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Name_______________________________ Date______________________ Period___

Nutrient Analysis Lab

PURPOSE

1) Perform chemical testing methods on foods to test for the presence of four nutritional components and pH.

2) Recognize and be able to discuss the importance of experimental controls and standards.

3) Demonstrate an understanding of how nutrition impacts health. MATERIALS

Hot plate Biuret reagent Pipettes Iodine solution Eye protection pH test strips Marking pen Distilled Water Test tubes Brown paper squares Test tube rack Glucose solution Tongs Starch solution

Disposable pipettes Vegetable oil Benedict’s solution Gelatin

Food samples (various) INTRODUCTION As you are reading this sentence, you are using energy. In fact, everything you do, including breathing, blinking, thinking, and sleeping requires energy. This energy comes from nutrients, the chemical substances found in food and drink that serve to nourish your body. Generally, nutrients are divided into two classes: micronutrients and macronutrients. Micronutrients are required in small quantities (ranging from micrograms to milligrams) and include vitamins and trace minerals. Macronutrients are required daily in large quantities (grams) and include carbohydrates, lipids, proteins, water, and some minerals. Of these, only carbohydrates, lipids, and proteins are energy-yielding. In this lab, you will chemically test various food and drink samples for the presence of protein, carbohydrates, and lipids. In addition, you will also test certain samples for pH. Some of the tests will be quantitative- meaning that you will observe and be able to measure or calculate data. Other tests will be will qualitative- meaning that you will simply observe something using your senses! GENERAL PROCEDURE You will need to start with a test tube rack and 6 test tubes, labeled #1 thru 6. You are responsible for washing out you own test tubes and cleaning up your lab area before leaving!

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You and your partner will rotate through different lab stations, each set up to test foods for different organic nutrients. CAREFULLY READ the directions at each station for how to perform each test. Fill out your data sheet at the lab tables as you go through the rotation. Note:

Eye protection should be worn when heating test tubes!

Do not mix food samples or pipettes! This will result in cross-contamination and cause false positive tests!

Part A) Testing for Protein The human body contains roughly 100,000 different types of proteins, with varied functions and structures. Biuret reagent can be used to determine the presence of protein polymers. In this experiment, you will use Biuret to test for protein in gelatin (your standard), water (your control) and other foods. When Biuret reagent is added to a solution containing protein, it will produce a pinkish or purplish color. CAUTION: Biuret reagent can burn your skin! Wash off spills and splashes IMMEDIATELY

with plenty of water and alert the teacher!

1. Use clean test tubes labeled 1 and 2. Using a metric ruler, label each test tube at the 1 cm mark (from the bottom) using the marking pen provided. This is your “fill to” line.

2. Using a pipette, add WATER to the 1 cm mark of Tube 1. Add GELATIN to the 1 cm mark of Tube 2.

3. Record each sample being tested in Table 1. 4. Using a pipette, add 5 drops of Biuret reagent to each test tube. Gently swirl or

“flick” the bottom of the test tube to mix. Wait about a minute, then mix again. 5. Observe the contents of each test tube and record your data in Table 1.

Table 1. Proteins

Test tube

#

Contents (sample) Initial color of indicator solution

Final color after test on food sample

+ or – test?

1

2

1. What is the purpose of testing water? Explain. 2. Does gelatin contain protein? How can you tell?

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3. What monomers are the building blocks of proteins? (pg. 56) 2. What is the name of the bond that holds the sub-units of proteins together? (pg. 57) Part B) Testing for Simple Sugars (monosaccharides) Benedict’s solution is a test reagent that reacts positively with all monosaccharides and most disaccharides, the building blocks of more complex carbohydrates. A positive Benedict’s test, indicating that simple sugars exist in a sample, can be seen by the formation of a colored precipitate. This color varies from high to low concentrations of sugars, in order: reddish-orange (high), yellow-orange (moderate), or green (low).

CAUTION: Benedict’s solution is a skin irritant! Wash off spills and splashes IMMEDIATELY with plenty of water and alert the teacher!

1. Use clean test tubes labeled 3 and 4. Using a metric ruler, label each test tube at the

1 cm mark (from the bottom) using the marking pen provided. This is your “fill to” line.

2. Using a pipette, add WATER to the 1 cm mark of Tube 3. Add GLUCOSE to the 1 cm mark of Tube 4.

3. Record each sample being tested in Table 2. 4. Using a pipette, add 5 drops of Benedict’s reagent to each test tube. Gently swirl or

“flick” the bottom of the test tube to mix. 5. Using your tongs, place each test tube in the hot water bath. Note color changes

after 2-3 minutes. 6. Record your data in Table 2. Note the COLOR of the precipitate in each tube!

Table 2. Simple Sugars

Test tube

#

Contents (sample) Initial color of indicator solution

Final color after test on food sample

+ or – test?

3

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1. (a) What are the structural differences between a monosaccharide, a disaccharide, and a polysaccharide? (pgs. 55-56) (b) Which (in the above question) are considered to be sugars, and which is a starch?

