
(Monosaccharides)
Indicator used to detect for…
Describe the color change
Starch
(Polysaccharides)
Lipid
Protein
2) You find a piece of food in your garbage disposal but can’t tell what it is. You decide to test it with the
same four indicators we used today. . You observe a positive response with iodine solution and Biuret
solution. What can you conclude about this food?
3) What is a good guess to what the food mentioned in number 2 is?
Part II - WHAT’S FOR BREAKFAST?
Objective:
As a hospital dietician, you are responsible for determining which breakfast foods are best for
patients with certain dietary restrictions.
Question:
What macromolecules are in typical breakfast foods such as eggs, bacon, toast, butter, and jelly?
Hypothesis: Write your hypothesis in the space provided before the data analysis section.
Materials:
At each lab table:
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6 test tubes
test tube rack
1 graduated cylinder
2 forks
2 spoons
mortar and pestle
5 disposable pipettes
stirring rod
water
Iodine solution
Biuret reagent
Sudan IV dye
Benedict’s solution
At Common Lab Station:
 Hot water Bath
 Bread
 Jelly
 Toaster
 Egg
 Bacon (meat and grease)
 Butter
Procedure: Using the test kit you developed in Part, test each of the breakfast foods for
monosaccharides, starch, lipids, and proteins. You will need to “mash” each food with a mortar
and pestle and a little water.
Design a data table that records all of your results. Make sure it is labeled!
CLEAN OUT ALL TEST TUBES AND THE LAB TABLE. BE SURE TO USE SOAP AND WATER TO CLEAN
YOUR EQUIPMENT. PLACE THE TEST TUBES UPSIDE DOWN ON THE TEST TUBE RACK TO DRY.
Hypothesis for Each Macromolecule (prediction of reaction with each indicator and what it shows):
DA T A :
Make a good, labeled data table to record the macromolecule contents of each of the above food items.
CONCLUSION
Write a conclusion for each macromolecule indicator. How is it useful to demonstrate the presence/absence of
particular macromolecules? What additional information would be useful to have regarding the nutritional content
of this meal?
QUESTIONS
Answer the following questions in complete sentences.
1.
When you eat bacon, what does your digestive system break the protein molecules into?
2. When you eat bacon, what does your digestive system break the large fat molecules which make up the
bacon into?
3. What do your cells use the smaller molecules in numbers 1 and 2 for?
4. When you eat toast, what does your digestive system break it down into?
5. What do your cells use the smaller molecules for?
6. Compare the molecules which make up the jelly to the molecules which make up the toast? What are some
similarities and differences?
7. Compare the egg white to the meat part of your bacon. How are they similar and/or different?
8. Which breakfast items would you give a patient that is weak and needs energy for their cells?
9. Which breakfast item would you put on the breakfast tray for a patient that needs the raw materials to
build new muscles and why?
10. Compare the butter to the white part of the bacon. How are they similar and/or different?
11. Fats (lipids) have more calories per gram than carbohydrates do. Which of the food items would you not
put on the breakfast tray of a heart patient that needs to lose weight?