You Are What You Eat - University of California, Irvine

You Are What You Eat 2009 (Nutrient Identification Lab)

Purp ose/ Objecti ve s: There are six basic nutrients of life: carbohydrates, proteins, lipids, minerals, vitamins, and water. Carbohydrates, proteins, and lipids are called organic compounds because they contain carbon atoms. A balanced diet will consist of certain amounts of each of these nutrients. Since your body is made up of these same nutrients, you will be testing for the presence or absence of carbohydrates, proteins, lipids (fats), and salts in various foods. By the end of this exercise, you should be able to: • • • •

Understand that organic compounds are the building blocks of life. Describe the expected outcomes of tests for different organic compounds. Explain the functions of carbohydrates, proteins, and lipids in the body. Use this information to make informed decisions about diet.

Backgr ound: Carbohydrates are compounds made up of carbon, hydrogen, and oxygen atoms. In living cells, carbohydrates may be used as a major source of energy or to build cell structures. Sugars, or simple carbohydrates, such as glucose, fructose, and lactose, supply quick energy to cells. Complex carbohydrates include starches and cellulose, which store chemical energy for the cell. In this experiment you will use iodine as an indicator of starch. If starch is present, the iodine, which is normally yellow-orange, will turn a dark blue-black color. You will then use a glucose test strip to test for the presence of sugar. If glucose is present, the indicator strip will turn green (darker for a stronger reaction). Proteins are large molecules comprised of long chains of amino acids. Amino acids are composed mainly of carbon, hydrogen, oxygen, and nitrogen. There are 20 common amino acids that combine to form a variety of proteins. Of all biological molecules, proteins are most diverse in structure and function. Some serve as structural components, others as enzymes that speed up the rates of chemical reactions, still others perform needed

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Minority Science Programs – School of Biological Sciences – University of California, Irvine


communication functions within the body, and finally some help to protect us from infection. There are 8 amino acids that cannot be synthesized by the human body, so they must be included in the diet. Your instructor will isolate the proteins in milk using a mild acid, vinegar, and drain off the liquid through cheesecloth. Then you will test for the presence of protein with a Biuret Test, using sodium hydroxide and copper sulfate. If protein is present, the reagent will turn violet (darker for a stronger reaction). Lipids include fats, oils, waxes, cholesterol, and most steroids. In the body, fat serves as a major source of energy, a thermal insulator, a cushion around organs, and as an important part of cell structure, particularly membranes. Lipids are also composed of carbon, hydrogen, and oxygen but contain more than twice the energy of carbohydrates and proteins. Since cells generally store excess energy in lipids for later use, most people try to limit fats in the diet to avoid becoming overweight. Animal fats (lard) are found in meats, milk products, eggs, and seafood. Plant oils come from nuts, olives, and seeds. In this experiment, you will be extracting and examining the lipids in chocolate chips, potato chips, and sunflower seeds using colored paper. If lipids are present, they will leave a clear residue on the paper.

Voc abu lar y: Element Compound Carbohydrate Lipid Protein

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Amino Acid Enzyme Mineral Vitamin Reagent



Materi als: • • • • • • • • • • • •

Various foods (including, apples, orange juice, milk, potato chips, chocolate, and sunflower seeds, peanuts or PB, potato, bread, crackers) Glucose test strips Iodine Silver Nitrate Sodium hydroxide Copper sulfate Vinegar Pipettes Beakers Styrofoam Plates Brown/colored paper Rolling pin

Meth ods/Pr ocedure : 1. Work in groups of 3 or 4. 2. Your group will be given 3 types of prepared foods. Record the name of each food in the data table. 3. Divide your styrofoam plates into 5 sections, each with samples of the 3 types of food. 4. Follow the directions below for each of the organic molecule tests, using a different styrofoam plate section for each test. 5. When all the tests are complete, write the results for your groups’ foods on the board. SIMPLE CARBOHYDRATE STATION: 1. Touch a single glucose test strip to each of your selected foods. Record your observations in the data table. COMPLEX CARBOHYDRATE STATION: 1. Put one drop of iodine on each of your selected foods. Record your observations in the data table.

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PROTEIN STATION: 1. Bring your selected foods to your instructor. Your instructor will apply the sodium hydroxide and copper sulfate to each of the foods. Record your observations in the data table. LIPID STATION: 1. Place one of your food items between a folded piece of colored paper. 2. Use a rolling pin (or your hands) to crush the food within the colored paper. 3. Pour off the crushed pieces and throw them away. 4. Observe the colored paper and record your observations in the data table. 5. Repeat steps 1-4 with your other food items. SALT STATION: 1. Bring your selected foods to your instructor. You instructor will apply one drop of silver nitrate on each of your selected foods. Record your observations in the data table. NOTE: If salt is present, the silver nitrate will turn cloudy and white. white If salt is NOT present, the silver nitrate will remain clear.

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Name: _____________________ Period: ___ Que sti on s: 1. Record your observations in the data table below. (18 points)

2. Complete the table of experimental design elements on page 1 of the lab write-up using only ONE food item and ONE organic compound test you performed. 3. Complete the Data/Observations and Analysis/Conclusions section on page 2 of the lab write-up for the SAME food and organic compound test.

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4. Fill in the blanks of the reaction diagram below. (8 points)

5. List two functions for each of the organic compounds below. (12 points) Carbohydrates: _________________________________________________________ Proteins: ______________________________________________________________ Lipids: ________________________________________________________________ 6. Given that the average American diet is high in salt, fat, and sugar, how can you use what you learned about the content of various foods to make healthier decisions about your diet? (4 points) _____________________________________________________________________________ _____________________________________________________________________________

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