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Part C) Testing for Complex Carbohydrates (polysaccharides, starches) Starch is a complex carbohydrate and a primary source of energy in the food we eat. Iodine is a good indicator for starch because it turns dark bluish/purplish/black when it chemically reacts with starch. A light brown color indicates a negative reaction.

1. Use clean test tubes labeled 5 and 6. Using a metric ruler, label each test tube at the 1 cm mark (from the bottom) using the marking pen provided. This is your “fill to” line.

2. Using a pipette, add WATER to the 1 cm mark of Tube 5. Add STARCH solution to the 1 cm mark of Tube 6.

3. Record each sample being tested in Table 2. 4. Using a pipette, add 5 drops of iodine solution to each test tube. Gently swirl or

“flick” the bottom of the test tube to mix. 5. Note any color changes and record your data in Table 3.

Table 3. Complex Carbohydrates

Test tube

#

Contents (sample) Initial color of indicator solution

Final color after test on food sample

+ or – test?

5

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1. How is glycogen different from starch? (pg. 56) 2. What is cellulose? Is it found in plants or animals? Part D) Testing for Lipids The term lipid is actually a generic name used to describe any organic compound that is soluble in organic solvents but not in water. The lipids found in food and the human body fall into four main classes: fats/oils, waxes, phospholipids, and steroids. In this lab, a positive result for a lipid will yield a translucent (see-through) stain on a piece of brown paper that will not dry after several minutes. Hint: think about the effect of oils soaking through a bag of fast food that contains greasy French fries. 1. Obtain 2 paper bag squares. 2. Place a drop of WATER on one and drop of VEGETABLE OIL on the other. Let sit for 1 minute.

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3. Pick up the paper bags, and put them up towards the light. Any food solution that contains lipids will appear translucent. 4. Record the color of the paper bag square in the data table and discard bag squares. Table 4. Lipids

Test Sample Observations + or – test?

1. What are the building blocks of fats (triglycerides)? (pg. 59) 2. Explain the difference between a saturated and unsaturated fat. 3. Are lipids hydrophilic or hydrophobic? PART E) Testing for pH All biological processes are dependent on pH. The pH of a substances tells us if it neutral, basic, or acidic. In this part of the lab, you will use pH indicator paper to test water, and 2 different solutions. You will NOT need your test tubes for this test! Simply dip the end of the test strip directly into the substances being tested.

1. Record each sample to be tested in Table 5 and make your predictions. 2. Obtain a test strip for each sample. 3. Dip the test strip into each liquid sample, shake off excess, and wait for

approximately 5 seconds for color change. When testing solid foods, rub the test strip onto the food.

4. Using the key provided on the package of the test strips, record data in Table 5. Write down the pH number, and whether it is neutral, basic, or acidic in your data chart.

Table 5. pH

Test Sample Prediction? acid, base, or neutral Observations, actual pH

Water

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1. Draw a pH scale here, and label on it where each of your samples would belong (see pg. 44 in textbook) Part F) Testing Additional Foods for Each Nutrient Now that you are familiar with the four nutrient tests, you will perform all 5 tests on the following food items. Bring your test tube rack with labeled test tubes to the main station. Add each sample to the 1 cm “fill line” of test tubes #1-6. To save time, conduct one test for test tubes #1-6. Then, thoroughly clean your test tubes #1-6 and move on to the next test. Complete Table 6, below, with your results from each test on each food item. Table 6

Test Tube # and food item

Presence of simple sugar?

(+/-)

Presence of protein? (+/-)

Presence of starch? (+/-)

Presence of lipid? (+/-)

1

Egg white (albumin)

2

milk

3 potato

4 oatmeal

5 soda

6 butter

Done? Clean your lab area, wash your test tubes out with soap and rinse thoroughly, and let them dry upside down in the test tube rack. Wash your hands.

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Post-Lab ANALYSIS & CONCLUSIONS (Answer on a separate sheet of paper, in complete sentences, restating the question in your answers)

1. What is the indicator for sugars? What about starches?

2. What color change represents a positive test for a sugar? What about a starch?

3. Which foods that you tested contained carbohydrates?

4. What is the indicator for proteins?

5. What color change indicates a positive test for proteins?

6. Which foods contain proteins?

7. What is a positive test for lipids?

8. Which foods contain lipids?

9. Why do you think water was used as one of the solutions?

10. Does water contain any of the chemical compounds you tested? Explain why water was used in most of your experiments.

11. Aside from the substances that you’ve tested today, name at least three foods that would test positive for each of the following macronutrients: lipids, simple sugars, complex sugars (starch), and protein. 12. Which tests performed in this lab are considered to be qualitative? What might be an advantage of using qualitative tests? What might be a disadvantage of using qualitative tests? 13. Which test(s) performed in this lab are considered to be quantitative?

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14. For healthy adults, the Recommended Dietary Allowance (RDA) for protein has been set at 0.8 grams for each kilogram (or 2.2 pounds) of body weight. Assuming you are an adult who weighs 140 pounds, calculate what your RDA for protein would be. (HINT: you need to convert the pounds to kilograms!) 15. We have all heard time and time again that we need to eat a balanced diet. But why is it so important? Choose one of the targets of the tests today (protein, lipid, or carbohydrate) and research what could happen to your health if too much or two little if the nutrient was consumed. Write a brief, but detailed summary of your research. Note: If you use the Internet or another resource other than your book, you must include it as a reference!

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Testing Procedures

Part A) Testing for Protein The human body contains roughly 100,000 different types of proteins, with varied functions and structures. Biuret reagent can be used to determine the presence of protein polymers. In this experiment, you will use Biuret to test for protein in albumin (your standard) and other foods. When Biuret reagent is added to a solution containing protein, it will produce a pinkish or purplish color. CAUTION: Biuret reagent can burn your skin! Wash off spills and splashes

IMMEDIATELY with plenty of water and alert the teacher!

6. Obtain a clean set of test tubes (one for each sample listed at the “protein” station)

7. Record each sample to be tested in Table 1 and make your predictions.

8. Using a metric ruler, label each test tube at the 1 cm mark (from the bottom) using the marking pen provided.

9. Using a pipette, add food samples to the 1 cm mark in each of the labeled test tubes. Be sure your tubes are labeled to keep track of which sample is in which tube! If testing a solid food sample, place a small piece into the tube then fill with distilled water to the 1 cm mark.

10. Using a pipette, add 5 drops of Biuret reagent to each test tube. Gently swirl or “flick” the bottom of the test tube to mix. Wait about a minute, then mix again.

11. Observe the contents of each test tube and record your data in Table 1.

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Part B) Testing for Simple Sugars Benedict’s solution is a test reagent that reacts positively with all monosaccharides and most disaccharides, the building blocks of complex sugars. A positive Benedict’s test, indicating that simple sugars exist in a sample, can be seen by the formation of a colored precipitate. This color varies from high to low concentrations of sugars, in order: reddish-orange (high), yellow-orange (moderate), or green (low).

CAUTION: Benedict’s solution is a skin irritant! Wash off spills and splashes IMMEDIATELY with plenty of water and alert the teacher!

7. Obtain a clean set of test tubes (one for each sample listed at the

“simple sugar” station) 8. Record each sample to be tested in Table 2 and make your

predictions. 9. Using a metric ruler, label each test tube at the 1 cm mark (from the

bottom) using the marking pen provided. 10. Using a pipette, add food samples to the 1 cm mark in each of the

labeled test tubes. Be sure your tubes are labeled to keep track of which sample is in which tube! If testing a solid food sample, place a small piece into the tube then fill with distilled water to the 1 cm mark.

11. Using a pipette, add 5 drops of Benedict’s reagent to each test tube. Gently swirl or “flick” the bottom of the test tube to mix.

12. Using your tongs, place each test tube in the hot water bath. Note color changes after 2-3 minutes.

13. Record your data in Table 2. Note the COLOR of the precipitate in each tube!

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Part C) Testing for Complex Carbohydrates (Starch) Starch is a complex carbohydrate and a primary source of energy in the food we eat. Iodine is a good indicator for starch because it turns dark bluish/purplish/black when it chemically reacts with starch. A light brown color indicates a negative reaction.

6. Obtain a clean set of test tubes (one for each sample listed at the “starch” station)

7. Record each sample to be tested in Table 3 and make your predictions.

8. Using a metric ruler, label each test tube at the 1 cm mark (from the bottom) using the marking pen provided.

9. Using a pipette, add food samples to the 1 cm mark in each of the labeled test tubes. Be sure your tubes are labeled to keep track of which sample is in which tube! If testing a solid food sample, place a small piece into the tube then fill with distilled water to the 1 cm mark.

10. Using a pipette, add 5 drops of iodine solution to each test tube. Gently swirl or “flick” the bottom of the test tube to mix.

11. Note any color changes and record your data in Table 3.

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Part D) Testing for Lipids The term lipid is actually a generic name used to describe any organic compound that is soluble in organic solvents but not in water. The lipids found in food and the human body fall into three main classes: fats/oils, phospholipids, and steroids. In this lab, a positive result for a lipid will yield a translucent (see-through) stain on a piece of brown paper that will not dry after several minutes. Hint: think about the effect of oils soaking through a bag of fast food that contains greasy French fries

1. Obtain 2 paper bag squares. 2. Place a drop of WATER on one and drop of VEGETABLE OIL on the other. Let sit for 1 minute. 3. Pick up the paper bags, and put them up towards the light. Any food solution that contains lipids will appear translucent. 4. Record the color of the paper bag square in the data table and discard bag squares.

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PART E) Testing for pH All biological processes are dependent on pH. The pH of a substances tells us if it neutral, basic, or acidic. In this part of the lab, you will use pH indicator paper to test water, and 3 different solutions. You will NOT need your test tubes for this test! Simply dip the end of the test strip directly into the substances being tested.

5. Record each sample to be tested in Table 5 and make your predictions.

6. Obtain a test strip for each sample. 7. Dip the test strip into each liquid sample, shake off excess, and wait

for approximately 5 seconds for color change. When testing solid foods, rub the test strip onto the food.

8. Using the key provided on the package of the test strips, record data in Table 5. Write down the pH number, and whether it is neutral, basic, or acidic in your data chart.